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AGRICULTURAL AND BIOLOGICAL PUBLICATIONS
CHARLES V. PIPER, Consulting Editor

THE FUNDAMENTALS

OF

FRUIT PRODUCTION

UMMiMl^ai^!!!") lHHLU,U>a^^^^

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ImlTTnlltTlTTTlTlMm

THE FUNDAMENTALS

OF

FRUIT PRODUCTION

BY

VICTOR RAY GARDNER
FREDERICK CHARLES BRADFORD

AND

HENRY DAGGETT HOOKER, JR.

OF THE department' OF HORTICULTURE OF THE UNIVERSITY OF MISSOURI

First Edition

McGRAW-HILL BOOK COMPANY, Inc.
NEW YORK: 370 SEVENTH AVENUE

LONDON: 6& 8 BOUVERIE ST., E. C. 4

1922

4lp

Copyright, 1922, by the
McGraw-Hill Book Company, Inc.

THE MA.FI<B PRESS YORK Pj

UBMMY

N. C. State College

PREFACE

Fruit growing in the United States is so widespread and so diversified
that no work of ordinary dimensions can codify it on the basis of empirical
practices, which differ from place to place. The fundamental factors,
however, are always the same and once they are understood, the adapta-
tion of practices to local conditions presents Httle difficulty.

The present work attempts to focus attention on the conditions
which make the fruit plant profitable; practices are considered only as
they affect these conditions, not as ends in themselves. Maintenance
of this point of view has necessitated a rather wide departure from con-
ventional arrangement of subject matter. The common orchard prac-
tices are not sacred in themselves; indeed, they are important only in so
far as they help vegetative growth and especially fruit production.
Fundamentally the plant's growth and functioning depend on the nature
of the environment and the adjustment thereto and not directly on cul-
tural practices, which only modify the relation of the plant to the environ-
mental complex. Consequently these practices appear inconspicuous in
the Chapter and Section headings.

Acquaintance with principles without the facts on which they rest
is itself empirical. Particular attention, therefore, is given to the
inclusion of sufficient illustrative matter to permit quantitative estimate
of the validity and applicability of the principles enunciated. Com-
paratively little that is original is presented; much of the material that is
novel to pomological texts is included because of its inaccessibility to the
average student. Many significant observations which have been neg-
lected because their ultimate bearing was not appreciated at the time
they were recorded, have been reviewed in the light of modern knowledge.
Plant physiology, plant chemistry, soil science and physics have been
requisitioned freely and advisedly; in no case, however, without an indi-
cation of applicability to pomology. Careful consideration has approved
this course because special applications to fruit growing are rare in the
general University courses in these subjects and because in the arrange-
ment of many curricula, pomology precedes some of the science courses
which are needed as preparatory training. Though every effort is made
to insure thoroughness, exhaustive treatment is not attempted, since it
would be useful to few readers.

The solution of a problem arising outside of the classroom depends on
obtaining all the pertinent data, systematizing them to ascertain the
factors involved and ^.pplying to the problem th,e knowledge so gained.

v

118x0

vi PREFACE

This text is designed to prepare the student to undertake these steps.
As with any text, much is necessarily left to the instructor, particularly
matters of opinion and of local application.

Finally, it hardly need be said that this text is intended for students
of college grade. It is not a manual on how to grow fruit; it does not
attempt to enter fields best covered by classroom discussion, laboratory
work or practical experience. It is intended, however, to be a supple-
ment and guide to these.

The writers wish to express their appreciation of the helpful criticisms
and suggestions offered by those to whom portions of this manuscript
have been submitted: to Dr. M. M. McCool of the Michigan Agricultural
Experiment Station (the Section on Water Relations); to Dr. William
Crocker of the University of Chicago and to Dr. E. J. Kraus of the
University of Wisconsin (the Section on Nutrition) ; to Dr. W. H. Chand-
ler of Cornell University (Chapters 14-18, dealing with Winter Injury);
to Dr. O. M. Stewart, Professor of Physics in the University of Missouri
and to George Reeder of the U. S. Weather Bureau (Chapters 19 and 20
on Frost Occurrence and Control) ; to Prof. Ray Roberts of the University
of Wisconsin (the Section on Pruning) ; to Dr. M. J. Dorsey of the Uni-
versity of Minnesota (the Section on Fruit Setting) ; to Prof. W. P. Tufts
of the University of California, to Dr. J. K. Shaw of the Massachusetts
Agricultural Experiment Station and to Paul C. Stark of the Stark Bros.
Nursery Co. (the Section on Propagation) ; to Prof. Roy E. Marshall of
the Michigan Agricultural College and to Prof. W. P. Tufts of the Uni-
versity of Cahfornia (Chapters 34 and 35 on Orchard Locations and
Soils); finally to Dr. C. V. Piper. Many valuable criticisms and sug-
gestions have been incorporated in the text. In a few instances the
writers have believed themselves justified in adhering to their original
interpretations of the evidence, so that these authorities who have
assisted the writers very materially are not to be held responsible for
any part of the book in its present form.

Acknowledgment is made also to Prof. C. E. Shuster of the Oregon
Agricultural Experiment Station for Figures and to Dr. J. K. Shaw of the
Massachusetts Agricultural Experiment Station for Figure 56.

Columbia, Mo. The AUTHORS.

August, 1921.

CONTENTS

Preface

SECTION I
Water Relations

CHAPTER I

The Water Requirements of Fruit Plants 3

Water as a Plant Constituent — The Water Requirements of Plants in Terms
of Dry Weight — The Water Requirements of Plants in Terms of Precipita-
tion— Amounts Used by the Plants Themselves; Total Amounts Required
for Plants and to Compensate for Evaporation, Runoff and Seepage — Plant-
ing Distances Related to Moisture Supply — Factors Influencing the Water
Requirements of Plants — Nutrient Supply; Cultivation; Light; in General;
Some Applications to Practice — The Wilting Point for Fruit Plants — Wilting
Coefficients; Wilting under Field Conditions; _ Wilting Coefficients and
Drought Resistance — Summary.

CHAPTER II

The Intake and Utilization of Water 18

Water Absorption — The Water Absorbing Organs — The Handling and
Transplanting of Nursery Stock — The Water Absorbing Process — Factors
Enabling the Roots to Exploit the Soil; Adaptation of Roots to Moisture
Conditions; Factors Influencing Rate of Absorption; Submergence and Root
Killing — Transpiration — Cuticular and Stomatal Transpiration Compared;
Variability in Number of Stomata in Accordance with External Conditions —
Factors Influencing Rate of Transpiration — Character of Cuticle; Age of
Leaf; Defoliation, Summer Pruning; Wind Velocity, Windbreaks; Light;
Temperature, Slope of Ground — The Water Conducting System of the Tree
— Summary.

CHAPTER III

Orchard Soil Management Methods and Moisture Conservation ... 31
Orchard Soil Management Methods Defined and Described — Orchard Soil
Management Methods and Surface Run-ofi' — Moisture Under Tillage and
Sod-Mulch Systems of Management — Some New York and Pennsjdvania
Records; Some New Hampshire Records; English Experience; Some
Kentucky and Kansas Records; in General; Practicability of Sod-mulch
System Influenced by Depth of Rooting — Influence of Depth and Frequency
of Cultivation upon Soil Moisture — Intercrops and the Soil Moisture Supply
—Cover Crops and the Moisture Supply — Efi'ects of Early and Late Seeding;
Winter-killed and Winter-surviving Cover Crops — Wind Velocity and
Evaporation, Windbreaks — Summary.

vii

viii CONTENTS

CHAPTER IV

Paob
Soil Moisture: Its Classification, Movement and Influence on Root

Distribution 47

Classification of the Water in Soils and Plant Tissues — The Response of
Water to the Force of Gravity and the Evaporating Power of the Air;
the Relative Saturation; Resistance to Freezing — Movement of Water in the
Soil — Percolation; the Rise of Water by Capillarity; Lateral Movement of
Water in the Soil — The Distribution of Fruit Tree Roots as Influenced by Soil
Moisture — The Idea^ Root System — Specific and Varietal Differences in Root
Distribution — The Distribution of Tree Roots under Varying Conditions —
In the Hood River Valley, Oregon and in Ohio ; in a Gravelly Loam, Underlaid
by Hardpan, in Maine; in a Thin Gravelly Loam, Underlaid by Rock, in
Maine; in Dwarfs; the Influence of Soil Moisture; the Influence of Culti-
vation; the Influence of Soil "Alkali" — Applications to Orchard Practice —
Summary.

CHAPTER V

The Response of Fruit Plants to Varying Conditions of Soil Moisture

AND Humidity 66

Influence of Soil Moisture on Vegetative Growth— New Shoots and their
Leaves; Annual Rings and Trunk Circumference; Moisture Supply and the
Growth Period in Early Spring; the "Second Growth " of Midsummer or Late
Summer — Influence of Water Supply on the Development of Fruit — Size;
Yield; Shape and Color; Composition; Disease Resistance and SusceptibiHty
— Residual Effects of Soil Moisture — On Vegetative Growth; on Yields —
Influence of Atmospheric Moisture on Growth — In General; Russeting of
Fruit; Fruit Setting — Summary.

CHAPTER VI

Pathological Conditions Associated with Excesses and Deficiencies in

Moisture 83

Disturbances Due to Moisture Excesses — The Splitting of Fruit; (Edema;
Fasciation and Phyllody; Chlorosis; Rough Bark or Scaly Bark Disease;
Watercore — Disturbances Due to Moisture Deficiencies — Defoliation,
Premature Ripening of Wood — Dieback — Cork, Drought Spot and Related
Diseases — Fruit-pit; Cork; Surface Drought Spot; Deep-seated Drought
Spot; Dieback and Rosette; Bitter-pit; Jonathan-spot; Black-end — Silver
Leaf — Lithiasis — Summary.

SECTION II

Nutrition

CHAPTER VII

Plant Nutrients and Their Absorption 101

Distribution of Elements Found in Ash — In Tissues of Different Kinds; in
Tissues of Different Age; at Different Seasons — Absorption — The Osmotic
System — Displacement — Availability of Ash Constituents — Availability
and Solubility Distinguished; Factors Influencing Solubility; Availability of

CONTENTS IX

Page
Phosphorus; Availabihty Varies According to Ivind of Plant; Availability of
Iron and Sulfur — Availabihty of Nitrogen — Nitrification — Aided by Liming;
Influenced by Methods of Soil Management; Influenced by Temperature and
Soil Moisture — Losses of Nitrogen from the Soil — Maintaining the Nitrogen
Supply of the Soil — Nitrogen Fixation— Soil Reaction, Acidity and
Alkahnity — Soil Reaction and the Availability of Phosphorus; Soil Reaction
and the Availability Of Iron; Acid Tolerance of Certain Crops — Concent-
ration, Soil "Alkah" — Tolerance of Different Fruits; Injuries from Excessive
Fertilization; some effects of Soil Alkali; Remedial Measures — Soil Toxicity
— General and Specific Effects; Protecting Against Toxins; Importance in
the Fruit Plantation — Antagonism; Aeration; Selective Absorption —
Transpiration — The Nutrient Requirements of Crop and Fruit Plants —
Summary.

CHAPTER VIII

Individual. Elements 130

Nitrogen — Synthesis of Organic Nitrogenous Compounds — Translocation
and Use of Elaborated Nitrogenous Compounds — Seasonal Distribution of
Nitrogen — In Leaves; in Branches, Trunks and Roots; in Spurs; in Fru't; in
Various Tissues of Trees of Different Age — Phosphorus — Synthesis of Phos-
phorus-contain'ng Orgaific Compounds — Translocation and Use of Phos-
phorous-containing Compounds — Amounts Used in Fruit Production —
Seasonal Distribution of Phosphorus — In Leaves; in Branches, Trunk and
Roots ; in Spurs ; in Fruit ; in Various Tissues of Trees of Different Ages — Potas-
sium— Synthesis, Translocation and use of Potassium-containing Compounds
— The Demand and the Supply — Seasonal Distribution of Potassium —
In Leaves; in Branches, Roots and Trunks; in Spurs; in Fruit; in Various Tis-
sues of Trees of Different Age — Sulfur — Iron — Magnesium — Calcium —
Seasonal Distribution of Calcium — In Buds and Leaves; in Bark and Wood;
In Fruits — The Demand and the Supply — Other Mineral Elements — Silicon;
Sodium; Chlorine; Aluminum and Manganese — Summary.

CHAPTER IX

Manufacture and Utilization op Carbohydrates 161

Assimilation and Limiting Factors Defined — Carbon Assimilation — Factors
Involved — Carbon Dioxide; Water; Light — Leaf Pigments — Variation with
Age; Variation with Light Supply — Temperature; Enzymes — Products
— Oxygen- — Carbohydrates — Daily and Seasonal Fluctuation in Leaves;
Forms of Storage — Seasonal Fluctuations of Stored Carbohydrates — Easily
Hydrolizable Carbohydrates; Starch; Sugars — Carbohydrate Utilization — •
In Tissue Building; in Retaining Moisture; Increasing Osmotic Concentra-
tion; as a Source of Energy; Relation to Pigment Formation — Summary.

CHAPTER X

The Initiation of the Reproductive Processes . 181

The Development of the Fruitful Condition — The Response of the Plant
to Changes in Relative Amounts of Nitrogen and of Carbohydrates — The
Significance of Carbohydrate Accumulation, Manufacture in Excess of
Utilization — In Fruit Spurs; Influence of the Nitrate Supply; Influence of the
Moisture Supp'y; Influence of Other Factors — Fruit-bud Formation —

CONTENTS

Page
Evidence of Differentiation— Time of Differentiation — In Relation to Posi-
tion; Varietal Differences; Differences Induced by Cultural Treatment —
Abnormalities; Winter Stages — Summary.

CHAPTER XI

Surpluses and Deficiencies 194

Surpluses — Nitrogen; Magnesium; Copper; Arsenic; Manganese; Other
Elements — Deficiencies — Nitrogen; Phosphorus and Potassium; Sulfur;
Iron; Magnesium and Calcium; Chlorine — Analysis of the Fertilizer Problem
— The FertiHzer Requirements of the Orchard.

CHAPTER XII

The Application of Nitrogen-carrying Fertilizers 204

The Influence of Nitrogenous Fertilizers on Vegetative Growth — In Peaches;
in Apples; in Strawberries; Negative Results, Nitrogen not a Limiting
Factor — Influence of Nitrogen on Blossom-bud Formation — in Peaches; in
Apples — Influence of Nitrogen on the Setting of Fruit — Influence of Nitro-
gen on Size of Fruit — Influence of Nitrogen on Coior of Fruit — Influence of
Nitrogen on Yield — The Correlation Between Vegetative Growth and
Yield — Influence of Nitrogen on Composition and on Season of Maturity —
Summary.

CHAPTER XIII

Fertilizers, Other Than Nitrogenous, in the Orchard 218

The Indirect Effects of Fertilizers — Phosphoric Acid; Sulfur; Lime —
Plant Nutrient Carriers, Different Forms of Fertilizers — Nitrogen from
Inorganic Sources; Nitrogen from Organic Sources; Phosphorus; Potassium;
Sulfur; Lime — Season for Applying Fertilizers — The Relations of Seasonal
Conditions to Response From Fertilizers — Summary.

SECTION III

Temperature Relations of Fruit Plants

CHAPTER XIV

Growing Season Temperatures 236

Heat Units — The Relative Values of Different Effective Temperatures —
Influence of Latitude on Heat Requirements — In the Early Harvest Apple;
in the Elberta Peach; in Chestnut Blight — Variations in Heat Requirements
from Season to Season — Acclimatization to Varying Amounts of Heat — In
General — Optimum Temperatures— Variation within the Species or Variety;
Differences within the Variety for Separate Processes; Variation in Quality
with Amount of Summer Heat; Variation in Season of Maturity with
Amount of Summer Heat — Soil Temperatures — Indirect Temperature
Effects — Summ ary .

CONTENTS xi

CHAPTER XV

Page

Winter Killing and Hardiness 250

Death from Freezing — Tissue Freezing is Accompanied by Cell Dehydration;
Freezing, Not Cold, Ivills; Freezing and the Deciduous Habit — Increasing
Hardiness — By Increasing Sap Density — By Increasing Water-retaining
Capacity — Water-retaining Capacity Associated with Pentosan Content —
Water Soluble Pentosans in Particular — Pentosan Content, Water-retaining
Capacity and Hardiness Responsive to Environmental Conditions — In-
creased Hardiness with Increased Maturity — Rapid Temperature Changes
— Killing with Slow and with Rapid Freezing; Slow and Rapid Thawing —
Variation in Critical Temperatures — Summary.

CHAPTER XVI

Winter Injury 264

Conditions Accompany Winter Injury; Winter Injuries Classified — Injuries
Associated with Immaturity — Affecting More or Less the Entire Plant —
Tender Plants May be More Resistant Than Hardier Plants; the Effect of
Summer Conditions Favorable for Late Growth; Second Growth Particularly
Susceptible; Preventive Measures — Localized Injuries — Crotch and Crown
Injury; Locahzed Injuries and Delayed Maturity; Contributing Factors;
Remedial Measures — Wiitter Injury Associated with Drought — Immaturity
and Winter Drought — Water Loss from Dormant Tissues — Water Conduc-
tion in Trees durmg the Winter — Relation of Freezing to Water Conduction
— Where Winter Drought Conditions Prevail — Protection against Winter
Drought Injuries — Winter Irrigation — Cultivation; Cover Crops —
Windbreaks — Effect of Wind Velocity; Effect on Evaporation; Effect on Soil
Moisture — Injuries Characteristic of Late Winter Conditions — The Rest
Period — Injuries to Fruit Buds — Changes in Water Content of Buds during
Winter^Contributing Factors — Protective Measures — Pruning; Fertiliza-
tion and Cultivation; Thinning; Whitewashing and Shading — In General —
Injuries to Vegetative Tissues — Distinguished from Summer Sunscald and
Injuries Associated with Immaturity; Moisture and Temperature Condi-
tions in the Affected Parts; Preventive Measures — Injuries Due to Sudden
Cold — General Effects; Trunk Splitting — Summary.

CHAPTER XVII

Winter Injury to the Roots 302

Soil Temperatures in Winter; Critical Temperatures for Tree Roots — Factors
Influencing Frost Penetration — Protection Afforded by Snow; Different Sys-
tems of Soil Management; Soil Type; Soil Moisture — Relation of Cover
Crops to Root Killing — Root Killing in Different Fruits — The Apple; the
Pear; the Peach; the Cherry; the Plum; the Grape; the Small Fruits — Pre-
ventive and Remedial Treatments — Deep Planting and Mulching; Use of
Hardy Stocks; Pruning; Handling Nursery Stock .in Cold Weather —
Summary.

CHAPTER XVIII

Winter Injury IN Relation TO Specific Fruits 318

The Apple — Injuries A.ssociated with Immaturity; Control Measures;
Varietal Differences — The Pear; the Peach; the Cherry; tTie Plum; the

xiv CONTENTS

Page
Endosperm — The Setting of the Fruit — What Constitutes a Normal Set of
Fruit — The June Drop and Other Drops — The First Drop; the Second Drop;
the Third Drop or June Drop — Fruit Setting, Fruitfulness and Fertility
Distinguished — Sterility and Unfruitfulness Classified — Summary.

CHAPTER XXVII

Unfruitfulness Associated with Internal Factors 489

Due Principally to Evolutionary Tendencies — Imperfect Flowers, Dioecious
and Monoecious Plants; Heterostyly; Dichogamy, Protandry and
Protogyny; Impotence from Degenerating or Absorbed Pistils or Ovules;
Impotence of Pollen — Due Principally to Genetic Influences — Sterility and
Unfruitfulness Due to Hybridity — Incompatibility — Interfruitfulness and
Interfertihty; in Reciprocal Crossings — Due Principally to Physiological
Influences — Unfruitfulness Due to Slow Growth of the Pollen Tube — Prema-
ture or Delayed Pollination — Nutritive Conditions Within the Plant — Effect
on Pollen Viability; Effect on Defectiveness of Pistils; Fruit Setting of
Flowers in Different Positions; Strong and Weak Spurs; Evidence from
Ringing Experiments; Evidence from Starvation Experiments — Summary.

CHAPTER XXVIII

Unfruitfulness Associated with External Factors 509

Nutrient Supply; Pruning and Grafting; Locahty — Season — End-season
FertiUty; Change of Sex with Season — Age and Vigor of Plant; Tempera-
ture; Light; Disturbed Water Relations; Rain at Blossoming; Wind; Fungous
and Bacterial Diseases; Spraying Trees When in Bloom; Other Factors That
Cause the Dropping of Fruit and Flowers — Summary.

CHAPTER XXIX

Factors more Directly Concerned in the Development of the Fruit . . 521
Stimulating Effects of Pollen on Ovarian and Other Tissues; the Effect of
Certain Stimulating Agents on Fruit Setting — Seedlessness and Partheno-
carpy — Seedlessness of Non-parthenocarpic Fruits; Vegetative and Stimula-
tive Parthenocarpy; Relation of Anatomical Structure of Fruit to
Parthenocarpy; the Value of Seedless and Parthenocarpic Fruits — The Rela-
tion of Seed Formation to Fruit Development — Structure of Fruit; Form;
Size; Composition and Quality; Season of Maturity; Specific Influence of
Pollen on Resulting Fruit — Summary.

CHAPTER XXX

Fruit Setting as an Orchard Problem 538

The Number of Pollenizers; Temporary Expedients; PoUinating Agents —
The Fruit Setting Habits of Different Fruits— Apple; Pear; Quince; Peach;
Almond; Plum; Apricot; Cherry; Grape; Strawberry; Currant and Goose-
berry; the Brambles; the Nuts; Persimmon — Summary.

CONTENTS XV

SECTION VI
Propagation

CHAPTER XXXI

Paqb

The Reciprocal Influences of Stock and Cion 552

The Congeniality of Grafts — Congeniality and Adaptability Distinguished —
The Influence of Stock on Cion — Stature; P^orm — Seasonal Changes — End-
season Effects, Ripening of Fruit; Maturity of Wood; Spring Effects — Hardi-
ness— Disease Resistance — Physiological Diseases — Yield — Fruit-bud Form-
ation; Fruit Setting; Size of Fruit — Quality — In Pomaceous Fruits; In
Stone Fruits; in Grapes; Qualitative Differences and Quantitative Varia-
tions— Longevity; General Influence of Stock on Cion — Influence of Cion
on Stock — Size and Number of Roots; Distribution and Character of Roots;
Longevity, Growing Season and Hardiness; Other Influences; in General.

CHAPTER XXXII

The Root Systems of Fruit Plants 584

Conflicting Interests of Nurseryman and Fruit Grower — Adaptation of Stocks
to Particular Conditions — Adaptation to Soil Temperatures; Adaptation to
Soil Texture and Composition; Immunity or Resistance to Soil Parasites —
Propagation by Cuttings — Advantages and Disadvantages — Grapes in
Particular; Apples and Pears — Propagating Apples and Pears by Layerage
and Hardwood Cuttings — Varietal Differences and Contributing Factors —
Sources of Nursery Stock — Grades of Nursery Stock — Selection of Seedling
Stocks; Grafted or Budded Trees; Double Worked Trees — Pedigreed Trees —
Some Results in Citrus Fruits; Some Results in Apples; in GeneraL

SECTION vn

Geographic Influences in Fruit Production
CHAPTER XXXIII

The Geography of Fruit Growing 612

Life Zones, Crop Zones and Fruit Zones — The Boreal Zone; the Tropical
Zone — Austral or Temperate Zone — Transition Zone; Upper Austral Zone;
Lower Austral or Sub-tropic Zone — Geography of Fruit Production as Influ-
enced by Temperature — Peach Growing as Influenced by Temperature;
Grape Growing as Influenced by Temperature; Temperature and the
Geographic Range of Apple Varieties; the Effect of Bodies of Water on
Temperature; Influence of Altitude on Air and Soil Temperatures —
Geography of Fruit Production as Influenced by Rainfall and Humidity —
Other Factors Influencing the Geographic Distribution of Fruits — Sunshine;
Parasites; Wind; Native Range of Parent Species; Length of Time in Culti-
vation; Uses and Quality of Product; Relation to Consuming Centers and
Transportation Facilities— Summary.

XVI CONTENTS

CHAPTER XXXIV

Orchard Locations AND Sites go-

Orcharding in or outside of an Established Fruit Growing Section; Land
Values; Transportation Facilities— Slope or Aspect— Influence on Soil Tem-
peratures and on the Plant; Specific Influence on Fruit Growing; Indirect
Effects; Abruptness of Slope— Air Drainage— Influence of Elevation— Ther^
mal Belts— Influence of Bodies of Water— Influence of Distance from Water;
Influence of Size and Shape of Body of Water; Indirect Temperature Effects-
Minor Temperature Effects— Importance During the Winter; Obstructions-
Local Variations and their Significance— Temperature; Evaporation, Rainfall
and Other Factors — Summary.

CHAPTER XXXV

Orchard Soils „_„

Considered from the Standpoint of Physical Condition— Requirements of
Different Crops; Requirements as to Depth; Classification of Soils according
to Size of Soil Particles; Mechanical Analyses of Various Fruit Soils-
Considered from the Standpoint of Chemical Composition— Requirements
of Different Crops— Chemical Analyses of Various Fruit Soils— Evi-
dence on Soil Requirements from Fertilizer Experiments— Vegetation
as an Index to Crop Adaptation— Adaptation of Varieties to Particular
Soils — Summary.

Glossary .... „„.
674

'"""" 679

THE FUNDAMENTALS OF
FRUrr PRODUCTION

SECTION I
WATER RELATIONS

The importance of moisture as a factor in the production of fruit
is appreciated only in part. In arid sections the lack is obvious; in
many regions certain lands are recognized as too moist for fruit plants.
In the majority of the so-called humid sections, however, there is a
tacit assumption that nature provides satisfactorily for the requirements
of fruit plants. Drought may diminish or destroy other crops, but as
long as trees survive there is considered to be sufficient moisture.

The forest trees, relied on as evidence of this sufficiency, show, even
in a limited area, striking differences in vigor^ according to their locations.
One of the most important factors recognized by the forester as affecting
tree growth, is moisture. Certain spots even in humid regions, are
chronically dry, some are nearly always wet; others, favorable in some
seasons, are subject rather frequently to excess or deficiency of moisture.

Much of the complacence concerning the water supply of trees is
based on the supposedly great range of their roots and the consequent
great amount of soil from which they can draw water# For this reason
a statement of the extent to which forest trees actually deplete the soil
moisture is pertinent. Zon^^^ cites data showing moisture contents
in June of 4.5 and 4.8 per cent, respectively at 4 and 8 inches in soil
through which forest tree roots were ranging, while adjacent spots within
the forest, exactly similar except that the roots had been excluded con-
tained, at the san>e depths, 13.8 and 11.0 per cent, respectively. At'
16 inches the root free soil had over twice as much moisture as that to
which the roots had access. Evidence is cited to the effect that the
water level is lowered under forest and that with the removal of the forest
the water level rises. Zon considers that the inability of many species
to grow under an established cover of trees, commonly called shade
intolerance, is in reahty due to the low supply of moisture in the soil.
When the roots of the top growth are excluded from an area, the intol-
erant species grow there with considerable vigor.

Deficient and excessive moisture are admittedly each a hmiting
factor in crop production. Table 1, based on estimates by crop reporters

1

2 FUNDAMENTALS OF FRUIT PRODUCTION

of the United States Department of Agriculture, shows the damage
caused by injurious moisture conditions in comparison with other factors.
The figures on apples and berries are averages for the period 1912-1919
and on other crops selected in comparison for the period 1909-1919.
According to these estimates small fruits suffer more from drought than
from any other single factor, while apples are injured more only by cold
weather.

Table 1

— Damage to

Crops from D

IFFERENT

Causes

(After Smith^'

V)

1

1

■^

i

1

*i

1

1

S

I

a

1 .

1 .

i

t

a
g
>-

4

i

1

1

i

1

a

Is

> c

1 "

^ s

t

s

i

&

•a

"S «■

>

a

p

1^

E

P

■3

1

2

1^

|§

a a

ii

1

Wheat

12.4
16.3

2.0
4.0

0.3
0.9

4.5
2.9

1. 1
0.4

2.0

2.2

0.3
0.5

22.9

27.7

2.7
0.2

2.1
2.7

0.2
0.2

0.2
0.7

28 8

Corn

31.1

6.7
14.4

3.1
3.1

1.5
0.2

0.3

1.6

0.1

0.4
0.7

1.8
0.1

14.1
20.7

1.2

4.4

0.8
3.2

0.3
0.1

0.1
0.3

Potatoes

30.0

Tobacco

8.7

3.7

0.6

1. 1

0.8

0.2

0.3

15.8

0.4

2.6

0.1

20.5

Cotton

12.3

4.3

1.0

1.4

0.5

1.6

0.7

22.3

2.0

9.7

0.2

35.5

Apples

5.4

1.6

0.2

14.6

0.8

0.5

0.9

24.9

3.7

3.6

0.1

39.6

Berries

9.3

1.7

0.2

7.3

0.5

0.6

0.2

20.3

1.1

0.6

0.1

24.9

Precipitation cannot be controlled. Soil moisture, however, is sus-
ceptible more or less to modification by various practices and adjust-
ments of fruits or of stocks for fruits can be made in some cases to the
moisture conditions of the soil. For these reasons recognition of soil
conditions, understanding of the water requirements of the various fruit
plants and knowledge of the relation of various cultural practices to
moisture control are of fundamental importance to the fruit grower.

CHAPTER I

THE WATER REQUIREMENTS OF FRUIT PLANTS

There is more or less acknowledgement of a difference in adaptability
of different fruits to varying moisture conditions in the soil; this is,
however, expressed in terms of tolerance more often than in terms of
requirements. It is stated frequently that sour cherries will stand a
dry soil or that pears will endure a wet soil; there is very little exact
information on what the various fruits actually require. Table 2 gives
some interesting results of investigation in California on the requirements
of fruit and other crops under conditions common in that section. The
requirements of the several fruits stated in terms of the amounts of free
water in the soil, exhibit a considerable difference. Other data to be
introduced later (Tables 11 and 12) show that the same fruit may have
different moisture requirements in different localities.

Table 2.-

-Relative Water Requirements of Different Plants

(After Loughridge^'')

Free water in

4 feet of soil

Plants for which the soil

Plants for which the soil

moisture is just above the

moisture is just below the

Percent-

Tons per

minimum; cultures did well

minimum; cultures suffered

age

acre

0.0 to 1.0

80

Apricots, olives, peaches, soy
bean

Citrus, pears, plums, acacia

1.0 to 1.5

120

Citrus, figs

Almonds, apples

1.5 to2.0

160

Almonds, plums, saltbush

Barley

2.0 to2.5

200

Walnuts, grapes, eucalyptus

2.5 to3.0

240

Apples, prunes

Prunes

3.0 to4.0

322

Pears, hairy vetch

Wheat

4.0 to 5 . 0

400

Wheat, corn

5.0 to.6.0

480

Sugar beets, sorghum

Sugar beets

/ Water as a Plant Constituent. — Water is a normal constituent of all
plant tissues, comprising from 50 to 75 per cent, of the leaves and twigs,
from 60 to 85 per cent, of the roots, and 85 per cent, or more of most
fleshy fruits.

FUNDAMENTALS OF FRUIT PRODUCTION

Table 3.— Typical Water Content

3F Fruit Plants in the Fall'29

Fruit

Flesh

Skin

Core

or
stone

Stem

Leaves

New
growth

Old
growth

85.64
86.78

89.74
86.07
88.78
88.06
89.98

85.81
78.32

85.71
83.62
32.67
32.83
46.81

59.52
68.76

75.18

53.00
38.20
63.78
61.10
65.10
65.97
48.14
66.25
33.28
69.00

49.40
50.33
49.52
49.59
49.51
50.36
38.15
44.20
41.33
54.33

Pear

Peach

Plum

Cherry

Currant ....

87.13
85.10
89.42
84.35
78.44

45.74

Blackberry

38.26

39.77

33.52

Table 4 indicates the amounts of water found in various parts of the
chestnut and walnut at different seasons and Table 5 shows the mois-
ture content of bearing, non-bearing and barren spurs of the apple at
various periods. All spurs have a maximum water content during or
directly after the time of blossoming, but blossoming spurs contain
much more water than spurs in the off year and these more than
barren spurs.

Table 4. — Typical Water Content of Roots, Branches and Leaves of the
Chestnut and Walnut^

Chestnut

May 30

July 4

Aug. 11

Sept. 25

Roots. . . .
Branches .
Leaves . . .

83.31
78.68
76.51

66.12
69.49
71.44

64.23
51.69

68.82

59.82
53.32
57.85

Walnut

July 31

Sept. 15

Nov. 6

Roots

Branches

Leaves

75.21
68.30
59.54 •

69.54
58.53
52.00

73.19
68.43

64.87

Besides being a plant constituent, water is a plant nutrient and as such
is indispensible for the manufacture of plant material, particularly in the
photosynthetic production of carbohydrates. Finally, water is the
medium in which all the nutrients essential to green plants, except carbon,
occur in solution. >

THE WATER REQUIREMENTS OF FRUIT PLANTS
Table 5. — Variations in the Water Content of Apple Sptjrs^^

Feb.

Mar.

Mar.

May

June

Sept.

Nov.

Jan.

4

11

26

13

26

2

19

24

Bearing Spurs:

Wealthy

49.9

65.5

61.1

53.2

50.5

45.7

Ben Davis

60.0

64.6

61.8

55.2

51.6

51.1

Jonathan

47.5

63.2

60.2

54.8

51.6

47.7

Non-bearing Spurs:

Jonathan

47.1

54.8

53.0

51.4

48.6

49.6

Ben Davis

50.8

59.8

55.1

48.6

48.5

48.9

Barren Spurs:

Ben Davis

45.6

52.7

47.8

47.6

44.6

45.5

Nixonite

47.4

....

56.2

51.4

47.6

48.6

43.1

'^ The Water Requirements of Plants in Terms of Dry Weight. — The

water requirement of any plant is defined as the amount of water used
while a unit weight of dry matter is produced. The weights may be
measured in grams or in pounds, but the ratio obtained is the same in
any easel Table 6 brings together data that have a bearing on this
point, as reported by several investigators.

Table

-Water Evaporated by Growing Plants for 1 Part of Dry Matter
Produced*'

Lawes and Gilbert
(England)

Hellriegel
(Germany)

Wollny
(Germany)

King
(Wisconsin)

Peas 235

Barley 262

Red clover 249

Beans 214

Wheat 225

Peas 292

Barley 310

Red clover... 330

Beans 262

Wheat 354

Oats 402

Buckwheat. ... 374

Lupin 373

Rye 377

Peas 479

Barley 774

Maize 233

Millet 416

Oats 665

Buckwheat. . . . 664

Rape 912

Sunflower 490

Mustard 843

Peas 447

Barley 393

Red clover. . . . 453

Maize 272

Potatoes 423

Oats 557

Though Table 6 does not include figures for fruit plants it is presumed
that as a class they do not differ materially from herbaceous plants in
this respect. yHilgard"^ states that oaks require from 200 to 300 pounds
of water for each pound of dry matter produced, while birches and lindens
use from 600 to 700 pounds in producing 1 pound of dry leaves; the
figures for beech and maple are intermediate. Hilgard estimates from

6 FUNDAMENTALS OF FRUIT PRODUCTION

30 to 70 units of water needed for the production of one unit of dry matter
in spruce, fir and pine trees. Thus the range in water requirement for at
least some of the ordinary deciduous trees is similar to that of herbaceous
crops grown under similar conditions.

Two striking points are shown by these figures on water requirements :
(1) the great differences in the water requirements of different species
and (2) the variation shown by the same plant in different sections,
according to the determinations of different investigators.

These differences carry two suggestions of practical import in fruit
production; first, that certain species or certain fruits can do more than
others with a given amount of water, second, that the same species of
fruit plant will produce more vegetative growth with a given supply of
water under certain conditions than under others.

The Water Requirements of Plants in Terms of Precipitation. —
Figures have been given showing the approximate water requirements
of plants in terms of the number of units of water used while one unit of
dry matter is produced. It is interesting to speculate as to what these
figures mean in terms of rainfall or amounts of irrigation water.

Amounts Used by the Plants Themselves. — Thompson ^^^ has calcu-
lated the average weight of wood, roots and leaves produced by a normal
healthy peach tree up to the time it has attained the age of 9 years as
approximately 215 pounds. This represents an average annual dry
weight production of wood, leaves and roots of approximately ^5 pounds.
With increasing age the amount would be somewhat greater. If a 300
bushel per acre yield is assumed, it means the production of approximately
20 pounds of dry matter per tree to be taken away in the form of fruit.
In other words, the mature peach tree would be expected to produce
about 45 pounds of dry matter per year. Assuming a stand of 100 trees
to the acre this would mean a production of 4,500 pounds of dry matter
per acre. If it takes 500 parts of water to produce one part of dry
weight, it would require 22,500 pounds, over 11 tons or nearly 3,000 gallons
per tree to mature the crop properly. This estimate considers only the
amount actually taken up by the roots and for the most part transpired
through the leaves and does not make any allowance for run-off from the
surface, or for seepage and evaporation.' It means 300,000 gallons per
acre equivalent to a rainfall of approximately 11 inches, or an equivalent
amount of irrigation water. For each additional 100 bushels of fruit
per acre approximately 2 acre-inches more would be required b}^ the
plant. Looking at the matter from another angle, for every acre-
inch under the 11 that is denied the trees, there would be a decrease in
yield of approximately 50 bushels. Of course, if the water requirement of
this fruit is only 300 instead of 500 under a given set of conditions, 7 acre-
inches actually available to the trees would mature as large a crop as
the 11 acre-inches in the first instance.

THE WATER REQUIREMENTS OF FRUIT PLANTS 7

That the first presented figures are probably representative for many
tree fruits is suggested by their close agreement with the 9 acre-inches
estimate of Hilgard^^ as the water requirement of 15-year old orange
trees in southern California and the 4,500 gallons per tree estimate of
Duggar43 as the requirement of a 30-year old apple tree. It is interesting
to note that a 12-inch summer rainfall has been estimated as sufficient for
the actual water consumption of 100-year old beech trees standing about
200 to the acre.^^ Data presented in Table 6 show that the variation in
the water requirements of individual crops often exceeds the difference
of 200 assumed in the case of the peach orchard. This emphasizes the
point that it is frequently a matter of much practical importance to
provide the tree with as nearly optimum nutritive conditions as possible,
to secure the economical use of water if for no other reason.

Total Amounts Required for Plants and to Compensate for Evaporation
Run-off and Seepage. — It should be noted that in the last paragraph when
7 to 11 acre-inches of water was mentioned, as approximately the amount
required to mature a peach crop of a certain size, reference was made
only to the water actually taken up and used by the plant. As is well
known, a considerable percentage of the water that reaches the land as
rain or snow or through the irrigation channel is made unavailable by
run-off, evaporation and seepage. The exact percentages removed in
these ways vary greatly, depending on the seasonal distribution of the
rainfall, the topography, the character of soil and subsoil, the atmos-
pheric humidity and other factors. It has been estimated that in the
forest, where conditions are more favorable than in most fruit plantations
for the reduction of run-off and evaporation, probably not more than 35
per cent, of the precipitation actually becomes available for tree growth. '^
In orchard practice then, it is doubtful if much more than one-third of
the natural precipitation or irrigation water can be considered to be
utihzed by the trees, and under poor methods of soil management or in
soils of poor water-absorbing and water holding capacity the percentage
may be much lower.

In the light of what has been said it obviously would be impracticable
to attempt the construction of a table showing the rainfall requirements of
different fruit crops, such as strawberries, cherries, apples and olives, for
there are too many contributing factors to be evaluated, but the general
principles that have been given should be capable of interpretation and
intelligent application to many concrete practical problems as they arise
in orchard management. For instance, with a fairly accurate knowledge
of the mean and minimum rainfall of a particular location and its seasonal
distribution, and after a first hand study of soil conditions as they relate
to moisture, it should not be difficult to determine more or less accurately
the practicability of growing a certain fruit crop without irrigation
facilities, or to determine the relative importance of certain moisture

8 FUNDAMENTALS OF FRUIT PRODUCTION

conserving practices. Experience may be a still better guide but only
to the extent that it gives ability to judge local conditions and so permits
a more accurate interpretation and application of general principles.

Some measure of the way these principles apply to concrete cases
may be obtained from the statement that it has been found practicable
to use irrigation water amounting to about 30 acre-inches for mature
peach trees on some of the gravelly loams of Utah and 40 acre-inches on
full bearing apple orchards on sandy loam in Idaho where rainfall aver-
aged 10 or less inches per year. On the other hand, heavy crops of sweet
cherries, prunes and apricots are obtained without irrigation from
orchards on a light sandy loam at The Dalles, Ore., with an average
annual rainfall of 16 or 17 inches.

Some years ago 16 or 18 inches of rainfall annually was generally
considered sufficient for the production of deciduous fruits in California,
but experience has demonstrated that the percentage of this amount
that is actually left for the trees after run-off, seepage and evaporation
is not adequate for the average orchard with the trees spaced the usual
distances. As a matter of fact there is a growing belief that even a
rainfall of 30 inches in California should be supplemented by provision
for irrigation to take care of occasional emergencies. i"

Planting Distances Related to Moisture Supply. — Application of the
principles just pointed out to particular fruits and particular locations
should be the main deciding factor in determining distance of planting for
orchard fruits, for water supply is most frequently the liqiiting factor in
this connection even though the grower seldom realizes it at the time of
setting. This is contrary, in the way it often works out, to the frequently
repeated statement that trees can be planted more closely in a "poor"
than in a "good" soil. If the soil is "poor" because it is shallow or of
poor water-holding capacity unproductiveness will only be increased by
closer spacing. In soils that are both fertile and well-watered, planting
distance should be governed by the size of the plants and the growing
habit. If they are infertile and well-watered, again planting distance
should be determined by size of plant and growing habit, and the fertility
question solved through the proper use of fertilizers. If moisture is the
limiting factor, regardless of the relative productivity of the land, spacing
should be determined largely by moisture requirements, though due
attention should be given to growth characteristics.

A notable instance of the intelligent and successful application of these
principles to the question of planting distance is found in some of the olive
orchards of northern Africa. Though the usual planting distance for this fruit
in irrigated sections, or in regions of ample rainfall is 18 to 22 feet, near Sfax in
Tunis the trees are planted 60 to 80 feet apart, making only 7 or 8 to the
acre. This arrangement makes possible a profitable dry-land industry without
irrigation, though the mean annual rainfall is only 9.3 inches and though there

THE WATER REQUIREMENTS OF FRUIT PLANTS 9

\

are often several successive years in which the total precipitation does not
exceed 6 inches."^

Another interesting application of the same principle has been recorded in
South Dakota. Cottonwoods planted rather close together for windbreak or
shelter belt purposes, thrive for a number of years, but eventually a stage is.
reached when they begin to die from crowding. If wider spacing or thinning is
practiced their longevity is increased correspondingly.^*

Factors Influencing the Water Requirements of Plants. — It is advisable
at this point to review some of the data available on the economy with
which the plant uses water. From what has been said regarding the total
water requirements of the plant it is evident that only an extremely
small percentage is finally held by the plant as a constituent of the proto-
plasm or is used in the manufacture of chemical compounds. The
greater portion of the water has been required to meet evaporation.
Since the water requirement is a ratio between the water used and the
plant material produced, it is evident that all other factors favoring the
nutrition of land plants will tend to decrease their water requirement and
that all factors tending to increase water loss through transpiration
will increase it. Experimental evidence bearing on the factors affect-
ing, nutrition is available, but the effects of factors altering water loss
have not been so thoroughly studied.

Nutrient Supply. — Table 7 show^s the mean water requirements of
oats and wheat as influenced by fertilizer treatments and Table 8 presents
data showing the effects of various amounts of nitrogen upon the water
requirement of the plant.

It is a reasonable assumption that when the soil solution is poor in
any indispensible element more water must be taken up by the plant to
obtain an ample amount of this element. However, this is true only
within certain limits, because of the abiUty of plants to withdraw from
the soil nutrient materials in proportions quite different from thofee in
which they occur there. Attention has been called to the considerably
higher water requirement of plants in the very rainy climate of Munich,
Germany, than in the drier portions of northern Germany or in Wis-
consin. It is suggested that as the moisture approaches the extreme in a
wet soil the soil solution is diluted; hence conditions are presented that at
least in a way are comparable with those found in a "poor" soil. More
water is required to absorb a given amount of nutrients. Possibly in this
case the poor aeration attendant upon a soil moisture content above the
optimum may also affect the water requirement. The effects of a very
dry soil, which Hkewise increases the water requirement, is attributed by
Briggs and Shantz^^ to the restricted area which the active roots and root
hairs occupy under these conditions. It seems a strange perversity of
fate that the soil conditions and soil treatment which are most likely to
result in a restricted root system, such as heavy soils, hardpan, water-

10

FUNDAMENTALS OF FRUIT PRODUCTION

logging, puddling and baking, are those which lead to an increased water
requirement of the plant.

Table 7. — Mean Water Requirements of Oats and Wheat with Different

Fertilizer Treatments

{From determinations made by Liebacher, Von Seelhorst, Bunrjer and Ohlmer^^)

Mean Water Require-
ments FOR Oats
AND Wheat

Fertilizer

KN P..
N P..
NK..

N..

P K..

P..

Check..

K..

238
243
246
259
294
297
308
314

Table 8. — Effects of Various Amounts op Nitrogen on the Water Require-
ment OF Plants

{After Hellriegel ^2)

CaNOa supplied
(grams)

Dry matter

produced

(grams)

Water

transpired

(grams)

Water
requirement

1.640
1.312
0.984
0.656
0.328
0.000

25.026
23.026
18.288
13 . 936
8.479
1,103

7451
6957
6317
4839
3386
956

292
302
345
347
399
867

Cultivation. — Bearing directly on this point are data obtained on the
effects of cultivation in lessening the water requirements of plants. Some
of these data are presented in Table 9. In every case the water require-

Table '

-The Influence of Cultivation Upon Water Requirements of Plants
in Different Soils'"^

Not cultivated

Cultivated

Sandy loam . . , .

Clay loam

Clay

Type not given .

603
535
753

451

252
428

582
265

ment was materially reduced by cultivation; in one case it was more than
cut in two. In certain soils the influence of cultivation was much more
pronounced than in others. Presumably cultivation affects the water

THE WATER REQUIREMENTS OF FRUIT PLANTS

11

requirements of plants by increasing both the moisture content of the soil
and the supply of available plant nutrients.

Light. — It should not be inferred from what has been said, that the
plant's water requirement is entirely governed by its nutrition. Investi-
gation has shown, for instance, that in tobacco, the amount of water
absorbed is quite independent of the amount of mineral constituents
taken in.** Thus the average ratio of water to ash for six plants grown
in the open was 2,548, while for six plants grown under shade it was 1,718.
These data, however, apply only to the water-ash ratio of plants growing
in full sunlight and in shade. For the water-dry-matter ratio in sunlight
and shade a somewhat different condition holds, probably because of the
influence of the sunlight in promoting photosynthetic activities and the
storage of elaborated materials.

Table 10. — Water Requirements per Unit of Dry Weight of Leaves in Sun and

Shade

{After HoneP^)

(Kilograms per 100 grams of dry leaves)

Species

Sun

Shade

Beech \ 76 . 18

Hornbeam ; 81 . 30

Sycamore 61 . 69

Scots pine 19. 15

Silver fir 13.91

Black pine 8 . 76

107.80

98.90

76.19

5.02

4.85
5.25

Data presented in Table 10 show that in all the broad-leaved trees
studied, the water-dry-matter ratio rose in the shade, though with the
conifers it was greatly lowered. The data on tobacco alone might
suggest that with the nutrition factor constant more water would be
required in exposed than in protected situations and that shading and
windbreaks might be expected to reduce materially the plant's water
requirements. On the other hand, the data of Hasselbring and Honel
together lead to the inference that though the mineral requirements of the
plant as related to water suppl}^ may be increased in exposed and de-
creased in protected situations, tissue building and the manufacture
and storage of elaborated materials may be promoted by the opposite
conditions.

In General. — Recent investigations by Briggs and Shantz^^ iead
them to conclude that when a crop is thoroughly adapted to a certain
environment it has its water requirement at the minimum and that its
water requirement gradually increases as it is forced to grow in more
and more uncongenial conditions, whatever they may be. Thus as a

12 FUNDAMENTALS OF FRUIT PRODUCTION

rule, cool weather crops have a lower water requirement in a cool than
in a warm climate, the reverse being true of warm weather crops. In
the latter instance, however, the difference is less pronounced, due to
the effect of increase in temperature upon transpiration in general.

As will be shown later, however, plants are able to adapt themselves
in certain ways to dry conditions, the result being a lowering of what
otherwise would be a very high transpiration rate. Only limited data
are available as to how these tendencies balance each other and as to
what is the final resultant. Leather^^ has found that at Pusa, India,
the water requirements of wheat, barley, oats and peas are nearly twice
those of maize, though this ratio does not hold in most sections (see
Table 6) . Apparently this high water requirement of these cool season
crops is associated with their maturing during the dry season, while
in India maize matures during the more humid season of the monsoon.
The greater water requirement of plants cropped by means of pasturing
as compared with that of plants which are allowed to continue their
growth uncropped,^^'' may be taken as an indication that new growth
has a higher water requirement than older growth. It would seem that
the water requirements of different plants vary mainly because of differ-
ences in the economy of their nutrition and })ecause of different physio-
logical and structural modifications affecting their rate of transpiration.

Some Applications to Practice. — The influence of both the chemical
and the physical conditions of the soil upon the water requirement
of the plant is of practical importance to the grower, the influence of
soil productivity being particularly significant. Few realize that, when
the soil provides conditions for tree growth that are optimum from the
standpoint of nutrient supply, actually less water is required for a given
yield than when the plant is handicapped because of the lack of some
nutrient as well. This difference in water requirement is not one of
academic interest only; it is large enough frequently to account for crop
failure or crop success under conditions of limited water supply.

A quotation from King^^ jg to the point: "In the long series of studies made
by the writer on the amounts of water required for a pound of dry matter, it was
found true, almost without exception, that strong vigorous growth and high
yields of dry matter are always associated with a small transpiration of water
when measured by the dry matter produced."

Even more significant is the statement of Leather,*'' who made a careful
study of this question in the dry climate of Pusa, India: "The effect of a suitable
manure in aiding the plant to economize water is the most important factor
which has yet been noticed in relation to transpiration."

It would probably be a mistake to advise watering or irrigating trees
by fertilizing them, because the advice would be taken too literally.
Nevertheless, the reduction of the water requirement of the plant by
maintaining the soil in a condition as near as possible to the optimum

THE WATER REQUIREMENTS OF FRUIT PLANTS 13

with respect to nutrient supply should be a constant and conscious aim
in scientific orchard management, though perhaps the water conservation
influence of optimum growing conditions may be more or less masked
by the increased requirements for the accompanying increased growth.

The Wilting Point for Fruit Plants. — There seems to be some differ-
ence of opinion as to how near to the hygroscopic coefficient plants can
exhaust the water supply of the soil. Loughridge states that certain
plants can remove enough of the hygroscopic moisture of the soil to
maintain life though they cannpt grow under these conditions; Hilgard
states that soils of great hygroscopic power can withdraw from moist
air enough moisture to be of material help in sustaining the life of vegeta-
tion in rainless summers or in time of drought, though only a few desert
plants can maintain normal growth.^* In most plants, however, wilting
will occur before the moisture content of the soil has been reduced to its
hygroscopic coefficient.

Wilting Coefficients. — The work of Briggs and Shantz^" has led them

to conclude that the wilting coefficients for most soils equal their

hygroscopic coefficient _,, , . .,, , . ^

— ^po I n nio Thus a sandy loam with a hygroscopic coefli-

cient of 3.5 per cent, would have a wilting coefficient of about 4.8 and a
clay loam with a hygroscop/c coefficient of 11.4 would have a wilting coeffi-
cient of 16.3 per cent. These investigators state, "The wilting coeffi-
cient is the same, within the limits of experimental error, for a plant in
all stages of development. In other words, the soil-moisture content
at the wilting point is not dependent to any material degree upon the
age of the plant. ... [It] is not materially influenced by the dryness of
the air, by moderate changes in the solar intensity, or by differences in the
amount of soil moisture available during the period of growth, "^o It
ranges for different soils from less than 1 per cent, in the coarsest sands
to as high as 30 per cent, in the heaviest clays. "The use of different
plants as indicators of the wilting point produces only a relatively small
change in the wilting coefficient of a given soil. Representing the mean
value of the wilting coefficient of a given soil by 100, a range from 95
to 105 approximately, would result from the use of different plants
as indicators, . . . The xerophytes tested gave a mean ratio inter-
mediate between the hydrophytes and mesophytes. This would indicate
that plants native to dry regions are unable to reduce the water content of
the soil to a lower point at the time of wilting than is reached by other
plants. . . . There is evidence that drought resistance in a plant is not
due to an additional water supply made available for growth by virtue
of a greater ability on the part of that plant to remove moisture from
the soil. "20

Wilting Under Field Conditions. — The work of Briggs and Shantz on
wilting coeflficients of different soils was done, however, under fairly

14 FUNDAMENTALS OF FRUIT PRODUCTION

uniform conditions of temperature (about 70°F.) and liumidity (about
85 per cent.), conditions under which the evaporating power of the air
is low. In other words the plants exhausted the water supply of the
soil slowly and because of favorable atmospheric conditions were actually
able to use the last of the "available" moisture before transpiration
demands overtook absorption. In the field, wilting does not usually
occur under such favorable atmospheric conditions — favorable from the
standpoint of soil moisture supply.

It has been found that when atmospheric conditions are such as to promote
rapid evaporation, "the departure of observed from calculated soil moisture
contents at permanent wilting is extremely marked for all soils; permanent
wilting in the open occurs with a soil moisture content from 30 to 40 per cent, in
excess of that present when the same or similar plants are wilted in a moist
chamber. . . . Marked increase in the evaporating power of the air acceler-
ates the outgo of water without producing a proportionate increase in its rate of
entrance from the soil. With every increase in transpiration rate above a
certain Umit, this rate becomes, therefore, more and more significant as a factor
determining the extent to which the soil water may be exhausted by the plant
before the advent of permanent wilting. Thus, permanent wilting under high
rates of evaporation does not at all indicate that the available soil moisture
has been exhausted. Instead, it merely indicates the reduction of the soil
moisture content to a magnitude which corresponds to the residue of water left
in the soil at the time when excess of transpiration over absorption has brought
the entire plant into the permanently wilted condition. Repeated determi-
nations, under widely varying conditions but with relatively high evaporation
rates, show that the magnitude of this residue is directly related to the intensity
of the evaporating power of the air."^^

It is these higher wilting coefficients under the comparatively high
transpiration rates of midsummer which interest the deciduous fruit
grower most frequently. Perhaps the wilting coefficient based upon soil
texture and calculated for low transpiration rates is most important in
determining whether the plant shall or shall not survive the period of
drought, for before death occurs there usually will be a shedding of
foliage and other protective measures will be taken to reduce moisture
requirements and lower the transpiration rate. On the other hand the
effects of drought upon the vegetative activities of the tree during the
summer, upon the size of its fruit and upon the abscission of its leaves,
flowers and partially grown fruit are exercised during periods of very
high transpiration rates. This means that correspondingly high wilting
coefficients prevail and that the aim of the grower should be, as far as
possible, to maintain the moisture supply of the soil well above these
higher amounts.

Wilt 171(1 Coefficients and Drought Resistance. — Tables 2, 11 and 12
compiled by Loughridge, showing the minimum water requirements oi

THE WATER REQUIREMENTS OF FRUIT PLANTS

15

certain fruits in comparison with those of certain other plants, are par-
ticularly interesting in this connection.

Table 11.

-Minimum Water Requirements of the Apricot in Different Soils'
(Records made in early September)

Locality

Condition of
trees

Moisture in 4 feet of soil (per cent.)

Total

Hygro-
scopic

Free

Tons of free

water per

acre

Dark loam Sisquoc Valley .

Loan

Loam

Loam

Loam

Loam

Black clay. . . .
Gravelly loam

East of Ventura (shallow
cultivation)

Ventura (shallow culti-
vation)

Ventura (deep cultivation)

Los Berrios Hill

Experiment station

Niles (no cultivation)

Niles (cultivation 3 inches)

Niles (cultivation 6 inches)

Woodland

Woodland

Sand East of Davisville

Alluvial Davisville

Good

5.5

3.1

2.4

Growth 6 inches

6.5

5.5

1.0

Growth 8 inches

5.6

4.2

1.4

Growth 36 inches

9.3

5.5

3.8

Good

1.7

0.8

0.9

Good

6. 1

5.0

1.1

Very poor

4.4

4.4

0.0

Fair

5.4

3.3

2.1

Excellent

6.3

3.3

3.0

Excellent

18.8

9.6

9.2

Poor

6.9

5.0

1.9

Good

4.8

3.6

1.2

Good

9.0

6.9

2.1

112
304
72
88
0
168
240
736
152
96
168

In commenting upon these tables Loughridge states: "The apricot, olive
and peach do well on less water than other orchard fruits, 1 per cent, of free
water being sufficient if constantly present. With this amount the citrus fruits,
pears and plums were found to suffer, though the citrus fruits were in good con-
dition with a little more water. The almond seems to require about twice the
water that the apricot does, while the prune was found to suffer with three times
the water in which the apricot was flourishing.

" Emphasis should be placed on the fact that this free water should be present
throughout the soil to the depth of 4 feet at least and especially around the
feeding rootlets of the tree. The surface of the soil may be wet, and yet the
tree may suffer if the ground below be so dry that the rootlets are not able to
draw sufficient moisture. This drying-out of the under-soil is one of the evil
effects of a severely dry season, and unless the rainfall of the succeeding winter be
sufficient to penetrate to the depth of several feet and moisten the soil around
the rootlets the trees will suffer almost as if no rain had fallen. The same is
true with regard to irrigation ; those who have to resort to the artificial application
of water to their lands because of insufficient rainfall, should so apply it that it
may reach the tree rootlets at the depth of several feet below the surface. This
is too often not done, and examination will show that the water has, even after
2 days' irrigation with running water in furrows, not soaked down more than 10
or 12 inches, if that much."^^

At first, it may seem that the field observations of Loughridge are
not in agreement with the conclusion of Briggs and Shantz that the
wilting coefficients are practically the same for all plants growing in the

16

FUNDAMENTALS OF FRUIT PRODUCTION

Table 12. — Relative Water Requirements of Different Fruits in Different

Soils
(After Loughridge^')

Free water in
4 feet of soil

Plants for which the soil

moisture is just above the

minimum; cultures did well

Plants for which the soil
moisture is just below the
minimum; cultures suffered

Percen-
tage

Tons per
acre

Sandy soils — hygroscopic moisture 1 to 3

1
2.0 160
2.5 200
3.5 280

Apricots, saltbush
Olives, peaches, wheat

Olives, peaches, plums, grapes
Cherries, pears
Citrus, prunes

Sandy loam soils — hygroscopic moisture 3 to 5

4 to 5

5 to 6

400
480
560
640
720

Saltbush
Apricots

Apricots

6 to 7

7 to 8

Almonds, plums
Apples, olives, peaches,
walnuts

8 to 9

Loam soils — hygroscopic moisture 5

4 to 5

5 to 6

6 to 7

7 to 8

400
480
560
640
720
800

Saltbush

Apricots, citrus, figs, walnuts

Prunes, grapes

Apricots, almonds
Prunes

8 to 9

9 to 10

Clay loams — hygroscopic moisture 5 to 7

6 to 7

7 to 8

8 to 9

560
640
720

Peaches, grapes

Peaches, plums
Wheat
Sugar beets

Clay soils^ — hygroscopic moisture 7 to 10

8 to 9

9 to 10

720
800
880
960
1120

Apricots
Grapes

Figs

10 to 11

Wheat

11 to 12

Citrus

12 to 14

Corn, sugar beets

THE WATER REQUIREMENTS OF FRUIT PLANTS 17

same soil. The greater tolerance of the apricot, olive and peach for drought
probably is not due to a utilization of the soil water in contact with their
roots greater than that of other plants, or in other words, to the reduction
of the soil water content to a lower wilting coeiEficient. It is possibly
associated with a greater ability of their roots to exploit every bit of soil
within their range, or to a wider range that their roots may possess.
It is important that both factors be kept in mind, namely, the marked
uniformity in the wilting coefficient for different plants and the marked
difference in their ability to get along on a limited water supply, for
both are factors that may alter materially cultural methods, the choice
of stocks upon which the fruits are grown and planting plans. As a rule
it is not necessary to wait until wilting actually begins to determine when
the danger point is at hand. Most plants will show signs of distress
before the moisture supply of the soil reaches its wilting coefficient.
Many weeds or cover crop plants growing among the trees may wilt
noticeably before the trees give visible evidence of moisture deficiency.
Temporary v/ilting at the middle of the day is quite likely to be an indica-
tion that the water supply of the soil is approaching a critical point and
efforts should be made to deal with the situation promptly.

Summary. — Water is an important plant constituent, composing
from 50 to 85 per cent, of most living tissue. It is the solvent for all
plant nutrients. The intake of from less than 30 to more than 1,000 parts
of water is required for each part of drj^ matter produced, the amount
varying with the species and with the conditions under which the plant
is grown, rWhen seepage, run-off and evaporation are included this
means that for the average deciduous fruit crop a precipitation of some-
thing like 30 inches is requiredJ Inability to secure the requisite amount
of water checks growth and reduces yield and often a relatively small
amount of additional available moisture at a critical period will make
possible material increases in the size of the crop. Planting distances
in the orchard should be determined largely by the available moisture
supply and the growing habits of the particular species or variety. The
minimum water requirement of the plant, in terms of units of water
per unit of dry matter, is correlated with thorough acclimatization and
optimum growing conditions. Favorable nutritive conditions in particu-
lar make for water economy. The final wilting coefficient is practically
the same for all plants in all soils, but it varies greatly for the same plant
with different soils, being low for soils of coarse texture and very high
for fine clays. In the field, temporary wilting generally occurs before
the wilting coefficient is reached, the evaporating power of the air being
an important determining factor. In practice it is therefore desirable\
to maintain the soil moisture supply well above the wilting coefficient,'^
Different species and varieties show considerable variation in their
ability to withstand drought.

CHAPTER II

THE INTAKE AND UTILIZATION OF WATER

Under favorable conditions the entrance of water into the plant,
its translocation and its egress take care of themselves, without conscious
manipulation by the grower. At times, however, one or another of
these processes should be controlled to some degree and pathological
symptoms or conditions may arise which can be understood only through
a knowledge of these processes.

WATER ABSORPTION

Proper absorption, as the necessary prelude to the other processes,
is of obvious importance. Furthermore, it is the process with which the
grower is most frequently brought into contact.

The Water Absorbing Organs. — The root is the absorbing system and
for practical purposes all the water which enters the plant is absorbed
through the root. There are indeed other sources from which moisture
can be obtained, such as, for example, the water resulting as an end prod-
uct of the oxidation of carbohydrates, which has been termed metabolic
water,^ but such sources are significant only in extreme circumstances.
The absorption of water by the root takes place chiefly through special
structures, the root hairs, which are extensions from the epidermal cells
of the root a short distance back of the growing point. The absorption
power of the root depends upon the extent of its surface and it is increased
to a marked degree by the presence of root hairs. The ratio of the
surface of the root supplied with hairs to one from which the hairs have
been removed has been calculated as 5.5 : 1 for maize and in the garden
pea 12.4 : l.^"^ These figures give some idea of the efficiency of the root
hairs for water absorption. Moisture can be absorbed by the root tip
and also through the surface of the root for some distance above the zone
of root hairs. In the older portions of the root the cortex and epidermis
die and peel off as a result of the formation of deep seated cork; hence,
this portion of the root is incapable of absorbing appreciable amounts
of water.

The number of root hairs varies with different plants and, in the same
plant, with the conditions under which it grows. Thus, the development
of root hairs is reduced in wet soil, or in very dry soil and may be entirely
prevented where the root is in contact with water. ^^ This occurs in
certain plants, such as the cranberry, which normally grow in bogs where
the roots do not develop root hairs.

18

THE INTAKE AND UTILIZATION OF WATER 19

The Handling and Transplanting of Nursery Stock. — The practical
bearing of the point just brought out upon the transplanting of fruit
trees or other plants is important. The transplanting of most deciduous
fruit trees and of many other plants is usually accompanied by the loss
of a considerable part of the large and of the fibrous roots and by the
destruction of practically all of the root hairs. New root hairs must be
produced before active absorption can begin; these new root hairs will
be formed only on new branch rootlets. This means that if the top of
the plant has any considerable water requirement at the time of trans-
planting it will suffer for lack of moisture and perhaps wilt and die if new
roots are not formed immediatel3^ The grower is likely to place a rather
high premium upon a large and extensive root system in nursery trees,
thinking that they will surely absorb enough water to maintain the
moisture supply of the tops until new roots are formed. A fairly ex-
tensive root system in the nursery tree may be an asset, but not because
these roots devoid of root hairs are of any material aid in the direct
absorption of water. This explains wh}'- tree roots pruned according to
the so-called Stringfellow method at the time of setting are usually as
sure to take root and grow as those pruned less severely, though the
subsequent growth may not be so satisfactory. More important still,
it explains also why it is desirable to prune back the tops of most plants
at the time of transplanting so as to reduce transpiration to a minimum
and prevent desiccation. It shows furthermore why in climates not too
cold, fall transplanted trees are more likely to give a good stand than
corresponding spring-set trees, for during the winter months new root
formation is initiated and water can be absorbed in the spring as fast as
the new shoots and leaves use it.^^^ The spring-set trees, on the other
hand, must wait until new roots are formed before they can take up
moisture and if soil conditions remain imfavorable for this root formation
and atmospheric conditions stimulate vegetative growth of the top, the
pushing shoots will wilt and die, and the tree will be lost. In the autumn
conditions are favorable for root growth for some time after good growing
conditions for the top have passed ; in the spring they frequently become
favorable for top growth before or simultaneously with suitable growing
conditions for the roots.

In the light of the facts presented it is not difficult to understand why the
transplanting of trees after their buds have once started in the spring is
attended with very uncertain results. It is simplj^ a case of a demand
for water for supplying the top, great in comparison with the demand
while in the dormant stage, a demand that cannot be met by the roots
because, temporarily, they are practically without absorbing organs. If
it is necessary to plant trees late in the spring, after some vegetative
growth may be expected to take place, it is well to remember that the
transplanted tree will have practically no root hairs for several days or

20 FUNDAMENTALS OF FRUIT PRODUCTION

even weeks after the transplanting operation and that, therefore, the
tree must be kept practically dormant until it is actually planted. This
may be done by holding it at a low temperature in shade, or, if suitable
storage facilities are not available, by repeatedly lifting and immediately
heeling in again. The effect of the low temperature is to keep the tree
dormant because no top growth will take place at a temperature approxi-
mating the freezing point. The effect of the repeated lifting and heeling
in again is to check growth of the top by preventing the formation of new
roots and root hairs though the temperature may be suitable for their
development and thus cutting off the tree's water supply without which
the shoots are retarded.

It is necessary to move evergreen trees of any considerable size, like
the pine or the orange or the avocado, with a ball of earth so that at least
a moderate portion of the real water absorbing organs of the plants are
retained and remain active; otherwise, the foliage wilts or falls off and
the plant is likely to die. The facts that have been presented explain
why excessive watering will not make up for the loss of roots, and particu-
larly of root hairs, by trees transplanted during their growing season.
Though their remaining roots may be surrounded by a nearly saturated
soil they cannot take up appreciable quantities of this moisture.

The Water Absorbing Process. — The process by which water is absorbed by
the root hairs is osmosis. A plant cell such as the epidermal cell of a root with a
root hair attached has a cell wall Hned with protoplasm surrounding a central
vacuole. When the root hair comes in contact with the moisture of the soil an
osmotic system is established and the protoplasm of the root hair becomes a
semi-permeable membrane separating two solutions, the soil solution on the
outside and the vacuole on the inside. These two solutions have different
concentrations, that of the vacuole being greater than that of the soil solution;
in other words there is less water in the vacuole than in a corresponding volume
of soil solution. To equalize the concentrations of water on either side of the
membrane water passes from the soil into the vacuole.

The absorption of water in this way by the cell must increase the size of the
vacuole and therefore induce a simultaneous distention of the cell wall. Eventu-
ally the elasticity of the cell wall will exert such a pressure on the vacuole that
no more water can be absorbed and there is a balance between the elasticity of
the cell wall and the osmotic pressure of the cell contents; the cell is in a state of
turgidity. Under ordinary conditions all the living cells of a plant are turgid,
but this turgidity may be lost, either by an increase in the plasticity of the cell
wall or by the loss of water from the vacuole. Either process destroys the
balance on which turgidity depends.

Factors Enabling the Root to Exploit the Soil. — Several factors cooperate in
enabling the plant to exploit the moisture content of the soil. The root hairs are
continuously formed anew at a certain distance from the tip of the growing root
so that a new supply is produced as fast as the older root hairs die. As these
extend into untouched portions of the soil, the roots are continually pushing into

THE INTAKE AND UTILIZATION OF WATER 21

new soil throughout the growing season, leaving those regions from which they
have already drawn their water and nutrient supply.

Furthermore, the absorbing capacity of the root hairs is not limited to that
portion of the soil with which they come in immediate contact. As the root
hair withdraws moisture from the water films about the soil particles, these films
become thinner than those about neighboring soil particles. Since surface
tension maintains an equilibrium between the amounts of water on contiguous
surfaces, water tends to distribute itself evenly. As a result it flows toward
those parts of the soil from which water has been withdrawn, hence, in the
direction of the root hairs. In this way the individual root hair is capable of
absorbing water which is a considerable distance away from it.

The movement of the roots, which their growth in length brings about, is
likewise a movement in a definite direction, for the root tip is sensitive to differ-
ences in the amount of moisture present on opposite sides and responds to this
difference by bending toward that side where there is more moisture." By this
means roots grow toward those portions of the soil which have the optimum
water content.

Adaptation of Roots to Moisture Conditions. — In addition to the factors
already discussed the adaptability of the root system to the condition of the
soil is important in enabling the plant to obtain a maximum supply of water.
A small water content of the soil, within certain limits, stimulates the roots to
greater development, resulting in a greatly increased absorbing surface. In
spite of this greater surface, however, the supply of water is often restricted
and the portion of the plant above ground is not capable of much development.
In one investigation the ratio of roots to tops for oats, grown in dry soil, was found
to be 1:7.4 and in wet soil 1:16.16.^'^^ In this second instance the roots
remained small because the optimum conditions for moisture were exceeded.
These figures give some indication of the correlation which exists between root
and shoot development though the relation may be quite different in other
plants and under other conditions. The accommodation of roots to soil con-
ditions varies with different species. Thus Weaver^^^ finds that 7 out of 10 species
investigated by him respond to changed environmental conditions. Pulling^"^
states that characteristically shallow rooted plants such as Picea Mariana,
Larix laricina and Betula alba papyrifera, as well as the more deeply rooted
Pinus Strobus and P. Banksiana do not adapt themselves, while the shallow
rooted Picea canadensis and the deeply rooted Popidus balsamifera exhibit con-
siderable plasticity. In another place the root distribution of orchard trees is
discussed in greater detail and some of its relations to water supply are mentioned
in that connection.

Factors Influencing Rate of Absorption. — The ability of plants to
absorb water depends upon the absorbing surface of their roots and on
the following external factors: the power of the soil to deliver water, the
temperature and aeration of the soil, its chemical properties and the
concentration of the soil solution. Other things being equal the higher
the temperature the greater the absorption until a certain optimum value
is reached; temperatures above this optimum retard water absorption.

22 FUNDAMENTALS OF FRUIT PRODUCTION

Though water absorption is greatly reduced at low temperatures many
plants are able to take up water when the soil temperature is below 0°C.,
for even at —3 or — 4°C,, much of the soil water is not frozen and the soil
is still capable of delivering water to the root surface. ^^

The amount of oxygen in the soil air has a marked effect on root
absorption; if for any reason the supply of oxygen is inadequate, absorp-
tion ceases. It should be remembered, however, that oxygen dissolved
in the soil water is available to the root system. In fact, the oxygen
absorbed by the living cells of the root must be dissolved in water before
it can be taken up. The susceptibility of the roots to differences in the
oxygen supply varies markedly with different plants. Thus roots of
Coleus Blumei and Heliotropium peruvianum showed injury after three
days' exposure to a soil atmosphere mixed with 25 per cent, nitrogen
gas, while roots of Salix sp. grew freely in pure nitrogen. ^^ There is some
indication that roots of deeper penetration are less responsive to changes
in aeration and temperature than the more superficial roots.

The effect upon top growth of reduced absorption by the roots occasioned
by poor aeration incident to a condition of the soil approaching saturation, is
strikingly illustrated by the behavior of established trees of certain kinds in
portions of India. Howard and Howard^^ record that these trees naturally
have a short resting period during midwinter, a period often accompanied or
preceded by leaf fall. With a rise in temperature during February, new leaves,
shoots and flowers are formed and rapid growth continues until hot weather
checks it. A second period of rapid vegetative growth is inaugurated with the
advent of the monsoon, but when the soil approaches saturation, growth slows
down again or nearly ceases. There is a third period of vegetative activity at
the and of the monsoon when, with the drying out of the soil, the attendant
aeration makes increased root activity possible. This third period of growth is
finally checked by the low temperature of the winter season.

Transpiration (and hence absorption) is decreased by the addition of small
amounts of tartaric, oxalic, nitric, or carbonic acid to the soil and is increased
by alkalies, such as potash, soda, or ammonia, though under field conditions
these factors are apt to be of minor importance. ^^ An increase in the concen-
tration of the soil solution likewise decreases water absorption by its effect on
the osmotic process. Such effects probably vary greatly with different plants.

Submergence and Root Killing. — The effects of submergence on decidu-
ous fruit plants are due primarily to the diminished aeration of the roots
which this ordinarily involves. It has been found that certain land plants
with submerged roots absorb water more rapidly at first but that later
the rate of absorption falls off to a marked degree, the plants wilt and
after a few days the leaves become yellow and drop.^^ After prolonged
submergence the roots below the surface die and no new roots develop;
eventually the entire plant succumbs. All of these effects, however,
were alleviated or eliminated when the roots were submerged in aerated

THE INTAKE AND UTILIZATION OF WATER 23

water. Under these conditions some plants have survived submergence
for three weeks. The roots hved in this aerated water but grew more
slowly and in some cases root hairs developed. Even the roots of the
cocoanut, though often found in a practically saturated soil, are sensitive
to a lack of aeration, for thej^ thrive only if the water bathing them is
continually moving and they die if it is stagnant.^ It is not the water
but the lack of air in standing water that is harmful. The submergence
to wliich the roots of orchard trees are occasionally subject in certain
locations is of a type that is generally accompanied by a lack of aeration.
The result is a prompt killing of the root hairs, followed more or less
closely by the death of the roots themselves. This is likely to be the
case when roots are submerged by the rise of the ground water in irrigated
sections and in orchards planted in low-lying poorly drained ground. It
is not so apt to be the case with trees planted on low but well drained
bottom lands, or alluvial soils subject to occasional overflow of short
duration during periods of flood. Even in the latter instance, however,
it is noteworthy that the trees are apt to be severely injured, or killed,
if the roots are submerged for more than several days during the growing
season or for a period of as many weeks during their dormant season.
Certain bog plants like the swamp blueberry and cranberry, however,
will stand complete submergence of their root systems for a period of four
of five months during the winter, though submergence of as many days
during the growing season is attended with great risk.^'' There is good
reason to believe that many of the troubles variously attributed to
winter injury, drought and soil infertility may be end products of tempo-
rary root submergence that leads immediately to a kind of root pruning.
It should be realized that root systems may be submerged though no
water stands on the surface of the soil. More attention is devoted to this
phase of the subject in a later chapter of this section and in the section
on Temperature Relations.

TRANSPIRATION

Large quantities of water are lost by evaporation from. the portions
of the plant above ground and particularly'- from the leaves. Duggar*^
estimates that an apple tree 30 years old might lose 250 pounds of water
a day or possibly 36,000 pounds a season. At this rate an acre of 40
trees would represent a water elimination of 600 tons a year. This
water loss from plants is not strictly a physical process of evaporation,
because it is influenced by factors such as light and is subject to some
degree of modification by the plant. Since evaporation is not affected
in the same way by these factors the water loss of plants must be con-
sidered a physiological process; hence it is designated transpiration.
Whether transpiration performs any useful role in aiding the process
of absorption of mineral constituents, or in lowering the temperature

24

FUNDAMENTALS OF FRUIT PRODUCTION

.'Pbf the leaves is an open question. The generally accepted opinion is
SSthat transpiration is a necessary evil rather than an advantage to the
;^plant.

. %t Cuticular and Stomatal Transpiration Compared. — Transpiration is
jgof two kinds; a small amount of water is lost from the cuticular surface
*^of the leaf, but by far the greater proportion is lost through the stomata.
^Some measure of the proportion between these is furnished by the data
'^presented in Table 13.

Table 1.3.— Relation Between

5TOMATAL Distribution and

Trans filiation

Stomata per square millimeter

Water transpired in 24 hours from
20 square centimeters

Upper surface

Lower surface

Upper surface
(grams)

Lower surface

(grams)

Pear

Apple

0
0
0
0
0

253

246

14.5

25

60

5
20

Red currant

Canna

35

Linden

49

The amount of cuticular transpiration is relatively constant while the amount
of stomatal transpiration can be regulated by the activity of the stomatal guard
cells. In sunlight these cells manufacture sugars by means of the chloroplasts
which they contain and thereby increase their osmotic concentration so that they
absorb water from the surrounding tissue and increase in turgidity. The walls
of the guard cells are peculiarly thickened so that when the cells are turgid, the
stomatal aperture is open and when turgidity is lost the aperture is closed. The
guard cells are likewise sensitive to light stimuli, to which they respond by changes
in turgidity more rapid than those produced in the manner just described.

The water lost by transpiration from the leaves first evaporates from the
surface of the mesophyll cells in the interior and collects as water vapor in the
intercellular spaces. This water vapor then passes from the intercellular spaces
of the leaf through the stomatal apertures to the outside. This is largely a
process of diffusion and follows Brown and Escombe's Law which states that
diffusion through an aperture is proportional to the radius and not to the area of
the aperture. Thus the diffusion which might take place through 10 small
apertures with a radius of 1 millimeter, would be equal to the diffusion which
could take place through one aperture with a radius of 1 centimeter. It is
evident that if the apertures are sufficiently small and are scattered over a surface
in such a way that the diffusion through one does not interfere with that through
another, then diffusion through such a perforated surface will take place as if no
surface were present. When the apertures are distributed over a surface so that
they are about 10 diameters distant from one another, the maximum amount of
diffusion is possible. This proportion holds roughly for the distribution of the
stomata in most leaves. It is evident that when the stomata are opened the
surface of the leaf offers little or no resistance to the diffusion of water vapor.

THE INTAKE AND UTILIZATION OF WATER

25

but that when the stomata are closed transpiration practically ceases except for . •
cuticular water loss. ^ ,

Variabilitii in Number of St07nata in Accordance with External Condi- .
iions. — The number of stomata on the leaf surface is not determined .*"
in the unopened bud, but varies with the conditions under which the
leaf develops.

Table 14 presents data showing the reduction in the number of stomata -"
per square millimeter when the available water supply in the soil is reduced.
Though the reduction in the number of stomata per unit of leaf surface
is not exactly proportional to the reduction in soil moisture, there is a very
material decrease, indicating a marked ability on the part of the plant to adjust
itself to its water supply. This flexibility is perhaps one of the reasons why
many plants are able to thrive under wide ranges of soil moisture and atmospheric
humidity.

Table 14. — The Influence of Soil Moisture Upon Number of Stomata

{After Duggar*^)

Percentage of water

Stomata per square millimeter

in sand

Corn

Wheat

38

181

103

30

130

85

20

129

82

15

124

81

11

107

59

However, the number of stomata cannot be modified after the leaf
once attains full size. This means that its ability to adapt itself
in this way to extremes of soil or atmospheric moisture must be exercised
early in the season. Foilage developing in the spring on a plant in a
moisture laden soil will probably transpire somewhat more per unit of
area later in the season, than it would had it developed under drier
conditions, though the increase will probably not be proportional to
the increase in number of stomata. However, the extra amount of water
required by such plants during the summer is due mainly to the in-
creased leaf area. If trees are so handled early in the season as to develop
large water requirements the cultivator should recognize the fact that
this demand will be more or less continuous through the summer and
shape his cultural practices accordingly.

Factors Influencing Rate of Transpiration. — The rate of transpiration
is influenced by a number of factors, such as the character of the
cuticle, the age of the leaf, defoliation, wind velocity, light and tempera-
ture.

26 FUNDAMENTALS OF FRUIT PRODUCTION

Character of Cuticle. — The cuticular water loss of plants is affected materially
by the thickness and character of the cuticle. The presence of a waxy coating
diminishes the amount of water loss. The effectiveness of such a coating may be
seen from data given by Boussingault^® which show that an apple loses 0.05
grams of water per cubic centimeter per hour through its cuticle, but that when
the cuticle is removed it loses 0.277 grams or 55 times as much from the same
surface. Cork is also an effective protection against water loss. A peeled
potato loses water 64 times as rapidly as an unpeeled potato. ^"^

Age of Leaf. — The amount of transpiration from a leaf hkewise varies with
age. The youngest leaves transpire most for the cuticle is thin and permeable;
as the leaf grows older the cuticle thickens and permeabiUty decreases, and with
it the rate of transpiration. Later this rate rises to a second maximum, lower
than the first, as the result of the development and functioning of the stomata.
Then as the leaf ages further there is another decline in the rate of transpiration
due possibly to changes in the properties of the epidermis.

Defoliation. Summer Pru7iing. — Data presented in Table 15 show
that the rate of transpiration is also affected by defoliation. This indi-
cates that, though midsummer or late summer pruning to protect a
plant and its fruit from drought injury will reduce its water requirements
somewhat, the reduction will not be directly proportional to the percent-
age of the foliage that is removed.

Tabt-e 15. — The Influence of Defoliation Upon Rate of Transpiration in a

5-YEAR Old Fir Tree

(After Hartig ^^)

Percentage Evaporation per Square Meter of

OF Foliage Surface (Grams)

100 270

60 272

30 460

10 607

Wind Velocity/. Windbreaks. — The agencies thus far mentioned as
affecting rate of transpiration have been internal to the plant. Various
external factors also have their effects. The most important of these
external factors are atmospheric humidity, wind, light and temperature,
which together determine the evaporating power of the air. It has been
found that the rate of water loss is a simple linear function of the evapo-
rating power of the air and that the leaf gives off water as if the water
were at a temperature about 1°C. higher than the surrounding air.^"

Water loss in wind is greater than in still air. This is brought out
by the data presented in Table 16. Attention has been called already to
the fact that one of the functions of the windbreak is to reduce the water
requirement of the plants in its shelter. Probably the decrease in the
amount of water required for a given unit of dry matter is not directly
proportional to the lessened rate of transpiration consequent upon de-

THE INTAKE AND UTILIZATION OF WATER

27

creased wind velocity, but in both cases the saving of water is great
enough to be of real importance in plant production.

Table 16. — The Influence of Wind Velocity Upon Rate of Transpiration

(After EberfW)

Wind velocity

Evaporation in 5 minutes from free-moving

Check in still air

second) humidity

Before (Grams)

After (Grams)

2
3

5

0.593
0.631
0.638

0.371
0.358
0.361

0.311
0.320
0.319

Light. — In its lower ranges increased illumination has been found to cause
increased transpiration irrespective of the action of the guard cells already-
discussed. '*'' The effect of light may be due to absorption of radiant energy or to
increased permeability of the membranes. The heat set free by chemical proc-
esses or received by radiation may pass directly into the latent form without
effecting a rise in the tempeature of the leaf: that is, it may be used completely
in vaporizing water. Protoplasmic membranes are more permeable in light
than in darkness and the same seems to hold for the non-cutinized cell wall.^^

This increased rate of transpiration produced by exposure to hght probably
accounts for the characteristic action of illumination in retarding the rate of
growth and the dependence of green plants upon hght for the differentiation of
tissues. ^^ The gradual reduction in the osmotic concentration of the stomatal
guard cells found by Wiggins^^^ may also be attributed to increased permeabihty
after exposure to hght. In the afternoon the manufacture of soluble carbohy-
drates is apparently more than offset by the increased permeabihty. Hence,
the osmotically active substances in the guard cells diffuse into the adjoining
cells, the guard cells lose their turgidity and the stomata close soon after dark-
ness sets in.

Temperature. Slope of Ground. — The rate of transpiration increases
with rising temperature. It is one of the reasons, though probably not
the main reason, why north slopes may be preferable to south slopes
when moisture is a limiting factor. It likewise furnishes the explanation
of most of the phenomena connected with the temporary wilting and later
recovery of turgidity in plants. Of particular interest is the effect of
temperatures below 0°C. on the transpiration from twigs. The data
presented in Table 17 on the transpiration from a branch of Taxus haccata
from which the leaves had been removed are interesting not only in show-
ing the influence upon transpiration of an increase in temperature, but
also in showing that transpiration takes place at temperatures consider-
ably below the freezing point. Water loss under these conditions is
associated with certain types of winter injury, a matter discussed in
more detail in another section.

28 FUNDAMENTALS OF FRUIT PRODUCTION

Table 17. — The Influence of Temperature Upon Rate of Transpiration

{After Burgerstein^^)

Water Transpired per Hour (in Per Cent.
Average Temperature (Centigrade) . of Weight op Branch)

- 2.0 0.288

- 2.8 0.227
-•5.2 0.131

- 5.7 0.127

- 6.2 0,093

- 6.8 0.028
-10.7 0.019

THE WATER CONDUCTING SYSTEM OF THE TREE

The conduction of water from the roots to the leaves has been investigated
by Dixon," from whom the following account is largely taken. The water
absorbed by the root hairs passes by osmosis from cell to cell through the cortex
of the root and into the cavities of the wood cells. It then passes through the
younger layers of wood from the roots through the trunk to the branches and
eventually to the tracheae of the leaf. From these cells it is abstracted by the
endodermis and eventually finds its way by osmosis to the mesophyll cells from
whose outer surfaces it evaporates. Water passes into the cavities of the wood
cells in the root by osmosis. The osmotic system involved here consists of the
water of the soil, the solution in the elements of the wood, and the cortical cells
of the roots which constitute the semi-permeable membrane separating these
two solutions. These cortical cells have a higher osmotic pressure than the
tracheae but, being fully distended, they function merely as a complex membrane
across which a flow of water takes place. The concentration of the solution
which fills the tracheae is higher than that of the soil solution and is maintained
by the secretion of sugars from the wood parenchyma cells with which they come
in contact.* This osmotic system may develop considerable pressure and result
in the exudation of Uquid from cut surfaces as in the well known phenomenon
of bleeding in the vine.

After the water has entered the wood cells in the root, it is carried up in the
woody tissue in an unbroken column, which extends into the veinlets of the
leaf. The water in the conducting tracts of high trees hangs there by virtue of
cohesion. It must not enclose bubbles, which would break the column of
water and permanently interfere with conduction. The structure of woody
tissue may be considered a special adaptation which confers stability on the
transpiration stream and prevents bubbles which may develop from occupying
more than an infinitesimal part of the cross section of the whole water current.
The imbibitional properties of the walls of neighboring water-filled tracheae
render the water continuous between them. If a bubble develops anywhere in
the transpiration stream it will enlarge until it fills the cavity of the cell in which
it originated, but the walls of the tracheae limit the bubble and prevent its further
expansion. From these considerations it follows that the column of water
will not be broken unless a very large number of the conducting tubes contain
air. Despite its mobiUty the water, as it rises in the wood, behaves very much
like a rigid body.

THE INTAKE AND UTILIZATION OF WATER 29

The vessels may be considered as the path of the most rapid portion of the
transpiration stream. The tracheids transmit water more slowly but continue
to function when the water supply is limited. Though the internal thickenings
on the walls of the trachea? are essential for the transmission and stabiHty of a
stream under tension, the whole wall is not uniformly thickened because the per-
meability of the thinner portions is necessary. The flow of water is further
facilitated by the presence of bordered pits, which are themselves remarkably
adapted to permit a flow of water under proper conditions and to prevent the
expansion of bubbles beyond the Hmits of a single cell. The membrane and torus
of each bordered pit is able to take up three positions, a median position when
it is not acted upon by lateral forces and two lateral positions when the membrane
is deflected against one dome or the other. When adjacent cells are filled with
water, the membrane assumes the median position and permits a flow of water
through the delicate membrane which surrounds the torus. When a bubble
develops in the trachea and gradually distends until it fills it, the membranes of
the pits in the walls of the trachea become deflected away from the bubble, until
the torus hes over the perforation in the dome like a valve in its seat. In this
position the tension of the water on the one side and the pressure of the gas on
the other are withstood.

The water after it reaches the tracheae of the leaf is drawn into the leaf cells
by osmosis. Thus the entire transpiration stream is raised by the activity of the
leaf cells. According to Dixon''^ these cells actually secrete the water and it is
removed by evaporation from their outer surfaces. The resistance encountered
by the current of water in passing through the wood at the velocity of the trans-
piration stream is probably equivalent to a head of water equal in length to the
wood traversed. Hence, the tension needed to raise the transpiration stream
in a tree must equal the pressure of a head of water twice as high as the tree.
In a tree 100 meters high, for example, a tension of 20 atmospheres is needed.
Dixon finds the cohesion of sap to be at least 200 atmospheres, so that it is in no
way taxed by the tension. He also finds that the osmotic concentration of the
mesophyll cells is adequate to resist the transpiration tension and is in many
cases much in excess of that required. Finally, he shows that the energy set
free by respiration in the leaves is sufficient to do the work of secretion against
the resistance of the transpiration stream.

Summary. — The total system of water absorption, conduction and
transpiration is more or less a unit. As a rule water is absorbed only to
replace water lost by transpiration and in the long run the amounts of
each are equal. For short periods, however, transpiration may slightly
exceed absorption. The chief factors determining the flow of water
through the plant are the available water supply and transpiration. If
for any reason more water is transpired than is absorbed and this condi-
tion continues for any length of time, the cells lose their turgidity and the
plant wilts. If the supply of water is renewed in time, the plant recovers
its turgidity without ill effects, but prolonged wilting is attended by
serious disturbances and eventually results in death.

Nursery stock loses its water-absorbing organs, the root hairs, upon

30 FUNDAMENTALS OF FRUIT PRODUCTION

digging and should be so handled until permanently planted that the
buds cannot start. Plants in leaf should be moved with a "ball of
earth." In most deciduous fruits aeration of soil is necessary for
absorption and continued submergence leads to the death of root hairs
and roots. Plants developing in the spring under circumstances such
that they have large water requirements, . continue to demand large
amounts throughout the season and cultural operations should be shaped
accordingly. Summer pruning may reduce water requirements some-
what, but the reduction is not proportional to the loss of foliage. Some
protection against water loss may be afforded by windbreaks and the
choice of northern slopes.

CHAPTER III

ORCHARD SOIL MANAGEMENT METHODS AND MOISTURE
CONSERVATION

Most cultural practices which involve the orchard soil are for the
purpose of influencing more or less directly its moisture supply or its
productivity. It is well, therefore, at this point to examine somewhat
carefully into the ways in which the several cultural practices commonly
employed in the fruit plantation affect the water content of its soil,
for though they must be considered also as they influence soil chemistry,
they concern water supply even more directly. In general farm practice,
certain soil treatments are given with the purpose of reducing, at least
temporarily, the water content of the soil. In the orchard, however,
excess moisture is taken care of by surface run-off and by natural or
artificial underdrainage if the orchard has been well located. The
efficiency of orchard soil management methods, therefore, is to be judged
by the way in which they conserve moisture rather than by the way in
which they dissipate it, though in some sections there may be occasion
to dry out the soil in the fall for the purpose of hastening maturity.

Orchard Soil Management Methods Defined and Described. —
The commonly recognized and more or less distinct methods of soil
management in the orchard may be listed as follows: (1) clean culture,
(2) clean culture with cover crop, (3) artificial mulch, (4) sod mulch,
(5) sod, (6) intercropping. There are almost endless combinations
and forms of treatments intermediate between any two of these methods;
consequently it is nearly impossible to differentiate clearly between them.
For instance, clean cultivation may be practiced in the orchard until
the first of August. If the land remains fairly clean and free from weed
growth during the fall and winter months, the orchard is said to be
under the clean culture method of management. If no cover crop were
seeded, but a heavy growth of weeds comes in and serves as a fall and
winter cover, the orchard is practically under a cover crop method of
management, though many growers would refer to it as a clean culture
orchard! Similarly, if the land were seeded down to bluegrass or alfalfa
or some other forage crop, the method of soil management would be
classed as sod, sod mulch or intercrop, depending upon what disposition
is made of the vegetation produced between the trees. If the vegetation
were cut and removed from the land, the orchard would be said to be
under an intercrop system of management, but if it were pastured off
by sheep the management probably would be called a sod system, though

31

32 FUNDAMENTALS OF FRUIT PRODUCTION

if the vegetation were cut and allowed to remain on the ground as a
mulch the treatment would be called a sod-mulch system. No attempt
is made here to go into any detail regarding some of these systems of
soil management that are very much alike or that are intermediate in
character between those that stand out clearly as types. However, it
is desirable to recognize how certain of the typical systems of soil manage-
ment may be expected to influence the water content of the soil and,
through it, the growth and behavior of the tree. With this information
at hand, it will not be difficult, as a rule, to predict more or less accurately
the results that may be expected from one of the intermediate or combi-
nation treatments.

Orchard -soil Management Methods and Surface Run-off. — A
word may be said first regarding the influence of these several methods
of soil treatment upon surface run-off. Much of course depends upon
the lay of the land, the character of the soil itself and the way in which
precipitation occurs. Most soils cannot take up the water that falls
in a torrential rain lasting but an hour so completely as they can the same
amount of rainfall distributed over a 12- or 24-hour period. Exact
figures are not available, but it has been observed many times that there
is much less run-off from sodded areas than from equal areas of similarly
lying bare land. The covering of vegetation or of mulching material
checks the flow of the water over the surface of the ground and gives
it a greater opportunity to soak in. Furthermore, if there is any con-
siderable amount of mulching on the ground it acts as a sponge, first
absorbing the water as it falls and then permitting it slowly to seep into
the soil. In this connection, mention should be made of the influence
of mulching material or vegetation of any kind upon erosion. There
are many orchards and parts of many others, planted on slopes so steep
that there would be much loss of soil from washing, were the land to be
cultivated and left bare any considerable portion of the year. Orchards
of this type should be left in sod or artificially mulched, regardless of
how these treatments may influence the water or nutrient supply avail-
able to the trees.

Moisture Under Tillage and Sod-mulch Systems of Management. —
There is Httle reason to beheve that there is much difference between
the methods of soil management in the amounts of seepage into the lower
layers of the soil. However, it is obvious that these several treatments
would have very different influences upon surface evaporation from the
soil and the evaporation that takes place through the plant itself. Fortu-
nately, considerable data are available upon certain phases of this
question.

Some New York and Pennsylvania Records. — The New York data
presented in Table 18 show nearly 5 per cent, difference in soil moisture
between the surface soils of the tilled and of the sodded orchards and

ORCHARD SOIL MANAGEMENT METHODS

33

nearly 4 per cent, difference in the respective subsoils. When it is con-
sidered that a part of the water in each case is unavailable for tree growth
because needed to supply the hygroscopic requirements of the soil, it is
evident that the tilled ground may contain many times as much available
moisture as the land in sod and that the difference between the two
methods of culture in respect to the available water is actually much
greater than the figures would suggest at first glance, The Pennsylvania
data presented in Table 19 show clearly that artificial mulching may be
and indeed usually is, a most efficient means of reducing evaporation.
They also throw some light on the effect of intercrops and cover crops
upon the water content of the soil, though no information is available as
to the season in which the determinations were made. Incidentally,
Table 19 shows how the soil-water supply influences the growth and the
yield of apple trees, though it should not be inferred that all the differences
in growth and yield are due directly to the variations in water supply.
It is significant, however, that there is a close correlation between the two.

Table 18. — Soil-moisture Determinations in a Mature Apple Orchard in

New York^^
(Under different methods of soil management)

1907

1908

1 to 6

inches

6 to 12 inches

Date

1 to 6 inches

6 to 12 inches

Date

Till-
age

Sod

Till-
age

Sod

Till-
age

Sod

Till-
age

Sod

6-28

12.71

6.23

12.90

6.31

7- 7

12.77

11.59

11.56

10.70

7- 2

14.88

11.20

14.86

6.99

1 7-10

12.43

6.62

10.89

6.29

7- 5

12.07

5.87

10.96

3.37

7-14

12.69

9.00

10.58

6.03

7- 9

13.12

6.96

12.04

6.53

7-22

18.31

14.02

17.76

9.59

7-12

16.43

13.51

15.31

9.26

7-24

15.25

11.85

16.14

9.37

7-16

13.77

9.63

11.75

8.69

7-28

12.40

10.84

11.67

8.25

7-19

11.68

9.51

9.48

7.80

7-31

15.50

13.31

15.56

10.09

7-23

13 42

8.36

9.19

7.80

8- 4

14.00

12.97

12,84

10.87

7-26

11.93

6.81

8.84

5.21

8- 7

15.35

9.72

15.31

7.61

7-30

11.69

5.46

9.84

4.72

8-11

15.27

10.08

15.28

8.02

8- 2

13.20

7.82

10.92

5.75

8-14

14.72

11.70

12.47

8.10

8- 6

10.64

7.08

10.72

5.47

8-18

14.56

14.07

12.98

12.71

8- 8

10.02

4.82

10.15

3.80

8-21

12.33

8.70

11.21

7.81

8-14

11.79

4.38

9.62

4.07

8-25

10.98

6.39

9.39

6.08

8-17

9.37
8.56

5.21
3.99

9.07
8.18

3.. 58
2.68

8-20

Average for
season

12.20

7.30

10.86

5.75

14.04

10.06

13.12

8.68

34

FUNDAMENTALS OF FRUIT PRODUCTION

Table 19. — Influence of Cultural Methods on Moisture, Growth and Yield

IN a Young Orchard

(Results from Experiment 331, first 7 years, 1908-1914122)

Treatment

Moist-
ure
content

1913,
per

cent.

Rela-
tion to
optimum
content,
per
cent.

Average
gain in
girth,
inches

Gain
over
tillage,
per
cent.

Total

yield

1914,

pounds

General
rank

Tillage

Tillage and intercrop

Tillage and cover crop. . . .
Cover crop and manure . . .
Cover crop and fertilizer . .
Mulch

10.6
5.5

8.5

9.2

9.4

17.1

18.2
18.1

53.0
27.6
42.7
45.9
47.2
85.6
90.8
90.4

6.84
7.69
6.84
8.31
7.76
8.29
8.76
8.93

12.4

21.5
13.5
21.2
28.1
30.5

1.5

21.6

7.0

135.4

18.9

38.5

300.5

390.1

8
6
7
3
5
4

Mulch and manure

Mulch and fertilizer

2
1

Some New Hampshire Records. — That the moisture supply in a tilled
orchard is not invariably superior to that in one under a sod-mulch system
of soil management is shown by the data presented in Table 20 from an
orchard on light sandy loam in New Hampshire. In this instance
measurements were taken of the percentage of moisture in the surface
7 to 9 inches of soil and in the subsoil (to a depth of 3 feet) at weekly
intervals during the growing periods of four successive seasons. The
figures represent seasonal averages.

Gourley, in reporting these observations, suggests that the lower moisture
in the tilled plot may be due in part to the greater permeability of the subsoil
and in part to the absence of a covering to shade the soil. Additional factors
cited as possible explanations are a slight mulch in the sod plot, the slight demand
made by the poor grass and finally, the increased drain on the soil in the tilled
plot due to the larger growth and larger leaves on the apple trees growing there.
It should be stated that despite the higher moisture content in the sod plot the
growth and yields there were inferior. Gourley, discussing a late summer
drought accompanied by a severe dropping of fruit, states, "The dropping was
just as severe in the heavier soil which showed 12 per cent, of moisture as in the
lighter soil which showed about 7 per cent, which would agree with the findings
of the soil physicists on the wilting point in light and heavy soils."

English Experience. — Bedford and Pickering^'' report some interesting data
showing that uniform results are not attendant upon similar treatments. "Pot
experiments under glass indicated that, during the summer months, 30 per cent,
more water was lost from the pots where there was a surface crop than from those
where there was none; but when the pots were in the open, exposed to the sun
and wind, the reverse was often — not always — the case, and the evaporation
from the pots with the surface crop might, during the season, be even less than
half of that from those without a surface crop."

ORCHARD SOIL MANAGEMENT METHODS

35

Table 20. — Moisture Determinations on Sod Cultivation and Cover Crop

Plots

(Light sandy loam in New Hampshire)

(After Gourleif)

Surface soil

Year

Sod

Tillage

Tillage and cover
crops

1913

16.02

13.69

14.20

1914

18.87

13.39

15.03

1915

25.63

19.29

20.82

1916

20.48

16.45

21.31

Average

20.25

15.70

17.84

Sub

soil

Year

Sod

Tillage

Tillage and cover
crops

1913

10.98

9.06

8.93

1914

14.14

9.78

10.26

1915

14.26

14.03

13.33

1916

14.82

12.74

13.24

Average

13.55

11.40

11.44

At Harpenden they found during May, June and July an average of 4 per
cent, more moisture in tilled soil than in grass land; in Ridgmont soil, grassed
land in August and September contained on the average 0.7 per cent, more water
than tilled land. In no case did the amount of moisture appear to be the chief
factoi- in tree growth. Irrigation increased the vigor of fruit trees growing in
grass land, but did not make them as thrifty as those grown in tilled ground.

The New Hampshire and the English results agree in the superior
growth made by trees in tilled ground, despite the absence of significant
differences in moisture, or indeed, despite the frequent superiority of
grass land in moisture content. In these cases there is evidence of the
effect of other limiting factors, some of which are discussed in the section
on nutrition.

Special cases deserve passing consideration. The Hitchings orchard
in New York showed under test as good results in growth and yield under
the sod-mulch system as under tillage.^*' This condition is explained as

36 FUNDAMENTALS OF FRUIT PRODUCTION

the result of seepage from the hill at the bottom of which the orchard is
located, supplying so much water that moisture is eliminated as a limiting
factor. Many orchards in the eastern United States are in just such
locations.

Some Kentucky and Kansas Records. — Some of the findings of the
United States Bureau of Soils on soil moisture conditions in grass land
and in cultivated soil may be summarized here. Records were made
during the months of May, June and July, 1895, of the water content of
soils at a number of places in the United States and under different
tillage conditions.^-^ These records bring out a great difference between
soils in the way this moisture content is influenced by treatment. For
instance, at Greendale, Ky., during the last half of May, the moisture
contents of uncultivated, bare land and of bluegrass sod were pract-
ically the same (about 18 per cent.) ; during June, however, the moisture
content under the bluegrass gradually decreased to about 10 per cent,
while that of the uncultivated bare land remained about 17 per cent,
except for a period of about 5 days at the end of the month when it
dropped practically to the figure shown by the sod land. During July
the bare, uncultivated land averaged 2 to 3 per cent, higher in moisture
content than the grass land. At Lexington, Ky., a similar series of
records showed an average moisture content about 5 per cent, higher dur-
ing May, 8 to 10 per cent, during June, and 1 to 5 per cent, during July,
in the bare, uncultivated land compared with that under bluegrass sod.
During June the bluegrass made its very heavy draft upon the moisture
supply of the soil, lowering it to the point where little water was available
for plant growth and cultivated crops consequently suffered.

This suggests that if the sod-mulch system of orchard culture checks
tree growth materially during the early part of the season or again after
mid-season it is not on account of its lowering the water content of the
soil, at least in those sections favored with summer rains. On the other
hand, orchards in sections likely to have little rain between the middle
of June and early fall probably would suffer materially from drought during
that period. In any case, the growth of grass mulching material would
take large amounts of water during June; during that month the itrees,
may or may not be able to spare it. The question of the practicablity,
desirability or efficiency of the grass mulch method of culture so far as it
concerns soil moisture therefore depends on what precipitation can be
expected reasonably during July, August and September or what can be
applied by irrigation — for orchards under these two methods of soil
management are very likely to enter this period with material differences
in the amount of available soil moisture. In Scott, Kan., on the other
hand, the moisture content of prairie sod land has been found to average
only about 8 per cent, during the last half of May, while cultivated land
averaged about 17 per cent. Rains late in May and scattered through

ORCHARD SOIL MANAGEMENT METHODS 37

June and July, brought up the averages in both soils to well above the
danger point for plant growth and the cultivated soil averaged only 2 to
5 per cent, more moisture during those months.

In General. — That the sod-mulch, or any other sod method of manage-
ment, makes something of a draft upon the water supply of the soil, as
compared with a tillage method of management, cannot be denied, though
this draft is often less than is supposed. It would be a very good sod-
mulch indeed that, would produce 1 dry-weight ton of mulching material
per acre. More frequently the amount does not exceed half that figure.
One-half ton of dry mulching material would require from 31,250 to
62,500 gallons of water, assuming from 250 to 500 parts of water for each
part of drj-- matter. This would be the equivalent of 13^ to 2}^ acre-inches
of rainfall or irrigation. Furthermore, most of this water is used by the
grass during the months of April, May and June, when the soil is most
likely to be well supplied with moisture and best able to part with it. If
the growing season of the grass is followed by moderate or heavy summer
rains or irrigation the requirements of the trees will be well taken care of
in this respect. On the other hand, if there should follow a period of
drought, it is easy to understand why trees under sod treatment would
suffer. An important factor, then, in determining the practicability of the
sod-mulch method of management is the likelihood or certainty of summer
precipitation, or, what amounts to the same thing, available irrigation
supply during the summer months. In sections such as the Willamette
valley of Oregon where winter and spring rains are abundant but the
summer is dry, the sod-mulch method of management cannot be employed
safely without irrigation. In such regions it is wise to use every means
of conserving the natural water supply. On the other hand, there are
many sections and many locations where summer rains can be counted
on to supply the requirements of the trees during their growing season
year after year; in other cases an orchard may be so located in a valley
floor or a piece of bench land that it is sub-irrigated by means of seepage
water. Under these conditions the sod-mulch method of management is
entirely practicable, though it should be stated that such orchards may
need somewhat different treatment, so far as nutrition is concerned, than
orchards in cultivation. A study of the records of the United States
Weather Bureau showing monthly precipitation over a series of years
will give important data as to the relative desirability or practicability
of these several methods of soil management for any particular region
or district.

Sometimes the choice of methods is influenced by considerations
of the cost of the systems. Hedrick^"* reports that the operations
involved in the sod-mulch and tillage systems cost per acre respectively:
for the Auchter orchard 80 cents and $7.39, for the Hitchings orchard
72 cents and $16.28. In many cases the tillage method will more than

38 FUNDAMENTALS OF FRUIT PRODUCTION

return the extra labor cost; however, when results are equal, costs should
be considered.

Practicability of the Sod-mulch System Influenced by Depth of Rooting. —
Mention of depth of rooting, a subject considered in more detail later,
is pertinent to this discussion. A tree with a root system penetrating
the soil to a depth of 8 or 10 feet can draw upon the moisture supply of a
large volume of soil. Such a tree is in a much better position to with-
stand temporary surface drying such as may be produced by evaporation
from the surface or from weeds and grass, than a tree whose roots are
limited to the upper foot or eighteen inches of soil. Consequently
it will thrive under the sod-mulch method of culture when a shallow-
rooted tree would suffer serious injury. To keep an orchard in sod under
conditions such that deep rooting is not possible and where there is not
an abundant summer rainfall or plenty of irrigation water, is to invite
trouble. However, there are successful orchards in sod where the
summers are long and dry and irrigation is not known. The explanation
lies in the deep root system of the trees that makes them independent,
to a great degree, of surface soil conditions.

In passing it should be mentioned that the grass, both cut and uncut,
of the sod systems of management affords some protection against surface
evaporation, the exact degree depending on the thickness of the protective
layer. As this layer is frequently rather thin, its importance in checking
evaporation is often exaggerated, for the stubble of the cut grass continues
to evaporate moisture into the air, even after it has turned brown and has
died down to the ground. In some cases this water-dissipating action
of the stubble during the summer months may even equal the protective
action of the mulch against evaporation.

Influence of Depth and Frequency of Cultivation Upon Soil Moisture.
Since cultivation is in general a means of conserving soil moisture,
the presumption is that the deeper the cultivation, within reasonable
limits, the more effective it will be. Table 21 affords a fairly accurate
idea of how depth of soil mulch influences the loss of water by evaporation.
It is worthy of note that with a soil mulch 6 inches deep the water lost
by evaporation is less than a quarter of that lost through a 1-inch mulch.
Regardless of the texture of the soil, cultivation is equally effective as a
protection against water loss : this protective influence is felt to a depth
of 6 feet.

Table 21 is interesting also because it shows the combined effects of
depth and frequency of cultivation. It is evident that increasing the
frequency of the cultivations, at least up to a certain point, increased the
effectiveness of the soil mulch under the conditions of the experiment.
Probably under arid or semiarid conditions with few or no summer rains
and less weed growth the more intensive tillage would not give materially
increased protection against evaporation.

ORCHARD SOIL MANAGEMENT METHODS

39

Table 21.-

-The Relative Effectiveness of Soil Mulches of Different Depths
AND Different Frequencies of Cultivation^*

Depth

Loss of water per acre
per 100 days

Cultivation

of soil
mulch,
inches

None

Once in
2 weeks

Once per
week

Twice per
week

1

Tons

724.1
6.394

724.1
6.394

724.1
6.394

551.2
4.867
23.88

609.2
5.380
15.88

612.0
5.402
15.49

545.0
4.812
24.73

552.1
4.875
23.76

531.5
4.694
26.60

527.8

4.662

2

Water saved, per cent

Tons

27.10
515.4

4.552

3

Water saved, per cent

Tons

28.81
495.0

4.371

Water saved, per cent

31.64

Intercrops and the Soil Moisture Supply. — The influence of various
intercrops upon soil moisture conditions in the young orchard has been
studied by Emerson.*^ Results of these studies, covering two successive
seasons, 1901 and 1902, are presented graphically in Fig. 1. These two
seasons afforded more or less extreme conditions of precipitation. The
summer of 1901 was characterized by very light rainfall, so light in fact
that the trees would have to depend largely upon stored moisture during
the period of their most active growth. On the other hand, the summer
of 1902 was a season of abundant rainfall. The crops grown in the
vegetable plot included water melons, bush beans, pole beans and turnips.

In commenting upon the results of this investigation Emerson says:
"The vegetables dried the soil but little more than clean cultivation. In
neither case did the percentage of moisture become dangerously low, even during
the protracted drought of 1901, when only a little over 7 inches of rain fell during
the 4 months from May to August inclusive. The crops of rye dried the ground
much more than any other method of culture tried. Not only was the rye ground
somewhat drier, but it became dry earlier, and moreover, since no rains occurred
to thoroughly moisten the ground after it had once become dry, the rye plot
remained dry nearly a month longer than any of the other plots. Next to rye,
the oat crop dried the soil most seriously during the dry season of 1910, though it
did not make the soil much drier than corn or cover crops. Its effect, however,
was noticeable much earlier in summer and lasted much longer. By the middle
of July, when the corn plot was becoming dry, many trees have completed their
greatest length growth and do not need so large a supply of moisture as they do
earlier in the season. The corn plot was very dry, therefore, only about half as
long as the oats plot. The important difference between the cover crop and the
corn, just as between the corn and the oats, is that the soil in the cover crop plot

40

FUNDAMENTALS OF FRUIT PRODUCTION

did not become dry for a week or two after the corn ground had become dry.
The great difference, as regards soil moisture between the clean cultivation
on the one hand and the rye and oats on the other is fully appreciated only when
it is remembered that the moisture in excess of 8 or 10 per cent, (in this particular
soil) is available to plants. . . , In 1902, the plots did not vary greatly as regards

Apnl_

o0.5

_May_

June

1901

Aug. Sept.

Oct.

^

^

\

^

^

%

1

c

Sl<

-/^

m

.\

-c \

^

'^

Jf

\

\

_^

1

\

V

/\

■f~^

J

"^^^--^

1

III

il 1

h

1

II

1

1

Fig. 1. — Percentages of soil moisture in orchard plots and inches of rainfall during
summers of 1901 and 1902. The curved lines indicate the fluctuations in soil moisture
content. The vertical bars show dates and amounts of rainfall. (After Emerson.*^)

soil moisture. Naturally, no method of culture dried the ground seriously at
any time during this very wet season, when over 28 inches of rain fell during the
4 months from May to August inclusive."^*

Table 22 presents data showing the effects of the various intercrops
in this Nebraska experiment upon the drought killing of newly set trees.

ORCHARD SOIL MANAGEMENT METHODS

41

Table 22. — Effect of Various Intercrops on Drought Killing of Young

Trees (After Emerson^^)

Apple

Cherry

Peach

Intercrop

Num-

Num-

Per

Num-

Num-

Per

Num-

Num-

Per

ber

ber

cent.

ber

ber

cent.

ber

ber

cent.

set

died

died

set

died

died

set

died

died

Watermelon crop

30

2

7

12

1

9

10

0

0

Watermelon crop

30

2

7

12

2

17

10

0

0

Corn crop

30

2

7

12

1

9

10

2

20

Clean cultivation

30

3

12

0

0

10

0

0

Oats crop

30

14

47

12

6

50

10

8

80

Cover crop, millet

30

13

12

2

17

10

1

10

Cover crop, oats

30

13

12

4

33

10

0

0

Cover crop, weeds

30

23

12

6

50

10

0

0

Table 22. — Continued

Intercrop

Num-

Num-

Per

ber

ber

cent.

set

died

died

,„

0

0

10

2

20

10

2

20

10

1

10

10

6

60

10

2

20

10

1

10

10

0

0

Plum

Total

Num-

Num-

Per

Num-

Num-

ber

ber

cent.

ber

ber

set

died

died

set

died

cent,
died

Watermelon crop.
Watermelon crop.

Corn crop

Clean cultivation.

Oats crop

Cover crop, millet
Cover crop, oats. .
Cover crop, weeds

1

7

76

4

0

0

76

6

0

0

76

7

0

0

76

2

5

36

76

39

0

0

76

9

1

7

76

10

2

14

76

15

5.4
7.9
9.2
2.6
51.3
11.8
12.2
19.7

The data for the cover crops indicate relatively more injury than would
occur in older orchards because the cover crops probably made a much
more vigorous growth than they would in competition with well estab-
lished trees. The suggestion is made, however, that cover crops should
be selected and used with considerable care in recently established
orchards. The danger from the use of the small grains as orchard inter-
crops is indicated plainly. On the other hand, little loss is occasioned
by the growing of tilled or hoed intercrops.

Cover Crops and the Moisture Supply. — Orchard cover crops are not
generally considered in relation to soil moisture, but rather as means of
adding organic matter to the soil and increasing productivity. Never-
theless they do influence water content in several ways and some data on
this question have already been presented in connection with the discus-
sion of intercrops. As this influence is, in many cases, important it seems
desirable that further consideration be given the matter.

42

FUNDAMENTALS OF FRUIT PRODUCTION

Effects of Early and Late Seeding. — Cover crops use considerable
water in their growth. A good cover crop probably produces at least
14, ton of dry matter per acre involving the transpiration of from 2 to 4
acre-inches of water. However, the cover crop makes its demand for
water upon the soil during the fall, winter and spring months — a time
when there is most likelihood of an abundant water supply and conse-
quently when the trees are not so likely to be injured by the draft of the
cover crops. It is true that cover crops are usually seeded in late July or
in August, but their growth is so limited before the middle or end of
September that they compete but little with the trees for either nutrients

Table 23.-

-Percentage of Soil Moisture in Bare Ground and Under Cover
Crops in Early November After a Drought^s

Depth in inches

Bare ground

Hairy vetch

Cowpea

1
1 to 12 6 . 48
12 to 18 1 8.52
18 to 24 , 7.60

1
12.15. 9.30
10.30 12.27
11.65 9.80

Table 24. — Percentage of Soil Moisture for Each Cover Crop from Nov. 1,
1905, to Feb. 17, 1906, and the Average for Three Determinations"

Crop

Percentage of moisture in soil to depth of 30 inches

Nov.
21-22, 1905

Jan.
2-3, 1906

Feb.
16-17, 1906

Average

Cowpeas

Soy beans

Crimson clover

Hairy vetch

Oats

Canada peas

Oats and Canada peas

Rye

Check

Millet

Rape

Turnip

Turnip and rye

Hairy vetch and Canada

peas

Oats and crimson clover. . .
Cowpeas and crimson clover

Average

17.7
18.9
18.6
17.4
17.0
17.7

17.3
17.6
18.1

17.1

24.5
23.2
23.7
24.6
22.7
21.4
25.5
22.5
22.4
23.4
24.0

23.5

21.9
23.4
23.4
20.5
21.2
18.8
22.0
21.7
20.4
20.6
21.7
19.3
22.5

19.2
20.0
26.7

21.5

21.7
21.9
21.9
20.8
20.3
19.3
21.1
20.2
19.7
20.0
20.7

20.7

ORCHARD SOIL MANAGEMENT METHODS 43

or water. Furthermore, the protective action of the cover crop through
checking wind velocity close to the ground and through shading the soil,
thus lowering its temperature, may fully compensate for its use of water
during the late smnmer and early fall. The data presented in Tables 23
and 24 show that later in the season, cover crops may actually contribute
indii-ectly to the soil moisture content. The examinations recorded in
Table 23 were made at Ithaca, N. Y., in November 1901, at the close of an
extended drought. Those recorded in Table 24 were made at intervals
during the winter of 1905-1906 in Wisconsin. The report upon this
latter investigation states that the moisture determinations taken in the
spring on the soil under these cover crops confirms the results obtained
in the fall and winter "in that it shows the average moisture content of the
covered ground to be considerably more than that of the bare ground."*^
There are distinct differences between various cover crops in their influ-
ence upon the water content of the soil.

However, if cover crops are started so early in the season that a
considerable amount of growth is made during July and August, or even
early September, they are likely to make serious drafts upon the water
supply of the surface soil, which might check the vegetative growth of the
trees prematurely and reduce the size of the fruit. Striking evidence on
this point is furnished by an experiment in which cylindrical cans were
filled with heavy soil from an orange grove. ^^ One was left undisturbed
as a check, in one a surface soil mulch was maintained and one was seeded
to barle^^ The experiment was started June 25, at which time the soil
contained 19.2 per cent, moisture. At the end of 38 days the soil in the
check cyhnder contained 10.1 per cent., the mulched soil 14 per cent, and
the soil seeded to barley 3.1 per cent, moisture. The soil seeded to barley
had reached its wilting coefficient 21 days after seeding.

In certain cultural experiments in Pennsylvania the beneficial effects
of cover crops expressed in vegetative growth and yield have been most
apparent during the moist seasons, and little or no benefit has been
derived from their use during dry years. ^^s ^p^g rapid drying effect of
oats, when used as a cover crop for peaches in Delaware, has prevented
"the best growth of new wood to produce the maximum number of fruit
buds."^^ The rate of growth of cover crops as the season advances is an
important factor in determining their draft upon the water supply of the
soil from week to week. From this point of view, the ideal cover crop is
one which grows slowly at first but rapidly late in the season when the
trees do not require so much moisture and when the supply is more
abundant. Figures on the rates of growth, under Wisconsin conditions,
of some of the more common crops of the Northern states are given in
Table 25. The indirect influence of cover crops upon soil moisture in
adding organic matter to the soil and thereby increasing its water-holding
capacity is more difficult to estimate accurately, but there is reason to

44

FUNDAMENTALS OF FRUIT PRODUCTION

believe that its importance in that connection has been overemphasized
often.

Table 25. — Rate of Growth of Different Crops from Aug. 25 to Oct. 2"
(Height in inches)

Aug. 25

Sept. 3

Sept. 15

Sept. 23 Oct. 2

Cowpeas

Soy beans

Crimson clover
Hairy vetch . . .

Oats

Canada peas. .

Rye

Rape

Turnip

Millet

3.0

10.0
8.0
3.0
4.5

11.0
8.0
8.0
4.0
4.0
5.0

12.0
13.0

3.5

5.0
16.0
13.0

9.0
10.0

7.0
11.0

14.0

14.5

4.0

5.5

18.0

20.0

10.0

14.0

8.0

12.0

20.0
22.0
6.0
8.0
24.0
24.0
12.0
16.0
12.0
18.0

Winter-killed and Winter-surviving Cover Crops. — Cover crops are
generally classed as leguminous and non-leguminous when considered
in relation to their influence upon soil productivity. Emerson suggests
that when they are being considered as they influence soil moisture a
better classification would be winter-killed and winter-surviving.**' The
degree of cold actually experienced in a particular section determines
whether a given crop is killed by or survives the winter. Hence, a crop
that belongs in the one class in one place may fall in the other in some
other section. Any cover crop that survives the winter and resumes
active growth draws upon the moisture supply of the soil in the spring
and will continue to do so until plowed under or until cultivation of some
kind is begun. Since it is generally considered inadvisable to -plow or
cultivate deeply while trees are in bloom or the fruit is setting and since
soil moisture conditions and the press of other work often make the
plowing of the orchard before blossoming impracticable, cultivation is of ten
not begun until late in May or early in June. This gives a winter-sur-'
viving cover crop an opportunity to make considerable growth in the
spring, often more than it was able to make the previous fall. The
general effect of this growth upon soil moisture is shown by the figures in
Table 26 and is presented graphically in Fig. 2. By June 3 the winter-
surviving cover crop had reduced the soil moisture to approximately
half the amount in the soil protected by a winter-killed crop. In fact it
had consumed practically all the available moisture, leaving the water
content of the soil but Httle above its wilting coefficient. In regions of
comparatively high rainfall during the spring months, this waiter loss due
to the growth of winter-surviving cover crops would be of secondary
importance and it would likewise be unimportant in sections with

ORCHARD SOIL MANAGEMENT METHODS

45

Table

-Effect of Various Cover Crops on Soil Moisture During the
Spring of 1901 «

Kind of crop

Percentage of soil moisture

Apr. 19 Apr. 27 May 20 June 3

Winter-killed crops:

Oats

Millet

Cane

Average

Winter-surviving crops:
Rve

28.7
26.0
24.0

26.2

22. G

20.2
21.8
22.1

21.4

17.4

20.5
21.9
21.7

21.4

12.2

20.1
20.7
20.7

20.5

11 2

abundant and cheap irrigation water, but in

those seasons with a light late spring and ^7

summer rainfall it could easily occasion 26

much more financial loss than would be is

compensated by the advantages accruing ^4

from the use of the cover crops. A certain ?3

quantity of organic material produced in ?2

the autumn is just as valuable for soil '21

improvement purposes as an equal amount eo

grown in the spring. c 19

Wind Velocity and Evaporation : Wind- ^ 18

breaks. — Attention has been called to the ^^ n

almost continual evaporation of water from 16

the soil. In regions of low precipitation 15

this amounts to a much larger percentage i4

of the total supply than in regions of fre- i3

quent and abundant rains. Assuming 12

uniform soil management methods, evap- >i

oration may be expected to rise with an 'O
increase in wind velocity and to vary
with temperature of the soil water, with
temperature of the air close to the evapo-
rating surface, with vapor pressure in. the

those sections

5

)l5 -

\^

f^=I

\^

X

fe

\'

1^

<

^

%

Vi
V^

V.

April

June

May

1901

Fig. 2. — Percentages of soil

moisture in plots of winter-killed

and winter-surviving cover crops,

spring of 1901. The dots show the

. . dates of making the moisture de-

air near the water and with atmospheric terminations and the exact percent-
humidity. The Onlv one of these factors ages of moisture found. The curved
ill" 1 ,. 1 "'^^^ indicate the probable fluctua-
at present under the control of the grower tions in moisture between these

to any considerable extent is wind velocity, ^^t^^- (^-^'«'' Emerso7i.''^)
Consequently it is discussed at this time. In one series of determinations
when the relative humidity was 50 per cent, and the air temperature 84°F.
evaporation was found to be 2.2 times as rapid with a wind velocity of 5

46 FUNDAMENTALS OF FRUIT PRODUCTION

miles per hour as in a calm atmosphere; 3.8, at 10 miles per hour; 4,9, at 15
miles per hour; 5.7 at 20 miles per hour; 6.1, at 25 miles per hour and 6.3
at 30 miles per hour.^"^ The influence of windbreaks upon wind velocity
varies with their height and density and much depends also on the topog-
raphy, Card^^ measured the evaporation in Nebraska at varying
distances from the protected side of a windbreak of forest trees some 30
feet high, during the period July 15 to Sept. 15, and for those portions of
the period when the wind was from the south, southeast and southwest,
these being the most drying winds. Expressing the evaporation at a
point 300 feet south of the windbreak as 100, evaporation 200 feet north
was 83 and 50 feet north, 55. During a 12-hour period on Aug. 3, when
the weather was hot and dry with a high wind, evaporation 50 feet north
of the windbreak was 29 and 200 feet north it was 67, compared with 100
at a point 300 feet south. It is thus evident that wind barriers of one
kind or another reduce evaporation very materially. However, the
moisture required for the growth of the windbreak materially reduces
their total moisture-conserving effect, though deep plowing or subsoiling
close to the windbreak reduces its injurious influence in this direction.

Summary. — There are six fairly distinct methods of soil management
commonly used in the deciduous fruit plantation: (1) clean cultivation,
(2) clean culture with cover crop, (3) artificial mulch, (4) sod mulch,
(5) sod, (6) intercropping. The sod and sod-mulch systems are most
effective in reducing run-off and in preventing erosion; in certain situa-
tions their use is to be recommended for these reasons if for no other.
The various systems of soil management employing tillage generally
conserve a larger percentage of the water that enters the soil and conse-
quently they are more effective in preventing injury from drought. The
sod-mulch method has its place where abundant summer rainfall, deep
rooting or availability of irrigation water largely removes the trees from
competition with the surface cultures for water. The moisture-conserv-
ing effects of tillage increase somewhat with its frequency and depth, but
when cost is considered there is a decreasing margin of profit with the
deeper and more frequent cultivation. Cultivated intercrops may be
used safely in the orchard, but the small grains are apt to make too serious
a draft on moisture at a period when the trees should be abundantly
supplied. Cover crops consume considerable moisture but unless planted
too early they are not likely to injure the trees seriously by their growth
in the fall. In fact they may actually conserve moisture for the trees
by cutting down surface evaporation and holding snow. In some sections
winter-surviving cover crops should not be used because of their draft the
on moisture supply in the spring when the trees require it. This is partic-
ularly true in sections with only moderate rainfall and long dry summers.
Evaporation increases rapidly with wind velocity and moisture losses
from this cause can be lessened materially in many cases by choice of
sites and use of windbreaks.

CHAPTER IV

SOIL MOISTURE: ITS CLASSIFICATION, MOVEMENT
AND INFLUENCE ON ROOT DISTRIBUTION

Within certain limits tiie size and general character of top growth is
influenced bj^ the root system that supports it. Similarly the size and
distribution of the root system depends to an important degree on the
moisture content of the soil.

CLASSIFICATION OF THE WATER IN SOILS AND PLANT TISSUES

The physicist finds it desirable to distinguish between water in the
solid, liquid and vapor form; the chemist distinguishes between free
water, water of crystallization and water of constitution. Similarly it is
convenient for the student of soils and plant physiology to classify water
according to the form in which it is held in the soil or in plant tissue and
the consequent uses to which it may be put. No one classification has
proven most satisfactory for all purposes. Attention is here directed to
those that seem more useful in explaining the response of the plant to
varying water content.

The Response of Water to the Force of Gravity and the Evaporating
Power of the Air. — The water of the soil is held in three conditions; (1) free,
or gravitational water, (2) capillary water and (3) hygroscopic water. The
free or gravitational water is that which moves down through the soil
under the influence of gravity. It is the surplus water that drains away
after heavy rains or heavy irrigation, finding its way eventually through
underground channels to streams or springs or to the so-called ground-
water level. Capillary water, on the other hand, does not move down-
ward in response to the force of gravity, but adheres to the soil particles
in the form of films of varying thicknesses. It does not drain away freely
with the seepage water, though there is some reduction in its amount
within a given soil depth if there is a material lowering of the water
table of the soil. However, it may be lost through evaporation from the
surface soil. Hygroscopic water is the moisture that is to be found in
air-dry soil exposed to a moist or saturated atmosphere. Like capillary-
water it exists in the form of thin films adhering to the surface of the soiL
The films, however, are much thinner than those of capillary moisture
and the soil retains this hygroscopic water with great tenacity. The
capillary and hygroscopic moisture together may be regarded as a product
of what the soil particle can hold against the pull of gravity on the
one hand and the evaporating power of the air on the other.

47

48

FUNDAMENTALS OF FRUIT PRODUCTION

The maximum amount of water that a given soil may contain depends on
the volume of its pore space. Both may range from about 32 to a Uttle over 52
per cent.'^' This amount of water is equivalent to a 4 to 6 acre-inch precipitation
and would weigh from 20 to 32 pounds per cubic foot of soil. Naturally these
large amounts of water are not found in any soil except below the water table line
or immediately after heavy precipitation or irrigation and before drainage has had
an opportunity to carry away the surplus moisture. It is the amounts of capil-
lary and hygroscopic water that a soil will retain rather than its total water-holding
capacity as determined by pore space that are of interest in fruit growing, for the
reason that little or none of the free or gravitational water is utihzed by the
plants. For most purposes and under most conditions it is only the capillary
moisture that they use, though Loughridge**^ is responsible for the statement
that in some instances plants are able to remain alive, even though they cannot
grow, in soils whose water supply is reduced to the point where only hygroscopic
moisture is present. The total amount of capillary water that a soil will retain
depends not so much on the pore space as on the size of the soil particles
and the distance from the level of the ground water below. Tables 27 and 28
show the percentage of water that certain typical soils will hold as capillary
moisture against the force of gravity. These figures were obtained from soils
of undisturbed field texture several days after heavy rains so that gravitational
water had had ample opportunity to drain away. It should be stated in con-
nection with these tables, that in each case the soil became somewhat more sandy
at greater depths.

Table 27. — Amounts of Capillary Moisture Held Against
Gravity in Certain Typical Soils"

THE Force of

Depth

Sandy loam,
per cent.

Clay loam,
per cent.

Humus soil,
per cent.

First foot.

17.65
14.59
10.67

22.67
19.78
18.16

44.72

Second foot ....

31.24

Third foot

21.29

Table 28.— Maximum Capillars

Capacity of Soils for Water

Percentage
of water

Pounds of
water per
cubic foot

Inches of
water

32.2
23.8
24.5
22.6
17.5

23.9
22.2
22.7
22.1
19.6

4.59

Second foot of reddish clay

4.26

Third foot of reddish clay

4.37

Fourth foot of clay and sand . . .

4.25

Fifth foot of fine sand

3.77

It is interesting to note that the optimum condition for the growth
of plants is afforded by a soil when the capillary water amounts to between
40 and 60 per cent, of the total water-holding capacity of the soil, leaving

SOIL MOISTURE 49

from 60 to 40 per cent, air space. Desert plants or plants coming from
dry climates are more tolerant of deficiency in soil moisture and the opti-
mum capillary moisture content for these plants is lower. The reverse
is true of certain other plants that thrive under moist conditions. The
almond is mentioned by Hilgard and Loughridge^^ as suffering from excess
moisture when approximately three-fourths of the pore space was filled
with water.

The hygroscopic moisture of the soil varies greatly with the composition.
In sandy soils it may be as low as 2 or 3 per cent, and in coarse sands even lower.
In ordinary loams it ranges from 4 to 5 per cent, and in heavy clays and adobes
it may be as high as 8 or 10 per cent.^"

The Relative Saturation. — Brown^^ suggested that a more useful way
of expressing the water content of the soil would be in terms of its relative
saturation. This would take into account the maximum water capacity
as well as the actual water content and would afford a more accurate
index of the biological or physiological wetness of the soil than the
standards of measurement now employed. In commenting upon this
question of relative saturation he says :

"The water content alone is . . . but an imperfect index of the soil con-
ditions. Since soils of different mechanical composition have different capacities
for water, the same quantity of water produces different changes in humidity in
these different soils. For example, the quantity of moisture sufficient to saturate
a given mass of sandy soil is insufficient to saturate a like mass of humous soil.
The degree of wetness or dryness, of a soil, therefore, really depends on the
amount of water which the soil can still take in before being saturated. Con-
sequently, a more perfect index to the 'wetness ' or 'dryness ' of a soil is to be had
by expressing the water content of the soil in terms of its maximum water capacity,
,, , . Water content

the ratio ^^^^^^^^^ capacity' ^^^"^ ^^"^^^ ^^^ ^^^^^^^ Saturation of
the soil . . . This value, and not the actual water content itself, will be the index
to the ' biological wetness' of the soil ... in comparing two soils whose actual
moisture contents are different, say, the ratios may indicate that both soils,
however, have the same degree of wetness, and so, in relation to the physiological
action of the plant are of similar conditions."

Resistance to Freezing. — Another classification of the soil water is
made by Bouyoucos.^^ This classification is based upon freezing point
determinations with the dilatometer. Water which freezes at or slightly
below 0°C. is termed free water, that which freezes between 0°C. or a
little below and — 78°C. is termed capillary or capillary-adsorbed water
and that which does not freeze except at temperatures below — 78°C, is
termed combined water. These classes do not coincide exactly with those
of the classification used before and they serve to bring out some of the
features of the water supply of the soil that have been overlooked and

50 FUNDAMENTALS OF FRUIT PRODUCTION

that investigations indicate are intimately associated with the question
of winter injury.

Bouyoucos" points out that the relative amounts of these forms of water
vary greatly in different soils. He says: "In some soils only one or two forms
predominate, while in others all three are about equally represented. In the
sands and fine sandy loams, it is the free water that predominates, which amounts,
in some cases, to about 95 per cent, of the total water present; the other 5 per
cent, consists as a rule, of combined water; capillary adsorbed water is apparently
not present in these classes of soil. In the loams and silt loams, it is the free
and combined water which predominates. Here, again the capillary-adsorbed
water is present in small amounts. In some of the heavy loams all three forms
are about equally distributed. In clay loams and humus loams and clay, it is
the combined water which predominates followed by capillary-adsorbed and
free. Although the amount of free water tends to decrease and the amount of
the capillary-adsorbed and combined water tends to increase correspondingly as
the soils ascend from the simple and non-colloidal to the complex and colloidal
classes. There are many exceptions to this rule.""

Of equal importance are the differences in the amounts of free or
easily frozen water in plant cells, as determined by McCool and Millar, ^^
using the dilatometer. The differences found suggest corresponding
differences in the amounts of adsorbed water in plant cells.

The different water-absorbing capacity of plant cells is attributed by Spoehr^^s
to their pentosan content. This is confirmed by the work of Hooker.'^^ It seems
probable, therefore, that the chemical composition of plant tissue, as of soils,
has a most important bearing on the condition in which its water is held. This
in turn has a direct relation to the susceptibility of plant tissue to environmental
changes, a subject that is discussed in greater detail in the section on Tempera-
ture Relations.

McCool and Millar ^^ measured the amounts of easily frozen water in plants
grown in soils of high, medium and low water content. They found that the
plants grown in soils of high water content contained more easily frozen water.
Rosa"'' has shown that with lower moisture content of the soil there is an increase
in the pentosan content of the plants grown in it. This amphfies the discovery
that pentosans are produced under xerophytic conditions and that the water-
retaining capacity of the cells is thereby increased. ^'^^ The greater amount of
adsorbed water that such plants contain would mean the presence of smaller
amounts of free or easily frozen water, such as McCool and Millar found. These
investigators have also shown a correlation between the depression of the freezing
point of plant sap and the amount of easily frozen water it contains; the lower
the freezing point the less easily frozen water is present. ^^ This suggests that
differences in the concentration of cell sap may be due in part to the relative
amounts of free and adsorbed water. It is obvious that with a given amount of
soluble material, the concentration of the sap will depend on the amount of free
water available for its solution. The less the proportion of free water and the
greater the proportion of adsorbed water the higher the concentration of the
solution.

SOIL MOISTURE 51

These differences in condition of the water present are important in
practical ways. They explain the increased moisture requirement of a
plant grown in moist surroundings; their application in cold resistance is
shown elsewhere ; it is possible that the greater adaptability of some plants
to varied environments is related to their capacity of forming water
retaining substances. These water retaining substances represent a
mechanism for the retention of moisture by living plant cells, a mechanism
which is entirely distinct from that represented by the anatomical modifi-
cations characteristic of xerophytic or semi-xerophytic plants. The
former has to do with the loss of water from the cells to the intercellular
spaces; the latter with the loss of water from the plant tissue to the
outside. The two means of protection against water loss may occur
together in which case the effectiveness of each would be increased, but
they may be quite independent of each other.

MOVEMENT OF WATER IN THE SOIL

After water once reaches the soil, following either natural precipitation
or irrigation, it becomes subject to the forces of gravity and surface
tension and in a general way these may be said to control its movement.
Percolation downward represents the result of the two forces working
together. Lateral movement and rise by capillarity represent what the
force of surface tension is able to do in opposition to the force of gravity.

Percolation. — It has been pointed out that optimum growing condi-
tions for most crop plants are found when from 40 to 60 per cent, of the
total pore space of the soil is filled with capillary water. Immediately
after heavy rains the soil moisture occupies a larger percentage of pore
space in the soil. Therefore, the movement of water through the soil
must be considered. In humid regions its vertical movement is of chief
interest; in irrigated sections both its vertical and its lateral movement
are important. Few realize the rate at which water percolates through
the soil and the percentage of the total precipitation or of the total
amount applied by irrigation that is lost in this way. Table 29 averages
the percolation data obtained during a period of 34 years at the Rotham-
sted Experiment Station on a rather heavy loam, or clay loam soil. It
shows the amounts of water percolating through the soil columns 20,
40 and 60 inches deep.

Attention is directed particularly to the great difference between the
proportions of rainfall removed by seepage in years of light and years of
heavy fainfall. The figures also show a much higher percentage of
percolation during winter months when there is comparatively little
evaporation than during the summer months when the evaporation
rate is high. As a rule, the hghter the soil, the larger is the percentage of
percolation water. Consequently in the irrigation of hght soils it is

52 FUNDAMENTALS OF FRUIT PRODUCTION

Table 29. — Rate of Percolation of Water Through Clay Loam Soil'"

Inches

of
rain-
fall

Inches of water drained
through soil columns

Per cent, of rainfall per-
colating through soil
column

20 40

inches inches
deep deep

inches
deep

20

40

nches

inches

deep

deep

60
Inches
deep

January . . .
Februarj' . .

March

April

May

June

July

August . . . .
September
October. . .
November
December.

2.32
1.97
1.85
1.89
2.11
2.36
2.73
2.67
2.52
3.20
2.86
2.52

1.82
1.42
0.87
0.50
0.49
0.63
0.69
0.62
0.88
1.85
2.11
2.02

2.05
1.57
1.02
0.57
0.55
0.65
0.70
0.62
0.83
1.84
2.18
2.15

1.96
1.48
0.95
0.53
0.50
0.62
0.65
0.58
0.76
1.68
2.04
2.04

78.5
72.2
47.6
26.5
23.2
24.0
25.3
23.2
35.0
57.8
76.7
80.3

88.4
80.0
55.6
30.0
26.1
27.6
25.6
23.2
32.8
57.5
76.3
85.4

84.5
75.2
52.0
28.0
23.6
26.3
23.8
21.7
30.0
52.3
72.4
81.0

Mean total per year.

28.98

13.90

14.73

13.79

48.2

51.0

48.0

Results for:
Maximum rainfall.
Minimum rainfall.

38.70
20.50

23.50

7.32

23.60
7.90

24.30

7.70

60.7
35.7

61.0

38.5

63.0
37.6

generally necessary to use more water than in heavy soils under similar
climatic conditions and with the same fruits. The extra amount of
water required by such soils may be reduced somewhat by lighter and
more frequent applications, but this too may be carried to an extreme and
result in an unnecessary waste through evaporation. An illustration of
this principle is furnished by certain orchards on the Umatilla Irrigation
Project in eastern Oregon. Many orchards on this project have required
7 or 8 acre-feet of water in order to bring a crop of fruit to maturity,
though the trees themselves could use only 9 or 10 inches. Evaporation
rates in the climate of that section are very high, but the main reason
for applying 9 to 10 times more than the trees actually use is the extremely
high percolation through light porous sandy soils and subsoils.

The Rise Of Water By Capillarity. —It is often thought that much of
the water that percolates through the soil again rises by capillary action
and becomes available to the trees later in the season. Investigations
of recent years tend to minimize the importance of this upward movement
of soil moisture. The generally accepted opinion of the present may be
summarized in the following statement by Rotmistrov;!"^ "As regards

SOIL MOISTURE

53

the mechanical raising of water, however, by capillary action it may be
assumed that the limit from which water can make its way upward lies
much higher than the limit accessible to the roots. All the data at my
command regarding moisture in the soil of the Odessa Experimental
field point only to one con-
clusion, namely, that water
percolating beyond the depth
of 40 to 50 centimeters (16 to
20 inches) does not return to
the surface except by way of
the roots." Briggs, Jensen
and McLane,23 in reporting
upon the results of irrigation
experiments in citrus groves
in California state that avail-
able soil moisture below the
third foot did not prevent
orange trees from wilting
when the moisture content
in the first 3 feet of soil fell
below its wilting coefficient
and the roots of the trees were
limited to the first 3 feet.
This is a point that must be
kept in mind in irrigation
practice for it means that
trees can utilize the moisture
supply in the volume of the
soil that the roots occupy,
but very little that percolates
to or stands at a lower level.
In other words, the tree can
make use of the water supply
at 3 or 4 or 5 or 10 feet in
depth only to the extent that
it can develop a root system
that penetrates to these
depths.

Lateral Movement of Water in the Soil. — The lateral movement of
water in soils is likewise dependent largely upon texture, though the
amount and kinds of soluble mineral salts, the soil colloids, the organic
material and other factors have their influences. In open, porous soils,
water spreads laterally to a considerable distance and with comparative
rapidity. In heavy, compact soils, its lateral spread is slight and slow.

20

40

50

GO

30
Days

Fig. 3. — Rate of movement of moisture in soil
in horizontal open flumes. Figures in circles indi-
cate points at which that number of liters of water
had been taken up. The dotted line for flume No.
71 (covered) is for comparison with flume No. 70
(open). {After McLaughlin.^^)

54 FUNDAMENTALS OF FRUIT PRODUCTION

For instance, in one experiment on a heavy soil in California, after an
irrigation considered sufficient to last about four weeks, the moisture
was found to have penetrated laterally only about eighteen inches from
the irrigation furrow. ^^ Figure 3 shows graphically the rate of this
lateral spread as it takes place through the force of capillarity and unaided
by gravity. The spacing of irrigation furrows must be made accordingly,
if the entire volume of the soil is to be wetted. It is for this reason that
basin irrigation or flooding is sometimes preferred to furrow irrigation in
comparatively heavy land.

THE DISTRIBUTION OF FRUIT TREE ROOTS AS INFLUENCED BY SOIL

MOISTURE

The size and distribution of the root system depends upon the opera-
tion of many factors, such as the moisture supply, aeration of the soil
and nutrient supply. In most cases it is impossible to assign to each
factor the part it has played, but as they are more or less interdependent
they may be discussed together.

The Ideal Root System. — Deep rooting is desirable for the purpose
of making the water (and nutrient) supply contained in a large volume
of soil available to the plant. For the same reason there should be at
least a moderate lateral spread. In other words the tree, or other
fruit-producing plant, that is equipped with an extensive root system
will be able better to endure extremes of drought or temperature or
exceptional demands for a supply of nutrients, than one with a limited
root system. Plants grown in a comparatively concentrated nutrient
solution or in rich soil have roots that are shorter, more branched and
more compact than those grown in a weak nutrient solution or in a
poor soil. Changing fertility is one explanation of the marked contrasts
in the degree of ramification of roots as they penetrate different strata. ^^
The ideal root system is, therefore, not the one with branches that reach
out or down the farthest, but the one that more or less fully explores
and occupies the soil to a reasonable depth and within a reasonable
radius. Otherwise, it would be necessary to regard the root system pro-
duced only in an infertile soil as the ideal.

Specific and Varietal Differences in Root Distribution. — Depth of
rooting and lateral spread of roots depend in the first place on the species
or variety of plant., Some, like the walnut and pecan, are character-
istically deep rooted; others like the spruces and hemlocks and the river
bank grape {Vitis riparia) are characteristically shallow rooted. The
roots of certain fruit varieties, like the Wealthy apple, are strong, stocky
and far ranging; those of other varieties, like certain strains of the Doucin,
are short, slender, compact and much branched. These characteristics
should be borne in mind when selecting fruits or fruit stocks for particular

SOIL MOISTURE 55

soils and when considering the influence of various environmental factors
and cultural practices upon root distribution, for though root distri-
bution is influenced profoundly there are limits to the plasticity of any
species; nothing stated in this connection should be construed as im-
plying that these usual limits for the species or variety may be exceeded.

The Distribution of Tree Roots under Varying Conditions. — Tree
roots often range deep, but such investigations as have been reported
show a surprisingly shallow root system in most of our orchard planta-
tions, at least in the humid regions.

In the Hood River Valley, Oregon and in Ohio. — For instance a report
upon the condition of the root system of apple trees in the Hood River
valley states:

"It was found that the majority of the feeding roots of fruit trees of bearing
age were located from 3 to 10 inches below the surface of the soil."^ A discussion
of the root systems of apple trees in Ohio includes the following statement: "The
main root systems, of apple trees, under the different methods of culture (clean
culture with cover crops, sod culture, and sod mulch), were found to be at a sur-
prisingly uniform depth — the greater portion of the roots, both large and minute,
being removed with the upper 6 inches of soil. . . . The fibrous or feeding-root
sj'^stem of a tree under annual plowing and clean culture with cover crops, practi-
cally renews itself annually — pushing up thousands of succulent, fibrous rootlets
to the very surface of the soil where they actually meet with the steel hoes or
spikes of the cultivator or harrow, especially in seasons when moisture is abun-
dant. Apparently but a small percentage of these rootlets penetrate the lower,
more compact colder soil, but they come to feed where warmth and air and mois-
ture combine to provide the necessary conditions for root pasturage. As a matter
of fact, these feeding rootlets are cleanly pruned away by the plowshare each
succeeding year, and without apparent injury to the trees or crops.""

The writers then go on to state that the destruction of the roots in
the upper 2 or 3 inches of soil by summer drought or by winter cold re-
sults in no serious injury to the tree, as those ranging deeper, 4 to 6
inches, can take care of the tree's requirements.

In a Gravelly Loam, Underlaid by Hardpan, in Maine. — Some valuable
data on the root distribution of apple trees growing under different soil
conditions were obtained by Jones" in Maine. Figures 4 and 5 show photo-
graphs of the tree roots obtained from a square foot of soil midway be-
tween two Baldwin trees set 27 feet apart and about 28 years old. The
photographs show the roots in successive layers of soil 4 inches thick.
This soil was a gravelly loam to a depth of 2 or 23^^ feet where a rather
impervious hardpan was encountered. Figure 4 shows roots growing in
a rather wet portion of the orchard; those in Fig. 5 were from a drier
portion. The tops of these trees were not meeting, yet in both the wet
and dry areas their roots were interlacing and the soil to a depth of over
2 feet was more or less thoroughly exploited. Though the greatest ex-

56

FUNDAMENTALS OF FRUIT PRODUCTION

SOIL MOISTURE

57

■ - a

58

FUNDAMENTALS OF FRUIT PRODUCTION

pansion of the root system was in the 4- to 8-inch layer, there was a
fairly large number of roots 20 inches deeper. There was also much
better expansion of the root system at both upper and lower levels in
the drier soil than in the one classed by Jones as a little too wet for the
best growth of the apple tree. The question is raised by Jones as to
whether interlacing of roots is not evidence that for a number of years
these trees had been suffering from lack of room, a suggestion supported
by the indifferent performance of the orchard for some time previous.

Table 30 shows the length of the roots, in feet, found in each cubic
foot of soil at successive distances from the tree trunk. These measure-
ments were taken for a Milding apple tree 9.33 inches in diameter 2 feet
from the ground, with an 11-foot spread of branches, and growing in a
stony loam. The last column shows the computed length of roots for the
cylinder of soil 1 foot in thickness surrounding the tree at a given distance
from the trunk, assuming that the section examined is typical for the
entire area of which the tree is the center. Figure 6 shows graphically
the data presented in Table 30. They afford some idea of the relatively
extensive development of a tree's root system under conditions that are

Table 30. — Root Distribution of a 25-year Old Apple Tree, Measured by

Sections
(After Jones''^)

Distance of
section in feet
from tree trunk

Length of roots

Length of roots

Total length

Computed

in first 6-

in second 6-

of root in

length for

inch layer of

inch layer of

cubic foot of

cylinder about

soil, feet

soil, feet

soil, feet

trunk, feet

1

112

32

144

144

2

66

109

175

1650

3

19

74

93

1460

4

3

72

75

1650

5

0

28

28

792

6

3

48

51

1712

7

0

48

48

2008

8

0

32

32

1508

9

4

72

76

4059

10

0

35

35

2089

11

5

37

42

2771

12

4

16

20

1445

13

3

26

29

2278

14

0

18

18

1527

15

0

12

12

1093

16

0

8

8

779

17

6

2

8

829

18

0

8

8

880

19

0

7

7

814

20

0

^2

M

61

SOIL MOISTURE

59

presumably more or less common. In this case plowing and cultivating
to a depth of 6 inches would have destroyed a little less than one-tenth
of the conducting roots. The percentage of the very small absorbing
and feeding roots would not necessarily be the same. Over 19,000 of
the total of 29,547 feet of conducting roots, in other words about 65 per
cent., lie beyond the spread of its branches. Probably the proportion
of feeding roots is still greater. Irrigation water and fertilizers should be
distributed accordingly; the treatment of the small area of soil immediately
surrounding a large bearing tree which is difficult of access with the tools
of cultivation would seem to be of small importance so far as either water
or nutrient supply is concerned.

120

iJ GO
+i 50

I 2 3 4 5 e 1 8 9 10 II l^ \3 14 15 16 n
Dis+ance from Tree,feet

Fig. 6. — Distribution of apple roots in surface six inches and second six inches in a
soil section one foot wide in rather heavy loam. Solid line shows surface layer; broken
line shows second layer. {After JonesJ^)

\l

\

\
\

._,

1

/

\

1

\

/

\

1

\

/

\

/

\

/

\

\

— ■

\

y

\

\,

''

'■>»^

s

^

^^

^

^

^

—

^

^

<

"~-

*^,

In a Thin Gravelly Loam, Underlaid hy Rock, in Maine. — The data
given in Table 31 represent extreme conditions. They are for an under-
sized, stunted seedling apple tree probably 40 years old, on level ground
at the top of a hill thinly covered with a rocky, gravelly clay loam The
soil was less than a foot deep and was underlaid by rock or ledge or with a
heavy clay mixed with gravel. For many years the orchard had been in
pasture and the trees, having received practically no care, had experienced
a hard struggle for existence and many had died.

Without doubt, limited nutrient as well as limited moisture supply had
been an important factor in forcing this tree to extend its root system so
far and wide in order to hold on in its struggle for existence. Whatever
may have been the exact combination of factors leading to this develop-
ment it shows a marked power of adaptation on the part of the plant. It
also carries the suggestion that in soils where deep rooting is impossible
the spacing of trees and other fruit plants should be much wider than
under more favorable conditions.

60

FUNDAMENTALS OF FRUIT PRODUCTION

Table 31. — Root Distribution of a 40-yeak Old Apple Tree in a Thin Rocky

Soil Under Sod for Many Years

(After Jones''^)

Distance

Length

Length

Distance

Length

Length

of section

of roots

of roots

Total

of section

of roots

of roots

Total

from

in top

in next

length,

from

in top

in next

length.

trunk,

6 inches,

6 inches.

feet

trunk,

6 inches,

6 inches,

feet

feet

feet

feet

feet

feet

feet

1

64

96

160

16

32

2

34

2

98

22

120

17

10

0

10

3

20

50

70

18

6

7

13

4

34

80

104

19

6

14

20

5

54

34

88

20

8

12

20

6

22

4

26

21

8

0

8

7

14

7

21

22

11

3

14

8

17

18

35

23

3

8

11

9

16

26

42

24

3

5

8

10

0

0

0

25

0

7

7

11

0

10

10

26

2

0

2

12

6

9

15

27

5

7

12

13

12

12

24

28

0

2

2

14

28

23

51

29

0

2

2

15

0

18

18

In Dwarfs.- — In contrast with the comparatively extensive root
systems of trees growing in the field are those of dwarfs occasionally
grown in the garden or under glass whose growth is restricted by various
means. Sometimes resort is made to root pruning; sometimes the roots
are restricted by planting in pots or tubs. Such trees develop very com-
pact and much branched root systems that exploit very completely the
soil within their range. Dwarf trees with such restricted root systems
are much more subject to injury from extremes of moisture than standards
with unrestricted root systems. Consequently their successful culture
necessitates much greater care in watering, fertilization, pruning, exposure
to light and management in general.

The Influence of Soil Moisture Content.- — Within the ranges possible
for the different species, depth of rooting depends to a very important
extent on soil moisture and the correlated factor, aeration. Roots do
not grow and branch freely in a very dry soil, or in one that is approach-
ing a water-logged condition. The water-logged soil probably inhibits
root growth and activity through a lack of aeration; the dry soil through
a lack of the stimulating effect of the water itself. Figure 7 gives some
idea of the influence exerted by the percentage of soil moisture on root
formation and root distribution when other factors are as uniform as it is
possible to make them. In this case, however, the soil moisture did not

SOIL MOISTURE

61

approach sufficiently near the saturation point to check root formation.
When roots find an abundance of water close to the surface they branch
freely through the surface soil and show Httle tendency to go deeper,
particularly if conditions are more and more unfavorable for root develop-
ment at greater depths. These two
factors together probably explain the
comparatively shallow rooting of
most tree, bush and vine fruits in a
large portion of the humid region.
Compact, water-logged subsoils or
a high water table prevent the roots
from penetrating deeply. " The sur-
face inch or so is too dry during a
major portion of the growing season
to encourage root growth ; the result is
a distribution of most of the roots be-
tween the depths of 3 to 10 or 15
inches.

When, however, moisture and
aeration conditions are favorable for
root development at considerable
depths, deep penetration occurs.
Thus Hilgard and Loughridge^^ state
that on some of the silty "low mesa"
soils of California the roots of cherry
and prune trees are frequently found
at depths of 20 to 25 feet. Such deep
rooting is also characteristic of fruit
trees in the loose soils along the
Mississippi and Missouri rivers.
"These are soils, however, with no
hardpan or plowsole and with the Sandy
water table many feet below the sur- '^''^S
face. In them soil grades insensibly
into subsoil. Indeed, subsoil in the
sense in which the term is generally
used, does not exist except below the
region of this exceptional root pene-
tration. It hardly need be pointed out that trees in such soils seldom
suffer from drought, even though there may be a series of dry years.

When plants, accustomed to growing in a soil where shallow rooting is
necessary, are transplanted to one in which deep penetration is possible,
they first send out shallow lateral roots, their distribution being much
like that of the same plant in the region or soil from which it came. They

Cloy

bandy
Clay

Pure
Sand

Clay

Sand

Clay

Fig. 7. — Influence of soil moisture
upon root distribution of Kuhnia gluli-
nosa. {After Weaver}^^)

62 FUNDAMENTALS OF FRUIT PRODUCTION

probably encounter in the surface layers, shortly after the time of setting,
those conditions of air and moisture approaching the optimum for growth.
Then as the season progresses and the surface soil dries, the roots in
many cases turn down and send branches into deeper layers and a distri-
bution is effected resembling that of native plants.®^ This may be looked
upon as a kind of adaptation, an accomodative change, to meet new con-
ditions of environment. That this change in rooting habit is very largely
a response to moisture and aeration conditions is indicated by the fact
that with a rise in the ground water table from heavy irrigation the roots
are again forced to occupy only a shallow layer of soil. This condition is
found in some of the orange groves of California. ^^ Three or four feet
beneath the surface the soil is so water-logged that roots will not penetrate
and the top 6 or 8 inches are so filled with feeding rootlets that each
cultivation results in more or less serious root pruning. Trees under such
conditions require heavier irrigation and more fertilization than those
with deeper roots and, what is perhaps more important, they are more
sensitive to extremes of any kind affecting the roots either directly or
indirectly. Consequently they are more exacting in their cultural
demands. The same danger from heavy irrigation is met in deciduous
fruit production. Thus it has been found in Utah that raising the water
table even temporarily by irrigation causes the death of the deeper roots
and results in a kind of root pruning or root training and that the general
shape of the root system of the tree may be controlled more or less by the
distribution of the iri'igation water. ^ One of the most difficult problems
in many irrigated sections is to apply the water in such a way that plants
are not made surface feeders and the natural advantages of a deep soil
lost.

The Influence of Cultivation. — Allen^ found that tillage methods influenced
root distribution in the Hood River district. He reports that where clean
culture had been practiced without the use of the plow but with disk and other
cultivators "a thick mat of fibrous roots was found immediately below the soil'
mulch. ... In the few restricted areas that received neither cultivation nor
irrigation, the roots were found to be distributed from near the surface to 1
foot and 16 inches in depth. Under sod and irrigation conditions the roots were
quite uniformly distributed from near the surface to 23-2 feet in depth." Immedi-
ately under the loose surface soil of the cultivated areas he found an impervious
hardpan or plowsole had developed, which was dry at the time of this examina-
tion. The untilled and irrigated land did not have this hardpan layer.

Different tillage methods had resulted in great variation in the physical
character and moisture content of the soil between the depths of 6 and
30 inches, and in corresponding variations in root distribution. Evidently
the varying tillage methods used in certain Ohio orchards^* did not
change materially the character of the soil below a depth of 6 or 10
inches and since few roots developed in it below this depth, root distri-

SOIL MOISTURE

63

bution was influenced but little in this particular case. Cultivation is
mentioned often as a means of forcing deeper rooting of fruit trees and
sod culture as encouraging shallower rooting. These practices often
have these effects, but they may have no such effect, as in the Ohio investi-
gation cited, or they may have the opposite effects, as in Hood River.
This brings out the point that tillage methods as such are not to be
regarded as direct means of influencing root distribution, but as means
of altering the physical and chemical condition of the soil and thus indi-
rectly leading to shallow or deep penetration. Root growth and distri-
bution is a response to these physical and chemical conditions. It is
noteworthy that in the Hood River orchards many of the symptoms of
drought injury were associated with extreme shallow rooting — premature
dropping of the foliage, dieback and fruit-pit.

Interesting data concerning the effect of cultivation on root distri-
bution are afforded by the figures in Table 32. Cultivation along one
or both sides of the tree row reduced the absolute lateral spread and the
ratio between the lateral spread and height of the trees. The greater
reduction accompanied cultivation along both sides. In the cultivated
soil the tree roots did not have to range so wide to meet the actually
increased water requirements of the trees as in the uncultivated land.
Incidentally the figures in Table 32 throw some light on the lateral
spread of tree roots as compared with the spread of their branches.
Though spread of top is not given it is reasonable to assume that in this
species it is less than tree height. It is often said that the lateral spread
of the roots is about equal to the lateral spread of the branches. In
uncultivated ground it was in this instance more than twice as great.

Table 32. — Effect of Cultivation Upon Root Spread of

THE Osage Orange^^

Amount of
cultivation

Cases
measured

Average lieight
of trees

Average root
extent

Average root extent;
proportion to height

8
25
35

20.0
17.2
21.7

43,7
28.9
29.2

218.7

One side of trees . .
Both sides

167.8
134.5

Mason^^ cites an instance in which the olive grown in an extremely dry soil
and climate had a root system radiating 10 to 11 feet in nearly all directions when
the top was only 6 feet in height, had a spread of only 7 feet and a trunk diameter
of 3% inches. In this case there was a total of 185 feet of roots 3-8 inch or
more in diameter and the area occupied by roots of this size was about nine
times that of the spread of the branches. This fruit as it grows in the Sfax
region of Northern Africa furnishes a good illustration of the adaptation of the
root system to moisture conditions. There it sends out numerous roots which
run for long distances comparatively close to the surface where they can make
use of the moisture that penetrates only a few inches into the ground at the
time of the infrequent light rains.

64 FUNDAMENTALS OF FRUIT PRODUCTION

The Influence of Soil "Alkali.'' — It should not be inferred from the
emphasis that has been placed upon moisture and aeration in determining
root distribution that other factors are of little significance. Other
factors are often controlling.

For instance in reporting upon an investigation of the effects of alkali on
citrus trees Kelley and Thomas^" state: "It is especially interesting that the
roots of the lemon trees have not penetrated deeply in this soil, more than 95
per cent, of them being within 18 inches of the surface. There is probably
some connection between this fact and the higher concentration of alkali salts
found in the third and fourth feet."

Applications to Orchard Practice. — The whole subject of the distribu-
tion of the root system of orchard plants may be summarized in this way :
though different species of plants and different varieties of the same
species have characteristic habits of root growth, the extent and the
distribution of their root systems are profoundly influenced by environ-
ment. Root development, both as to amount and direction, may be
regarded as a response of the plant to this environment. The functioning
of that part of the plant above ground is conditioned to a very important
degree by the functioning of the part of the plant below ground, and
therefore by the distribution of the roots in the soil. Root distribution
is under control to the extent that soil conditions — texture, moisture,
aeration and nutrient supply — are under control and to a certain extent
by the pruning that is afforded the top, a matter discussed in detail later.
If the soil is one in which these conditions are not favorable for a suitable
root distribution or in which they cannot be made favorable, it should
not be devoted to fruit culture, because fruit culture cannot be successful
on it. As soon as the orchard is planted, or before if possible, and as
long as the orchard remains, it is well to study from year to year the way
in which various soil treatments influence those factors determining root
distribution and then employ those practices that lead indirectly toward
ideal root systems. Orchards do not die out or become unprofitable only
because of fungi, bacteria, summer drought or winter cold. These are
always possible contributing factors and often determining factors, but
in many cases the fundamental cause of distress is a root system inade-
quate for requirements of the tree in an emergency — inadequate perhaps
because too shallow, or in too severe competition with the roots of other
plants or because it is not exploiting enough soil. Sometimes, though
the contributing causes to the death or failure of the trees may be un-
avoidable, the fundamental factor may be completely under control.

Summary. — In terms of response to gravity and the evaporating
power of the air, soil moisture may be classified as gravitational or free,
capillary and hygroscopic. Only the capillary moisture is available to the
plant in any considerable amount. The capillary supply is derived from

SOIL MOISTURE 65

precipitation and irrigation or to a limited extent from the gravitational
water that reaches the ground water level. The optimum water content
for the growth of plants is reached when its relative saturation is approxi-
mately 50 per cent. A certain percentage of the soil moisture is held in a
capillary adsorbed or colloidal form and is not frozen at the ordinary
freezing point of water. This portion of the water supply is of great
importance to the plant. The evidence indicates that a part of the water
of plant tissues is held in a similar manner and that this moisture is
significant in determining drought and frost resistant qualities of the
tissue in question. The percentage of the rainfall that percolates
beyond the range of the tree roots varies greatly with many factors, total
precipitation being one of the most important. Comparatively little
water that percolates beyond the range of the roots becomes available
for later use through capillary rise. The lateral movement of soil
moisture depends principally upon soil texture and the method by which
irrigation water is applied to the soil should be determined accordingly.
Root distribution is governed first of all by the growth characteristic
of the species or variety in question. To an important extent, however,
it is influenced by soil conditions, particularly soil moisture and soil
aeration. A deep, moderately wide-ranging root system is preferable to
one that is shallow, wide spreading or narrow. Though the great major-
ity of the roots of most orchard trees are in the upper foot or fifteen inches
of soil, there is little evidence that ordinary tillage results in an injurious
root pruning. Shallow soils, soils underlaid by hardpan or with a high
water table, should be avoided for fruit culture because of the restricted
root range that they necessitate and the consequent susceptibility to
drought injury of one kind or another. Depth of rooting can be con-
trolled to a considerable extent by cultural practices, such as tillage, the
use of cover crops or intercrops of different kinds, irrigation and drainage.

CHAPTER V

THE RESPONSE OF FRUIT PLANTS TO VARYING CONDITIONS
OF SOIL MOISTURE AND HUMIDITY

Water as a factor in growth thus far has been discussed only in its
general importance in the development of the plant as a whole. There
are, in addition, certain specific responses made by the plant to a varying
water supply.

Influence of Soil Moisture on Vegetative Growth. — One of the most
important of these specific responses is in new tissue formation, an in-
crease in size or bulk. Data have been presented in Table 19 showing
the influence that various methods of culture, such as tillage, tillage and
cover crops and artificial mulches, have upon vegetative growth measured
by trunk circumference.

New Shoots and Their Leaves. — Table 33 gives certain averages found
by Hedrick in sod-mulched and cultivated plots in a New York apple
orchard. Every phase of vegetative growth measured showed a gain
from tillage. Moreover the tillage plot averaged considerably higher
in moisture during the growing season. Probably much of the influence
of tiflage was due to the increased moisture available in the soil, yet it is
difficult to say how much is to be attributed to this factor and how much
to the influence of the tillage on plant nutrients, particularly nitrates.

Table 33.— Influence of Tillage Methods Upon Vegetative

Apples^^

Growth in

Sod

Cultivated

Avprnorp IpTurfVi nf npw Int.prals in infihpf?

3.40
1.90
0.87
1.10

6.70

Average number of new laterals per year

4.40

Average weight of leaves in grams

1.15

Average gain in trunk diameter in inches in 4 years

2.10

More direct evidence of the effect of water on vegetative growth is
furnished by certain orchard irrigation experiments. The following
quotations from a report on an investigation in Utah bear on this point.
"Frequent applications of irrigation water applied to peaches on a
gravel loam (about 15 feet deep) at intervals of 7 or 8 days produced a
more continuous and greater total twig growth than the same total
amount of water applied with larger applications at intervals of every
10 to 12 days. The more porous the soil the more frequently the trees

66

RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL

67

should be watered. . . , With varying times of application of irrigation
water the season of most rapid twig growth is during the season of
watering."'^ Barss,^ reporting upon the results of some pot irrigation
experiments with pears, states: "The most noticeable variation in
response to the application of different amounts of water, was found in the
development of the new wood. All the lots started vegetative growth at
about the same time . . . but terminal bud formation took place early
on the poorly watered trees and much later on the trees of the other lots.
Furthermore there were great differences in the rate of wood growth in
these different lots while they were actually growing. . . . The spurs
on the better-watered trees were larger and more vigorous. . . . From
leaf samples, collected and weighed in order to bring out any existing
differences in weight, it is apparent that, on the average, the leaves
in the lots receiving most water were far heavier than those in the lots
receiving less water." He also found the leaves on the trees receiving the
smallest water supply were variable in both size and shape, their petioles
were slender, their lower surfaces were markedly pubescent and their
color was dark green. Callus tissue formed much more frequently on the
well watered trees.

An7iual Rings and Trunk Circumference. — The results of study on the
relation between tree growth and total yearly rainfall in Arizona are

1870 1880 1890 1900 l^iQ

Fig. 8. — Actual rainfall compared with rainfall calculated from growth of trees,
Arizona. Solid line equals calculated rainfall. Broken line equals observed rainfall.
{After Douglass J^)

interesting in this connection. Under the comparatively arid conditions
of that region the correlation between the two was found to be so close
that with a knowledge of the total rainfall of any one year the average
increase in diameter of trees could be estimated with an average accuracy
of 82 per cent.; conversely, knowing the average diameter increment
of a small group of forest trees for any one year it was possible to estimate
with equal accuracy the total precipitation of that year. Figure 8 shows
graphically the closeness of this correlation. Huntington^^ employed
this method of estimating annual rainfall for the study of climatic varia-
tions during the last 1,000 years, obtaining growth records from the giant
Sequoias of California. Hartig,^^ however, found that in parts of
Germany where low moisture content of the soil apparently is not the
limiting factor to growth, the beech makes a smaller annual ring during

68

FUNDAMENTALS OF FRUIT PRODUCTION

seasons that are cold and wet than during years of more nearly average
temperature and humidity. The decreased growth during the wet
season may be correlated with poorer aeration in the soil.

Moisture Supply and the Growth Period in Early Spring. — Most
deciduous fruits have a short period of very rapid vegetative growth in the
spring, followed by a longer period of comparatively slow growth that
precedes the resting stage. That this is a characteristic of most deciduous
woody plants is brought out by data condensed in Table 34. Of the
70 species of trees, shrubs and vines considered hardy enough for outdoor
culture in central Michigan approximately one-fourth had completed
their shoot growth and formed their terminal buds by June 1, and over
two-thirds had reached a similar stage by June 20. In no case was there
appreciable shoot growth before May 1. Gourley^^ states that this

Table 34. — Numbers of Trees, Shrubs and Vines Completing Shoot Growth
AT Different Dates

(After Baileif)

Date of terminal bud formation

June 1 or
earlier

June 1 to
10

June 10 to
20

June 20 to
July 1

July 1 to
15

After July
15

Number ....

16
23

8
11

24
34

14
20

5

7

3

Per cent

4

period of rapid growth in the apple lasts only about 25 days in New
Hampshire and that it is during this period that external factors, such
as moisture, have their greatest influence upon new tissue formation.
In his work approximately 43,000 measurements were taken and his
data point to the conclusion that there was no very close correlation
between the humidity and rainfall curves and the growth curve during
this period, though it was not possible to control all factors under field
conditions. The growth curve showed a closer correlation with tem-
perature than with any other factors studied. In Idaho, irrigation of
apple trees after July 15 had no effect upon shoot growth but as a rule
the more irrigation water applied before July 1, the greater was the shoot
growth. ^2* A similar correlation between growth and soil moisture
during the months of May, June and July has been observed in Indiana^^^
and it was in the plots with the lowest water content that there was the
closest correlation between growth and soil moisture. With moisture
conditions approaching the optimum, an increased rainfall or surplus irri-
gation water has comparatively little influence in forcing growth.

Pearson^^^ h^s made a valuable contribution to the knowledge of
the importance of an adequate soil moisture supply during the com-

RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL

69

paratively short period of rapid vegetative growth. Figure 9 presents
graphically the results of his series of observations upon yellow pine
seedlings near Flagstaff, Arizona.

In commenting upon the data presented in this figure he says: "Contrary
to what might be expected, there is no apparent relation between height growth
and annual precipitation, summer precipitation or winter precipitation, m fact,
the growth from year to year often varies inversely with the precipitation for
any of these periods. When it is considered that of the total annual precipi-
tation at Fort Valley, the mean amounting to about 23 inches, approximately 40
per cent, comes during the winter months (December to March), 30 per cent,
during July and August, and less than 10 per cent, during the spring months
(April and May), the foregoing statements are startling. In order to clarify the
problem, it is necessary to analyze the growth habits of Western yellow pine as
well as the cUmatic and soil conditions under which it grows in this locality.

■

y'

\

/

\

/

\

1

\

/

\

\

1

S

""■^-^

/

\

1

/

\

V

/

\

\

/

\

^^

>.

.-^

~>vv

X

">

Nr--r"

/.

>

^?\

^...

'^

'^^^v^

A

/

^

/

\

/

-e--

,^^

.^^"

\

1915

1916 1917

1909 1910 1911 1912 1913

Year

Fig. 9. — Seasonal precipitation and annual height growth of western yellow pine
saplings from 1909 to 1917. a, Annual precipitation; h. Winter precipitation (December-
March preceding the corresponding year's growth) ; c, Summer (July-August) precipita-
tion; d, Annual height growth; e, Spring (April-May) precipitation. {After Pearson y^"^)

The terminal shoots begin to elongate about the middle of May, and by July 1
they have practically completed their growth. Thus it appears that the entire
height growth occurs during the period of lowest precipitation of the year. From
the middle of May to the middle of July the rainfall is normally less than one half
inch, and comes in such small showers as to be of no benefit to deep-rooted plants.
It is evident,therefore,that the moisture utihzed in making this growth is drawn
almost entirely from a stored supply. It is also evident that the midsummer
rainfall, since it does not begin until July, when height growth has practically
ceased, is of httle or no consequence, as far as the current year's height growth is
concerned. The water storage which makes growth possible is mainly the
result of the preceding winter's precipitation; but it is the supplementary sup-
ply in April and May which determines whether the growth is to be above or

70 FUNDAMENTALS OF FRUIT PRODUCTION

below normal. ... It is evident from the precipitation figures for 1913 that
the pines in that year depended entirely upon winter precipitation for their height
growth. Since the total precipitation in April, May, and June was only 0.25
inch, it may be readily seen that an addition of 2 or 3 inches during this period
would have resulted in an appreciable increase in soil moisture and presumably
in height growth. Such was the case in 1914 and in a more marked degree in 1915
and 1917. If, as is often the case, the first of April marks the end of the season's
storms, a dry period of 3 months prior to the beginning of the summer rains may
be expected. Since yellow pine, on account of the low temperature, does not
begin growth until about the middle of May, a dry period of 6 weeks intervenes
between the last storm or the disappearance of snow and the beginning of growth.
During this period a large portion of the stored moisture supply is dissipated
without benefit to the tree. If, on the other hand, belated storms continue
through April and into May, the stored water supply is not only conserved, but
may be actually augmented. A typical example of the first type of spring was in
1916. Despite a winter precipitation of over 16 inches, the highest on record in
9 years, soil moisture conditions, after it became warm enough for growth, were
decidedly below normal. . . . The years 1915 and 1917 are examples of the
second type of spring. The winter precipitation was only 9.4 inches in 1914-15
and 6.1 inches in 1916-17, but in both years the precipitation between April
1 and May 15 was around 6 inches."

The '^Second Growth" of Midsummer or Late Summer. — A second
period of rapid vegetative growth frequently occurs in late summer or
fall. Usually it takes place after terminal bud formation on both spurs
and shoots in the case of spur bearing species. Sometimes the terminal
buds on the shoots "break" and a new shoot growth is pushed out;
sometimes terminal buds on many of the spurs "break" and a secondary
spur growth takes place and sometimes the lateral buds, rather than
the terminals, initiate this new shoot growth. In some instances terminal
bud formation has not yet occurred in the primary shoots of the season,
though growth has slowed down very materially, so there is a sudden
flush of rapid vegetative development. Occasionally this "second
growth," as it is generally called, is as extensive in amount as that made
early in the season, though this is not usually the case. Without doubt
nutritive conditions within the plant and in the soil have something to
do in determining "second growth" but the fact that it occurs almost
invariably after heavy rains or irrigation following a drought, leads to
the conclusion that it is due at least in part to changed moisture con-
ditions. It is to be regarded as a phenomenon likely to accompany irregu-
larity in moisture supply late in the season, and is a response of the
plant to disturbed moisture relations. This second growth is sometimes
accompanied by fall blooming in some of the tree fruits. Without
doubt the "flush" of certain evergreen plants of tropical countries is
a related phenomenon. It sometimes gives rise to two "annual" rings
in one season in the trunks and limbs of trees and other woody plants.

RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 71

If this second growth comes fairly early so that the new tissues have
time to harden and mature properly before winter freezing, little harm
may result, but often when it comes late in the season the tissues do not
mature thoroughly and serious winter killing or winter injury follows.
It is doubtful if, irrespective of susceptibility to winter injury, much
"second growth" is desirable in sections with more or less severe winter
weather, for there is reason to believe that the tissues are formed at the
expense of stored materials that could be used perhaps to better
advantage the following spring and summer.

Influence of Water Supply on the Development of Fruit. — The
influence of soil moisture on the development of the fruit is no less
important than its influence on vegetative growth.

Size. — The largest fruits are found on the best watered trees and
there is abundant experimental data to show the effect of soil moisture
upon fruit size. Thus Hedrick,^^ who found his tillage plots to contain
more soil moisture than his sod-mulch plots reports the average weight
of apples from the cultivated trees to be 7.04 ounces while the average
weight of those growing in sod was only 5.01 ounces. This difference
of 40 per cent, was presumably due mainly to the difference in moisture
supply and accounts in large part for the difference in yield between
the two plots, which averaged 36 barrels per acre.

In the discussion of the influence of soil moisture upon vegetative
growth it is pointed out that new shoot growth and new leaves are made
early in the season and it may be only during a comparatively short
period in spring and early summer that this growth is influenced in amount
by soil moisture. On the other hand, most of the growth of the fruit
tissues takes place after midseason and therefore it is reasonable
to believe that soil moisture exerts its greatest influence on their
development during the last half of the summer and during the autumn.
That this is actually the case is indicated clearly by a number of irriga-
tion experiments. In Idaho, irrigation of winter apples before July 10
had very little influence on their size, though irrigation after that date
had a very decided influence. ^^^ Batchelor^^ in reporting upon the
results of irrigation experiments with peaches, states: "No amount of
water applied early in the season to a crop of peaches on a gravelly soil
will compensate for the lack of water during the month before harvest.
... A larger amount of water is evidently required if the irrigation is
deferred until late in the season than in case the water is applied throughout
a longer period of growth." There is ample evidence to show that for
the production of fruits of large size the trees should be well supplied
with available soil moisture throughout their growing season. Through
measurements of apples made at intervals of two weeks throughout the
season it has been found that size increased steadily from the time of
setting to maturity. ^^^ This suggests the advisability of cultural treat-
ments to promote a steady growth. That there is a limit, however,

72 FUNDAMENTALS OF FRUIT PRODUCTION

to the increase in fruit size that can be effected through increased
moisture supply is shown by many irrigation experiments. For instance,
with peaches on a deep gravelly loam in Utah, it was found that 31
acre-inches of irrigation water gave as large size and as large yields as
62 acre-inches under the same conditions. ^^

An interesting moisture relation within the plant itself that often
affects fruit size is pointed out by Chandler. ^^ He shows that the con-
centration of the sap within the leaves of the tree is higher than that
within its developing fruits. Consequently in times of drought, when
the roots are unable to supply the amounts transpired, the leaves actually
can withdraw moisture from the fruits, even to the point of causing
wilting while the leaves themselves remain turgid. This not only checks
temporarily all increase in fruit size but may result in a reduction. Chan-
dler cites several instances in which, under these extreme conditions,
more disastrous results occurred in cultivated than in uncultivated
orchards. Cultivation had been given largely for the purpose of con-
serving moisture; nevertheless toward the end of a long drought when
the moisture supply of both cultivated and uncultivated orchards was
approaching the wilting coefficient, the trees in the cultivated orchard
suffered more because they had larger leaf systems and required more
water to support them. Had summer pruning to reduce the leaf systems
been done promptly in these cases, evaporation would have been
reduced and wilting of the fruit prevented. Chandler states, however,
that summer pruning for the purpose of increasing fruit size through
reducing leaf area has not been successful.

Yield. — The increases in yield from an increased moisture supply, up to
the optimum, are in general still more striking than the increases in size
because of the indirect effects of moisture through better fruit setting
and the formation of more fruit buds.

A striking illustration of the influence of rainfall upon yield is recorded
for the palm oil tree (Elaeis guineensis) in the British Colony of Lagos.
Data showing the yearly rainfall and the yearly exports of palm oil and of
palm kernels are condensed in Table 35. The following quotation fur-
nishes comment on these data:

"The yield of fruit from the palm oil tree (Elaeis guineensis) varies according
to rainfall. With a sufficiency of moisture the tree flowers every five or six weeks,
and bears eight or nine mature bunches of fruit in the year, but if the rain supply
is scanty the tree flowers only every ninth or tenth week, and the annual yield
is reduced to about five bunches. In normal times the Elaeis bears eight heads
(so-called nuts) in the year, but it follows a similar habit to the cocoanut, the
heads being formed spirally in the axils of the leaves at regular intervals, which
are long or short, according as the season is favorable. The mischief arising from
insufficient rainfall does not finish with the number of heads, for the oil is
extracted from the fiber of the thin outside layers of the fruit, which are either

RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 73

Table 35. — Yearly Rainfall and Exports op Palm Oil from Lagos'"

Year

Rainfall,

Palm oil,

Palm kernels.

inches

gallons

tons

1887

70.80
49.87

1888

2,446,705

42,525

1889

61.61

3,349,011

32,715

1890

90.88

3,200,824

38,829

1891

64.26

4,204,835

42,342

1892

69.68

2,458,260

32,180

1893

82,55

4,073,055

51,456

1894

70.10

3,393,533

53,534

1895

80.62

3,826,392

46,501

1896

74.23

3,154,333

47,649

1897

51.10

1,858,968

41,299

1898

80.20

1,889,939

42,775

1899

83.46

3,292,881

49,501

1900

72.82

2,977,926

48,514

1901

112.59

3,304,055

57,176

1902

47.82

5,240,137

75,416

• 1903

70.08

3,174,060

63,568

red, ripe, succulent and rich with oil, or starved, yellow, and destitute wholly or
partially of oil, according to the amount of moisture afforded to the tree during
the time the fruit has been maturing, "^o Three things are of particular interest
in connection with the behavior of the palm oil tree in Lagos: (1) Moisture affects
yield mainly through influencing the frequency of flowering and fruiting. (2)
The chemical composition of the fruit is greatly modified. (3) Variations in
rainfall are as likely to influence fruit production the succeeding season as during
the current j^ear. This is explained by the existence of two seasons of heavy
rainfall — one early and one late. If the excess or the deficiency is mainly in the
latter period, its influence is more evident in production the following calendar
year. More attention is devoted to this phase of the question under Residual
Effects of Soil Moisture.

Shape and Color. — The influence of soil moisture on the color and
shape of fruit is of little importance relatively but it is none the less of
interest. In Oregon it was found that with the use of increasing amounts
of irrigation water apples tended to become more angular and elongated^^
and the same phenomenon has been noted in irrigated orchards in Idaho. ^^4
Many observations have indicated that apples in a very dry soil are
flatter than those of the same variety grown near by but in a somewhat
better watered medium. In irrigation experiments with peaches in
Utah, poor color was associated with a small amount of water and high
coloration with abundant and particularly with late, watering.^^ A
brighter red color was found on Esopus apples that were well irrigated, as
compared with a darker and duller red on fruit of the unirrigated or

74 FUNDAMENTALS OF FRUIT PRODUCTION

lightly irrigated plots in Oregon. ^^ Barss^ observes that Bartlett pears
from trees well supplied with moisture are a clear green at picking time;
those from trees suffering for lack of moisture he describes as bluish-gray
green. Increased moisture may lead indirectly to poorer color of varieties
of apples, pears and peaches that have more or less red coloring matter
in their skin by producing a larger wood and leaf growth and thus
more shade, the formation of the red pigment in these cases being depen-
dent upon sunlight reaching the fruit itself. Though this effect of soil
moisture is noted only late in the season as the fruit is maturing, it is
not an effect of surplus moisture at that time or just previous, but is
rather to be attributed to surplus moisture during the spring months
when most of the shoots and leaves are developed. Thus trees with
fruits showing the effects of drought in poor size and quality may at the
same time show the effects of too much moisture during the spring months
in poor color. Such a condition suggests the contrasting extreme, namely
high color from good exposure to the light incident to proper foliage and
shoot development early in the season and good size and quality incident
to abundant moisture late in the season. Either extreme can be produced
or at least approximated by skillful culture, particularly in irrigated
sections where water supply is under control.

Composition. — That the composition of fruit is influenced materially
by water supply is suggested by the large percentage of water in the
tissues of the fruit. It is probable, however, that the most important
influence of soil moisture upon quality and composition is not in modi-
fying its water content, but rather in its effect upon other constituents.
Thus the poor quality of strawberries ripening during or immediately
after a rainy period is due more to a low sugar than to a high water con-
tent. Exact figures are not available to show how chemical composition
of fruits varies with definite changes or variations in soil moisture, con-
ditions being otherwise the same, but it is presumable that such figures
would show material differences. Developing oranges may contain 25 to
30 per cent, less moisture during the middle of the day, when transpi-
ration is at its highest, than at night when it is at its minimum, ^^ but the
moisture content of apple leaves has been found to vary only from 62.8
per cent, to 64.8 per cent, when the soil moisture in the plots in which the
trees were growing ranged from 11 to 24 per cent.^^^ This suggests that
such extreme variations as have been found in the orange are only tempo-
rary and that the plant possesses a marked ability to construct its
tissues along a chemical pattern independent of available soil moisture
to a considerable degree. However, comparatively slight differences in
chemical composition are often responsible for large differences in flavor
or quality. In addition, differences in soil moisture may cause shght
differences in texture and in the size and cohesion of individual cells or
groups of cells, resulting in great differences in quality. The comparative

RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 75

crispness of fruit grown where there is an abundance of soil moisture is
a matter of common knowledge. Bartlett pears grown with an extremely
limited water supply are distinctly and unpleasantly astringent, though
fruit of that variety under usual conditions is without astringency.^
Peaches supplied early with abundant irrigation water but suffering
because of its lack late in the season, may be especially sweet and of
high quality but somewhat shriveled and of little commercial value.^^

Many claims are made for and against fruits grown in irrigated
sections. The discussion is based on the assumption that there is some
more or less direct influence of irrigation water on the composition and
consequently on flavor and quality. If this were the case the evidence
would not be conclusive, for fruit raised either in an irrigated or in an
unirrigated section is a product of the many factors constituting environ-
ment and not solely of differences in soil moisture. Chemical analyses
of many hundreds of fruits of different kinds grown with and without
the use of irrigation water, have led to the conclusion that in most decidu-
ous fruits differences between those irrigated and those not irrigated are
negligible.''^ Onl}^ in the strawberry were important differences found.
In that fruit the irrigated berries were lower in dry matter, sugar, acid
and crude protein and these differences were accompanied by a marked
difference in keeping quality. There appears to be little reason for the
popular belief that irrigated fruits as a rule are softer and more watery
than those not irrigated. It seems to make no difference whether the
soil receives its water from rains or through an irrigation flume.

Disease Resistance and Susceptibility. — Correlated with the influence
of soil moisture on the texture and composition of the tissues of shoot,
leaf and fruit is its influence on resistance and susceptibility to certain
diseases. This has been noted many times in the common bacterial
fireblight of apples and pears. This disease works much more freely in
soft succulent tissues, slowing up or ceasing entirely as it reaches older
and harder wood. Thus high moisture content of the soil, forcing a more
succulent and vigorous growth, favors the development of the disease
and there are sections where the most practicable method of controlling
it on certain varieties is such culture as will maintain the soil moisture
at a point somewhat below the optimum for growth though well above
the wilting coefficient. An investigation of the relation between water
content of soil and the prevalence of fireblight in Idaho showed that
the soil moisture averaged 3 to 8 per cent, higher in badly blighted
orchards than in nearby orchards having little of the disease. ^^4 Similar
differences were found in the soil moisture content of slightly blighted
and badly blighted parts of the same orchard and in the soil under
diseased and disease-free trees. Extreme atmospheric humidity may
occasionally be a contributing factor. Presumably soil moisture exerts
equally great influence on susceptibihty or resistance to many other

76 FUNDAMENTALS OF FRUIT PRODUCTION

bacterial and fungous diseases. A series of dry seasons is almost certain
to be accompanied by an increase in the virulence of the Illinois blister
canker in those regions where that disease is prevalent. ^^ The influence
of soil moisture on certain physiological disturbances is discussed later.

Residual Effects of Soil Moisture. — The influence of precipitation or
of irrigation early during the growing season is more or less immediate.
On the other hand water falling or applied late during the growing season
may have less of an immediate effect on the plant and a correspondingly
greater effect at a later period, or even the following year. Particularly
is this true of late fall or early winter rains or irrigation. This is due
partly to the fact that some of the water is stored in the soil for later use
and partly to the fact that the benefit that the plant derives from absorb-
ing some of it immediately may not be apparent until considerably later.
It is thus proper to speak of the residual effects of soil moisture.

On Vegetative Growth. — It is a common observation that trees suffer-
ing from drought in late summer and early fall shed their foliage early.
This is particularly true of species and varieties ripening their fruit
comparatively early. The function of the foliage during late summer
and fall is to manufacture food materials which, for the most part,
are stored through the winter for use in tissue building in the spring. A
large part of the new growth (roots, shoots, leaves and flowers) in early
spring is at the expense of stored foods. Premature defoliation, from
drought or any other cause, therefore, is likely to result in a check to
growth the following spring through cutting down the available reserves.
Though exact experimental data in support of this line of reasoning are
not available there is abundant circumstantial evidence and the record
of numerous observations is very suggestive.

Whitten^^^ has assembled some data bearing on this question for the
years 1894-1898 (see Table 36). In commenting on these he says: "It will be
observed that the last part of the years 1894 and 1897 were marked by severe
drouths, and that the average growth of uncultivated trees fell off to a marked
degree during the next year or two after each of these dry seasons. Where
trees were well cultivated, to conserve the moisture in the soil, this falling off of
growth was not noticeable. . . . The unfavorable effects of drouth upon
uncultivated trees may not be so apparent during the dry year itself as it is 1 or
even 2 years later." Though unfortunately data are not available as to the
exact moisture content of the soils in these plots during the 5-year period in
question, there is little doubt about soil moisture being mainly responsible for the
differences in growth recorded.

On Yields. — The residual effects of soil moisture are not limited to
vegetative growth. In all probability they have rather general influence
and affect yield. This is indicated by investigation of the olive industry
near Sfax in Northern Africa.''^

RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL

77

Table 36. — Showing Certain Residual Effects of Soil Moisture

(After Whitten^^*)

Growth (

in inches)

Variety

Age

Kind of cultivation

1895

1896 1897

1898

Ben Davis

7

17.6

21.7

23.2

24.5 Clean cultivation.

Ben Davis

11

12.1

12.4

16.6

14. 5| Clean cultivation; cover crops.

Ben Davis

14

17.0

9.5

16.2 10.8 Seeded to clover.

Jonathan

9

17.2

9.3

13.6

11.0

In clover; cultivated under each tree.

Jonathan

10

7.3

6.6

11.4

9.6

Clean cultivation; cover crops.

Genet

30

4 ?,

6 1

10 4

6 6

In bluegrass and clover; some culti-

vation around each tree.

Genet

30

3.6

5.5

8.9

4.4

In bluegrass pasture.

Genet

14

13.0

9.3

11.2

7.4

In clover.

Rainfall in Inches During the Growing Season for Each of the 5 Years

Month

1894 1895 1896 1897 1898

2.02 I 1.04

4.33 6.09

3.04 5.78

1.20 I 4.93

1.29 I 2.30

7.57 I 1.48

October 0.98 i 0.25

April . . .
May . . .
June. . .
July...
August .
September .

3.08
5.61
4.33
3.79
1.85
3.61
2.45

4.83
3.19
6.59
4.28
1.89
0.51
0.69

2.76
8.39
9.02
4.60
0.47
5.43
2.61

The following quotation illustrates the point :

"Although the records do not cover a sufficientlj^ long period to establish a
definite relation, it would appear that there is some connection between the size
of the crop and the amount of rainfall of the preceding year or years, but not
that of the spring preceding the ripening of the crop. Thus, the comparatively
heavy rainfall (3.6 inches above the normal) in 1897 doubtless had something
to do with the large crop of 1898, although the total rainfall of the first 5 months
of the latter year was less than half of the normal. Again in 1901, when the
crop was less than half the average of 9 years, the rainfall for the first 5 months
was not greatly below the normal, but that of the pre\aous year was less than half
the normal, and during the 3 years previous the annual rainfall was only a little
more than half the normal. It is noteworthy that in 1900, after 2 years of
rainfall much below the normal, the crop was about an average one. This was
probably due to the heavy rainfall of November, 1899, which was more than three
times the normal for that month, while the precipitation during the first 5 months
of the year in which the crop was made was less than 40 per cent, of the normal."

Still further evidence is fm-nished by a report on the relation of
certain climatological factors to fruit production in California:

78 FUNDAMENTALS OF FRUIT PRODUCTION

"The character of the autumn, particularly with reference to rainfall, deter-
mines in large measure the size and the quahty of the fruit crop of the following
year. An interesting example of this relation is apparent in the 1919 deciduous
fruit crop, which is the largest of this kind ever grown in California. During
September, 1918, the heaviest rains recorded in a month of September in California
during 69 years of record were general throughout the central portions of the
State."ioi

Regularity of bearing, as is pointed out later, is probably more closely
associated with and dependent upon, natural flowering habit and the
nutritive conditions within the plant than upon soil moisture. However,
the following quotation from a report on a series of orchard soil experi-
ments in Pennsylvania suggests the wisdom of looking after the moisture
supply when it is more or less under control: "In two treatments, the
yields of Baldwin and Spy have remained almost constantly between
400 and 700 bushels per acre annually for the past 7 years, while marked
fluctuations in yield were occurring in adjacent plots under other treat-
ments. The essential features of the former treatments have been
an ample food and moisture supply, the absence of excessive yields in
any one year, and undisturbed root system. "^^^

In most of the cases cited it is impossible to differentiate between the
direct influence upon the plant of water from the rains of the preceding
summer and fall stored over winter in the soil and what has been termed
indirect effects through immediately influencing leaf fall and food storage.
To the grower it is the combined effect that is important. The facts
presented carry a particularly significant lesson for the grower in an
irrigated section where fall and winter rains cannot be depended on, but
irrigation water is available. They suggest also that the tree that
matures its crop early in the season, whether a cherry, apricot, peach or
summer apple, has as real, though perhaps not as great a need of late
summer, fall and winter irrigation as one maturing its crop in October.

Influence of Atmospheric Moisture on Growth. — It is difficult in
many cases to distinguish clearly between the effects of soil moisture and
of atmospheric humidity on the plant. Atmospheric humidity has an
influence on plant development independent and distinct from that of
soil moisture, though it often happens that both influences tend in the
same general direction.

In General. — Under average outdoor growing conditions abundant
soil moisture is likely to be accompanied by relatively high humidity and
low soil moisture by a dry atmosphere. In practice, therefore, these two
factors of environment are more or less interdependent. The relation of
the two is brought out by data presented in Table 37. In a general way
it may be stated that extreme moisture, either of soil or of air, hinders
the differentiation of tissues while dryness accentuates the develop-
ment of strengthening and conducting tissues. Examples of these

RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL

79

Table 37. — The Influence of Moist and Dry Soil and Air on Size of Leaf
OF Tropaeoltjm Majus

_ (After Kohl^^)

Soil

Air

Relative size of
leaf blade

Moist
Moist
Dry
Dry

Moist
Dry
Moist
Dry

5

4
3

1

results are to be found in aquatic plants on the one hand and in desert
plants on the other. In the former the cuticle is usually thin and per-
meable, the stomata are numerous and exposed, frequently the surface
of the epidermis is enlarged and woody tissue, sclerenchyma and col-
lenchyma are poorly developed. In xerophytic plants, growing under
very dry conditions, the cuticle is thickened and rendered imperme-
able by waxy impregnations; the surface of the entire plant is reduced to a
minimum, the stomata are few in number and frequently situated at the
base of depressions in the surface of the leaf. Wood and fibers are
developed to a marked degree and specially differentiated water storage
tissue is of frequent occurrence.

Apparently atmospheric humidity, rather than soil moisture, soil, or tempera-
ture, is the factor determining the limits for the production of certain
varieties of dates. Those of the Deglet Noor type thrive only in the driest
cUmates, Hke that of the desert oasis with a mean humidity of 35 to 40 per cent.
Dates of a different type are grown in the vicinity of Alexandria, Egypt, with a
mean annual humidity of 68 per cent.*^

Russeting of Fruit. — In addition to the more general influences of
atmospheric humidity and soil moisture on plant development there
are certain more or less specific influences on fruits and fruit plants.
One of the most conspicuous and frequently observed is the effect on the
russeting of the skin of certain pomaceous fruits, particularly the apple
and the pear. This results from a cracking and weathering off of the
epidermis and an increased development of the corky parenchyma
beneath. It occm-s especially in humid climates or during rainj^ sea-
sons. For instance the Bosc and Winter Nelis pears as grown in the dry
atmosphere of the Rogue River valley of southern Oregon are practi-
cally smooth skinned fruits. Grown in the more humid Willamette
valley a hundred miles farther north their surface is almost completely
russeted. The Cox Orange apple is a half russet variety as grown in
England; it is a smooth-skinned fruit as grown in the Okanogan region in
British Columbia. The fruit trade generally considers that fruit pro-
duced in irrigated sections has a higher "finish" than fruit of the same

80 FUNDAMENTALS OF FRUIT PRODUCTION

varieties produced in non-irrigated orchards. The reason Kes in the
lower atmospheric humidity of the sections where irrigation is practiced
and is in no way directly connected with the irrigation.

This russeting of the skin is often attributed to the action of certain spray
materials and without doubt is sometimes partly or even entirely caused by
them. In most cases, however, atmospheric humidity is an important contribut-
ing factor. The following quotation from a report by Morse, ^^ who has made a
study of the subject particularly as it relates to spray injury, is instructive:

"One of the most prominent facts shown by the tabulated results of 1916 is
the relatively high per cent, of russeted fruit on each plot, even on the un-
sprayed check which showed 20.57 per cent. This duplicated a condition which
prevailed in 1913 when over 31 per cent, of russeted fruit was obtained on the
plot upon which no insecticide or fungicide was applied, and the different sprays
produced a corresponding increase in amount. Although this russeting was
materially increased by different sprays it is evident that much of it must be
attributed to natural causes. The weather conditions of 1913 and 1916 were
remarkably similar in many ways, and differed from previous seasons in which
abnormal fruit russeting did not occur. In 1913 the first spray apphcation was
followed by a month of unseasonably, cold weather, with frosts and cold, north-
west winds, associated with much cloudiness and heavy rainfall. In 1916,
similar conditions prevailed previous to and following the first application.
This was also followed in 1916 by heavy rains and continuous cloudy weather
in June after the second application, which was not the case in 1913."

In extreme cases this russeting may be accompanied by cracking and
malformation of the fruit, resulting in considerable loss. Sorauer"^
notes that in the grape similar atmospheric conditions may lead to the
development of cork pustules on the peduncles or pedicels as well as on
the fruit. The cork generally starts to develop under the stomata and
the disorder is likely to make its initial appearance comparatively early.

Some of the effects of high humidity previously mentioned, for
example increased leaf surface and the russeting of fruit, are phenomena
that likewise accompany a decreased light supply. This raises the ques-
tion as to whether a part of the apparent direct influence of atmospheric
humidity may not be due in reality to its action in intercepting light.

Fruit Setting. — Inquiry shows that atmospheric humidity is often of
greater importance in the setting of fruit than is generally realized.
Hot drying winds at blossoming time may evaporate the moisture from
the stigmatic secretions and thus prevent the germination of the pollen.
Extreme atmospheric humidity may interfere with the work of insects
in carrying pollen or it may encourage the development of certain fungi
such as brown rot and apple and pear scab that work on the flowers and
destroy or injure them. The well known effects of rain during the blos-
soming season in preventing pollination, in washing away and destroying
pollen and in diluting stigmatic secretions may be mentioned. A study

RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 81

of the "June drop" of the Washington Navel orange in CaHfornia indi-
cates that a large part of this drop is due to abnormal water relations
during that part of the day when transpiration is at its highest. ^^

"During the day the fruits (of the Washington Navel orange) decrease in
water content as much as 25 to 30 per cent. It has been definitely established
that under severe conditions when the atmospheric pull is high the leaves actually
draw water back out of the young fruits to maintain themselves. But this supply
is not sufficient and they decrease in moisture content also. The combined
effect of this tremendous loss from leaves and fruits results in tensions in the
water-conducting systems of the tree. These tensions as well as the water deficits
have been found to be at their maxima when environmental conditions are most
severe, that is, between 10 a.m. and 3 p.m.

"Meteorological records show that the atmospheric humidity of the interior
valleys is quite low during the growing months, relative humidities of 15 per cent,
being not uncommon. Such humidities may and do occur without marked
increase in air temperature. In other words, it is possible for extremely dry
weather to occur without the characteristic hot-norther.

"Experiments have been performed in the laboratories at Berkeley in which
this process of abscission of leaves on cut branches has been induced by artificial
means. The process itself has been studied and found to consist in the gelatini-
zation and dissolution of the cell walls resulting in complete separation of the
cells. . . .

" The major part of the June drop occurs early in the season and has to do with
blossoms and small fruits. It is caused by a stimulus to abscission arising from
abnormal water relations within the plant due to peculiar climatic conditions.

"Further evidence that the cause as indicated is substantially correct lies
in the fact that in certain orchards which are provided with efficient windbreaks
and interplanted with alfalfa and heavily irrigated, the water deficits in leaves
and fruits have been found to be much reduced. Such orchards have less drop
and are notable for their comparatively large yields. The Kellogg orchard at
Bakersfield is planted to alfalfa and is shielded by a fairly efficient windbreak.
Meteorological measurements made in this orchard and on the desert to windward
show that the climatic complex is greatly ameliorated. . . . The alfalfa tran-
spires at a tremendous rate and literally bathes the trees in a moist atmosphere.
The windbreak retards the movement of this relatively moist air away from the
vicinity. The vaporization of water from soil and plants tends to lower the
temperature of the air. As the soil is largely shaded, the high soil temperatures
are reduced, which temperatures operate to cut down root absorption at the time
of day when water loss from the leaves is greatest. . . .

"It thus seems probable that under the prevalent practice of clean cultivation,
during the middle of the day when transpiration is greatest the root absorption
is actually reduced, resulting in water deficits in all parts of the tree.

" Not only are clean cultivated orchards subjected to higher soil temperatures,
but inasmuch as the root system tends constantly toward the surface layers, it is
much reduced by the annual spring plowing which shears off many of the fibrous
feeders, thus reducing the root area just before blooming and at the very time
the trees are under the greatest strain. "^^

6

82 FUNDAMENTALS OF FRUIT PRODUCTION

To what extent a very high transpiration may lead to the formation
of abscission layers and the dropping of fruit in other varieties and in
other species is not known, but presumably the phenomenon is not
limited to the Washington Navel orange. On the other hand there is a
limited amount of experimental evidence showing that very high atmos-
pheric humidity tends to cause the abscission of partly developed
apples from the spur.''^

Summary. — Evidence from both tillage and irrigation experiments
shows increased vegetative growth, as measured by length of new shoots,
leaf area and increment in trunk circumference, with increasing moisture
supply up to a certain limit (the optimum for growth). The amount of
soil moisture available during the short period of rapid growth in early
spring is particularly important. When the optimum moisture supply
is exceeded the correlation becomes negative. Second growth of mid-
summer and the late summer months is generally associated with an
irregular moisture supply. An increased moisture supply late in the sea-
son results in an increase in size of fruit and in larger yields. Regularity
of bearing is encouraged by an adequate and continuous moisture supply.
There is a limit, however, to what can be accomplished in this direction
through increasing soil moisture. In certain species, as the apple, dry
soil conditions tend to promote an oblate form of fruit. There is no
very direct relation between moisture supply and fruit color, though
good moisture conditions tend to yield fruits with brighter colors than
are obtained from soils that are too dry for best growth and development
of tree and fruit. The higher colors of fruit from irrigated sections may
be attributed to more nearly cloudless skies, in comparison with those of
more humid regions. Fruits that develop where the soil moisture is
either deficient or in excess are inferior in quality to those developing
where soil moisture conditions are more nearly normal. Disease suscepti-
bility is often modified materially by the rate of growth, as influenced
by soil moisture conditions. The injurious effects of deficient moisture
supply may be more evident the season following the drought than during
its occurrence, taking the form of decreased vegetative growth and lowered
yields. The effects of variations in atmospheric humidity are hardly less
pronounced than those in soil moisture supply. Russeting of fruit is
common in many species when the humidity is high. Water deficiencies
at the time of fruit setting are likely to result in an undue amount of
dropping.

CHAPTER VI

PATHOLOGICAL CONDITIONS ASSOCIATED WITH
EXCESSES OR. DEFICIENCIES IN MOISTURE

Not only is water a limiting factor to growth, but when there is a
deficiency or when it is present in excess well defined pathological condi-
tions may arise. Some of the most difficult disorders with which the
fruit grower has to deal are to be regarded as drought or as excess moisture
diseases.

DISTURBANCES DUE TO MOISTURE EXCESSES

Excessive moisture conditions are likely to be accompanied by a
disproportionate development of certain tissues usually parenchyma and
this is at the expense of conductive tissue.

The Splitting of Fruit. — One of the most frequent troubles incident to
the presence of too much water at certain seasons of the year is a splitting
of the fruit. This is most likely to occur shortly before maturity when
rains follow a period of drought during which the fruit has been checked
in its growth. Apparently the checking of growth is accompanied by
changes in the fruit skin rendering it less elastic so that when growth
processes are accelerated following a rain it is unable to expand rapidly
enough to make provision for the developing tissues within. Heavy,
late irrigation following a long dry season has the same effect. The
stone fruits are particularly subject to this trouble and certain varieties
of apples, for example the Stayman Winesap, are likewise susceptible.
In the stone fruits, splitting is sometimes limited to the stone, the flesh
and skin remaining intact. Treatment of this trouble, as of most dis-
turbed conditions due to abnormal water relations, should be preventive
rather than remedial. Cultural practices should be directed toward
maintaining in the soil a moderate amount of available moisture so that
growth will not be checked, even though there may be an extended
period of dry weather. Splitting of flesh and of stones seldom occurs if
the tissues of the fruit are kept growing. It is suddenly renewed growth
following a check that causes the trouble.

In the fig, splitting may accompany high atmospheric humidity during the
ripening period even though there be no rain or no sudden changes in water
content of the soil. However, they are much less likely to split under such con-
ditions than when rain accompanies a humid atmosphere so that the trees can
take up an increased amount of moisture. ^"^ Should dry, warm weather follow
the splitting of this fruit the fissures may close and partially heal over without
fermentation setting in.

83

84 FUNDAMENTALS OF FRUIT PRODUCTION

Related to the splitting of the skin and fleshy tissues of many fruits
and the splitting of the stones of drupaceous fruits is the cracking of
carpels and seed coats frequently found in apples and occasionally in
pears and other pomaceous fruits. This is often accompanied by the
development of a whitish mold-like growth along the edges of the cracks,
giving rise to a condition spoken of as "tufted" carpels or "tufted"
seeds. According to Sorauer^^^ this condition is due to an excessive
moisture supply and the consequent disproportionate growth of certain
cells and tissues. The "tufting" itself is hardly to be regarded as a
diseased condition, for it is more or less common in certain varieties, but
apparently an excess of moisture greatly accentuates the condition. It
in no way injures the quality or value of the apple, except as it provides
a favorable place for the work of certain fungi which may gain entrance
to the seed cavity through a broken calyx tube.

CEdema. — Q^^dema may be described as a swelling of certain parts
of a plant caused by a great enlargement of the component cells. In
extreme cases the cell walls break and the cells collapse, resulting in the
death of the affected tissues. This condition is due frequently to an
excess of moisture. It is favored in the case of the tomato by insufficient
light, too much soil moisture or a soil temperature too high in comparison
with the air temperature so that transpiration cannot take care of water
absorption.^ Sorauer^^^ states that in fruit trees these swellings are
usually covered by cork but that sometimes they break open. He notes
that the trouble is fairly common when either currants or gooseberries
are grafted upon the Golden Currant (Ribes aureum). The swellings
develop just below the union and the cion does not make a satisfactory
growth. In this case the excess of water is to be regarded as a local
rather than a general condition.

A similar disorder in which the bark develops at the expense of the
wood, has been described in the pear, under the name "parenchyma-
tosis."^^* The swellings may be on one side only of the limb or trunk or
they may extend around it, giving rise to a barrel shaped or cylindrical
enlargement, which may be accompanied by a splitting of the bark.

Thei'e has been described a disorder of the grape also, more or less
closely related to oedema, due to excessive atmospheric humidity. It is
most frequently found in grapes grown under glass. On the leaves and
peduncles intumescences develop which are characterized by great
turgidity, a high oxalic acid and low starch content. ^^"^

Fasciation and Phyllody. — Fasciation, or the production of a flat
branch which resembles several branches grown together is regarded
generally as a malformation belonging in the field of teratology rather
than as a pathological or diseased condition induced by agencies more or
less under control. Sorauer,^!'' however, places it among the distur-
bances due to overfeeding and associated with excessive water supply.

PATHOLOGICAL CONDITIONS 85

A form of phyllody, known as "false-blossom" or "Wisconsin false-
blossom," apparently caused by an excessive water supply has been
observed in some of the cranberry bogs of the Northern states. It is
characterized by more or less leaf-like calj^x lobes and petals, aborted
or malformed pistils and stamens, the production of little or no fruit and
an appearance of the plant suggestive of witches' broo'm. The trouble
"is usually associated with extreme wet or dry conditions of the bog,
but most frequently with an excessive water supply. In most of the
localities in which it has been observed the affected plants were growing
in a deep, coarse peat soil having an excessive water supply during the
greater part of the growing season. "^^° What is evidently a very similar
disorder, often caused by disturbed water relations, has been described
under the name "virescence" as affecting the coffee tree in Indo-China.^^

Chlorosis. — Chlorosis in plants is generally associated with some form
of malnutrition and some attention is devoted to it in that connection.
However, Taylor and Downing^24 found it accompanying over-irrigation
in a number of Idaho apple orchards. Indeed they came to regard it as
one of the evidences of excessive applications of irrigation water. It is
possible that the chlorotic condition of the trees was induced through
some influence of the excess water supply on the plant nutrients in the
soil or the foods in the plant, but directly or indirectly the surplus
moisture was responsible for it. A chlorotic condition of the peach
induced by over-irrigation has been reported in Baluchistan.^" Its early
symptoms were much like those of the "peach yellows" of the eastern
United States and at one time it was thought to be that disease. It was
accompanied often by much gumming and imless promptly treated the
tree died. The use of less irrigation water and the employment of cultural
practices leading to a better aeration of the soil were efficient correc-
tives. Chlorosis has been found in heavily watered seed beds of the
western pine in Nebraska while check plots showed none.^'

Rough Bark or Scaly Bark Disease. — This disease according to
Sorauer^'^ results in a scaling off of the bark from the roots and to a less
extent from the stem. It has been described as affecting the apple,
cherry and plum when growing on low, wet ground. When appearing
on the roots it is likely to cause the death of the tree; when it attacks
the trunk it is less serious. Histologically what takes place is an excessive
lengthening of some of the bark cells. This process may continue deep
into the bark layer and interfere with normal functions at the diseased
spot.

Watercore. — Curiously enough it is sometimes difficult to decide
whether a certain disturbance is due to drought or to an excess of mois-
ture. The temporarj^ rising of the ground water table may result in
the death of a considerable part of the root system. Later, with lowering
of the water table the soil dries out and if there is a prolonged dry period,

86 FUNDAMENTALS OF FRUIT PRODUCTION

the tree with its reduced root system may suffer for lack of water and
drought injury ensue. It is a case of drought injury but in the last
analysis excess soil moisture at another season is the real determining
factor. It is likewise a paradox that some forms of watercore must be
regarded as due to drought. Though many cases are to be attributed to
other factors, Sorauer^^^ describes at least one form as associated with a
deficient soil moisture supply. In this form, water fills the intercellular
spaces and the affected tissues become hard and glassy. The outer
portion of the fruit is involved more directly than the tissues immediately
surrounding the core. The seeds remain white and do not ripen and the
affected fleshy tissues turn dark upon exposure to air more rapidly than
normal tissues. They have less dry matter, less ash and less acid.
Zurich Transparent, Gloria Mundi, White Astrachan and Virginia
Summer Rose are mentioned as varieties particularly susceptible to this
disease.

The watercore more frequently occurring in the United States is
found in the core of the fruit and in the region of the main vascular
bundles, though it not infrequently extends to the surface or may be
limited even to the surface layers. This form of watercore is particularly
virulent in regions of intense sunlight and abundant soil moisture.
Tompkins King, Fall Pippin, Yellow Transparent, Early Harvest,
Rambo and Winesap are mentioned as particularly susceptible varieties. ^^

DISTURBANCES DUE TO MOISTURE DEFICIENCIES

A deficiency in the water supply is likely to be accompanied by dis-
turbances in the conductive system and an excessive development of
stone cells and strengthening tissue.

Defoliation. Premature Ripening of Wood. — Summer drought often
leads to premature ripening of the fruit, early leaf fall and premature
entrance into the winter rest period. Frequently the attacks of certain
fungi hasten these processes so that distinction between their influence
and that of drought is difficult ; nevertheless there can be no doubt that a
lack of available moisture has an important influence of this kind. These
effects of drought are manifest in various ways in the different fruits.
For instance, the leaves of the peach and cherry turn yellow and fall,
those of the grape turn yellow or red at the edges or between the veins
and those of the pear do not become yellow but appear brown or burned
in spots and remain clinging to the trees. ^^* When yellowing is due to
drought injury it is as a rule those parts of the leaf farthest removed from
the veins that yellow first. A somewhat unusual form of defoliation due
to a drought has been mentioned as a pectin disease."* It has been
observed on the grape and consists in the formation of an abscission layer
between the leaf blade and petiole, resulting in the premature falling of
the blade. The loss of leaves from drought robs the plant of essential

PATHOLOGICAL CONDITIONS

87

mineral matter, particularly nitrogen and may interfere in this way with
its nutrition as well as through reducing the manufacture and storage of
elaborated organic materials. Table 38 shows the mineral constituents
of Syringa leaves at the time of defoliation from drought and at the time
of normal abscission. The yellowing and dropping of the leaves of
dwarf pear trees in times of drought while those of standard trees remain
normal is clear evidence that the trouble is due mainly to a lack of
moisture, the limited root system of the quince being unable to supply
the requirements of the cion in such emergencies."*

Table 38. — Mineral Constituents of Syringa Leaves at Different Periods
IN Percentages of Dry Weight

{After Soraiier^^*)

When defoliated by
summer drought

When normally drop-
ping in the fall

1.847
0.522
2.998
1.878
8.028

1 370

PhosTjhoric ;icid

0 373

Potash

Calcium oxid

Ash

3.831
2.416
9.636

Apparently related to these troubles induced by drought is the tip-
burn of certain plants occurring during periods of very high transpiration.
Even a few hours of very rapid transpiration in intense sunlight, high
temperature and low atmospheric humidity may lead to so great a reduc-
tion of the water content in the edges of the leaves of the potato that
recovery of turgidity is impossible. ^^ The affected tissues die, a condition
known as tip-burn.

Another closely related form of drought injury has been found on the
grape in New York. It is perhaps best described in the words of the
original report :

"Vines affected with the trouble first show a streaked pallidness of the
leaves in the intervascular spaces. Later these streaked areas become yellow.
The discoloration is more marked near the margins and eventually the pallid
areas coalesce and form a yellowed band extending around the margin. As the
season advances this band dies and becomes functionless. Isolated areas of the
leaf blade deaden and when these join, a considerable part of the leaf tissue may
become functionless. When the entire leaf is affected the outer margin often
curls upward. The injury is cumulative unless favorable conditions are estab-
Ushed in the succeeding years, i.e., optimum rainfall, etc. As a result of the
injury to the foliage, growth is materially checked and the wood usually fails to
mature well. The fruit does not color nor is the normal amount of sugar fixed.
'Shelling' may result.

88 FUNDAMENTALS OF FRUIT PRODUCTION

"Considering the facts at hand it would seem that a lack of available soil
moisture, at critical periods in the vine's growth, or a lack of root aeration as a
result of the impervious subsoil together with the shallow depth of surface soil,
are the principal contributing factors to the affection. With this soil type the
sickness is at its height in seasons of drought as well as in those of excessive
rainfall. Soils such as the yellow silt are generally deficient in organic matter,
and hence in their water-holding capacity. With them the affection is worst in
seasons of drouth and least in those of normal rainfall. During early summer the
vine makes a rapid growth of succulent shoots and leaves which require large
amounts of water to develop."^" Newly planted vineyards, where the vines
do not yet have extensive root systems, are more Ukely to be affected.

Dieback. — From the form of drought injury described in the grape,
it is but a step to more serious conditions resulting in the death of
some of the twigs, shoots or branches of the tree. This may occur in
trees of almost any kind, the symptoms varying somewhat in different
species. However, there is no mistaking the disease when it is present.
Without doubt dieback may be due to any one of a number of factors.
Chief among these is an inadequate water supply, not necessarily at the
time the symptoms are first noticed, but perhaps many months earlier.
Batchelor and Reed^^ have described dieback as it occurs on the English
walnut. Since its appearance there is fairly typical of its occurrence on
many other fruit trees the following account is taken from their report:

"We have very convincing evidence to show that trees which enter the
dormant period in the fall in a perfectly normal and healthy condition may
suffer from dieback due primarily to a lack of sufficient soil moisture during the
winter months. During the winter, trees give off moisture through the Umbs
and twigs. If for a prolonged period there is not enough soil moisture available
to the roots, the trees are unable to obtain sufficient water to offset the loss by
evaporation from the branches. In that case young branches, the thin bark of
which permits rapid loss of water from the wood, may die as a result of desic-
cation. This injury is first evident when such branches fail to produce new growth
the following spring. . . . Frost injury is usually confined to 1-or 2-year old
wood, but winter drought may kill back limbs 8 years old.

"Another condition which is equally critical and apt to injure bearing trees,
as well as young ones, is the occurrence of a fluctuating water-table. The sudden
rise of a fluctuating water-table kills that portion of the root system which is
located in the saturated stratum. In severe cases where the major portion of the
root system is killed the twigs and young hmbs of the tree later exhibit typical
cases of 'dieback.' It might seem paradoxical that the top of the tree should dry
out and die when the roots stand in an excessively wet soil, but there is nothing
contradictory in the situation when it is seen that the death of the major portion
of the roots makes it impossible for the top to receive the necessary moisture to
sustain life."

Though much of the dieback or exanthema found in citrus trees is
due to disturbed conditions of nutrition there seems to be no doubt that

PATHOLOGICAL COX DIT IONS 89

the disease is generally associated with abnormal moisture conditions.
Trees subject to poor drainage, underlaid with hardpan or subject
during the previous season to extreme drought or to an irregular water
supply are most subject to the disease.'*^ Drought, therefore, must be
regarded as an important contributing factor. Other than the dying
back of the limbs, this disease presents a number of well defined symptoms
in citrus trees that may be mentioned as further illustrations of the dis-
turbed and pathological conditions which may arise from, or be end
products of, an abnormal water supply. Among them are: the produc-
tion of gum pockets, stained terminal branches, ammoniated fruits, bark
excresences, multiple buds, exceptionally deep green color of the foliage,
the production of S-shaped terminal shoots and of coarse leaves somewhat
Hke those of the peach in shape. •*'■*

Cork, Drought Spot and Related Diseases. — Under these names have
been described numerous disorders of fruit trees that are apparently
related. Indeed differentiation between them is frequently difficult, if
not impossible. This is understood easily because they are in fact
closely related and are perhaps only different symptoms of the same
fundamental disturbance in the physiology of the plant. The following
descriptions are from the reports of those who have made a close study
of them.

Fruit-pit. — " In the early stages of fruit-pit one finds numerous sunken areas
from 2 to 6 millimeters in diameter on the surface of the apple. These
depressions are somewhat hemispherical in shape and have the appearance of
bruises. At this stage the spots are not brown and often show no difference in
color from the surrounding surface of the apple. . . . Later they begin to take
on a brown tint, but at first this seems to show through from rather deeply
seated tissue and not to arise from any discoloration of the epidermal or imme-
diately underlying cells. Sections of such spots show that this is the case, and that
the browning and shrinking of the cells occur in the pulp of the fruit and in the
tissue that is transitional between it and the hypodermal parenchjona.
Later the surface cells also become dark brown. ... As the disease advances
spots situated near each other often become confluent, developing into one large
spot. In all such cases examined it was found that the original spots were
closely connected with one vascular branch. . . . The surface spotting is often
accompanied by browning of the tissue immediately surrounding the vascular
bundles. Upon cutting such an apple one sees numerous apparently isolated
brown spots. Further study shows that these are not isolated but are in reality
continuous strands of brown tissue surrounding the vascular bundles. The
portion of the vascular system that is most commonly affected is that lying
within fifteen miUimeters of the surface of the apple. The surface spots often
occur without the internal browning and also the internal browning may occur
unaccompanied by any surface derangement. "^^

Cork. — Cork is most commonly observed when the apple is anywhere from
half grown to nearly mature. It may be briefly characterized as internal brown-

90 FUNDAMENTALS OF FRUIT PRODUCTION

ing, described by Brooks in the preceding paragraph, but without external pits
and with the surface of the apple thrown into a series of elevations and depres-
sions. A large number of brown corky areas occur throughout the flesh, follow-
ing closely the course of the vascular bundles. In no case do these extend
outward as far as the skin, consequently there are no external brown pits charac-
teristic of true fruit-pit or stippen. A further difference from the usual type
of fruit-pit is that the spots are not more abundant in the peripheral zone, but
are scattered throughout the flesh of the fruit. There is no bitter taste connected
with this disease in Fameuse apples. ^^

"Under the microscope the internal brown spots of cork appear as aggrega-
tions of cells with brown shrunken contents. A number of the cells, though not
all, are shrunken and collapsed. Around the corky portion the healthy cortex
cells form a ladder-like arrangement of smaller, more nearly rectangular cells.
It is as though they had been stimulated to rapid division in response to the
decreased pressure from the direction of the diseased area. Outside of this zone
the pulp cells are normal in size and form. The close relation of the dead spots
to the vascular system is very evident under the microscope. "^^

Surface Drought Spot. — "An early stage of the disease is manifested by an
irregular light-brown area in the skin. When the fruits affected are large, two
or three centimeters in transverse diameter, the surface of the fruit is usually
smooth and regular, there is no shrinkage or sinking in, nor anj^ abnormality
in the flesh beneath. . . . When the spot first appears tiny drops of a clear or
yellowish gummy exudate may occur on its surface. Under the microscope this
exudate shows as a clear gum. ... It is considered to be merely an expression
of cell sap from the diseased hypodermal cells. . . . Most of the fruits
affected when young drop from the tree. Some of them . . . persist, and as
they grow the affected areas become roughened and cracked."'^

Deep-seated Drought Spot. — "This type of lesion is characterized by the
presence of brown, corky areas in the flesh of the apple and by a sinking in of
portions of the epidermis. On young fruits, from 1 to 2 or 2J'^ centimeters in
transverse diameter, the disease appears as a large brownish area in the skin of the
fruit, usually near the blossom end, which is irregularly sunken and wrinkled,
indicating shrinkage of the tissues beneath. Cross-sections show brown areas
in the flesh near the periphery. These are opposite the main vascidars, and often
in the center of one of them there is a large cavity, the apex of which reaches one of
these vessels. (Occasionally, apples are found in which there is one of these
corky areas or cavities opposite each of the 10 main vasculars.) These internal
spots are often connected by a narrow brown streak running close to the periphery
of the apple. Sometimes these streaks do not connect, but extend only a short
distance in either direction from the central spot. The shrinkage of the skin
over a considerable area, and the presence of these brown corky spots and streaks
in the periphery, suggest the type of fruit-pit described by McAlpine as 'con-
fluent bitter-pit' or 'crinkle.' . . . Microscopically, sections of the diseased
spots show that the trouble is confined to two or three layers of the hypodermal
parenchyma, usually the inner layers, though sometimes the entire hypodermis is
affected and a few dead cells are also found in the flesh. The diseased
cells retain their normal outline, but their contents have become brown and
amorphous. "^^

PATHOLOGICAL CONDITIONS 91

Dieback and Rosette. — Dieback in its early stages appears usually in the
spring. Some or all of the buds toward the ends of the shoots remain dormant,
while lower buds start. The shoot ends that do not vegetate may remain alive
all season or they may dry out and die earlier. "The appearance of one of these
dieback shoots the following summer was that of a completely dead tip from
6 inches to 1 foot long, often with a distinct marginal crack between it and the
living part below. From some point back of this tip a healthy lateral developed
to renew the branch."'^

The early stages of dieback may be observed in cross sections of dieback
twigs of the current season's growth. "Such a twig usually shows entirely dead
tissue near its tip and a discoloration in the cambial area running back for a
variable distance. Under the microscope this discolored zone shows, if the
sections are taken near the tip, a large number of cells with browned contents in
the cambium, phloem and pericycle. If sections are made from parts of the
twig a short distance below, it will be seen that growth has been made subsequent
to the injury. The injured cambium has produced a quantity of the so-called
parenchyma wood, the browned cells of the phloem and pericycle being pushed
outward. Finally, the parenchj^ma zone becomes buried by a layer of new
xylem, outside of which are found normal bark and cambium." . . . Often
some of the buds on the lower part of such dieback shoots "developed clusters
of very small, lanceolate leaves with shortened petioles. In some cases the twigs
made a very short terminal growth, resulting in a thickened, shortened axis an
inch or so long, bearing a cluster of leaves, some normal and some short lanceolate,
the general effect being that of a long bare twig capped by a rosette of leaves. "^^

In commenting on these diseases Mix remarks: "It is evident that we have
under consideration, not two distinct apple diseases, but at the most, two types
of the same disease: (a) Drouth spot, with which are associated abnormalities
of the foliage, called drouth dieback and drouth rosette; and (6) cork, which
may occur in association with drouth spot, but which often occurs independently,
and is then not associated, except rarely, with any disease of the foliage.

" The writer's observations show that these diseases may occur in both wet and
dry seasons. There is, however, a marked relation of weather conditions to the
disease. They tend to disappear during wet weather and are much more serious
during a dry period, especially dry weather occurring early in the season.

"Since, however, in a wet season, and under conditions where there seems to
be no deficiency of moisture, these diseases may occur in trees that have been
previously diseased year after year, insufficient soil moisture cannot be looked
upon as the sole cause. . . .

"It is suggested that the exact manner of occurrence of the injury may be
by the leaves robbing the fruit of water during a critical period of low root supply
and high transpiration. Rapid wilting of the fruits can be brought about by
excessive transpiration from the leaves. It has been seen that this wilting may
result in the death of certain cells near the vascular bundles, forming lesions
resembling those of drouth spot, and occasionally, of cork. Chandler has pre-
sented evidence that transpiration from the leaves may bring about a scarcity of
water in the fruit under field conditions. It is not impossible that this is at least
one of the ways in which the disease may be caused.

"This seems more likely than that injury is due to an excessive transpira-

92 FUNDAMENTALS OF FRUIT PRODUCTION

tion from the fruit itself, or, as suggested by McAlpine for 'crinkle,' to the failure
of the vascular network over large areas. The striking thing about these diseases
is the presence, not the absence, of meshes of this vascular network in close
proximity to the dead cell areas.

"In making the above suggestion as to the cause of cork and drouth spot, the
writer realizes that the small amount of experimental work done does not warrant
a definite conclusion. There is, undoubtedly, much yet to be learned of the
real nature of these diseases.

"Furthermore, it is not intended to advance this theory to explain the cause
of true fruit-pit, or stippen, which occurs in a late stage of the fruit's growth and
is said to develop in storage."

The findings of Brooks and Fisher,^^ who also made an extended study
of drought spot and cork in apples, in the main corroborate the conclusions
of Mix just quoted. They succeeded in producing drought spot experi-
mentally by subjecting Winesap trees to a sudden and severe drought
when the fruit was about 1 inch in diameter. Furthermore, trees of
other varieties accidentally receiving similar treatment through mishaps
to the irrigation system produced fruits exhibiting the same condition.
It was noted in the course of the investigation that many trees after once
producing drought spot fruits continued to bear them in later years,
even though suitable soil moisture conditions were provided. This the
investigators believed to be due to the loss of many roots when the
drought occurred. They found cork, or troubles very similar to it, in
many of the apple producing sections of the Pacific Northwest and in
New York, Virginia and West Virginia. In summarizing their findings
they state:

"In nearly every case where the disease has been observed either in the
East or West, its occurrence in the orchard has been closely correlated with certain
peculiar soil conditions ; sometimes an excess of alkali or an out-cropping of slate,
but more often a shallowness or openness of the soil. In most sections cork
has been most serious when there was a shortage in soil-water supply, either
resulting from Ught rainfall or a lack of irrigation.

"The observations reported above seem to indicate that cork is a form of
drouth injury; yet the disease appears to differ from typical drouth spot, both
in characteristics and conditions of occurrences. With certain varieties of
apples drouth spot can apparently be produced on any soil under conditions of
sudden and extreme drouth. Cork seems to be the result of a less severe but
more chronic drouth on trees located on certain peculiar soils, especially on soils
that are lacking in humus and are not retentive of moisture. Bhster is closely
associated with cork and is probably produced by the same agencies.

"It should be noted in this connection that the harmful effects of drouth are
not always in proportion to the degree of desiccation. Other factors must be
considered in a study of drouth troubles, and among these are the percentage
of harmful substances in the soil water and the general growth condition of the
plant."26

PATHOLOGICAL CONDITIONS 93

In the pecan there is a related disorder, though its most conspicuous
symptom is the appearance of rosetted branches. This is associated with
a deficiency of humus as well as an insufficient moisture supply in the soil
but destruction of roots through drought or an extreme depletion of the
soil moisture are important contributing factors. ^^

Bitter-pit. — In bitter-pit "the diseased tissue is dry and spongy, the cells are
collapsed but still full of starch, and the cell walls show no sign of thickening or
disintegration. . . . The pits are usually associated with the terminal branches
of the vascular bundles, and the surface spotting is often accompanied by a
browning of the vascular tissue deeper in the fruit, giving the appearance of nu-
merous brown spots in the flesh when the apple is cut. . . .

"The results of the various experiments have been uniformly consistent in
showing that heavy irrigation favors the development of bitter-pit. Heavy
irrigation throughout the season has given less of the disease than medium irri-
gation followed by heavy, and light irrigation throughout the season has resulted
in more bitter-pit than heavy irrigation followed bj^ light. Heav"^^ irrigation the
first half of the season caused the trees to develop a more luxuriant foliage and
probably produced a lower concentration of cell sap in the apples, both of which
facts would tend to make the fruit less susceptible to the forcing effects of late
irrigation. The amount of irrigation in August and September has apparently
largely determined the amount of disease.

"Sudden changes in the amount of soil water do not appear to have had any
effect upon the amount of disease. No evidence has been found that bitter-pit
is brought about by a rupture or bursting of the cells.

"Large apples have been more susceptible to bitter-pit than small ones, but
the increase in the disease from heavy irrigation has been almost as great on the
small and medium sized fruits as on the large. . . . Apparently apples are not
susceptible to bitter-pit merely because they are large, but rather because of
conditions that may sometimes accompany an increased growth.

"The results as a whole point to the harmful effects of heav>^ late irrigation
regardless of the size of the fruit. In looking for the final cause of the disease not
only the direct growth-forcing effects of the water should be considered but also
the effects of the excess water upon the soil flora and soil solutes.""

Jonathan-spot. — " 'Jonathan-spot' is the term applied to superficial black or
brown spots that are especially common on Jonathan apples. ... In the early
stages of the disease only the surface color-bearing cells are involved and the
spots are seldom more than 2 mm. in diameter, but later the spots may enlarge
to a diameter of 3 to 5 mm., become slightly sunken and spread down into the
tissue of the apple to a considerable depth. . . . The results of both years
gave some evidence that heavy irigation was more favorable to the disease than
light irrigation, but there was nothing to indicate that the amount of soil moisture
was an important factor in determining the amount of Jonathan spot."^^

To what extent these, or similar diseases are to be found in other
fruits is unknown. There is reason to beheve, however, that just as some
of these diseases of the apple have been dismissed as winter injury or as

94 FUNDAMENTALS OF FRUIT PRODUCTION

some other rather obscure disorder, so some of the serious troubles of these
other fruits may prove eventually to be due directly or indirectly to
drought. Rosette and little-leaf are certainly not unknown in the cherry,
apricot, plum and pear though little attention has been devoted to them.

Barss'" records "cork" as of frequent occurrence in pears in Oregon and a
"drought spot "or "gum-spot "as not uncommon in prunes. Both are attributed
to disturbed water relations. In speaking of the gum-spot of prunes he says:
"It comes on just about in midseason and appears first as watery-looking spots
on the fruit. These usually swell and burst open by a crescent-shaped sht, from
which there is an exudation of transparent gum that hardens on the surface. In
the flesh of such prunes small brown flecks always appear, beneath the gum-
spot. These usually consist of a few dead pulp cells situated in the region of the
outer network of veins. Such injury is often slight and the prunes mature with
very little evidence of the trouble. More severe injury, however, may result in
the death of larger areas of the pulp. The resulting collapse of the tissues and
cessation of growth produces an irregular or corrugated surf ace. Such affected
prunes usually color up prematurely and drop off.

"In some years, as the prunes approach maturity great losses to growers
result from an internal breaking down of the flesh, with brown discoloration and
disagreeable odor, which has sometimes been erroneously mistaken for brown
rot. This internal browning usually starts immediately around the pit, but often
extends outward until in some cases it reaches the skin and involves the whole
flesh. The trouble is . . . presumably due to disturbed water balance in
the tree and perhaps is similar in origin to 'punk' in the apple."

The assumption should not be made, however, that all these diseases
described and discussed here under the names of cork, fruit-pit, bitter-
pit, Jonathan-spot, dieback, rosette, etc. are always due exclusively to
disturbed water relations. Though without doubt they often are caused
directly or indirectly by excessive moisture or by drought, there are
other contributing factors and in some instances their occurrence
may be due to these other factors alone. For instance, White ^^^ ^nd
Ewert*''' ^^ present evidence that in Australia much of the bitter-pit in the
apple is due to localized poisoning caused by the presence of minute
quantities of certain mineral toxins absorbed either from the soil or from
the coating of certain spray materials on the fruit itself.

Black-end. — Under the name black-end has been described a physiological
disease of pears in which the skin around the apical end of the fruit turns black
while the flesh immediately underneath becomes hard and dry and may crack. i°
Such fruits are likely to be rounded at the apical end instead of depressed in the
usual manner. The blackened area often blends gradually into healthy tissue.
This disease is found most frequently in the hotter and drier portions of Oregon ,
and "all the circumstantial evidence points to the probabiHty that excessive
evaporation in hot weather or insufficient soil moisture are responsible for its
development, since it appears usually on soils either unfavorable for root
growth or unretentive of moisture or both."

PATHOLOGICAL CONDITIONS 95

Silver Leaf. — Sorauer^^'' describes one type of silver leaf occurring
on apricots, plums, cherries and apples. The immediate cause of the
silvery or milky appearance of the leaves is the partial separation of the
epidermal cells from one another and from the palisade cells, the inter-
cellular spaces becoming greatly enlarged. The older leaves are more
subject than the younger. This disease is usually associated with some
gummosis of the limbs and in aggravated cases the affected branches die.
Aderhold suggests that the failure of the middle lamella to cement
adjoining cells is due to a lack of calcium, which permits the pectin to
become soluble. As the disease generally occurs locally in the plant,
the lack of calcium is not the result of a deficiency in the soil but is due
to a local disturbance in the conducting system.

Some other forms of silver leaf occasionally appearing in the orchard
and affecting entire trees or entire orchards may be due to quite different
causes.

Lithiasis. — Drought at or shortly before the riaaturing season of pears
has been noted often to cause increased grittiness of the flesh, the stony
aggregations around the core becoming larger. Sorauer^^^ describes an
aggravated form of this trouble under the name lithiasis. In this drought
disease sclerotic tissue develops near the surface of the fruit, particularly
on the sunny side. Ordinarily it is found only in cases of extreme
drought.

Summary. — Either an excess or a deficiency in soil moisture is likely
to be accompanied by a disturbed condition within the plant and often
by the appearance of some pathological symptom. Among those brought
on by excesses in the moisture supply are fruit splitting, fasciation, phyl-
lody, oedema, chlorosis, scaly bark and water core. High atmospheric
humidity is an important contributing factor in oedema; fruit splitting
is due to an irregular soil moisture supply as much as to an excess.
Measures against all of these troubles should be preventive rather than
remedial. They include provision for adequate drainage and caution
in the use of irrigation water. Premature defoliation and the attend-
ant ripening of the wood is one of the more serious results of a moisture
deficiency. It is likely to be followed by decreased vegetative growth,
lessened yields and in extreme cases, dieback. The earlier entrance
into the rest period and the poorer maturity of the wood both tend
toward susceptibility to winter injury. Dieback, rosette and little-
leaf are closely related disorders of the tree due in many cases to summer
drought. Often associated with these tree diseases, but sometimes more
or less independent of them, are a number of closely related diseases of the
fruit itself that have been described under the names: fruit-pit, cork,
drought spot, bitter-pit, Baldwin-spot, Jonathan-spot and black-end.
It is probable that some of these terms as commonly used refer to one and
the same trouble, or at least they overlap. This group of disorders,

96 FUNDAMENTALS OF FRUIT PRODUCTION

though directly due to (h'ought, frequently may be a result of too much
moisture, or a water table too high at some other season, resulting in a
restricted root system. Here again, protection lies more in preventive
than in remedial treatments.

Suggested Collateral Readings

1. Schimper, A. F. W. Plant Geography. (English Translation) Oxford, 1903.

(Particularly pp. 159-173, 81-85.)

2. Bowman, I. Forest Physiography. New York, 1914. (Chapter 3 on Water

Supply of Soils; Relation to Plant Growth and Distribution, pp. 41-54.)

3. Weaver, J. E. The Ecological Relations of Roots. Pub. 286 Carnegie Inst, of

Washington. 1919. (Particularly pp. 27-28, 100-108, 121-127.)

4. Hilgard, E. W., and Loughridge, R. H. Endurance of Drought in Soils of the

Arid Region. Rept. Cal. Agr. Exp. Sta. for 1897-8. Pp. 40-64.

5. Loughridge, R. H. Moisture in California Soils During the Dry Season of 1898.

Rept. Cal. Agr. Exp. Sta. for 1897-8. Pp. 6.5-96.

6. Mason, S. C. Drought Resistance of the Olive in the Southwestern States.

U. S. D. A., Bur. PI. Ind. Bui. 192, pp. 9-33. 1911.

7. Huntington, E., and others. The Climatic Factor as Illustrated in Arid America.

Pub. Carnegie Inst, of Washington, pp. 101-174. 1914.

8. Whitten, J. C. An Investigation in Transplanting. Mo. Agr. Exp. Sta. Res.

Bui. 33. 1919.

9. Bates, C. G. Windbreaks; Their Influence and Use. U. S. D. A., Forest Service

Bui. 86. 1911.

10. Gourley, J. H. Some Observations on the Growth of Apple Trees. N. H.

Agr.Exp. Sta. Tech. Bui. 12. 1917.

11. Green, W. J., and Ballou, F. H. Orchard Culture. Ohio Agr. Exp. Sta. Bui. 171.

1906.

12. Hedrick, U. P. A Comparison of Tillage and Sod Mulch in an Apple Orchard.

N. Y. Agr. Exp. Sta. Bui. 314. 1909.

13. Hedrick, U. P. Tillage and Sod Mulch in the Hitchings Orchard. N. Y. Agr.

Exp. Sta. Bui. 375. 1914.

14. Mix, A. J. Cork, Drouth Spot and Related Diseases of the Apple. N. Y. Agr.

Exp. Sta. Bui. 426. 1916.

15. Gladwin, F. E. A Non-parasitic Malady of the Vine. N. Y. Agr. Exp. Sta.

Bui. 499. 1918.

16. Briggs, L. J., and Shantz, H. L. The Water Requirement of Plants. A Review

of Literature. U. S. D. A., Bur. PI. Ind. Bui. 285. 1913.

Literature Cited

1. Agr. Jour. India. 13: 150. 1918.

2. Allen, R. W. Ore. Agr. Exp. Sta. Rept. of the Hood River Branch Exp. Sta.

Pp. 20-24. 1914-15.

3. Andre, G. Chimie agricole. 1:485. Paris, 1914.

4. Atkins, W. R. G. Some Recent Researches in Plant Physiology. P. 201.

London, 1916.

5. Atkinson, G. F. Cornell Univ. Agr. Exp. Sta. Bui. 53. 1893.

6. Babcock, S. M. Wise. Agr. Exp. Sta. Research Bui. 22. 1912.

7. Bailey, L. H. Mich. Agr. Exp. Sta. Bui. 31. 1887.

8. Ballantyne, A. B. Utah Agr. Exp. Sta. Bui. 143. 1916.

WATER RELATIONS 97

9. Barss, A. F. Bienn. Crop Pest and Hurt. Rept. Ore. Agr. Exp. Sta. 1 : 38-49.
1913-14.

10. Bars.s, H. P. Bienn. Crop Pest and Hort. Rept. Ore. Agr. Exp. Sta.

3: 159-166. 1921.

11. Batchelor, L. D. Utah Agr. Exp. Sta. Bui. 142. 1916.

12. Batchelor, L. D., and Reed, H. S. Cal. Agr. Exp. Sta. Circ. 216. 1919.

13. Bates, C. G. U. S. D. A., Forest Service Bui. 86. 1911.

14. Bedford, H. A. R., and Pickering, S. U. Science and Fruit Growing. P. 283.

London, 1919.

15. Bergman, H. F. Ann. Bot. 34: 13-33. 1920.

16. Boussingault, J. Agronomic. 6: 349. 1878.

17. Bouyoucos, G. J. Mich. Agr. Exp. Sta. Tech. Bui. 36. 1917.

18. Bowman, I. Forest Physiography. P. 42. New York, 1914.

19. Ibid. P. 66.

20. Briggs, L. J., and Shantz, H. L. U. S. D. A., Bur. PL Ind. Bui. 230. 1912.

21. Briggs, L. J., and Shantz, H. L. U. S. D. A., Bur. PL Ind. Bui. 285. 1913.

22. Briggs, L. J., and Shantz, H. L. Proc. Pan-Amer. Sci. Cong. 3:95-107.

1915-16. (Reviewed in Exp. Sta. Rec. 41:632. 1919.)

23. Briggs. L. J., Jensen, C. A., and McLane, J. W. U. S. D. A. Bui. 499. 1917.

24. Brooks, C. Torrey Bui. 35: 423-456. 1908.

25. Brooks, C, and Fisher, D. F. Jour. Agr. Research. 13: 109-137. 1918.

26. Brooks, C, Cooley, J. S., and Fisher, D. F. U. S. D. A., Farmers' Bui. 1160.

1920.

27. Brown, G. Jour. Ecology. 3: 30-31. 1915.

28. Burgerstein, A. Oester. bot. Zeitsch. 25: 6. 1875.

29. Burgerstein, A. Sitzungsb. d. Wien. Akad. 73: abt. 1 Riehe 2; 78. 1876.

30. Buttenshaw, W. R. Mo. Weather Rev. 32: 470. 1904.

31. Caldwell, J. S. Physiological Researches. 1. 1913.

32. Cannon, W. A. Carnegie Inst. Wash. Yearbook. 17: 83-85. 1919.

33. Card, F. W. Neb. Agr. Exp. Sta. Bui. 48. 1897.

34. Chandler, W. H. Mo. Agr. Exp. Sta. Research Bui. 14. 1914.

35. Coit, J. E., and Hodgson, R. W. Cal. Agr. Exp. Sta. Bui. 290. 1918.

36. Corbett, L. C. S. D. Agr. Exp. Sta. Bui. 44. 1895.

37. Coville, F. V. U. S. D. A., Bur. PL Ind. Bui. 193. 1910.

38. Craig, J. Cornell Univ. Agr. Exp. Sta. Bui. 198. 1902.

39. Cramer, P. J. S. Phillipine Agr. Rev. 3:94-100. 1910.

40. Darwin, F. Proc. Roy. Soc. B87: 281-299. 1914.

41. Delwiche, E. J., and Moore, J. G. Wis. Agr. Exp. Sta. Rept. P. 382. 1907.

42. Dixon, H. H. Transpiration and the Ascent of Sap in Plants. London, 1914.

43. Duggar, B. M. Plant Physiology. P. 87. New York, 1912.

44. Eberdt, O. Die Transpiration der Pflanze and ihre Abhangigkeit von aiisseren

Bedingungen. P. 88. Marburg, 1889.

45. Emerson, R. A. Neb. Agr. Exp. Sta. Bui. 79. 1903.

46. Ibid. Bui. 92. 1906.

47. Ewert, A. J. Proc. Roy. Soc. Victoria. 24 (N. S.): 367-419. 1911.

48. Ibid. 26 (N. S.): 2-44, 226-242. 1914.

49. Floyd, B. F. Fla. Agr. Exp. Sta. Bui. 140. 1917.

50. Gladwin, F. E. N. Y. Agr. Exp. Sta. Bui. 499. 1918.

51. Gloyer, W. O. N. Y. Agr. Exp. Sta. Bui. 485. 1921.

52. Gourley, J. H., and Shunk, V. D. N. H. Agr. Exp. Sta. Tech. Bui. 11. 1916.

53. Gourley, J. H. N. H. Agr. Exp. Sta. Tech. Bui. 12. 1917.

54. Green, W. J., and Ballou, F. H. Ohio Agr. Exp. Sta. Bui. 171. 1906.

98 FUNDAMENTALS OF FRUIT PRODUCTION

55. Haberlandt, G. Physiological Plant Anatomy. English translation. P. 219.

London, 1914.

56. Hartig, T. Allg. Forst u. Jagdzeit. N. F. 54. 1878.

57. Hartig, T. Bot. Centralblatt 36: 388-391. 1888

58. Hasselbring, H. Bot. Gaz. 57: 72-73. 1914.

59. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 314. 1909.

60. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 375. 1914.

61. Heinicke, A. J. Cornell Univ. Agr. Exp. Sta. Bui. 393. 1917.

62. Hellriegel, F. H. Beitrage zu den Natur wissenschaftlichen Grundlagen des
Ackerbaus. Pp. 662-664 Braunschweig, 1883.

63. Hilgard, E. W. Soils, 6th Edition. Pp. 168-171, 245. New York, 1914.

64. Ibid. P. 200.

65. Ibid. P. 263.

66. Hilgard, E. W., and Loughridge, R. H. Cal. Agr. Exp. Sta. Rept. Pp. 41, 56.

1897-8.

67. Hooker, H. D., Jr. Ann. of Bot. 29: 265-283. 1915.

68. Hooker, H. D., Jr. Mo. Agr. Exp. Sta. Research Bui. 40. 1920.

69. Hooker, H. D., Jr. Proc. Am. Soc. Hort. Sci. 17: 204-207. 1920.

70. Howard, A. Rept. Agr. Research Inst. Pusa. P. 43. 1913-14.

71. Howard, A., and Howard, G. L. C. Agr. Research Inst. Pusa. Buls. 52 and 61.

1915-16. (Abs. in Plant World. 20: 260-262. 1917.)

72. Huntington, E. The Climatic Factor as Illustrated in Arid America. Pp.

101-174. Carnegie Inst. Washington, 1914.

73. Jones, F. R. A Study of the Development and Extent of the Roots of Apple

Trees. 1912. Unpublished Thesis on file in the Library of the University of
Maine.

74. Jones, J. S., and Colver, C. W. Ida. Agr. Exp. Sta. Bui. 75. 1912.

75. Kearney, T. H. U. S. D. A., Bur. PI. Ind. Bui. 125. 1908.

76. Kelley, W. P., and Thomas, E. E. Cal. Agr. Exp. Sta. Bui. 318. 1920.

77. King, F. H. Physics of Agriculture. 2d Edition. P. 131. Madison, Wis.

1901.

78. Ibid. P. 189.

79. King, F. H. U. S. D. A., Bur. Soils Bui. 26. 1905.

80. Kohl, F. G. Die Transpiration der Pfanzen. Brunswick, 1886.

81. Korstian, C. F., Hartley, C, Watts, L. F., and Hahn, G. G. Jour. Agr.
Research. 21: 153-169. 1921.

82. Kosaroff, P. Einfluss verschiedenen ausseren Faktoren auf die Wasseraufnahme

der Pflanzen. Dissertation. Leipzig, 1897.

83. Leather, J. W. Cited by J. W. Patterson. Jour. Agr. Victoria. 10:353. 1912.

84. Lepeschkin, W. W. Beih. Botan. Centralbl. 19: 409-452. 1906.

85. Lewis, C. I., Kraus, E. J., and Rees, R. W. Ore. Agr. Exp. Sta. Bui. 113. 1912.

86. Loughridge, R. H. Cal. Agr. Exp. Sta. Rept. Pp. 61, 64, 66. 1897-98.

87. Ibid. Pp. 82, 94, 95, 96.

88. Lutman, B. F. Vt. Agr. Exp. Sta. Bui. 214. 1919.

89. Lyon, T. L., and Fippin, E. O. The Principles of Soil Management. 4th

Edition. New York, 1911.

90. Ibid. P. 192.

91. Mason, S. C. U. S. D. A., Bur. PI. Ind. Bui. 192. 1911.

92. Mason, S. C. U. S. D. A Bui. 271. 1915.

93. McCool, M. M., and Millar, C. E. Soil Sci. 9: 217-233. 1920.

94. McCue, C. A. Del. Agr. Exp. Sta. Bui. 120. 1918.

95. McLaughlin, W. W. U. S. D. A. Bui. 835. 1920.

WATER RELATIONS 99

96. McMurran, S. M. U. S. D. A. Bui. 756. 1919.

97. Mix, A. J. N. Y. Agr. Exp. Sta. Bui. 426. 1916.

98. Morse, W. J. Me. Agr. Exp. Sta. Bui. 271. 1918.

99. Nisbit, J. Studies in Forestry. P. 77. Oxford, 1894.

100. Palladin, W. Ber. Deutsch. Bot. Ges. 8: 364-371. 1890.

101. Palmer, A. H. U. S. D. A., Mo. Weather Rev. 48: 151-154. 1920.

102. Pearson, G. A. Jour. Forestry. 16: 677-683. 1918.

103. Pulling, H. E. Plant World. 21:223-233. 1918.

104. Rixford, G. P. U. S. D. A. Bui. 732. 1918.

105. Rosa, J. T. Jr. Proc. Am. See. Hort. Sci. 17: 207-210. 1920.

106. Rotmistrov, V. G. Nature of Drought According to the Evidence of the

Odessa Experiment Station, Russia. Eng. Edition. P. 20. Odessa, 1913.

107. Russell, T. Cited by S. B. Green. Minn. Agr. Exp. Sta. Bui. 32. 1893.

108. Schnee, F. tJber den Lebenszustand allseitig verkorkter Zellen. Dissertation.

Leipzig, 1907.

109. Schwartz, F. Unters. a. d. Bot. Inst, zu Tubingen. 1:140. 1883.

110. Shear, C. L. U. S. D. A., Farmers' Bui. 1081. 1920.

111. Smith, J. W. U. S. D. A., Mo. Weather Rev. 48: 446. 1920.

112. Sorauer, P. Pflanzenkrankeiten. 3te Auflage. 1:169-170. Berlin, 1909.

113. Ibid. P. 210.

114. Ibid. P. 275, 284-285.

115. Ibid. P. 286.

116. Ibid. P. 324.

117. Ibid. P. 332.

118. Ibid. P. 335.

119. Ibid. P. 422.

120. Ibid. P. 435.

121. Spoehr, H. A. Carnegie Inst. Wash. Publ. 287. 1919

122. Stewart, J. P. Pa. Agr. Exp. Sta. Bui. 134. 1915.

123. Stewart, J. P. Pa. Agr. Exp. Sta. Bui. 141. 1916.

124. Taylor, E. P., and Downing, G. J. Ida. Agr. Exp. Sta. Bui. 99. 1917.

125. Thompson, R. C. Ark. Agr. Exp. Sta. Bui. 123. 1916.

126. Tucker, M., and von Seelhorst, C. Journ. f. Landw. 46: 52-63. 1898.

127. Tufts, W. P. Letter to one of the authors, dated March 21, 1921.

128. U. S. D. A., Div. Agr. Soils Buls. 1, 2 and 3. 1895.

129. Van Slyke, L. L., Taylor, O. M., and Andrews, W. H. Geneva Agr. Exp. Sta.

Bui. 265. 1905.

130. Von Seelhorst, C. Journ. f. Landw. 58: 83-88. 1910.

131. Weaver, J. E. Cam. Inst. Wash. Publ. 286. 1919.

132. White, J. Proc. Roy. Soc. Victoria. 24 (N. S.): 2-16. 1911.

133. Whitehouse, W. E. Ore. Agr. Exp. Sta. Bui. 134. 1916.

134. Whitten, J. C. Mo. Agr. Exp. Sta. Bui. 49. 1900.

135. Whitten, J. C. Mo. Agr. Exp. Sta. Research Bui. 33. 1919.

136. Widtsoe, J. A. Dry Farming. P. 185. New York, 1911.

137. Wiggins, P. G. Am. Jour. Bot. 8: 30-40. 1921.

138. Woodbury, C. G., Noyes, H. A., and Oskamp, J. Purdue Univ. Agr. Exp.

Sta. Bui. 205. 1917.

139. Zon, R. Proc. Soc. Amer. Foresters. 2: 79. 1907.

SECTION II
NUTRITION

Nutrient supply is generally considered the most important of the
factors limiting growth and productiveness. Certainly it ranks second
to no other in determining the success or failure of the orchard enter-
prise within those sections or areas where climatic conditions make
possible a fruit industry and where economic conditions make practicable
its development. Though there are many single cases in which the
water supply, the prevalence of pests or some other factor assumes
paramount importance, the most common limiting influence is associated
with nutritive conditions. Much of the effort of the careful grower is
directed toward relieving his plants from unnecessary competition and
struggle for a nutrient supply.

Few general questions pertaining to fruit growing have been less
thoroughly understood than soil productivity as it relates to tree growth.
This condition has existed mainly because of the assumption by analogy
that the requirements of trees, vines or other fruit producing plants are
practically identical with those of annual crops and because until very
recently experimental evidence upon which to base reliable interpre-
tations and Conclusions has been lacking. Trees, shrubs and vines have
life histories, even seasonal life histories, quite different from those of
annuals. It is to be expected, therefore, that they possess quite different
nutrient requirements or at least, quite different feeding habits. These
nutrient requirements and feeding habits must be studied thoroughly
before there can be a proper appreciation of the orchard soil productivity
problem.

100

CHAPTER VII

PLANT NUTRIENTS AND THEIR ABSORPTION

Plants require for their nutriment water, carbon dioxide, oxygen,
nitrates (or other nitrogen carrying compounds), sulphates, phosphates,
salts of iron, magnesium, potassium and calcium. Though chemical
analysis of plant tissue shows that almost every clement may be found
in one plant or another, carbon, hydrogen, oxygen, nitrogen, phosphorus,
sulphur, potassium, magnesium, iron, calcium, chlorine, silicon, sodium,
aluminum and manganese are found in practically all plants. The
first ten of these are necessaiy for all the higher plants. Water, nitrogen
and all the mineral elements are absorbed by the roots from the soil.
Absorption by the leaves also occurs under certain circumstances but
ordinarily this process may be disregarded. The water relations of
plants have been treated in the previous section; the other plant nutrients
absorbed from the soil form the subject of this chapter.

DISTRIBUTION OF ELEMENTS FOUND IN ASH

The mineral constituents of plants, except a part of the sulfur, are
left as ash after the tissue has been burned. Some conception of the
amount and composition of plant ash may be derived from the analyses
of the wood, bark and leaves of the beech in Table 1.

Table 1. — Ash Analyses of Wood, Bark and Leaves of Beech"*

Ash K2O

CaO

MgO

FeaOs

P2O5

SO3

Si02

Wood

Bark

Leaves

0.355
5_J60
5.140

14.4

5.1

21.8

69.2
88.4
44.3

4.5
3.6

7.2

2.3
0.7
2.3

2.7
2.1

7.8

3.5
1.0

2.4

10.0
3.7
10.5

In Tissues of Different Kinds. — The data in Table 2 on the amount
and composition of the ash of apple trees, give an idea of the variations
that maj^ occur in the composition of different parts. The distribution
of ash in the apple tree at the time of leaf fall is shown in Table 3. The
ash percentage of bark is always many times that of the wood as Table 4
shows. The ash content of seeds varies from 2 to 6 per cent. Thus,
seeds of the chestnut contain 2.38 per cent, of ash, almonds 4.9 per cent,
and coffee 3.19 per cent.^ The composition of such ash appears from
data presented in Table 5.

101

102

FUNDAMENTALS OF FRUIT PRODUCTION
Table 2. — Ash Analyses of Apple Varieties^*"

Ash in
percent-
ages of
dry weight

Si02 P2O6 SO3 CaO MgO NaaO K2O

(In percentages of ash)

Branches :

Haas

Golden Sweet
Hurlburt

Trunks:

Haas

Golden Sweet
Hurlburt

Roots :

Haas

Golden Sweet
Hurlburt

3.93
3.04
4.92

2.04
2.29

2.89

5.64
3.53
4.34

1.81

7.35

3.02

43.68

10.02

2.51

2.49

5.89

2.96

40.60

8.07

7.09

2.60

4.44

3.57

41.55

2.88

4.98

2.04

2.13

7.55

44.52

9.30

1.33

4.98

4.61

1.17

41.96

4.61

3.91

3.93

4.08

3.85

44.80

5.22

2.48

26.84

9.44

5.11

32.98

9.30

4.74

27.65

7.71

2.83

26.99

4.84

3.87

25.72

4.17

6.19

25.20

10 . 37

7.22

8.59
3.37
5.16

6.96
8.02
1.31

5.43
2.00
9.86

Table 3. — Ash Analyses of a 7-year Old Apple Tree at the Time of Leaf-fall^^
(In percentages of dry weight)

Summer growth 3 . 57

1-year old branches 2 . 83

2-year old branches 2 . 76

3-year old branches 2 . 75

4-year old branches 1 . 87

5-year old branches 1 . 78

Trunk 1.33

Large roots = . . . . 1 . 83

Small roots 4.51

Table 4. — Ash Content of Wood and Bark®
(In percentages of dry weight)

Wood

Mahaleb cherry
Sweet cherry . . .
Horse chestnut .

1.38
0.23

2.58

Table 5. — Ash Analyses of Seeds^"

K2O

CaO

MgO

P2O5

SO3

Chestnut

56.6
26.5

3.8

8.4

7.4
16.1

18.1
34.8

3.8

Plum !

7.1

PLANT NUTRIENTS AND THEIR ABSORPTION

103

In Tissues of Different Age. — Age is likewise an important factor
influencing ash content. The percentage of ash increases with age in
the leaves and wood, but diminishes in the roots, branches and fruit.
Though in these last it increases in absolute amount, the proportion falls
off since organic matter increases at a greater rate. Table 6 shows the
increase in ash content of beech wood with age.

Table 6. — Ash Content of Beech Wood^os
(In percentages of dry weight)

Years of Rings
1 to 15
15 to 25
25 to 35
35 to 45
45 to 60
60 to 83
83 to 94 (sap-wood)

1.162
0.825
0.645
0.612
0.555
0.458
0.205

At Different Seasons. — An increase in the percentage ash content
of apple, pear, cherry and plum leaves during the season is shown in
Table 7. The absolute amount of ash present declines, however, before
the leaves fall (Table 8). Developing fruits, on the other hand, show a

Table 7. — Ash Content of Leaves^^^ (in percentages of dry weight)

Apple

Pear

Cherry

Plum

May 9

8.304

8.017
9.166

10.889

6.908

7.157
9.454

9.552

9.006

10.510
12.319

14.446

May 14

May 18

June 22 .

7.369
15.031

Aug. 29

Sept. 30

Oct. 2

17.757
20 . 987

Oct. 15

Table

8.— C

RAMS OF Ash

IN 100 Leaves'*'^

Apple Pear

Cherry

Phun

Ash

Fresh
weight

Ash

Fresh
weight

Ash

Fresh
weight

Ash

Fresh
weight

Julv 14

2.876
3.016
3.576
3.214

95.15
89.60
95.10
91.81

1.270
1.469
1.548
1.638

47.19
46.73
42.98
42.93

2.494
2.568
2.814
2.920
3 214

76.48
64.73
65.83
64.98
74 61

3.038
2.721
2.693

2.822

3.076

70 07

Julv 31

59.73

Aug. 18, 21

49.67

Sept. 3, 4, 6

50.20

Oct. 7

Oct. 23, 27, 29

1.311

36.22

2.215 52.97

55 85

Nov. 4

2.541

66.46

104

FUNDAMENTALS OF FRUIT PRODUCTION

decrease in the percentage of ash and an increase in the absolute amount.
The data in Table 9 illustrate these changes. The large increase in the

Table 9. — Ash Content of Fruit'^''

Pear

Apple

Date

Percent-
age of dry
weight

Absolute

amount,

grams

Date

Percent- Absolute

age of dry amount,

weight grams

May 26

7.96
5.50
4.32
2.87
3.27
2.73
. 2.27
1.76
1.46
1.56
0.91
,,3I

.0.0017
0.0068
0.0198
0.0269
0.043
0.057
0.069
0.068
0.079
0.098
0.065
0.090

June 2

8.88

0.0019

June 12

5.09
3.44
2.89
1.80
1.33
1.78
1.43
1.33
1.07
0.80
1.67
1.58

0.0066

June 15

June 22

0.011

June 25

July 2

July 12

July 22

Aug. 1

0.026

July 5

0.034

July 15

0.044

July 25

0.070

Aug. 11

Aug. 21

Aug. 31

Sept. 10

Sept. 20

Sept. 30

0.075

Aug. 14

0.076

Aug 24

0.079

Sept 3

0.066

Sept 8

0.160

0.150

ash content of the fruit affects the ash content of the spur on which the
fruit is borne. Figure 10 shows a rapid decrease in the percentage ash

Fig. 10. — Ash content of apple spurs in percentages of dry weight; bearing spurs
represented by continuous lines marked W, B and / for Wealthy, Ben Davis and Jonathan
respectively; non-bearing spurs shown by broken lines marked J and B; barren spurs
represented by dot-dash lines marked B and A'' for Ben Davis and Nixonite. {After
Hooker.^oo)

content of bearing spurs beginning the latter part of May or in June
and continuing until the fruit is picked. i"" In a summer apple Hke
Wealthy, the curve rises in September, the fruit having been picked in

PLANT NUTRIENTS AND THEIR ABSORPTION 105

August. In Ben Davis and Jonathan, the fruit of which is picked the
beginning of October, the curve does not rise until November. Spurs
in the off year and barren spurs have no such characteristic decrease
in ash content during June.

ABSORPTION

Mineral constituents and nitrogen are absorbed by the plant mostly
through the roots. They are present in the soil as salts in solution and
are taken up in large part by osmosis along with the soil water, the
osmotic system being the same as that involved in water absorption.

The Osmotic System. — The soil solution and the cell sap are sepa-
rated by a semi-permeable membrane, through which the salts present in
the soil solution are able to enter though the organic substances within the
cell are, for the most part, incapable of passing in the opposite direction.
Inorganic salts dissociate to a considerable degree, so that in a solution of
sodium chloride, for example, there are present, besides molecules of
salt, ions of sodium and ions of chlorine. These separate ions have the
same value in regard to osmotic concentration as entire molecules;
consequently a solution of inorganic salts is capable of producing a higher
osmotic pressure than a solution of organic compounds having the same
number of molecules in a given volume. In order that absorption of the
various mineral constituents should take place by osmosis, the concentra-
tion of each salt within the plant must be less than its concentration in
the soil solution. Though, as previous analyses have shown, plant
tissue contains considerable amounts of these mineral elements the plant
is still able to absorb material from an exceedingly dilute soil solution
which, in many cases, contains a lower percentage of a given constituent
than the plant tissue itself. This is possible because the constituents in
the plant are insoluble or are combined in an organic form. Since in
either case they are removed from the osmotic system, the effective con-
centration of inorganic salts within the plant remains less than that of
the soil solution. It is evident, though, that a certain concentration of
salts in the soil is necessary for osmotic absorption. In other words, the
plant is unable to avail itself of all the mineral matter of the soil solution.
However, very dilute solutions are often sufficient for ordinary growth.

Thus "Birner and Lucanus many years ago found that mature crops of good
yield could be grown in a well water containing about 18 parts potassium (K)
and about 2 parts phosphoric acid (PO4) per million of solution and very satis-
factory'' growth of wheat has been obtained in the water from the Potomac
River, which contained about 7 parts per million of potassium. "^^

When these facts are combined with the conclusions reached by
Cameron and Bell,^* that the concentration of the soil solution, with
respect to the principal mineral plant nutrients, is sufficient for the growth

106 FUNDAMENTALS OF FRUIT PRODUCTION

and development of crops and that the magnitude of the concentration
is the same for practically all soils, one might easily be led to the belief
that fruit plants seldom suffer from lack of an adequate supply of mineral
nutrients. However, this inference is hardly warranted for, as is shown
later, mineral nutrients may be in solution and still be unavailable to the
plant. In other words solubility and availability are not synonymous.

Furthermore, it may be noted that the 5 parts of water soluble nitrates
per million of dry soil found by Gom-ley and Shunk^^ in sod-mulched orch-
ards during the growing season were apparently insufficient for satisfactory
wood growth and fruit production, while a concentration of 15 to 40 parts
per million under certain other systems of culture proved entirely ade-
quate. In this case all the nitrogen measured was in an available form.
Whether in the sodded area nitrogen could be absorbed by the trees only
when the concentration in the soil reached a certain minimum, or whether
a very limited amount was absorbed even at the lowest concentrations,
cannot be stated from available data; they show clearly, however, that
the trees were unable to remove nitrates completely from the soil and
further, that a nutrient solution very dilute in respect to this element
provides only for very slow growth.

Displacement. — The amounts of the various inorganic constituents
in the soil are subject to variation and exchanges of bases may occur when
they are present as silicates. Potassium, ammonium, magnesium,
sodium and calcium form a series in which each member is capable of
displacing any member following it in the series. One of two things
may happen: an essential element may be lost to the plant by becoming
soluble and being washed out of the soil, or it may be changed from an
unavailable to an available compound and so placed at the disposal of
the plant.

Of most common occurrence is the displacement of calcium by
potassium or sodium, resulting in the calcium salts going into solution.
However, large amounts of calcium are capable of displacing small
amounts of potassium ^''^ or any other base standing ahead of it in the
series. Hence, calcareous soils are likely to be deficient in potash
and the application of calcium in great amounts tends to deplete the
potassium supply. Grape-fruit seedlings have been observed to show
injuries characterized by yellowing of the foliage due apparently to
the presence of ground limestone; more injury was evident in sandy
soils than in loams. ^® One type of this yellowing is "frenching," a
lack of green color in the areas between the largest veins, which is shown
later to be a characteristic symptom of potassium starvation. "French-
ing" was produced also by sulphate of ammonia or organic fertilizers
containing ammonia. This effect may be attributed to displacement
of potassium in the soil by relatively large amounts of ammonia.

The effects on the plant of displacement of bases may be indirect

PLANT NUTRIENTS AND THEIR ABSORPTION 107

rather than direct, for the displacement elements may combine to form
more soluble salts and thus be rendered more available.

As an instance, according to Loew:^-* "Lime and gypsum can also in cer-
tain cases release such potash in the soil as is still unavailable. This, as well as
the enhanced root-hair production under the influence of the increased amount
of ume, accounts for the greater absorption of potash by the plant on soils rich
in lime."

Displacement would of course be of little value to the plant if the
elements released were washed from the soil as a result of the greater
solubility of their salts.

Availability of Ash Constituents. — The soil constituents are of use
to the plant only when combined in certain specific chemical compounds.
Thus, sulphur must be present as sulphate, phosphorus as phosphate, and
the various bases as relatively soluble salts.

Availability and Solubility Distinguished. — Solubility, however, is
only the first prerequisite to availability and absorption; it is not an
absolute criterion of the crop-producing power of soils, as is indicated by
studios on many soils in this country^^ and by investigations on the red
soils of the "djati" forests of Java.^^ Nevertheless, "in general it can
be said that a very heavily fertilized or extremely rich soil gives a greater
solubility product than an unfertilized or poor soil."^^ Conversely
"as a result of laboratory studies it appears that the constituents of
soils which have been cropped for a long period of years go into solution
at a somewhat slower rate than do those of the corresponding virgin
soils. "^^'^

Factors Influencing Solubility. — The solubility of soil ingredients is
affected by such factors as temperature, moisture content, chemical
composition of the soil and root activity. According to McCool and
Millari3o the rate of solution is more rapid at 25°C. than at 0°C. The
concentration of the soil solution apparently depends also on the
relative masses of the soil and water.

"At the ratio of 1 of soil to 5 of water the rate of solubility of natural soils
is also slow and the extent of solubility extremely small. In fact, the amount of
material that went into solution at this water content is only about half as much
as that at the water content of 1 of soil to .7 of water, and yet an apparent
equilibrium was attained. . . . The amount of material that goes into solution
seems to increase as the ratio of soil to water is increased up to about the opti-
mum moisture content and then it decreases."^*

The effect of chemical composition on solubility is discussed by
Bouyoucos.^^

"As a whole it appears that the phosphates tend to depress solubihty and that
they probably act as conservers of bases under field conditions." Other salts,

108

FUNDAMENTALS OF FRUIT PRODUCTION

however, tend to increase solubility. "The result of solubility of these singly
salt treated soils goes to indicate that a salt or fertilizer treatment leaves a resid-
ual effect upon the soil and this residual effect continues to be manifested in in-
creased solubility and in increased crop-producing power."

Availability of Phosphorus. — It has been stated that phosphorus
is available to the plant only when present as a phosphate and that sul-
phur is absorbed only as sulphate. However, all phosphates and sulphates
are not equally available; furthermore, a phosphate that is highly avail-
able for the plants of one species may be much less available to those of
another. This principle is well illustrated by the data presented in
Table 10 showing the percentage of normal growth made by plants grown
in nutrient solutions that were uniform except for the form in which
phosphorus was presented.

Table 10. — Comparative Growth of Various Plants with Different
Phosphates
(After Truog^^^)
(Growth on acid phosphate represented by 100)

Kind of
plant

Kind of phosphate

Blank

Alumi-
num

Tri-
calcium

Ferric

Ferrous

Rock

Mag-
nesium

Man-
ganese

Oats

Buckwheat. .

Rape

Corn

Barley

Alfalfa

Clover

Millet

Serradella. . .

6.8
3.6
0.8
8.6
16.7
1.5
1.0
0.7
0.6

96.4

88.0

96.4

56.3

104.7

78.6
84.2
86.7

78.7

70.5
70.1
76.2
26.8
62.2
99.2
64.5
34.8
90.4

79.9
32.5
23.4
40.3
133.5
93.6
68.9
103.8
111.7

82.9
63.3
61.5
19.3
79.7
28.1
23.6
31.0
28.2

9.1

70.0

46.8

10.0

25.8

38.3

6.1

4.1

3.2

21.3
15.5
7.1
26.7
16.0
49,9

76.4
125.3
20.8
4.2
73.8
51.7

In commenting on these data Truog'*^ remarks: "The great differences
exhibited by the various plants in their growths on the different phosphates
indicate tliat plant characteristics play an important role in this connection.
The fact that rape made a better growth on rock phosphate than on ferric
phosphate, while in the case of oats the opposite was true, indicates that solu-
biUty alone is not the only factor involved in the utilization of these phosphates
by plants. The remarkably vigorous growth of the barley with ferric phos-
phate is another indication that aside from solubility or availabiUty, some
phosphates seem to serve the needs of certain plants better than others. The
remarkable adaptability of certain soils to certain crops may partly be due to
causes of this nature."

Availability Varies According to Kind of Plant. — In general the avail-
ability of inorganic soil constituents is increased by the activity of the

PLANT NUTRIENTS AND THEIR ABSORPTION 109

roots. Their solvent action is yet to be accounted for satisfactorily.
Crocker suggests that the strong, insoluble pectic acids found in the
walls of root hairs may be responsible for the absorption of bases and
the setting free of mineral acids, which would have a localized and
temporary solvent action on the soil. Various plants show great differ-
ences in the dissolving power of their roots, or at least in their ability to
obtain required nutrients.

Hartwell*^ found that carrots secured all the phosphorus they required from
a soil in which rutabagas and cabbage were practically unable to grow, while
wheat, oats, white beans and soy beans ranged between these extremes. Simi-
larly, he found "an ability of the soy bean to obtain from the deficient [in avail-
able potassium] plots about two-thirds of their maximum requirements, whereas
carrots obtained about half their needs, mangels about one-fourth and summer
squash only about one-tenth."

It is not clear to what extent this characteristic feeding power of
various plants may be due to varying ability to dissolve the materials
they encounter in a solid or colloidal form, what part may be due to
varying ability to use nutrients combined in different forms (e.g., potas-
sium in the form of a chloride instead of sulphate), or what part may be
due to varying ability to absorb from very dilute solutions. This
question needs careful investigation, particularly in its application to
orchard and vineyard fruits of different kinds and to the stocks upon
which they may be grown. It is conceivable that the high feeding power
of a certain stock in respect to some particular material may be of as
great significance in the success of a fruit plantation in a certain soil
as the question of "congeniality" of stock and cion. From the data
presented by Hartwell, the inference may .be drawn that the potassium
found in the soil and practically unavailable to mangels and summer
squash would be made available to them were soy beans first grown
upon the land and then plowed under, for, after the soy beans had
dissolved and used it, other plants wovild find it in a different form.
There may be little occasion for special efforts to make potash more
available to orchard trees by using intcrcultures, for evidence is presented
later that for fruit trees potash is seldom a limiting factor. Nevertheless,
the general principle involved may be important in relation to other
elements.

Availability of Iron and Sulphur. — Certain types of bacteria oxidize sulphur or
hydrogen sulphide to sulphates and others, ferrous oxide to ferric oxide. These
organisms may play some part in rendering sulphur and iron available, though
the most important type of bacterial action in the soil is concerned with general
decomposition and particularly with the nitrogen supply.

Availability of Nitrogen. — Just as sulphur is available only in the form
of sulphate and phosphorus in the form of phosphate, most nitrogen is

no FUNDAMENTALS OF FRUIT PRODUCTION

absorbed in the form of nitrate. However, nitrites and salts of ammonia
can be utilized to a limited extent, different plants showing considerable
variations in this respect. Organic nitrogen also may be a substitute for
nitrate, though inorganic nitrogen compounds are used in preference.
It has been shown that such nitrogenous soil constituents as nucleic
acid, hypoxanthine, xanthine, guanine, creatinine, creatine, histidine,
arginine and choline serve as sources of nitrogen when nitrates are absent,
but not to any great extent when large amounts of nitrate are pres-
gjj^ 163, 169. Moreover, the absorption of nitrate by plants grown in
culture is always reduced when creatine or creatinine is present, though
the total nitrogen intake remains fairly constant. These organic nitrogen
compounds have no effect on potash or phosphorus absorption.

Bacteria are of great importance in making organic nitrogen com-
pounds in the soil more available to the plant and incidentally in destroy-
ing toxic substances. Putrefying bacteria, for example, convert the
nitrogen of organic compounds to ammonia and nitrogen gas.

Hart and Tottingham*^ have shown that "soluble phosphates increase
enormously the number of soil organisms and the rate of ammonification and
destruction of organic matter, while the sulphates activate but slightly in these
directions. The processes mentioned are admitted to be of great importance
to the plant's nutrition and environment, involving, as they must, not only a
more rapid formation of readily soluble compounds of nitrogen and a possible
destruction of harmful organic materials, but a greater saturation of the soil
moisture with carbon dioxide, resulting in increased solution of mineral materials
necessary for rapid growth." Work at the Utah Experiment Station^^ indicates
that sulphates have a particularly stimulating effect on soil bacteria under certain
conditions.

Nitrification. — The ammonia produced by bacterial action is in its turn
converted to nitrites and these nitrites to nitrates by nitrifying bacteria,
each of these changes being carried out by distinct organisms. These
organisms require, for the process of nitrification, good aeration, involving
both oxygen and carbon dioxide, a certain water supply, the presence of
calcium or magnesium compounds, a medium temperature and freedom
from an excess of soluble organic compounds or from free ammonia. It
is evident that conditions favoring the action of nitrifying organisms will
tend to increase the supply of available nitrogen.

Aided by Liming.— It has been found that applications of lime in many
cases increase nitrification. Table 11 presents the results of one such
experiment with orchard soils in New Hampshire. Obviously in this
instance liming benefited the soil in at least this one direction and it is
possible that at the same time it exerted no harmful influence. However,
data are presented later to show that it may have a very harmful effect
through rendering iron unavailable. Consequently a single fertilizer
application may produce at the same time both beneficial and harmful

PLANT NUTRIENTS AND THEIR ABSORPTION

111

Table 11.— Nitrates in Limed and Unlimed Plots »i

(In parts per million of dry soil)

Limed plot

Unlimed plot

Year

Surface soil

Subsoil

Surface soil

Subsoil

1913

82.33

19.60

57.46

6.16

1914

82.46

23.43

57.09

15.21

1915

29.98

13.78

24.26

17.24

1916

98.48

24.16

80.36

11.56

Average

73.31

20.23

54.79

12.54

effects. These may just about neutralize each other and leave the plants
practically uninfluenced by the treatment, or the one influence may
greatly outweigh the other. Caution should be exercised, however, in
making applications of lime to the orchard.

Influenced by Methods of Soil Management. — Moreover different
methods of soil management, particularly as they effect aeration and soil
temperature have a marked effect on nitrate production.

Gourley and Shunk*' found that "the ratio of nitrates between sod, tillage
and tillage with cover crops is as 1 : 5.4 : 10.6 in the surface soil and in the sub-
soil as 1 : 3.3 : 3.7. At no time during the experiment have we obtained a
sample under sod that showed more than 14.78 parts nitrates per million and the
average for the 4 years is 3.18 p. p.m. with an average of 17.40 p. p.m. and for
tillage plus a leguminous cover crop it has shown as high as 132 p.p.m. and the
average is 33.91 p.p.m. for the 4 years."

The nitrate determinations showing the result of 4 years' experiments
on orchard soils are summarized in Table 12, Whether the small
amount of nitrate under sod is the result of reduced nitrate produc-
tion or merely the residue from a greater nitrate consumption by the
plants constituting the sod, the effect on the orchard trees is the same.
Under sod there is but little available nitrate. In Indiana also, it was
found that in a young orchard most nitrates are formed under the clean
culture-cover crop system of soil management, and the straw mulch
ranked next.-"*^ The heavier the mulch, the later in the spring does
bacterial activity begin because of the lower temperature and the later
in the fall does it persist as a result of the higher temperature of
the soil.

It is probably because of their influence upon nitrate formation that
various tillage methods have so generafly proved superior to sod manage-
ment methods in promoting both vegetative growth and fruit production.
This is true particularly in areas that are more humid or have deeper
soils. On the other hand, in sections having a long dry period during

112

FlXDAMEXTAl.S OF FRVIT rRODlCTIO.X

TaBI.K V2. WaTKK Soi.lBl.E XlTKATE IN PaHTS TEK Mll.LlON OK DuY SoIL"

i,.\voi;igo por \i\oO

Year

Sod

Surfaoo soil

Tillage

I'illago with oovor
crop

1913
1914
1915
1916

Averngo

4 41
2 00
o 59

3. IS

IS. 25
14.01
21.05
16.29

17.40

oS . o<
37 27
IS 75
41.20

33.01

Subsoil

1913

1 . 55

6.90

0 S7

1914

3 56

6.62

10. SI

1915

1.51

10.76

6.SS

1916

2. IS

5.05

S 05

Averasro

2 20

7.33

S 15

iho sunmior. wherever the soils are of sueh nature that they encourage
shallow rooting the iuHuenee of these various systems of soil management
iipcMi moisture supply is probably a factor of equal or greater unportance.
However, it is neither difficult nor expensive to furnish trees growing in
sod with an adequate supply of nitrates through the use of certain fertil-
izers. Indeed, it is in orchards of this kind that nitrogenous fertilizers
have given some of the most striking results and the question maj- be
raised whether some nitrogen-carrying fertilizer may not be a more or
less constant requirement if orchards permanently under this method of
soil management are to be kept growing and producing most efficiently.

Influt'wecl by Temperature and Soil Moisture. — The effects of moisture
and of temperature on the activity of nitrifying bacteria are shown by a
seasonal variation in nitrate content. For example, in Illinois soils -^''
the most active season of nitrate production and accumulation is late
spring and early summer when optimum moisture and temperature
conditions are approached. Early autumn is the next most active
season, when these optimum conditions for nitrate production are fre-
quently approached. During the summer little nitrate is produced
unless the weather is cool and moisture plentiful; in winter there is no
evidence of nitrate production.

Similar conditions are i-eported for orchard soils in Indiana^^ where
very little nitrate was found in late fall and winter, though maxima were
found in early summer and early fall. Orcharding, however, is carried

PLANT NUTItlKNTS AND TIIEIli AHSOIil'T ION 1]:^

on in inany scMrtioiis where seasonal and soil conditions an; iriat(!i'ially
dilferent from thoso of Illinois and Indiana antl it is concoivabh; lliat
under Certain environinontal conditions nitrate production, evcni under
sod, inif2;ht keep pace; wilh the tn^e's requirements for nitrog(!n.

Losses of Nitrogen from the Soil. — Nitrates are very soluble in
\vat(M- ajid unlike most of the mineral nutrients, are not adsorbed or
otherwise; fixed in the soil to any considerable degree. Heavy rains or
heavy irrigation washes them out and carries them away in the drainage
water. In one Florida experiment this loss from leaching was found to
('(pial the nitrate content of over 800 pounds of nitrate of soda per acre
during a 10-month period/ Not the least important function of cover
crops is to take up the nitrates that are being formed in late summer and
autumn, to store their nitrogen in organic form during the winter and to
return it to the soil — thence to the trees — the following growing season,
thus preventing a large loss through drainage. The advantage of a
soil, and of orchard management methods, permitting deep rooting and the
storage of large quantities of capillary water minimizing seepage losses,
is evident.

Maintaining the Nitrogen Supply of the Soil. — Despite the means
that may be taken to prevent undue loss of soil nitrates, crop production
alone removes considerable quantities and unless the supply of nitro-
genous coinpounds from which they arc derived is maintained the time
will come when they cannot be formed in quantities sufficient for maxi-
mum crop production. The organic matter of the soil is the storehouse
of these nitrogenous compounds and with its gradual depletion the
nitrogen problem becomes acute. It is well known that constant tillage
is one of the most effective means of reducing or "burning out" humus
supply. Consequently the cultural methods in the orchard that make
nitrogen available most rapidly, deplete the total supply most rapidly.
Indeed it may be questioned if, over a long period, the orchard under a
strictly clean-culture method of management will not need heavier
nitrogen fertilization than the one in sod.

Some measure of the cumulative effect of tillage as compared with a sod
covering on total nitrogen supply is contained in the following statement:
"Analysis of soil taken from this land at the time the experimental work was
started indicated a nitrogen content of 5,000 pounds per acre. After this soil
had been cropped and cultivated for 20 years, the nitrogen content was approxi-
mately 4,000 pounds per acre. Adjacent soil which was in grass during the 20-
year period contained 5,600 pounds of nitrogen."^ It is significant that, though
there was a loss of 20 per cent, of the total nitrogen supply of the soil during the 20
years in the cultivated land, there was an actual increase of 12 per cent, in the
sod land during the same period. This can be attributed to nitrogen fixation,
particularly by leguminous plants in the sod, in addition to the nitric acid
contributed by rain water.

8

114 FUNDAMENTALS OF FRUIT PRODUCTION

The likelihood of trees under one of the two standard systems of
orchard culture suffering from lack of available nitrogen and, on the other
hand, the nearly absolute certainty that under the other system the
soil will have its total nitrogen I'eserve seriously depleted, suggest
that a combination of the two methods possibly might afford a means of
maintaining permanently the nitrogen supply of the soil and at the same
time obviate the necessity of supplying the trees artificially with readily
available nitrates. Such a combination might consist in alternating
sod and cultivation each in 2-year periods or, better still, in maintaining
alternate tree rows, the "middles," under the two respective systems
and then occasionally reversing the treatments on these alternate strips.
The marked success that frequently has attended such a combination is
evidence of its practicability under many conditions. Such a combina-
tion treatment is a compromise also in its influence upon soil moisture
supply and soil erosion. In some instances it might prove undesirable
because of the increased difficulty in controlling certain orchard pests
which are best held in check by cultivation.

Few, if any, of the plant nutrients obtained from the soil are subject
to such great variation from season to season and even from week to
week as is nitrogen; likewise few are so completely under the control of
the grower through methods of soil management. It is largely because of
the first two facts that the problem of maintaining fertility in the orchard
generally centers around the nitrogen supply. The discussion that has
preceded serves also to bring out clearly the fact that proper treatment
of the soil may reduce or altogether remove the necessity for nitrogen
fertilization and that, on the other hand, there are instances where it may
be true economy not to employ those practices that will lead to greatest
nitrate formation but deliberately to limit this process and supply the
deficiency by artificial means.

Nitrogen Fixation. — Nitrogen gas is not available to the higher plants,
but it is acted upon by nitrogen-fixing bacteria which convert it either
to nitrates or to other nitrogenous compounds that in due time are con-
verted into nitrates. Some of these bacteria are able, independent of any
association with the roots of higher plants, to fix this atmospheric nitro-
gen and thus effect the first step in rendering it available. ^^' ^^ Indeed
there are conditions under which their activity is so great that the resul-
tant accumulation of nitrates renders the soil toxic to trees and other
plants.^' For the most part, however, nitrogen fixation by bacteria
is effected by forms living in colonies on the roots of leguminous plants
where they produce nodules or tubercles.

As very few of the species bearing edible fruits belong to the legume
family, nitrogen-fixing bacteria are of comparatively little direct benefit
except when they fix nitrogen in the absence of host plants. However,
they become of great value indirectly when leguminous cover crops or

PLANT NUTRIENTS AND THEIR ABSORPTION 115

a sod including legumes is maintained. There are conditions under
which it is difficult or impracticable to grow legumes in the orchard;
nevertheless their special value should not be overlooked, particularly
where there is need of increasing the available nitrate supply. Their
judicious use in place of some of the other cover or mulching crops or
in the place of some other system of orchard management often obviates
the necessity of supplying the trees with nitrogen through mineral or
animal fertilizers.

An instance of the results that can be obtained by the use of leguminous plants
as cover crops is described by Coville.'*^ " The trees in one newly planted orchard
of Grimes apples have been kept in a remarkable condition of growth by one
initial application of manure in the year of their planting, succeeded by the
following rotation: In May the ground is sowed to cowpeas. These are plowed
under in September and followed immediately by the sowing of rye mixed with
hairy vetch. In the following May the mixed crop is plowed under. The
same 1-year rotation has been followed year after year. Under this treatment
the soil, which has the appearance of almost pure sand, has become so fertile
without the application of lime, commercial fertilizer or manure that an occa-
sional crop of cowpeas has been cut for hay without serious interference with the
progress of the orchard." The successful use of such a system would depend
upon an abundant water supply.

Were it possible to maintain permanently a good stand of clover,
vetch, alfalfa or some other leguminous crop in the orchard and to leave
the growth that it produced on the ground for a mulch, it would afford
an almost ideal sod system of management — from the standpoint of
maintaining Soil fertility — though water competition between the trees
and the intercrop would make it entirely impracticable under many
circumstances. Under average conditions, however, the maintainance
of such a sod is next to impossible because bluegrass or other species
crowd out the legumes. Where such a legume sod can be maintained
and the competition for moistm-e can be largely eliminated by irrigation,
a system of soil management is possible that affords the trees excellent
nutritive conditions for vigorous growth and heavy production and is
at the same time economical. Various fungi found in the roots of certain
heaths (Ericaceae), are likewise capable of fixing nitrogen. It is probable
that the cranberry and blueberry obtain at least a portion of their nitro-
gen supply through similar agencies.

Soil Reaction : Acidity and Alkalinity. — The absorption of available
inorganic salts by the root is affected to an important degree by acidity,
concentration, toxicity, aeration and temperature of the soil and of the
soil solution. The reaction of the soil solution is of great importance.
Most plants thrive best when the soil is very weakly acid. Many water
plants live better in a very weakly alkaline solution, while land plants
show marked differences in the amount of acidity which they will endure.

116 FUNDAMENTALS OF FRUIT PRODUCTION

When the acidity of the soil increases beyond the low value which is
most favorable to land plants, it becomes an important factor.

Soil Reaction and the Availability of Phosphorus. — The effect of soil
acidity on the availability of phosphorus is shown by the following
quotation from Harris :^^

"In addition to the work that has been done, on determining the degree of
soil acidity, many investigations have been undertaken to determine the relation
of soil acidity to the quantity of available phosphorus in the soil. As a result
of the work of Wheeler, Thorne, Whitson and Stoddart, it has been show that the
content of this element is generally low in acid soils and largely unavailable for
use by plants. Stoddart explains this by saying that acid soils convert any
calcium phosphate that may be present into soluble compounds which are either
washed out or are fixed in an insoluble form by the formation of iron and alumi-
num phosphates."

Soil Reaction and the Availability of Iron.- — An excess of calcium salts
affects the availability of iron in such a way that many plants grown on
calcareous soils suffer from lack of iron, even though iron is present in
considerable amounts. It is from this cause that grape vines and fruit
trees become chlorotic on some of the calcareous soils of France and
England, pineapples and sugar cane on Porto Rican soils containing
large amounts of lime and citrus fruits in Florida when ground limestone
is added to the soil.

"In Porto Rico the extension of the pineapple industry has been retarded
by a disease known as chlorosis, the principal external mark of which is the
yellowing of the foliage and the consequent poor nutrition of the plant. From
investigations by Gile and by Loew it appears that the yellow color of the leaves
and the accompanying weakness of the plant are due to the lack of iron, and that
where the soil contains an excess of lime the organic acids which are needed to
dissolve the iron of the soil are themselves neutralized and the iron, although
present, is not available for absorption by the pineapple roots. "^*

According to Gile and Carrero," sugar cane grown on the calcareous soils
of Porto Rico suffers from chlorosis. Analysis shows that the ash of these chlor-
otic leaves has less iron then normal leaves.

Floyd^^ describes two types of injury to grape-fruit seedlings from the presence
of ground limestone in the soil. In addition to frenching which has been dis-
cussed, chlorosis occurs. This type of injury may be attributed to iron deficiency
and is probably quite distinct from frenching, since no case of the latter was
observed to develop into complete chlorosis. The larger the amount of limestone
in the soil the greater was the injury observed.

The unavailability of iron in calcareous soils is probably attributable
to the alkaline reaction produced by an excess of calcium salts in solution.
Colloidal iron hydroxide is formed in alkaline solutions and is for the
most part unavailable to plants. Similar conditions prevailing in man-
ganiferous soils confirm the idea that the basic reaction of the soil solu-

PLANT NUTRIENTS AND THEIR ABSORPTION 117

tion, rather than the presence of specific calcium or manganese compounds,
is responsible for the formation of iron hydroxide.

Pineapples grown in Hawaii on the black manganese soils of the island of
Oahu suffer from chlorosis. This condition is recognized by yellowing of the
leaves, stunted red or pink fruits, many of which crack open and decay and
other toxic effects. ^^^ Other crops grown on these manganese soils suffer
similarly, especially corn, pigeon peas, cowpeas and rice. On the other hand,
sugar cane is less sensitive and certain weeds such as the sow thistle, Waltheria
americana and Crotalaria sp., show no effects from manganese. ^"^ The difference
between these two types of plants was revealed by ash analyses. Those to
which the soil is toxic have less iron in their ash when grown on manganiferous
soils than when grown on ordinarj^ soils. The ash of the weeds growing wild on
the manganese soils without apparent ill effects showed no decrease in iron, con-
taining even more than when grown on other soils. ^'^

The other elements in the ash showed no such significant variation, though
in practically every instance the absorption of manganese was increased on the
manganese soil and with it the absorption of calcium.

The unhealthy growth on the manganese soil thus appears to be due
to a lack of available iron. The plants suffered from iron starvation in
spite of the 10 to 30 per cent, of iron, oxide in the manganese soils.

Applications of iron sulphate to the soil, at rates varying from 500 to
3000 pounds to the acre, were unsuccessful in preventing chlorosis;
but less than 50 pounds of iron sulphate per acre sprayed on the leaves
effected a prompt cure.^^ This is of particular interest for it shows that
pineapple leaves can absorb enough iron to cure chlorosis, though the
roots are not able to do so under the circumstances. It has been found
that the chlorosis of many coniferous seedlings growing on a calcareous
soil can be remedied by spraying with a 1 per cent, solution of iron sulphate
and this treatment has become a regular practice in certain nurseries. ^'^
An interesting treatment more or less generally and successfully used
in France and Germany for the cure of chlorosis in grape vines^*^
consists in brushing the cut surfaces of pruned vines with a concentrated
solution of ferrous sulphate. Filling, with a soluble iron salt, holes bored
in chlorotic trees frequently has been tried in New Mexico and generally
with satisfactory results. ^^^

From this discussion of the effects of calcium and manganese on
iron, it is evident that fertilization may be of value, not only for adding
plant nutrients to the soil, but also under certain conditions, for rendering
soluble and available to the plant, nutrients that though present are
unavailable. Conversely, ill advised fertilization may change mineral
elements that are present from a soluble to an insoluble form and there-
fore make them unavailable to the plant. Through this effect liming has
led to chlorosis of the pineapple in Porto Rico.^^ It would be of interest
to know the results following direct attempts to change the reaction of the

118 FUNDAMENTALS OF FRUIT PRODUCTION

solution of calcareous or manganiferous soils where chlorosis is produced.
Possibly the application of acid in some form would be as effective in
preventing chlorosis as the apphcation of iron salts to the leaves or cut
surfaces.

Acid Tolerance of Certain Crops. — Most deciduous orchard fruits are
acid tolerant to a considerable degree. The strawberry has been shown
to prefer an acid soil-"^ and the blueberry^^ demands a soil markedly
acid in reaction. In the practically neutral reaction of a good garden
loam it fails to thrive or even dies out. The superior development
of wild raspberries, blackberries, dewberries and haws in soils that are
at least slightly acid suggests that their cultivated relatives may be
at home in similar soil conditions. That deciduous fruits are not alone
in their tolerance or preference for soil acidity is indicated by the behavior
of citrus trees in acid soils.

CoIIison" in reporting the results of a series of fertilizer experiments in Florida
says: "So far as could be noted an acid soil has no injurious effect on the growth
of the orange tree. On some of the most acid plots in the grove the trees are
vigorous and have made very good growth, ranking well up among the best plots
in the grove."

Furthermore, practically all of the best orchard cover crops are dis-
tinctly acid tolerant. The following commonly used cover crops belong
in this class; cowpeas, soy beans, hairy vetch, crimson clover, rye, oats,
millet, buckwheat and turnip. ^^

Since deciduous fruit plants are predominantly acid tolerant, they
should not be exposed to a markedly alkaline reaction of the soil. Ammo-
nia in considerable amount depresses root growth and eventually kills
the roots, because of its effect on the soil reaction. Injuries resulting
from an excess of "alkali," as the term is generally used in the arid and
semiarid sect ons, are due not to any effect these salts may have on
the reaction of the soil, but rather to the excessive concentration of
the potassium and sodium salts that are present. The difference between
the toxic symptoms attending an alkaline or basic soil reaction and those
attending impregnation with "alkali" is well marked. A soil solution
having an alkaline reaction affects the roots before the shoots; the toxic
effects of a soil solution which is too concentrated are evident first in the
shoots.

Concentration: Soil "Alkali." — As just pointed out, the term "soil
alkali" does not refer to the soil reaction, but to an excessive concentra-
tion of certain salts. The carbonates, chlorides and sulfates of sodium
and potassium are concerned chiefly, though occasionally other salts
accumulate in such amounts as to be injurious.

Tolerance of Different Fruits. — The degree of tolerance of various fruit
crops to salts of different kinds is indicated by data presented in Table 13.

PLANT NUTRIENTS AND THEIR ABSORPTION

119

Table 13. — Highest Amount of Alkali in Which Fruit Trees Were Found

Unaffected

{After Lo ughridge^'^^)

(Pounds per acre in 4 feet depth)

Sulphates

Carbonates

Chlor

id

Total

alkali

(Glauber salt)

(Sal soda)

(Common

salt)

Grapes. . .

40,800

Grapes 7 , 550

Grapes ....

9,640

Grapes..

. 45,760

Olives . . .

30,640

Oranges. ... 3,840

Olives

6,640

Olives . . .

. 40,160

Figs

24,480

Olives 2,880

Oranges . . .

3,360

Almonds.

. 26,400

Almonds .

22 , 720

Pears 1,760

Almonds. . .

2,400

Figs

. 26,400

Oranges. .

18,600

Almonds.... 1,440

Mulberry . .

2,240

Oranges .

. 21,740

Pears. .. .

17,800

Prunes 1 , 360

Pears

1,360

Pears —

. 20,920

Apples. . .

14,240

Figs 1,120

Apples

1,240

Apples. . .

. 16,120

Peaches. .

9,600

Peaches 680

Prunes ....

1,200

Prunes . .

. 11,800

Prunes. . .

9,240

Apples 640

Peaches

1,000

Peaches .

. 11,280

Apricots.

8,640

Apricots 480

Apricots. . .

960

Apricots .

. 10,080

Lemons. .

4,480

Lemons 480

Lemons. . . .

800

Lemons. .

. 5 , 750

Mulberry

3.360

Mulberry... 160

Figs

800

Mulberry

. 5,740

Loughridge^^^ makes the following comments on these data: "The amount
tolerated depends largely upon the distribution of the several salts in the vertical
soil column, the injury being most severe in the surface foot, where under the
influence of the unfortunate practice of surface irrigation the feeding rootlets
are usually found. It is therefore important that in alkali regions such methods
of culture and irrigation should be followed as to encourage deep rooting on the
part of crops.

"The amount tolerated varies with the variety of the same plant, as shown
in the grape." For instance, Flame Tokay is reported as "not growing" with a
total of 24,320 pounds of alkali^in the surface 4 feet per acre while Trousseau is
reported as thrifty in the presence of 31,360 pounds, though the sal soda content
of the Flame Tokay soil was somewhat higher but still well within the general
tolerance limit of the grape for this salt.

"The amount of alkali tolerated by the various cultures varies with the
nature of the soil. It is lowest in heavy clay soils and fine-grained soils, in
which the downward movement of plant roots is restricted; and highest in loam
and sandy soils, in which the roots have freedom of penetration."

Injuries jrom Excessive Fertilization. — It is evident that continued
application of fertilizer such as sodium nitrate may produce concentra-
tions that are harmful.

In discussing experiments with citrus trees Kelly and Thomas^"^ state:
"While the growth of the trees was notably stimulated by sodium nitrate during
the first few years of the experiment, and healthy, normal appearing trees were
produced, since that time excessive mottle leaf has appeared on every tree in
this plot. The mottling here became so severe during the past 2 or 3 years as
to render the trees wholly unprofitable. No marketable fruit whatever is now
produced by these trees."

120 FUNDAMENTALS OF FRUIT PRODUCTION

Table 14 presents data showing the toxic limits of citrus seedlings
for various nitrate salts and for ammonium sulphate and the toxic limits
for these salts in the presence of lime. Their lesson in connection with
the use of commerical fertilizers in the orchard is well summarized in the
words of Breazeale;^^

" It will be seen that marked differences occur in the toxic limits of the various
salts, sodium nitrate being five times as toxic as calcium nitrate. The toxic
limits for this group of salts are so high that the matter may appear to be of no
practical import. But a simple calculation will show that the surface feeding
roots of citrus trees are at times subjected to fertilizer concentrations in field
practice so great as to approach toxic conditions. Application of 2 to 3 pounds of
nitrate of soda per tree, or 200 to 300 pounds per acre, which is not an unusual
practice for some citrus growers, would correspond approximately to a concen-
tration of 70 to 100 parts per million in the soil of the surface foot. The fertilizer,
moreover, is ordinarily applied to the open ground between the tree rows — that is
not more than one-half the total soil area. If the moisture content of the soil
were reduced to 10 per cent, of the weight of the soil, the concentration of the
sodium nitrate in the soil solution would range from 1,400 to 2,000 parts per
million — that is, it would approach the toxic limit. The surface crusts in citrus
groves are often highly toxic to citrus seedlings."

Table 14. — Toxic Li.mits of Nitrates and Ammonium Sulphate p^or Citrus

Seedlings^*

Toxic Limit
Salt Parts per Million

Sodium nitrate 1 , 800

Potassium nitrate 3 , 500

Calcium nitrate 10,000

Ammonium sulphate 1 , 000

Sodium nitrate and calcium carbonate (solid phase) 6,000

Ammonium sulphate and calcium carbonate* (solid phase) 2,000

Some Effects of Soil Alkali. — The effects of excessive concentration
produced by "alkali" on citrus trees are described by Kelly and
Thomas. 10^

"Different varieties and species of citrus trees are affected differently by
alkali. Lemon trees show the effects by a pronounced yellowing of the margins
and burning of the tips of the leaves, followed by unusually heavy shedding of the
leaves in the latter part of the winter and spring. The subsequent new growth
may appear to be quite normal and vigorous for several months, but later a large
portion of the leaves turn yellow in irregularly shaped areas around the margins
and fall excessively. In the presence of excessive concentrations of salts, espe-
cially chlorides, complete defoliation may take place. Mottle leaf frequently
occurs, and sometimes chlorosis. Both the quality and quantity of the fruit are
impaired.

"It has been found that orange trees affected by alkaU are unusually sus-
ceptible to injury from adverse cUmatic conditions. Hot winds burn the young
leaves and frosts produce more serious injury than with normal trees. Alkali

PLANT NUTRIENTS AND THEIR ABSORPTION 121

injury is also accentuated by the lack of care, such as improper tillage, the insuffi-
cient use of manure or other fertilizers, and withholding irrigation, thereby allow-
ing the soil to become too dry. If the soil be allowed to dry out excessively, the
concentration of alkali in the soil moisture may become harmful, while a more
abundant supplj^ of water would so dilute the salts present as to reduce the
concentration to a point where normal growth could take place.

" In certain localities the dissolved salts are predominantly chlorides, in others
sulphates and in still others bicarbonates. A few wells have been found to contain
large amounts of nitrates."

Alkali in the soil may also have a marked effect on root distribution.

"It is especially interesting that the roots of the lemon trees have not pene-
trated deeply in this soil, more than 95 per cent, of them being within 18 inches
of the surface. There is probably some connection between this fact and the
higher concentration of alkali salts found in the third and fourth feet.

"Local areas occur in a Valencia orange grove near Garden Grove in Orange
Count}'' where many of the trees have been severely injured by alkali brought up
as a result of a temporarily high water table in the winter and spring of 1916.
The water table receded within a few months but the alkali salts remained in the
soil. A considerable number of trees have recently died, and all of them in cer-
tain areas became excessively chlorotic, following the rise of the alkali."

When irrigation is practiced, the composition of the irrigation water is an
important factor. Kelly and Thomas found from their investigations, "a
remarkably close relationship between the composition of the irrigation water,
on the one hand, and the accumulation of alkali salts and the condition of the
orange and the lemon trees, on the other. In every case we have studied, where
saline irrigation water has been applied for a series of years, alkaline salts have
accumulated in the soil and the citrus trees have been injured in consequence.
The rates at which salts have actually accumulated vary, however, in different
soils, depending on (1) the composition of the water, (2) the amounts appUed,
and (3) the freedom with which it penetrated into the subsoil. "^"^

The injurious effects of high concentrations produced by excessive
amounts of alkaH or other salts in the soil are due largely to the inability
of plants to absorb water by osmosis from a solution having a higher
osmotic concentration than that of the plant itself. Hence, the harmful
effects of alkali are partly those of starvation and drought. The con-
centration of the soil solution requires attention only under conditions
where the salt content of the soil is naturally high, as in salt marshes and
in regions near salt water generally, or where the moisture supply is
restricted, as in arid or semiarid regions. However summer drought
may produce temporarily excessive concentrations in any soil and so
bring about injury.

Remedial Measures. — When a soil once becomes impregnated with
alkali about the only effective treatment is flooding the land with irriga-
tion water to dissolve out the excessive amounts which are then either
forced down to a depth where they will do no harm or carried away in
the drainage water. Provision for thorough drainage is very important

122 FUNDAMENTALS OF FRUIT PRODUCTION

in places where there is danger from alkah, as the rise of the water table
attending poor drainage may result in bringing salts from lower soil
to the surface and thereby increase concentrations in the upper layers
as evaporation takes place. Moderate, as opposed to excessive, irrigation
is a preventive measure. Though there is not often a choice between
two or more sources of irrigation water, the irrigation fruit grower should
remember that certain water supplies are more or less saline and that
special precautions must be taken to neutralize the injurious effect when
such water alone is available. Much can be done to avoid the effects of
soil alkali through the choice of alkali-tolerant fruit crops and particularly
the selection of stocks having this characteristic, though the roots of the
cion may be susceptible. The importance of caution in the use of fertil-
izers, particularly in irrigated sections, has been mentioned.

Finally, it should be pointed out that insufficient as well as excessive
concentrations may exist. That extremely low concentrations permit
growth has been emphasized but it is the insufficient concentration of
particular salts that renders the use of fertilizers necessary.

Soil Toxicity. — The chemical composition of the soil solution must be
considered in its effect on absorption. In this connection the presence
of toxic substances is of great importance. The toxins may be organic
compounds formed by bacterial activity from dead plant tissue. They
are not, as a rule, excreted as such from plant roots, though this occurs
under exceptional conditions, as for example when the supply of oxygen
is deficient. Fragments of dead root hairs, roots and possibly aerial
portions of the plant washed down into the soil, constitute the material
acted upon by microorganisms to produce poisons.

It must not be overlooked that bacterial activity may also produce
compounds beneficial to plant life in so far as the products of bacterial
action may serve as a source of food, as has been pointed out.^*^^

General and Specific Effects. — The general effects of toxins are shown
in decreased green weight and inhibited growth. The specific morpho-
logical effects vary considerably with different substances, some producing
more marked effects on the roots than on the green parts of the plant.
For instance, vanillin-affected plants show decreased growth of the top
and root growth is strongly inhibited. Dihydroxystearic acid affects
the tops but especially the roots, the root tips becoming darkened, their
growth stunted; the root ends are enlarged and often turned upward
like fishhooks and their oxidizing power is strongly inhibited. Pyridine
and picoline affect the green parts more than the roots. Cumarine-
affected plants have stunted tops and broad distorted leaves; quinone-
affected plants are tall and slender, with thin narrow leaves. Guanidine
has apparently no effect on the roots, but the green parts develop small
bleached spots which spread, the plant becomes weakened and the leaves
break at the stem, wilt and die.^^i''^*

PLANT NUTRIENTS AND THEIR ABSORPTION 123

The manner in which these toxic substances check growth is shown
by a study of the absorption of mineral constituents. Though absorp-
tion is always decreased, the various toxins have more or less specific
effects. Cumarin and salicylic aldehyde depress potash and nitrate
absorption more than phosphate absorption; quinone depresses phosphate
and nitrate more than potash , dihydroxystearic acid and perhaps vanil-
lin, retard phosphate and potash more than nitrate absorption.

Protecting Against Toxins. — The harmful effects of these toxins may
be counteracted in numerous ways. Fertilizer treatment is efficacious; as
might be expected, various salts act differently in overcoming the respec-
tive effects of the toxic substances. Phosphatic fertilizers, for example,
are most efficient in overcoming the effects of cumarin, potassic fertilizers
in overcoming the effects of quinone and nitrogenous fertilizers in over-
coming the effects of vanillin.

Another way of ameliorating the effects of toxic substances in the soil
is treatment with absorbing agents. Roots appear able to oxidize
organic materials in such a way that their toxic properties are lost. The
large amount of root surface which most plants have makes this oxidizing
power important in relation to the destruction of toxic substances through
crop rotation.

Schreiner, Reed and Skinner^^^ found that toxic solutions lost much of their
toxicity after plants had been grown in them. They state: "The vanillin'
solution, for example, was so reduced in toxicity that a solution originally con-
taining 500 parts per million was no more toxic to the second set of plants than
a solution of 50 parts per million was to the first. It has been found that an
equal number of wheat plants can remove in a similar length of time not more
than 30 to 50 parts per million of nitrates from solution and there is no reason
to believe that toxic substances should be removed at a much more rapid rate."

Breazeale^^ reports that peat extract in dilute concentrations (20 parts
per million) and calcium carbonate protect citrus seedlings against the
toxicity of distilled water, usually associated with the presence of small
amounts of copper. Sodium carbonate on the other hand augments the
toxicity of soluble organic matter.

Thus, "When soluble organic matter which is acid in reaction and stimulating
to citrus seedUngs in concentrations up to 1,000 parts per million or more is added
to a sodium carbonate solution of 400 parts per milUon which in itself is not
toxic, a highly toxic solution is formed which will kill the root tips of citrus
seedlings. This reaction appears to be of importance in connection with the
toxicity of soils containing small amounts of sodium carbonate."'*

Importance in the Fruit Plantation. — To just what extent organic soil
toxins are important in the fruit plantation is not known. That they are
of greater significance than is generally realized there can be no question.

124 FUNDAMENTALS OF FRUIT PRODUCTION

Most deciduous fruit crops occupy the same soil for a considerable num-
ber of years and consequently are subject to the influence of any toxins
that arise from the disintegration of their own leaves, rootlets or other
dead tissues. In addition they are subject to the action of toxins that
may arise from the growth or decay of intercrops or cover crops that are
grown between them.

It has been shown^^ that ordinary crop plants exert an important
influence upon those which follow them and that this influence "seems
not to be attributable, at least primarily, to differences in the amount of
fertilizer nutrients removed by the crops grown before." Thus the yield
of buckwheat following redtop, rye, buckwheat and onions was as 7 : 30 :
45 : 88, in a nutrient medium deficient in nitrogen but well supplied with
other plant nutrients, even though the nitrogen removal of the preceding
redtop, rye and buckwheat crops was as 1.00:2.72:2.42.^^ The pre-
sumption is that the differences in the yields of the second crops were due
to the effect of toxins,

Pickering ^^^ has been able by means of various field trials and pot
experiments to eliminate the influence of one plant upon another through
its effect on moisture and nutrient supply, soil temperature, soil reac-
tion, texture, carbon dioxide and bacterial content and thus to deter-
mine both quantitatively and qualitatively their mutual influence through
•toxic substances.

He comments as follows on the results of his investigations:

"It has now been established with a reasonable amount of certainty that the
deleterious effect of one growing plant on another is a general phenomenon.
By means chiefly of pot experiments . . . the following plants have been found
susceptible to such influence: apples, pears, plums, cherries, six kinds of forest
trees, mustard, tobacco, tomatoes, barley, clover, and two varieties of grasses,
whilst the plants exercising this baleful influence have been apple seedlings,
mustard, tobacco, tomatoes, two varieties of clover, and 16 varieties of grasses.
In no case have negative results been obtained. The extent of the effect varies
very greatly: in pot experiments the maximum reduction in growth of the plants
affected has been 97 per cent., the minimum 6 per cent., whilst in field experiments
with trees the effect may vary from a small quantity up to that sufficient to
cause the death of the tree. The average effect in pot experiments may be
roughly placed at a reduction of one-half to two-thirds of the normal growth
of the plant, but no sufficient evidence has yet been obtained to justify the con-
clusion that any particular kinds of plants are more susceptible than others, or
any particular surface crop is more toxic than another; that such differences
exist is highly probable, but all the variations observed so far may be explained
by the greater or lesser vigour of the plants in the particular experiments in
question. Similarly as regards the effect of grass on fruit trees, though the extent
of it varies very greatly, and in many soils is certainly small, we must hesitate
to attribute this to any specific properties of the soils in question ; for when soils
from different localities (including those from places where the grass effect is

PLANT NUTRIENTS AND THEIR ABSORPTION 125

small) have been examined in pot experiments, they have all given very similar
results; and this appUes equally to cases where pure sand, with the addition of
artificial nutrients, has been taken as the medium of growth."'^" Evidence
which will serve partially to differentiate between the influence of a living plant
and the disintegration products of its dying roots is afforded by the following:
"... a quarter of an acre of land, over which some 15 apple trees, 20 years
of age, were distributed, was planted uniformly with Brussels sprouts; those
under the trees suffered to the extent of 48 per cent, in their growth; but there
were patches in the ground where trees had been growing until the preceding
winter, when they had been cut down, leaving the roots undisturbed in the soil,
and in these patches the sprouts did better than elsewhere to the extent of 12
per cent. In other parts of the ground canvas screens had been erected, at a
height of 6 feet above the surface, to simulate, and even exaggerate, the shading
of the trees, and under these the sprouts gave exactly the same values as on the
unshaded ground. Thus, the trees themselves materially injured the crop,
though the soil under the trees was more fertile than elsewhere, and though
the shading was inoperative."'^"

The degree of susceptibility of the apple tree to the toxic influence of
some other plant is indicated by Pickering's^^'' statement that the color of
the fruit may be materially affected "in cases of trees weighing about 2
hundredweight when only 3 to 6 ounces of their roots extended into
grassed ground."

Though, as stated already, data are not available for the accurate
•estimation of the importance of organic toxins in fruit production, the
limited data are very suggestive.

In commenting upon the investigations that have just been cited and on
others of a similar character Alderman'' remarks: "Do they not at least open to
some question many of our preconceived ideas bearing upon plant growth and
plant nutrition? . . . Do they not raise a question as to the arrangement of
many crop rotations {e.g., of cover crops or other intercultures) which were
originally worked out with the economic convenience of the grower in view rather
than the growth reactions of the plants under consideration? . . . If it is true
in Rhode Island that onions will yield 412 bushels per acre following redtop and
only 13 bushels following cabbages, it is probably true elsewhere and the place
of the onion in the cropping system of the truck grower deserves the most serious
study. If grass affords direct injury to apple trees growing in shallow soils
underlaid with an impervious stratum of subsoil, it is probably as offensive in
North America as in England. The writer and others interested in plant nutri-
tion have repeatedly pointed out the difference in reaction to fertilizers between
orchards in sod and those under cultivation. It has been generally believed that
this difference was due to soil exhaustion of important plant food material or to
an influence on moisture supply but the work of Pickering is a direct challenge
to such a belief. Perhaps it is not important to the grower of fruit to know
whether an application of nitrate of soda to a sod orchard is beneficial because
it supplies some element of plant food material heretofore lacking or because it

126

FUNDAMENTALS OF FRUIT PRODUCTION

hastens the change of toxic substances to harmless or beneficial materials, but it
is extremely important to the investigator for it strikes back to a fundamental
problem in plant nutrition."

The whole question of the interrelationship of plants in the orchard
still needs thorough investigation.

Antagonism. — Beside organic poisons, certain inorganic salts may
have toxic effects; for example, magnesium compounds may become
injurious to the higher plants. The toxic action of magnesium is modified,
however, by calcium because of the antagonism between these two ele-
ments. Salts of either calcium or magnesium by themselves tend to
increase the permeability of protoplasm more than a mixture of calcium
and magnesium salts in proper proportion. Therefore, the action of
calcium in offsetting the toxic effect of the magnesium probably is due
to diminished magnesium absorption when both elements are present in
suitable proportion. Antagonism occurs also between calcium and
potassium and many other salts.

Aeration. — In the absence of aeration roots are unable to function prop-
erly and toxic substances are secreted. Moreover poor aeration favors
the formation of toxins by bacteria and in the absence of an adequate
supply of oxygen, numerous soil bacteria reduce nitrates, utilize the oxy-
gen and leave gaseous nitrogen which is not available to the higher plants.

The physical character of the soil has an important effect on aeration;
stiff, retentive clays, for example, do not drain as well as sandy soils;
consequently they are usually not so well aerated. The application of
Hme or organic fertilizers to such clays may render them mellow, better
drained and more readily cultivated.

Selective Absorption.— Within certain limits, plants are able to
absorb larger amounts of one mineral constituent at their disposal than
of another and in this way to exert a selective action. This is strikingly
shown by Table 15, which compares the percentage composition of the
ash of duckweed with the water in which it grew.

Table 15.

-Analyses of Ash of Duckweed and of the Mineral Matter Con-
tained IN THE Water in Which It Grew'"*

K2O

Na^O

CaO

MgO

FeaOs

P2O5

SO 3

Si02

CI

Duckweed

Water

18.29
5.15

4.05
7.60

21.86
45.55

6.60
16.00

9.57
0.94

11.35 7.91
3.42 10.79

16.05
'4.23

5.55
7.99

This selective abihty of the plant may be explained by greater action
on certain constituents which are thereby rendered osmotically inactive
within the plant. This leads to further absorption of these particular
constituents. However, selective action has definite limits and plants

PLANT NUTRIENTS AND THEIR ABSORPTION 127

absorb a certain amount of any constituent which is present in an
available form and to which the protoplasm is permeable. Thus, salt
marsh plants contain relatively large amounts of sodium chloride which
may raise the osmotic concentration of their cell sap, but is of no
apparent nutritive value. Similarly plants grown in nutrient solutions
absorb whatever salts are present in solution, though the rate is greatest
and growth best when the nutrient substances are available to the plant
in a ratio corresponding to that in which they are utilized.

Investigations by Schreiner and Skinner^'^^ bearing on this subject are very
suggestive: "In this study the growth relationships and concentration differ-
ences were observed between sohition cultures in which the phosphate, nitrate
and potash varied from single constituents to mixtures of two and three in all
possible ratios in 10 per cent, stages. The better growth occurred when all these
nutrient elements were present and was best in those mixtures which contained
between 10 and 30 per cent, phosphate; between 30 and 60 per cent, nitrate;
and between 30 and 60 per cent, potash. The growth in the solutions containing
all three constituents was much greater than in the solutions containing two
constituents, the solutions containing the single constituents giving the least
growth. The concentration differences noticed in the solutions were also very
striking, the greater reduction in concentration occurring where the greatest
growth occurred. The change in the ratios of the solutions and the ratios of
the materials that were removed from the solutions showed that where greatest
growth occurred, as above outlined, the solutions suffered the least change
in ratio, although the greatest change in concentration occurred. The more the
ratios in these solutions differed from the ratios in which the greatest growth
occurred, the more were the solutions altered in the course of the experiment,
the tendency in all cases seeming to be for the plant to remove from any and all
of these solutions the ratio which normally existed where greatest growth occurred,
but was hindered in doing so by the unbalanced condition of the solution. The
results show that the higher the amount of any one constituent present in the
solution, the more does the culture growing in that solution take up of this
constituent, although it does not seem able to use this additional amount
economically."

Similarly surpluses of lime in plants are not uncommon. ^^4 ^ p^j-t
of the lime may be precipitated as calcium oxalate, or in some plants
as calcium carbonate, of which cystoliths are largely composed.

Transpiration. — The ash content of plants varies considerably under
different conditions of soil water, available salt supply and temperature.
Data have been reported^"^ indicating that increased transpiration
does not increase the ash absorption of plants growing in soil. For
this reason conclusions from experiments involving nutrient solutions
should be applied to field conditions with extreme caution. Transpira-
tion and the absorption of nutrient salts are largely independent of each
other.

128 FUNDAMENTALS OF FRUIT PRODUCTION

Schreiner and Skinner""''' discuss this subject as follows: "Many writers in
agricultural literature seem to be under the impression that the only way that a
plant can get the nutrients from a solution is to use all the water it can in building
tissue and to lose the remainder by transpiration, so as to obtain the necessary
nutrients dissolved in the soil water or nutrient solution. In other words, that
the plant maintains a current of water entering at the root as the nutrient
solution and leaving the plant as pure water at the leaf surfaces, that is, by
transpiration or evaporation. From their arguments it follows that if a half
strength solution is presented to the plant it will have to take up and transpire
twice as much water to obtain the same nutrients. In other words, the plant
is supposed to absorb the mineral constituents in the same concentration as the
solution in which the roots bathe. This is, however, not in accordance with
the facts. The plant has greater difficulty in obtaining the mineral elements from
the weaker solution, but it does not accomplish this by expending the extra energy
involved in transpiring double the amount of water.

"For instance, the loss of water from a 250-cubic centimeter [nutrient]
solution during this 3-day period is only about 10 per cent., whereas the analysis
of the solution after supplying this water showed the mineral nutrients to be
reduced from 80 to as low as 23.8 parts per million, or a decrease of 70 per cent.
It is obvious that the plants have taken the nutrients faster than the water, and
this under conditions of good growth.

"Not only does the absorbing power of the root enable the plant to take more
nutrients per cubic centimeter of water absorbed than is contained in the same
volume of the soil solution, but it also enables the plant to obtain a different
ratio of the mineral nutrients for its use than exist in the nutrient solution.

"These facts are extremely important, as they show that the absorbing power
of the plant is not regulated by the amount of transpiration, but rather by the
life processes within the plant and the requirements of these life processes."

THE NUTRIENT REQUIREMENTS OF CROP AND FRUIT PLANTS

Typical crop plants and typical deciduous fruits make distinctly
different demands upon the soil. For most crops the soil should not be
acid and the nitrogen requirement is relatively low. For most fruit
trees, soil acidity, unless very high, is not a factor of concern and the
demands for nitrogen are great. It is suggested that this more or less
characteristic difference which requires agronomists and horticulturists
to adopt correspondingly different attitudes on the problem of soil
productivity is connected with the different ecological habits of these
plants, together with the type of crop desired. Cereal crops in particular
are adapted to an early stage in ecological succession which has not
proceeded beyond an association where grasses are dominant. Humus
has not yet collected in great amount; hence, crops flourish in soils of low
acidity and require relatively little nitrogen (though they may do equally
well or better in soils abundantly supphed with it). Fruit trees belong to
a much later stage in an ecological succession which has reached an
association of forest trees and in which the character of the soil has

PLANT NUTRIENTS AND THEIR ABSORPTION 129

been affected by previous plant associations that have grown on it.
Humus is therefore more abundant and the plants are adapted to soils
of relatively high acidity and great nitrogen content. Hence, lime
is most useful for crops and nitrogen the fertilizer most often required by
fruit trees. It is more profitable to grow cereal crops on the great plains,
prairies, savannahs and pampas while fruit trees thrive best in the regions
of coniferous and deciduous forests.

Summary. — The various mineral elements and nitrogen are absorbed
by the plant from the soil solution. These mineral elements, except a
portion of the sulphur, may be recovered in the ash of the plant. In
addition to the necessary mineral elements, the ash generally includes
small quantities of a number of non-essential elements occurring in the
soil solution. The ash content of plants varies with the kind of plant
and with the soil upon which it is grown. The ash content of different
tissues also varies with the kind of tissue, its age and the season. Nutri-
ent elements must not only be in solution but must be in an available
form — that is, combined with certain other elements and in certain
compounds. Nitrogen is absorbed mainly as nitrates. The nitrate
supply in the soil is subject to great fluctuations, depending on tem-
perature, moisture, aeration, bacterial activity, the supply of nitrogen-
carrying materials from which nitrates can be formed and many other
factors. An important part of the orchard soil fertility question consists
in maintaining a liberal supply of nitrates in the soil during the growing
season. Most crop plants prefer a soil practically neutral in reaction.
Deciduous fruits are distinctly acid tolerant and certain of them thrive
best in an acid soil. The best orchard cover crops are likewise acid
tolerant. The chlorotic conditions frequently found in strongly cal-
careous and manganiferous soils apparently are due to iron starvation
incident to an alkaline reaction. Many organic disintegration products
are known to be toxic to certain crop plants and there is evidence that
they are often of considerable importance in determining the produc-
tivity of orchard soils. Some of the injurious effects of sod upon trees
evidently are due to these toxins in the grass land. Excessive concen-
trations of certain salts, particularly of sodium and potassium, are toxic to
orchard trees and give rise to the so-called "alkali" conditions. Treat-
ment for disorders of this kind may be both remedial and preventive.
Optimum conditions for absorption are provided when the various
nutrient elements are found in the soil solution in certain rather definite
proportions. Sometimes harmful influences result when these ratios
do not obtain. Both transpiration and soil aeration influence somewhat
the rate of absorption. Within certain limits plants are able to absorb
from the soil solution the elements most necessary, taking them out in
proportions sometimes very different from those in which they exist.

CHAPTER VIII

INDIVIDUAL ELEMENTS

The intake of nitrogen and mineral constituents in inorganic form
has been described. Their incorporation into the plant is now considered
with particular reference to orchard or fruit plants. In the study of
nitrogen content analyses are expressed in percentages of fresh weight or
of dry weight or in the absolute amounts present in a certain tissue such
as 100 leaves; ash analyses are given in percentages of fresh weight or
of dry weight, in percentages of total ash or in absolute amounts.
Careful distinction should be made between determinations expressed
in these different terms since they are not comparable. For example,
during the development of a tissue — say the leaf — some ash constituent
may decrease in terms Of percentage of total ash, remain constant in
percentage of dry weight and increase in absolute amount. Absolute
amounts are particularly valuable data and show the actual changes
in the amount of substance present. Percentages of dry weight will
indicate the same changes provided there is no increase or decrease
in the absolute dry weight. If there is, then these changes must be
taken into consideration. Expression of percentage in terms of fresh
weight involves in addition changes in the water content. Percentages
of total ash show the relative proportions of the various ash constituents.
Each of these determinations has its value, but each expresses different
relations.

NITROGEN

Nitrogen enters the roots from the soil solution as a salt of nitric acid,,
such as potassium or sodium nitrate, or sometimes as ammonia. The
supply of nitrates in the soil varies with temperature and moisture,
usually being greatest in late spring and early autumn, but persisting
throughout the summer.

Synthesis of Organic Nitrogenous Compounds. — Most of the inorganic
nitrogen absorbed is carried up the trunk and branches to the leaves
where it is elaborated into amino-acids and other nitrogenous organic
compounds. The elaboration of nitrates to amino-acids takes place for
the most part in the chloroplasts of the leaf mesophyll cells. Light has
been shown^^^ to increase nitrogen assimilation, blue-violet and ultra-
violet light being particularly effective. Light from the blue end of the
solar spectrum is relatively stronger in cloudy weather; light from the
other end of the spectrum which is the more important for the photo-

130

INDIVIDUAL ELEMENTS 131

synthetic process, predominates in direct sunlight. According to one
investigator^^^ the influence of Hght in favoring protein formation and
the elaboration of inorganic to organic nitrogenous compounds becomes
more pronounced as the stage of development advances. Nitrogen
elaboration can take place in the absence of chlorophyll and light, in
which case presumably carbohydrates are used.-"^ The amino-acids
which are the first products of elaboration are either used directly in
the leaf or are conducted through the phloem to all parts of the plant
where they are used in the building up of every nitrogen-containing
organic compound found in plants as well as of certain nitrogen-free
organic substances (essential oils, resins and polyterpenes). The amino-
acids are combined to form the proteins which occur in all protoplasm.
Other nitrogenous organic compounds are the purines and pyrimidines
which enter into the composition of nucleic acids, nucleins and nucleo-
proteins, substances characteristic of the cell nucleus. Lecithins and
chlorophyll contain nitrogen. Nitrogen-containing compounds which
are not of universal occurrence are the alkaloids, ptomaines, amines,
cyanogenetic glucosides and indican (natural indigo blue).

Translocation and Use of Elaborated Nitrogenous Compounds. — The
elaboration of nitrates to amino-acids beginning at the time the leaves
are well developed, proceeds as long as they remain green, reaching a
maximum when temperature, light and soil supply conditions are at an
optimum. The elaborated nitrogen-containing compounds are con-
stantly passing out of the leaves throughout the season of elaboration as
fast as they are made. They are used for new tissue development, for
shoot growth, new leaves, increments to branches, trunks and roots, new
roots and especially for fruit and seed development. A considerable part
of the remainder is stored in the phloem. Storage is particularly rapid
in the fall when growth has ceased and before the leaves are separated
from the plant by abscission layers.

New tissue growth in early spring is at the expense of stored foods,
including stored nitrogen. This reserve supplies the developing shoots,
leaves, flowers, rootlets, much of the new tissue in trunk, branches and
roots and the fruit in its initial stages. Hence for good spring growth of
tissues, especially shoots, leaves and spurs, abundant nitrogen storage the
previous season is a prime requisite. This, in turn, depends on a
good supply of available nitrogen in the soil between June 1 and Sept. 15
or Oct. 15, a supply more than sufficient for fruit and tissue development.
Summer defoliation or a diseased condition of the leaves evidently checks
growth the following year by cutting down the supply of stored and elabo-
rated nitrogen.

Attention should be called to the apparent usefulness of unelaborated
nitrogen to the apple and pear tree and probably to other fruits, through
enabhng them to set a larger crop. It is a common experience to secure

132

FUNDAMENTALS OF FRUIT PRODUCTION

a good set of fruit when liberal applications of some readily available
nitrogen-carrying fertilizer, such as nitrate of soda, are made to weak
trees just before blossoming, though without such applications these
same trees would bloom heavily but set little or no fruit. This response
by the tree is obtained within 2 or 3 weeks after application of the fer-
tilizer and at a season when there is practically no leaf area to build up
elaborated foods. It would seem, therefore, that the synthesis of organic
nitrogenous compounds can take place in tissues other than the leaves.

Seasonal Distribution of Nitrogen. — A study of the seasonal variation
in nitrogen content of different parts of the plant gives a perspective of
the processes of nitrogen elaboration, storage and utilization.

1/

<;}-

—

c3 ^

rO

^

3

3

^'

^^ ^

->

3
—>

<

< «n

Fig. 11. — Nitrogen content of plum leaves in percentages of dry weight. (Plotted from
data given by Richter.*^^)

In Leaves. — Since the leaf is the principal organ of nitrogen elaboration the
seasonal distribution of this element in the leaf is important. Leaf buds have a
high percentage of nitrogen; certain analyses show 3.687 per cent, of the dry
weight in the cherry and 3.779 per cent, in the plum.i^e Fruit buds have a
slightly higher percentage composition in nitrogen, corresponding analyses
showing 3.771 per cent, in the cherry and 4.142 per cent, in the plum.i^^

Table 16 shows the decrease in percentages of nitrogen in apple, pear and
cherry leaves from May to October. ^^^ This is shown even more clearly by the
graph in Fig. 11. The accompanying composite table (Table 17) is a good
illustration of the steady decrease in the percentage nitrogen content of plum
leaves. Though there is a continuous decline in the percentage of nitrogen from
May through October, there are two periods of rapid decrease, one in May and
the other in September. Between the periods of rapid decrease the percentage
composition of the leaf is fairly constant. The first period of decrease is at the
time when the leaf is growing rapidly and the available nitrogen supply is limited,
because of rapid and simultaneous shoot, wood and root development. The
period of relatively constant nitrogen content occurs when nitrogen intake is

INDIVIDUAL ELEMENTS

133

Table 16.— Nitrogen in Leaves of Apple, Pear and Cherry '^^
(In percentage of dry weight)

Apple

Pear

Cherry

May 9, 14

4.152
2.628
2.015
1.198

4.087
2.782
2.041

0.917

4.867
2 639

Aug 29

2 160

Oct. 2, 15

1 . 022

Table 17. — Nitrogen of Plum Leaves^"
(In percentage of dry weight)

May 18, 1908 4.917

May 27, 1907 3.809

June 22, 1908 2.208

July 14, 1909 2.917

July 31, 1909 2.816

Aug. 21, 1909 2.402

Aug. 29, 1908 2.398

Sept. 6, 1909 2.413

Sept. 30, 1908 1 . 152

Oct. 28, 1909 1.096

very nearly balanced by the demands for new vegetative tissue and for the develop-
ment of the fruit and seed. The second period of decrease indicates rapid deple-
tion of the nitrogen content of the leaf, the withdrawal being much in excess of
the, amount supplied. This picture presented by the plum is fairly typical of
other deciduous fruits.

On the other hand, the absolute amount of nitrogen in the leaves does not
decrease throughout the season. Table 18, showing grams of nitrogen in 100
apple, pear, cherry and plum leaves from July to October, brings this out clearly
and shows that the absolute nitrogen content of leaves does not decrease
materially until after September. In all probability it is increa.sing until August.

T.\ble 18. — Grams of Nitrogen in 100 Leaves^

Apple

Pear

Cherry

Plum

July 14

July 31

Aug. 18, 21....
Sept. 3, 4, 6. ..

Oct. 7

Oct. 23, 27, 29.
Nov. 4

0.704
0.734
0.795
0.742

0.232

0.401
0.421
0.409
0.368

0.121

0.713
0.553
0.624
0.593
0.602
0.178

0.555
0.477
0.376
0.389

O.ISO

A comparison of the data showing absokite nitrogen content with the data
showing percentage composition of the dry weight indicates that in young leaves
with their high percentage of nitrogen, growth and carbohydrate formation
proceed at such a rate as to reduce the percentage composition of nitrogen even
though the intake of nitrates during this period is greater than the outgo of
elaborated nitrogen. During July and August and sometimes later, the leaf

134

FUNDAMENTALS OF FRUIT PRODUCTION

supplies the branches with an amount of elaborated nitrogen about equal to the
amount of nitrates taken in. From September on, however, the leaves receive
less nitrate in proportion to the elaborated nitrogen which passes back into the
branches; consequently the percentage nitrogen content of the leaf is cut in
half and only one-third the amount the leaves once contained remains in them
when thej^ fall.

In Branches, Trunks and Roots. — A study of the seasonal variation in the
content of various parts of a tree shows what becomes of the nitrogen that passes
out of the leaf. Table 19 shows the distribution of nitrogen in a 7-year old apple
tree at different seasons. Nitrogen content is expressed in percentages of dry
weight.

Table 19. — Seasonal Changes in the Nitrogen Content of a 7-year Old

Apple Tree^^

(Percentages of dry weight)

Dormant,
Dec. 3

Buds
swelling,
Apr.

20

In bloom.
May 18

Active

growth

over,

July 12

Leaves
falling,
Oct. 12

Summer's growth. . .
1-year old branches .
2-year old branches.
3-year old branches.
4-year old branches.
5-year old branches.

Trunk

Large roots

Small roots

0.80
0.63
0.42
0.40
0.39
0.23
0.41
0.79

1.01
0.68
0.62
0.41
0.32
0.32
0.47
0.78

0.69
0.38
0.32
0.29
0.28
0.27
0.46
0.70

0.64
0.40
0.32
0.27
0.24
0.23
0.22
0.28
0.48

0.61
0.57
0.50
0.37
0.30
0.25
0.24
0.31
0.77

These figures bring out two important points — first, that the younger the
tissue the greater is its nitrogen content and second, that practically all tissues
have a minimum when active growth has ceased and a maximum at the time of
bud swelling. The increase in all tissues, except leaves, during the fall indicates
nitrogen storage. The nitrogen that is stored over the winter evidently comes
from the leaves.

Reference to the last table shows that in two places only is there a decrease
in the percentage of nitrogen before bud swelling, namely, in the smaller roots
and in the 5-year old branches. The decrease in the roots probably is due to
their beginning to function and to renew growth earher in the spring than do the

In Spurs. — The seasonal changes in the nitrogen content of bearing, non-
bearing and barren spurs from mature apple trees is shown in Fig. 12.
The variations in non-bearing spurs, or more accurately productive spurs in the
off year, are similar to those in the roots, trunks and branches with a maximum
in March at the time of bud swelling and a minimum at the end of June when
growth is over.^°" Barren spurs have a lower nitrogen content throughout the

INDIVIDUAL ELEMENTS

135

year and there is little evidence of accumulation in the fall; this may be associated
with the absence of fruit bud differentiation in these spurs.

Bearing spurs are peculiar, however, in that their nitrogen content increases
after the buds have broken, though in all other tissues of spur-bearing trees it
decreases when the plant is in bloom. This indicates that though the vegetative
tissues use locally stored nitrogen with the result that their nitrogen content
decreases, the blossoming spurs draw on a general supply and latet- upon the new
supply of the current season with the result that their nitrogen content is aug-
mented up to the time of fruit setting. This reserve supply is located probably
in the phloem, for a marked decrease in the nitrogen content of bark has been
found in many plants.^" In Rhus elegans for example the bark has been found

A

\*

/.

r

\

/

/

K

/

B

/

\

\

y

/

A

A

\

\

W

5

^

N

J

\^

\

\

^^ —
\ 1

w

■^

^.^

^^.^

^

fe

1.0

TT

•^

,

^

s.

\

\L-

^■'

-•^

><

Ct

P

n

--V

A

d"

^

fr.

i-ji.

z

''H

n-v

=^"

—

'T

^

^

'-'

^s^r^ to z J|

Fig. 12. — Nitrogen content of apple spurs in percentages of dry weight, bearing spurs
represented by continuous lines marked W , B and / for Wealthy, Ben Davis and Jonathan
respectively; non-bearing spurs shown by broken lines marked B and J; barren spurs
represented by dot-dash lines marked B and N for Ben Davis and Nixonite. {After
Hooker. ^°<^)

to contain 1.52 per cent, of nitrogen in the winter and only 0.36 per cent, in the
spring. Similarly in the bark of Acer platanoides 26 per cent, of the stored
nitrogen disappeared from winter to spring; in the bark of the cherry 37.16 per
cent, and in the red beech 30 to 50 per cent, disappeared during shoot growth.

The nitrogen that is moved from the bark into the blossoming spur passes on
into the developing fruit, so that in the biennially bearing spur the nitrogen
content decreases as long as the fruit is attached. Murneek^" has shown recently
that the total nitrogen content of apple spurs is proportional to the leaf area and
that it decreases as a result of defoliation.

In Fruit. — Though the nitrogen of the fruit, measured in percentages of dry
weight, decreases throughout development on account of the increment in dry
matter, the absolute amount present increases continuously. Table 20 shows
the nitrogen content of apples in percentages of dry weight and in absolute
amounts.

136 FUNDAMENTALS OF FRUIT PRODUCTION

Table 20. — Nitrogen Content of Developing Apples'"

White A.strakan

Pleissner Rambour

Date

Percent-
age of dry
weight

Grams in
1,000 fruits

Date

Percent-
age of dry
weight

Grams in
1,000 fruits

Xvlay 29

3.28
2.20
1.57
1.21
0.71
0.51
0.29
0.37
0.58
0.23

0.87
3. 81
9.75
14.70
15.00
19.00
16.60
28.60
23.40
16.80

June 2

June 12

June 22

July 2

July 12

July 22

Aug. 1

Aug. 11

Aug. 21

Aug. 31

Sept. 10

Sept. 20

Sept 30

3.65
2.78
1.76
1.26
1.48
0.54
0.65
0.63
0.56
0.39
0.61
0.66
0.47

1.12

June 8

June 18

5.76
11.40

June 28

19.70

July 8

July 18

52.20
34.20

July 28

56.00

Aug. 7

Aug. 17

Aug. 27

73.60
59.20
62.40
91.20
114.00
86.40

An examination of the graphic presentation in Fig. 13 of the increase in the
absolute nitrogen content of apples and pears shows that the increase is rapid

\

/

/

\

/

r^

^^^

^'

/^

f

,^-

*^

/;

l^

■r=-=^

\

y^

^

/

^

"^^^

p=

\

J

u

■f-'^

2&

6 15 25 5 15 25 4- 14 24- 3 13 23 3
May June July Aug. Sept. Oct.

Fig. 13. — Grama of nitrogen in one thou.sand fruits of the apple shown by broken lines
and of pears shown by continuous lines. (Plotted from data given by Pfeiffer.'^')

at first, that in August there is little or no change and that in September in two of
the apple varieties, there is a second period of increase. These periods of increas-

INDI VI D UAL ELEMENTS

137

ing nitrogen content correspond to those seasons when temperature and moisture
conditions are such as to favor nitrification in the soil.

The percentage nitrogen content of j^oung fruit is very high. So also is that
of the seed, to which in fact the nitrogen content of the young fruit is in large
part due. In terms of drj' weight, the nitrogen content of apple seeds has been
found to be 3.17 per cent.; of almonds 4 per cent.; of coffee {Coffeo arabica) beans
1.96 per cent.; and of cocoanuts 1.65 per cent.^*

In Various Tissues of Trees of Different Age. — A studj' of the nitrogen content
of trees of various ages will round out the picture of nitrogen distribution.

Table 21 shows the percentages of nitrogen in the leaves, new growth, trunk,
roots and fruit of apple trees of ages ranging from 1 to 100. Since the material
was collected from various sources, the analyses are not strictly comparable,
though they are suggestive.

Table 21. — Analyses of Apple Trees
(1 to 9 from Thompson,^^^ 13 and 100 from Roberts,^^' 30 from Van Slyke i*")
A Nitrogen in percentage of dry weight. B Absolute amounts of nitrogen in
gram.s.

Age

Leaves

New gi-owth

Trunks and
branches

Roots

Fruit

A

B

A

B

A

B

A

B

A

B

1

1.71

0.44

0.30

0.29

0.39

0.20

2

2.09

1.51

0.57

1.36

0.88

1.14

3

2.36

2.08

0.52

4.00

0.73

3.29

4

1.66

2.24

0.45

6.35

0.59

2.99

5

1.76

7.84

0.89

1.93

0.48

17.20

0.64

9.85

6

1.74

10.50

0.94

2.41

0.39

16.60

0.62

17.70

....

7

1.45

13.60

0.84

3.66

0.45

30.55

0.64

26.10

0.35

4.34

8

1.74

41.00

0.93

6.06

0.36

45.30

0.62

47.70

0.43

5.93

9

1.70

61.50

0.82

9.08

0.35

85.50

0.58

81.00

0.31

10.55

13

1.85
2.09
1.04

131.50
394 . 00
435.00

30

0.95
1.04

13.60
390.00

0.31

258 00

100

0.27

2863.00

0.22

417.00

These figures show that the young tree is specially rich in nitrogen. The
roots have a higher percentage content than the trunk, but a lower content than
the new growth. The percentage nitrogen content of both roots and trunk falls
to a very low level in the 100-year old tree, due to the great preponderance of
woody tissue. That of the leaves was estimated from samples collected in the
fall and consequently is probably too low, except in the case of the 100-j^ear old
tree, where the sample was taken in July.

The most striking observation to be made concerns the large proportion of
the total nitrogen of the plant that is in the leaves, roughly about one-fourth in
trees up to 9 years of age. Since these figures represent the amounts at leaf fall,
even larger amounts must be present in the leaves during the summer.

138

FUNDAMENTALS OF FRUIT PRODUCTION

From the data available it is impossible to say how much of the nitrogen of
the trunk is stored and how much is a permanent part of its tissues. Hence any
attempt to calculate the amount taken up yearly from the soil would be guess-
work. However, it is interesting that in a 30-year old tree, two-thirds as much
nitrogen goes into the crop as falls with the leaves and the amount used for new
growth is insignificant in comparison.

Similar relationships hold for fruits other than the apple as Table 22 shows.

Table

-Pounds of Nitrogen in Parts of a Full Grown Tree'^"

Apple

Peach

Pear

Plum Quince

Fruit or fruit pulp

Stones

Stems

Leaves

New growth

0.57

0.12

0.08

0.08

0.03

....

0.02
0.01

0.87

0.52

0.15

0.12

0.03

0.05

0.02

0.02

0.09

0.09
0.01

The data presented in Table 23 show the nitrogen contents of various fruits.

Table 23

Almonds

Apricots 1 . 94

Apples 1 . 05

Bananas 0.97

Cherries 2.29

Chestnuts 6.40

Figs 2.38

Grapes 1.26

Pounds of Nitrogen in 1,000 Pounds of Fresh Fruit^^

7.01 Lemons 1.51

Olives 5.60

Oranges 1 . 83

Peaches 1.20

Pears 0.90

French primes 1 . 82

Plums 1.81

Walnuts 5.41

PHOSPHORUS

It has been pointed out that the nitrates absorbed by the roots
probably are carried to the leaves and there elaborated into organic nitro-
gen-containing compounds. Though there is no direct evidence to show
where the elaboration of inorganic phosphates to organic phosphorus-
containing compounds takes place, the remarkable similiarity that exists
between the variations in nitrogen and in phosphorus content of practi-
cally all tissues, suggests that phosphorus, like nitrogen, is elaborated for
the most part in the leaf.

Synthesis of Phosphorus-containing Organic Compounds. — The
amount of phosphorus assimilated is stated to be closely related to the
amount of illumination ^^^ the plant receives and appears to be connected
with photosynthetic activity. Red and yellow light have been found
more effective than blue or violet in promoting phosphorus assimilation. ^^^

Wherever phosphorus is found in organic combination it exists as
phosphate. Thus it occurs in nucleic acids, nucleins and nucleo-proteins

INDIVIDUAL ELEMENTS

139

— substances always present in the cell nucleus — in lecithins, in hexose
phosphoric acid which is essential to zymase activity in yeast and prob-
ably to the activity of similar enzymes in all plant tissues. The globoid
in aleurone grains is composed of calcium-magnesium phosphate. /

Translocation and Use of Phosphorus-containing Compounds. — The
distribution of phosphorus in the fruit tree is very similar to that of
nitrogen. Young tissue is richer in phosphorus than older tissue, young
leaves and young bark being particularly rich in this element and much
the same relations hold in regard to elaboration, storage and utilization
of phosphorus as with nitrogen. Most tissues contain approximately
six times as much nitrogen as phosphorus. This holds roughly for
trunk and branches, new growth, buds and young leaves. The older
leaves have less phosphorus, the fruit and the apple spur more. The
general constancy of the phosphorus-nitrogen ratio indicates that the
two elements may be combined in the same molecule. Nucleins, nucleo-
proteins and lecithin contain both elements and are of universal occur-
rence in all living plant tissues. Table 24 shows the relative amounts of
the various types of organic phosphorus in developing grape seeds. The
bulk is nuclein phosphorus and should this be the case in most plant
tissues the relative constancy of the nitrogen-phosphorus ratio would
be explained.

Table 24.

-The Phosphorus Content of Grape Seeds''
(In percentages of fresh weight)

Hard, Sept. 6

Softening, Sept.
30

Ripe, Oct. 30

Lecithin P. . . .
Nuclein P. . . .
HCl-soluble P

0.0017
0.0159
0.0019

o.oinr,

o.oois

0.0184
0.0016

0.0218

0.0021
0.0197
0.0016

0.0234

Nevertheless distinct differences exist between the variations in the
nitrogen and in the phosphorus content of the same tissue and these
show that phosphorus compounds do not play the same part in plant
metabolism as nitrogen compounds.

If organic phosphorus-containing compounds are built up chiefly in
the leaves, they pass out of the leaves as fast as they are made and are
used by the developing fruit and in the growth of vegetative tissues.
Before the leaves fall, a considerable amount of their phosphorus is
withdrawn and stored in the phloem. The phosphorus used in the first
stages of growth in the spring and in the initiation of fruit development is
obtained from stored compounds.

140

FUNDAMENTALS OF FRUIT PRODUCTION

Amounts Used in Fruit Production. — In general the tree may be said
to require relatively large amounts of phosphorus for fruit production,
much larger than for mere vegetative growth. However, analyses would
indicate that the total amount required by the trees for the development
of their fruits and of their new vegetative tissue would not be more than
8 pounds per acre in a peach orchard yielding at the rate of 300 bushels;
the total phosphorus draft of most other deciduous fruits is not materially
greater. Considering the limited amounts of phosphorus used by decidu-
ous fruit trees, and the comparatively large amounts present in nearly
all soils as well as the supply in the subsoil available to deep-rooted trees,
it is evident that under average orchard conditions phosphorus is not
likely to be a limiting factor and that phosphorus fertilization is likely
to be of little direct use in assisting tree growth or in promoting fruit
production. On the other hand it may be of great value in promoting
the growth of grasses, legumes or other crops grown between the trees
for mulching or other purposes. This subject is discussed in some detail
under the heading of indirect methods of fertilization.

Seasonal Distribution of Phosphorus. — There is a close similarity
between the seasonal distribution of phosphorus and nitrogen in many
parts of the fruit tree.

0.5

0.3

\

1

1
1

^s

\

1
1
1

1

1

Fig. 14.

-Phosphorus content of plum leaves in percentages of dry weight. (Plotted
from data given by Richter.i^*)

In Leaves. — Though leaf buds have a slightly higher percentage nitrogen
content than fruit buds, they have a sKghtly lower percentage of phosphorus.
The phosphorus content of the former has been found to be 0.576 per cent, of the
dry weight in the cherry and 0.594 per cent, in the plum; of the latter, 0.570
per cent, in the cherry and 0.592 per cent, in the plum.'^*

The young leaf has about the same high percentage of phosphorus as the bud,
but this decreases rapidly with age as does the nitrogen, there being two periods
of rapid decUne, one in May, the other in September (see Table 25 and Figure 14).
The ratio of phosphorus to nitrogen in the young leaf is 1 : 6. Before leaf fall
it is 1 : 10 or 1 : 15. This indicates that the plant uses its phosphorus supply

INDIVIDUAL ELEMENTS

141

more thoroughly than its nitrogen, withdrawing it more completely from tissues
that are exfoliated and either using it immediately in tissue building or storing it.

Table 25. — The Phosphorus Content of Leaves^^*
(In percentages of dry weight)

Apple

May 9, 14, 18

June 22

Aug. 29

Sept. 30, Oct. 2, 15

0.566
0.245
0.207
0.126

Pear

0.595
0.181
0.177
0.069

Cherry

0.602
0.302
0.329
0.273

Plum

0.510
0.305
0.289
0.197

The absolute amounts of phosphorus in leaves of various ages are shown in
Table 26. As with nitrogen, the total amount of phosphorus in the leaf is low at
first, despite the high percentage, becau.se of the small size of the leaf. It then
increases as the leaf grows, reaches a maximum and finally decUnes, the dechne,
however, coming only a short time before abscission.

T.\BLE 26. — Grams of Phosphorus in 100 Le.wes'^*

Apple

Pear

Cherry

Plum

July 14

July 31

Aug. 18, 21

Sept. 3, 4, 6

Oct. 23, 27, 29, Nov. 4.

0.036
0.043
0.034
0.034

0.072
0.069
0.068
0.061
0.061

0.054
0.049
0.049
0.044

In the work from which this table is computed the possibihty of loss of nutri-
ent elements by cUmatic agencies was considered. Le Clerc and Breazeale'*^
caUed attention to the possibility that plant tissue may lose considerable amounts
of mineral constituents through the dissolving action of rain. In this way
apple leaves attached to the branches lost 3 per cent, of their nitrogen,
25 per cent, of their phosphorus, 18 per cent, of their potash. and 6 per cent, of
their Ume simply by washing in water. This indicates that considerable amounts
of soluble substances exuded from the surface may be washed off the leaves during
the period between the formation of the abscission layer and the time of actual
leaf fall.

In Branches, Trunk and Roots. — The percentage of phosphoric acid (P2O5) in
the ash of sap-wood is usually higher than in bark ash; for example, in the pear it
has been recorded as 12.62 per cent, in the sap-wood, as 2.98 per cent, in the bark
and in the grape 7.625 per cent, in the sap-wood and 4.705 per cent, in the bark.«*

This does not mean, however, that the bark contains less phosphorus than the
sap-wood, for as has been pointed out, the total ash content of wood and
especially sap-wood is much less than that of bark. The figures indicate that
though the sap-wood contains relatively large percentages of phosphoric acid, in
the pear and grape at least the bark contains larger absolute amounts.

142

FUNDAMENTALS OF FRUIT PRODUCTION

Table 27.-

-The Phosphorus Content of a 7-year Old Apple Tree^^
(Expressed in percentages of dry weight)

Dormant,

Dec. 3,

1914

Buds
swelling,
April 20,

1915

In bloom.

May 18,

1915

Growth
over, July
12, 1915

Leaves

faUing,

Oct. 12,

1915

Summer's growth

1-year old branches

2-year old branches

3-year old branches

4-year old branches

5-year old branches

Trunk

Large roots

0.14
0.11
0.08
0.07
0.05
0.04
0.10
0.16

0.16
0.11
0.10
0.07
0.06
0.06
0.12
0.17

0.10
0.07
0.06
0.05
0.04
0.04
0.09
0.14

0.14
0.10
0.08
0.07
0.06
0.05
0.06
0.11
0,14

0.13
0.10
0.08
0.07
0.06
0.05
0.06
0.12
0.17

Phosphorus, like nitrogen, is present in greatest amounts in the younger
roots and branches and is at a maximum in nearly all tissues when the buds are
swelling (see Table 27). The chief difference between phosphorus and nitrogen

035

0.30

o.es

0.20

0.15

0.10

/

\

/

\

/

IV

\

J

^

^

<^

X,

\\

i^^

^

N.

J

^3-

\

h>

v.

\N

^

Ji

^

\

/

>^

!S

^^

,.

-^

y.

^

>5

\

\
\

'/

N

-^

J

^-

^^

J

Bv

\

V;

U

■*-

----

-^

r-*

.

--■

\

\

7

y

-'"

\

V

Fig. 15. — Phosphorus content of apple spurs in percentages of dry weight; bearing
spurs represented by continuous lines, non-bearing spurs by broken lines and barren spurs
by dot-dash lines. {.After Hooker y^'^)

is that phosphorus reaches a minimum in most tissues in May when the tree is
in bloom, while nitrogen does not reach a minimum until July when active growth
is over. In all woody tissues there is an accumulation of phosphorus, as of nitro-
gen, in the fall, indicating storage.

In Spurs. — Figure 15 shows the seasonal variations in the phosphorus content
of apple spurs. 100 In non-bearing and in barren spurs, the variations are similar
to those in other woody tissues, with a minimum in May. However, in June

INDIVIDUAL ELEMENTS

143

during the period of fruit bud differentiation there is a marked increase which is
particularly pronounced in spurs differentiating fruit buds. Phosphorus accu-
mulation in the fall is well marked, especially in productive spurs.

In bearing spurs there is a considerable increase in phosphorus during
blossoming, indicating that these organs draw upon a supply of stored phos-
phorus, which may be assumed, by analogy with nitrogen, to be in the bark.
Moreover, the phosphorus content of bark is at a maximum in the spring.

In Fruit. — As soon as the fruit begins to develop, the phosphorus content
of the bearing spur decreases. At this time the spur probably is supplying the
young fruit with phosphorus, which accumulates, to a considerable extent, in
fruits and seeds. This increase is illustrated by the figures in Table 28 showing
the amounts in ripening grapes.

Table 28. — Grams of Phosphorus in 1,000 Berries of the Grape*'*

July 27 0.169 Sept. 17 0.434

Aug. 9 0.315 Sept. 28 0.550

Aug. 17 0.262 Oct. 5 0.619

Aug. 28 0.206 Softening Oct. 12 0.455 Fully ripe

Sept. 7 0.373 Oct. 22 0.320 Rotten

In Various Tissues of Trees- of Different Ages. — The percentages and absolute
amounts of phosphorus in the tissues of apple trees of various ages is shown in
Table 29. In general the new growth and the leaves, even at the time of leaf
fall, are richest in phosphorus, the fruit next, then the roots; the trunk and older
branches have the least.

Table 29. — Phosphorus Content of Apple Trees of Various Ages
(1 lo 9 computed from Thompson,^^^ 13 and 100 from Roherts,^^'' 30 from Van Slyke^^°)

Leaves

New Growth

Trunk and
branches

Roots

Fruits

Age

Per cent.

Per cent.

Per cent.

Per cent.

Per cent.

dry

Grams

dry

Grams

dry

Grams

dry

Grams

dry

Grams

weight

weight

weight

weight

weight

1

0.12

0.03

0.03

0.03

0.03

0.02

2

0.13

0.10

0.07

0.17

0.10

0.13

3

0.14

0.13

0.07

0.50

0.11

0.47

4

0.10

0.13

0.06

0.80

0.06

0.31

5

0.11

0..51

0.11

0.24

0.05

1.96

0.06

1.00

6

0.10

0.63

0.13

0.34

0.04

1.85

0.07

1.99

7

0.10

0.90

0.11

0.47

0.06

4.14

0.06

2.48

0.08

1.03

8

0.11

2.68

0.13

0.82

0.05

6.03

0.07

5.33

0.08

1.44

9

0.15

5.33

0.15

1.64

0.08

19.15

0.09

12.62

0.07

2.38

13

0.21

15.83

30

0.13

27.70

0.13

2.00

0.6

49.00

100

0.17

73.20

0.16

61.40

0.04

705.00

0.04

83.00

Of particular interest is the comparison of the absolute amounts of phosphorus
in the fruit and leaves with the nitrogen content of these tissues. In a 30-year
old tree in full bearing more phosphorus is lost with the crop of fruit than falls
with the leaves, even if it be assumed that 25 per cent, of the original amount was

144

FUNDAMENTALS OF FRUIT PRODUCTION

removed by the dissolving action of rain. This is true of many fruit trees, as
Table 30 shows. ^^^ This relation does not hold for young trees just in bearing.
That more phosphorus is lost in the crop than with the leaves of mature trees
may be attributed to several factors. As has been emphasized, only one-tenth

Table 30. — Pounds of Phosphorus in Parts of a Full Grown Tree'^o

Apple

Peach

Pear

Quince

Plum

0.105

0.061
0.004

0.026
0.004
0.031
0.004

0.013

0,017

0.013

Stones

0.004

0.008 0.004

0.008

New growth

0.004

0 004

0.004

to one-fifteenth as much phosphorus as nitrogen is left in the leaf, but the fruit
contains one-fifth as much phosphorus as nitrogen. This in turn may be cor-
related with the finding that the phosphorus content of leaves on peach trees
in heavy bearing is less than that of the leaves on trees bearing a small crop.^*'^

Table 31. — Phosphorus Content of Peach Leaves in Bearing and Non-bearing

Years'"
(Percentage of dry weight)

First four years 0 . 30

Five years of bearing 0 . 24

1904 (no crop) 0.29

The data in Table 29 suggest that this may hold for the apple as well as the peach.
Table 32 gives the phosphorus content of various fruits in absolute amounts. It
is present in seeds in greater amounts.

Table 32. — Pounds of Phosphorus in 1,000 Pounds of Fresh Fruit^"

Almonds 0.45

Apricots 0 . 29

Apples 0.14

Bananas 0 . 07

Cherries 0.31

Chestnuts 0.52

Figs 0.38

Grapes 0.05

Lemons 0 . 25

Olives 0.55

Oranges 0.23

Peaches 0 . 37

Pears 0.15

French prunes 0.30

Plums 0.33

Walnuts 0.65

POTASSIUM

Though the history of potassium in a fruit tree like the apple is in
many respects similar to that of phosphorus, there are important
differences.

S3mthesis, Translocation and Use of Potassium-containing Com-
pounds.— It is not known where potassium is elaborated and there is no
evidence to show that the inorganic potassium taken from the soil by
the roots is combined in organic form in the leaves to any greater extent
than in any other part of the plant. In just what form of organic com-
bination potassium is necessary for the proper activity of the plant is also

INDIVIDUAL ELEMENTS 145

unknown. However, certain proteins crystallize as potassium salts;
sinigrin is myronate of potash. Complex salts of calcium, magnesium
and potassium are not uncommon. Gum arable contains a calcium-
magnesium-potassium salt of arable acid.

During the winter, potassium is stored in both the sap wood and bark
and in older branches than nitrogen or phosphorus. In the spring, it is
translocated and used in the development of new tissue, but preeminently
for fruit and then for leaves. Heavy crops reduce the potassium content
of the leaves and much more potassium goes into the fruit than is lost
with the leaves. In general wherever potassium is present in large
amounts as in seeds and in young tissue, calcium is present in small
quantities and wherever there Is a small amount of potassium, calcium Is
present in large amounts.

The Demand and the Supply. — In one way or another the idea has
gained credence that fruit trees make heavy demands on the soil for
potash and consequently that potash is one of the most necessary in-
gredients in fertilizers for orchards. Indeed, so firmly has this Idea
become estabUshed that " Fertilize trees with nitrogen for wood growth
and with potash for fruit production" is a time-honored recommendation
In the literature of fruit growing. It has also been a rather general
opinion that potash mainly is responsible for the red coloration of fruits
and that consequently potash-carrying fertilizers are especially desirable
for Improving color. That this last idea is erroneous is shown by the
results of many carefully conducted Investigations of recent years, in-
vestigations that are reported In more detail later in this section. The
data in this chapter afford some idea of the approximate amounts of
potash that are required for usual tree growth and production. Though
these are considerable in comparison with the amounts required by
many farm crops, the enormous quantities of this element found within
reach of tree roots in most soils make the application of potash-carrying
fertilizers seem of doubtful promise, at least so far as supplying the plant
with larger quantities of this element is concerned. This statement is
supported by numerous experiments In which potash in different forms
has been applied to orchard trees apparently without positive results,
and also by soil investigations like those of Hopkins and Aumer,i°^
showing that in 6 feet of soil covering an area of 1 square mile of the
Illinois corn belt there Is as much potash as is applied annually in fertil-
izers to all the farms of the United States. It is true that many orchard
soils are not so liberally supplied with potash as those of the Illinois corn
belt; nevertheless, so far as data are available, they indicate the presence
of quantities much in excess of probable requirements for many years,
if not for many generations. Beneficial results in greater vegetative
growth and Increased yields have been reported occasionally from the
application of potash-carrying fertilizers to orchard soils. The question

146

FUNDAMENTALS OF FRUIT PRODUCTION

m"ay be raised, whether this increase in growth or yield is not due to
indirect effects of the potash on some other factor, such as the availa-
bihty of phosphorus, or to the influence of other elements with which
potassium is combined in the fertilizer. This last suggestion receives
some support from the fact that in most cases when the muriate and
sulfate of potash have been used side by side, the sulfate has almost
invariably given a much more pronounced response than the muriate and
has often yielded positive results when the muriate has given entirely
negative results.

Seasonal Distribution of Potassium. — Rather marked differences between
potassium and the elements already considered, in translocation, storage and
utilization are shown by the seasonal changes in its distribution within the plant.

In Leaves. — Fruit buds are much richer than leaf buds in potassium con-
trasting with the condition presented by phosphorus.

The potash content of fruit buds has been found to be 2.290 per cent, of the
dry weight in the cherry and 2.344 per cent, in the plum, while that of leaf buds
was 1.961 per cent, in the cherry and 2.213 per cent, in the plum.^^'^

The variation in the percentage content of potash in leaves during the growing
season is illustrated by the figures in Table 33. As with phosphorus and nitrogen
the percentage of potassium decreases as the leaf grows older and the absolute
amount present in the leaf passes through a maximum, as Table 34 shows.

Table
(Ir

33. — Potash Content of Leaves
I percentage of dry weight'"'^)

Apple

Pear

Cherry

May 9

May 14

3.150

1.886
1.927

1.601

2.460

1.690
1.770
1 . 320

3 006

June 22

2 782

Aug. 29

Oct. 2

Oct. 15

2.637

3 . 080

However, the decrease in the potash content of leaves during the fall is slight
in all fruits for which data are available and there is no decrease in the pear. The

Table 34. — Grams of Potash in 100 Leaves '^^

Plum

INDIVIDUAL ELEMENTS 147

marked difference in this respect between potassium and phosphorus or nitrogen
suggests a corresponding difference in their utihzation by the plant. Possibly
the elaboration of potassium is not localized in the leaf.

Though the amounts of potassium removed from the leaves before they fall
seem small in comparison with phosphorus, there is none the less evidence of
potassium storage in the branches. Table 35 gives data showing the withdrawal
of potash from the leaves into the branches.

Table 35. — Grams of Potash in 100 Branches of the Horse-chestnut and
Their Leaves*

Branches Leaves

July 29 1.763

Sept. 11 2.249

Oct. 14 2.575

Nov. 16 I 2.671

18.876
14 . 236
13.400

In Branches, Roots and Trunks. — The leaves lose more potassium than can be
accounted for by the gain in the branches on which they were borne, indicating
that considerable amounts of potash are washed from the leaves by rain. The
relative amounts of potash in the ash of sap-wood and bark resemble those of
phosphorus. In one series of determinations the ash of the sap-wood of the pear
was 22.25 per cent, potash, of the bark 6.2 per cent.; the sap-wood ash of the
apple was 16.19 per cent, potash, the bark ash 4.93 per cent, and the sap-wood
ash of the grape was 20.84 per cent, potash, the bark ash 1.77 per cent.^^ In
the sap-wood ash there is more potash than any other element except calcium ; in
the bark the potash content is lower and the calcium content higher, but the
absolute amount in the bark is probably greater than in the sap-wood on account
of the bark's higher ash content, as has been pointed out in the discussion of
phosphorus.

Table 36, showing seasonal variations in the potash content of the root, trunk
and branches of a 7-year old apple tree, gives additional evidence of the storage
of potassium in the branches.

Apparently potassium is stored in old branches to a relatively greater extent
than nitrogen or phosphorus, for in the 3-, 4- and 5-year old branches the potash
content reaches a minimum in May though the 1- and 2-year old branches have a
high content at that time and do not reach a minimum until later. The young
roots and branches are richer in potassium, as in phosphorus and nitrogen, than
the older parts of the tree.

Potassium probably is stored in both bark and sap-wood. The layers of
bark nearest the cambium are richest in this element. Furthermore, the young
bark of the oak, horse-chestnut and walnut contains more potash in percentage
of total ash at the time of greatest vegetative activity in the spring than later in
the season. ^2 Similar seasonal differences oc(iur in the potash content of the sap-
wood of these trees, while the heart-wood not only contains considerably less but
its content is subject to much smaller fluctuations." Weber^^^ found that in
beeches producing many seeds, the sap-wood was particularly rich in potash

148

FUNDAMENTALS OF FRUIT PRODUCTION

Table 36. — The Potash Content of a 7-year Old Apple Tree
(Expressed in percentages of dry weight")

Dormant,
Dec. 3

Buds
swelling,
Apr. 20

In bloom.
May 18

Growth

over,
July 12

Leaves
falling,
Oct. 12

Summer's growth

1-year old branches

2-year old branches

3-year old branches

4-year old branches

5-year old branches

Trunk

0.46
0.33
0.30
0.24
0.20
0.15
0.42
0 57

....
0.49
0.33
0.27
0.25
0.22
0.21
0.40
0.45

0.62
0.39
0.28
0.20
0.17
0.20
0.39
0.45

1.03
0.52
0.33
0.31
0.25
0.20
0.18
0.43
0.54

0.60
0.47
0.40
0.33
0.29
0.28
0.25

Large roots

0.40
0.65

while the phosphorus content was not materially greater than in trees bearing
few seeds. Warren^^'' found that in peach, apple, plum and pear trees the ash of
the leaves contained less potash in years when the crop was large (see Table 37).

Table 37. — The Potash Content op Peach Leaves in Bearing and Non-bearing

Years'"

In percentages of
dry matter

In percentages of
total ash

First four years

Five bearing years

1904 (no crop)

2.12
1.42
1.80

17.7
11.2
15.8

This suggests that fruit trees usually take up more potassium from the soil than
is actually required, when they are not bearing fruit.

2: 5:

Fig. 16. — Potassium content of apple spurs in percentages of dry weight; bearing
spurs represented by continuous lines, non-bearing spurs by broken lines and barren spurs
by dot-dash lines. (After Hooker.'^°°)

hi Spurs.— Figure 16 shows that the potassium content of bearing spurs rises
to a very high maximum in May. This increment passes into the fruit and the

INDIVIDUAL ELEMENTS

. 149

potassium content of the spur falls to a minimum in September. The low figure
for barren spurs throughout the year is noteworthy, as is also the increase in the
potassium content of spurs in the off year at the time when fruit buds are being
differentiated (June).

In Fruit. — The data in Table 38 illustrate the increase in i-)otash content
accompanying fruit development.

Table 38
July 27

-Grams of Potash in 1,000 Berries of the Grape'

J . 875

Aug. 9 2.306

Aug. 17 2.490

Aug. 28 (softening) 2 . 194

Sept. 7 4.288

Sept. 17 4..824

Sept. 28 5.588

Oct. 5 6.179

Oct. 12 (fully ripe) 4.924

Oct. 22 (rotted) 4.317

The leaves, fruit and seeds are the parts richest in potassium (see Table 40).
In most edible fruits potash comprises 30 to 60 per cent, of the total ash and the
absolute amounts shown in Table 39 are very considerable.

Table 39. — Pounds of Potash in 1,000 Pounds of F'resh Fruit^^

Almonds 9 . 95

Apricots 3 . 01

Apples 1 . 40

Bananas 6 . 80

Cherries 2.77

Chestnuts 3.67

Figs 4.69

Grapes 2.55

Lemons 2 . 54

Olives 9.11

Oranges 2.11

Peaches 3 .94

Pears 1.34

French prunes 3. 10

Plums 3.41

Walnuts 8.18

The potash content of seeds is about the same as that of fruits, being usually
20 to 50 or even 60 per cent, of the total ash.^^

Table 40. — Potash Content of Apple Trees of Various Ages
(1 to 9 from Thompson,^^^ 13 and 100 from Roheris,^^'' 30 from Van Slyke^^'^)

A

Percentage of dry weight. B Grams

Leaves

New growth

Trunk and

Roots

Fruit

Age

A

B

A

B

A

B

A

B

A

B

1

1.25

0.33

0.21

0.20

0.30

0.18

2

1.22

0.88

0.34

0.81

0.55

0.71

3

1.35

1.22

0.30

2.31

0.53

2.39

4

1.13

1.53

0.31

4.37

0.48

2.43

5

1.65

7.79

0.72

1.56

0.47

16.84

0.57

9.34

6

1.00

6.04

0.61

1.56

0.35

14.87

0.50

16.30

....

7

1.24

11.64

0.55

2.40

0.36

24.45

0.46

18.70

1.12

13.87

8

1.42

33.50

0.64

4.17

0.31

39.00

0.48

36.95

1.20

16.56

9

2.08

75.20

0.61

6.76

0.33

80.60

0.49

68.40

1.17

39.83

13

1.76

127.00

30

0.59

122.00

0.60

9.00

0.70

589.00

100

1.43

598. 00

0.80

4.00

0.41 2697.00. 0.22

t 1

417.00

....

150

FUNDAMENTALS OF FRUIT PRODUCTION

In Various Tissues of Trees of Different Age. — Table 40 shows the variations
with age in the several parts of apple trees. It is noteworthy in connection
with what has been said of the relations of potash content to bearing that the
30-year old trees have the lowest percentage of potash in the leaves. These trees
were in full bearing as reference to the last column of the table shows. Further-
more, there is no reduction in the percentage of potash in the leaves of the 100-
year old tree which had ceased bearing.

The leaves of a tree in full bearing contain much less potassium when they
fall than its fruit. This is true of potassium' even to a greater degree than of
phosphorus, as Table 41 shows.

Table 41. — Pounds op Potash in Parts of a Full Grown Treei'"

Apple

Peach

Pear

Plum

Quince

Fruit or fruit pulp

Stones

1.28

0.27
0.02

0.29
0.01

0.27
0.03

0.16

0.09
0.02

0.14
0.01
0.01
0.15
0.01

0.19

Otems

Leaves

0.04

0.01

SULPHUR

Data are not available to present a picture of what happens to sulphur
in the fruit tree as has been attempted with nitrogen, phosphorus and
potash. The inorganic sulphate taken from the soil is incorporated into
organic compounds as both sulphate and sulphide sulphur. As sulphate,
it occurs in some of the mustard oils, such as sinigrin; as sulphide, it
occurs in cystin, one of the amino-acids used in the construction of most
proteins.

Because considerable amounts of sulphur are lost in ashing, deter-
minations of the sulphur content of ash are of little value. There are
indications that plants contain as much or more sulpKur than phosphorus,
but satisfactory analyses are yet to be made.

The data in Table 42 are representative of a few reliable analyses of
sulphur in fruit plants. They show that fruit contains approximately as
much sulphur as phosphorus.

Table 42. — Pounds op Sulphur in 1,000 Pounds of Fresh Fruits'"^

Apples 0.43

Raspberries 0 . 35

Gooseberries 0.12

Dewberries 0.37

Cherries 1.08

Red currants 0 . 56

Blackberries 0.40

Grapefruit 0 . 20

Peach pulp 0.14

Oranges 0 . 26

Lemons 0 . 22

Limes 0 . 47

Pineapple 0 . 39

Sulphur has been thought generally to be present in most soils in
amounts sufficient to meet the requirements of crop plants and recent

INDIVIDUAL ELEMENTS 151

investigations would indicate that this condition holds for a great many
soils. Thus the sulphur content of Illinois soils has been reported as
ranging from 280 to 750 pounds per acre in the top %% inches. ^^'^ Since
the average growing crop removes only 4 to 10 pounds of this element per
acre and losses through seepage arc likely to be nearly offset by additions
through rainfall, it would appear that the application of sulphur as fer-
tilizer to such soils does not offer much promise of increased crop returns.
However alfalfa removes 40 pounds per acre per year and cabbage nearly
as much. Moreover there are many soils not so well supplied with
sulphur and Shull^^^ is authority for the statement that "the normal
sulphur content of soils is sufficient for from 15 to 70 crops, provided
there are no additions from outside sources as from rainfall. Even if we
count in the rainfall sulphur, it is probable that sulphur is just as often a
limiting factor as is phosphorus, or nitrogen, or potassium." The soils
poor in sulphur and applications of compounds containing this element
of the Rogue River valley in southern Oregon have been found very
have greatly increased jdelds of leguminous crops. ^^^ In some instances
these increases have amounted to 500 to 1,000 per cent. Without doubt
these conditions are very exceptional; nevertheless the results suggest
that sulphur may be a much more important Hmiting factor in soil pro-
ductivity than has been considered generally. Recent investigations
indicate that sulphates have a special influence on root development.^^
This is particularly marked with red clover and rape, where sulphate
applications resulted in root elongation and consequently in an extension
of the feeding area and a greater ability to withstand drought. Little is
known regarding the direct effect of sulphur-carrying fertilizers on
deciduous fruits. However, the application of 178 pounds of sulphur per
acre to certain vineyard soils has resulted in increases in yield of 19.2 to
32.7 per cent, and in increases of 25.03 to 27.3 per cent, when applied with
14 tons of stable manure.-^ Though no direct influence of sulphur-
carrying fertilizers upon tree growth or production was reported in the
Rogue River valley experiments the crops so greatly benefited by their
application were those commonly grown as intercrops and cover crops in
the orchard. Through them the trees might be greatly benefited in
later years.

These facts taken with the lack of data on the distribution of sulphur
in plants accentuate the importance of more analytical and experimental
work on this element. Sulphur has been neglected because it was
thought to occur in relatively small amounts, but the small amounts
found were due to faulty methods of analysis and sulphur is just as
essential to plants and as worthy of consideration as phosphorus.

IRON

Iron occurs in plants in even smaller amounts than sulphur. It is
found in organic combination in some nucleic acids. ^"^^

152 FUNDAMENTALS OF FRUIT PRODUCTION

Iron usually constitutes 1 to 4 per cent, of the leaf ash. Grape leaves have
been known to have an exceptionally high figure, 10.20 per cent." The absolute
iron content of leaves increases with age, though the percentage composition of
the leaf remains fairly constant.

Table 43. — Iron Oxide Content of Beech Leaves"^
(In percentage of total ash)

May 16 0.8

July 18 1.4

Oct. 15 1.3

The ash of bark ranges from 0.2 to 3 per cent, of iron, the amount often
increasing with age; for example 0.2 per cent, has been found in the apple and
2.545 per cent, in the grape.^^^ Wood ash has but little iron, usually from 0.1 to
0.8 per cent. — 0.16 per cent, in the pear, 0.42 per cent, in the apple and 0.635 per
cent, in the grape.*^^ Exceptionally high figures have been found in the olive,
2.11 per cent, of the ash, and in the orange, 3.08 per cent.*"

Table 44. — The Iron Oxide Content of Fruits*'* and Seeds^*

(In percentages of total ash)

Fruits Seeds

Banana 1 . 46 Grape 0 . 37

Plum 2.54 Almond 0.55

Apple 1 . 40 Walnut 1 . 32

Pear 1.04 Coffee 0.65

Orange 0 . 46 Chestnut 0.14

Grape 1.04

Olive- .. . 0.72

Iron is a constituent of practically all soils; furthermore it is always
found in quantities sufficient for the requirements of crop plants. How-
ever, in many cases it is held in the soil in a form unavailable to the plant;
consequently the plants may suffer because of iron starvation. Refer-
ence has been made to this in connection with the discussion of soil
reaction and more is said regarding the disturbances caused by a lack of
iron under the heading of Surpluses and Deficiencies.

MAGNESIUM

The most important organic compound containing magnesium is
chlorophyll. This element also occurs in organic combination in salts of
arable acid and in the globoid of aleurone grains. Some proteins are
thought to contain magnesium. Anthocyan pigments are complex
compounds with salts of magnesium, calcium or other metals. *^^

The absolute amount of magnesia in leaves increases as they grow
older. Thus 500 leaves of Platanus were found to contain 0.24 gram
of magnesia on June 13, 0.85 gram at the end of August and 0.69 gram
at leaf fall, showing a slight decline. ^^ However, there is not much change
in the percentage of magnesia in the total ash. On May 16, in beech

INDIVIDUAL ELEMENTS

153

leaves it was found to be 4.36 per cent.; on July 18, 5.63 per cent, and
on Oct. 15, 4.12 per cent.^^^ The magnesium, like the iron content, keeps
pace with leaf development; this increase may be associated with the
chlorophyll content of the leaf. However, there is some evidence that
magnesium is withdrawn to the branches from the leaves late in the
season. There are also indications of magnesium storage in the sap-
wood, which is slightly richer in magnesium than the heart-wood. Dur-
ing the spring, there is more rnagnesium in the sap-wood than at other
times. Weber found that in beeches producing many seeds, the sap-wood
was especially rich in magnesia and potash, as compared with trees
bearing few seeds. ^^^ The sap-wood ash of the pear has been found to
contain 3 per cent, magnesia, of the grape 4.4 per cent, and of the apple
8.49 per cent.^^

The magnesia content of bark ash decreases with age. In young
bark it is 3 to 8 per cent., as in the leaves; in old bark 2 to 5 per cent.
Thus the magnesia of pear bark has been found to be 9.4 per cent, of the
ash, while in the apple bark it is 1.5 per cent, and in grape bark 0.8
per cent.^^ The sieve tubes sometimes contain magnesium phosphate;
this may be a form of storage.

As a rule fat-storing seeds are richer in magnesia than starchy or reserve-
cellulose seeds; in the almond, magnesia has been found to be 17.66 per cent, of
the ash, in the walnut 13.03 per cent., while in coffee {Coffea arabica) beans it is
9.69 per cent, and in chestnuts 7.47 per cent.^^

Table 45 shows that the leaves of fruit trees contain much more magnesium
than the fruit. In the apple the magnesia content of the fruit has been found to
be 0.10 per cent, of the dry weight; of the leaves 1.03 per cent, and of the new
growth 0.30 per cent.^">

T.\BLE 45. — Pounds of Magnesia in Parts of a Mature Tree'®"

Apple

Peach

Pear

Plum

Quince

Fruit or pulp

Stones

0.18

0.47
0.01

0.02
0.01

0.24
0.02

0.02

0.06
0.01

0.02

0.01
0.07
0.01

0.02

Stems

Leaves

N-nv growth

0.05
0.01

Table 46. — The Magnesia Content of Fruits*'
(In percentages of total ash)

Pineapple 9 . 79

Banana 9.21

Strawberry 2 . 93

Plum 4 . 69

Apple 8 . 75

Pear 5 . 22

Orange 8 . 06

Grape 2.61

Olive 0.18

154

FUNDAMENTALS OF FRUIT PRODUCTION

Though magnesium is necessary for plant growth, it is not required
in large quantities and so far as is known all soils contain sufficient amounts.
Certainly no data are available showing the necessity of fertilizing fruit
plantations with magnesium-carrying compounds.

CALCIUM

Calcium is for the most part absent from the growing points and from
embryonic tissues generally and it accumulates in all tissues with age.
This indicates that calcium is utilized in ways very different from the
other essential elements, a surmise substantiated by the fact that it is not
necessary for the growth of fungi.

It is found organically combined in calcium oxalate crystals, in
calcium peCtate of the middle lamella which holds adjoining cells together,
in salts of arable acid, in the globoid of aleurone grains and in the antho-
cyan pigments. It is prevalent also as calcium carbonate.

Seasonal Distribution of Calcium. — Calcium differs from the elements
previously discussed in its seasonal history in the tree. It has been
mentioned that where potassium is present in large amounts, calcium
is usually present in small amounts and vice versa.

In Buds and Leaves. — The calcium content of buds Is not great as compared
with that of other plant tissues. Leaf buds have more lime, but less potassium,
than fruit buds. In percentages of dry weight, the Ume content of leaf buds has
been found to be 1.364 per cent, in the cherry and 2.365 per cent, in the plum;
that of fruit buds was 1.113 per cent, in the cherry and 1.761 per cent, in the
plum.i^^ Very heavy deposits of calcium oxalate have been found in resting
fruit buds, the amount decreasing after growth begins. As leaves grow older
their percentage lime content increases, as Table 47 shows. The absolute lime
content increases also (cf. Table 48).

Table 47. — Lime Content of Leaves^^^
(In percentage' of dry weight)

Apple

Pear

Cherry

Plum

May 9.
May 14.
May 18.
June 22.
Aug. 29.
Sept. 30
Oct. 2..
Oct. 15.

1.186

2.166
2.762

3.723

0.754

1.977
3.147
3.473

1.511

2.699
3.987
4.558

1.025
3.512
4.591
5.696

INDIVIDUAL ELEMENTS

155

Table 48.— Grams of Lime in 100 Leaves^"

I

Apple

Pear

Cherry

Pium

Julv 14

0.894
0.966
1.191
1.010

0.793

0.396
0.445
0.475
0.515

0.335

0.727
0.791
0.892
0.939
1.100
0.765

0.738

July 31

Aug 18, 21

0.697
0.699

Sept. 3, 4, 6

Oct. 7

0.7.58

Oct. 23,27,29

Nov. 4

0.978

In most cases there is a reduction in the absohite calcium content before leaf fall,
probably because of the dissolving action of rain. The lime content of full
grown leaves is often very great, sometimes constituting 52.82 per cent, of the
ash of the olive, 54.33 per cent, of the ash of the apple, 56.83 per cent, of the ash
of the orange and 34 to 60.9 per cent, of the ash of the grape. ^^

The data in Table 49 showing the simultaneous changes in the calcium
content of leaves and branches indicate that there is no removal of calcium from
the leaves to the branches.

Table 49. — Grams of Lime in 100 Branches of Horse-chestnut and Their

Leaves^

Branches

Leaves

July 29.
Sept. 11
Oct. 14.
Nov. 16

4.274
6.549
5.938
5.804

27.292
39.785
51.201

In Bark and Wood. — Young bark contains considerable lime, about 40 per
cent, of the ash, chiefly in the form of calcium carbonate. It increases with age to
70 or 80 per cent, of the ash, sometimes reaching 95 per cent, in oak bark.^^
Pear bark ash has been found to contain 33.88 per cent. Ume, apple bark ash
51.84 per cent, and grape bark ash 42.05 per cent." The seasonal variation is
counter to that of potassium, there being proportionately less calcium in the
bark in the spring than at other times. For example, in the walnut, bark ash was
found to contain 8.37 per cent, calcium on May 31 and 70.08 per cent, on Aug.
27.^^ Calcium increases with age in the wood also and the heart-wood contains
progressively more than the sap-wood, as Table 50 shows.

In general 60 to 78 per cent, of wood ash is lime. In the orange it has been
known to rise to 68.88 per cent.^^ In the sap-wood there is less; in the pear
there has been found 27.39 per cent., in the apple 18.65 per cent, and in the grape
25.67 per cent.^'* In the heart-wood, the vessels and sometimes the tracheids,
wood fibers and parenchyma cells are filled with spherites of calcium carbonate.
The older the wood, the more calcium there is in its ash.

156

FUNDAMENTALS OF FRUIT PRODUCTION

Table 50. — Ash Content of He art- wood in a Red Beech ^o*
(In percentages of dry weight)

Rings

Ash

CaCOs

Ito 15

1.162

0.579

15 to 25

0.825

0.251

25 to 35

0.645

Trace

35 to 45

0.612

Trace

45 to 60

0.555

60 to 83

0.458

83 to 94 (sap-wood)

0.205

/?t Fruits. — In fruit trees, the calcium required by the crop is insignificant
compared with that lost with the leaves and sometimes it is less than that in
the new growth. This is shown in Table 51. In one set of determinations the

Table 51. — Pounds of Lime in Parts of a Full Grown TreeI'"'

Apple

Peach

Pear

Plum

Quince

Fruit or fruit pulp

Stones

Stems..'

Leaves

New growth

0.12

1.42
0.08

0.02
0.00

0.79
0.14

0.03

....
0.25
0.04

0.01
0.00
0.02
0.22
0.09

0.01

0.19
0 07

lime in apple leaves was 3.10 per cent, of their dry weight; in new growth 2.39
per cent, and in the fruit 0.06 per cent.'*" However, the lime content of fruits
is not inconsiderable (see Table 52).

Table 52. — Pounds of Lime in 1,000 Pounds of Fresh Fruit ^^

Almonds .

1 . 04 Lemons 1 . 55

Apricots 0.16

Apples 0.11

Bananas 0.10

Cherries 0 . 20

Chestnuts 1 . 20

Figs 0.85

Grapes 0 . 25

Olives 2.43

Oranges 0 . 97

Peaches 0.14

Pears 0.19

French prunes 0 . 22

Plums 0.25

Walnuts 1 . 55

According to Trabut, "a high lime content is a very favorable factor in grow-
ing olives for oil production, as olives produced in limestone regions are richer in
oil and the oil is of better quality than where the soils are deficient in
this component. "^"^

The Demand and the Supply. — In general it may be said that the
calcium requirements of fruit trees are insignificant compared with the
amounts usually available in the soil. For instance, it has been shown
that certain typical Illinois soils contain quantities sufficient in the sur-

INDIVIDUAL ELEMENTS 157

face layers to produce 5,000 to 55,000 heavy corn crops if the supply is not
replenished and if it becomes available gradually. ^'^^ All the chemical
analyses of fruit soils given in the chapter on Orchard Soils indicate that
the danger from calcium starvation in the orchard is very remote. In
all probabihty the amounts of calcium found in plant tissues are often
much in excess of their nutritive requirements. There is no doubt that
calcium is of use in the elimination of poisonous products of catabolism,
such as oxalic acid, but it seems not at all unlikely that in many cases the
oxalic acid is produced as a means of rendering a surplus of calcium
insoluble.

Many orchard fertilizer experiments have been conducted in which
lime has been used, either alone or in combination. The results attending
these experiments have been variable, but on the whole negative in
character. Certainly there is no clear evidence available to show that
liming the soil is of any direct benefit to the trees. It has been pointed
out that applications of lime may aid nitrification in the soil and may be
of use to other cultures that are being grown in the fruit plantation and
thus -indirectly to the trees; on the other hand, it has been shown also
that they may have a very deleterious influence on tree or vine growth and
these deleterious influences are of sufficiently frequent occurrence in
actual field practice to suggest caution. It may be recalled that the
purpose for which lime is generally used with field crops, namely the
correction of soil acidity, needs but little consideration in deciduous fruit
production.

OTHER MINERAL ELEMENTS

Beside the elements already discussed, there are others that are of
universal occurrence in plants, though they are generally considered to be
unessential. However, copper which occurs in very small amounts
in plant tissues is considered by Maquenne and Demoussey''^ to be an
essential element.

Silicon. — Silica is universally present, though the amount is very variable.
In leaves, for example, it may be present in mere traces or it may constitute 80
per cent, of the ash. In grape leaves amounts ranging from 1.61 per cent, to
39.44 per cent, have been found, the amount usually increasing with age.**
Table 53 illustrates this point.

T.VBLE 53. — Grams of Silica in 100 Branches of Horse-chestnut and Their

Leaves ^

Branches

Leaves

July 29

0.095
0.165
0.084
0.056

14.187

Sept. 11

18 812

Oct. 14

Nov. 16

18.195

158 FUNDAMENTALS OF FRUIT PRODUCTION

Bark ash usually contains less than 2 per cent, of sihca; for example, 0.4 per
cent, in the pear and 0.6 per cent, in the apple. ^* The ash of grape bark has been
shown to contain 14.3 per cent. siUca.^ Wood ash usually contains less than
3 per cent, of silica; for example, 0.3 per cent, has been recorded for pear wood,
1.65 per cent, for apple wood and 2.8 per cent, for grape wood.^'' The ash
of olive wood has been found to contain as much as 14.23 per cent, silica. ^^ As a
rule the heart- wood contains a higher percentage than the sap-wood.

Fruits contain silica in amounts shown in Table 54. The seed usually con-
tains less, as the same table shows, though a trace at least is always present.

Table 54. — The Silica Content of Fruits^'' and Seeds"

(In percentages of total ash)

Fruits Seeds

Pineapple 5 . 77 Chestnut 1 . 54

Banana 5.93 Grape 1 . 04

Fig 2.34 Coffee 0.54

Plum 3.15 Cocoanut 0 . 50

Apple 4.32 Walnut Trace

Pear 1.49

Orange 0 . 44

Grape 1 . 00

Olive 0.65

SiUcon usually is associated with the cell wall and sometimes confers strength
and stability on a plant tissue. However, the strongest and hardest of plant
materials are often of very nearly pure cellulose ; hence, a lack of silicon does not
necessarily involve mechanical weakness of mature tissues.

Sodium. — Sodium also is of universal occurrence in plant tissues. Leaves
usually contain 1 to 3 per cent. Table 55 indicates the seasonal variation in
absolute amounts in five hundred Plalanus leaves.

Table 55. — The Seasonal Variation in Soda Content of Platanus Leaves"
(Grams in 500 leaves)

June 13 0.3152 Oct. 8 0.2898

May 15 0.4187 Oct. 24 0.2439

Aug. 22 0.4299 Nov. 5 0.2273

Sept. 7 0.5641

Bark and wood ash usually contain but little soda, 3.495 per cent, having been
recorded in the ash of apple bark and 0.27 per cent, in that of grape bark.^^ The
wood of the sweet cherry has been known to contain as much as 10.13 per cent.^®
As a rule there is less soda in the ash of heart-wood than in that of sap-wood,
certain sap-wood records showing for the pear 1.84 per cent, soda; for the apple,
3.275 per cent, and for the grape, 2.06 per cent.«^ Fruits contain soda in the
widely varying amounts shown in Table 56.

Table 56. — The Soda Content of Fruits ^^
(In percentages of total ash)

Pineapple 6.75 Apple 26.09

Banana 26.27 Pear 8.52

Fig 19.63 Orange 13.47

Plum 9.05 Olive 7.53

INDIVIDUAL ELEMENTS 159

Seeds usually contain less than fruits, from 1 to 2 per cent., but walnuts have
been recorded as having 2.25 ])er cent., cocoanuts 8.39 per cent, and dates 9.03
per cent.^'

Though sodium is regarded as unessential for the growth of very many
plants, investigations with turnips, radishes, beets, cucumbers, buckwheat,
oats, potatoes and a number of other crop plants, indicate that this
element can partially replace potassium when the latter is not present in
amounts sufficient for good growth. ^^ "In the field, however, more
potassium was removed in the larger crops which usually resulted when
sodium was increased in connection with an insufficient amount of
potassium, and this was in spite of the fact that sodium frequently de-
creased the percentage of potassium in the crop. A portion of the bene-
fits arising from the use of sodium in the field is, therefore, attributable to
indirect action, but the solution work indicates that also direct beneficial
effects were probably obtained in the field. "^^

Probably this function of sodium is of little direct importance in the
deciduous fruit plantation, since it is very seldom that a lack of potassium
is a limiting factor; however, it is at least a matter of interest.

Chlorine. — Chlorine occurs in many plants, but seldom in large amounts except
in salt marsh plants. In leaves the amount varies from 25 per cent, of the total
ash to mere traces. The chlorine content of bark ash is low, certain records in
the pear showing 1.7 per cent., in the apple 0.33 per cent, and in the grape 0.4
per cent.^ The chlorine content of wood ash is even less, being 0.31 per cent, in
the pear, 0.255 per cent, in the apple and 0.02 per cent, in the grape. ^"^ The
chlorine content of fruits is more variable, but never very great.

Table 57. — The Chlorine Content of Fruits"
(In percentages of total ash)

Pineapple Trace Plum 0 . 38

Banana 2.69 Orange 2.35

Fig 0.83 Olive 0.16

Seeds usually have 0.5 to 1.5 per cent, of chlorine in the ash, but the amount
present varies greatly. Walnuts and almonds have mere traces. Other records
are: for chestnuts, 0.52 per cent, of the ash, for grape seeds, 0.27 per cent, and for
the cocoanut, which grows on the sea-shore, 13.42 per cent.^'*

There is no definite relation between the amount of sodium and the amount
of chlorine a tissue contains.

It would appear from the preceding statements that no benefit would
be derived from the chlorine in fertilizers carrying this element. Com-
mon salt has often been suggested as having possible value as a fertilizer
and has been tried in a limited way. So far as records are available they
indicate that it is of no value for deciduous or for most other fruit trees.
However, greatly increased yields of the mango have been reported in the
province of Bombay, India, from applying 10 pounds to the tree and

160 FUNDAMENTALS OF FRUIT PRODUCTION

likewise marked increases in yield from its application to cocoanuts.'^^
To what extent these increases were due to direct or indirect effects of the
sodium Or the direct or indirect effects of the chlorine is not known.

Alumintun and Manganese. — Manganese is a common constituent of the
bark, where it seldom exceeds 1 per cent, of the ash. The other parts of the
tree usually have less than the bark. Aluminum and manganese combined
average 0.5 to 0.9 per cent, of wood ash. Aluminum is not uncommon in seeds.
It sometimes comprises 0.062 per cent, of the ash of fig seeds and 0.138 per cent,
of the ash of almonds.'*^ Aluminum is capable of forming complex salts with
the anthocyan pigments." The color of the pigment depends on the base which
it contains, which accounts for the fact that the hydrangea {H. hortensis) develops
blue instead of pink flowers when soluble aluminum compounds are applied to
the soil in which it grows. "^

Summary. — Certain elements, especially nitrogen, phosphorus, potas-
sium and sulphur are present in greatest amount in young tissues. Cer-
tain amounts are stored in the bark over the winter and in the spring a
supply is on hand for the rapid development of leaves and shoots, flowers,
fruit and seeds. Since the seeds themselves are storage organs and in addi-
tion contain embryonic tissue, they accumulate these elements in relatively
large proportions. Magnesium and iron likewise are stored in the bark
and in the wood as well. They are utihzed in new growth, though they
appear to be more equally distributed in mature and in embryonic
tissues. All of these elements show more or less mobility and are trans-
located to regions where they are more in demand. The plant con-
serves its supply and withdraws at least a part of the amount contained
in the leaves, after they have ceased to function.

Calcium and silicon are very nearly absent from embryonic tissues.
They accumulate throughout the plant with age. There are no indica-
tions that these elements are stored for future use and to a great degree
they remain where they are deposited.

With respect to the other mineral elements found in plants, little
can be said in generalization. This is because no regularity has been
observed in the amounts present or in their seasonal variation.

CHAPTER IX

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES

. The essential elements discussed in the previous section are used
ultimately in the construction of the plant's substance. They are indis-
pensible because the plant cannot be constructed unless each one of
them is present.

ASSIMILATION AND LIMITING FACTORS DEFINED

The term assimilation, in its broadest sense, is used to describe the
process by which a plant builds up the substances that comprise it out of
compounds obtained from its environment. To be sure any compound
will not serve; certain specific materials are necessary. Assimilation
depends on a supply of such materials and on a source of energy. The
amount of assimilation and hence of growth is determined by the opera-
tion of the principle of limiting factors.

Most plants require at least seven elements in combined form from
the soil, namely, S, P, N, K, Fe, Mg and Ca. If «S, )8P, 7N, 5K,
eFe, rMg and 7?Ca combine exactly to produce a unit amount of growth
in some particular plant, say an apple tree, and if aS, 6P, cN, dK, eFe,
/Mg and gCa are present in a particular soil in available form, the maxi-
mum amount of apple tree tissue that can be grown in that soil will be
the smallest of the fractions a/a, h/^, c/y, d/8, e/e, //f, g/rj. That
element which gives the smallest fraction is the limiting factor of growth.®^

The principle of limiting factors applies not merely to nitrogen and the
essential mineral elements, but also to water, to carbon dioxide and to
oxygen which likewise are essential nutrients entering into the composi-
tion of the plant. Moreover the principle covers the effects of external
factors such as temperature and light which also may be limiting factors
of assimilation. All of these possible limiting factors of assimilation
and growth constitute the external stimuli to which the organism reacts
and these reactions tend to overcome the limiting factors of assimilation
and so bring the organism in the most favorable situation for assimila-
tion that circumstances permit. In consequence of the reactivity of
the plant and its apparent complete adjustment to its environment
the principle of limiting factors sometimes may seem not to be operative.
This, however, is not the case, for the principle of limiting factors is
always effective. The principle is generally recognized in the saying
that a chain is^no strenger than its weakest link and it is so universally
11 161

162 FUNDAMENTALS OF FRUIT PRODUCTION

applied in everyday life that it is taken as a matter of course and
consequently overlooked.

The principle of limiting factors is particularly important for an
understanding of the process of carbon assimilation and it has a direct
practical application in the use of fertihzers. These two subjects are
discussed in the following pages.

CARBON ASSIMILATION

The synthesis of organic compounds in plants depends on the assimi-
lation of an element which occurs in and is characteristic of all organic
compounds, namely, carbon. This element is provided by the carbon
dioxide of the air, which, together with water absorbed by the roots,
furnishes the materials for the synthesis of carbohydrates. These
compounds contain more potential energy than those from which they
are formed; this energy is supplied by the sun, whose radiant energy is
transformed into the potential energy of carbohydrates by means of the
green pigments of the leaf, the chlorophylls. The reaction or reactions
by which water and carbon dioxide in the presence of light and through
the agency of chlorophyll form carbohydrates and oxygen depend on two
other factors, namely, enzymes and temperature which affects the rate of
all chemical reactions.

Factors Involved

The rate of carbon assimilation depends on six factors:

1. The supply of carbon dioxide.

2. The supply of water.

3. The intensity, duration and quality of light.

4. The amount of chlorophyll.

5. Temperature.

6. The amount of enzymes.

Carbon Dioxide. — The carbon dioxide content of the atmosphere is
practically constant, varying little from 3 parts in each 10,000 of air.
Carbon dioxide enters the leaf mainly through the stomata, though the
epidermis with its cuticle is slightly permeable to it. Hence the diffu-
sion of carbon dioxide into the leaf depends on about the same factors as
the outward passage of water vapor, namely, the number of stomata, the
rate at which carbon dioxide is utilized within the leaf and the condition
of the air outside the leaf, whether it be moving or still.

The amount of carbon dioxide assimilated has been shown to depend
on the number of stomata on the upper and the lower surfaces of the leaf.
For example, Table 58 shows the relation in leaves illuminated on the
upper surface. In leaves with stomata confined to one surface the cor-
relation of assimilation to number of stomata holds, but with leaves
bearing stomata on both surfaces there is more intake of carbon dioxide

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 163

Table 58. — The Relation of Carbon Dioxide Assimilated to the Number of

Stomata in Leaves Illuminated on the Upper Surface

{After Brown and Escomhe--)

Stomatal ratio
Upper surface
Lower surface^

CO2 assimilated
Upper surface
Lower surface

100

0

0

100
100
119
100
269

100

Catalpa hignonioides

Colchiciini speciosum

0

0

100
100

Rutncx (ilpitius .

72
100

144

than might be expected from the number of stomata on the upper side.
This is because the leaves were ilhmiinated from above, resulting prob-
ably in a greater degree of opening of the stomata and a more rapid
utilization of carbon dioxide by this side of the leaf. Both of these
factors would favor a more rapid intake of carbon dioxide.

The large amount absorbed by a leaf during active assimilation
despite the low partial pressure of carbon dioxide in the atmosphere and
the small fraction of the leaf surface occupied by stomata is explained
by Brown and Escombe's law"^ which states that diffusion through a
perforated membrane is proportional to the diameter of the apertures and
not to their area. Because of the small size of the stomata, their great
number and their distribution over the surface, the amount of carbon
dioxide that theoretically could be taken in by the leaf under the most
favorable circumstances is much greater than any observed quantity
absorbed. Some idea of the amount used by leaves is given by an experi-
ment of Brown and Escombe^^ on the sunflower, in which they found
that approximately half a liter of carbon dioxide was used by each square
meter of leaf surface in an hour.

The carbon dioxide content of the atmosphere is constant; therefore
it is not a factor to be considered in fruit growing. However, when it
is artificially changed, in the absence of other limiting factors, the rate
of assimilation increases in proportion to an increase in the carbon dioxide
supply until an atmospheric concentration of 30 to 50 per cent, is reached.
Cummings and Jones^" have obtained very marked results from aerial
fertilization with carbon dioxide. Legumes fertilized in this way showed
increased carbohydrate storage and an increased production of pods
and beans. Potatoes produced better tubers and strawberries showed
distinct effects. This probably holds until an atmospheric concentration
of about 30 per cent, or more is reached. Atmospheric concentrations

164 FUNDAMENTALS OF FRUIT PRODUCTION

of 50 per cent, carbon dioxide have a narcotic effect and depress assimi-
lation. Changes in the rate of assimilation in so far as they depend on
carbon dioxide supply are affected only by those factors that determine the
rate of intake. This is increased by movement of the air, by the degree
of stomatal opening and by any factors increasing the rate of utilization.

Water. — The water supply of plants is treated in a preceding section
and no further discussion need be added here. However, it must not be
forgotten that water is one of the materials out of which carbohydrates
are made.

Light. — In the absence of limiting factors and particularly of high
temperatures and extremely high light intensities, carbon assimilation
increases with the intensity of light. Under such circumstances equal
areas of different plants, equally illuminated, produce the same amounts
of carbohydrates. There is evidence that at the intensities of the different
wave lengths in the solar spectrum, red light is the most and green the
least effective for photosynthesis.

Light acts indirectly on carbon assimilation by raising the tempera-
ture of the leaf and by stimulating the guard cells of the stomata to
open, thus increasing the absorption of carbon dioxide. ^^

Leaf Pigments. — The chloroplasts of all green plants contain four
pigments, two green and two yellow. They are:

L Chlorophyll a, blue-black in the solid state, green-blue in solution.

2. Chlorophyll b, green-black in the solid state, pure green in
solution.

3. Carotin, forming orange-red crystals.

4. Xanthophyll, forming yellow crystals.

In the fresh nettle leaf, these four pigments occur in the following
quantities, chlorophyll a, 24 parts in 12,000; chlorophyll b, 9; carotin 2
and xanthophyll 4.'"='

In the chloroplast these pigments occur in a colloidal mixture with fats,
waxes and salts of fatty acids. The chlorophyll content of leaves varies from 9.6
to 1.2 per cent, of the dry weight. Shade leaves have a higher chlorophyll
content than sun leaves in terms of dry weight, but not in proportion to leaf
surface. The yellow pigments comprise 0.1 to 1.2 per cent, of the dry weight and
there is no higher percentage in shade leaves than in sun leaves. There is no
diurnal fluctuation in the amounts of the pigments, the mean ratio of chloro-
phyll a to chlorophyll b being 2.85:1. On the whole, shade leaves con-
tain less chlorophyll a than other leaves, their ratio of chloroph.ylls being
2.93:1. Less difference in this ratio is found in real shade plants like the beech
than in plants that are ill adapted to growth in the shade. The mean ratio of
carotin to xanthophyll for ordinary leaves is 0.603 : 1 and for shade leaves
0.421 : 1. Xanthophyll is relatively more abundant in shade leaves.

Variation with Age. — The chlorophyll content of leaves increases
with age; so also the assimilatory power of the leaf, though not in the

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 165

same degree. Hence, it appears that mature leaves contain an excess
of chlorophyll and some other factor limits the rate of assimilation.
In autumn the chlorophyll content decreases but as chlorophyll is not
usually the limiting factor, assimilation does not decrease in proportion
at first. If leaves remain green, they maintain their assimilatory power
until they fall — a matter of no small importance in food storage.

Variation with Light Supply. — The development of chlorophyll in most
plants depends on the action of light in which the red rays seem the most effect-
ive.", 189 In all probabiUty precursors of chlorophyll are present and exposure
to light effects certain chemical reactions necessary for the complete development
of the pigment. Light is not always essential to chlorophyll development, how-
ever, for conifer seeds germinate and become green even in the dark.

Light not only aids in the development of chlorophjdl but at higher intensities
brings about its destruction probably through oxidation. The decomposition of
chlorophyll occurs outside the plant as well as within its tissues. This can be
demonstrated by exposing a test tube containing a solution of chlorophyll to
the light and comparing it with another kept in darkness. Red and yellow
light are most effective in destroying chlorophyll. Consequently it is found
that at low light intensities plants grown in yellow light contain the most chloro-
phyll but that at higher intensities plants grown in blue hght contain the most,
owing to the destructive effect of the yellow light at these higher intensities.^"^
Similar effects from red light have been observed. !*■* The double effect of Hght
in stimulating the development of chlorophyll and in bringing about its destruc-
tion, leads to noticeable differences in the chlorophyll content of plants growing
in different latitudes and altitudes. It has been found that the minimum amount
of chlorophyll necessary for growth is approximately the same at all latitudes
but that the maximum amount increases toward the equator. ^^"^ Hence, a
plant may have twice as much chlorophyll in the tropics as at 60° north latitude.
For a given species, however, the amount is less at both extremes of its range
than at the center and it has been suggested that this may be due to greater
oxidizing action at the limit on the equator side where the light would be more
intense. The significance of these discoveries lies in the relation of carbohydrate
accumulation to fruitfulness. Plants growing at high altitudes contain less
chlorophyll than those growing in the lowlands. ^^ In Alpine plants carbon assimi-
lation requires greater light intensities but lower temperatures.

Temperature. — At low and medium temperatures in the absence of
other limiting factors, the rate of assimilation is a coefficient of the tem-
perature. Assimilation has been detected at — 6°C. and from this point
to 25°C. the rule stated above has been found to hold with the plants
investigated. Above 25°C., the rate of assimilation does not remain
constant at any given temperature. The higher the temperature, the
more rapidly it decreases; at any given temperature the initial decrease
is greatest. This "time factor" that enters at higher temperatures
probably is indicative of the interference of another factor, namely,
enzymes.

166 FUNDAMENTALS OF FRUIT PRODUCTION

Enzymes. — Assimilation is an enzyme reaction. Enzymes are
organic catalytic substances that accelerate the rate of a reaction. Their
chemical composition is unknown and their existence is shown only
by their activity. They are not used up in a reaction, remaining after
the process is completed. A minute amount of enzyme can effect the
formation of a relatively large amount of end product; however, this
is proportional to the amount of enzyme present. The effects of tem-
perature described above are characteristic of enzyme reactions. The
time factor manifesting itself at temperatures above 25°C. is not due
to any direct effect of the temperatures on assimilation, but may be
due to the permanent inactivation or decomposition of enzymes at
high temperatures. Under these circumstances the rate of assimilation
would decrease because the amount of enzyme diminished. The longer
the temperature acted, the more enzyme would be decomposed. Simi-
larly the narcotic effect of strong concentrations of carbon dioxide and
the harmful influences of high light intensities are attributable in part
to their effects on the assimilatory enzymes. Such adaptations as
different species may show in their ability to assimilate best at higher
or lower temperatures or light intensities probably are attributable to
differences in their enzymes.

The principle of limiting factors applies to the six factors determining
carbon assimilation.^^ If any one factor is limiting, the rate of assimila-
tion cannot be increased by any other. The carbon assimilation of green
plants is usually limited by the seasonal variation in temperature and the
diurnal variation in light. When temperature and light are both favor-
able, the supply of carbon dioxide is probably the limiting factor.^^
Water may be a limiting factor either through a direct effect on assimila-
tion or indirectly by closing the stomata and so shutting off the supply
of carbon dioxide.

Products

The products of photosynthesis are oxygen and carbohydrates.

Oxygen. — The relation between the amount of oxygen evolved in the
process of carbon assimilation and the amount of carbon dioxide taken in
is not accurately known. When the respiration of the assimilating
tissue is evaluated, it appears that the volume of oxygen evolved is prac-
tically equal to, or very slightly greater than, the amount of carbon dioxide
absorbed. The path by which oxygen escapes from the leaf is the same as
that by which carbon dioxide enters or water vapor is lost, namely,
through the intercellular spaces and the stomata. Oxygen is used in
respiration, however, and when assimilation proceeds very slowl}^, the
oxygen given off by assimilation may be entirely consumed by respiration.
Similarly the carbon dioxide evolved by respiration may just about equal
that used in assimilation under these circumstances.

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 167

Carbohydrates. — What carbohydrate is the first product of carbon
assimilation, is not known. Assuming it to be glucose, the reaction may
be written as follows: 6CO2 + 6H2O + light + chlorophyll = CeHiaOe
+ 6O0.

Simple, naturally occurring carbohydrates may contain five or six
carbon atoms and are called accordingly pentoses or hexoses. There are
two pentoses of common occurrence, arabinose and xylose; neither of these
has been shown to be formed directly by assimilation. Four naturally
occurring hexoses are known: glucose, fructose, mannose and galactose.

Besides these simple sugars, there are compound sugars made up of
two or more molecules of the simple, less one or more molecules of water.
The disaccharides yield two molecules of simple sugars on hydrolysis.
The two most common disaccharides are sucrose (cane sugar) which
yields one molecule of glucose and one of fructose when hydrolyzed by
dilute acids or inverted by an enzyme and maltose (malt sugar) which
yields two molecules of glucose.

In addition to the sugars there are complex carbohydrates, called
polysaccharides; these yield an indefinite number of molecules of simple
sugars on hydrolysis. They are for the most part less soluble in water
than the sugars. One kind of sugar or a mixture of different kinds may
be formed on hydrolysis. If the predominant sugar produced is a hexose,
they are called hexosans; if a pentose, pentosans.

Hexosans are classified according to the nature of the predominating
sugar produced on hydrolysis. Thus there are glucosans which include
starch, soluble starch, dextrin and cellulose; fructosans such as inulin;
mannans, a constituent found in the wood and leaves of the hme, apple
and chestnut, and galactans such as agar-agar. Pentosans include gums,
mucilages and pectins, on which the jelling properties of fruit depend.
The relationships of the carbohydrates are shown diagrammatically in
Fig. 17.

Daihj and Seasonal Fluctuation in Leaves. — Though no reliable data
are available on which to base a detailed picture of the carbohydrate
changes in the leaf, the following statements may be made.^"^ Hexose
sugars and sucrose increase during the day, reach a maximum about mid-
day, after which the quantity present decreases; these changes closely
parallel the temperature variations and probably the variations in light
intensity. There is no diurnal fluctuation in the amount of pentoses or
of pentosans. As a result of the accumulation of sugars, starch is formed;
the process occurs only in cell plastids, either in chloroplasts which are
green or in leucoplasts which are colorless. Species vary greatly in their
capacity to form starch. Many plants — the onion, for instance — form
none at all. Starch and sucrose formation in the leaf are only temporary.
The carbohydrates are continuously conducted from the leaf as hexoses,
which occur in greater amounts than other sugars in the conducting

168

FUNDAMENTALS OF FRUIT PRODUCTION

> O-

Ml

rt o c

-^Bi

^.^

C 03

flfS

O o

SM

//

-^2

03 fl

II

1

Sj rt S

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 169

tissues. The starch present in the leaf accumulates there only because
the manufacture of sugars is proceeding more rapidly than their removal.
During the night the starch is digested by enzymes to maltose and the
maltose to glucose, which then passes out of the leaf.

The seasonal variation in the carbohydrate supply of leaves has been
studied by Michel Durant.^^'' He distinguishes two stages in the life
of a leaf: (1) a period of carbohydrate synthesis and polymerization,
extending from the time the leaves begin to function until the end of
summer or in annual plants until the seeds begin to develop, during
which period carbohydrate assimilation is active and carbohydrates of all
types increase in amount; (2) a period of hydrolysis and simplification
beginning about the time when the leaves turn yellow. This is marked
by a decrease in the amount of compound carbohydrates and a further
accumulation of simple sugars. The development of the abscission layer
at the base of the leaves of deciduous plants is correlated with this
accumulation of simple sugars in the leaf blade, so that their removal
to the branch is soon stopped. The sugars increase until they are re-
spired, fermented or washed out by rain. In leaves of annual plants, a
larger proportion of these sugars is removed to the developing seeds and
fruits; consequently, accumulation of simple sugars is less pronounced
than in tree leaves. Nevertheless, at the end of this second period
there are always appreciable amounts of carbohydrates left in the leaf.

In evergreen leaves, the accumulation of simple sugars in the fall
and winter is accentuated by photosynthesis which continues and pro-
duces appreciable effects because cold weather retards respiration more
than photosynthesis. Starch disappears or persists in small amounts
and disaccharides containing fructose, such as sucrose, are prevalent.
In the spring, starch is resynthesized at the expense of soluble sugars. In
June, the polysaccharides of the leaves decrease, being added to stores
in the branches or used in the development of the fruit. The carbohy-
drate content remains low until the end of autumn. In general, the older
the leaf, the greater its carbohydrate content and a maximum in poly-
saccharides corresponds to a minimum in simple sugars.

It has been found that the pentosans form a larger and larger propor-
tion of the matter insoluble in alcohol and that the pentoses increase as
the season advances, the latter probably representing hydrolytic products
of pentosans.^-

The entire plant depends on the assimilating function of its leaves
for its supply of carbohydrates and of those compounds manufactured
from them. The carbohydrates synthesized in the leaves are trans-
located as hexoses through the phloem to all parts of the plant where they
are either stored or utilized in ways specified later.

Forms of Storage. — Since starch is the most common form in which
carbohydrates are stored, it is important to consider the structure of the

170 FUNDAMENTALS OF FRUIT PRODUCTION

starch molecule in order to gain some idea of the factors involved in its
formation. When starch is hydrolyzed slowly, it yields maltose and
dextrin. Both of these yield glucose on further hydrolysis. Corn
starch contains palmitic acid, a fatty acid and a related unsaturated
compound. These fatty substances are liberated only after hydrolysis
and are probably attached to the carbohydrate of the starch molecule. ^^^
There is enough fatty acid in the corn starch molecule to make com-
mercially profitable, in the manufacture of glucose from corn starch,
the use of this residue as soap stock. Moreover, starch probably is not
chemically homogeneous. At least two substances with distinct prop-
erties have been separated and called amylose and amylopectin.

When the concentration of hexoses is sufficiently great, starch is
usually formed in the plastids. In fact, leaves of plants such as the
onion which do not ordinarily form starch, will do so when floated on a
10 per cent, solution of fructose.

Starch will be formed, therefore, whenever the concentration of
sugars reaches a certain point and other conditions such as temperature
permit. In the summer and early autumn, starch is stored in the
branches. In the peach, great amounts are found in the leaf gaps. In the
younger apple shoots, it accumulates predominantly in the pith, being
especially abundant at the nodes.

The association of fat with the starch molecule indicates that the
latter is the starting point for fat formation in plants. Fatty oils there-
fore may be considered as a reserve food derived from carbohydrates
especially in fruits like the avocado, in the seed of fruits like the apple
and cocoanut and also over the winter in the younger roots and branches.
Fats are esters which yield on hydrolysis one molecule of glycerine and
three molecules of fatty acids. The commonest fatty acids found in
plant fats and oils are: (1) oleic acid, in olive oil, almond oil, quince oil,
cherry-, plum-, peach- and apricot-kernel oil; (2) linolic acid, in the oils
from pumpkin, watermelon, melon, apple, pear and orange seeds; (3)
palmitic acid, in cocoanut oil and cocoa butter and (4) dihydroxystearic
acid, in grape-seed oil. Fats contain less oxygen in proportion to the
carbon present in the molecule than carbohydrates. They, therefore,
yield more energy when oxidized and may be regarded as concentrated
energy in chemical combination.

Sucrose and even glucose must at times be considered forms of carbo-
hydrate storage.

Seasonal Fluctuations of Stored Carbohydrates. — The seasonal varia-
tion in the carbohydrate content of plants gives evidence of storage.

Easily Hydrolyzable Carbohydrates. — ^Leclerc du Sablon's^'^ deter-
minations of the easily hydrolyzable carbohydrate in the roots and
branches of the pear and chestnut are given in Table 59. This type of
carbohydrate which includes sugars, starch and other easily hydrolyzed

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 171

Table 59. — Easily Hyduolyzed Carbohydrate in Percentages of Dry Weight

IN Pear and Chestnut Trees'"

Pear

Date

Branches

Roots

Feb. 18

23.0
21.3
23.7

24.7
25.7
25.4

39 3

Apr. 13

22 4

June 16

27 9

Aug. 4

29 2

Sept. 24

33 8

Dec. 1

29 3

Chestnut

Jan. 11

24.7
24.7
21.5
19.9
20.4
21.1
25.9
26.4
24.7
23.0

27 2

Feb. 26

25 7

Mar. 28

24 7

May 20

19 8

June 22

21 8

July 27

24 3

Sept. 12

30 3

Oct. 19

29 1

Nov. 22

28 9

Dec. 12

27 3

polysaccharides, but not crude fiber, is at a maximun in September
and at a minimum in May. Moreover there is a steady increase from
May to September and a fairly steady decrease from September to May.
Similar data showing the variations in the easily hydrolyzed polysac-
charide of 7-year old apple trees are given in Table 60. Here also much

Table 60.

-Easily Hydrolyzed Carbohydrate in Percentages of Dry Weight
IN 7-YEAR Old Apple Trees^^
(Each figure is the average of analyses from two trees)

Dormant,
Dec. 3

Buds

In

Growth

swelHng,

bloom,

over.

Apr. 20

May 18

July 12

30.54

30.31

19.21

25.22

29.38

13.24

26.59

35.75

11.68

32.26

31.58

18.48

30.03

31.29

16.08

25,07

34.08

17.80

32.23

38.38

21.77

28.90

36.47

36.47

31.87

Leaves
falling,
Oct. 12

New growth

1-year old branches .
2-year old branches
3-year old branches .
4-year old branches .
5-year old branches .

Trunk

Large roots

Small roots

21.36
22.13
22.41
20.44
20.43
25 . 83
29.90
29.36

27.34
26.50
26.72
26.10

27.88
27.28
27.96
32.02
33.88

172

FUNDAMENTALS OF FRUIT PRODUCTION

the same picture is presented except an increase from December to April,
accounting for which is difficult. The minimum in May is apparent, but
the maximum in September does not appear, as samples were not collected
at that time.

In all the data presented, the roots have shown a higher percentage
and a greater fluctuation in carbohydrate than the shoots. However,
this does not indicate a greater absolute carbohydrate content. Esti-
mates by Curtis^^ indicating the probable relationships at the time of bud
swelling (April) are shown in Table 61. According to these figures the

Table 61.-

-EsTiMATED Number of Pounds of Carbohydrate in Tops and Roots
OF A 7-year Old Apple Tree^''

1 year twigs 1

Older branches 5

Trunk 5

10

25

Large roots 5.71

Small roots 2 . 43

Total 13.24

Total .

14

portions of a tree above ground contain half again as much as the roots.
The conditions found in apple spurs are shown in Table 62. These
figures evidently are comparable to the data of I^e Clerc du Sablon on the
pear and chestnut.

Table 62.

-Total Carbohydrate (not Including Crude Fiber) of Apple Spurs'
(In percentages of dry weight)

Bearing (average
of three trees)

Non-bearing

(average of two

trees)

March . .
May 13.
June 25.
Sept. 2.
Nov. 19
Jan. 24.

25.1
24.0
25.2
30.1

24.5
23.9

The increase in carbohydrate from May to September is explained by
the assimilatory activity of the leaves. The decrease from September
to May must be attributed to several factors. The major part is due to
the use of carbohydrates for the formation of other substances — probably
of nitrogenous compounds which increase in September and of fatty
substances, which are discussed presently. The decrease in carbo-
hydrate is also in part the result of consumption in respiration, which
proceeds from September to May, but most actively after growth has
begun and in part the result of translocation into the newly developing
leaves, flowers and eventually fruits. Hence the lower minimum in the

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 173

carbohydrate content of bearing spurs in May may be associated with
flowering. The higher maximum in these same spurs in September is
probably connected with the development of specialized tissues in the
purse during fruit development.

The study of the various types of carbohydrate, particularly starch
and sugars, shows similar seasonal fluctuations despite some variation.

Starch. — The only analytical data on the seasonal variation in starch
content are on spurs. In woody tissues, starch is a relatively small
fraction of the total polysaccharides, but probably a significant fraction
of the available carbohydrates. Figure 18 shows the starch variations
in bearing, non-bearing and barren spurs of the apple. ^°°

5

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Fig. 18. — Starch content of apple spurs in percentages of dry weight; bearing spurs
represented by continuous lines, non-bearing spurs by broken lines and barren spurs by
dot-dash lines. {After Hooker. ^^'')

There are two maxima for starch and two minima. This was shown
microchemically by Mer and d'Arbaumont.'^^ The maximum in Septem-
ber and the minimum in May correspond to the maximum and minimum
for total carbohydrates. The second minimum in January and the
second maximum in March are due to conversion of starch to sugars and
a resynthesis of starch in spring just before vegetation commences. The
second maximum is not, however, so high as the first — except in bearing
spurs — which indicates that a certain amount of carbohydrate has been
consumed in respiration or used for the formation of other substances.
Determinations of the ether extract permit an estimate of the fat and oil
content and show that fats increase during the winter. The previous
discussion of the structure of starch indicates that this is the point

174

FUNDAMENTALS OF FRUIT PRODUCTION

of departure for fat formation. Table 63 shows the seasonal variation
in ether extract in 7-year old apple trees. It is evident that the younger
the tissue, the more fat it contains and that the fat content is at a maxi-
mmn just before active growth begins and at a minimum after active
growth is over.

Table 63. — Ether Extract in Percentages of Dry Weight in 7-year Old Apple

Trees23
(Each figure is the average of analyses from two trees)

Dormant,
Dec. 3

Buds
swelling,
Apr. 20

3.26

5.18

2.77

3.58

2.49

2.92

1.75

1.50

1.28

1.07

0.85

0.96

2.25

1.86

6.79

5.03

In
bloom,
May 18

Growth

over,
July 12

Leaves
falling,
Oct. 12

New growth

1-year branches
2-year branches
3-year branches
4-year branches
5-year branches

Trunk

Large roots

Small roots

5.00
3.03
2.39
1.57
1.14
0.79
2.02
4.06

3.15
2.68
2.31
1.99
1.31
1.18
0.72
2.38
5.85

4.11
3.01
2.92
2.71
1.07
0.91
0.70
1.31
6.55

Characteristic differences between the starch content of bearing
and non-bearing spurs appear in Fig. 18. In winter the spurs with
fruit buds have more starch. Moreover starch accumulation commences

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Fig. 19. — Total sugar content of apple spurs in percentages of dry weight; bearing
spurs represented by continuous lines, non-bearing spurs by broken lines and barren spurs
by dot-dash lines. {After Hooker. ''■°'>)

in non-bearing spurs in May and in bearing spurs in June. This differ-
ence is connected with carbohydrate utilization by the fruit. The
relation of this to fruit bud differentiation is discussed later.

Sugars. — The seasonal variation in the sugar content of spurs is
shown in Fig. 19. The rapid drop in sugar during the spring is explained

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 175

by respiration, translocation to the leaves and fruit, and utilization in the
formation of complex carbohydrates. The assimilatory activity of the
leaves soon restores the sugar content of the spurs, but a marked increase
does not commence until September, This is due to continued demands
for sugar by the developing fruit on bearing spurs and to starch accimiula-
tion in non-bearing spurs. The increase in sugars after September is
associated with the decrease in starch during this period and represents a
partial conversion of starch to sugars. Some of this sugar is sucrose,
a form in which carbohydrate is stored during the winter, as the figures
in Table 6-4 show.

Table 04.-

-AvER.\GE Non-reducing Sugar Content
OF Dry Weight'ou

OF Spurs in

Percentages

Bearing
spurs

Non-bearing
spurs

Barren
spurs

March

0.59
0.44
0.00
0.09
1.27
0 56

0.47
0.27
0.05
0.45
0.77
2 40

0 97

May 13

June 26

0.45
0 19

Sept. 2

Nov. 14

Jan. 24.

0.35
0.91
1 66

The sugar used in the development of fruit is considerable, as Table
65 indicates. In the apple, the percentage and absolute amounts in
the fruit increase steadily, the rate of increase becoming greater as
maturity approaches. This holds for prunes also.^^^ In pears the
percentage decreases at first and then increases, while the absolute
amounts increase steadily. In either case the increase in absolute
amount extends to the end of August or the middle of September.

Michel Durant^^'' points out that a period of carbohydrate synthesis followed
by one of hydrolysis and simplification is found in fruits as well as in leaves.
Ripe fruit therefore contains more sugar than unripe fruit. The increase in the
sugar content may continue even after the fruit is picked. This occurs in drying
prunes when sugar is formed by the hydrolysis of starch. If prunes after
removal from the tree are exposed to the sunlight for 2 or 3 days, their sugar
content increases, but after 5 days' exposure their sugar is rapidly consumed in
respiration and fermentation.'*^

In recapitulation, it is emphasized that the carbohydrate supply
of the plant is manufactured in the leaves and that the leaves supply the
entire plant. In consequence, movement of carbohydrate is usually
away from the leaves to the growing points, cambium and storage organs.
Carbohydrate is stored mostly in the immediate vicinity of places where
it may later be used. Thus the work of Magness'^s andof Curtis" indi-

176 FUNDAMENTALS OF FRUIT PRODUCTION

Table 65. — Reducing Sugar Content of Devei.oping Apples and Pears"'

Apples

Date

Pears

Pleissner
Rambour

Red Easter
Caville

Date

Salzburg

Liegel's Honey

Per-
centage
of dry
weight

Grams

in 1,000

fruits

Per-
centage
of dry
weight

Per-
centage
of dry
weight

Grams

in 1,000

fruits

Per-
centage
of dry
weight

Grams

in 1,000

fruits

Grams
in 1,000

fruits

June 2

June 12

June 22

July 2

July 12

July 22

Aug. 1

Aug. 11

Aug. 21

Aug. 31

Sept. 10

Sept. 20

Sept. 30

Dec. 12

3.05
10.70
14.91
22.90
24.19
17.11
39.45
34.65
39.69
43.07
51.28
60.04
52.99

0.9

22.0

97.0

368.0

870,0

1,150.0

2,540.0

4,260.0

4,250.0

6,600.0

7,530.0

10,850.0

9,630.0

3.28
6.75
12.70
16.51
19.78
20.29
23.19
26.42
30.17
31.47
35.41
36.28
33.73
48.14

0.7

8.8

43.0

150.0

370.0

670.0

950. 0

1,400.0

1,740.0

2,400.0

3,040.0

3,. 550.0

3,200.0

4,730.0

May 26

June 5

June 15

June 25

July 5

July 15

July 25

Aug. 4

Aug. 14

Aug. 24

Sept. 3

Sept. 8

4.98

2.17

1.66

1.92

2.78

4.56

7.16

16.43

30.03

35.02

51 . 35

1.0

2.7

7.7

18.0

36.0

95.0

218.0

637.0

1,660.0

2,230.0

3,590.0

4,180.0

5.03
3.26
2.50
4.56
6.74
12.01
23.60
36.49
43.68
50.61

0.8

3.6

10.2

32.0

68.0

175.0

536.0

770.0

1,520.0

1,800.0

cate that the carbohydrate stores in the roots do not return to the tops.
They are used by the roots. Cambial activity depends on the carbo-
hydrate stored in the medullary rays and the starch sheath. Bud
development in the spring depends largely on the carbohydrate stored
in the pith or leaf gap near the bud.

CARBOHYDRATE UTILIZATION

Carbohydrates are used in any one of the following ways:

1. For tissue building, that is for the construction of other carbo-
hydrates, or of different substances manufactured from carbohydrates,
which enter into the composition of plant cells.

2. For the retention of moisture.

3. To increase osmotic concentration.

4. As a source of energy.

In Tissue Building. — According to Czapek, glucose is a constituent
of every living cell and therefore may be considered a necessary part
of the chemical equipment of living matter. The great value of glucose
in metabolism is probably associated with the ease with which it is altered
to a number of different but related compounds. Through its enolitic
form it may be changed to fructose and mannose. Glucose, fructose
and mannose exist in at least five forms each. Wherever glucose is
present in solution, as in protoplasm, certain of these forms — depending

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 177

on the prevailing conditions — tend to develop until a complex equilib-
rium is established. Since each form has different physical and chemical
properties the multiplicity of ways in which glucose may become the
basic material for a great diversity of physiological processes is evident.
Besides the forms in which glucose may be stored temporarily, it is utihzed
for the construction of the permanent framework of the plant, being
the substance from which many forms of carbohydrate as well as of
other groups of organic compounds are made. The cellulose wall is
secreted by each cell from its supply of hexose sugars. So also is the
middle lamella, which is a pentosan, a salt of pectic acid. It has been
suggested that fats probably are derived from carbohydrates and that
starch is presumably an intermediate stage in fat formation. Glucosides
give rise to one or more molecules of sugar on hydrolysis and it is shown
presently that organic acids arise from the respiration of carbohydrates.
Little is known concerning the seasonal quantitative variation in
many of these contituents. It may be said, however, that crude fiber,
which is composed chiefly of cellulose and lignin increases steadily with
age in roots and branches and that seasonal variations are insignificant
in comparison to this regular trend.

Complete vegetative development depends on an adequate carbohydrate
supply and a plant is unable to attain its full size and ordinary shape in dark-
ness or particularly in the absence of red light. This is true especially of leaves.
If they are supplied with carbohydrates in a form in which they can be absorbed,
the effect of the absence of light on the size of the leaf can largely be eliminated.
However, different plants show more or less characteristic responses to an ab-
sence of light in this respect, which seems to be associated with the amount of
carbohydrate that tends to accumulate when the leaves are kept in darkness.
Bean leaves, for example, contain small amounts of carbohydrates when kept
in the dark; consequently the leaves do not grow. This is the case with most of
the fruit plants. In a certain number of plants such as wheat, starch is always
present in the leaves and considerable amounts of carbohydrate accumulate
even when the leaves are kept in darkness; these attain their usual size under
such conditions, though they may be narrower than the leaves of illuminated
plants.'''^ There are, however, other peculiarities in the form and structure of
plants grown in darkness which cannot be attributed in any way to the carbo-
hydrate supply.

In Retaining Moisture. — Pentosans have, according to Spoehr,i"
the property of holding moisture. Certain pentosans develop under
conditions where the moisture supply is limited and furnish the plant
with a water-retaining mechanism which minimizes the effect of the water
deficiency. The moisture held by pentosans seems to be in a colloidal
mbcture, where it is retained tenaciously and offers resistance to desic-
cating agencies. This colloidally held water should be differentiated
from free water since it is characterized by distinct physical properties.

178 FUNDAMENTALS OF FRUIT PRODUCTION

Increasing Osmotic Concentration. — Sugars are important to the
plant because they are osmotically active. Since the osmotic concen-
tration depends on the number of molecules and not on their size, it is
evident that the formation of disaccharides from simple sugars reduces
the osmotic concentration. Conversely, the hydrolysis of compound
sugars or polysaccharides to simple sugars increases the osmotic concen-
tration. Thus the building up and splitting down of carbohydrates
regulates the osmotic concentration. On the other hand, it unques-
tionabl}^ plays an important part in controlling synthetic and hydrolytic
processes. Thus compound sugars and especially starch are usually
produced wherever the concentration of sugars is high, though other
factors are involved, particularly enzymes. The hydrolysis of compound
carbohydrates proceeds most rapidly when the concentration of sugars
is low; therefore their consumption in respiration, their removal to other
organs and their use in the formation of other compounds, particularly
of substances like cellulose that are insoluble and consequently not
involved in the osmotic system, accelerate the processes of hydrolysis.

As a Source of Energy. — One of the most important properties of
carbohydrates is that of yielding energy in the process of respiration. In
fact most of the energy used by plants and animals is the stored potential
energy of fats and carbohydrates. By means of carbohydrates the roots
are able to utilize the energy of sunlight.

Respiration involves several processes. There are many theories, but
according to the most suggestive, respiration consists of two main reac-
tions; one is a process of cleavage, in which the simple carbohydrate
molecule is split into carbon dioxide and certain intermediate substances,
probably alcohols or acids; the other is a process of oxidation, in which
these intermediate substances are oxidized to carbon dioxide and water.
The first process is essentially a fermentation for which the enzyme,
zymase, is essential. The second process — of oxidation — depends on
enzymes called peroxidases which act only in the presence of peroxides.
Peroxidases supposedly transfer oxygen from organic peroxides to the
products of cleavage formed during the first process in respiration,
oxidizing them to carbon dioxide and water. According to some investi-
gators there are other enzymes involved but if this be true, they play
subsidiary parts and need not be considered here.

In general the amount of carbon dioxide given off is approximately
equal to the amount of oxygen used in respiration so that the respiration
of a hexose may be represented by the formula C6H12O6 + 6O2 = 6H2O
+ 6CO2 + energy. The two processes of respiration, cleavage and
oxidation, are more or less independent of each other, so that an accumu-
lation of acid may occur in plant tissues during periods of active respira-
tion, through the incomplete oxidation of carbohydrates and other sub-
stances. The inverse correlation existing between starch content and

MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 179

acidity in apple spurs is shown in Figs. 20 and 21, In the spring, starch
and sugar decreased rapidly in these spurs and acidity rose. This may be
interpreted as indicating the hydrolysis of starch to sugar and the incom-

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1

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A

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X

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s.

se

^

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N

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,r

V

-I

r<

-^

■~~»

\

/

\

A

w

1

\

f

y

/

/

/

Fig. 20.- — Starch, reducing sugar content and titratable acidity of bearing apple spurs
compared. (After Hooker .''^'>°)

plete oxidation of the sugar to acid. Some of the decrease in sugar is
explained by removal to the developing leaves and flowers. The increase
in acidity in the spring lasted longer and reached a higher maximum in

/

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{

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y

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7

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nuc

ING

^

i^

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Fig. 21.— Starch, reducing sugar content and titratable acidity of non-bearing apple spurs
compared. (After Hooker. '^'^°)

bearing spurs. At the same time the consumption of reducing sugars
was more complete. This may be associated with greater respiratory
activity in flowers. Respiratory activity is particularly pronounced
in floral parts, germinating seeds and growing parts in general.

180 FUNDAMENTALS OF FRUIT PRODUCTION

Relation to Pigment Formation, — A supply of carbohydrates is necessary for
the development of certain pigments in leaves, flowers and fruits. Laurent^^*^
showed that fruit pigments are of two types ; some develop only as a result of
direct exposure to light; others do not require direct illumination of the fruit
but for their development the leaves must be able to manufacture carbohydrates
and the connection between the leaves and the fruit must not be interrupted.
Kraus^^^ suggests that pigments of both sorts occur in apples. The effect of
low temperature or parasitic attack in increasing the pigmentation of fruit or
leaves is attributed to an attendant accumulation of sugars, especially glucose,
fructose and sucrose.

Summary. — The elaborated plant foods used in tissue building are
manufactured from the nutrient materials obtained from the soil and air
at a rate depending principally on (1) the available supply of the several
materials including water, (2) the intensity, duration and quality of the
light reaching the plant, (3) the amounts of the green leaf pigments,
(4) temperature and (5) the presence of certain enzymes. Any of these
factors of the plant's environment or composition may become limiting
in plant food synthesis, their degree of importance varying with condi-
tions. The immediate products of photosynthetic activity of the plant
are oxygen and carbohydrates. Oxygen for the most part is set free
and is in effect a by-product. Glucose is assumed to be the first synthetic
product of photosynthesis. Glucose may be considered a starting point
for the formation of more complex substances, such as the other hexoses,
disaccharides, polysaccharides, pentosans and pentoses. Starch is the
most common form in which carbohydrates are stored. They are also
stored frequently as sugars and sometimes they are transformed into
fats. The seasonal distribution of the more important of these materials
is discussed. Their storage is more common in or near the prgans where
they are later used. Carbohydrates are used principally for new tissue
building, for the retention of moisture, for increasing osmotic concentra-
tion and as a source of energy. Glucose particularly is a basic material
in the construction of plant tissues; for a great diversity of physiological
processes, pentosans are particularly important because of their water-
retaining capacity. Sugars are important in determining osmotic
concentration. Carbohydrates supply energy in the process of respira-
tion. The formation of certain pigments also depends on carbohydrates.

CHAPTER X

THE INITIATION OF THE REPRODUCTIVE PROCESSES

The initiation of the reproductive processes of the plant should be
considered in the light of chemical conditions and the concurrent mor-
phological changes.

THE DEVELOPMENT OF THE FRUITFUL CONDITION

There is much evidence that conditions associated with carbohydrate
accumulation have an important relation to fruitfulness in plants.

The Response of the Plant to Changes in Relative Amounts of
Nitrogen and of Carbohydrates. — Kraus and Kraybilli^^, studying the
effects on the tomato of various treatments, found that striking differences
in chemical composition and in behavior with respect to fruitfulness and
vegetative growth could be produced by controlling the environmental
conditions. They summarize their work as follows:

"1. Plants grown with an abundant supply of available nitrogen and the
opportunity for carbohydrate synthesis, are vigorously vegetative and unfruit-
ful. Such plants are high in moisture, total nitrogen, nitrate nitrogen and low in
total dry matter, free reducing substances, sucrose and polysaccharides.

"2. Plants grown with an abundant supply of nitrogen and then transferred
and grown with a moderate supply of available nitrogen are less vegetative but
fruitful. As compared with the vegetative plants, they are lower in moisture,
total nitrogen, and nitrate nitrogen, and higher in total dry matter, free reducing
substances, sucrose and polysaccharides.

'•'3. Plants grown with an abundant supply of nitrogen and then transferred
and grown with a very low supply of available nitrogen are very weakly vegeta-
tive and unfruitful. As compared with the vegetative plants, they are very much
lower in moisture and total nitrogen and are lacking in nitrate nitrogen; they
are much higher in total dry matter, free reducing substances, sucrose, and poly-
saccharides."

Three typical effects, measured principally in terms of total nitrogen,
carbohydrate and moisture have been produced by these three distinct
environments. The first is characteristic of vigorous vegetative growth.
"An abundance of moisture and mineral nutrients, including nitrates,
coupled with an available carbohydrate supply, makes for increased
vegetation, barrenness and sterility." ^^^ The second condition represents
a readjustment through which the plant must pass before it becomes
fruitful. "A relative decrease in nitrates in proportion to the carbo-
hydrates makes for an accumulation of the latter; and also for fruitful-

181

182 FUNDAMENTALS OF FRUIT PRODUCTION

ness, fertility, and lessened vegetation.""^ The third condition, in
which "a further reduction of nitrates without inhibiting a possible
increase of carbohydrates, makes for a suppression both of vegetation and
fruit fulness,""^ is evidently the manifestation of the effect of a limiting
factor, nitrate supply. In addition to these three, a fourth condition
was found. "Though there be an abundance of moisture and mineral
nutrients, including nitrates, yet without an available carbohydrate
supply, vegetation is weakened and the plants are non-fruitful. . . .
The available carbohydrate supply or the possibility for their manu-
facture or supply, constitute as much a limiting factor in growth as the
available nitrogen and moisture supply.""^

Those instances (3 and 4), in which nitrogen or carbohydrate supply
are limiting factors of growth, reveal the necessity of a proper balance
between carbohydrate and nitrate supply for the best vegetative
development.

"In other words, this experiment indicates first, that the limitation of the
nitrates resulted in the suppression of growth and the accumulation of the more
complex carbohydrates; second, that the limitation of the carbohydrates, even
with large quantities of available nitrates in the soil, results in a suppression of
growth; third, that a rapid vegetative extension results from an adjustment of
the carbohydrates and nitrates relative to one another so that both may be
utilized in the formation and expansion of such structures; and fourth, that such
a relationship can be secured either by increasing the nitrates without decreasing
the carbohydrates, or by decreasing the carbohydrates without increasing the
nitrates. While it is apparent that the amounts of these compounds relative to
one another would be the same in both the above cases, the total amounts would
be greater in the former and less in the latter, a condition faithfully reflected
in the amount of growth produced. "^^*

In this passage Kraus and Kraybill show that there is a distinct
nutritive relation between the supply of nitrates and of carbohydrates,
for vegetative growth and development. A carbohydrate supply
is therefore not only just as essential for the manufacture of protoplasm
as are nitrogen and the essential mineral elements, but it combines
with them in definite proportion for the building up of the plant tissue.

The Significance of Carbohydrate Accumulation. Manufacture in
Excess of Utilization. — The differences between the conditions char-
acteristic of vigorous vegetative growth which is unfruitful and vegeta-
tion accompanied by fruitfulness are of interest. There is no evidence
to show that the utilization of nutrient substances is any different in a
plant showing fruit bud differentiation from that in one which does not,
or that the nutritive relation between carbohydrate and nitrate supply
in particular is altered. Kraus and Kraybill's work shows that, in so
far as the materials determined by them are concerned, the chief differ-

THE INITIATION OF THE REPRODUCTIVE PROCESSES 183

ence is associated with circumstances making for carbohydrate accumula-
tion in fruitful plants rather than a difference in the method of carbo-
hydrate utilization. In other words, the carbohydrate supplied must be
in excess of the amount used.

Carbohydrate accumulation depends primarily on light conditions. Under
experimental conditions carbohydrate assimilation varies with light intensity,
in the absence of other limiting factors; however, other factors become limiting
for plants grown in the open, so that carbohydrate assimilation and hence car-
bohydrate accumulation depends on the number of hours of sunlight rather than
on the hght intensity. ^^'^ Garner and Allard^i have shown experimentally that
an increase in the duration of light exposure determines f ruitfulness in some plants
and they suggest that the daily increase in duration of illumination which reaches
a maximum on June 21, may have an important relation to the time at which
these plants blossom. It is interesting to observe that fruit bud differentiation
in the apple usually occurs the latter part of June or early part of July, though
it has been observed to occur at almost every season. However, Garner and
Allard found that many plants do not blossom unless the duration of light exposure
is short. Voechtingi^- found that a decrease m light intensity reduced the number
of blossoms and eventually prevented flowering altogether in some plants, while
in others there was a tendency for the development of cleistogamous flowers.

Klebs"" found that when blossoming depends on the intensity of illumination,
red hght which is the most effective in photosynthesis is essential, blue light
having much the same effect as darkness.

Defoliation previous to the period of fruit bud differentiation obviously
interferes with carbohydrate manufacture and the recent work of Harvey^" shows
that this is reflected in the chemical composition of defoliated apple spurs which
contain less hydrolyzable polysaccharides and total carbohydrates than normal
spurs. This is particularly important in connection with the decreased fruit
bud differentiation observed by Harvey on defohated fruit spurs.

In Fruit Spurs. — Hooker^"^ in a study of the seasonal changes in the
chemical composition of apple spurs of certain varieties and bearing
habits found that, when there was a relatively low total nitrogen content,
starch accumulation occurred while fruit buds were being differentiated.
When there was a relatively high total nitrogen content, starch accumula-
tion did not occur at the same time, though it followed later, and the
spurs remained vegetative for another year. These conditions, were
found in spurs showing characteristically different behavior regardless
of whether spurs of only one or of several different bearing habits were
found on the same tree at one time. Some of these results, shown
graphically in Figs. 22 and 23, emphasize two principles involved in the
development of the fruitful condition; (1) At certain critical periods in the
life of the plant, its activities are directed into one channel or another,
depending on the nature of the conditions affecting its equilibrium at that
particular time. This lends weight to Kraus and Kraybill's surmise

184

FUNDAMENTALS OF FRUIT PRODUCTION

that "the conditions for the initiation of floral primordia and even bloom-
ing are probably different from those accompanying fruit setting." In
fact, recent work by Murneek^^ shows that the conditions favoring fruit

4

\

A

\

^1

\

3

\

\

0

\

,^

\

\

2

=-/

N1

TRO^GEN

\

^

^^^

^

^

\

/

PHOSPHORUS

^

^

1

\

/

\

1

\

1

0

Fig. 22. — Nitrogen, phosphorus and starch contents of bearing apple spurs compared.
The arrow indicates the season when fruit bud differentiation would occur in non-bearing
spurs. {After Eooker>^^)

setting in apples are quite different from those determining fruit bud
differentiation. (2) Different parts of a plant may act quite indepen-
dently of one another, depending on the local factors affecting them.

/^

\,

\

vy

\

\

\

/'

\

\

/

\

2

\;

\

y

/,

^o,

V

^

^

N^

VN.

^

i

'-rrr\

N

^

1

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Nil

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1 1

Fig. 23. — Nitrogen, phosphorus and starch contents of non-bearing apples purs compared.
The arrow indicates the season of fruit bud differentiation. (After Hooker. ^'">)

Influence of the Nitrate Supply. — When the nitrate supply was varied
in Kraus and Kraj^bill's experiments the amount of carbohydrate utilization
varied with it, in accordance with the nutritive relation between carbo-

THE INITIATION OF THE REPRODUCTIVE PROCESSES 185

hydrates and nitrates. Hence, in the absence of any other Hmiting
factors for vegetative development, the balance of carbohydrate manu-
facture over utilization depends on the nitrate supply. When this is
kept high, though carbohydrates are manufactured in large quantities,
they are immediately utilized for vegetative development and the plants
are unfruitful and vigorously vegetative. If the nitrate supply is reduced
moderately, carbohydrate utilization is checked and there is opportunity
for carbohydrate accumulation; fruitfulness follows. To be sure carbo-
hydrate accumulation occurs when the nitrate supply is still further
reduced, but here the situation is comphcated because nitrate then
becomes a limiting factor to fruitfulness by inhibiting such vegetative
development as appears necessary for fruit bud differentiation. Plants
of this type are stunted and altogether lacking in nitrate nitrogen.

Influence of the Moisture Supply. — Nitrate supply is not the only factor
which may determine the balance of carbohydrate manufacture over
utilization. This may be accomplished also by a decrease in any other
factor involved in the process of growth and development. For example,
Kraus and Kraybill report that "withholding moisture from plants grown
under conditions of relative abundance of available nitrogen results in
much the same condition of fruitfulness and carbohydrate storage as
the limiting of the supply of available nitrogen." A diminution of the
water supply is well known to be frequently associated with fruitfulness.
In this case, as in that of nitrate supply, there is probably a limit beyond
which a further reduction of the water supply results in unfruitfulness
and stunted growth.

Influence of Other Factors. — Klebs^^^ concluded from numerous investi-
gations that a reduction in the supply of nutritive salts leads to the fruit-
ful condition provided there be adequate facilities for photosynthesis
and hence for carbohydrate accumulation. Recent work of Walster^^^
has shown that heat may be a limiting factor to vegetative development
as well as water or any of the essential nutrient and food materials and
that diminished heat, even with a high nitrogen supply, leads to carbohy-
drate accumulation and culm formation in barley. These investigations
indicate that any environmental factor may check growth and lead to
carbohydrate accumulation and that fruitfulness may result provided
vegetative development is not seriously retarded or altogether stopped.
It is shown later in this section that vigorous vegetative growth is not
inimical to fruitfulness. On the contrary, the facts just presented indi-
cate that fruitfulness and vegetative development are associated functions.

FRUIT-BUD FORMATION

Since carbohydrate accumulation seems associated with fruit bud
differentiation and the conditions for carbohydrate accumulation change
during the season, it is evident that there must be considerable variation

186 FUNDAMENTALS OF FRUIT PRODUCTION

in the time when fruit buds are formed. A knowledge of the approximate
time when their differentiation occurs is of fundamental importance,
particularly in connection with possible means of influencing their number
by cultural treatment. Furthermore, the stage of advancement in which
the fruit buds enter the winter is shown elsewhere to have an important
relation to winter injury.

For many years flower buds of the ordinary deciduous fruit trees
have been known, in a rather indefinite way, to have their inception in
the summer previous to their opening; more exact knowledge is compara-
tively recent and is even now rather incomplete.

Investigation of the apple has been more extensive than is the case
with the other fruits; there is, however, enough similarity between them
to permit the use of the apple as the type. One difference, however,
between buds of apple and those of some of the other fruits, pointed out
elsewhere, should be borne in mind. The fruit bud of the apple is, with
trivial exceptions, a mixed bud, containing leaves and blossoms; in the
other type, as the peach, fruit buds contain no leaves.

Evidence of Differentiation. — The growing point of the apple shoot or
spur presents a rounded surface surrounded by embryonic leaves and it is
characterized by its relatively large amount of meristematic tissue.
Sooner or later its aspect changes, taking one of two forms.

In one case the change consists principally in the greater breadth of
the surface with a somewhat smaller degree of convexity and in the
absence of the swellings at the periphery that in the actively growing
shoot precede the formation of a rudimentary leaf. The amount of
meristematic tissue becomes relatively smaller. The growing point is
at the resting stage; surrounded by protective scales and embryonic
leaves, it constitutes the leaf bud.

In the alternative case the growing point differentiates into structures
that form the essential part of the flower or fruit bud. The first evidence
of differentiation in this direction is the rapid elevation of the crown or
surface of the growing point into a narrow conical form, rounded at the
apex, with the fibro-vascular connections and pith areas advancing
concurrently. In the axils of the young leaves within the bud appear
other protuberances which soon become blunt at the top. At the same
time other leaf primordia develop rapidly higher in the spiral in which
they appear and in turn younger protuberances (the floral primordia)
appear in their axils. The apical protuberance, destined to become the
central (terminal) flower of the cluster, is differentiated last; however,
when it does take shape it is already larger than those previously laid
down. It soon takes and thenceforth maintains the lead in development
over the other flower primordia (see Fig. 24).

Whether a bud which has entered the resting stage as a leaf bud, can,
without a renewal of growth, develop into a fruit bud later the same

THE INITIATION OF THE REPRODUCTIVE PROCESSES 187

season is a matter obviously difficult of determination. Indirect
evidence, however, points to this possibility and suggests that fruit buds
may be initiated at any time when conditions are favorable. It is
certain that a spur after forming a leaf bud may start into second growth
and then form a fruit bud, all during the same growing season.

Magness^^^ has traced the development of axillary buds. He finds that:
"axillary buds originate very close to the tip or apex of rapidly growing shoots.
As the shoot elongates, the leaves are given off at the side of the growing point,
and the young bud appears first as simply an undifferentiated mass of rapidly
dividing cells in the axils of these leaves ... no primordia were found de-
veloping in the axils of leaves that were not fairly well formed.

"The buds developed very rapidly and those subtended by half-grown leaves,
1 to 2 inches above the terminal, were well differentiated, with a growing point or
apex, and bud scales being rapidly formed. The cells of the growing tip were
not well differentiated and this, with the high staining reaction of this region,
indicated that much growth was still taking place." By July 9 some of the older
axial buds had nearly reached the condition in which they would pass the winter.

Time of Differentiation.^ — Drinkard"^ reported that fruit bud differ-
entiation in the Oldenburg apple occurred about June 20 in Virginia.
Goff^^ found the first clear evidence in the Hoadley apple on June 30 in
Wisconsin. Bradford'^ in Oregon found similar stages during the first
10 days of July, though resting stages of leaf buds were apparent in May.
The earliest differentiation observed by Kirby^"^ in Iowa was about the
first of July.

In the pear it was observed in Virginia in samples of Kieffer taken
about the middle of July, somewhat later than the initial period for the
apple. ^^ In Wisconsin evidence was found in the Wilder Early on July
21.^^ Albert first found differentiation in the pear early in August
In the Champion quince Goff found embryonic flowers in bud examined,
late in the autumn, but did not determine the exact period of their
inception. Alber't found differentiation in the Japanese quince in August.
In the Luster peach initial stages of flower formation were observed in
Virginia the first week in July;''^ Quaintance^^^ in Georgia found no
indication of differentiation in Demming's September peach on June 14,
but on July 23 he reported: "the embryo flower is well under way
and the calyx lobes are quite pronounced." Apparently, then, the initial
stages must have occurred late in June. Goff,^'' working with a
Bokhara peach, considered that "flowers began to form about the middle
of September the past season." At Davis, California, the first evidence
of differentiation in the almond has been reported as about Aug. 18. ^^^

The plum as investigated by Drinkard shows some variation in the
time of initiation of fruit buds. Whitaker, one of the Wildgoose group,
gave no evidence until the first week in September; "observations on sev-
eral varieties of Japanese plums showed that the initial formation of fruit

188 FUNDAMENTALS OF FRUIT PRODUCTION

buds occurred during the second week in July; and the individual fruit
buds within the cluster were clear and distinct on August 7th. "^^ In
Wisconsin, flower formation has been found under way in the Aitken plum
on Aug. 9 and some differentiation in the Rollingstone on July 8 in 1899
and on July 5 in the following year.'^

In the Louis Phillippe cherry of the Morello group, signs of differ-
entiation have been noted on June 30 in Virginia. Goff, working with
the King's Amarelle cherry, found the earhest indications of flowers
on July 11^^ and in the following year on July 8. At Heidelberg,
Germany, blossom primordia of the sweet cherry were visible during
July.«*

Investigations of flower-bud formation in the small fruits were
made by Goff. In the strawberry Sept. 20 was the date of the first
indication of flower buds.''^

Differentiation was found to occur in the Pomona currant about
July 8 and in the Black Victoria currant about Aug. 3.^^ In the Down-
ing gooseberry there was evidence on Aug. 30; in the cranberry no clear
signs were found until Sept. 16. Less definite observations were made
in raspberries and blackberries; nevertheless, unquestionable evidence
shows that the flowers are formed the year previous to blossoming.
"In the raspberry and blackberry," states Goff, "the buds that form
in the axils of the leaves of the young shoots contain a whole branch in
embryo — often several nodes, with a leaf at each node. The bud at
the apex of this branch and the axillary buds along it, if they form, are
flower-buds . . . embryo flowers in those buds are formed the season
before their expansion, at least in part. "

Fruit bud formation in the grape occurs during the summer previous
to blossoming. A single bud contains in embryo a shoot with blossom
primordia. General observations to this effect are recorded by Goff^''
and Bioletti^^ but no precise determination of the time is available.
Behrens^^ states that the first shoot primordia appear concurrently with
the first swelling of the buds in which they develop (mid-June). Since
these are laid down continuously through the summer many stages are
present on a vine at any one time. Subsequently the blossom primordia
appear. The buds laid down late in the season are likely to be arrested
in their development before the formation of blossom primordia occurs.
Behrens emphasizes the importance of early differentiation in securing
a crop for the following season.

In the filbert (Corylus Avellana) Albert^ found signs of catkins on
June 10, before embyronic leaves were laid down; female blossoms were
not found until early in September. In the beech he was unable to
find blossom buds until the beginning of leaf fall, but since the pollen
mother cells in the anthers had already formed, differentiation must
have occurred much earlier.

THE INITIATION OF THE REPRODUCTIVE PROCESSES

189

In Relation to Position. — Not all fruit buds are differentiated simul-
taneously, even on the same tree. Investigations by Goff"^ convinced
him that in the apple and pear fruit-bud formation may occur after the

Fig. 24. — Stages in fruit bud development of the Yellow Newtown apple. Above, to
the left Sept. 10, to the right Nov. 25; below, to the left Feb. 14, to the right Mar. 6.
(After Bradford.^')

first of September; he suggested as alternatives either (1) two periods
of flower formation or (2) a continual differentiation through the season.
Bradford, working with the Yellow Newton apple, reports least variation
in spurs which have borne previously but are not bearing in the current

190 FUNDAMENTALS OF FRUIT PRODUCTION

season (see Fig. 24) ; terminal fruit buds on long shoots obviously must be
differentiated at a later period than is known to characterize formation
on spurs. Considerable variation in the time of differentiation occurs
also in young spurs which have never before formed fruit buds. Even in
bearing spurs, when they form fruit buds, the formation may occur from
early July to late August. Spurs which had blossomed during the current
season but failed to set fruit varied still more; some of the earliest
differentiation observed was found in spurs of this class and later differ-
ention also occurred.

Magness^^T [^ q^ careful study of axial buds found resting stages of
leaf buds in several varieties as early as July 9 and early in September
he recognized differentiation into flower buds. Some of his preparations
taken in December suggest an initial differentiation into fruit buds,
though he evidently did not regard them as such. In the Tetofski apple
he considered some differentiation to have occurred about the first of
August. He states that a spur bud of July 23 showed as much develop-
i^ent as the most advanced axillary buds of Sept. 2. In the investi-
gations of the following year the "main period of axillary fruit-bud
formation in the varieties studied began after August 1, and a great
many buds were apparently being differentiated on September 8. This
was fully one month later than spur buds on the same trees."

Direct comparisons of the time of differentiation in buds of stone
fruits in different positions are not available. Roberts, ^^^ however,
finds in September a difference in the development of buds on sour
cherries according to their positions on the 4- or 5-inch shoot. This
difference suggests that flower formation is initiated first both in the basal
and in terminal regions. It is probable that a similar condition occurs
in the peach.

Goff'''^ found little or no difference in the comparative develop-
ment of flower buds in rooted runners and parent plants in the
strawberry.

Varietal Differences. — Bradford"-^ found considerable difference be-
tween varieties of apple in the stage of development attained early in
August, indicating a lack of uniformity in the time of differentiation.
Of the varieties observed, Stark, Red Astrachan and Oldenburg seemed
farther advanced than Jonathan, Northern Spy and Grimes. The
season of ripening of the fruit appears to make little difference in the
time of differentiation; there appears to be, however, some correspond-
ence, though not absolute, between the order of blossoming and the order
of differentiation. Magness^^T found White Pearmain, Tetofski and
Yellow Transparent noticeably advanced in development in early July
as compared with Lady and Jonathan.

Goff''^ found considerable difference between varieties in the time
of fruit-bud formation, some forming fruit buds before Aug. 1 while some

THE INITIATION OF THE REPRODUCTIVE PROCESSES 191

were considered to form none until after the first of September. Differ-
ences between varieties of plums have been mentioned earlier.

Differences Induced by Cultural Treatment. — Kirby^''^ notes an earlier
differentiation of fruit buds in apples growing in sod than in the same
varieties in cultivated soil. Still finer distinctions were noted.

"The earliest time," he states, "at which flower buds were formed occurred
on clover sod, with a low percentage of soil moisture. Flower buds formed
earUer on a clover sod than on a blue grass sod having slightly less soil moisture.
On the other hand, flower buds formed earlier on a blue grass sod than on a clover
sod having about 2.5 per cent, more soil moisture. These facts indicate two
things ; first, that the addition of nitrates in the clover sod causes the flower buds
to form earlier; and second, that the amount of soil moisture is a very important
if not the chief external factor in determining the time at which flower buds form.

"The formation of flower buds began about the first of July on the plots
where it occurred earliest and extended until the middle of September on the
plots where it occurred latest, thus occupying a period of about 2>2 months.
The time occupied by each tree in forming flower buds was about 4 weeks."

The time of differentiation in the Baldwin apple in New Hampshire
has been found somewhat variable, suggesting the effect of influences
proceeding directly or indirectly from weather conditions. ^^

Goff^'' supplied water to a 9-year old Gideon apple tree in a dry season.
Comparison on Aug. 9 with a similar unwatered tree showed very little
difference in the stage of development reached at that time, though buds
on the non-watered tree were somewhat more advanced.

In the sour cherry very strongly growing shoots and shoots partly
defoliated by shot-hole fungus were retarded in their development. ^^^
Buds on younger trees were less advanced than those on older trees of
the same variety. Since these studies were made at the approach of
winter they do not furnish conclusive evidence as to the time of differen-
tiation. However, they harmonize with the available direct evidence.

Abnormalities. — Finally, the occurrence of the so-called second
bloom should be noted. Paddock and Whipple^^^ mention a case of
this kind. Similar teratological variations reported by Daniel were
attributed by him to excessive pruning. This occurrence has been
attributed at times to late frosts which destroyed the first blossoms and
induced the formation of another set. This may be a correct explanation
in some instances. The occurrence of blossoms on the vegetative shoots
of several spurs bearing fruit in normal position was noted in an Olden-
burg apple at Columbia, Mo., in 1920; the following year the same tree
showed this phenomenon in about 20 per cent, of its spurs before any
injurious frost occurred. Whether these buds were differentiated the
preceding season cannot be stated positively. However, in the Rome
Beauty apple vegetative shoots from fruiting spurs were observed to
grow to a length of 4 to 6 inches, forming 6 or 7 leaves and then —
still early in the season — to open solitary blossoms. In this case differ-

192 FUNDAMENTALS OF FRUIT PRODUCTION

entiation undoubtedly occurred in the spring. Hand pollination in some
cases resulted in the formation of fruits with seeds of normal appearance
and in Oldenburg without such assistance a considerable proportion
of the crop actually harvested developed from secondary bloom.

Apple trees in tropical climates, though they blossom little, seem not
to be restricted in the time of fruit-bud formation.

The conclusion seems warranted that a fruit bud may be formed
at any time, though ordinarily the period is rather restricted. The
period evidently can be varied somewhat by cultural treatments, includ-
ing perhaps any practice that modifies the rate of growth. In general
the earlier the period of differentiation, the greater the number of fruit
buds finally formed, but as shown elsewhere, with some qualifications,
the less hardy those buds are.

Winter Stages. — Kraus^^* has described in detail the development of
the individual flower within the bud. The sepals are differentiated first,
followed closely by the primordia of the petals. Either simultaneously
with, or directly after, their appearance those of the stamens are laid
down; after these come the primordia of the carpels. The ovules do not
appear until the resumption of growth in the spring.

During November and December in Virginia, Drinkard^^ found
little development of the gross parts of the apple flower but noted some
cytological changes. "During December," he states, "the pollen
mother cells developed large, prominent nuclei. . . . Nearly all changes
which occurred during the month of January took place in the stamens.
... On February 19, there was some indication of renewed develop-
ment in the anthers; these had enlarged appreciably on February 24.
. . . Early in March there was a beginning of development of ovules
in the cells of the ovary. These became very distinct by March 22. At
the same time tetrad formation was going on in the pollen mother cells."

Drinkard found some development during the winter in buds of pear
also. In the peach, growth during winter seemed more active. The ovule
appeared late in December and tetrad formation in the pollen mother cells
late in January, in both instances considerably in advance of the apple.
Similarly the plum was found to show more or less development, practi-
cally throughout the winter. These observations are of interest in con-
nection with the differences in hardiness of fruit buds discussed elsewhere.

However, it has been reported that in New York fruit buds do not
develop from the middle of November until about the first of March^o^
■ and in Wisconsin no evidences of activity were found from the beginning
of freezing weather until after the middle of March. ^^ In fact it was
stated that there was no change in pear flowers from Dec. 1 to Mar. 30.^^
Albert reports pear blossoms to be unchanged until March, though he
records development in the pistils of the filbert during November and
December. In Japanese quince he found that development is arrested

THE INITIATION OF THE REPRODUCTIVE PROCESSES 193

only during cold weather and is resumed whenever temperatures permit.
Many of these blossoms are killed by cold.

Magness^" noted a difference in the stage of development of buds on
spurs in successive years. Buds of the Tetofski apple in November,
1914, showed ovules developed, while in December, 1915, they had not
reached that stage.

"The blooming season during the spring of 1915 was fully one week earlier,"
he states, "than that of 1916. It is quite probable that factors operating during
the late summer and fall to hasten or retard flower development, as well as factors
operating during the spring, materially influence the time of blossoming in our
orchard fruits." This statement is of particular interest when correlated with
Sandsten's work, discussed under Temperature Relations.

Summary. — The available data do not permit a definite statement of
the exact cause or causes of fruit bud differentiation or an exact de-
cription of the internal nutritive conditions associated with fruitfulness
and unfruitfulness. However, there must be at least two antecedents
to an initiation of the reproductive processes: (1) There must be an
excess of carbohydrates above the amount required for vegetative
development. The rate of manufacture must exceed the rate of utili-
zation. (2) There must not be any limiting factor that entirely stops
vegetative growth which must continue within the bud even though there
be no new shoots and leaves formed or even no visible indication of an
increase in the size of the buds that are differentiating flower parts. In
Jthe orchard the supply of available nitrogen is probably the most common
limiting factor. If nitrogen is present in large amounts it forces the rapid
utilization of carbohydrates so that their accumulation cannot occur. If
it is very limited in amount, growth is practically stopped before fruit
bud differentiation can take place. Carbohydrate accumulation may
not in itself be the cause of the fruitful condition in the plant as a whole
or in its individual parts. It may simply be another result of the same
factors that lead to fruitfulness; at least, however, the two are associated.

In practically all the deciduous fruits growing in temperate climates
fruit bud differentiation occurs during the summer or fall previous to the
opening of the buds. Every bud that is formed may be considered a
potential fruit bud, but practically differentiation takes place only when
suitable nutritive conditions are provided. Ordinarily each bud develops
to a certain point and then comes to a comparative rest. Later develop-
ment is as a vegetative bud or a flower bud, depending on whether con-
ditions do or do not favor differentiation of flower parts in the slow growth
that takes place during the period of comparative rest. The exact time
of differentiation varies considerably with variety, seasonal conditions,
moisture supply, method of culture, position on the plant and other
factors. In cold climates there are practically no changes within the bud
during the winter.

CHAPTER XI
SURPLUSES AND DEFICIENCIES

Though much has been written on the function of individual mineral
constituents, it is questionable whether definite roles can be assigned
to them, except in so far as they enter into the composition of specific
organic compounds that have known functions. Thus magnesium is a
component of the chlorophyll molecule, which is essential for photosyn-
thesis. It is important, nevertheless, to know the effects attending a
surplus or a deficiency of one or more mineral elements, so that the symp-
toms may be recognized and the condition corrected. However, patho-
logical conditions found to follow an excess or deficiency of any one
element do not necessarily indicate a direct relation of the element to
the symptoms. Thus, though a deficiency of iron is known to produce
chlorosis, a disordered condition in which chlorophyll does not develop,
iron does not occur in the chlorophyll molecule.

From the considerations in the previous chapters, it follows that
either a surplus or a deficiency of any soil element may affect the plant
by disturbing the balance between its various constituents. A defi-
ciency of an element may also affect the plant when that element is a
limiting factor of growth. In all cases, a surplus or a deficiency must be
understood to mean an amount greater or less than that which is utilized
along with the other elements of the soil. The effect of a surplus of any
essential soil constituent must be upon the balance or equilibrium of the
plant. There may be no effect, since the plant may adjust itself to a
surplus which is merely tolerated. There is much evidence that the
quantities of potassium and calcium in plant tissues are often much in
excess of the amounts used in metabolism. The same undoubtedly
holds for other essential and many non-essential elements such as sodium,
chlorine, aluminum and sihcon. On the other hand, distinct pathological
conditions may ensue which lead eventually to the death of the plant.
Likewise elements which are not essential to the nutrition of the plant
may be tolerated or they may produce disturbances, the effects of which
may be either to stimulate assimilation or to induce pathological con-
ditions and eventually death. As a general physiological theorem, it
may be stated that any substance which is toxic in certain amounts is
stimulating in smaller amounts.

SURPLUSES

The evidences for the existence of pathological conditions due to the
absorption of a surplus of some soil nutrient are practically limited to the
cases of nitrogen and magnesium.

194

SURPLUSES AND DEFICIENCIES 195

Nitrogen. — The results of an excess of nitrogen usually appear the
year following the actual surplus nitrogen absorption. They are shown^*"^
in trees by a tendenc}^ in the fruit to physiological decay. Dieback,
or exanthema, and gummosis of citrus trees also are attributed to a
surplus of nitrogen. '^'■'^ This causes a diseased condition in the growing
tissues of the tree characterized primarily by gum pockets, stained
terminal branches, "ammoniated" fruits, bark excrescences and multiple
buds. The secondary symptoms are an unusually deep green color of
the foliage, distorted growth of the terminal branches, frenching of the
foliage and thick coarse leaves shaped like those of the peach. Mineral
sources of nitrogen, even in great quantities, are not known to produce
dieback though they may accentuate the symptoms in trees already
affected, ^^ but organic fertilizers containing nitrogen often lead to its
development when they are appHed in large amounts.

Magnesium. — The poisonous action of an excess of magnesium
absorbed by the plant is attended by a browning of the roots and of
vessels in the wood, cessation of growth in the roots and eventually death
of the root hairs, the entire roots and leaves. These toxic effects may be
counteracted in large part by calcium through its antagonistic action on
magnesium, previously discussed. It should be pointed out that toxic
effects similar to those following an excess of magnesium have been
observed to develop from oxalic acid and that the toxic effects of other
salts and salt mixtures, such as potassium nitrate with potassium
phosphate, may be corrected by calcium.

Copper. — Of the effects of non-essential elements, those of copper are
among the most striking. Copper salts are poisonous even in exceed-
ingly small concentrations. Water distilled in copper receptacles is
frequently toxic. Coupin''^ found that the lethal dose for grains grown
in water culture was for each 100 cubic centimeters of nutrient solution,
0.0049 gram copper bromide; 0.005 copper chloride; 0.0056 copper
sulfate; 0.0057 copper acetate and 0.006 copper nitrate. Copper salts
absorbed by the roots of the grape are likely to stop root growth. On the
other hand, the stimulating effect of a mixture of copper sulfate and lime
sprayed on leaves is well known. Leaf development is stimulated, the
chlorophyll content increased, the palisade cells become longer and nar-
rower and the spongy parenchyma has smaller intercellular spaces.^"
Without doubt the amounts of copper absorbed by the sprayed leaves are
less than those which produce toxic effects when absorbed by the roots.
Ewert,^^ however, has demonstrated that concentrations of 1 to 100,000,-
000 of copper sulfate are toxic to the pulp cells of the apple and that
minute quantities entering through the stomata after spraying or taken
up by the roots may result in one of the forms of bitter pit. If the con-
tention^^^ that copper is an essential nutrient be correct, then the observed
effects may be the result of counteracting a limiting factor of assimilation.

196 FUNDAMENTALS OF FRUIT PRODUCTION

Arsenic. — Arsenic is another mineral toxic to plants in exceedingly
small amounts. In many of the higher plants exposure to a concentra-
tion of 1 part in 1,000,000 is sufficient to inhibit growth. ^^^ When arsenic
is absorbed by the roots, they show its effects first.

The toxic effects of arsenic on fruit trees are described in an article in the
Horticulturist. ^°2 "When a little arsenic is introduced into the circulation of
a fruit tree at that season (early spring) it first discolors the sap vessels of the
inner bark, then the leaves suddenly flag, and droop; the branch shrivels and
turns black; and finally if the dose is large enough, the whole tree dies." Stimu-
lating effects from arsenic have been observed, presumably when absorption was
restricted to amounts smaller than that indicated above as toxic.

The question of the toxic action of arsenic is one of much interest
since nearly all deciduous orchard fruits require one or more applications
of arsenical sprays each year. In old bearing orchards the total arsenic
used per acre each year is Hkely to be as much as 4 pounds, figured as
arsenic trioxide. Though applied directly to the foliage and fruit, most
of it reaches the ground in the course of the season. It is generally
applied in some very insoluble and chemically inactive form, such as
arsenate of lead. However, there is a considerable accumulation, espe-
cially in the surface soil, as spraying is continued. This has led to con-
siderable uneasiness among growers and much injury has been reported
to be due to these accumulations in some of the irrigated sections. The
injury has taken the form of collar and root rot and in addition it has
often been followed by premature ripening of the fruit and wood in the
fall and the death of the tree the following year. However, it is only in
irrigated sections and in soils with a rather high alkali content that this
trouble has been encountered. This suggests that the injury is attribu-
table to the action of various alkali salts reacting with the arsenic to make
it soluble, to the combined action of alkali salts and arsenic, or possibly
to alkali salts alone, since similar injuries are known to result from alkali
poisoning. Results with Ben Davis apple trees sprayed in one season with
as much arsenic as ordinarily would be apphed in 10 to 40 years and under
conditions where soil alkali was not a factor, have led to the conclusion
that such arsenical poisoning as has been reported from certain sections
is not attributable to the arsenic.^ Some of these applications were so
heavy that the trees not only remained whitened all summer, but the
"ground under the entire head of the tree was so saturated with the
arsenic as to appear moldy white to a depth of 3 or 4 inches." No injury
appeared in the trees or even in the vegetation (including strawberries,
alfalfa and a number of weeds) under some of them. This makes it
evident that little is to be feared from the toxic effect of the arsenic used
in spraying unless the soil has a fairly high alkali content and then the
problem is one of dealing with the alkali rather than with the arsenic.
Arsenic is, however, a contributing factor. Ewert^^ believes that there is

SURPLUSES AND DEFICIENCIES 197

possibility of the absorption through the stomata and cuticle of the fruit
of quantities sufficient to cause local poisoning in the apple, giving rise
to the disorder known as bitter pit.

Manganese. — The relation of an excess of manganese to iron deficit
and the method of curing the diseased condition have been discussed.
In excess, this element produces interesting symptoms, illustrated by
pineapples grown on manganese soils.

The root system is reduced by the death of a large percentage of the fine
branched rootlets some months after their formation. The roots that remain
alive have a superabundance of root hairs, almost every epidermal cell elongating
into one, and also a blunt growing tip, about half as large as a lead pencil,
frequently swollen into an enlarged fleshy end. The formation of these
enlargements seems to mark the end of growth and death soon follows. The
leaf has an irregular surface due to shrinkage from loss of water, producing
prominences which become dark brown. The cells have brown walls and
in some cases the protoplasm eventually disintegrates. The green cells thus
lose their color, become plasmolized and in some cases the nuclei turn brown.
Here also the protoplasm loses its granular structure and disintegrates. As a
result of the lack of chlorophyll, the leaves contain limited amounts of starch,
but at the base of the leaves, in the stalks and roots, starch is abundant, having
been stored there before the decomposition of the chlorophyll. Frequently no
fruit develops, but that which does is reddish pink, without a trace of green,
undersized and excessively acid.>°^

Apparently manganese poisoning is rare in deciduous fruits. In
very dilute amounts manganese has a stimulating effect. ^^

Other Elements. — Compounds of many other elements such as lead,
mercury, zinc, boron^^ and silver are toxic in certain concentrations, but
toxic effects from them are rare. However, these materials are known
occasionally to be absorbed in considerable quantities — zinc for example
up to 13 per cent, of the ash, mercury and copper up to 1 per cent.®^
Ewert^^ has shown that extremely minute quantities of these, in con-
centrations varying from 1 in 1,000,000 to 1 in 1,000,000,000, may
cause local browning in the tissues of the fruit of the apple and induce the
condition known as bitter pit.

Mention may be made here of certain toxic gases such as hydrogen
sulfide, sulfur dioxide, hydrogen cyanide and chlorine. Sulfur dioxide
injury is of considerable practical importance because the damage done
to vegetation by smelter fumes is due largely to this compound.

The bulk of the evidence on the toxicity of inorganic mineral soil
constituents that has been discussed, suggests that the effects are largely
local in the plant. Amounts small enough to be stimulating are unques-
tionably absorbed by the roots, or in the case of spraying, by the leaves,
but amounts large enough to poison the plant seem to induce injury
chiefly by affecting the absorbing organs. Hence cessation of growth

198 FUNDAMENTALS OF FRUIT PRODUCTION

and eventually death of the roots are the primary symptoms. Dis-
orders proceeding from the causes just outlined should be distinguished
from the toxic effects produced by organic compounds or by excessive
soil concentrations, discussed previously.

DEFICIENCIES

The lack of a sufficient amount of any essential soil constituent may
lead to the development of distinct pathological conditions, or it may
result simply in checking vegetative development and fruit production
without producing obvious pathological symptoms. The use of fertil-
izers for correcting both of these conditions is discussed in the two
following chapters in which particular emphasis is accorded the correc-
tion of conditions interfering with fruit production on a commercial
scale. The discussion immediately following concerns the more impor-
tant pathological symptoms which are associated with the presence of
unduly small amounts or with the complete exhaustion of essential
mineral elements.

Nitrogen. — A deficiency of nitrogen may become evident in several
different ways. The plant may be dwarfed, though it develops com-
pletely and produces flowers, fruits and seeds. As a rule, however, the
leaves are pale green because of the relatively small amounts of chloro-
phyll and the development of the mature fruit is affected in one way
or another. There may be an incomplete development of the sexual
organs, and consequent unfruitfulness;^^° in case fruits develop they may
be seedless, as in apples, pears and grapes, ^^^ or the fruit may develop
somewhat but drop prematurely. This is a common result of nitrogen
deficiency in apples and pears. The latter sometimes show excessive
thorn development in connection with a lack of nitrogen. ^'^^

Phosphorus and Potassium. — A deficiency of phosphorus appears
to produce no characteristic symptoms. Chlorophyll development is
not affected, but the plant does not increase in dry weight.

A deficiency of potassium^''" is usuallj^ associated with a scarcity
of carbohydrate reserves. In trees, the terminal shoots show weak
development and eventually dry out, or shoot formation may be
suppressed wholly. Plants suffering from a lack of potassium often
maintain a health}'- appearance longer than those lacking nitrogen or
phosphorus. Whatever potassium is available apparently is used first for
vegetative growth and development and, if there is no residuum, the plant
does not blossom. Eventually the leaf blade becomes yellow on the
edges and between the veins, then brown and finally white, while the
veins and petiole remain green. This condition is known as a frenching
of the foliage. A potassium deficiency renders the roots susceptible to
rotting and the plant eventually dies. When nitrogen or phosphorus is
deficient, plants are likely to remain alive longer in a stunted condition.

SURPLUSES AND DEFICIENCIES 199

Sulphur. — As a result of sulphur deficiency, cell division is retarded
and fruit development is suppressed, '^^^ but the plant is able to develop
vegetatively to a limited extent.

Iron. — A lack of iron produces the well-known condition of chlorosis
or yellows. This is not characteristic solely of iron want, for it may
result eventually from a lack of either nitrogen or magnesium, but the
effects of iron deficiency in producing chlorosis are more rapid than
those of nitrogen insufficiency and consequently more striking. When
iron is deficient, developing leaves are at first able to avail themselves
of iron in older tissues. Later the new leaves are green only at the tips
and eventually the newly developed leaves are entirely yellow. Chloro-
plasts develop in them, but they contain no chlorophyll. Recent
investigation^*^ has shown that organic compounds containing the pyrrol
ring, which appears in the structure of chlorophyll, correct the condition
of chlorosis produced by iron want, suggesting that iron may have
something to do with the formation of this ring. However, since iron is
just as essential for fungi and other parasitic plants which have no chloro-
phyll as for green plants, its importance cannot be limited to the part
it apparently plays in the synthesis of the pyrrol ring.

Magnesium and Calcium. — A deficiency of magnesium^" reduces
fruit formation and eventually produces chlorosis. This is to be expected
since magnesium is a constituent of chlorophyll. Cell division in the
epidermis is also affected.

A lack of calcium interferes with carbohydrate transportation and
utilization, but does not stop its manufacture. These disturbances
may be associated with the formation by calcium of insoluble salts with
substances which are products of carbohydrate utilization, as oxalic
acid. A lack of calcium would result in an accumulation of oxalic
acid, which is toxic in solution. This might be expected to interfere
with the processes of carbohj^drate utilization. Root growth is retarded
or stopped, an effect already mentioned as resulting from an excess
of magnesium. Hence some of the effects of calcium deficiency may
be associated with the resultant effect on the calcium-magnesium ratio. ^^^

Chlorine. — Though chlorine is not an essential element, some mention
should be made here of the effects of an absence of chlorine. There
are conditions in the field under which the best development occurs
only when chlorides are added to the soil."" Recent investigations show
that the effects of chlorides are markedly different on different plants,
but that in many cases they serve directly or indirectly as a fertilizer. ^^^

AN ANALYSIS OF THE FERTILIZER PROBLEM

The data that have been presented on the factors affecting soil
productivity on the one hand and the metabolic processes going on within
the plant on the other, emphasize the incompleteness of the knowledge

200 FUNDAMENTALS OF FRUIT PRODUCTION

of plant nutrition. Much important information has been obtained
regarding changes occurring in the soil and something is known of the
synthesis, translocation, storage and utilization of organic materials.
At best, however, this information is fragmentary and much generah-
zation regarding the use of fertilizers in the orchard is unsafe. Some
idea of the complexity of the problem is obtained when we consider
the numerous ways in which fertilizers may act: (1) to change conditions
in the soil and (2) to disturb or restore equilibria within the plant.
Among the more important of these methods of action may be mentioned
the following:

1. Altering the physical properties of the soil.

2. Affecting the displacement (lyotropic succession) of various elements.

3. Changing the solubility of other soil constituents.

4. Changing the availability of other soil constituents.

5. Changing the concentration of the soil solution.

6. Changing the reaction of the soil solution.

7. Influencing bacterial activity in the soil.

8. Correcting or disturbing the balance between certain soil constituents, e.g.,
calcium and magnesium antagonism.

9. Stimulating or checking chemical reactions in the soil or absorption by the
roots.

10. Acting as toxins or protecting against their influence.

11. Serving directly as nutrients for the plant.

12. Restoring or disturbing chemical equilibria within the plant after absorption.

The Fertilizer Requirements of the Orchard. — In the discussion that
has preceded some attention has been devoted to each of these factors
in the nutrition of the plant. There has been presented also a general
resume of some of the available information regarding synthesis, trans-
location and use of certain plant constituents. Incidentally the following
facts have been brought out:

1. Many elements that evidently are not required are found in plants.
Seldom are they harmful; they are merely tolerated. Among them may
be mentioned sihcon, aluminum, sodium, manganese, titanium and
probably chlorine. These elements are not required in fertilizers. They
may be combined with certain others that are of importance and they may
have some indirect influence upon the physical condition of the soil or the
chemical nature of the soil solution. They may often serve a useful pur-
pose in furnishing some of the so-called "indifferent" ash and occasionally
some distinctly beneficial response attributable to their presence may be
obtained when they are carried in fertihzers, but on the whole they need
not be given serious consideration in the problem of orchard fertihzation.

2. Certain elements are found universally in plants and are necessary
constituents; however, except in very unusual cases, they exist in the soil
in sufficient quantities and in forms sufficiently available to meet the
requirements of orchard trees. The plant often takes up more than it

SURPLUSES AND DEFICIENCIES 201

uses. This surplus is merely tolerated and usually no harmful influence
results. Among these elements may be mentioned potassium, calcium
and magnesium. As with the preceding list, their application in fertilizers
may indirectly benefit the plant through improving physical and chemical
conditions within the soil, or restoring a proper ratio between them in the
case of the last two.

It would seem that sufficient evidence to support these statements has been
presented in the discussion of the individual elements that has preceded. It is
realized, however, that they run counter to the opinions that have been expressed
in a great number of published statements dealing with this question, to many
recommendations that have been made for the fertilization of fruit trees, to
what has in some instances become more or less well established practice and to
the apparent results of certain plot experiments. This is true particularly in the
cases of potassium and calcium. It seems desirable, therefore, to bring together
the results of some of the orchard fertilizer experiments with potash and lime
and examine them somewhat critically. Table 66 presents such data gathered
from many sources. It does not include all the records that might be assembled,
but it represents the results of American plot trials.

In some cases the application of potassium- or of calcium-carrying fertilizers
has resulted in increased yields; in others in decreased yields. The increases
outweigh the decreases in both number and amount; but in the Pennsylvania
experiments alone, of those included in the table, are the increases striking or
to be regarded as of considerable significance. These particular Pennsylvania
records are extremes purposely chosen from a large number, the great majority
of which show no such marked response from potash applications. Furthermore,
the different check plots in these two orchards show such variation as to justify
some hesitancy in drawing conclusions when comparing the results of one fer-
tilizer treatment with those of another on a plot some distance removed from
the first. For instance, it may be questioned if the plots treated with lime alone
and with nitrogen alone were as good at the outset as those receiving nitrate of
soda and muriate of potash. In nearly every case in which comparison is possible
between potash or lime treated plots and those treated with nitrogen alone or in
combination, nitrogen stands out as the element most needed, the one from the
application of which the greatest response is obtained. The fact that in most
cases the application of nitrogen alone resulted in yields exceeding those afforded
by potash or lime is further evidence that there was an ample supply of these
two elements in the soil for larger crop production, that they were present in an
available form and that they were not the real hmiting factors. Theoretically
potassium and calcium are to be considered as possible limiting factors just as
nitrogen or iron or phosphorus or sulfur. Here and there is to be found evidence
that occasionally they actually are not present in an available form and in
quantities sufficient for the trees' requirements, but in the great majority of
cases there is no occasion to supplement the supply already present in the soil.

3. Certain elements, such as copper, arsenic and lead, are occasionally
found in plant tissues and when present in considerable amounts they
have toxic effects. However, their presence is the result of spray applica-

202 FUNDAMENTALS OF FRUIT PRODUCTION

Table 66. — Influence of Potash-carrying Fertilizers upon Fruit Yields

Investigator

Alderman^. . . .
Alderman-. . . .
Alderman^. . . .

Mc Cue"i

Mc Cue"i

Mc Cue"i

Gladwin'*

Gladwin'*

Gladwin'*

Gladwin'*

Bailout

Ballous

Hedrick, et alw
Hedrick, et al^'

Reimer'5*

Reimeri"

Reimeris*

Reimeris*

CoUison'o

CoUison'"

ColUson'"

Collison^o

CoUison^o

CoUison^o

Chandler25. .. .

Brown^o

Franklin 6 8

Munsoni37. . .
Munsoni37. . . .

Stewarti's

Stewart'"

Stewart! '8

Stewarti'8

Stewart"'

Stewart!"

Stewarti"

Stewart'"

State

West Virginia
West Virginia
West Virginia
Delaware
Delaware
Delaware
New York

New York
New York

New York

Ohio

Ohio

New York

New York

Oregon

Oregon

Oregon

Oregon

New York

New York

New York

New York

New York

New York

Missouri

Oregon

Massachusetts

Maine

Maine

Pennsylvania

Pennsylvania

Pennsylvania

Pennsylvania

Pennsylvania

Pennsylvania

Pennsylvania

Pennsylvania

Crop

Fertilizer

Yield

Yield of
check

Gain, per
cent.

Peach

K + P

42.42

49.48

-14.2

Peach

K + N

71.93

49.48

45.3

Peach

Lime

60.82

49.48

22.9

Peach

K

764.40

684.30

11.7

Peach

K

1565.90

684.30

129.6

Peach

N

2210.80

684.30

223.0

Grape

K2SO4

NaN03 +

940. 50

711.00

32.3

Grape

K2SO4

1185.50

711.00

66.7

Grape

N+K + P
N+K+P+

1230. 50

711.00

73.0

Grape

Lime

1118.00

711.00

57.2

Apple

KCl

96.00

69.90

27.2

Apple

NaNOs

315.60

69.90

351.2

Apple

KCl

4877. 00

4375.00

11.5

Apple

KCl + P + N

4823. 50

4375.00

10.2

Apple

KCl

3.31

2.85

16.1

Apple

N

14.50

2.85

408.5

Peach

KCl

30.00

30.80

-2.6

Peach

N

42.25

30.80

37.2

Apple

N+P + KCl

79.00

76.80

2.9

Apple

N + P

77.10

76.80

0.4

Cherry

N + P + KCl

122.70

111.60

9.9

Cherry

N + P

105. 90

111.60

-4.9

Grape

Lime

280. 00

220. 00

27.2

Grape

Lime

261.00

443.00

-69.7

Strawberries

KCl

11.10

14.20

-21.8

Strawberries

K2SO4

222.00

230. 00

-3.5

Cranberries

K

43.25

48.18

-10.3

Apples

KCl

f.60

2.30

11.5

Apples

K2SO4

2.28

2.30

-0.9

Apples

N + KCl

318.20

117.80

170.2

Apples

N

186.20

98.00

90.0

Apples

P + KCl

113.10

75.60

49.6

Apples

P + K2SO4

91.30

93.20

-2.4

Apples

Lime

73.70

67.70

8.9

Apples

N + KCl

350. 40

230. 30

52.1

Apples

N

236. 80

208. 40

13.1

Apples

Lime

61.00

53.80

13.4

tions or unusual conditions of one kind or another and the problems
incident to their presence are hardly to be considered as belonging in the
field of nutrition.

4. Two elements, phosphorus and sulfur, are found in all soils and
in all plants. Though they are necessary for plant growth, deciduous
fruits are able ordinarily to obtain all of them they require. However,
their apphcation in fertiUzers is frequently warranted, mainly because
of their indirect value to the trees through the effect they may have
on intercrops or cover crops. Some attention is devoted to this phase
of the orchard fertihzer problem.

5. Two other essential elements, iron and nitrogen, though found in all
soils, are often either deficient in quantity or present in forms unavailable

SURPLUSES AND DEFICIENCIES 203

to the plant. The result is arrested development or, in extreme cases,
the appearance of pathological conditions. An excess of nitrogen
also leads to disturbed nutritive relations and to pathological symptoms.
Considerable attention has already been devoted to the question of iron
deficiencies and to methods of dealing with them.

6. Elaborated organic compounds of many kinds have uses in growth
processes equal in importance to those of the mineral constituents.
Though for the most part they are synthesized within the plant, the
materials for their manufacture are water, carbon dioxide and the
nutrients just mentioned.

It is therefore evident that the question of fertilizers for deciduous
fruits, in so far as such fertilizers serve more or less directly as nutrients
for the plant, centers largely around the proper use of nitrogen. This is
far from stating that fertilizers other than those carrying nitrogen are
never of direct nutrient value. For instance, work with grapes and
strawberries^^ suggests strongly that sulfur-carrying fertilizers in the one
case and phosphorus-carrying compounds in the other supplied the plants
directly with these nutrients, though it is possible that certain of their
indirect influences may have been more important than their direct
effects. Furthermore, there is reason to believe that many of the results
obtained from the use of phosphorus-, potassium- and calcium-carrying
fertilizers on deciduous fruits of different kinds and generally attributed
to their direct nutrient value have in reality been due to their functioning
in other ways. These statements are not made to minimize the possible
effects or uses of fertilizing elements other than nitrogen. That they
often are of value in the orchard there is no doubt. The point is that
nitrogenous fertilizers act more or less directly as nutrient-carrying
substances; others act rather indirectly through correction of unfavorable
soil conditions or by protecting the orchard plants from harmful sub-
stances or only indirectly as nutrients through assisting the growth of
intercrops or cover crops. Clear differentiation between these different
modes of operation is important, for only when there is a clear conception
of how a fertilizer works can it be used intelligently and with certainty
as to results.

CHAPTER XII
THE APPLICATION OF NITROGEN -CARRYING FERTILIZERS

The general purpose of fertilizer application is to increase yields.
In the orchard this may result from larger tree growth, from increased
fruit bud formation, from better setting of the fruit, from the production
of fruit of larger size, or from a combination of two or more of these
rather distinct responses.

The Influence of Nitrogenous Fertilizers on Vegetative Growth. —
An abundant supply of available nitrogen in the soil has long been
associated, by well informed gardeners, with strong, vigorous growth.
So well is this connection recognized that gardeners and florists generally
have become skilled in the art of using nitrogenous fertilizers for vege-
tables and ornamental plants. Fruit growers, however, though inclined
to recognize the general value of such fertilizers, have, for one reason or
another, not employed them to any considerable extent and it is not until
recent years that much experimental evidence has been available as to
their place in orchard practice.

In Peaches. — Alderman^ reported the results of a series of fertilizer
experiments with peaches in West Virginia. The trees were growing in
a rather thin shale loam, a soil commonly used in that section for apples
and peaches, though it would generally be classed as rather unproductive.
Some of his data pertaining to shoot and leaf growth are assembled in
Table 67. They show that wherever nitrogen was used, shoot growth was

Table 67. — Effect of Fertilization on Vegetative Growth of the Peach
{After Alderman-)

Fertilizer treatment

Average
shoot

length,
4-year

average

(inches)

Average
leaf area,
3-year
average
(square
inches)

Number

per tree,
3-year
average

Leaf area „

Per cent

per tree,

3-year

average

(square

feet)

of fruit
buds,
4-year

average

Nitrogen and phosphoric acid.

Nitrogen and potash

Complete fertilizer

Potash and phosphoric acid. .

Check

Complete fertilizer

Complete with potash doubled
Complete with potash tripled. .
Lime.

16

10

14

47

15

00

8

16

7

28

14

40

15

59

15

00

7

84

28
26
06
63
89
12
39
4.26
3.26

25,424
24,808
23,208
8,768
10,596
29,536
32,368
22,648
14,172

755.6
734.4
654.3
160.1
212.6
845.0
986.7
670.0
320.8

80.6
75.5
74.0
58.0
57.9
76.6
75.2
76.2
64.4

204

THE APPLICATION OF NITROGEN -CARRYING FERTILIZERS 205

practically doubled; this increased shoot growth was accompanied by a
corresponding increase in leaf number. Furthermore there was a great
gain in leaf size; this increase coupled with the greater number of leaves
multiplied the total leaf area by three or four. In commenting on this
effect of nitrogen, Alderman- remarks: "... for every foot of bearing
surface on the check tree the fertilized tree carried over 23^-^ feet of wood
upon which fruit might be borne. This difference in size has been increas-
ing so that the ratio would be much greater in favor of the nitrogen
fertilized trees at the present time after 4 years of treatment." Inci-
dentally the data presented in this table verify earlier statements to the
effect tjiat few orchards require potash, phosphoric acid or lime.

In Apples. — Lewis and Allen^^^ have reported practically the same
influence on the shoot growth and foliage of apple trees in the Hood River
valley, Ore., when nitrate of soda was applied to bearing apple trees in a
rather weakened condition. They observed an even more striking change
in the color of the foliage, which was pale j^ellowish green in the check
plots and dark rich green in those that were fertilized. Still another
effect noted many times is delayed leaf fall. This delay may vary from
a few days to several weeks. Since the leaves late in the season can
build elaborated foods for winter storage and spring utilization, this
delayed maturity may bring about an accumulation of materials which
might promote greater vegetative growth the following season and main-
tain the tree in a more vigorous condition. At the same time, however,
danger from sharp fall frosts or early freezes is increased, especially if
applications are heavy enough to force the formation of new vegetative
tissues late in the season. Consequently considerable caution should be
exercised to apply nitrogen so as to postpone leaf fall but not materially
to delay maturity of wood.

In Strawberries. — Chandler-^ reports that nitrogen in either nitrate
of soda or dried blood applied to strawberry plants in the spring before
the crop is harvested causes excessive leaf growth and that when the
latter material is applied even a year before the crop is to be harvested
it causes considerably increased vegetative growth. This excessive
leaf growth was found to be associated with decreased fruit production.
I Negative Results. Nitrogen Not a Limiting Factor. — On the other
Tiand, Hedrick and Anthony^*^ in reporting the results of 20 years of
experimentation with fertilizers in apple orchards in New York state:
"... heavy applications of nitrogen in a complete fertilizer and in ma-
nure have not increased tree growth. " The results obtained by Stewart^^^
in Pennsylvania from the use of nitrogen-carrying fertilizers in bearing
apple orchards are for the most part in accord with those of Lewis and
Allen; at least most of his applications of nitrogenous fertilizers resulted
in increased vegetative growth. However, some of these increases
were comparatively small and there were a few instances in which no

206

FUNDAMENTALS OF FRUIT PRODUCTION

increase was obtained. Gourley^^ found substantially the same general
condition in his experimental plots in New Hampshire — particularly
during the early years of the experimental treatments. Table 68
assembled from data presented by him and some of his associates,^
recapitulating the first 5-years' results, explains some of the preceding
statements that at first appear more or less conflicting. This table
shows practically no increased vegetative growth accompanying the
use of fertilizers, as compared with plots under clean cultivation or plots
growing annual cover crops, even though one of the fertilizers contained

Table 68.

-Response in Vegetative Growth from Fertilizer Applications

{After Gourleif^)

Treatment

Nitrates
in soil in
parts per

million,
4-year

average

Yield of
fruit, 5-

year
average

Shoot
growth,

4-year
average

Size of
fruit, 4-

year
average

Leaf
area,
1913

Fresh

leaf

weight,

1913

Sod

3.18

17.40
33.91

100
132
176
213
216

191

195

166
163
161

100
140
163
190
212

222

198

200
217
202

100
168
165
142
135

165

155

168
196
206

100
107
113
119

124

129

126

126
125
131

100

111

Cultivation every even year

117
123

123

Cultivation, cover crop and complete

135

Cultivation, cover crop and complete

131

Cultivation, cover crop and excess
PjOs

131

Cultivation, cover crop and excess N.

Cultivation, cover crop and excess

K-0

128
134

relatively large amounts of nitrogen. However, soil cultivation,
particularly when coupled with cover crops, made available to the
plants an abundant supply of nitrogen — a supply that obviously was
present in the sod land, but unavailable. This abundant supply met
the trees' nutritive requirements and the surplus resulting from appli-
cations of nitrate did not effect any consistently increased growth.
In a report on the same series of experiments 5 years later Gourley^"
states that though there was no special or marked increase in yield in
the fertihzed plots over those not receiving fertihzer "the orchard is
developing in that direction." In other words, the period of maximum
production without applications of nitrogenous fertilizers had been
reached. This period might last for a number of years, or be of short
duration; in either case greater and greater increases in vegetative
growth and fruit production could be expected from proper fertiliza-
tion. As trees increase in age and size they require larger amounts of

THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 207

nutrients and with the actual reduction in the total nitrogen supply of
cultivated soils taking place each year it is easy to see how the margin of
safety may disappear entirely. Increased vegetative growth follows
the apphcation of nitrogen-carrying fertilizers only when the supply
of available nitrates in the soil is less than the plant must have for its
best growth and there is a limit to what the plant can use. Within
limits, surplus amounts of available nitrogen, like surplus amounts of
available potassium or calcium or other materials, are simply tolerated.
Analyses are not at hand showing the exact amounts of available nitrates
in the West Virginia and Oregon soils to which reference has just been
made, but it may be presumed that they contained very small amounts
or amounts smaller than those required by the trees for maximum
growth and production.

Many orchards will not respond to nitrogenous fertilizers because
the soils and the methods of soil management are of such a character
that nitrogen is not a limiting factor. On the other hand experience
shows that there are many orchards in which nitrogen is a limiting factor
and in which, consequently, nitrogen-carrying fertilizers can be used
profitably. To conclude from one experiment or a series of experiments
giving negative results that orchard fertilization in general is not needed
or that it does not pay is as erroneous as it is to conclude from striking
returns on a nitrate deficient soil that orchards generally should be
regularly fertilized with that element. Statements that have been made
give some idea of the symptoms of nitrogen starvation. Short, slender
shoot growth and small pale leaves are perhaps the most frequent indices
of this condition, though there are many others. However, some of
these symptoms likewise characterize injuries resulting from deficient
water supply, borer attack or other troubles and care should be exercised
to identify the real cause or causes of the trouble before deciding upon
fertilization of any considerable area.

A given supply of available nitrogen in the soil though entirely ade-
quate for the requirements of one fruit crop may not prove sufficient for
the best growth of another. Thus Chandler-'^ has found that in a certain
clay loam in New York applications of nitrogen-carrying fertilizers
resulted in greatly increased shoot and leaf growth in gooseberries and
red raspberries, though currants and black raspberries showed but little
response. Reimer^^^ reports that in the Rogue River of southern Oregon
the Yellow Newton apple does not respond to fertihzer applications so
readily as Esopus (Spitzenburg). Much yet remains to be done toward
determining the actual total yearly nitrate requirements of different
fruit crops and also their varying requirements from season to season
with increasing age.

Influence of Nitrogen On Blossom Bud Formation. — It is not the
intention at this point to discuss in detail the many factors influencing

208 FUNDAMENTALS OF FRUIT PRODUCTION

blossom bud formation. It is generally conceded, however, that fruit
bud initiation is in a way a response to nutritive conditions within the
plant and it has been shown that these nutritive conditions are modified
by the nature of the soil solution. At least theoretically, then, it should
be possible to influence fruit bud formation through the use of fertilizers.

In Peaches. — In a preceding paragraph Alderman- is quoted as report-
ing that in his fertilizer experiments with peaches in West Virginia the
application of nitrogen-carrying fertilizers resulted in more than double
the shoot growth and hence double the amount of possible fruit-bearing
surface. Data on fruit bud formation on these shoots are presented in
the last column of Table 67. If these figures for numbers of fruit buds
per unit of shoot length were plotted, the curve would take the same general
direction as one for figures on total shoot length, though the two would
not be exactly parallel. In commenting on these data Alderman^ says:
the ' ' table . . .shows during the first 3 years a uniformly high percentage
of fruit buds formed on the nitrogen-fed plots and a correspondingly low
percentage in plots 4, 5 and 9 (those receiving nothing, potash and
phosphoric acid or lime only). By 100 per cent, set of buds we mean that
practically all the new growth is filled with double buds from base to tip
. . . while a 50 per cent, set would indicate that buds were found over
only about one-half the twig and were single in many cases."

In Apples. — The situation is somewhat more complicated in fruits
like the apple that bear mainly upon spurs. However, Roberts^^^ has
reported that there is a distinct correlation between the annual increase
in length of spurs and their blossom bud formation. Both those spurs
making a very short and those making a very long annual growth did
not form many fruit buds, but, on the other hand, those that made a
medium growth were highly fruitful. Length was in turn correlated
directly with number of leaves and total leaf area and within certain
hmits {i.e., for the shorter spurs) there was also a correlation between
spur length and average leaf area. Experiments on the influence of nitrog-
enous fertilizers on spur length are reported by Roberts^''^ as follows: "In
1918 the difference in spur growth of non-bearing Wealthy was as follows:
check trees 4.89 mm.; nitrate of soda 11.98. In 1919, when there
was a larger growth on checks than usual, less difference was also noted.
The figures for different trees than those used in 1918 are: check 7.41;
nitrate 9.25." In general the influence of the nitrate was to increase
the length of the spurs and consequently leaf numbers and total leaf
areas. In the trees with spurs too short for fruit bud formation the effect
would be to encourage that process; in those trees with spurs averaging
just long enough or a little too long for maximum fruit formation the effect
would be to discourage it. Roberts'^^ also points out certain correlations
between the amount of shoot growth and the number and character of
fruit spurs. This suggests a further indirect correlation between fertilizer

THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 209

applications and fruit bud formation, for the amount of shoot growth is
greatly influenced by the available nitrate supply. The work of Hookeri"*'
and others showing the importance of the synthesis and storage of organic
compounds in late summer and fall in determining the amount and char-
acter of growth early the next season suggests still further indirect correla-
tions— correlations no less important, though less easily recognized, than
those first mentioned.

Influence of Nitrogen on the Setting of Fruit. — The influence of
nitrogenous fertilizers on shoot and leaf growth and on the formation
of fruit buds is not less striking than their effect on the setting of fruit,
especially in rather weak trees that still bloom heavily. This is well
brought out by the data presented in Table 69, for apple trees in the Hood
River valley.

Table 69.— Influence of Nitrate of Soda Applications upon Set of Fruit in
'_/ Two Hood River (Oregon) Apple Orchards

{After Lewis and Allen^-^)

Number of

Percentage

Percentage

Average

Treatment

blossoming

of fruit set

of fruit set

yield per tree

spurs

June 4

Sept. 30

(bushels)

First orchard:

Check (unfertilized)

483

35.3

16.4

3.75

Fertilized with nitrate. . .

.542

68.0

.30.7

21.50

Second orchard:

Check (unfertilized)

386

9.0

4.6

1.33

Fertilized with nitrate . . .

620

58.0

15.1

9.50

^The setting of fruit in the fertilized plots ranged from 100 to 300 per
cent, higher than that in the check plots. Furthermore this influence
was evident right after blossoming, certainly not later than the time of
the so-called June drop. This was only a very short time after applica-
tion and shaws the prompt response obtained from such a quickly avail-
able fertilizer. Similar results have attended the spring use of nitrate
of soda in many other experiments with apples and pears. Indeed so well
is the use of this fertilizer gaining recognition for this purpose that large
quantities are now used in commercial orchards to deal with many of the
difficulties that formerly were considered pollination problems. There
are few data showing the influence of quickly available nitrogenous
fertilizers on the set of other deciduous fruits, such as peaches, cherries,
apricots and grapes. In view of their known influence in apples and
pears this subject demands careful investigation.

Influence of Nitrogen on Size of Fruit. — Since the size the fruit
attains is an expression of the plant's vegetative activities it may be
supposed that the factors or treatments leading to an increased shoot

210

FUNDAMENTALS OF FRUIT PRODUCTION

and leaf development will likewise lead to increased size of fruit. This
expectation is justified by the results of many field trials with orchard
fertilizers. Representative of many data that might be introduced
are those presented in Table 70 for apples. In terms of percentages,
the increase in size there reported amounts to 25 or over.

Table 70.

-Size of Apples as Influenced by Nitrate Applications

(After Lewis and Allen^-^)

Per cent, grading

Treatment

175 to 150 per
bushel

138 to 112 per
bushel

100 per bushel
and larger

Check (no fertilizer)

22.09 39.76
2 28 26 91

38.15
70 76

Pears from nitrate fertilized trees in the Rogue River valley have
been reported to average about 178 to the box, while those from unfertil-

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>/v

^>x^.

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s

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^--

-^

^^

Fig. 25. — Response of apple trees to fertilizer treatments, showing increases or decreases
in yield, fruit setting and fruit coloration accompanying increased shoot growth. (Plotted
from data given by Stewart. ^''^)

ized plots averaged 225.^^"* The graphs in Figs. 25 and 26 indicate in a
general way the observations of Stewart in Pennsylvania and Alderman in

THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 211

Virginia on the influence of fertilizer treatments on fruit size, especially
as increases in size are correlated with increased or decreased vegetative
growth and with increased or decreased yield. In some of the cases
reported by Stewart, but not shown in the graphs, fertilizer applications
were accompanied by decreased size of fruit. In commenting on his

120

90

80

60

50

.-^0

20

^/^ata Stewart^^* says: "In the
matter of fruit size, some benefits
are indicated . . . but they have
proved less as a rule than is com-
monly supposed. Manure has
naturally been most consistent in
increasing the average size of the
fruit, probably chiefly on account
of its mulching effect . . .in
general we believe that the plant
food influence will always be sec-
ondary to moisture conservation
and proper thinning, wherever
greater fruit size is desired."
Alderman^ in his fertilizer work
with peaches found but little in-
crease in size from the use of
fertilizers, nitrogen in combination
with potash showing slight gains. 0
At the Missouri Station it was
found that in some cases the fer-
tilization of peaches with nitrogen "i-O
was attended by a marked decrease Fig. 26.— Response of peach trees to

„ „ •- ,1 • 1 fertilizer treatments, showing increases or

m Size Ot truit, this decrease some- decreases in yield and fruit setting accom-

times amounting to as much as 40 panying increased shoot growth. (Plotted

, „„„ from data given by Stewart.''*)

per cent. 202

The explanation of the frequent failure of the fruit from fertilized
trees to show an increase in size over that from unfertilized trees and of
the occasional decreases in size lies in the increased wood growth and
leaf area of the plants and consequently in their increased demand for
water. As this increase in leaf surface may sometimes amount to over
100 per cent, it is easy to understand how water may become a limiting
factor. Especially is this true when it is remembered that the osmotic
concentration of the leaves is greater than that of the developing or
maturing fruits and hence in times of stress the fruits may actually lose
water to the leaves which supplies their transpiration requirements
and keeps them turgid. ^^ This, however, is an indirect effect of nitrog-
enous fertilizers on size of fruit, occasionally important in orchard
practice and suggesting that increased attention should be given to

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GROwnL^

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^

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212 FUNDAMENTALS OF FRUIT PRODUCTION

meeting the trees' requirements for moisture when nitrogenous fertilizers
are used. It also raises a series of interesting and important, but wholly
unanswered, questions as to the relative influence different fertilizers may
have on different parts of the tree — for example, roots, leaves, fruit. It
is clear that, at present, there are no means of increasing the size of fruit
directly through the use of any particular fertilizer. Fertilizers can lead
to the production of larger fruit only as they lead to increased vegetative
growth and the consequently increased amounts of manufactured foods
and as they lead to a greater extension of the root system and to a conse-
quently greater intake of water or in still other indirect ways.

Influence of Nitrogen on Color of Fruit. — There has been much dis-
cussion in pomological Hterature concerning the use of fertilizers for
aiding the coloration of fruits and applications of potash and phosphoric
acid have been rather generally recommended for this purpose. Hedrick
was one of the first to submit experimental data bearing on this question.
After a 10-year trial with several varieties in an old New York apple
orchard growing in a rather heavy clay he concluded that no influence
on color of fruit could be ascribed to the potash or phosphoric acid
\/^ which had been used.^" Stewart ^''^ in summarizing the results of his k
work with apples in Pennsylvania says: "None of the fertilizer treat-
ments has resulted in any marked improvement in color. Slight
and irregular benefits are shown by potash and by some of the phosphate
applications, but nothing of any importance ..." Some of the graphs
in Figs. 25 and 26, plotted from data presented by Stewart, furnish clear
evidence in support of his conclusions. Alderman^ reports a reduction of i^
the red color in peaches accompanying the use of nitrogenous fertilizers
and ascribes it to late maturity and to increased density of the foliage.
Conversely, some slight increases in color from the use of potash or phos-
phoric acid he ascribes to the slight checking effect these materials some-
times have on vegetative growth. It is significant that the curves
representing average influence of fertilizers on color are almost exactly
the reverse of those representing their influence on vegetative growth. .
In other words, the two phenomena, those of color formation and new
vegetative growth, are negatively correlated.

Influence of Nitrogen on Yield. — In general the tendency of nitrog-
enous fertilizers is to increase vegetative growth, promote the formation
of fruit buds, increase the percentage of flowers setting fruit and lead
to larger size in the individual fruits. It is inevitable therefore that their
general influence must be greatly to increase yields. Many data might
be presented in support of this general conclusion. Those given in
Tables 71 and 72 represent some of the more striking results that have
been obtained; these, however, have been duplicated in orchards in
many parts of the country. Table 73 is particularly interesting as
emphasizing the importance of nitrogen compared with the other nutrient

THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 213

elements, in increasing yields. Perhaps it should be noted that the trees
in both of these orchards were in a rather weak vegetative condition
before fertilizers were applied.

Table 71.:^Influence of Quickly Available Nitrogenous Fertilizers on
Yield of Apples in the Hood River Valley
{After Lewis and Allen^-^)
Treatment Average Yield per Tree

(in Loose Boxes)
0.90

Check (no fertilizer) .
Nitrate of soda

10.01

In contrast to such striking results from the use of fertilizers it
should be mentioned that nitrogen, alone and in combination with other
nutrients, has been applied to many orchards without resulting in materi-
ally increased yields. Thus Hedrick and Anthony^*^ summarize the
results of a 20-years' experiment in a New York orchard as follows:
"Adding acid phosphate at the rate of 340 pounds per acre per year has
not given a noticeable increase in yield. The addition of 196 pounds of

Table 72i'^^VERAGE Annual Results from Orchard Fertilizers in Ohio
(After Bnllou")

Treatment

Average

yield
per tree
(pounds)

Average
gain per

acre
(barrels)

Value of
increase
per acre

Net
increase
per acre

31.5.6

67.7

$169.25

$163.25

20.5.8

37.4

93 . .50

83.50

93. S

6.5

16.25

8.25

214.2

39.8

99.50

91.50

96.0

7.2

18.00

15.50

100.1

8.3

20.75

20.75

69.9

^vFitrate of soda 5 pounds

Nitrate of soda 5 pounds, acid phos-
phate 5 pounds, muriate of potash
2}4 pounds

Tankage 5 pounds, bone 5 pounds,
muriate of potash 5 pounds

Nitrate of soda 5 pounds, acid phos-
phate 5 pounds

Muriate of potash 5 pounds

Stable manure 2.50 pounds

CGhecks (no fertilizer)

muriate of potash to the 340 pounds of acid phosphate seems to have
resulted in an increased yield. The annual application of 50 pounds of
readily available nitrogen in addition to the phosphoric acid and potash
has caused no increase in yield." Gourley,^^ likewise, working in New
Hampshire with a soil of entirely different character, obtained but slightly
increased yields from the use of nitrogen alone or in combination over
those attending a clean cultivation-cover crop method of soil management
without fertilization. The first of these two investigators states, how-
ever: "An analysis of the soil before the experiment was begun shows that
at that time there was, in the upper foot of soil, enough nitrogen (total)

214

FUNDAMENTALS OF FRUIT PRODUCTION

per acre to last mature apple trees 183 years, of phosphoric acid, 295
years, of potash, 713 years. "^^ Evidently amounts of these nutrients
sufficient for the trees' growth and production were being made available
year after year by various natural agencies. 'The second of the two
investigators, though not reporting on the total nitrogen supply of the
soil, presents data to show that the clean cultivation-cover crop method
of management made available each season plenty of nitrogen, though
after some years there was some evidence that nitrogen applications in
the near future would increase yields. ^"^^ In the presence of abundant
supplies additional applications gave no increased yields worth mention-
ing. Interesting in this particular connection are data presented in
Table 73 showing the effects of various amounts of nitrogen-carrying
fertilizers on yield of pears. The trees were yielding well without

Table 73. — Effects of Various Amounts of Nitrogen-carrying Fertilizers
ON Yield of Pears

{After Reimer^^*)

1917 treatment

Yield,

boxes

per tree

1918 treatment

Yield,

boxes

per tree

Check

12.13
15.12
15.45
16.53

17.03
15.06

Check

15 00

10 pounds nitrate of lime per tree

10 pounds nitrate of soda per tree

5 pounds nitrate of soda per tree

10 pounds nitrate of lime per tree. . . .
10 pounds nitrate of soda per tree

5 pounds nitrate of soda and 5 pounds

superphosphate per tree

18.84
18.37

16 63

5 pounds nitrate of soda per tree

5 pounds nitrate of soda per tree

5 pounds nitrate of soda

17 72

5 pounds sulphate of ammonia

18.23

fertilizer applications but when small amounts of quickly available
nitrogen were applied they at once responded, production apparently
reaching a maximum (thinning being practiced) for the size of trees in
question. Applications of larger amounts of fertilizer under these
conditions resulted in no greater yield. If larger amounts are available
they are not taken up or if taken up they are not used in increased fruit
production. It is economical for the grower to apply only such fertilizers
in such amounts as the tree can use with profit to himself.

The Correlation Between Vegetative Growth and Yield. — Bearing
directly on the question of the influence of fertilizers, particularly nitrog-
enous fertilizers, on yield and also on that much disputed question as to
whether vegetative growth and fruit production are antagonistic tenden-
cies, are the graphs shown in Figs. 25 and 26, plotted from data on apple
yields and growth as influenced by fertilizers in Pennsylvania and from
data on peach yields and growth in West Virginia. The solid lines in
Fig. 25 represent increase in yield (in percentages) resulting from the
use of various fertilizer combinations. The dash-dot lines represent

THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 215

increases in vegetative growth, figured in the same way, length of terminal
shoots being taken as a measure of vegetative vigor. Both lines represent
10-year averages of a number of experiments on mature apple trees
growing under various soil conditions. Though these curves show slight
irregularities, those for increases in growth take the same general direc-
tion as those for increases in yield. In other words, as vegetative growth
has increased, yields have increased, but yields have increased much more
rapidly than vegetative growth. This latter fact would seem to prove
beyond all question not only that increased vegetative growth due to
fertilization is not generally antagonistic to heavier fruit production, but
that within limits it actually encourages heavier fruiting. Data recently
presented for apple tree growth and yields in Delaware lead to the same
general conclusion. ^"^^ Graphs shown in Fig. 26, made from 4-year
averages for increases in peach yields in West Virginia through fertiliza-
tion, show the same relationship between vegetative growth and yield.
Here, though yields have not quite kept pace with the increased vegeta-
tive growth, the conclusion is obvious that in the peach increased wood
growth is associated with increased fruit production.

The same graphs showing the general relationship between vegetative
growth and yield also throw some light on the way in which the fertilizers
have increased production. Under the conditions of these tests about
half of the increased yield was due to the greater wood growth; in other
words, to the effect of the fertilizer in producing additional fruit spurs and
fruit-bud-bearing shoots. The other half oi the increase was due appar-
ently to the greater activity of the old spurs. Presumably increased
yield was not obtained in the New York and New Hampshire experiments
to which reference has been made because the trees' nutritive require-
ments for new wood growth were fully met by the supply already avail-
able in the soil and because they were already producing heavy crops.
That decreased yield often accompanies increased vegetative growth
following the use of nitrogenous fertilizers is indicated by results with
strawberries in Missouri ^^ and with red raspberries in New York."

Influence of Nitrogen on Composition and on Season of Maturity. —
The composition of various plant tissues, especially in so far as their
mineral constituents are concerned, has been shown to be influenced
considerably by the character of the soil in which they grow. Their
composition would be expected, therefore, to show the influence of
fertilizer application. Some interesting experimental data on this
question have been obtained with rj'^e, buckwheat and certain other crops.
These crop plants were grown in what were considered normal media and
in media possessing excessive amounts of certain nutrients. The following
statements from the report on these experiments may be quoted here:^^
"In general it appears as if the nutrients actually required for normal
growth of the crops, when there are plenty of other ingredients to furnish

216 FUNDAMENTALS OF FRUIT PRODUCTION

the indifferent ash, need not exceed 2.0 per cent, of nitrogen, 1.5 per cent,
of potassium oxid, and 0.5 per cent, of phosphoric oxid ... In compar-
ing excessive percentages with the foregoing amounts, it may be noticed
that in certain instances . . . the percentages have increased to the
following high magnitudes: Nitrogen, 3.96 and potassium oxide 5.56 in
1911 in rye; and phosphoric oxide 1.36 in 1916 in buckwheat. Of course,
these amounts are much in excess of what was necessary." The olive
has been said to have a higher oil content when grown on a limestone
soil.^^^ Presumably fertilizing the olive orchard heavily with lime would
have some influence in the same direction. Strawberries on nitrogen-
fertilized plants have been found to wilt more in times of severe drought
than those on unfertilized plants.-^ Wickson^''^ states: "Puffiness of
oranges is clearly due in some cases to excess of nitrogenous manures"
and "the effect of excessive use of stable manures, or of other manures
very rich in nitrogen, upon the products of the vine has been frequently
noted as destructive to bouquet and quality."

There are a number of indirect ways in which fertilization, particu-
larly with nitrogenous fertilizers, influences composition. For example,
the use of nitrate of soda in the apple orchard has been shown frequently
to result in increased size of fruit; such differences in size are often
correlated with differences in texture, in juiciness and in what is generally
termed quality. These influences are not well enough understood,
however, to make possible definite recommendations for the developing
of certain quahties or substances, as sugar or acid or pectins, through the
use of fertilizers. Often resistance or susceptibility to certain diseases is
closely correlated with the chemical composition of the tissues subject to
invasion and even a slight change in composition that might be brought
about either directly or indirectly through the use of some fertilizer might
be of great use in reducing injury from the invading parasite or its toxin.

The effect of nitrogenous fertilizers on season of maturity of the
wood has been mentioned. In the section on Temperature Relations
it is shown that the breaking of the winter rest period in certain fruits
is closely correlated with the time of maturing of the wood in the fall
and in turn susceptibility to low temperatures in late winter is associated
with the breaking of the rest period. Thus, indirectly, applications
of nitrogen may have an important influence on certain forms of winter
injury. Indeed the peach and some other fruits are probably grown
sometimes under conditions where fertilization with nitrogen-carrying
materials may be profitable for this reason if for no other.

Application of nitrate of soda has delayed the ripening of peaches
in West Virginia from 1 week to 10 days, the delay being greater in
the later varieties.^ Observations elsewhere indicate that almost any
material carrying quickly available ' nitrogen has a similar influence
on many other fruits.

THE APPLICATION OF NITROGEN-CARRYING FERTILIZERS 217

In a later chapter it is shown that, within certain Hmits, the plant
shows very much the same response to certain kinds of pruning as it
does to apphcations of nitrogen-carrying fertihzers. In other words it is
possible within certain Hmits to accomplish by proper fertilization
results comparable to those produced by pruning. This is true par-
ticularly in the effects of these two practices on new shoot and leaf growth,
on the better setting of fruit and on the size of fruit. Probably for
best results there should be a judicious combination of both practices.
For commercial production, however, it will often be found more practic-
able to reduce the pruning to a minimum and to depend rather on
fertilization. Fertilizers are comparatively cheap and they are quickly
and easily applied. On the other hand pruning that is properly done
requires considerable judgment and skill and is comparatively expensive.
To the extent that the same results can be obtained by the two methods,
much greater profits will be realized from the investment in fertilizers.

Summary. — In many cases the use of quickly available nitrogenous
fertilizers in the orchard has resulted promptly in considerably increased
vegetative growth, the response being evident in longer shoots and in
greater numbers of leaves that are larger in size and darker in color
than those of unfertilized trees. For the most part these responses
have been made by trees recently showing a lack of vegetative vigor,
trees most likely to be found in sod land or in infertile soils. On the
other hand there has been little evidence of increased vegetative growth
from the application of such fertilizers to moderately rich soils in which
the trees are already making a good growth. In many orchards, therefore
nitrogen is not a limiting factor to growth and in those where marked
responses are obtained from moderate applications, larger applications
often evoke no greater response. Increased blossom bud formation
often accompanies the increased vegetative growth that follows the
use of nitrogenous fertilizers. Fruit setting in trees showing poor vege-
tative vigor is greatly increased. The size of the fruit may be decreased
or increased by the use of nitrogenous fertilzer depending on whether water
is a limiting factor. The correlation between the amount of new vegeta-
tive growth and fruit size is generally positive but not high. Yield, which
is a product of fruit bud formation, fruit setting and subsequent develop-
ment, naturally is often increased greatly by nitrogen applications.
The development of the red color of many fruits is somewhat checked
by the use of nitrogenous fertilizers because of the heavier shade incident
to the increased vegetative growth. Within fairly wide limits fruit
production is found to increase with an increase in vegetative vigor.
The general effect of nitrogenous fertilizers is to delay maturity of
both wood and fruit. Though some influence is shown on the composi-
tion of the fruit, in most cases this is of secondary importance.

CHAPTER XIII
FERTILIZERS, OTHER THAN NITROGENOUS, IN THE ORCHARD

The conclusion should not be drawn from the statements in pre-
ceding chapters that in practice only nitrogenous fertilizers are of value
in the deciduous fruit plantation. A single instance in which a favorable
response attended the use of some other fertilizer would indicate that
the problem should be considered from other points of view; there are
many such instances.

The Indirect Effects of Fertilizers. — Repeated reference has been
made to the direct and possibly indirect effects of fertilizers on the solu-
biUty or availabihty of other soil ingredients, on soil reaction, or on the
plants that constitute the mulch or the cover crop. Without doubt
this last mentioned influence is one of the most important, especially
in orchards not under clean cultivation. In either a sod- or grass-mulch
or a cover-crop method of culture the vegetation produced between the
trees is returned to the soil. Only those mineral constituents are
returned that are obtained from the soil, but in every case there is added
a considerable amount of organic matter which, through its effect on soil
texture and water-holding capacity as well as through the chemical effects
of its decomposition products, plays a very important part in the general
aspect of productivity; with leguminous crops the nitrogen supply is
actually augmented. Furthermore the mineral constituents may be so
changed in form by these intercrops as to be much more available to the
crop plants. It is generally considered that the value of these inter-
cultures is more or less directly proportional to the amounts of vegetation
produced. If this is the case any soil treatment or fertilizer which results
in an increased growth of the interculture may be of indirect benefit to
the tree. As a rule these crop plants grown between the trees are greatly
helped by apphcations of nitrogen-carrying fertilizers made primarily
for the trees' direct and immediate use. Under such circumstances the
trees consequently receive a double benefit from their application, an
immediate benefit from such portions as they are able to absorb before
it leaches away or is used by the other plants and a deferred benefit
realized only when these plants decay.

Phosphoric Acid. — Phosphoric acid is frequently of much indirect
benefit to orchard trees. Some measure of this influence may be obtained
from data presented in Table 74, for an orchard under the sod-mulch
method of management in southern Ohio. Acid phosphate alone in-
creased the yield of mulching material more than threefold and a so-

218

FERTILIZERS, OTHER THAN NITROGENOUS

219

Table 74. — Effects of Certain Fertilizers on the Production of Mulching

Material
{After Ballon'')

Annual fertilizer treatment per acre

Kind of cover crop

Acid phosphate 350 pounds

Acid phosphate 350 pounds, muriate of
potash 175 pounds

Acid phosphate 350 pounds, muriate of
potash 175 pounds, nitrate of soda 350
pounds

Unfertilized

Red clover
Red clover

Timothy, red top, blue grass
Poverty grass, weeds

called complete fertilizer increased it over fourfold. Of equal signifi-
cance was the change effected in the nature of the dominant vegetation.
The unfertilized areas are reported as covered with a thin growth of
poverty grass and weeds. ^ When these areas were fertilized with nitrate
of soda alone or when that material was used in large quantities in com-
bination with other fertilizers, timothy, redtop, bluegrass and orchard
grass rapidly took the place of the weeds and poverty grass. When
acid phosphate was used alone or in combination with potash, clover
came in thickly and crowded out the grasses. The ground was stocked
with all of these species before any fertilizer was applied. The effect
of the different applications was simply to furnish one group or another
with conditions particularly suitable for its growth while the plants of
the other group remained small and stunted. This effect is particularly
interesting in the case of the acid phosphate, as the clover whose develop-
ment it made possible is a nitrogen gatherer and thus the application of
phosphorus would result ultimately in an increased nitrogen supply for
the trees. Probably it w^ould not be safe to recommend generally the
maintenance of the nitrogen supply in the orchard through the use of
acid phosphate, but there are conditions where such a method of pro-
cedure might be entirely practicable and there are probably many other
orchards in which it would be desirable to supplement nitrogen-carrying
fertilizers with those carrying phosphorus.

Sulphur. — Similarly there is reason to believe that vegetative growth
and production maybe increased by the use of sulphur-carrying fertilizers,
even though the soil may contain a supply of available sulphur well in
excess of the trees' actual requirements. Elsewhere in this section it is
stated that in certain fruit-growing sections sulphur is a limiting factor
for the growth of leguminous intercultures, especially alfalfa. In such
cases the judicious use of sulphur-carrying fertilizers may have a far-reach-

220 FUNDAMENTALS OF FRUIT PRODUCTION

ing influence on the trees, though they themselves may not be able to
use any of it. The good results frequently obtained from the use of
acid phosphate and credited to the influence of the phosphorus may be
due in part to the sulphur carried by that fertilizer.

This question of the influence of different fertilizer treatments on the
nature of the plant population in undisturbed soil has been studied very
carefully at the Rothamstead Experimental Station in England. Differ-
ences are to be expected with varying soil conditions and without doubt
the response in an orchard would be different from that in an open meadow
such as that in which the Rothamstead investigations were conducted.
Nevertheless the following statement from the summary of this work
is very suggestive:

"In the produce grown continuously without manure the average number of
species found has been 49. Of these, 17 are grasses, four belong to the order
Leguminosfe, and 28 to other orders. The percentage, by weight, of the grasses
has averaged about 68, that of the Leguminosae about nine, and that of species
of other orders about 23.

"In the produce of the plot already referred to as the most heavily manured,
and yielding the heaviest crops, the average number of species found has been
only 19, of which 12 to 13 are grasses, one only (or none) leguminous, and five to
six only represent other orders; whilst the average proportions by weight have
been — of grasses about 95 per cent., of Leguminosse less than 0.01 per cent., and
of species representing other orders less than 5 per cent.

"On the other hand, a plot receiving annually manures such as are of little
avail for gramineous crops grown separately in rotation, but which favor beans
or clover so grown, has given, on the average, 43 species. Of these, 17 in number
are grasses, four Leguminosse, and 22 belong to other orders, but by weight, the
percentage of grasses has averaged only 65-70, that of the Leguminosae nearly
20, and that of species belonging to other orders less than 15. . . .

"It is found that there is a considerable difference in the percentage of dry
substance in the produce, and very considerable difference in the percentage of
mineral matter (ash) in that dry substance. There is still greater difference in
the percentage of nitrogen in the dry matter, and, again, a greater difference still
in the percentage of individual constituents of the ash. When, indeed, it is
remembered that a plot may have from 20 to 50 different species growing upon
it, each with its own peculiar habit of growth, and consequent varying range and
power of food-collection, it will not appear surprising that different species are
developed according to the manure employed; and, this being so, that the charac-
ter and amount of the constituents taken up from the soil by such a mixed herb-
age should be found much more directly dependent on the suppUes of them by
manure than is the case with a crop of a single species growing separately.

"In further illustration it may be mentioned that, not only does the per-
centage of nitrogen in the dry substance of the produce of the different plots
vary considerably, but the average annual amount of it assimilated over a given
area is more than three times as much in some cases as in others. Again, the
percentage of potash in the dry substance is three times as much in some cases

FERTILIZERS, OTHER THAN NITROGENOUS 221

as in others; whilst the difference in the average annual amount of it taken up
over a given area is more than five times as much on some plots as on others —
dependent on the supplies of it by manure, and the consequent description of
plants, and amount, and character, of growth induced. The percentage and
acreage amounts of phosphoric acid also vary very strikingly; and ao again it is
with other mineral constituents, but in a less marked degree.""*

Li7ne. — Calcium has been mentioned as an element practically always
present in quantities far greater than orchard trees require. Indeed
very large amounts are likely to lead to chlorotic conditions through mak-
ing the soil reaction alkaline and thus rendering iron unavailable. Never-
theless liming the soil accelerates nitrification and may thus indirectly
help the orchard plants to obtain a larger supply of nitrogen. The
strawberry has been mentioned particularly as a plant preferring an acid
soil and as being actually harmed by applications of lime. Yet it is
common experience that strawberries do exceptionally well following
clover, though clover is very sensitive to acid soils and usually profits
greatly from liming. In this case it is entirely practicable to apply lime
to the clover field a year before the sod is turned under for the strawberry
plants. The lime stimulates the growth of the clover and its effect on
soil reaction wall have largely, if not wholly, disappeared by the time the
ground is ready for the strawberries. Ultimately the strawberries will
profit greatly from the lime applied to the clover that preceded them,
though its direct application would result in serious injury.

Illustrations might be given of other indirect influences of fertilizers,
but enough has been said here and at other places in this section to afford
some idea of the many ways in which they may affect orchard trees.
Enough has been said, also, to make it clear that these indirect are often
as important as the direct influences, for there may be no occasion to
supply the plant with more nutrients. With our present knowledge it
is impossible to predict with certainty all of the effects, direct and
indirect, that any particular fertilizer will have in a given orchard. How-
ever, this should not prevent the careful study of each situation as it
arises.

Plant Nutrient Carriers ; Different Forms of Fertilizers. — The neces-
sity that the different plant nutrients be in certain forms if they are
to be taken up by the tree has been discussed under the subjects of Solu-
bility and Availability in Chapter VII. This does not mean, however,
that fertilizers must contain these elements in these particular forms,
for as soon as applied they become subject to numerous changes through
the physical, chemical and biological factors always at work in the soil.
Nevertheless there are certain advantages and certain disadvantages
inherent in different fertilizers because of the form in which they carry
the elements for which they are valued. A brief discussion of this matter
as it applies to orchard problems is included at this point.

222 FUNDAMENTALS OF FRUIT PRODUCTION

Nitrogen from Inorganic Sources. — The more common of the nitrogen-
carrying commercial fertilizers are nitrate of soda, sulphate of ammonia
and dried blood. Only the first of these three materials contains nitrogen
in a form in which it is used in any considerable amounts by most plants.
It is therefore one of the most readily available forms of nitrogen, though
the nitrogen of the other two materials soon becomes available. The
first two of these fertihzers are readily soluble in water and in the soil
solution; dried blood is less soluble. This at once raises the practical
question of loss through leaching. Some expression of the differences
between these fertilizers in this respect as well as in their rates of avail-
ability is obtained from an investigation on a light sandy loam in
Florida. ^^ The report on this investigation states: "For the period from
July 13, 1911, to July 17, 1913, 41 per cent, of the sulphate of ammonia
applied to the soil leached thru and was lost in the drainage water;
72.5 per cent, of the nitrate of soda, and 38.3 per cent, of the dried blood
were lost. . . . The larger loss of nitrate of soda is explained by the
fact that this material is very readily soluble in the soil moisture and that
the soil has very little if any power to retain or fix nitrogen in the nitrate
form. ... In its original form the nitrogen of dried blood is not readily
soluble in the soil water, and consequently very little is lost in the leaching
process until nitrification occurs. In this change the organic nitrogen
of the blood is changed first to ammonia, then to the nitrite and finally
to the nitrate form, when it becomes as readily soluble as the nitrate of
soda and is leached out as readily. Nitrification of the dried blood is a
gradual process, extending over a period of time which may be of several
weeks' duration, depending on soil conditions. Because of this, some of
the nitrogen of dried blood, or for that matter, any similar organic mate-
rial, will remain in the soil a considerably longer time and be available
to the crop over a longer period than nitrate of soda. This is especially
true where heavy rains occur after the latter has been applied to the
soil. . . . While sulphate of ammonia is readily soluble in the soil water
the soil has the power of fixing or absorbing at least a portion of the
ammonia, thus preventing it from leaching away. This takes place
through chemical means and is common to all soils. Very sandy soils
can absorb only a small amount of ammonia; loam and clay soils are able
to absorb much larger quantities."

Attention may be called also to the opposite influences of nitrate of
soda and sulphate of ammonia on soil reaction. In the former the
nitrogen is combined with a basic and in the latter with an acid radical.
As the nitrogen is used by the plants the soil is gradually rendered more
basic in the first instance and more acid in the second ; in the latter case
the sulphate generally combines with calcium, resulting ultimately in a loss
of this element from the soil through leaching. CoUison^^ has found that
in some soils this loss of calcium when sulphate of ammonia is used as a

FERTILIZERS, OTHER THAN NITROGENOUS 223

fertilizer amounts to over twice that taking place when nitrate of soda
is appHed. The change in soil reaction occasioned by one or two succes-
sive applications of the same material would seldom be large enough
to have great practical importance in the orchard, but since the effects
are cumulative repeated applications for many years might conceivably
result in injury to the trees. The remedy for this situation is the use first
of the nitrate of soda and then of the sulphate of ammonia, keeping the
soil reaction about as it is at the outset.

Attention should be called to the inconsequential difference obtained
in actual field trials from the use of these nitrogen-carrying fertilizers
when nitrogen is the limiting factor and when amounts are used carrying
approximately the same quantities of nitrogen. Nitrate of calcium
has been emploj^ed occasionally as a fertilizer in an experimental way and
the response has not differed materially from that to nitrate of soda.

The diiferent influences of these nitrogenous fertilizers on the inter-
cultures in the orchard may be of greater significance than the differences
in their direct influence on the trees. The acidic influence of the sulphate
of ammonia is likely to increase gradually the growth of certain species
like bluegrass, timothy, redtop and orchard grass and to decrease the
growth of the clovers and certain other legumes. The basic influence of
the nitrate of soda has the opposite effect. This is brought out strik-
ingly by work at the Rothamstead Experimental Station'^o extending
over a period of 30 years. Therefore if certain leguminous cover crops
are to be grown or more especially if it is desired to keep the orchard in a
permanent clover or alfalfa sod, some caution should be exercised in the
use of sulphate of ammonia. Sodium, calcium or potassium nitrates could
be used more safely.

The results of many investigations^"" with field crops indicate that a
given quantity of nitrogen in the form of nitrate of soda has a greater
influence than the same amount carried in many other fertilizers. That
is, it has more crop producing power when held in one form than in
another. Furthermoi'e this relative efficiency varies with many factors,
such as the kind of crop plant and the character of the soil. Presumably
this varying crop producing power is associated with secondary or indirect
effects that the fertilizer or its disintegration products may have on the
plant through their influence on soil reaction, the availability of other soil
constituents and many other soil conditions and processes. Very little
is known regarding the varying crop-producing value of nitrogen qarried
in different fertilizers when they are used on fruits.

Nitrogen from Organic Sources. — A word should be said regarding the
use of certain nitrogen-carrying organic fertilizers. Barnyard compost
and green manuring crops have been recommended often as the best
sources of nitrogen for the orchard. There can be no doubt but that
they are effective fertilizers when nitrogen is a limiting factor, often

224 FUNDAMENTALS OF FRUIT PRODUCTION

yielding returns greater than those obtained from commercial fertilizers
used in quantities carrying equal amounts of nitrogen. However, a part
of their beneficial influence is without doubt due to other nutrients that
they carry and to the effects on the physical condition of the soil.

Thus Schreiner and Shorey/^" in discussing the physical condition of
the soil as affected by organic matter, state: ''The organic matter may,
and in fact generally does, play an intimate part in the behavior of the
mineral particles, entering into chemical combination, coating them or
cementing them together. The organic matter becomes, therefore, of
the greatest importance in its influence on the great controlling factors in
crop production, such as the solubility of the soil minerals, the physical
structure of the soil granules, and the water-holding power of soils. To
illustrate this, there was found in California a soil which could not be
properly wetted, either by rain, irrigation, or movement of water from
the subsoil, with the result that the land could not be used profitably
for agriculture. On investigation it was found that this peculiarity of
the soil was due to the organic matter, which when extracted had the prop-
erties of a varnish, repelling water to an extreme degree. The soil,
once freed of this ingredient, had a high water-holding power."

Some suggestion of the many ways, direct or indirect, in which organic
matter affects tree growth and production may be derived from the follow-
ing statements pertaining to the rosette of pecans: "The experimental
and other evidence indicates very strongly that pecan rosette is a sign of a
soil deficient in humus, fertihty, and moisture supply, . . . The
constant addition of large quantities of humus-forming materials, thereby
both bettering the physical condition of the soil and increasing its water-
holding capacity and fertility, is absolutely necessary to produce healthy
trees from those already diseased and to prevent the development of
new cases of rosette. . . . some consistent and definite soil-building
policy should be adopted in the pecan orchards of the South if rosette
is to be overcome and healthy productive orchards maintained. The
program of work should involve the growing of one crop, preferably a
legume, which may be returned to the soil. ... In these experiments,
heavy applications of stable manure, cottonseed meal and stable manure,
and cottonseed meal alone, in connection with legumes, have proved
highly beneficial to rosetted trees." ^^^ Though in cases like this it is
impossible at present to distinguish between the influence of the nitrogen
and that of the other components of the organic matter there is no reason
for minimizing their combined effects or for failing to resort freely to the
use of organic fertilizers in orchard practice where observation and experi-
ence indicate that they may be of decided benefit. The nitrogen of
organic fertilizers is more slowly available than that of the common
nitrogenous commercial fertilizers and experience shows that for quick
results the commercial sources are more satisfactory. Investigation

FERTILIZERS, OTHER THAN NITROGENOUS 225

shows that the nitrogen of both barnyard manure and of green manure
crops plowed under in April or May becomes available only gradually for
plant growth during the latter half of the growing season.-"^

Phosphorus. — Though experiments have shown little or no direct
benefit to deciduous fruits from the application of phosphatic fertilizers
these are often useful in stimulating the growth of intercultures or in
promoting desirable changes and reactions in the soil.

The leading phosphatic fertilizers available for use in the orchard are
rock phosphate or "floats," acid phosphate or superphosphate and ground
bone. The phosphorus in raw rock phosphate or "floats" and in ground
bone is held in the form of tri-calcium phosphate, which is very nearly
insoluble in water or in the soil solution and hence becomes available for
plant growth very slowly as it is acted upon gradually by various soil
agencies. The phosphorus of acid phosphate or superphosphate is held
as mono-calcium phosphate, which is soluble and is the form in which
plants are supposed to absorb most of their phosphorus. When added
to the soil it unites with more calcium to form di-calcium or "reverted"
phosphate which is intermediate in solubility between the mono- and
tri-calcium compounds. Gradually this di-calcium phosphate unites
with more calcium to form tri-calcium phosphate and it finally exists in
the soil in the same form as in raw rock phosphate. For this reason
"floats" or raw rock phosphate might be inferred to have equal value with
the acid phosphate as a fertihzer. This is not the case, however, since
the acid-treated material, being readily soluble, goes down into the soil
and becomes fairly evenly distributed throughout the area reached by
the roots. Furthermore, the plants are able to obtain considerable quan-
tities before it becomes "reverted" or certainly before it is changed to
the very nearly insoluble tri-calcium form. Mention may be made again
of the possibihty that some of the benefit from acid phosphate is due to the
sulphur that it carries as well as to the phosphorus. Unlike nitrogen,
phosphorus is not lost from the soil in large quantities through leaching.
The reasons for this have been brought out in the preceding discussion.
Some indication of the phosphorus fixing power of soil is afforded by an
experiment with a light sandy loam in Florida m which it was found that
at the end of four years only 0.05 per cent, of the amount applied in
fertilizers had been lost through the drainage water, i"^"

Potassium. — Though there are a number of different forms in which
potassium may be applied, the two most common are the muriate and the
sulphate. Where these two forms of potash have been used side by side
in the fruit plantation the sulphate has usually, though not always, given
more striking results. The suggestion may be repeated that when there
is an apparent need of potash fertihzers, as indicated by a material
response from the use of the sulphate, the possible need of sulphur be
thoroughly investigated. In marked distinction to the case afforded by

226 FUNDAMENTALS OF FRUIT PRODUCTION

phosphorus we have but httle evidence of an indirect benefit to the trees
through any increased growth of the intercultures resulting from the use
of potash-carrjang fertihzers.

Sulphur. — Too httle evidence on the use of sulphur-carrying fertilizers
in the orchard is available to warrant an extended discussion of the differ-
ent forms in which it may be applied. Evidently many different forms
are eligible, for it has resulted in increased yields of certain orchard inter-
cultures when used in the form of both potassium sulphate and calcium
sulphate (gypsum) and increased grape yields have been reported from
the use of both gypsum and flowers of sulphur. ^^ Indeed it has been
noted that alfalfa and certain other legumes have been greatly benefited
from the sulphur contained in the lime-sulphur spray, which had
dripped from sprayed trees or had drifted to the ground in the process
of spraying.

Lime. — Though calcium is one of the elements essential for the growth
of plants, the point has been made that there are but few soils to which
its application in fertilizers is desirable for the purpose of supplying the
tree directlj'^ with additional amounts and though there are indirect ways
in which it may frequently benefit orchard trees, there are indirect ways
in which it may also injure them. The data that have been presented
make it clear, furthermore, that the same plant may be either benefited
or injured by liming, according to the condition of the soil. That there
are marked differences between species — and even varieties of the same
species — in their tolerance of lime or their tolerance of the soil basicity
with which it is likely to be associated or in their response to lime applica-
tions, should be emphasized. The results of work at the Rhode Island
Experiment Station may be cited. Those results have been summarized
as follows: "According to experiments made by the Rhode Island Agri-
cultural Experiment Station on acid soils in that State, the plants tested
may be classified with regard to their behavior toward lime as follows:
Plants benefited by liming: . . . alfalfa, clover (red, white, crimson
and alsike) . . . oats, timothy, Kentucky bluegrass, Canada pea,
Cuthbert raspberry, gooseberry, currant (white Dutch), Orange quince,
cherry, Burbank Japan plum, American linden . . . plants but little
benefited by liming . . . rye, . . . Rhode Island bent, and redtop;
plants slightly injured by liming . . . Concord grape, peach, apple,
and pear; plants distinctly injured by liming . . . velvet bean, . . .
blackberry, black-cap raspberry, cranberry, Norway spruce, and Amer-
ican white birch. Other plants said to be injured are the chestnut,
azalea, and rhododendron." ^^^

Another point that may be mentioned in connection with the appli-
cation of lime is that there is little occasion to use it in the fruit plantation
for flocculation purposes. Soils with a texture so impervious that the
flocculating effects of lime are needed to promote drainage and aeration

FERTILIZERS, OTHER THAN NITROGENOUS 227

are generally too poorly suited to fruit production, even with the aid of
such palliative measures as liming.

Season for Applying Fertilizers. — Comparatively few data are avail-
able upon which to base a decision as to the best time for appl^ang
fertilizers of different kinds in the orchard. Without doubt many factors
have a bearing in this connection. Among the more important may be
mentioned: the varying states or conditions of the plant as the season
advances, the changing nutrient value of the soil, moisture supply includ-
ing the possibihty of losses from leaching and bacterial activities of differ-
ent kinds. It is only as these are understood and properly evaluated in
each individual case that fertilizer applications can be timed to best
advantage. When easily soluble nitrogenous fertilizers are required
large amounts should not be put on in the fall, during the winter or too
early in the spring, on account of the danger of leaching. Indeed, this
is always a prime consideration in making nitrogen applications, though
relatively unimportant with other fertilizers. On the other hand,
fertilizers carrying nitrogen in organic combination must be applied
sufficiently early to give disintegration processes time for making
the nitrogen available to the plants before it is too late for them to
absorb it.

Frequent observation and experience indicate that orchard fruits
respond very quickly to easily soluble nitrogenous fertilizers such as
nitrate of soda and sulphate of ammonia, when these are made as growth
is starting in the spring or later during the growing season. Thus
Ballou^ reports a greatly increased set of fruit in weak, devitalized apple
trees when nitrate of soda was applied just before the opening of the
flowers. In this case not more than 3 weeks had elapsed before it was
clearly evident that the trees were receiving benefit from the application.
In fact this immediate effect of quickly available nitrogen has led to the
general practice of applying it just as growth is starting and it would
seem that experience bears out the wisdom of so timing nitrate appli-
cations. On the other hand, when nitrogen is needed, not so much for
aiding the setting of fruit or perhaps for increasing the vegetative growth
made during the early part of the current season — this latter being an
influence which, as yet, has not been very accurately determined — but
rather for its effects the following season, through organic products
elaborated during the summer and fall months and stored through the
winter, the best time for fertilizer apphcations may be quite different.

Some evidence in support of this last suggestion is furnished by experi-
mental work in England. ^^ Apphcations of quickly available fertihzers
to orchard trees of a number of varieties in August, supplemented by
applications in the spring at the time of fruit setting, caused trees to bear
annual crops. The immediate effect of the midsunnner applications is
to cause the trees to hold their foliage later in the fall, thus accumulating

228 FUNDAMENTALS OF FRUIT PRODUCTION

larger stores of elaborated foods and making possible the formation of
stronger, if not more, fruit buds.

The Relation of Seasonal Conditions to Response from Fertilizers.—
Many features of environment may be limiting factors to growth. The
supply of nutrients in the soil constitutes only one series or group of
these factors. With a change in other factors it is to be expected that a
definite balance of nutrients in the soil will limit growth in different ways
and a corresponding variation is to be expected from the use of a par-
ticular fertilizer on a particular soil and for a particular crop, depending
on temperature, humidity, rainfall and other factors. Such differences
have been studied in certain grain and forage crops. Thus applications
of nitrogenous fertilizers to grass land give much more striking results
when the season is comparatively dry than when it is wet.^^^ Little
is known regarding the responses of fruit trees to the same fertilizer with
varying seasonal conditions. The great differences found in field crops,
however, suggest that some variations may be expected.

Summary. — Potash, phosphoric acid and lime-carrying fertilizers
are seldom required by orchard trees, which rarely show a direct response
to their application. However, these fertilizers often increase greatly
the growth of intercrops or cover crops and when these are used for mulch-
ing or green manuring purposes tree growth and production are indirectly
increased. This indirect influence is particularly important in case the
intercrop is a legume. Nitrate of soda, sulphate of ammonia and dried
blood have proved the best of any of the nitrogenous fertilizers tried;
the first two are in most common use. Sodium nitrate tends to leave the
soil more basic in reaction and sulphate of ammonia has the opposite
effect. These different residual effects may be of considerable importance
under some conditions. Phosphorus is generally applied as acid phos-
phate ; potassium, either as muriate or sulphate. Data as to the best time
for fertilizer applications are meager. They indicate, however, that for
increasing the setting of fruit, quickly available nitrogenous fertilizers
should be used just as the trees are starting growth in the spring. The
nature and relative magnitude of the response from similar fertilizer
applications may be expected to vary considerably with different growing
season conditions.

Suggested Collateral Readings

Ewert, A. J. On Bitter-Pit and the Sensitivity of Apples to Poisons. Proc. Roy.
Soc. Victoria. 24(N.S.): 367-419. 1912.

Kraus, E. J., and Kraybill, H. R. Vegetation and Reproduction with Special Refer-
ence to the Tomato. Ore. Agr. Exp. Sta. Bui. 149. 1918.

Gourley, J. H. Studies in Fruit Bud Formation. N. H. Agr. Exp. Sta. Tech. Bui. 9.
1915.

Wiggans, C. C. Factors Favoring and Opposing Fruitfulness in the Apple. Mo.
Agr. Exp. Sta. Res. Bui. 31. 1918.

NUTRITION 229

Hooker, H. D., Jr. Seasonal Changes in the Chemical Composition of Apple Spurs.

Mo. Agr. Exp. Sta. Res. Bui. 40. 1920.
Hedrick, U. P. Twenty Years of Fertilizers in an Apple Orchard. N. Y. Agr. Exp.

Sta. Bui. 460. 1920.
Roberts, R. H, Off-year Apple Bearing. Wis. Agr. Exp. Sta. Bui. 317. 1920.
Bedford, H. A. R., and Pickering, S. U. The Effect of Grass on Trees, etc. Pp.

259-312. Science and Fruit Growing. London, 1919.
Jorgensen, I., and Stiles, W. Carbon Assimilation. New Phytologist Reprint

No. 10. London, 1917.
Palladin, V. I. Plant Physiology, Edit, by B. E. Livingston. Chapters 3, 4, 5, 7, 8.

Pp. 60-117 and 139-212. Phila., 1918.
Russell, E. J. Soil Conditions and Plant Growth, Chapters 2, 6, 7. Pp. 19-51 and

117-152. London, 1915.

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17. Bradford, F. C. Ore. Agr. Exp. Sta. Bui. 129. 1915.

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21. Brown, H. T., and Escombe, F. Phil. Trans. Roy. Soc. London. 190B:233-

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22. Brown, H. T., and Escombe, F. Proc. Roy. Soc. London. 76B:29-111. 1905.

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24. Cameron, F. K., and Bell, J. M. U.S.D.A.,Bur. Soils Bui. 30. 1905.

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26. Chandler, W. H. Mo. Agr. Exp. Sta. Res. Bui. 14. 1914.

27. Chandler, W. H. Proc. Am. Soc. Hort. Sci. 17:201-204. 1920.

28. Chauzit, J. Compt. rend. Acad. Agr. France. 5:83.5-837. 1919. Cited in

Exp. Sta. Rec. 42:222. 1920.

29. Colby, G. E. Cal. Dept. Agr. Mo. Bui. 10:35. 1921.

30. Collison, R. C. N. Y. Agr. Exp. Sta. Bui. 447. 1920.

31. Collison, S. E. Fla. Agr. Exp. Sta. Bui. 154. 1919.

230 FUNDAMENTALS OF FRUIT PRODUCTION

32. Coupin, H. Compt. rend. 127:400. 1898.

33. Coupin, H. Compt. rend. 170:753-754. 1920.

34. Coville, F. V. U.S.D.A., Bur. PI. Ind. Bui. 193. 1910.

35. Coville, F. V. U.S.D.A. Bui. 6. 1913.

36. Cummings, M. B., and Jones, C. H. Vt. Agr. Exp. Sta. Bui. 211. 1919.

37. Curtis, O. F. Am. Jour. Bot. 7:101-124. 1920.

38. Czapek, F. Biochemie der Pflanzen. 2:156-158. Jena, 1905.

39. Ibid. 2:188.

40. Ibid. 2:198.

41. Ibid. 2:737.

42. Ibid. 2:739.

43. Ibid. 2:740.

44. Ibid. 2:744.

45. Ibid. 2:745.

46. Ibid. 2:762.

47. Ibid. 2:764, 765.

48. Ibid. 2:765.

49. Ibid. 2:766.

50. Ibid. 2:769.

51. Ibid. 2:772.

52. Ibid. 2:776.

53. Ibid. 2:791.

54. Ibid. 2:795.

55. Ibid. 2:797.

56. Ibid. 2:798.

57. Ibid. 2:800.

58. Ibid. 2:805.

59. Ibid. 2:830.

60. Ibid. 2:868.

61. Daniel, L. Rev. hort. 10(N.S.):102. 1910.

62. Davis, W. A., Daish, A. J., and Sawyer, G. C. Jour. Agric. Soc. 6:406-412.

1914.

63. Drinkard, A. W. Va. Agr. Exp. Sta. Ann. Kept. P. 159. 1909-1910.

64. Emmons, E. Agriculture of New York, Vol. 1. Albany, 1849.

65. Ewert, A. J. Proc. Roy. Soc. Victoria. 24(N.S.):367-419. 1912.

66. Floyd, B. F. Fla. Agr. Exp. Sta. Ann. Rept. Pp. 35R-46R. 1917.

67. Ibid. Bui. 140. 1917.

68. Franklin, J. H. Mass. Agr. Exp. Sta. Bui. 168. 1916.

69. Fred, E. B. Va. Agr. Exp. Sta. Ann. Rept. Pp. 132-134. 1908.

70. Ibid. Pp. 138-142.

71. Garner, W. W., and Allard, H. A. Jour. Agr. Res. 18:553-606. 1920.

72. Gile, P. L., and Carrero, J. O. Porto Rico Agr. Exp. Sta. Rept. Pp. 10-20.

1917.

73. Gile, P. L., and Carrero, J. O. Jour. Agr. Res. 20:33-62. 1920.

74. Gladwin, F. E. N. Y. Agr. Exp. Sta. Bui. 458. 1919.

75. Goff, E. S. Wis. Agr. Exp. Sta. Ann. Rept. 16:289. 1899.

76. Ibid. 17:266. 1900.

77. Ibid. 18:304. 1901.

78. Gonehalli, V. H. Bombay Dept. Agr. Bui. 29. 1914. (Cited by Tottingham,

W. E. Jour. Am. Soc. Agron. 2:6. 1919.)

79. Gourley, J. H. N. H. Agr. Exp. Sta. Bui. 168. 1914.

80. Ibid. Bui. 190. 1919.

NUTRITION 231

81. Gourley, J. H., and Shunk, V. D. N. H. Agr. Exp. Sta. Tech. Bui. 11. 1916.

82. Graves, J. E., Carter, E. G. and Goldthorpe, H. C. Jour. Agr. Res. 16:107-
135. 1919.

83. Gray, J., and Pierce, G. J. Am. Jour. Bot. 6:131-155. 1919.

84. Haberlandt, G. Bot. Ztg. 1877. (Cited by Albert, P. Forst. naturwiss.

Ztschr. 3:9. 1894.)

85. Harris, J. E. Mich. Agr. Exp. Sta. Tech. Bui. 19. 1914.

86. Hart, E. B., and Tottingham, W. E. Jour. Agr. Res. 5:223-250. 1915.

87. Hartwell, B. L. R. I. Agr. Exp. Sta. Bui. 183. 1920.

88. Hartwell, B. L., and Damon, S. C. R. I. Agr. Exp. Sta. Bui. 177. 1919.

89. Hartwell, B. L., Pember, F. R., and Merkle, G. E. R. I. Agr. Exp. Sta. Bui.

176. 1919.

90. Harvey, E. M., and Murneek, A. E. Ore. Agr. Exp. Sta. Bui. 176. 1921.

91. Hawaii Agr. Exp. Sta. Rept. P. 44. 1919.

92. Headden, W. P. Col. Agr. Exp. Sta. Bui. 131. 1908.

93. Ibid. Bui. 160. 1910.

94. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 289. 1907.

95. Ibid. Bui. 339. 1911.

96. Hedrick, U. P., and Anthony, R. D. N. Y. Agr. Exp. Sta. Bui. 460. 1919.

97. Henrici, M. Verhandl. Naturf. Ges. Basel. 30:43-136. 1919.

98. Hodgsoll, H. E. P. Jour. Pomol. 1:217-223. 1920.

99. Hooker, H. D., Jr. Science. 46(N.S.):197-204. 1917.

100. Hooker, H. D., Jr. Mo. Agr. Exp. Sta. Res. Bui. 40. 1920.

101. Hopkins, C. G., and Aumer, J. P. III. Agr. Exp. Sta. Bui. 182. 1915.

102. Horticulturist. 1:60. 1846.

103. Jorgensen, I., and Stiles, W. Carbon Assimilation. New Phytologist Reprint

No. 10. London, 1917.

104. Jost, L. Pflanzenphysiologie. 3te Auflage. P. 103. Jena, 1913.

105. Kearney, T. H. U.S.D.A., Bur. PL Ind. Bui. 125. 1908.

106. Kelley, W. P. Hawaii Agr. Exp. Sta. Bui. 26. 1912.

107. Kelley, W. P., and Thomas, E. E. Cal. Agr. Exp. Sta. Bui. 318. 1920.

108. Kiesselbach, T. A. Nebr. Agr. Exp. Sta. Res. Bui. 6. 1916.

109. Kirby, R. S. la. Acad. Sci. 25:265. 1918.

110. Klebs, G. Abh. Naturf. Ges. Halle. 25:116. 1906.

111. Klebs, G. Proc. Roy. Soc. London. 82:547-558. 1910.

112. Korstian, C. F., Hartley, C, Watts, L. F., and Hahn, G. G. Jour. Agr. Res.

21:153-169. 1921.

113. Kraus, E. J. Bienn. Crop Pest and Hort. Rept. Ore. Agr. Exp. Sta. 1:71-78.

1911-12.

114. Kraus, E. J. Ore. Agr. Exp. Sta. Research Bui. 1. Pt. 1. 1913.

115. Kraus, E. J., and Kraybill, H. R. Ore. Agr. Exp. Sta. Bui. 149. 1918.

116. Laurent, E. Compt. rend. Soc. roy. bot. Belg. 29(2):71-76. 1890.

117. Laurent, E. Bui. Acad. roy. Belg. (3) 32:815-865. 1896.

118. Lawes, J. B., and Gilbert, J. H. Rothamstead Memoirs. 2:291-292. 1880.

119. Ibid. 2:390-405.

120. Lawes, J. B., Gilbert, J. H., and Masters, M. T. Rothamstead Memoirs.

2:1252-1263. 1882.

121. Leclerc, J. A., and Breazeale, J. F. U.S.D.A. Yearbook. Pp. 389-402. 1908.

122. Leclerc du Sablon. Rev. gen. Bot. 16:341-368; 386-401. 1904. 18:5-25;

82-96. 1906.

123. Lewis, C. I., and Allen, R. W. Hood River Branch (Ore.) Agr. Exp. Sta. Rept.

1914-1915.

232 FUNDAMENTALS OF FRUIT PRODUCTION

124. Loew, O., and May, D. W. U.S.D.A., Bur. PL Ind. Bui. 1. 1901.

125. Loughridge, R. H. Cal. Agr. Exp. Sta. Bui. 133. 1901.

126. Lubimenko, V. N. Mem. Acad. Sci. Petrograd. 8:33. 1916. (Cited in

Physiol. Abstr. 4:413-414. 1919.)

127. Magness, J. R. In Ore. Agr. Exp. Sta. Bui. 139. 1916.

128. Ibid. Bui. 146. 1917.

129. Maquenne, L., and Demoussey, E. Bui. Soc. Chem. 27:266-278. 1920.

130. McCool, M. M., and Millar, C. E. Mich. Agr. Exp. Sta. Tech. Bui. 43. 1918.

131. McCue, C. A. Trans. Peninsular Hort. Soc. 1915.

132. McMurran, S. M. U.S.D.A. Bui. 756. 1919.

133. Mer, E. Bui. Soc. Bot. 45:299. 1898. d'Arbaumont, J. Ann. Sci. nat.

Bot. (8)13:319-423; 14:125-212. 1901.

134. Michel Durant, E. Variation des substances hydrocarbonees dans les feuilles.

Dissertation. Nemours. 1917.

135. Molisch, H. Bot. Ztg. 55:49-61. 1897.

136. Montemartini, L. Atti. Inst. Bot. Univ. Pavia. (2)15:1-42. 1918.

137. Munson, W. M. Me. Agr. Exp. Sta. Bui. 89. 1903.

138. Neubauer, C. Ann. Oenol. 5:343-364. 1875.

139. N. Mex. Agr. Exp. Sta. Ann. Rept. P. 31. 1912-13.

140. N. Y. Agr. Exp. Sta. Ann. Rep. Pp. 166-168. 1891.

141. Nobbe, F., Baeseler, D., and Will, H. Landw. Versuchs-Sta. 30:381-423.

1884.

142. Oddo, B., and Polacci, G. Gazz. chim. ital. 50(l):54-70.

143. Paddock, W., and Whipple, O. B. Fruit Growing in Arid Regions. P. 330.

New York, 1911.

144. Palladin, V. I. Plant Physiology. Edit, by B. E. Livingston. P. 82. Phila.,

1918.

145. Ibid. P. 83.

146. Ibid. P. 254.

147. Partridge, N. L. Proc. Am. Soc. Hort. Sci. 16:104-109. 1919.

148. Petit, P. Comp. rend. 111:975. 1893: Ascoli, Lieb. Physiol. Chem. 28:426.

1899.

149. Pfeiffer, O. Ann. Oenol. 5:271-315. 1875.

150. Pickering, S. U. Ann. Bot. 31:183-187. 1917.

151. Quaintance, A.L. Ga. Agr. Exp. Sta. Ann. Rept. 13:350. 1900.

152. Rassiguier. Prog. Agr. et Vit. 18(No. 35):204-206. 1892. (Cited by Gile,

P. L., and Carrero, J. O. Jour. Agr. Res. 20:38. 1920.)

153. Reimer, F. C. Ore. Agr. Exp. Sta. Bui. 163. 1919.

154. Reimer, F. C. Ore. Agr. Exp. Sta. Bui. 166. 1920.

155. Richter, L. Landw. Versuchs-Sta. 73:457-477. 1910.

156. Rivera, V. I problemi agrari del mezzogiorno. Mem. R. Staz. Ratal. Veg.

P. 18. Rome, 1919.

157. Roberts, I. P. Cornell Univ. Agr. Exp. Sta. Bui. 103. 1895.

158. Roberts, R. H. Proc. Am. Soc. Hort. Sci. 14:105. 1917.

159. Roberts, R. H. Wis. Agr. Exp. Sta. Bui. 317. 1920.

160. Schreiner, O., and Shorey, E. C. U.S.D.A., Bur. Soils Bui. 74. 1910.

161. Schreiner, O., and Skinner, J. J. U.S.D.A., Bur. Soils Bui. 70. 1910.

162. Ibid. Bui. 77. 1911.

163. Ibid. Bill. 87. 1912.

164. Ibid. Bui. 108. 1914.

165. Schreiner, O., Reed, H. S., and Skinner, J. J. U.S.D.A., Bur. Soils Bui. 47.

1907.

NUTRITION 233

166. Shedd, O. M. Ken. Agr. Sta. Bui. 188. 1914.

167. Shibata, K., Shibata, Y., and Kasiwagi, I. Jour. Am. Chem. Soc. 41:208.

1919.

168. ShuU, C. A. Science. 52(N.S.):376-378. 1920.

169. Skinner, J. J. U.S.D.A., Bur. Soils Bui. 83. 1911.

170. Sorauer, P. Pflanzenkrankheiten. 3te. Auflage. 1 :289. Berlin, 1909.

171. Ibid. 1:292.

172.

Ibid. 1:297.

173.

Ibid. 1:305.

174.

Ibid. 1:310.

175.

Ibid. 1:312.

176.

Ibid. 1:391.

177.

Spoehr, H. A.

178.

Stewart, J. P.

Carnegie Inst. Wash. Publ. 287. 1919.
Pa. Agr. Exp. Sta. Bui. 153. 1918.

179. Stewart, R. 111. Agr. Exp. Sta. Bui. 227. 1920.

180. Stewart, R. 111. Agr. Exp. Sta. Circ. 245. 1920.

181. Stoykowitch, W. Recherches phj'siologiques sur la prune. Dissertation.

Nancy, 1910.

182. Taylor, R. H. Cal. Agr. Exp. Sta. Bui. 297. 1918.

183. Taylor, T. C, and Nelson, J. M. Jour. Am. Chem. Soc. 42:1726-1738. 1920.

184. Teodoresco, E. C. Ann. Sci. nat. Bot. (8) 10:141-164. 1899.

185. Thompson, R. C. Ark. Agr. Exp. Sta. Bui. 123. 1916.

186. Tottingham, W. E. Jour. Am. Soc. Agron. 2:1. 1919.

187. Trabut, W. Cited by Kearney, T. H. U.S.D.A., Bur. PL Ind. Bui. 125. 1908.

188. Tr^iog, E. Wis. Agr. Exp. Sta. Res. Bui. 41. 1916.

189. Tsuji, T. La Planter. 60:413-414. 1918.

190. Van Slyke, L. L., Taylor, O. M., and Andrews, W. H. N. Y. Agr. Exp. Sta.

Bui. 265. 1905.

191. Vasnievski, S. Bui. intern, acad. sci. Cracovie B. Pp. 615-686. 1917.

192. Voechting, H., Jahrb. wiss. Bot. 25:149-208. 1893.

193. Walster, H. L. Bot. Gaz. 69:97-125. 1920.

194. Warren, F. G. N. J. Agr. Exp. Sta. Rept. P. 199. 1906.

195. Webber, H. J., U.S.D.A. Yearbook. P. 193. 1894.

196. Weber, R. Landw. Versuchs-Sta. 18:18-48. 1875.

197. Weber, R. Forst. naturwiss. Ztschr. 1:13. 1893.

198. Westgate, J. M. Hawaii Agr. Exp. Sta. Press Bui. 51. 1916.

199. Wheeler, H. J. U.S.D.A. Farmers Bui. 77. 1905.

200. Wheeler, H. J. Manures and Fertilizers. Pp. 113-124. New York, 1914.

201. Whiting, A. L., and Schoonover., W. R. 111. Agr. Exp. Sta. Bui. 225. 1920.

202. Whitten, J. C, and Wiggans, C. C. Mo. Agr. Sta. Buls. 131, 141, 147. 1915-

1917.

203. Wickson, E. J. California Fruits. P. 164. San Francisco. 1910.

204. Wiegand, K. M. Bot. Gaz. 41:373. 1906.

205. Wiesner, J. Die Entstehung des Chlorophylls. Vienna, 1877.

206. Woodbury, C. G., Noyes, N. A. and Oskamp, J. Ind. Agr. Exp. Sta. Bui.

207. 1917.

207. Wright, W. J. Proc. Am. Soc. Hort. Sci. 11:9-14. 1912.

208. Zaliesski, W. Die Bedingungen der Eiweissbildimg den Pflanzen. P. 53

Charkow. 1900.

209. Zimmerman, A. Ztsch. angew. Chem. 6:426. 1893.

SECTION III

TEMPERATURE RELATIONS OF
FRUIT PLANTS

Of the four great factors of plant environment, moisture, soil, light
and temperature, the fruit grower can modify two considerably. He
can irrigate or drain, he can fertilize, if necessary; he can, to some extent,
modify soil texture; light and temperature he must take as they come.
The object of the present section is to indicate how, though temperatures
cannot be changed, except in certain minor respects, fruit growing can be
modified to capitalize favorable temperatures or to minimize the unfav-
orable effects. Knowing the various effects of heat or its lack the grower
is able to chose fruits best adapted to existing conditions, to avoid
attempting the impossible or the very hazardous, to pick favorable
sites and so to manipulate his plants that they will have the best possible
adjustment to the various temperature conditions of their environment.

Temperatures influence plants in several ways bearing directly on
fruit growing: (1) they delimit zones beyond which the growing of specific
fruits becomes commercially hazardous because of low winter tempera-
tures; (2) they delimit zones beyond which the growth of certain fruits
becomes unprofitable because of high summer temperatures; (3) they
make certain areas unprofitable for some fruits because of low summer
temperatures; (4) they render much good land of doubtful value for
several fruits because of danger from spring frosts; (5) within areas ordi-
narily safe for growing certain specific fruits an occasional deviation
from normal may cause considerable damage; (6) some insects and
diseases are more or less dependent on proper temperatures for their
optimum development.

Lest this statement should give an unpleasant connotation to tem-
perature relations, it should be stated conversely that these very limita-
tions predicate the presence at some places of temperatures favorable
to fruit growing. The existence of fruit growing at all is obvious proof.
Unfortunately attention is centered rather on the Umitations, so that,
though many unfavorable conditions are fairly closely understood,
optimum temperatures for the various fruits are not defined so clearly.

Schimper,^^* commenting on the difficulty of temperature investigations,
states: the "existence of such action on vegetable organisms is less clearly
recognizable than is that of water. We can directly observe the ingress of water
into a plant and its egress, we can explain physiologically the effects caused by

234

TEMPERATURE RELATIONS OF FRUIT PLANTS 235

these, and we can follow the transpiration current along its course, whereas the
action of heat is carried on in the molecular region of the protoplasm beyond
our ken, and is visible to us only in its final consequences, such as the acceleration,
retardation or complete cessation of physiological processes. The cecological
phenomena display similar processes. Protective adaptations against a want
or superfluity of water are within our power of observation, those against cold
and heat are entirely beyond them. We can directly see whether any plant
naturally inhabits a dry or a moist station, but not whether it belongs to the
flora of a cold or warm climate. Indeed plants from hot deserts frequently have
a strong resemblance in habit to those of polar zones."

The metabolism of a plant may be regarded as a complicated set of
chemical reactions, subject to several influences. Among the factors
governing chemical reactions and vital processes the chemist and the
physiologist recognize temperature. There are certain limits, apparently,
for all vital reactions, limits wide in some instances, narrow in others.
Some plants require a relatively high temperature for setting in motion
the processes known as growth; others will carry on similar processes
at a lower point. One may go on at a certain temperature in a given
plant, while another in the same plant may require more heat. At a
low temperature a plant is said to rest; certain processes are in truth
suspended, but others are inaugurated. Finally, there is a point so
low that the plant cannot exist; it dies apparently from cold. On the
other hand, all plants show their maximum growth activity within the
limits of a comparatively small range of temperature; above these
limits some reactions are retarded or some are so accelerated as to
become harmful, or new injurious reactions begin and the net results that
are recognized as growth or fruitfulness are diminished; here again the
point is finally reached where the equilibrium of reactions is broken and
death ensues.

Withal, it must be considered that temperature is only one of the
factors affecting plant growth. Even a single plant may be limited at
various times by quite different features of its environment.

Investigation has shown that in soy beans in Maryland growth was controlled
during one fortnight by temperature, but in the next by the rainfall-evaporation
ratio. 1-^ In Ceylon it has been found that with ^^awe and FwrcrtEa temperature
is always the limiting factor; with Dendrocalamus sometimes it is temperature,
sometimes water supply. In January Vitis is Umited in growth by temperature
and in July by the water supply, while with Capparis and Stiff tea the Umiting
factors are water supply during the day and temperature during the night. ^^^

MacDougaP^^ shows the operation of limiting factors in his study of the
growth of tomato fruits. As the temperature of the fruits increased, growth
progressed until the rise caused a loss of water exceeding the gain. The higher
temperatures did not accelerate growth unless the relative humidity of the atmos-
phere was high; a rise in temperature with decreased humidity retarded or stopped
growth or even caused an actual diminution of volume.

CHAPTER XIV

GROWING SEASON TEMPERATURES

Horticulturists, particularly in the Old World, have recognized in
a manner the importance of growing season temperatures to fruit plants.
Most of the efforts at precise study of this nature, however, have been
made by those particularly interested in phenology.

HEAT UNITS

Various investigators have made efforts to show that, wherever
a given plant is grown, to complete its cycle that plant requires a certain
amount of heat. When it has received this amount of heat, whether
in n days or n + r or n -\- s days, it will have completed its cycle. The
outline of this idea was enunciated first, probably, in 1735 by Reaumur. ^
Numerous writers since that time have attempted to refine the methods
used in studies of this sort. Adanson, for example, recognizing that
averages which included readings below freezing were misleading, inas-
much as such temperatures do not reverse plant activity but merely
suspend it, discarded all such readings. Others have assumed higher
temperatures as the zero points for their calculations. Gasparin con-
sidered that "effective temperatures" began at 5°C. He also considered
a thermometer in full sunshine on sod to show the true temperature of
the plant more nearly than one registering air temperature alone and
that "the warmth in the sunshine is to the warmth of the air in the shade
as though one has been transported in latitude from 3 to 6° farther
south. "^ DeCandolle^^ believed sunlight in itself to influence vital
processes independently of temperature, since several annuals which
he had under observation required a greater total of heat degrees for
flowering and for ripening in the shade than they received in full sunlight.

The Relative Values of Different Efifective Temperatures.— Most
investigations in phenology until comparatively recent date have been
based on the assumption that, above the basic temperature which
initiates plant growth, each degree is of equal value with any other.
Lately, however, the principle of Van't Hoff and Arrhenius, namely,
"that within limits, the velocity of most chemical reactions doubles or
somewhat more than doubles for each rise in temperature of 10°C.,"
has been shown to have considerable bearing on certain processes in
plants. As the Livingstons^*'^ point out, certain of the purely physical
processes involved in growth do not follow this principle and its applica-

236

GROWING SEASON TEMPERATURES

237

tion to plants Is, therefore, qualified. Fully recognizing the numerous
limitations inherent in the data at present available, they have, never-
theless, tentatively assigned "efficiency indices" to the various degrees of
temperature, reproduced in part in Table 1, and applied them to the
temperature data at various points in the United States.

In a subsequent paper Livingston proposes a different system, based
on Lehenbauer's studies of root growth in maize. ^°^

This system differs from the others in that it is based on observed rates of
growth and in taking cognizance of a decreased rate of growth with temperatures
above the optimum. A comparison of the values obtained with the three
systems is given in Table 1. Livingston evidently regards this work only as a
step toward further study, since he states: "... these indices are to be re-
garded as only a first approximation and . . . much more physiological study
will be required before they may be taken as generally applicable. In the first
place, they are based upon tests of only a single plant species, maize, and there are

Table 1. — A Comparison of Temperature Index Values, Starting with 40°F.
AS Unit, According to Three Systems

System

Temperature

Remainder

Exponential

Physiological

40

1

1 . 0000

1.000

50

11

1.4696

6.333

58

19

2.0000

16.111

68

29

2.9391

46.000

76

37

4.0000

82.333

86

47

5.8782

120.000

94

55

8.0000

103.333

99

60

9.6980

73.111

112

7.3

16 . 0000

3.778

probably other plants ... for which they are not even approximately true.
... no doubt other phases of growth in the same plant may exhibit other
relations between temperature and the rate of shoot elongation. Third, these
indices refer to rates of shoot elongation, and there are many other processes
involved in plant growth, which may require other indices for their proper inter-
pretation in terms of temperature efficiency. Fourth, they apply strictly only
under the moisture, Hght and chemical conditions that prevailed in Lehenbauer's
experiments . . . Fifth, and finally, plants in nature are never subject to
any temperature maintained for any considerable period of time. . . ."

Influence of Latitude on Heat Requirements. — Phenological data
on any single fruit plant gathered over a wide area are rather scarce at
present and those available are not altogether satisfactory. However, in
combination with temperature data compiled by the Weather Bureau

238

FUNDAMENTALS OF FRUIT PRODUCTION

some of these data are interesting, particularly since, to some extent,
they corroborate findings of other investigators.

In the Early Harvest Apple. — Table 2 is compiled from phenological
data gathered by Bailey^ and from daily normal temperatures for the
various points, ^^ except that the temperature for Columbia, Mo., is
joined with the phenological data for Boonville, a short distance away.
Some of the phenological data may be open to question, as, for example,
the ripening date for Thomasville, Ga., but even with some allowance for
errors, there is apparent a general tendency for temperature summations
at southern points to exceed those of more northern location. Though

Table 2. — Heat Units Calculated on Several Systems Compared with Dates
OF Blossoming and of Ripening in the Early Harvest Apple

Date

Normal
temperature
at average
date of blos-
soming,
Fahrenheit

Remainder

Expo-
nential
Jan. 1 to
ripening

Physio-
logical
Jan. 1 to
ripening

Locality

Jan. 1
to blos-
soming

Blos-
som to
ripening

Total
Jan. 1
to ripen-
ing

Blos-
soming

Ripen-
ing

Thomasville, Ga....

Augusta, Ga

Atlanta, Ga

Raleigh, N. C

Boonville, Mo

Erie, Pa

Ithaca, N. Y

Rochester, N. Y . . .

Mar. 10
Mar. 27
Apr. 8
Apr. 6
Apr. 20
May 23
May 10
May 21

July 10
May 30
July 1
July 2
June 23
Aug. 18
July 28
Aug. 11

59
59
59
56
56
60
55
59

933
922

819
597
347

558
283
470

3,952
1,820
2,573
2,560
1,729
2,600
2,102
2,267

4,945
2,742
3,392
3,157
2,076
3,158
2,385
2,743

536
315
378
366
234
341
261
293

8,383
3,455
5,005
4,758
2,979
2,110
3,305
1,547

relative positions -of certain stations change with different systems of
computing the effective temperatures, the same tendency holds through-
out and is perhaps most evident with the physiological index summations.
If a different zero point — say 50°F. — be assumed, the relative differences
are not reduced materially; in fact they are rather intensified, for though
northern points would have somewhat lower summation totals, those for
Thomasville, Ga., would not be reduced at all, since the normal daily
temperature for early January is 50°F.

In the Elberta Peach. — Gould" reports ripening dates for the Elberta
peach at various points in the United States. Certain of these seem near
enough to stations for which Bigelow^^ has computed daily normal tem-
peratures to make comparisons valid. Table 3 shows summations to the
date of ripening and for the year at these points, with the proportion
which they bear respectively to each other, Linsser^'^^ has suggested
that this ratio should be constant, but the data here presented do not
support his suggestion. The same tendency to greater summations in
the south than in the north is apparent here. Waugh^''^ found heat units
for the blossoming of the "American Wild Plum" in 1898 as follows:

GROWING SEASON TEMPERATURES

239

Stillwater, Okla., 967; Parry, N. J., 909; State College, Pa., 725; Burling-
ton, Vt., 577.

Table 3.

-Heat Units to the Date of Ripening of Elberta Peach at Various
Points and Total Heat Units for the Year

Date of
ripening

Remainder

Linsser's
constant

Expo-

Locality

To
ripening

For year

index to
ripening

Atmore, Ala

Plain Dealing, La

Van Buren, Ark

Vacaville, Cal

Manteo, N. C

Central Ind

Lewiston, Idaho

Palisades, Col

Port Clinton, Ohio

Freewater, Ore

Lake region, Mich

Ipswich, Mass

July 11
July 10
July 15
July 6
Aug. 10
Sept. 15
Aug. 1
Aug. 26
Aug. 25
Aug. 17
Sept. 10
Sept. 17

4,654
4,572
3,817
3,332
4,911
4,090
3,006
4,483
3,639
3,622
3,483
3,880

9,540
8,143
8,006
7,478
8,475
5,346
5,260
6,001
5,170
5,488
4,292
4,669

48.8
56.1
47.7
44.6
57.9
76.5
.57.1
74.7
70.4
66.2
81.1
83.1

522.9
519.2
432.6

562.6
499.4
334.2
500.0
392.8
403.4
374.1
418.2

In Chestnut Blight. — Stevens has made an interesting application of these
various constants to studies of the growth of tlie chestnut blight fungus. Assum-
ing 45°F. as the lowest effective temperature, he compares the summations of
temperatures above that point at various localities with the observed growth of
the blight cankers and finds that "the temperature summation falls off somewhat
more rapidly northward than does the amount of growth." In a later paper he
reports that the summations on the "Physiological basis" do not fit the observed
growth so well as the summations of remainder or exponential indices. ^^^' ^^^

Variations in Heat Requirements from Season to Season. — Sand-
sten^^^ made a study of heat units accumulating at blossom time for the
apple and plum during several seasons at Madison, Wis. As appears from
Table 4, composed of items taken from his data, he found considerable
variation from year to year and from variety to variety. Combining

Table 4. — Number of Positive Temperature Units (above 32°F.) Receh^ed
Each Year from Jan. 1 to the Date of Fir.st Bloom

Variety

1902

1903

1904

1905

Wealthv

810.5
837.0
837.0
785.0
785.0

837.5
810.5
928.0
837.5
810.5

752.0
727.0
752.5
707.0
752.5

690 0

Borovinka

599 0

Charlamoff

713 0

Hibernal

599 0

Grimes.

652 0

240

FUNDAMENTALS OF FRUIT PRODUCTION

with these figures the total heat units for the last 6 months of the pre-
vious growing season he secured a closer approach to uniformity as ex-
pressed in percentage of the smallest yearly total to the greatest yearly
totals for any variety (see Table 5). Sandsten interprets his data as
showing that other factors besides the heat units from Jan. 1 have a

Table

-Number of Positive Temperature Units (above 32°F.) Received
From Preceding July 1 to Date of First Bloom

Variety

1901-1902

1902-1903

1903-1904 1904-1905

Wealthy . . .
Borovinka .
Charlamoff
Hibernal . . .
Grimes. . . .

5,106.5
5,133.5
5,133.5
5,081.5
5,081 . 5

4,827.5
4,801.5
4,918.5
4,827.5
4,801.0

4,601.5
4,576.0
4,601.5
4,556.0
4,601.5

48,01.5
47,10.5
48,24.5
47,10.5
47,63.5

bearing on the time of flowering and enumerates as possible factors the
stage of advancement of the buds at the time of growth cessation in the
fall, the size of the crop borne in the previous year, "soil conditions and
the amount of plant food present in the soil; and fifth, the individual
characteristics and state of health of the tree or plant." General observa-
tion on peach trees shows a sequence in opening blossoms corresponding
to the stage of advancement of these buds in the fall, the difference in
time of flowering on the same branch amounting sometimes to several
days, which would make a difference occasionally of 50 units or more on
the Fahrenheit scale. Magness makes an interesting suggestion in this
connection which is referred to under Fruit Bud Formation.

Seeleyi^" applied the method of temperature summations to the Late
Crawford peach, as recorded in the Mikesell data for Wauseon, Ohio.
His summary of results, shown in Table 6, indicates no close agreement
from year to year for the same locality. Somewhat closer tallying was
secured when maximum figures were used (line 4) . Seeley shows that air
temperatures as recorded by thermometers in the conventional shelter do
not indicate at all closely the actual temperatures of the leaves.

Table 6. — The Least and the Greatest Temperature Summations in the Life
Phase of the Late Crawford Peach

{After Seeleij''^)

Summation

Jan. 1 to
blossoming

Blossoming
to ripening

Jan. 1 to
ripening

Ripening to
blossoming

Average

Least

183

362

50

64

2,776

3,991

70

71

3,030

4,347

70

72

486

1,250
38
61

Greatest

Percentage

Maximum (per cent.)

61

69

GROWING SEASON TEMPERATURES 241

Acclimatization to Varying Amounts of Heat. — It is conceivable that
through acclimatization plants graduallj^ may require more or less heat
for a given function; evidence to this effect is cited by Bailey.^ Cuttings
of Concord grape from Maine, central New York and southern Louisiana
planted simultaneously under uniform conditions at Ithaca, N. Y., made
in a given time the following respective growths: 2.66 inches, 1.6 inches
and 1.3 inches. The seed potato trade of ]\Iaine is founded on the quick-
ened response to a given temperature by potatoes grown there. Data
already cited in this chapter show a tendency for plants in northern
sections to attain a given stage of development with less heat than in
southern sections. Elsewhere it is shown that plants accommodate them-
selves to a wide range of moisture, nutrient and light conditions; there-
fore it is not surprising that they show a corresponding adaptation to
various temperature conditions.

In General. — It is possible that more detailed measurements, taken
perhaps on a different basis than that used by climatologists, would
secure more uniformity than the figures cited above. Temperatures
taken in sunlight would seem to be more reliable expressions of conditions
in buds and leaves than those taken in shade. Some writers have sug-
gested maximum temperatures as the basis for calculations. In any case,
however, it seems doubtful if temperature alone can be made the index
of plant activities.

Schimper^"^ aptly points out that "different organs and functions require
very different amounts of heat, that unfavorable temperatures cause subsequent
inhibition, and that other factors besides heat, especially humidity, cooperate
and intervene. We need not, then, be surprised if there is very Uttle accord in
phaenological observations, and that the utmost one can do is to admit their
having a certain importance for purely descriptive geographical botany in the
characterization of certain districts. No importance, on the other hand, need
be assigned to the theoretical views, nor to the sum total of temperatures."

OPTIMUM TEMPERATURES

It is well known that some plants grow at lower temperatures than
others. The necessity of a certain amount of heat during the growing
season is recognized in the statement that in some regions the summers are
too cool for certain fruits.

Variation within the Species or Variety.— In considerable areas of
north central Europe, peach growing is limited, not by the cold of winter
but by the low summer temperature. The same limitation, though
less obvious, probably applies to pears, as is indicated by the transition
from open exposures in the south of France to the trained and sheltered
trees in the north. Among plants of warmer climates the date palm
shows a heat requirement that is not satisfied in all sections where the

242 FUNDAMENTALS OF FRUIT PRODUCTION

winters are sufficiently mild. The grape is among the plants most
frequently cited by phenological workers as showing this same exaction
in its requirement. Variety adaptation in apples probably depends on
growing season temperature, among other factors. In addition it seems
rather likely that this factor is operative in another way though its
effects necessarily are masked by their own results; low summer tem-
perature may delay maturity to such an extent that an ensuing winter of
medium intensity is injurious. The obvious and immediate cause of
trouble here would be winter injury but the antecedent cause would be
the cool summer. Much of the winter injury characteristic of parts of
Europe seems to be involved with low summer temperatures.

The effects of temperature alone in certain phases can be compared
best, perhaps, in plants of the deserts, since these regions show rather
greater uniformity in other conditions than most humid sections. In
the date palm temperature assumes considerable importance.

According to Swingle i^^^ "The northern limit and the limit of altitude in
northwestern Africa at which dates can be grown are set more by the deficient
summer heat failing to ripen the fruit than by the cold in winter." Very early
ripening dates, he reports, can be grown far to the north where the summers are
not warm enough to ripen later varieties. Swingle confirms DeCandoUe's
calculation of 64.4°F. as the point below which no effect is produced on flowering
or fruiting of the date palm. Affirming that under desert conditions temperature
summations have considerable significance he states that 2000°C., using 18°C.
as the zero point, are necessary to ripen Deglet Noor dates satisfactorily.

Mason^23 cites Caruso as authority for the statement that 51° to 52°F.
is zero point for the olive and adds that in California zero may be some-
what higher, probably 55° to 56°F. He assigns a definite number of heat
units as necessary for ripening the olive before autumn, but points out
that in some localities with low summer temperatures and little or no
frost in winter the fruit may remain longer on the trees. In some
places the requisite number of heat units is not accumulated until
December.

The apple shows some indications of the effects of excessive summer
heat at some points in the United States and of deficient summer heat at
others. Along the southern limits of its successful culture there is a
general tendency to vigorous vegetative growth with httle fruit produc-
tion and much of the fruit that is borne rots on the tree. In that period
when apple varieties were being tested and when the varietal composition
of the orchard was not determined by market standards of the large
cities, the Ribston Pippin attained a much greater popularity in eastern
Maine than in any other section of the country then growing apples.
Other Enghsh varieties were more favorably received there than in any
other state. Downing^^ considered that the Ribston attained far better

GROWING SEASON TEMPERATURES 243

quality along the Penobscot River than in the middle states. Inci-
dentally he mentioned English gooseberries as succeeding better around
Bangor, Maine, than elsewhere. It seems probable that the cool sum-
mers of that section favored the best development of these fruits.

The converse limitation is less generally understood but it is none the
less potent. Most varieties of apple have certain heat requirements for
the attainment of their best quality or indeed for their ripening. Cions
of the Baldwin, favored by a succession of mild winters in Aroostook
County, bore fruit which failed to ripen because it was arrested in its
development by cold weather while still green.^^ Shaw^'^ found marked
differences in Ben Davis grown in various sections, indicating incomplete
development in much of the northern apple growing section. The limits
of successful culture of many varieties are conditioned by the minimum
winter temperatures, thus rather obscuring the importance of suminer
heat but, as with other fruits, there seems to be some reason for consider-
ing winter hardiness in some cases to be affected by summer temperatures.
So far as climatological data show, the minimum winter and average
winter temperatures for Boston, Mass., and Columbia, Mo., are almost
identical, but their summer temperatures differ considerably. Winesap is
considered tender and unsatisfactory in Massachusetts while in Missouri
it is one of the best commercial varieties. Apparently the limitation is
set by winter temperature in the Mississippi valley and by summer
temperature, directly or indirectly, along the Atlantic seaboard. The
northern commercial limit of York Imperial crosses the Mississippi near
the southern Iowa border and the Atlantic coast in New Jersey. ^^^ Here
again the correspondence between the northern limits east and west is
better in summer temperatures than in those of winter. The same con-
trol is evident with Rome Beauty.

Shaw^^^ concluded after extended study that a certain optimum
summer temperature may be assigned to each variety of apple, ranging
from 52°F. for Hibernal and Oldenburg to 67°F. for Terry and Yates.
As appears from Table 7 the temperature range of the chief commercial
varieties is somewhat more narrow. A considerable effect, however, on
the limits of commercial cultivation of apple varieties must be assigned
to summer temperature.

Table 7. — Optimum Average Summer Temperatures for Leading Commercial

Varieties
{After S/iaw)'")

Baldwin 56°F. Yellow Newtown 60°F.

Rhode Island 56 York Imperial 62

Northern Spy 56 Grimes 62

Wealthy 56 Stayman 63

Jonathan 59 Winesap 64

Delicious 59 Ben Davis 64

244 FUNDAMENTALS OF FRUIT PRODUCTION

In the United States, Lippincotti°" traced isotherms for combined June, July,
August and September temperatures and correlated them with the grapes growing
in the zones thus marked out. Here a combined selection is exercised by summer
and by winter temperatures and in addition, as pointed out elsewhere the summer
temperatures doubtless have some influence on the effect of winter cold. How-
ever, there can be no doubt that summer temperatures have a direct effect of
their own. In favored localities in the zone with a mean of 65°F. he found
Chnton and Delaware, with a few other varieties. In the 67°F. zone he included
Concord and Hartford Prolific; Isabella, Diana and Rogers' Hybrids he con-
sidered to require 70°F. Catawba, Norton's Virginia, Herbemont and Scupper-
nong were assigned to regions with average summer temperatures of 72° or higher.

Differences within the Variety for Separate Processes. — Different
processes in the same plant have different optimum temperatures.

Phytolacca decandra at Carmel, Cal., grows well but flowers only under certain
conditions as, for example, when prostrate branches receive sufficient additional
heat from the soil to enable them to form viable seeds, while the erect stems
do not.^" In connection with fruit setting it is shown that lower temperatures
than usual convert male blossoms of the papaya into perfect flowers. Schimper
points out the difference in the temperature curve for the two forms of gaseous
exhange and states that assimilation occurs at lower temperatures than any
other function. He cites evidence of assimilation in Abies excelsa and other
plants at — 40°C. and cites Bohm as finding the optimum for the walnut at 30°C.
No distinct respiration could be observed in Abies below — 10°C.; this function
increases, speaking in general terms, with the temperature until the lethal point is
approached. Quoting Schimper"^ again: "There are, however, certain physio-
logical processes for which not only the optima, but also the upper zeros are so
low that, as a rule, they can take place only in winter, late autumn, or early
spring. The category of functions that are active at low temperatures only
includes among others the obscure processes which are fermentative in nature,
according to Sachs' hypothesis, and which awaken into activity hibernating
parts of plants ; among such processes may be cited the conversion of starch into
fatty acids and the reverse. . . . Lower temperatures exert a favourable influ-
ence on the sexual organs and on the parts oecologically connected with them
(perianths, inflorescence axes) in many parts of the temperate and frigid zones.
The cardinal degrees for the growth — and perhaps for the inception — of the
primordia of flowers are often much lower than for the growth of vegetative
shoots, so that the former are favoured by a relatively lower temperature, and the
latter by a high temperature, during development. It is well known that
Crociis, Hyacinthus, and other perennial herbs do not send out flowers or inflores-
cences at a high temperature, but shoot out luxuriantly into leaf. Also in the
forcing of fruit trees the temperature must be kept moderate before, and espe-
cially during, the blossoming period. For the same reason many temperate
plants seldom blossom in the tropics; for example, most of our fruit trees. . . .
Kurz found in the mountains of Burmah that increased coolness due to increased
altitude expedited the blossoming of temperate plants such as Rhododendron and
Gentiana, but delayed that of tropical ones."

GROWING SEASON TEMPERATURES

245

As Schimpei-i^i points out, the forcing of fruit under glass is merely a
shortening of the dormant season and the period of maturity is advanced
only as much as the inception of growth precedes that in the open. The
temperatures found best for the trees indoors are those they receive at
corresponding stages out of doors in favorable regions; higher temperatures
are not beneficial.

Price 1^^ reports investigations showing certain temperatures more
favorable to the opening of fruit buds than others. With branches of
various fruit trees in incubators maintained at different temperatures he
found progressive acceleration in the opening of the buds with the higher
temperatures. Some of the data he reports are used in compiling Table 8.

Table S. — Influence of Temperature on Opening of Fruit Buds

Fruit

Date of
beginning

Davs to full bloom

70°F.

79°F.

88°F.

Abundance plum. . .

Hale plum

Luster peach

Kieff er pear

Oldenburg apple

Rome Beauty apple

Jan. 28, 1908
Dec. 3, 1909
Feb. 2, 1909
Mar. 7, 1910
Apr. 1, 1909
Apr. 22, 1909

Tufts''^ reports interesting indications that very high temperatures may
retard the ripening of fruit. "Here," he states, referring to the Winters section
in the Sacramento valley, "... the apricot ripens some two or three weeks prior
to the ripening of the apricot crop in the Santa Clara Valley, although apricot
trees in the Santa Clara Valley bloom ten days earUer than they do in the Winters
section. Undoubtedly the nearness of the ocean and the influence of the San
Francisco Bay profoundly modify the climate of the Santa Clara Valley. The
Apricot crop in the Winters section is entirely harvested by July 1.

"When it comes time for the prune harvest, however, we find that the Santa
Clara Valley is generally pretty well along — about half way through — before the
prunes in the Sacramento Valley are ready. The only explanation we have for
this apparent inconsistency is the fact that probably the temperatures for the
ripening of the apricot crop are optimum in the Winters section. However, after
the first of July the weather gets excessively warm, with the result that the prunes
are retarded in their development, and the optimum temperatures for the develop-
ment of the prune crop probably exist in the Santa Clara Valley during the latter
part of the growing season."

Schimper/^" emphasizing that different functions require different
temperatures, states: "the oecological optimum temperature does not
remain constant during the whole development of a plant, at least in tem-

246

FUNDAMENTALS OF FRUIT PRODUCTION

perate regions, but . . . shows a rise as development proceeds. . . . We
learn too from the art of fruit forcing that we must regard the rise not as
constant but as oscillating." He cites Pynaert in giving the tempera-
tures shown in Table 9 as most favorable in forcing the peach. At two
periods the temperature is lowered. Ward ^^i in England and Schneider^^^
in northwest Europe differ somewhat in detail from this temperature
statement; Schneider indicates a lowering of temperature at the time of
stoning.

Table 9. — Optimum Temperatures in Forcing the PeachI'"
(Degrees Centigrade)

Day temperature

Night temperature

First week

Second week

Third week

To flowering ....

At flowering

After flowering . .
During stoning . .
After stoning. . .
At fruit ripening

9 to 10
10 to 12
12 to 15
15 to 18

8 to 12

15 to 18
12 to 15

16 to 19
20 to 22

5 to 7
7 to 9
9 to 11

11 to 14

6 to 10

11 to 14
9 to 11

12 to 15
15 to 17

Variation in Quality with Amount of Summer Heat. — The fruit
which has received the most careful study in its relation to temperature
conditions is the grape. Blodgettj^" writing in 1857, when grape growing
in America was in an experimental stage, predicted very closely, from
climatological data, the geographic distribution of the industry in the
United States.

Boussingault^^ early remarked on the variation in yield and quality of wine
of a vineyard in Flanders, the variation depending on the temperature of the
growing season, and reported data shown in Table 10. Baragiola,'^ taking succes-
sive samples of grapes through two autumns, found a striking correspondence
between sugar increase and temperature, regardless of the stage of ripening at
which the low or high temperatures occurred. A brief period of warm weather
late in the season compensates apparently to a considerable degree for earher
deficiencies : a brief period of cool weather at the same stage apparently goes far
to nullify previous favorable conditions. Heat requirements for grapes during
the growing season can be understood best from European experience since the
climatology of this fruit has been studied most extensively there and is to a
considerable degree free from the compUcation of winter temperature limitations.
Boussingault22 considered that the mean temperature of the growing season
must be at least 59°F. and of the summer 65° to 67°F. to produce Vinifera grapes
satisfactorily. In some of the equatorial table lands of South America, he
states, where the mean temperature is 62° to 66°F. with little range, though the

GROWING SEASON TEMPERATURES

247

Table 10. — Relation of Summer Temperatures to Yield and Character of

Wine--

M

ean temperature

Wine, per
acre (gallons)

Percentage
of alcohol

Year

Growing
season, de-
grees Centi-
grade

Summer,

degrees

Centigrade

Beginning
of autumn,

degrees
Centigrade

Alcohol per
acre (gallons)

1833

14.7

17.3

11.4

311

5.0

11.4

1834

17.3

20.3

17.0

314

11.2

46.3

1835

15.8

19.5

12.3

621

8.1

50.0

1836

15.8

21.5

12.2

544

7.1

38.6

1837

15.2

18.7

11.9

184

7.7

14.0

vines flourish the grapes never become thoroughly ripe and good wine cannot be
made where the constant temperature is not at least 68°F. Besides a warm
summer, a mild autumn free from continued low temperature is necessary.
Some regions are assured of sufficient heat in every summer; others must have
a summer warmer than the average to produce a satisfactory wine. Along
the doubtful zone of grape growing the careful selection of site is emphasized.

Variation in Season of Maturity with Amount of Summer Heat. —

The effect of summer temperatures on the time of ripening and on keeping
quahties is well known. Thq Wealthy, a fall or early winter apple in
Minnesota, becomes a summer apple in Missouri. The Baldwin loses
quality and becomes progressively a poorer keeper toward the south
except at higher and cooler altitudes. Sometimes the transition is rather
abrupt. The Dudley, a winter apple in Aroostook County, Maine, is a
fall apple at Bangor and a summer apple farther south. ^^ Apples grown
in southern latitudes develop color over a larger part of the surface, but
the colors are more intense in the north.

SOIL TEMPERATURES

That the temperature of the soil is not without influence on plant
growth is evident from the florist's resort to bottom heat for certain
plants and the rather definite heat requirements for the rooting of cut-
ings. It has been shown that Opuntia versicolor can be stimulated to con-
siderable vegetative growth despite unfavorably cool atmosphere by the
maintenance in the soil of favorable temperatures for root growth.^"
Lindley^''* statedthatacertain variety of A^^e^ww^ntw though in full vegeta-
tive vigor was without flowers when the soil temperature was 85°F., but
blossomed at 70 to 75°F., while another variety ceased blossoming at
this same temperature.

Obvious difficulties are encountered in attempting a determination
of suitable temperatures for root growth in trees. Lindley^"^ arranged
a statement of favorable soil temperatures for various fruits, based on

248 FUNDAMENTALS OF FRUIT PRODUCTION

observations in sections where these fruits flourish; the growing season
temperatures thus indicated range from 54°F. for the gooseberry, 59°F.
for the apple, and 65°F. for the peach to 85°F. for the mango. Goff^''
found that root growth begins very early in most fruit plants in Wisconsin,
starting in most cases in advance of the buds. When currant buds were
but little swollen some of the new roots were 3 inches long. Goff stated,
however, that warmer temperatures did not accelerate root growth as
much as might be expected from the early start. Comparison of the
growth of young apple trees under various systems of culture, with accom-
panying differences in soil temperature, has shown that the two systems
inducing the greatest extremes in temperature resulted in practically
the same growth. ^^^ xhe extremes, however, were not widely separated.
It would seem that in some cases when a choice of stocks is possible
the adaptability of the several stocks to soil temperatures should be
considered, along with other factors. It appears rather illogical, for
example, to plant prune trees on peach roots in a soil so cold that it
would not be considered suitable for peaches. An instance of at least
partial adaptability to soil temperatures has been reported in Baluchistan,
where plums, peaches, etc., on Black Damask and Mazzard roots repeat-
edly failed to thrive, though the same combinations are satisfactory
in Great Britain. ^^ Using other stocks such as Mariana, Myrobolan
and Mahaleb, that apparently are better adapted to hot, dry soils, much
better results were secured.

INDIRECT TEMPERATURE EFFECTS

Finally, another limiting effect of growing season temperatures should
be considered, namely, that on fungous diseases. Apple scab, for example,
has a generally northern range, suggesting adaptability to cool summers,
while blotch is confined to sections with rather warm summers. Pear
blight is distinctly a warm weather disease; brown rot is favored by
high temperatures in conjunction with humidity. All these diseases take
toll of the fruit grown where they are present; brown rot, in conjunction
with curculio, makes plum growing a hazardous occupation in the south-
east United States and blight practically prohibits the commercial
production of the European pear in the southeast and in the Mississippi
valley.

Summary. — Functional activity and growth of any kind in a plant
have definite temperature requirements. Within the limits between
which the growth processes can proceed development is slowest near each
extreme — that is, close to the lower and close to the upper hmit. Growth
is most rapid at an optimum temperature somewhere between the two
extremes, but usually nearer the upper than the lower limit. Further-
more the optimum for certain growth processes is quite different from
that for others within the same plant and the extremes hkewise may

GROWING SEASON TEMPERATURES 249

be different for different activities. Consequently it becomes extremely
difficult, if not impossible, to assign definite values to different temperatures
in their total growth effects, and the "heat units" necessary for com-
pleting certain changes, or carrying the plant through certain aspects
of its seasonal life history, vary considerabl}^ with conditions. In general
fewer heat units are required by a given plant in northern than in southern
latitudes. Other conditions being equally favorable, there is the best
varietal adaptation in sections where growing season temperatures
most nearly approach the optimum for the variety in question. The
importance of summer growing temperatures in determining the com-
mercial limits of fruit varieties is underestimated. Summer temperature
likewise exerts an important influence in determining the season of
maturity of the fruit. Soil temperature is of possible importance in
influencing growth and in determining the geographical range of certain
varieties. Injurious effects of soil temperatures can be minimized
sometimes by the use of stocks of the right kinds. Summer tempera-
tures also have an important indirect effect on orchard plants through
their influence on the range or activity of certain parasites.

CHAPTER XV

WINTER KILLING AND HARDINESS

The limits to fruit growing set by low winter temperatures have been
indicated. This limitation has been shown to be influenced more or
less by other factors, precipitation in some cases, summer temperatures
in others. Low winter temperatures are important, however, in other
respects than merely marking boundaries separating a section where
a given fruit is grown from another section where it is not. Damage
by freezing is not confined to any one region; it is as definitely an injurious
factor in CaUfornia and Florida for tender species as it is in Montana
or Wisconsin for the more hardy fruits. It is not confined to the border-
lands of a fruit zone but in one way or another makes itself felt well
within the regions adapted to fruit growing. It is not a simple matter
of uniform, predictable reaction to a given temperature but is modified,
intensified or palliated by varying factors and is itself probably a group
of fatal or damaging reactions assembled for convenience or for want
of discriminating classification under the single name of winter killing.

DEATH FROM FREEZING

Several explanations of the actual process of killing of tissue by low
temperatures have been made; it seems possible that there may be more
than one way by which the killing is brought about. Parenthetically,
it should be stated that the original theory and the one still most fre-
quently advanced by practical men, i.e., that death by cold is due to
expansion accompanying freezing and a consequent rupture of the cell
walls, is not tenable as can be proved mathematically or by microscopic
examination. The bursting of trunks and limbs, cited to justify this
contention, is considered later. The view held most generally by inves-
tigators ascribes death to withdrawal of water from the cell, a process
comparable to death by plasmolysis.

Tissue Freezing is Accompanied by Cell Dehydration. — Numerous
investigators have shown that ice is very rarely formed within the cell
unless the cooling is very rapid, more rapid, in fact, than would occur in
nature. Before freezing begins, since the cell sap contains substances
in solution and because of capillary supercooling, most tissues must be at
a temperature several degrees below the freezing point. The first evident
step in the process of freezing is a contraction of the protoplasm and the
appearance of water in the intercellular spaces where it has been forced
or drawn from the cell. Ice formation begins at various points in the

250

WINTER KILLING AND HARDINESS 251

intercellular spaces, frequently making lens-shaped masses of hexagonal
crystals, larger at the side which draws on the greater number of cells.
As the growing ice needles deplete the water of the intercellular spaces,
more is drawn from the cell contents.^^^ The continuance of this process,
however, makes the sap remaining within the cells more concentrated
and thus increases "the force with which the remaining quantities of
water are held."^^"' A still stronger force, operating as a reserve, is that
known as molecular capillarity, holding with extreme tenacity a certain
amount of water of imbibition. Hence, it is with increasing difficulty
that ice formation continues and it must cease sooner or later unless the
temperature be lowered further. Moreover, the very process of solidi-
fication liberates a certain amount of heat. Therefore it is not surprising
that, as the temperature falls, the ice formation for each degree becomes
progressively less. Mliller-Thurgau found, at 4.5°C., 63.8 per cent, of
the water of an apple frozen, while at -15.2°C. only 79.2 per cent, had
frozen. 214 Wiegand-^^ found very little ice in dormant twigs of many
species of forest trees at 20°F. At 0°F. ice was plainly visible in buds of
19 species out of the 27 examined"; 6 of the remaining 8 showed ice,
but in small scattered crystals, at — 15°F. These buds "all contained
little cell-sap and small cells with rather thick walls."

As the ice crystals increase, the cell walls collapse and become packed
together in dense masses. Buds and bark of hardy trees show this
condition, as do evergreen leaves, but at suitable temperatures they
expand, draw back the water and become normal.

Wiegand"^ reports: "The ice was found to occur always in broad prismatic
crystals arranged perpendicular to the excreting surface; and usually formed a
single continuous layer throughout the mesophyll of the scale or leaf, to accom-
modate which the cells were often separated to a considerable distance. This
ice sheet was composed of either one or two layers of the prismatic crystals,
depending on the water content of the adjacent surfaces, and was often as thick
as the whole normal scale. The cells surrounding the ice, having lost their water
content, were in a more or less complete state of collapse, depending upon the re-
sistance of the walls, and often occupied a space smaller than the ice itself. These
cells were uninjured, however, and would resume their normal condition on
thawing. ... In young anthers the ice often filled the entire anther cavity
and in it the pollen grains were imbedded in a completely collapsed state."
At temperatures between — 23.5°C. and — 18°C. in the apple and pear the
tissue was "packed full of ice in shoot and in the mesophyll of the scales." In
general, the species in which ice formed most readily had larger cells, a higher
water content and a greater proportion of water to cell wall and protoplasm.

"In the twigs," Wiegand states, "ice is also present in very cold weather,
where it may be found in three different localities. The largest quantity occurs
in the cortex, where the ice crystallizes in prisms arranged in single or double
series according to the law of freezing tissues. The ice is more frequently in
the form of a continuous ring, or really a cylinder, extending entirely around the

252 FUNDAMENTALS OF FRUIT PRODUCTION

twig, prying apart the cells of the cortex in which it lies. The outer cylinder
of cortex in such twigs is completely separated from the inner layers when frozen.
In a few species instead of the continuous layer, lens-shaped ice masses are inter-
polated irregularly throughout the cortex. The cortical cells after the withdrawal
of water are as completely collapsed as were those in the bud scales, but they also
usually regain their normal condition on thawing. In the wood ice rarely forms
in large quantities. It is usually confined to small masses in the vessels them-
selves, or, according to some authors, sometimes extends in radial plates in the
pith rays. In sectioning twigs I, m.yself, have never seen ice in the wood else-
where than in the vessels or wood cells. In the pith the ice, so far as I have
been able to observe, always occurs within the cells and therefore in very small
masses." As Wiegand points out, Miiller-Thurgau found ice in the large vessels
and frequently in the wood cells of pear and most distinctly in the grape.

Frozen twigs of several species were found to expand on thawing, two apple
twigs, for example, increasing in diameter from 2.97 milUmeters and 3.89 milli-
meters to 3.03 millimeters and 3.95 millimeters respectively. In the willow, the
only species on which this determination was made, more than half the total
expansion was in the bark, the percentages being, respectively, 13.5 for the bark
and 2.5 for the wood. To explain the contraction of twigs on freezing Wiegand
suggests: "When the water is extracted from the walls of the wood-cells, the
latter contract to a slight extent just as they do when wood seasons. This ac-
counts for a part of the shrinkage. The rest and greater part occurs in the cortex.
Here the intercellular spaces are quite large and numerous and are normally
filled with air. When freezing occurs the ice forms in the spaces and the cells
collapse while the air is mostly driven completely out of the twig. The contrac-
tion in the cortex will be approximately equal to the volume of the air expelled
plus that of the air compressed minus the expansion of the ice while freezing."
Curiously enough in all cases studied, except in Populus and Acer and including
apple, pear and plums, Wiegand found that buds increased decidedly in size upon
freezing. Prillieux^^^ demonstrated conclusively a loss of air and of weight in
frozen plant tissues.

Freezing, Not Cold, Kills. — Most investigators do not accept the
view that, aside from some cases occurring above the freezing point,
absolute cold kills any plant, whether by "shock," "cold rigor" or other
effects. Again quoting Wiegand: "Most plants are killed by the first
ice formation within the tissue. If they survive this, a considerably
lower temperature is required to kill them, or they may be capable of
enduring any degree of cold. It has been demonstrated . . . that, in
the case of delicate tissues at least, death occurs when the ice formation
has progressed to a certain extent. . . . Death seems due to the actual
withdrawal of water to form ice, not to the cold. The ice formation
dries out the cells and the plant suffers therefore from drought con-
ditions. Every cell has its critical point, the withdrawal of water
beyond which will cause the death of the cell, whether by ordinary
evaporation or by other means. It may be supposed that the delicate
structure of the protoplasm necessary to constitute living matter can no

WINTER KILLING AND HARDINESS 253

longer sustain itself when too many molecules of water are removed
from its support. In the great majority of plants this point lies so high
in the water content that it is passed very soon after the inception of ice
formation, hence the death of many plants at this period. Others may
be able to exist with so little water that a very low temperature is
necessary before a sufficient quantity is abstracted to Qause death.
From some plants enough water cannot be abstracted by cold to kill
them." Several investigators have shown that certain tissues, cooled
to a temperature which is fatal if ice formation occurs, will withstand
that same temperature if ice formation does not occur.

After investigating several possible ways in which bud scales and wool
packing might serve to protect the embryo flowers and shoots during the winter,
Wiegand concluded that their main function is not to shut out cold or even to
retard temperature changes (about 10 minutes seemed the limit for the greater
part of any change), but rather to retard the loss of moisture and to prevent me-
chanical injury especially when the buds are frozen. Lilac buds lost in 3 days,
at temperatures between — 18°C. and — 7°C., 2.8 per cent, of water when bud
scales were left on ; with bud scales removed the loss of water was 39 per cent.
Heat absorption due to the color of bud scales in horse-chestnut buds amounted
to 15°F. Chandler^* also found that "scales of peach buds do not serve to
protect them from low temperature. Buds frozen in the laboratory with the
scales removed were shghtly more resistant to low temperature than were buds
with the scales not removed."

Freezmg and the Deciduous Habit. — The view that death from low tempera-
tures is due to a withdrawal of water is supported by the consideration that the
deciduous habit is in most cases essentially a protection against water loss during
the winter and that the leaves of evergreen plants are particularly adapted to
reduce the rate of transpiration to a minimum.

An interesting and suggestive parallelism exists between the autumnal be-
havior of trees in temperate regions and the changes in trees in regions subjected
to prolonged dry but warm weather. In both cases they assume a distinctly
xerophytic character. The most obvious phenomenon accompanying this
transition is leaf-fall. Of this Coulter, Barnes and Cowles^^ say: "The leaf
behavior of deciduous trees and of tropical evergreens obviously is related to
external factors, in the former being associated with climatic periodicity (either
of moisture, as in the monsoon forests of India, or of temperature, as in the north-
ern deciduous forests), while in the latter it is associated with uniform moisture
and tem.perature. That the deciduous and the evergreen habits are related to
external conditions may be inferred from many trees and shrubs (e.g., poison
i^y, Virginia creeper, various oaks) which shed their leaves in regions of cold
winters, but retain them in warmer climates; furthermore, various plants (as
the grape and the peach) become evergreen in uniform tropical climates, and
even those species that remain deciduous (as the persimmon and the mulberry)
have much longer periods of leafage.

"The exact factors involved in leaf-fall, that is, in the development of the
absciss layer, are imperfectly known. In the monsoon forest and in other regions

254

FUNDAMENTALS OF FRUIT PRODUCTION

of periodic drought, it is probable that leaf -fall results directly from the desicca-
tion incident to the increased transpiration and decreased absorption during the
dry period. Autumnal leaf-fall in cool climates probably is due to desiccation
resulting from continued transpiration at a time when absorption is diminished
by reason of low temperature, although desiccation due to dryness in the soil or
air may cause the absciss layer to develop in early summer. A severe frost in
early autumn may retard leaf-fall through injury to the tissues that develop the
absciss layer.

"The shedding of leaves at the inception of a cool or dry period is of inestima-
ble advantage, especially in trees with delicate leaves, because of the enormously
reduced transpiration thus resulting. The leafless tree is one of the most per-
fectly protected of plant structures, since impervious bud scales and bark cover
all exposed portions."

Accompanying leaf-fall the moisture contents of the various tissues
change. From summer to early winter there is a considerable lowering
of the moisture percentage as shown in Table 11, adapted from data by
Baake et al.,^ showing the moisture percentage in twigs of several varieties
of apple.

Table 11. — Percentage Moisture Content of Apple Twigs

Dormant

Bud
swelling

Blossom-
ing

Summer
growth
period

Wood
ripening

Hibernal

Oldenburg

Wealthy

Yellow Transparent . . . .

Mcintosh

Red Astrachan

Jonathan

Winesap

Grimes

Ben Davis

Average, 17 varieties

42.43
45.64
45.04
46.32
46.82
47.30
43.52
47.58
48.23
47.76

45.765

48.65
53.31
51.66
52.10
50.52
54.86
52.00
50.57
49.54
51.94

65.53
62.15
65.57
61.87
65.79
62.62
64.48
65 . 22
63.20

58.98
60.50
61.11
61.49
57.76
60.82
58.77
58.67
58.95
59.44

52.56

64.19

58.92

53.67
52.98
55.04
51.88
55.31
51 . 63
51.53
54.16
51.09

52.55

INCREASING HARDINESS

By Increasing Sap Density. — A logical consequence of the theory of
death through withdrawal of water by freezing is the correlation of an
increased sap density (molar concentration) with a lower killing tem-
perature for any given species. Chandler's investigations have demon-
strated this. Sap density was increased by various means, such as with-
holding water, watering with mineral solutions, inducing absorption of
various substances and it was reduced by shading; in each case with

WINTER KILLING AND HARDINESS 255

greater density there was greater hardiness. Unfortunately, attempts
to increase sap density and therefore hardiness, in peach trees, cabbage
and tobacco plants, by heavy applications of potash fertihzers were
not successful in attaining either object. ^^ European writers have
claimed increased hardiness from phosphate or potash applications;
their evidence, however, is not entirely convincing.

Wilted tissue, presenting another case of increased sap density through
withdrawal of water, was tested for hardiness by Chandler with no
significant results. This seems entirely consistent since the sap density
in this case is the result, not of the addition of substances in solution, but
rather of the withdrawal of water and may be closely comparable to the
initial stage of freezing itself. When a longer and slower wilting appeared
to be induced on dormant peach twigs, possibly resulting in a somewhat
more fundamental change in the protoplasm, hardiness seemed increased.

By Increasing Water-retaining Capacity. — Another consequence of
the theory that death is due to the withdrawal of water from the cell
and later from the tissue, is that resistance to cold must be increased by
factors tending to increase the water-retaining capacity of the cells.

Observations on the moisture content of apple twigs reported by
Beach and Allen, ^^ shown in Table 13, reveal an important relation to
hardiness. From July to December there is considerable variation in the
moisture content of the several varieties. On Jan. 15, however, following
several days of severe cold, the two hardiest varieties. Hibernal and
Wealthy, have a noticeably higher moisture content than the tenderer
varieties; furthermore, the loss of water from July to January is very
much less in these two hardiest varieties than in the others.

Data of similar purport, drawn on for Table 12, are reported by
Strausbaugh^^^ in Minnesota. Water losses accompanying markedly
cold weather were greater in the less hardy plums. Following a period of
relatively warm weather the less hardy varieties showed a marked
increase in moisture content, possibly because they were less dormant,
possibly because they had lost more.

These observations indicate that the actual moisture content of a
tissue at most times has less connection with hardiness than its water-
retaining capacity. The water lost is less significant than the water
retained. Protection against injury from low temperatures depends on
the amount of water the plant can retain at a critical moment against the
great force which tends to draw water out of the cells to form ice crystals
in the intercellular spaces. This force can be appreciated by the familiar
ability of growing ice crystals to split rocks. To hold water against this
influence, the protoplasm must have a certain amount of its moisture
supply in a form which is not easily frozen. In the section on Water
Relations plant tissue is shown to contain, in addition to its free and readily
frozen water, water in an adsorbed or colloidal state, which does not

256

FUNDAMENTALS OF FRUIT PRODUCTION

Table 12. — Changes in Water Content of Fruit Buds of Several Varieties

OF Plums
(Arranged from Straushaugh^^^)

Stella
(semihardy)

Tonka
(semihardy)

Assiniboine
(hardy)

Nov. 19

Dec 1

50.38
43.51

6.87

50.51

43.93

6.58

46.51
45.49

1.02

Dec. 26

49.30
5.79

50.70

6.77

46.80

Increase

0.86

Jan 16

45.98

44 . 34

1.64

44.41

39.16

5.25

47.36

Jan 23

47.31

Loss

0.05

Feb. 21

Mar. 5

41.98

39.78

2.20

43.24
40.46

2.78

46 . 83
46.16

0 67

Loss Nov. 19 to Mar. 5

10.60

10.05

0.35

Table 13. — Moisture Content

OF Apple

Twigs on Different

Dates le

Variety

July 15

Nov. 15

Dec. 26

to 28

Jan. 15

Decrease

July 15 to

Jan. 15

Delicious

Gano

60.3
57.2
60.7
53.5
60.4

50.5
53.2
52.0
50.4
50.6

50.5
51.2
57.7
52.0
51.0

42.5
44.3
43.6
46.8
47.5

17.8
12.9

Grimes

17.1

Hibernal

6.7

Wealthv

9.0

freeze except at temperatures ranging to — 78°C. If a plant tissue con-
tains enough adsorbed water, it presumably can withstand any winter
temperature. Its free water freezes, but there is enough water which is
not readily frozen to maintain the hfe of the protoplasm.

It seems paradoxical that tender plant tissues usually contain more
water than those which are hardier. In fact Johnston found the ratio
of water content to dry weight of fruit buds a fairly good index of the
relative hardiness of certain peach varieties and similar observations have
been made by many other investigators. However, it is shown presently
that the development of the water-retaining capacity follows as a reaction
to a diminished water supply. Hence, there is a direct relation between

WINTER KILLING AND HARDINESS 257

the lower total water content of hardy tissues and their greater content of
adsorbed water which is not readily frozen. Furthermore, the water-
holding capacity operates less effectively in dilute solutions. ^'^'*

Water in the adsorbed or colloidal condition cannot hold materials in
solution but may cause higher results in sap density determinations.
Since in hardy plants there is a smaller amount of free water which can
hold materials in solution, the sap solutes must be held ordinarily in a
more concentrated solution than in tender plants. Hence the correlation
between sap density and hardiness found b}' Chandler and confirmed by
other investigators; however, since there is no direct causative relation
between hardiness and sap density, it sometimes happens that the correla-
tion does not hold. Pantanelli,^" for example, was unable to find a
relation between resistance to cold and molecular concentration (sap
densitjO with wheat or beets, though the correlation held for sunflower,
tomato and corn.

Clear distinction is necessary between cell water loss and tissue
water loss. Cell water loss is the cause of death by freezing. Tissue
water loss must, in many cases, accentuate cell water loss and thus
indirectly lead to killing. Though the two forms are distinct, in most
cases each promotes the other. It is probable that some plants are reten-
tive of cell water and not of tissue water, hence hardy but not drought
resistant; others are presumably retentive of tissue water but not of cell
water, hence drought resistant but not hardy. However, there is a
strong tendency toward parallelism in drought resistance and cold resis-
tance. The data presented above are based on this parallelism.

Xerophytic adaptations are well known to students of morphology;
they serve primarily as protection against tissue loss, but may have an
ultimate bearing on cell loss and therefore on hardiness. Strausbaugh'^^
shows that the lenticel area on the twigs of a semihardy plum is from
three to six times that of a hardy variety. He shows also a greater loss
of water from the twigs of a tender than from those of a hardy variety.
Thus, occasionally, morphological differences may influence, though
indirectly, cell water loss. Rather extensive investigations, however,
have failed to establish consistent morphological differences between
hardy and tender varieties. Cell water loss, then, must depend on
something other than structure.

Water-retaining Capacity Associated with Pentosan Content. —
Plant tissue which withstands freezing must be supposed to contain or be
able to manufacture substances which will hold water in an adsorbed or
colloidal condition. These substances must themselves be colloids, they
must have a great water-holding and water-absorbing capacity, they must
be known to occur in practically all plants capable of withstanding winter
conditions and they must be distributed generally through practically all
plant tissues. The compounds which answer best to these specifications

17

258

FUNDAMENTALS OF FRUIT PRODUCTION

are the pentosans, more particularly the water soluble pentosans. Evi-
dence is presented in the section on Water Relations to show that pentosans
of some sort are probably the compounds holding water in an adsorbed or
colloidal condition in plant tissues; this is confirmed by determinations of
Hooker, '*'* given in Table 14, which show a correlation between pentosan
content and hardiness.

Table 14.

-Pentosan Content of Plant Tissues in Terms of Fresh Weight^^
(1920 Wood)

Nov. g

, 1920

Dec. 2

, 1920

Bases,
per cent.

Tips,
per cent.

Bases,
per cent.

Tips,
per cent.

Wealthy

6.52
5.15
3.29

4.72
5.64
3.90

5.41
3.55
4.37
3.28
5.19
3.22

5.99
5.89
5.01
5.26
5.59
4.04

5.11

Yellow Transparent

Missouri Pippin

5.06
4.91

Stayman Winesap

Ben Davis (short shoots — mature) . . .
Ben Davis (long shoots— immature) .

3.96
4.56
3.79

Currant

4.78
5.20
1.61

4.44
3.09

1.28

5.01

4.28
killed

3.68

Cuthbert raspberry (mature)

Cuthbert raspberry (immature)

3.24
killed

This evidence supports the idea that pentosans largely determine the
water-retaining capacity of plant cells, though the particular compounds
concerned remain to be determined.

Water Soluble Pentosans in Particular. — Water soluble pentosans,
such as gums or pectins, seem the most likely to act as water-retaining
substances. Studies by Rosa indicate that this is the case. Some of his

Table 15.

-Soluble and Insoluble Pentosans in Cabbage and Tomato

{After Rosa'^')

Total
pentosan

Hot-water-
soluble pectin

Insoluble
(by difference)

Cabbage :

Tender

Hardy (dry grown) . .

Hardy (by exposure)
Tomato:

Tender

Dry grown

Exposed

0.215
0.423
0.530

0.693
0.720
0.682

0.075
0.292
0.408

0.070
0.071
0.071

0.140
0.131
0.124

0.623
0.649
0.611

WINTER KILLING AND HARDINESS

259

data, reported in Table 15, show the tomato to have a higher total
pentosan content than the hardier cabbage, but the soluble pentosans
are quite differently arranged. The increase of total pentosans in
cabbage of differing degrees of hardiness is due entirely to the increase
in soluble pentosans; with the tomato, in which no treatment materially
increases hardiness, there is no increase in soluble pentosans.

Investigation is likely to show that other substances may exercise
water-retaining properties and therefore tend toward hardiness. Fat
emulsions conceivably may act in this way.

Whatever the compounds may prove to be, their water-adsorbing
power undoubtedly is affected to a marked degree by the factors which
generally increase or decrease the water-retaining properties of colloids.
The effects of nitrogenous compounds and hydrogen-ion concentration
on hardiness have been emphasized by Harvey and may be of a similar
nature.

Pentosan Content, Water-retaining Capacity and Hardiness Respon-
sive to Environmental Conditions.^ — The water-retaining capacity of
plant tissues is increased by any condition which limits the water sup-
ply without producing actual injury. This is discussed in the section
on Water Relations. Rosa presents data, given in Table 16, showing
an increase in the pentosan content of plants hardened by exposure to
low temperatures in a cold frame. This indicates also that the hardening
or maturing of plant tissue by exposure to cold is essentially a reaction to
a limited water supply.

Table 16. — Pentosans of Vegetable Plants in Percentages of Fresh Weight

{After Rosa^^^)

Cabbage

Leaf lettuce Cauliflower

Moisture, series on greenhouse plants

1. Tender plants grown in wet soil

2. Medium hard}' plants grown with moder-

ate moisture supply

3. Hardy plants grown in dry soil

4. Hardy plants, partly wilted for 2 weeks . . .

Coldjrame series

1. Tender greenhouse plants

2. Hardened 1 week

3. Hardened 2 weeks

4. Hardened 3 weeks

0.191
0.403

Rosa shows also that there is a fairly constant increase in the pentosan
content of vegetables from early fall until the plants are killed by cold.
The data in Table 17 indicate that maturity is associated with increased
pentosan content and greater water-retaining capacity.

260

FUNDAMENTALS OF FRUIT PRODUCTION

Table 17. — Pentosan Content of Garden Plants in Percentages op Fresh

Weight'"''

Date

Kale

Cabbage

Celery

Oct. 7

0.511
0.528
0.537
0.722
1.064

0.289
0.580
0.545
0.621

0.782

0.567

Oct. 20

0,801

Nov. 3

0.793

Nov 10

1 029

Nov 18

Increased Hardiness with Increased Maturity.^ — The most generally
recognized and most potent single factor influencing killing by cold,
particularly in tissues withstanding a fair amount of freezing, is the
degree of maturity attained at the time of exposure. So widely is this
state recognized in field conditions, that experimental evidence on this
point, though available, is hardly necessary. Some less known, but
widely occurring, phases of immaturity in trees are considered later.
The greater susceptibility of immature tissue to injury from cold is due,
in part, to the fact that pentosans or other water-retaining substances
have not developed : The greater water content of such tissue is evidence
of the lack of those drying conditions necessary for the proper develop-
ment of pentosans and hence of maturity. Chandler found no constant
difference in the moisture content of the twig cortex during the winter,
though its hardiness varied considerably. With reference to density he
states: "It would seem certain then that while a part of the increased
hardiness of tree tissue in winter may possibly be accounted for by the
greater sap density, not all of it can ; certainly not the greater hardiness of
December tissue over that of October." The same investigator offers the
following suggestion based on experimental evidence; "It would seem
highly probable that, except in the case of cambium, the additional hardi-
ness acquired by the different tissues of the trees as they pass into winter,
is a change in the protoplasm such that it can withstand the great loss
of water rather than a change in the percentage of moisture or in sap
density."

RAPID TEMPERATURE CHANGES

Since maturity is a reaction to dry conditions whether produced by
exposure to cold or by actual limitation of the water supply, it is logical
to expect distinct differences in the amount of injury produced by rapid
freezing when no time is allowed for the development of pentosans and
by a gradual reduction of temperature permitting an increase in the
water-retaining capacity of the tissue to develop.

Killing with Slow and with Rapid Freezing. — The injurious effects
of rapid freezing seem to have received little attention until the recent
work of Winkler and of Chandler,

WINTER KILLING AND HARDINESS 261

Winkler, 217 working with dormant twigs that killed at — 22°C. upon rapid
freezing, found that by small successive reductions of temperature, at — 16°C.
for 3 days, at -18°C. for 2 days, at -20°C. for 3 days, at -22°C. for 2 days,
at — 25°C. for 3 days, the twigs were enabled to withstand 12 hours of freezing
at from — 30°C. to — 32°C. Chandler^** reports on the results of his work,
in part, as follows: "The rate of temperature fall is very important indeed,
especially in case of winter buds. In fact apple buds can be frozen in a
chamber surrounded by salt and ice rapidly enough that practically all of them
will be killed at a temperature of zero F., or slightly below, while it is well known
that they may go through a temperature of 20°F. to 30°F. below zero with but
slight injury where the temperature fall is not so rapid . . . the killing tem-
perature of rapidly frozen twigs was four and a half degrees higher than that
of the more slowly frozen twigs, and even then the buds of the rapidly frozen
twigs killed the worst, . . . rapid falling in the early part of the freezing
temperature down to — 12°C., does more harm than rapid fall in the latter part
of the period, from — 12°C. to the killing temperature." "Many young fruits
and succulent plants were also frozen slowly and rapidly but there was so little
apparent difference betAveen the results that the data are not given. The killing
temperature lies so near the freezing point that possibly the slowly frozen tissue
kills badly because it is exposed to temperatures around the killing point
longer." "... the rate of temperature fall with winter twigs and buds ex-
erts the greatest influence on the extent of killing at a given temperature of any
feature we have so far discussed. And in the case of very forward, rather tender,
fruit buds, the rate of temperature fall exerts great influence. Thus on March
24, 1913, when all buds, especially the peaches, plums and cherries, had made
much growth, a temperature of — 11.5°C. killed as many buds with rapid tem-
perature fall as a temperature of — 16.5°C. with a slower temperature fall."

A factor involved in very rapid lowering of the temperature is the
possibility of ice formation within the cells. Though the rate of tem-
perature fall involved probably does not occur in nature, it may have
been produced in some of the experiments just described.

Slow and Rapid Thawing. — Practical men have long held that rapid
thawing intensifies damage from low temperatures and many investi-
gators have accepted this view. The fruit grower who heats his orchard
during the cold nights of the growing season tries just as carefully to
keep the early morning sun from the blossoms; the young florist is taught
by older men to supply heat very slowly if accident has lowered the
temperature of the greenhouse to a critical point.

Wiegand^i* found that thawing generally occurs at temperatures
below 0°C., or about at the freezing point (-3.5°C. to -2.3°C. for buds).
Sudden thawing or several rapid alternations of freezing and thawing
did not seem injurious.

It has been held that rapid thawing induces excessive transpiration
and prevents the return into the cell of the the sap withdrawn in freezing.
The trend of opinion among recent investigators, how^ever, fails to support

262 FUNDAMENTALS OF FRUIT PRODUCTION

this view, it having been found to hold only in a very few cases. As
already indicated, it can be shown definitely, sometimes at least, that
death occurs before any thawing begins; furthermore, the method used
by Sachs and much in vogue among gardeners to induce slow thawing,
namely, immersion or sprinkling with water, is in reality a method leading
to more rapid thawing than would occur in air. The water causes a coat-
ing of ice on the exterior, thus liberating heat to the tissue. Though ob-
jections might be adduced, to this view, the chief matter of interest here
is that investigators have found, in practically all cases, no difference
in killing to ensue whether the thawing be rapid or retarded. It should
be pointed out, however, that there are no reports of inquiry into the
effect of sunlight on frozen tissue. Injuries due to the effect of light
on frozen tissue might easily be attributed to rapid thawing. There
seems to be enough evidence in field conditions of association of sunlight
and injury to warrant careful study, particularly in view of the increased
permeability known to accompany increased light.

VARIATION IN CRITICAL TEMPERATURES

Definite evidence, under experimental conditions, has shown that
the critical temperature at which killing results is not a definite point
for any species, variety or individual plant but is the result of a complex
of conditions. It probably depends to a great degree on water-retaining
capacity or the amount of water present that is not readily frozen, but
other factors may be equally important under certain circumstances
and unquestionably there are a number of factors affecting the water-
retaining capacity of the cell colloids. All of these may constantly be
fluctuating more or less independently of one another and their product,
the killing temperature, must therefore assume many different values.
This is abundantly borne out in field observations of winter-killing.

Summary. — The most tenable of the theories explaining killing from
cold ascribes death to dehydration of the cells. Ice formation generally
begins in the intercellular spaces and the process draws water from the
cells. The water is withdrawn gradually, each decrease in temperature
being followed by further water loss from the cells, though the rate of
this loss becomes progressively lower. Death occurs when the dehydra-
tion proceeds beyond a certain point. The increasing density of the
cell sap with continued water loss tends to hold the remaining water more
tenaciously and thus protects the cell somewhat against further loss
and eventual death. The cell colloids, particularly the water soluble
pentosans, operate in the same direction and play a still more important
part. These substances (the water soluble pentosans) develop in some
plants in response to certain environmental conditions — particularly
decreasing temperature and a decreased moisture supply. These facts

WINTER KILLING AND HARDINESS 263

suggest that certain cultural treatments may be employed to increase
the hardiness of plant tissue. Rapid freezing is probably more danger-
ous than slow freezing to plant tissue because there is not time for the
plant to develop a greater water-retaining capacity; consequently it
loses a larger percentage of its moisture at a given temperature. Con-
trary to general belief there is little evidence that rapid thawing is more
injurious than slow thawing. However, this should not be taken to
mean necessarily that rapid thawing in bright sunshine is not more
injurious than slow thawing under cloudy conditions, since the increased
permeability accompanying increased light may have an influence.
Critical temperatures for a given species will vary considerably with
conditions.

CHAPTER XVI
WINTER INJURY

Macoun'2o enumerates ten manifestations of winter injury in orchard
fruits, viz.: root-killing, bark-splitting, trunk-splitting, sunscald, crotch
injury, killing back of branches, black heart, trunk injury, killing of
dormant buds and winter-killing of swollen buds. As one form of bark-
splitting, Macoun includes a condition considered here as crown rot.
These forms may occur singly or in varying combinations; some are
products of severe conditions that almost of necessity entail other forms
characteristic of less severe freezing; some may be responses of varying
plant conditions to the same weather and some may be responses of
identical plant conditions to varying weather. Still other manifestations
are recorded occasionally.

Conditions Accompanying Winter Injury. — Nine of the ten forms of
winter injury distinguished by Macoun ^^'^ appear above ground. This
diversity is due probably to a wider range of internal conditions in the
tops and to a wider range in above-ground environmental factors. It
may be attributed also to the greater facility with which top injuries are
studied; were observations of parts below ground more easily made,
what is now referred to simply as root injury might be found to consist of
several kinds. Above ground so diverse are the manifestations of
winter injury that the whole condition seems confusion confounded,
abounding in contradictions. Certain trees in an orchard suffer winter
injury and others do not. Excess soil moisture causes winter injury in
one instance and lack of soil moisture causes it in another. Cold leads
directly to winter injury yet sometimes high temperatures induce it
hardly less directly. At times young trees suffer more; at others, older
trees. Orchards in high wind-swept spots are damaged; again it is the
low-lying orchards that are afflicted. Late maturing trees suffer in one
locahty; somewhere else it is the early maturing trees. Now it is trees
weakened by neglect that lack hardiness; again it is the highest cultivated
trees that fail. An early winter freeze is the cause at one time; in another
case a late winter freeze brings destruction. An early freeze has been
known to kill peaches while pecans survived.

Table 18, arranged from data assembled at the New York Agri-
cultural Experiment Station, at Geneva''*" and showing climatic condi-
tions at that point, is designed to show the varying conditions that may
induce or accompany winter injury. Unusual climatic features that
have, conceivably, a bearing here, are shown in heavy type. The

264

WINTER INJURY

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266 FUNDAMENTALS OF FRUIT PRODUCTION

highest and the lowest rainfalls for August, September and October, the
highest mean temperatures for August, September and October and
the lowest mean temperatures from October to February are thus distin-
guished and the minimum temperatures for each month indicated.
The winters of 1895-1896, 1903-1904 and 1917-1918 may be considered
the seasons of greatest winter injury for this section in recent years.
It is evident at once that the rainfall preceding the winter of 1895-1896
was the lowest of any season reported; that preceding the 1903-1904
season was the highest and that preceding the 1917-1918 winter was very
close to an average. The three destructive winters were, then, preceded
by both extremes and an average rainfall. Though the rainfall for the
months considered was in 1897 only 0.02 inch more than that of 1896, no
serious damage was reported; though the rainfall for these months in
1915 was only 0.58 inch less than that of the same period in 1903-1904,
no widespread damage followed.

The seasons with highest average temperatures for the last of the grow-
ing season, 1900 and 1906, were not followed by the greatest destruction.
The lowest monthly temperatures for October, November, January and
February came in years not distinguished for greatest winter-killing.
Only in December did the lowest monthly temperature occur in a winter
of extensive injury. The absolute minima for October, for November
and for January fall outside the years of greatest damage.

Reviewing by seasons: the 1895-1896 winter shows extreme condi-
tions (heavy type) in low rainfall and low late winter temperatures; the
most noteworthy divergence of the 1903-1904 winter was the heavy
rainfall, while for 1917-1918 the high and low monthly precipitations
combined to make an average rainfall and the noteworthy features for
that winter were the low temperatures of November and December. Not
far from Geneva, at Ithaca, Bailey* wrote of the 1895-1896 winter, "the
phenomenal injury wrought by last winter was probably not wholly the
result of low temperature. The drought of the last summer and fall no
doubt augmented the injury." In reviewing the winter of 1903-1904,
for states east of the Mississippi, Stockman^** stated that the severity
"was not due to occurrence of very low minimum temperatures but to
the number and succession of days whose mean temperatures continued
below the normal ... At only two stations having 25 years or more of
records was the record of lowest temperatures broken. No record of
minimum temperatures at a regular Weather Bureau station was broken
during December and February."

It seems, then, that an extreme of any one feature of the climate is
not of itself likely to cause widespread injury, but that injury depends
considerably on a combination of accentuated, rather than on isolated
extreme, conditions. Thus 1895-1896 may be described as in many ways
a characteristic Dakota winter in its drying out effects; in 1903-1904

WINTER INJURY 267

late maturity with late cold and in 1917-1918 immaturity and early
cold are the distinguishing features.

Speculation is uncertain but in this case rather interesting. It can-
not, of course, be proved but it seems possible that had the rainfalls of
1895 and 1917 been exchanged the damage would have been less in both
cases; or, had the rainfall of 1915 been combined with the August-October
temperature of 1900 and the November minimum of 1904, how great
might have been the danger! Out of the 35 seasons covered in Table
18, only six have no notable climatic extreme to be recorded.

Winter Injuries Classified. — Winter-killing of hardy fruits in temper-
ate regions, then, may depend on: (1) a lack of maturity in tissues, (2)
a lack of ability to resist winter drought conditions, (3) too ready response
to short periods of warm weather in the winter. These are listed
here in the probable order of their relative importance and frequency,
though in any given section the sequence may be changed. In the
Minnesota-Dakota section, for example, it is probable that winter drought
and absolute cold are more frequently the causes of winter-killing; in the
northeast the lack of maturity of tissues is probably the one dominant
factor, while farther south much of the winter-killing of buds is the result
of the breaking of dormancy by unseasonable warm weather, followed by
ordinary cold.

These classes can be recognized in many cases by the form of the resul-
tant injury, though sometimes different causes appear to have nearly
identical effects. Crown injury and crotch injury may be related
with some certainty to lack of maturity. Killing back of branches results
from the same factor, but may be regarded also as a sign of varietal ten-
derness or it may be caused by winter drought. Killing of apple fruit
buds in northern sections appears to be a result of absolute cold, but with
peaches in climates such as that of Missouri it is to a considerable extent
induced by ready development before cold weather has passed. Winter
sun-scald is a localized manifestation, ordinarily, of a late winter freezing.
Trunk splitting is frequently associated with an immature condition and
at times with a sudden and considerable drop in temperature.

The diversity of causes and multiplicity of effects make it quite evi-
dent that any attempt at setting definite temperatures as injurious or fatal
without regard to other conditions is futile. Though there is a generally
accepted belief that — 14°F. is fatal to peach fruit buds, they have been
known to survive — 20°F. It is not always the coldest winter that does
the greatest damage. Much depends on the character of the preceding
autumn, whether it induced proper "ripening" of the wood or forced
late growth and on the period at which the cold weather occurred; of
course much depends on the treatment accorded any given orchard or
tree during the preceding summer and autumn.

268 FUNDAMENTALS OF FRUIT PRODUCTION '

INJURIES ASSOCIATED WITH IMMATURITY

Early maturity of wood is of paramount importance in most of the
northeastern United States and is by no means a negligible factor outside
that region. Most of the injury in Washington state orchards in the
disastrous freeze of late November, 1896, can be attributed clearly to
immaturity rather than to the actual temperature ( — 12°F.) attained. ^^
Any region with a comparatively short growing season and with fairly
heavy late summer and autumnal rainfall is subject to winter killing
because of immaturity. Other combinations of conditions may produce
occasionally the same susceptibility in regions ordinarily free from these
dangers. Thus in most irrigated sections climatic conditions are such
that injuries of this type are not to be expected; however, they are fre-
quently brought about by the injudicious use of irrigation water early
enough in the autumn to prolong growth. In the freeze of 1896, in
Washington, most of the orchards that had been irrigated in late summer
suffered more than others. ^^ L^te irrigation should be very late, if
immunity to this form of injury is to be insured. Furthermore, it should
be borne in mind that maturity is only a relative term, the so-called
"maturity" of the Willamette valley, for example, being quite different
from the "maturity" of Wisconsin. Therefore, a given temperature,
common in Wisconsin but unusual in the Willamette, might be harmless
in the one location but very injurious in the other, even to trees of the
same variety.

Much of the damage from winter temperatures in England and in
northern France and Germany is evidently associated with lack of ma-
turity, since particularly cool summers followed by winters of moderate
severity have frequently proved more damaging than colder winters that
followed favorable growing seasons. A "cold winter" for England
would be considered mild in the northern states or Canada; in England
it might cause considerable damage and none in New York or Michigan.
The prevalence of "frost cankers" as the chief manifestation of winter
injury in England lends weight to this view.

Affecting More or Less the Entire Plant. — Emerson^" states: " Resist-
ance to cold in trees is due often almost wholly to the habit of early
maturity rather than to constitutional hardiness. Black walnut trees
at the Experiment Station (Nebraska), grown from northern seed, by
virtue of perfect maturity, passed through the extremely severe winter of
1898-1899 without apparent injury while similiar black walnut trees from
southern seed, owing to imperfect maturity, have had their new growth
killed back from a few inches to two or three feet for the past six years and
yet notwithstanding this great difference in resistance to cold in winter, a
comparatively hght freeze late in the spring of 1903 killed the new growth
of the northern trees just as completely as it did that of the southern ones.

WINTER INJURY 269

Northern trees are constitutionally no hardier than southern but their
superior resistance to winter cold was due to their habit of ripening their
new growth perfectly in the fall."

Macoun''^ introduces evidence to the same effect: "From the writer's
experience with over 3,000 species and varieties of trees and shrubs,
exclusive of cultivated fruits, from many countries and climates, which
are under his care and observation at the Central Experiment Farm,
Ottawa, we have drawn the following conclusions regarding the hardiness
of trees: A tree or shrub which will withstand a test winter at Ottawa
must be one which ripens its wood early. Trees or shrubs which are
native to places having a longer or much longer growing season than at
Ottawa grow larger than native species or those from a somewhat similiar
climate to the native species, and when a test winter comes their wood is
not sufficiently ripened, or winter-resistant, and they are more or less
injured or perish. . . . Another observation regarding tender trees has
been that after a season when the growth has been strong more injury is
likely to occur than in a season when the growth is short . . . the
season of all the hardiest varieties [of apples] is summer or autumn . . .
apples which mature early and are in condition for eating in summer and
autumn are grown on trees which ripen their wood early, and, on the other
hand, an apple which is not ready for use until winter is usually grown
on a tree which does not ripen its wood early."

Attention may be called to the doubtful wisdom of fall planting in
northern regions of trees grown far to the south. These trees, to be
shipped in time for planting in the north, must be dug when they are
still quite immature. They are, if planted in the fall, exposed to cold
winter temperatures and are thus doubly at a disadvantage. It is true,
the digging may in itself induce a degree of maturit}^ through drying out,
but hardly as much as would be attained by trees grown farther north.
The wisdom of delaying digging as long as possible is obvious.

Tender Plants may he More Resistant than Hardier Plants. — A tempera-
ture of 15°F. at South Haven, Mich., on Oct. 10, 1906, uniformly
killed peach trees while pecans, in the same orchards, survived. ^^* Here
is undeniable evidence of a tender species being more hardy at that time
because of maturity than a species that is far more hardy in its mature
condition. Similarly, records show that apple trees planted 2 and
3 years in Wyoming were killed by a temperature of 12°F. in Septem-
ber, when they were still in full leaf ,^^ though there are numerous instances
of trees surviving approximately equal temperatures without material
injury when they were partly leaved out in the spring.

The Effect of Slimmer Conditions Favorable for Late Growth. — During
the winter of 1903-1904 in Ohio, though the chief damage was to trees of
low vitality, vigorous trees succumbed in numerous cases. These were
almost invariably in "low, moist, rich black soil favoring extreme growth

270

FUNDAMENTALS OF FRUIT PRODUCTION

of soft, poorly matured wood, or in orchards in rich soils, receiving late
cultivation."^^ Emerson^^ found similar susceptibility in peaches grow-
ing in rather moist soils or receiving late cultivation in Nebraska. Zero
weather or even 6°F. above is considered more harmful in very early
winter in Montana than -30°F. or -40°F. later.e^

Selby^^^ supplies other interesting cases of injury in Ohio associated
with immaturity. In 1880-1881, late cultivation in two orchards,
accompanied by heavy August rainfall and normal September rainfall,
produced heavy and prolonged growth. Late November brought zero
weather; the December minimum was -13°F. These temperatures
ordinarily are of no great significance but in this case they caused complete
destruction of Baldwin apple trees. On a larger scale and over a wider
area, the same climatic conditions, when approximated in the growing sea-
son of 1906, were followed by widespread winter injury. In this case the
following winter was severe but, as is shown in Table 19, arranged from
Selby's data, in no month of this winter did the temperature closely
approach recorded minima. It was definitely established that much of
the injury was done by a temperature of + 18°F. on Oct. 12. The
unusual features of these two damaging years were, not the winter
temperatures, but the summer and fall temperatures and rainfall.

Table 19. — Climatic Conditions Accompanying W

INTER

Injury in Ohio^"

Temperature (degrees. Fahrenheit)

R

linfall (inches)

Month

1880 Average 23
years

1906

1880

Average
23 years

1906

Mean

^^"'- Mean
mum

Mini-
mum

Mean

Mini-
mum

May

65.8
63.4
74.5
71.0
64.8
52.3
33.9
25.7

35.5 61.2
45.5 69.7
52.0 73.9
48.0 71.5
41.5 65.5
30.5 53.5
-5.0 40.9

19
29
34
31
23
8
-8
-32

61.3
69.8
72.1
74.6
68.9
52.7
41. 1
32.3

24
34
43
43
36
18
14
-15

1.24
5.65
6.06
5.03
2.02
2.27
2.39
1.06

3.63
3.94
3.37
3.04
2.71
2.13
3.05
2.74

2 17

July

August

4 77

September

2 92

October

3 19

1881 1

1907

1881

1907

January

24.2
29.0
35.6

-2.0 27.8
-2.5 26.8
13.0 38.8

-34
-39

-17

32.2
26.0
45.9

-23
-19

-2

1.31
3.25

2.75

2.70
2.66
3.39

6.11
0 85

March

5.55

"Second Growth" Particularly Susceptible. — Excessively dry summer
weather also, if followed by a fair precipitation in early autumn, may
result in immature wood at the entrance into winter. ^^^ The dry sum-
mer may cause a "premature dormancy" followed by second growth.

WINTER INJURY 271

Instances of this are furnished sometimes by the fall blossoming of fruit
trees. The severe winter of 1917-1918 resulted in greater damage to old
trees in Indiana than to young and the suggestion is made that this con-
dition "is possibly accounted for by the fact that many old trees made a
late second growth while on vigorous young trees the growth was not
arrested by dry weather in late summer and they matured normally. "^^
It is interesting to contrast this condition with the greater damage to
young trees in Ohio following the wet summer of 1906.

Preventive Measures. — Unfortunately the weather cannot be predicted
reliably far ahead. However, it seems evident that August rainfall
frequently is important in the northeast in determining tree maturity
in October and that orchard operations in that section should be varied
somewhat during August according to the rainfall. A very dry August
should be accompanied by late cultivation to lessen the likelihood of
second growth; a very wet August would indicate the wisdom of stopping
cultivat;ion altogether and sowing a quick-growing, moisture-consuming
cover crop. A warm, moist October -cannot be foretold but its effects
can be forestalled, at least in part, by a suitable cover crop which will
reduce soil moisture.

Localized Injuries. — Aside from the occasional serious and widespread
damages just mentioned, there are, probably every winter, minor localized
injuries. It is impossible, however, to draw any sharp line between
what is here termed localized injuries and more general injury. For
instance, the killing back of shoots, canes or limbs, if severe, would be
considered in the latter class; if it were light it might as readily be con-
sidered localized.

Crotch and Crown Injury. — A form of injury, often unnoticed for
some time after its occurrence, but with greater potentiality of ulti-
mate serious consequences, is the killing of more or less limited areas
of bark on the trunk, particularly at the crown of the tree or at the
crotches. Attention may be drawn to the dead area first by its sunken
appearance consequent to the growth of the surrounding uninjured tissue
or it may become evident through the cracking of the bark at the injured
area or sometimes by the loosening of the bark.

Of the apple varieties commonly grown in the regions where this
injury has been most studied, Ben Davis seems most susceptible, with
Baldwin showing considerable tenderness in this respect. King, though
less widely grown, is so notoriously subject to this malady that the injury
is sometimes called the "King disease." It seems significant that all
of these varieties are late growers. Gravenstein, in Nova Scotia, is
also reported as susceptible. ^^^

Grossenbacher'*2 i-epoi-ts crown rot much more common in cultivated
land than in sod and particularly in land formerly in sod but recently
plowed. He also reports high, wind-swept situations with thin soils to

272 FUNDAMENTALS OF FRUIT PRODUCTION

be more subject, though it seemingly appears in any situation. No
one side of the trees is uniformly injured, according to his observations,
though all cases occurring at any one time in a given orchard are likely
to be confined to some particular exposure. Trees which have made a
rather unusually large, or rather late, growth appear more liable to
injury.

In the 1913 freeze, in the citrus regions of California, the crotches
were the parts of the trunk found most damaged. -"'' Crotch injury
and those forms of crown rot not due primarily to the attacks of parasitic
organisms are probably most frequently associated with early winter
injuries associated with immaturity. Consequent to the winter injury,
fungus infestation of the dead area may appear but, excepting the fire-
blight bacillus, no organism has been shown definitely to be the primary
causative agent in producing this disorder.

Localized Injuries and Delayed Maturity. — Chandler^^ states: "The
wood at the base of the trunk and at the crotches of all rapidly^ growing
branches seems to reach a condition of maturity in early winter more
slowly than does other tissue. "

This view corroborates studies by Mer^^^ on the duration of cambial
activity in various trees, reported in part as follows. "Just as it awakes
gradually in the different regions of a tree cambial activity ceases pro-
gressively at the end of summer. ... It disappears from the branches
before disappearing from the trunk. In trees that are closely grouped, it
leaves first the low branches, less vigorous than those of the top, and the
basal and median parts of these branches before their extremity. It is
only following this that it leaves the higher shoots. In the large branches
of an isolated tree it stops earlier at the tips than at the middle. It is at
the level of the basal swelling that it persists the longest. In the trunk
it stops first at the top, then at the middle and finally at the base. When
growth is not very active it ceases, on the contrary, earlier in the lower
region. ... It is in the portion of the trunk situated immediately
below the soil that cambial activity is confined last.

"It is evident that in the regions of the trunk where the vegetative
activity is the most pronounced, because they are the youngest or
because they are the best nourished, that cambial activity awakes
first. . . . It is there also, that in general, it stops latest. On the other
hand, in all circumstances where growth is slow, we see cambial activity
manifesting itself slowly and stopping earlier. . . . Between the length
of the cambial activity and its intensity there is, then, a manifest
relation."

This statement seems in itself adequate explanation for much of the
localization of winter injury associated with immaturity. Field studies
in several regions seem to correlate immaturity with this type of injury
rather uniformly.

WINTER INJURY

273

Contributing Factors. — The drying effect, of wind should be considered,
as also the effect of cold winds on the temperature of the exposed tissues.
Winter killing is sometimes more severe in the three or four rows nearest
the windward side of the orchard. Many of the older prune orchards in
the northern end of the Willamette valley still showed, 15 years later,
the marks of the freeze of November, 1896, in the shape of dead areas on
the northwest sides of the trunks, corresponding to the direction of the air
drift at the time of the freeze. In many cases of this sort the dead tissue
ceases abruptly at the point where snow stood at the time of the injury,
suggesting at least that the injury was due to the temperature effect of
the wind. The effect of snow on soil temperatures will be shown
later. This protective influence evidently is not confined to the soil,
as data shown in Table 20 clearly indicate.

Table 20.

Temperature Under 10-Centimeter Snow Covering
{After Goeppert^^^)

Date

Under snow,
degrees Centigrade

Air,
degrees Centigrade

Feb. 4

-3.0
-4.6
-6.5
-6.0
-5.0
-2.0
-15

-12.6

Feb. 5

-14.7

Feb. 8

-16.7

Feb. 10

-14.9

Feb 11

-15.8

Feb. 13

- 5.7

Feb. 15

- 2.8

Consideration should be given, also, to the unequal maturing of
tissues on different sides of the tree trunk. Casual observations in
autumn have indicated that maturity may be attained more rapidly on
one side of the stem than on another. It would follow, then, that a given
temperature in autumn might prove injurious to the tissues of one side
and not of the other, without the intervention of other causal agents.
Furthermore, it should be considered that the temperature a few inches
above the soil may be, on clear cold fall nights, 10° colder than is indicated
by a shelter thermometer, so that an official temperature record of 20°F.
may mean that the tissues at the crown were exposed to a temperature
of 10°F.

Remedial Measures. — In view of the different circumstances under
which this type of injury occurs it is probable that not all the factors
mentioned are operative in any given instance and that only one of them,
if sufficiently intensified, may produce the injury. The one condition
apparently requisite to crown rot and to crotch injury is immaturity
in the tissues at the point involved. The prospective grower is safe in

18

274 FUNDAMENTALS OF FRUIT PRODUCTION

utilizing protection, natural or created, from winds, particularly those
prevailing in early winter, and the grower whose orchard is on an exposed
site should pay careful attention to the attainment of as complete
maturity as possible in his trees. Banking, though laborious and
expensive, is justified under threatening conditions. For trees already
damaged the best treatment is to cut away the injured bark and to cover
the exposed surfaces with grafting wax or paint and possibly to
bridge-graft.

WINTER INJURY ASSOCIATED WITH DROUGHT

In spite of the great water-retaining capacity of the tissues of the
most hardy deciduous fruits in a dormant state, they are not able to
withstand an indefinite amount of desiccation. Especially when the
evaporating power of the air is high they gradually lose water. This will
result eventually in a desiccation that may mean the death of the tissue
unless the water lost is replaced promptly. Recovery from winter
desiccation, or the ability to withstand long continued hard freezing
(physiological drought) or long continued winter drought (atmospheric),
depends therefore on a supply of available moisture upon which the
roots may draw. In many sections there is seldom, if ever, a winter
when soil moisture would be a limiting factor in this connection. In
others it is frequently a limiting factor and gives rise to those injuries that
are classed here as associated with winter drought.

Fundamentally all injury to dormant tissues from cold is to be regarded as
induced by drying out. Paradoxically, it is generally the tissue containing the
most moisture that is most subject to damage. The injury, however, comes from
immaturity and not from excess moisture. Apparently there is a certain quan-
tum of water, varying with the kind of plant and with conditions, that is essential
to protoplasmic life and this is retained more tenaciously by mature tissue.
Hence, in considering winter injury a distinction must be drawn between mois-
ture in the plant tissues (water of composition and surplus moisture) and
moisture in the environment. Though the two are closely related, freezing
(drying out) of immature tissue in a moist environment should be distinguished
from freezing (drying out) due to dry environment though the final lethal
process is the same.

Immaturity and Winter Drought

Injury from drying out may have certain manifestations in agreement
with that from immaturity. It is, however, somewhat more evident
in the tops though it may extend to the trunk. Fruit buds in the apple
are killed more generally by this type of freezing than through imma-
turity. Wood formed the previous year suffers heavily; with more
extreme conditions the damage extends downward. Injury associated
with immaturity may start either on the young twigs or on the trunk.

WINTER INJURY

275

In one case the young twigs suffer because they are immature; in the
other because they are the most subject to drying out, just as they would
be in excessive growing season drought. Winter drought injury may
discolor wood on older parts of the tree but it does not kill cambium
readily.

It should be remarked, also, that in some regions it is quite conceiv-
able that nmch of the winter killing in the tops may originate primarily
as root killing. Conditions there are favorable to root injury and it has
been definitely shown many times to occur. Early winter root killing
would be followed by a drying out of the top. The latter symptom natu-
rally would be more evident and would pass as killing of the top, the
true cause being obscured. However, the preventives for both classes of
injury agree in requiring a high soil moisture content after danger of
inducing late growth has passed.

Water Loss from Dormant Tissues

Some measure of the loss of water by dormant trees is afforded by the
data presented in Table 21 showing decreases in weight of 8-year old
apple trees during two winters in Wisconsin.!''^ Obviously these losses
are in trees severed from their roots. If the loss in moisture of standing
trees, where the supply of water would be renewed to some extent, should
be determined, it would be considerably greater but the degree of exhaus-
tion would be less because, as has been shown earlier, the loss by evapora-
tion diminishes as the degree of exhaustion increases. If the dry weight
of the trees could be deducted, the percentage loss of moisture would be
correspondingly increased. Quite noticeable are the differences in
moisture losses during the two winters recorded in Table 21. The winter
of 1903-1904, though severe, was moist and many cloudy days occurred.
There was little winter injury in Wisconsin during that season.

Table 21.

-Loss IN Weight of Apple Trees During Two Winters'^*
(Weight, pounds)

Dute

Tree 1

Tree 2

Tree 3

Tree 4

Dec. 19, 1902

36.6

24.6

35.7

30.4

Feb. 27. 1903

34.7

23.5

34.4

29.0

Apr. 3,1903

31.4

21.4

31.6

26.5

Loss

5.2

5.2

4.1

3 9

Dec. 5,1903

26.2

24.2

Mar. 26, 1904

25.6

23.6

Loss

0 6

0,6

276 FUNDAMENTALS OF FRUIT PRODUCTION

Bailey^"^ estimates that a large apple tree loses from 250 to 350 grams
of water each day through the winter. Observations on moisture content
of apple twigs in Iowa show an actual increase from November to Decem-
ber in many varieties; on Jan. 15, however, following several days of
severe cold, there was a very marked decrease, though the respective
intervals between observations were 5 weeks and 3 weeks^*^ (see Table 13).

Water Conduction in Trees During the Winter

Bailey ^° cites evidence gathered in New York showing loss of moisture
in twigs during winter and a higher moisture content during a thaw than
during a previous period of cold weather, indicating a conduction of sap
during the milder weather. Indeed such a conduction must be conceded
else the tree would inevitably dry out. Wiegand^i"* showed a conduction
of water to Pinus Laricio buds at temperatures between — 18°C. and
— 6.7°C. Buds severed from the tree but sealed immediately on the
cut surfaces showed an average water content of 41.2 per cent, after 3
days while buds taken fresh from the tree at the end of this time, even
though the twigs had been frozen, showed an average content of 47.5
per cent. It is probable that interference with conduction, or an evapora-
tion rate much higher than conduction, is just the condition requisite for
winter drought injury.

Relation of Freezing to Water Conduction. — It is well known to every
wood-chopper of the northern woods that trees freeze even to the center
in prolonged cold weather. Investigations have shown that in trees of 6
to 8 inches diameter the difference in temperature between the center and
the outside in the morning is only 1 ° or 2°R. , though in trees 2 feet in diam-
eter it may be on single days 5°, 6° or 7°Il. ; with air temperatures of — 13°
to — 15°R. the tree temperature was —12° to — 14°R.; most important,
the longer the temperature of the air remains uniform the more the tem-
perature of the tree approaches that of the air.^^^ The temperature of the
alburnum or sap wood in maple has been shown to follow the air tempera-
tures fairly closely. ^^^'^ More detailed figures taken morning, noon and
night, at a depth of 8 centimeters in a box elder tree, indicate that tree
temperatures follow the trend of the air temperatures very closely, not,
however, reaching the full extremes of the outside fluctuations unless
these are maintained for some time.'^^ Figure 27, arranged from a part
of these figures, shows typical daily fluctuations of air and tree tempera-
tures. Table 22 shows the averages of the temperatures recorded during
January and February. Observations in Lapland show winter tempera-
tures in live and dead trees to be practically the same."^

Grape vines have been grown in a greenhouse, so trained that certain
canes passed outside and were then brought back into the house. The
base and the upper parts, inside the greenhouse, opened their buds
quickly and continued to grow. On cold mornings, however, with the

WINTER INJURY

277

outside temperature around — 10°C., the leaves on the upper part of
the stem were very much wilted, because of the interference with sap
conduction in the portion of the stem outside. With rising temperature,
however, they recovered. ^^

10 II 12 13 14- 15 16
February

Fig. 27. — Temperature fluctuations in a tree trunk. (After Squires^^)

Table 22. — Tree and Air Temperatures

(After Squires''-^^)

Januarv

February

Air, degrees
Centigrade

Tree, degrees
Centigrade

Air, degrees
Centigrade

Tree, degrees
Centigrade

6 to 7 a.m
12 to 1 p.m

6 to 7 p.m
En tiro dav

10.84
6.60
9.20

s.ss

-9.37
-8.90
-7.50

11.93
4.35
8.65
8.31

-10.46
-7.55

- 7.00

- 8.34

These considerations make it evident that prolonged cold weather
must interfere materially with sap conduction while at the same time the
conditions accompanying extreme cold are the very conditions which
favor greater drjnng out. It should be considered, too, that the conduc-
tive regions in the tree are near the outside of the stem. Many cases of
twig killing must, therefore, be considered as due to drought, short,
perhaps, but intense in localized areas. Possibly the greater suscepti-
bility of twigs to this injury is not due entirely to failure in conduction

278 FUNDAMENTALS OF FRUIT PRODUCTION

but may be explained in part by the lack of a sufficient amount of sap-
wood to serve as a local reservoir. Even prolonged cold does not affect
the upper part of tall trunks as much as it does the low, smaller branches
though conduction from the ground is conceivably as difficult; the tissues
on the trunk, however, have both relatively and absolutely a greater
amount of sapwood on which presumably they may draw.

Where Winter Drought Conditions Prevail

Winter drought conditions are in a measure independent of soil con-
ditions and can be considered as of possible occurrence over a wide range
of territory. The coldest weather in humid sections is accompanied by
dry atmospheric conditions; occasionally after a dry summer and fall
these sections suffer from winter killing due to desiccation. Long con-
tinued severe, though not excessive, cold would induce physiological
drought. The winter of 1895, already mentioned, was of this type. It
is, however, infinitely more common, in proportion to the amount of
fruit grown, in regions of prevailingly dry atmosphere and intense cold.
Wyoming, the Dakotas and parts of Minnesota furnish abundant
examples. Rainfall is comparatively light in those sections and the soil
frequently freezes with a low moisture content. Winter precipitation is
less than summer, frequently only a fourth as great and there is much
clear, cold weather.

Protection Against Winter Drought Injuries

Necessarily protective measures against winter injury associated with
drought must be preventive. They must either reduce water loss or
increase water supply.

Winter Irrigation. — Buffum^^ advocates in Wyoming thorough irriga-
tion "late in the fall, before the ground has frozen and when growth
has ceased. The later this irrigation can be done the better as the
object is to store moisture in the soil sufficient for winter . . .where
orchards are planted on bottom lands that have a continual supply of
moisture fall irrigation may be unnecessary. But on upland it is the
surest way to prevent trees from winter killing and when possible irri-
gations through the winter will be found advantageous. " In North
Dakota, Waldron^^^ writes: "Parts of our own plantation have been
cultivated every year until the ground freezes with only the best results
. , . the treatment that provides the trees with the greatest amount
of soU moisture in the fall will tend to prevent winter kUling." Else-
where the same writer states: "The cause of winter killing in mild
weather is the drying up of the twigs .... Trees and shrubs that are
neglected during the latter part of summer so that the ground becomes
hard and dry, ripen their wood prematurely and unless fall rains are
abundant the drying process sets in before winter begins, leaving the

WINTER INJURY

279

plant in poor shape to endure further drying. . . . Some of the plants
that defer this change (to winter condition) the longest are among the
hardiest we have.''^*'*'

Cultivation. — Experimental demonstrations with Wealthy apple trees,
on 15 widely separated farms in South Dakota, give quantitative

Table 23. — Effect of Cultuhal Conditions

Dakota^-s

ON Winter Killing in South

Lot
number

Number
trees,
1916

Number

trees dead,

1919

Number

trees

severely

injured,

1919

Number

healthy

trees, 1919

Average
growth

(inches,)

Average per-
centage of
soil moisture,
Nov. 15

Average per-
centage of
soil moisture,
Feb. 15

1

2
3
4

50
50
50
50

41
16

22

7

7
18

13

11

2
16
13

32

2.0
9.0
6.5
15.0

14.70
17.95
15.50
31.50

14.2
19.2

15.2
33.8

verification of the opinions just quoted (Table 23). Lot 1, showing the
lowest moisture content and the greatest injury to trees, was composed of
trees planted in prairie sod; Lot 2 was cultivated each 10 days till Aug.
10; Lot 3 was "cultivated each 10 days till July 1, followed by a cover
crop of fall rye or buckwheat" and Lot 4, which showed least injury,
was cultivated each 10 days until Aug. 10, just as Lot 2, but in addition
received a heavy watering just before the ground froze for the winter.
The investigator concluded that "summer cultivation is positivelj^ needed
and in very dry seasons fall watering or irrigation of some sort is not
only advantageous but necessary."

Cover Crops.— Another point of interest here is the lower soil moisture
in the cover crop lot and the somewhat greater attendant injury, as
compared with the clean cultivated lot. Had a winter favorable to
root killing intervened, the results in these two plots might have been
different. However, the danger from cover crops in this region of light
rainfall is apparently more frequently present than the danger from their
absence which is discussed presently. This point doubtless has occasion-
ally equal application in dry situations in other regions. Comparison of
these results with those of Emerson, reported below, indicate that the
best insurance against winter injury in general in this region — and in
occasional sites in more humid sections — is a frost-tender cover crop
with a heavy late fall irrigation. To be sure, in those districts where
irrigation water is not available, the preventive measures against the
winter injuries associated with drought must of necessity be incomplete.
However, the recognition of the liability of a given site to this form of
injury may enable the grower so to shape his cultural practices early in
the season as to minimize the danger.

280

FUNDAMENTALS OF FRUIT PRODUCTION

Studies by Emerson''^ in Nebraska show the effect of cover crops of
different kinds on the hardiness of young peach trees. The cover crops
are considered in two classes, frost-resistant and frost-killed. Table 24,
reproduced from Emerson's report, shows the effect of these crops on soil
moisture content.

Table 24. — Effect of Various Cover Crops on Soil Moisture During the Fall

OF 1900^^

Kind of cover crop

Sept. 20

Oct. 9

Oct. 27

Nov. 7

Nov. 20

Dec. 11

Frost-resistant crops:
Rye

15.2
15.1
15.8
19.5

16.4

16.5
17.3
17.6

17.1

20.0
18.6

19.3

11.8
13.3
12.8
15.8

13.4

12.6
15.1
13.8

13.8

18.4
17.8

18.1

12.1
12.3
11.8
14.7

12.7

12.4
13,8
13.5

13.2

20.3

18.2

19.3

14.1
14.9
14.4
17.2

15.2

19.4
20.0

18.7

19.4

20.6
19.1

19.9

15.5
13.9
14.2
15.0

14.7

18.9
19.6
19.0

19.2

19.8
18.3

19.1

16.0

Oats

14.4

Rape

14.0

Field peas

Average

Frost-killed crops:

Millet

15.6
15.0
17.6

Cane

Corn

17.9
19.7

18.4

No crop:
Few weeds

18.1

Few weeds

18.5

Average

18.3

Figure 28, also from Emerson, a graphic representation of the same
figures, shows these effects even more strikingly. Both classes reduced

7 20 II
NOV. DEC.

Fig. 28. — Percentages of soil moisture in bare ground and under frost-killed and frost-
resistant cover crops. (After Emerson^^)

soil moisture sharply in September and October, a very desirable effect
when the need for ripening of wood is considered. Early in November,

WINTER INJURY 281

however, the frost-killed crops, no longer growing, ceased to draw on the
moisture supply while the frost-resistant crops kept the moisture content
low. When it is recalled that Emerson's earlier work showed 19 dead
trees and none uninjured out of 25 in soil with 15.2 per cent, moisture, as
here under frost-resistant crops, while soil with 19.8 per cent., the nearest
figure to that of the soil under frost-killed crops, showed three dead and
12 uninjured, the importance of this difference is evident. The graph
for the soil with no cover crop shows a somewhat higher moisture content
in December than either class of cover crops but it also shows a high
moisture content in September and October, suggesting a prolonged
growing season and poor maturity in the tops. This is what actually
occurred. Emerson's work emphasizes the importance of a water supply
after maturity is attained.

A plentiful supply of available water is an important factor deter-
mining the recovery of plant tissues from the effects of low temperatures.
Pantanelli has shown that the activity of the roots is of great importance
in determining the recuperative power of the plant after the aerial parts
have been exposed to low temperatures and that all those factors that
reduce the absorbing capacity of the roots, such as insufficient aeration,
salinity, alkalinity and the presence of toxic substances reduce the
recuperative power of the plant.

Windbreaks. — The relation to the orchard of shelter belts composed of
hardy trees and shrubs has been the subject of much discussion, of some
observation but of little precise study. Variations in local conditions
of exposure to prevailing winds and in the character of these prevailing
winds, as well as the topography of the orchards themselves, pre-
clude the possibility of windbreaks being universally beneficial or injurious.
Their efficacy, when properly placed, in cutting down the windfall
loss from summer storms, is not a matter for discussion here. In
the Michigan and New York fruit sections much of the advantage
claimed for them is the protection they afford from those types of
winter injury that are associated with drying out and they are set usually
on a northern boundary of the orchard. In the north central states
windbreaks seem to be planted more as protection against the hot drying
winds of summer; hence, they are generally set on southerly boundaries.

Ejfect of Wind Velocity. — Of quantitative data on windbreak effects,
little is available. The increased snow deposit in places sheltered from
the full sweep of the wind is a matter of common observation. After the
snow has fallen the windbreak acts to preserve it from evaporation by
protecting it from the full force of the wind. Fernow^^ states that
snow evaporates ten times as fast in warm wind (velocity not stated)
as in calm air. Provided the snow accumulation is not great enough
to injure the tops of young trees this effect must be beneficial since
data to be introduced show the great power of snow in protecting roots

282

FUNDAMENTALS OF FRUIT PRODUCTION

against freezing. How much the windbreak prevents the drying out
of the tree tops during the high, desiccating cold winds of winter is a
matter which with present data can be only conjectured.

Certain experiments have shown that "with the temperature of the air at
84 and a relative humidity of 50 per cent, evaporation with the wind blowing at
5 miles an hour was 2.2 times greater than in the calm; at 10 miles 3.8; at 15
miles 4.9; at 20 miles 5.7; at 25 miles 6.1 and at 30 miles per hour the wind would
evaporate 6.3 times as much water as a calm atmosphere of the same temperature
and humidity. "*°

Bates^^ found, in comparing wind movements in the open with those at a
leeward point distant from the windbreak five times its height, that "a wind
which reaches a velocity of 25 miles per hour in the open will, in the shelter of a
good windbreak, have a velocity of . . . only 5 miles per hour."

Combining these sets of figures, the evaporation in this case would
be only 39 per cent, of that in the open. Figure 29, reproduced from
Bates' study, shows the percentage of protection to increase with the
wind velocity.

100

90

80

^10

I 50

^ 30
20

to

0 t) lu lb 21)

"Wind Velocity in Open(miIes per hour)

Fig. 29. — Wind at points five times the heights of windbreak to leeward, in terms of
wind in open. (After Bates^^)

Effect on Evaporation. — Card^' in Nebraska determined the rates of evapo-
ration at different distances from a windbreak 8 rods wide and 25 to 40
feet high. Though these observations were made in summer, they are somewhat
indicative of winter conditions and furthermore they have an important bearing
on the state of trees as they approach dormancy. If the evaporation on the
windward side of the windbreak during all the time that drying winds were
blowing be represented by 100, then the evaporation at a point 12 rods distant
on the leeward side would be proportionally 83 and at 3 rods distant it would be
55. During a period of high though not particularly dry wind the respective
rates were as 100 to 67 to 29. Numerous interesting studies of evaporation
rates are reported by Bates, as shown in Table 25, arranged from his data.

Effect on Soil Moisture. — The importance of soil moisture in relation
to winter drought has been shown. For this reason, Card's determi-
nations of soil moisture at varying distances on the leeward side of a wind-

V

'

\

^^

C^^ ,

1

^^"■"^^^rro^.^nn.

\

-iii:il_tf5^2__

\

\

V M/W/

TE PINE BEJJL —

WINTER INJURY

283

Table 25. — Mean Efficiency of Windbreaks in Area of Greatest
Protection {After Bates^^)

(Area

12 times as wide as height of trees) .

Kind of windbreak

Width,
feet

Height,
feet

Moisture saved at different
velocities, per cent.

Period of

5

10

,.

20

Cottonwood grove (underplanted)

25
100

75
20
50

70

40
23
32

23.9
31. 1
12.3

11.7

12.8
26.0

31.9
33.3

18.6

13.9

20.2
27.2

28.7

38.7
35.8
26.6

15. 5

23.7
27.2

40.1

33.4

17.0

25.8
27.5

July, Sept.
Nov.

Cottonwood row (natural density)
Cottonwood belt (no low

branches)

Cottonwood row (reinforced with

ash)

June, July, Aug.
Aug., Sept.
Sept

Osage orange hedge (lower

branches trimmed)
Mulberry, single row

June, July, Aug.
Aug.

break are of particular interest. Table 26, arranged from his report
of determinations made November 5, shows a difference well worth
consideration, particularly as they were made at the approach of winter.
Assuming, as Card does, that soil moisture up to 10 per cent, is not
available for plants, the average available moisture up to a distance of
about 7 rods was 2.55 per cent.; beyond that point it was 0.65 per cent.

Table 26. — Soil Moisture at Varying Distances from a Windbreak^'

Distance (rods)

Percentage of moisture

Available for plants

1

14.0

4.0

3

12.6

2.6

5

11.3

1.3

7

12.3

2.3

9

10.7

0.7

11

10.5

0.5

13

10.0

0.6

15

10 s

0.8

The area protected by a windbreak is variable. It has been stated
that in the Rhone valley each foot in the height of a windbreak protects
plants for 11 feet to the leeward. ^^ From rather general observations in
Iowa and Nebraska it has been estimated that a rod of ground is sheltered
for each foot in height of the windbreak, and other estimates state that a
windbreak 25 feet in height will protect 10 rods of orchard. Bates
found that the area extended on the average not more than 20 times the
height of the windbreak; at this distance the wind velocities were found
to be almost as great as on the windward side. Card's soil moisture
determinations indicate that for this windbreak the effects were not

284 FUNDAMENTALS OF FRUIT PRODUCTION

evident beyond 7 rods. Unfortunately these figures were made in an
open field and there is at present no means of stating just to what extent
the orchard will protect itself at points beyond the sheltering effects of
the windbreak, though observation indicates that it does to a considerable
extent. Injury from cold drying winds in the 1903-1904 winter was
found to be more severe in the outside rows of many orchards.

INJURIES CHARACTERISTIC OF LATE WINTER CONDITIONS

Primarily all winter injuries are induced by cold. This fact should
be kept in view though for convenience the late winter injuries are treated
as due to warm weather. It is not the heat that does the harm but cold
weather, even in moderate degree, following warm weather. In one
form or another, all fruit growing sections in temperate regions suffer
through injuries proceeding from these causes.

The Rest Period

Discussion of the rest period at this point should not be taken to mean
that it is regarded among the effects of temperature; it is considered here
very briefly because of its relation to them. Periodicity of growth is
found in plants wherever they are; equatorial regions with uniform
temperatures present the phenomenon of plants in the resting stage while
others are in growth. Sometimes on the same tree one branch is resting
while others are growing. Other factors than temperature are undoubt-
edly concerned with the inception and with the end of the rest period.

The dormant season should not be confused with the rest period,
though the two overlap more or less ; in temperate regions the former may
begin after — or before — and generally extends beyond, the latter. In
the peach, for example, the rest period may begin to ''break" in January
though the temperatures prevailing may prolong the dormant season
into April. The rest period is not a time of complete cessation of plant
activities. The activities commonly recognized as growth are at a
standstill, but other functions, undoubtedly of equal necessity to the
l^lant, are active. The beginning and end are probably gradual processes.

If an attempt is made to force peach trees into growth in a greenhouse
during November or early December little success is attained; if the
attempt is made in late December less difficulty is encountered while in
January there would be still less difficulty. In the first instance the
trees are in the rest period; in the second, the rest period is breaking.
In the first case, no matter how favorable the environment, there is no
response; in the second, the response is rapid whenever the environment
is suitable.

Chandler^^ shows an interesting parallelism between the percentage
of buds killed in 1905-1906 and the percentage of buds of the same
varieties that could be forced into development early in the following

WINTER INJURY

285

winter. The data are summarized in Table 27, which is arranged from a
more detailed statement in Chandler's report. The relation is close
enough to indicate why a given variety, of the Persian type for example,
may be tender in the south where its rest period is likely to be broken
and still be hardy in the north where cold weather is constant, or why in
the same orchard it may be hardy during a winter of steady and fairly
severe cold and still be tender during a mild winter.

Recent studies indicate some correlation, even in Minnesota, between
hardiness and the intensity of the rest period in certain plums, as shown
in Table 28. These suggest that the rest period may be more important
in the north than it generally has been considered, though they do not
explain observed differences in bud killing early in the winter.

T.^£LE 27. — Percentage of Buds Starting Early and of Buds Killed'''

Group

Percentage of
buds started
Dec. 12, 1906

Percentage of

buds started by

Dec. 22, 1906

Percentage of

buds killed in

1905-1906

Hill's Chili type

3.6
0.0

0.0

0.0

27.9

12.6

40.7 39.7

Chinese Cling type

Chinese Cling, excluding Elberta,
a hybrid

13.0

6.7

8.7

86.7

65.7

51.2
44.3

50.6

Heath Cling type

79.1

78.9

Table 28. — Time Required for Blooming under Laboratory Conditions at
Different Intervals During the Winter

{After Straushaugh^^^)

Stella (semi-hardy)

Tonka (semi-hardy)

Assiniboine (hardy)

Date

collected

Date of

Days

Date of

Days

Date of

Days

bloom

required

bloom

required

bloom

required

Oct. 3...

Oct. 17

15

Oct. 17

15

Did not bloom

Nov. 8...

Nov. 22

15

Nov. 22

15

Did not bloom

Nov. 19...

Dec. 4

16

Dec. 4

16

Did not bloom

Jan. 24...

Feb. 2

10

Feb. 2

10

Feb. 18

26

Feb. 6...

Feb. 15

10

Feb. 15

10

Feb. 23

18

Feb. 21...

Mar. 2

11

Mar. 2

11

Mar. 8

17

Feb. 28...

Mar. 7

9

Mar. 7

9

Mar. 14

16

Mar. 5..

Mar. 13

9

Mar. 13

9

Mar. 19

,5

Different plants appear to have rest periods of unequal length; in fact
some, such as certain spiraeas, seem to have none. However, the rest
period for each plant seems to be fairly constant provided no disturbing

286 FUNDAMENTALS OF FRUIT PRODUCTION

influence acts upon the plant. It follows, then, that the earlier the plant
enters upon its period of rest the earlier the period is over. This is a
matter of some practical import, as appears later.

The rest period can be shortened, or broken, by various treatments.
Etherization, light, wounding, desiccation, hot-water baths and exposure
to freezing all bring it to an early end. For the forcing of certain flowers,
such as lilacs, etherization is sometimes used; the greenhouse man who
wishes to force fruits exposes the trees to cold. Northern greenhouses
in Europe can force fruit and have it on the markets somewhat in advance
of the greenhouse fruit crop from many more southern parts because the
trees can be exposed to a freezing temperature earlier in the north and
the rest period broken earlier. For the orchardist, however, the chief
interest is in prolonging the rest period; this can be done in some cases,
discussed later, by postponing its advent. In northern sections, though
the temperatures are undoubtedly severe enough early in the winter to
break the rest period, they are low enough to prolong dormancy and the
rest period is relatively of less importance there. Farther south, where
warm periods come during the winter, it is of much greater significance.

The exact natures of the changes involved in the beginning and the end of the
rest period are not known. A puzzling fact is mentioned by Schimper: A low
temperature in the growing season will not have the same effect as in the dormant
season; the change of starch to sugar in the potato accompanying cold in the
winter is not dupUcated in the summer. Since ordinary growing temperatures
are without effect on the rest period, chemical changes appear not to be the con-
trolUng factors. Since time is a recognized factor a physical change is suggested.
It seems significant that all processes known to shorten the rest period are known
also to increase permeability.

Injuries to Fruit Buds

The killing of fruit buds which have started into activity is more
evident in southern sections. Whitten^i" discusses winter killing of the
peach in Missouri as of this nature. He states: "The growth of buds
during warm weather in winter renders them very susceptible to injury
from subsequent freezing. This is the most common cause of winter
killing to peach buds in this state. Very often a warm spell as early as
February causes peach buds to make considerable growth. If growth
starts to any great extent the subsequent cold weather is almost sure to
kill the buds." Chandler^^ states that "there has very seldom been a
year when buds in the peach section of southern Missouri have not been
started sufficiently by Feb. 1 to be killed by a temperature considerably
higher than would be required to kill buds in northern Missouri, or
certainly in Michigan, New York or New England on the same date."

It is possible that occasionally the injury in these cases of warm
weather followed by cold is due merely to the sudden drop in temperature.

WINTER INJURY

287

Indeed, Chandler'^ cites convincing evidence to this effect: "In the
year of 1901-1902 all of the buds were killed at the Missouri Experiment
Station orchard by a temperature of — 23°F. on Dec. 20. In 1902-
1903 practically all buds were killed by a temperature of — 15°F. on Feb.
17. In 1903-1904 buds were killed on all varieties except General Lee,
Chinese Cling, Thurber, Carman, Gold Drop, Triumph and Lewis by
a temperature of — 14°F. on Jan. 29. During the winter of 1904-1905
nearly all the buds were killed, yet practically all trees had a few left
alive and Triumph and Lewis a fair crop following a temperature of
-25°F. on Feb. 13. ... on Jan. 12, 1909, practically all the buds were
killed except on the most hardy varieties by a temperature of — 11°F. In
fact, fewer peaches were borne at Columbia following the winter of 1908-
1909 than following the winter of 1904-1905 when the temperature fell
to — 25°F. on Feb. 13. ... there was not more warm weather to start
the buds preceding the freeze of Jan. 12, 1909, at Columbia . . than
preceding the freeze of Feb. 13, 1905, at Columbia.

"It would hardly seem possible that the buds in either case could
have been started into slight growth preceding the freeze. Buds start
very slowly even at high temperature early in January. . . . the low
temperature of Jan. 12, 1909, came suddenly following high temperature
while that of Feb. 13, 1905, came following 42 days of rather low tempera-
ture. For 16 days the maximum temperature did not go above the
freezing point. "

Chandler suggests two possible reasons for buds surviving the colder
temperature of the 1904-1905 wint-er: the long exposure to low tempera-
ture which hardened them and the very slow falling of the temperatures.

Changes in Water Content of Buds During Winter. — There is, how-
ever, abundant evidence that development in peach buds during warm
periods of the winter is frequently a contributing factor in winter injury.
Investigations in Maryland show a progressive change which easily may
be accelerated by pronounced warm weather.^^ It seems significant that

Table 29.-

—Water Content of Peach Fruit Buds
(After Johnston^'>)

Date of

sample

Average green weight
(grams)

Average dry weight
(grams)

Ratio water con-
tent to green
weight

Ratio water con-
tent to dry weight

Elberta

Greens-
boro

Elberta

Greens-
boro

Elberta

Greens-
boro

Elberta

Greens-
boro

Nov. 8

0.124
0. 144
0. 144
0.164
0.327
1.050

0.121
0.129
0.123
0.128
0.220
0.750

0.073
0.079
0.082
0.082
0. 115
0.205

0.073
0.073
0.075
0.075
0.092
0.180

0.41
0.46
0.43
0.49
0.65
0.80

0.40
0.43
0.38
0.42
0.58
0.76

0.84
0.76
0.99
1.85
4. 12

0.65

Dec. 6

0.76

Jan. 7

0.62

Feb. 7

Mar. 7

Mar. 28

0.71
1.37
3.17

288 FUNDAMENTALS OF FRUIT PRODUCTION

the more tender variety of the two studied shows this change in greater
degree.

Contributing Factors. — Roberts, ^"^^ in Wisconsin, investigating blos-
som bud kilHng in the sour cherry, concluded that suceptibility is in direct
relation to the degree of advancement, the more advanced blossoms
suffering most. He states: "The amount of injury is in relation to
the degree of development of the blossom buds, which, in turn, is usually
in [inverse] proportion to the amount of growth the tree is making."
These conclusions were reached after microscopic investigation as well
as field studies.

The position of the hardiest buds was investigated by Chandler^^
whose report follows, in part: . . . "the hardy buds are those borne at
the base of the whips (last year's growth). ... at the base of the
whips on trees not cut back only a slightly larger percentage of buds were
killed than were killed at the tips of cut back trees. . . . Now it is
possible to head back so severely that no fruit buds will be formed except
at the outer end of the branches. This is especially true if the tree has
a narrow dense head. ... If the tree be spreading in form, heading
back is not so likely to cause the next season's wood to be in very long
whips that either have branches at the basal nodes instead of fruit buds,
or have the leaves at these basal nodes killed by the shade before fruit
buds can be formed. This is true because the spreading heads would
afford room for a larger number of whips to grow and obtain light, and
the larger the number of nearly equal growing whips, other conditions
of the tree being equal, the shorter necessarily will be the growth in
each whip." Data are cited showing a loss of 60.2 per cent, of fruit
buds on a large low-growing, spreading Oldmixon as compared with
86.4 per cent, on a tree of the same variety making very large, upright
growth and 90.8 per cent, on still another Oldmixon making small
upright growth.

Protective Measures. — Late entrance into the resting stage has been
said above to cause a delay in breaking the rest period. This may be
effected in a number of ways.

Pruning. — One of the means of inducing late growth and late entrance
into the resting period is pruning heavily enough to stimulate vigorous
growth. Chandler^^ reports results of investigations in forcing twigs
of a large number of peach varieties which he summarizes as follows:

"Average per cent, started on trees making large growth

(cut back) 20.5

Average per cent, started on trees making small growth

(not cut back) 31.2

Number of varieties in which trees not cut back started first . . 20

Number of varieties in which trees cut back started first 3.

Number in which both started about equally 4.

WINTER INJURY

280

" . . . If we take the average of buds started on twigs taken
December 22, or later, that is, when the resting period is nearly ended, we
have ; —

For trees making large growth (cut back) 28.3 per cent, started.

For trees making smaller growth (not cut back) 48.6 per cent, started.

"Taking only those varieties in which one tree had 60 per cent
of the buds started, and therefore may be considered to have finished its
resting period, we have as an average —

On trees making large growth (cut back) 44.3 per cent, of the buds
started;

On trees making smaller growth (not cut back) 83.4 per cent, of the
buds started."

It is apparent that the more favorable the conditions become for
breaking of the rest period the more evident becomes the restraining
influence of late maturity.

That this retardation of development by pruning actually results in
lessening winter injury of the type under discussion is shown by numerous
instances cited by Chandler. After a succession of warm days followed
by a fall to — 3°F., which would hardly kill any considerable number of
buds unless they had started into development, a count was made of
dead buds on pruned and unpruned trees. Table 30, arranged from
Chandler's data, shows one instance. Even more striking is his enumera-
tion of results at Brandsville, Missouri, following the freeze of Mar. 16,
1911, when 98.08 per cent, of the buds on unpruned trees were killed
while only 81.9 per cent, were killed on the severely pruned trees. ^* The

T.\BLE 30. — Buds Ivjlled at — 3°F. on Pruned and Unpruned Trees'^

Variety

Per cent, killed

Pruned

Unpruned

Elberta

Oldmixon Free

Triumph

Lewis

Early Tillotson

Average

48.5
62.9
30.0
16.0
23.9

36.2

67.8
78.0
59.1
25.7
.54.7

59.8

killing on the pruned trees seems high but 18.1 per cent, of peach buds
may produce a full crop, as they did in this instance, while the unpruned
trees bore only a few peaches.

Fertilization and Cultivation. — Nitrogenous fertilizers, stimulating
vegetative growth, have much the same effect as pruning, according to

290

FUNDAMENTALS OF FRUIT PRODUCTION

Chandler. In one case, at Brandsville, Mar. 16, 1911, unfertilized trees
lost 98.4 per cent, of their buds while trees fertilized with ammonium
sulfate lost 77.6 per cent, and those which had received nitrate of soda
lost 87.1 per cent. In one instance the fertilizer saved enough buds to
make a full crop, in the other enough for a fair crop.

Late cultivation has been reported to have the same results in
retarding the rest period and increasing hardiness.

Thinning. — Thinning has been observed to have beneficial effects
on hardiness. Chandler^^ cites a case in which buds of certain varieties
survived a winter that killed those of most varieties. These trees then
bore a full crop but in the following winter their fruit buds succumbed
while the varieties tender in the previous year survived. To secure
experimental data the fruit on half of each of several heavily loaded trees
was thinned with the results shown in Table 31. When the experiment

Table 31. — Effect of Thinning Fkuit on Hardiness of Buds'^

Percentage of buds killed

Variety

Thinned

Unthinned

Seedling .

18.5
31.6
44.5
41.7
40.9

35.4

58 9

Elberta Seedling

36 7

Oldmixon Cling. . .

53 4

Poole's Favorite

52 8

Poole's Favorite No. 2

55 4

Average

51.4

was repeated in 1908,''* the effects of the freeze of Jan. 12, 1909, following
weather such that all buds may be regarded as dormant at the time, were
quite different, the unthinned limbs losing 92.5 and the thinned 93.2
per cent, of their buds. Laboratory results are reported as follows:
"These results suggest that thinning has its effect on the rest period
rather than on the intrinsic hardiness of the buds. Where the tree is
bent under a heavy load and under the strain of bearing a heavy crop,
as when it is not thinned, the moisture supply probably being partially
shut off, the same condition will prevail, at least to some extent, as when
the trees are not cultivated; they will become dormant earlier and end
their rest period earlier. Thus thinning, like heavy pruning and ferti-
lizing with nitrogen can be expected to increase the hardiness of peach
fruit buds only in climates like that from Central Missouri South, where
there is likely to be weather warm enough to start the buds into growth
before the effect of the rest period ends."

WINTER INJURY

291

Whitewashing and Shading. — Sunlight is an important influence
in forcing buds.^^" The spraying of peach trees with whitewash resulted
in a reduction of heat absorption, with the effects on blossoming shown
in Table 32, arranged from a similar table by Whitten. These data

Table 32. — Blossoming Dates of Whitewashed Peach Trees^i"

First blossoms

Full bloom

Last blossoms

Variety

White-
washed

Not white-
washed

White-
washed

Not white-
washed

White-
washed

Not white-
washed

Heath Cling

Wonderful

Rivers' Early . .
Silver Medvil , . .

Apr. 13
Apr. 14
Apr. 13
Apr. 13

Apr. 11
Apr. 11
Apr. 9
Apr. 7

Apr. 21
Apr. 22
Apr. —
Apr. 18

Apr. 18
Apr. 18
Apr. 21
Apr. 13

Apr. 29
Apr. 29
Apr. 29
Apr. 28

Apr. 27
Apr. 25
Apr. 27
Apr. 21

do not, however, show the full force of reduced sunlight absorption as its
effectiveness would be greatest during the warm periods of winter
while atmospheric temperatures are lower and when even slight develop-
ment may result in winter-killing. Somewhat similar results have
been obtained with plums in Ontario, but not with the apple, "^ which
blossoms much later when the air temperature has greater influence
in proportion to heat of insolation than it has earlier in the season.
Even farther south, because of the difficulty in keeping trees well covered
with whitewash and the consequent expense involved together with the
ever-present possibility of conditions that will kill buds despite the
covering, this method is little used.

Board shelters have been found even more efficacious than white-
washing but again the expense involved precludes their use.^^*' However,
a choice tree or two can sometimes be located on the shady side of a
building to good effect and sometimes a hill can be of advantage in secur-
ing partial shade from the low midwinter sun for a good sized orchard.

In General. — The peach has been used as illustrative matter here,
because it has been studied the most thoroughly. More or less similar
appHcation may be made to Japanese plums, apricots, almonds and
cherries.

Finally it should be emphasized that the breaking of the rest period
in the buds is entirely independent of the roots and that efforts to retard
blossom development during warm periods in the winter by mulching the
ground to keep it frozen or by spreading snow on the ground around the
trees are absolutely wasted. Trees open their buds while the soil about
the roots is still frozen or after they have been cut away from the roots.
Time and again evidence to this effect has been presented and afterward
the same useless effort repeated. The winter rest period of buds can be
influenced through the roots during the growing season only.

292 FUNDAMENTALS OF FRUIT PRODUCTION

Attention must be called to the greater application of the principles
just outlined the farther south the location and their diminished applica-
bility northward. Wiegand^^^ reported that in New York fruit buds
did not grow from about Nov. 15 until about Mar. 1, when apple and
apricot buds began a relatively rapid development culminating in open
blossoms 8 and 7 weeks later respectively. Peach buds did not begin
their spring growth until Mar. 23 and came into blossom with the apricots
on Apr. 23. It appears from these observations that the cooler and
shorter growing season in the north, though it stops growth earlier
by the calendar, makes the peach buds less advanced at the onset of the
dormant period and less easily started into growth, while the colder
winters add to this effect.

However, an interesting case is reported by Maynard^^^ in Massachu-
setts. Early in November, 1884, peach buds appeared fully matured.
Following warm weather late in the month the stamens and pistils in-
creased measurably in size and the bud scales loosened. The minimum
temperature to Dec. 11 was 18°F.; at this time some buds had been killed,
but the majority were unhurt and the petals had begun to take on color.
Following a minimum of 10°F. on Dec. 19 and 20 all fruit buds were
destroyed.

Premature starting from the rest period is, however, a less common
occurrence in northern peach regions. The very practices recommended
for retarding it, if carried out too thoroughly in northern regions, though
they might conceivably benefit the grower once in 20 seasons, would in
the other 19 make his trees more liable to injury because immature and he
would probably have damaged trees in 10 of these years. The southern
grower guarding perhaps once against immaturity would suffer from pre-
cocious bud development 10 times. Each grower must determine the
danger more commonly met in his orchard and steer wide of this particular
rock, hoping he will no more than scrape his keel on the other. At the
same time the grower in ''southern" regions may be on the northern
limit for certain of the southern peach groups and thus in the same
orchard he may have to contend with short rest period in one variety
and with immaturity in another.

Injuries to Vegetative Tissues

Sunscald is the common name of a late winter injury likely to occur
in the north as well as in the south. It is found on all types of fruit trees,
on European chestnut and on various shade and forest trees. Very
small trees are rarely troubled by winter sunscald and trees old enough
to develop thick, scaly bark are less subject in the parts so protected.
Attention is drawn to the injury by the dead and dry appearance of the
bark on the southwest side of the trunk where the sun strikes strongest
between noon and 2 o'clock. Sometimes this area is filled with a fer-

WINTER INJURY 293

merited fluid and the injury is called "sour sap." Later the bark may
loosen and fall away leaving an exposed area of dead sap-wood. Many
trees pruned to an open center are affected at the crotch or even high on
the south side of those scaffold limbs that lean to the north. In this
last position the sun's rays are received nearly at right angles and the
injury there is in many cases very severe.

The chief importance of this injury lies in its ultimate effects rather
than in its immediate results. It leads at once, obviously, to partial
obstruction of conduction of nutrient and food materials, but of greater
moment is the exposure to fungi and borers and the resultant mechanical
weakening of the tree.

Distinguished from Summer Sunscald and Injuries Associated with
Immaturity. — Distinction between this type and winter killing associated
with immaturity on the one hand and between this type and summer
sunscald on the other is sometimes difficult. In fact some writers have
denied the existence of sunscald and some have maintained that summer
heat never kills bark. Evidence showing that bark is sometimes killed
by high temperatures is easily gathered. Fisher^* quotes Vonhausen as
finding, between the sapwood and bark, a temperature of 120°F. when the
air temperature was 91°F., while in Bavaria, Hartig observed a tempera-
ture of 131°F. between the bark and sapwood of some isolated 80-year
old spruce trees. This is a lethal temperature for leaves and herbaceous
shoots and is presumably so for cambium cells. In forests when an open-
ing is made, the standing trees on the north side of the clearing in many
cases show the sunscald high on the south side of their trunks. Young
apple trees set late in the spring in sandy soil and headed back so they
had little protecting top, have been observed even in New Hampshire,
to show severe sunscald by midsummer.

Caution should be observed, however, in attributing all injuries on the
southwest side of the tree to late winter sunscald. Balmer^'- describing
the effects of a November freeze in Washington mentions that trees with
high trunks, leaning from the afternoon sun, suffered notably. In several
cases the bark on the southwest side of the trunks split open. Investiga-
tors seem to have overlooked the possible effects of radiation in this
connection. It is shown under Frost Injury that the temperature
near the soil on a frosty night may be 10° or more lower than that recorded
by a sheltered thermometer near by. An October temperature of 20°F.
is not uncommon; with suitable radiation conditions the ternperature
near the soil, if 10° lower, would be 10°F., low enough to cause consider-
able injury to immature tissues. Since somewhat lower temperatures
occur over sod under these conditions than over cultivated ground the
occurrence of "sunscald" in sod orchards need not be surprising. Injury
of this kind is obviously associated with immaturity. Therefore it is not
safe to consider sunscald altogether a late winter injury.

294 FUNDAMENTALS OF FRUIT PRODUCTION

Moisture and Temperature Conditions in the Affected Parts. — The

winter sunscald, however, is much more common. It is not induced by
simple insolation but by interacting effects of heat and cold. This is
quite evidently the malady described by Downing^'* in 1846 as "frozen
sap blight" and rather confused with pear blight by many of the early
American pomological writers. The description by Downing clearly
indicates this form, as he includes Ailanthus, Spanish chestnut and
catalpa among the plants affected. He attributed the trouble to sudden
thawing and proposed as a remedy shading the south side of the trunk
and whitewashing. Somewhat later he recorded that on Dec. 19, 1846,
a bright mild day, with snow on the ground, a naked theremometer regis-
tered 97°F. while one with a whitewashed bulb registered 79°F.^^ Various
suggestions as to the way sunscald is brought about have been made, in-
cluding rapid thawing, increased flow of sap followed by freezing so that
the bark is pushed off, breaking of the rest period in the warmed area and
alternate freezing and thawing. Miiller-Thurgau''^ found in March a
water content of 53.8 per cent, in the bark on the south side of a plum
tree and 48.5 per cent, on the north while the bark of a tree wrapped
with rushes showed moisture percentages of 51.5 and 51.3 on the south
and north sides respectively. He considered these figures to corroborate
the suggestion that a localized breaking of the rest period subjected the
affected areas to injury from subsequent cold.

The most extensive investigation on this phase of winter killing is
that of Mix. ^3* Particular attention was given to the cambium since
this tissue suffers severe injury "and without injury to the cambium and
outermost xylem the bark would not separate from the wood." Obser-
vations of temperature under the bark on the northeast and southwest
sides of apple trunks showed no significant differences on cloudy days but
marked variations on bright days, demonstrating the warming effect of
the sun's rays. Tables 33 and 34 are selected from data reported by
Mix from these observations and are representative of his more extended
figures. The temperatures for Mar. 10 are worthy of special attention,
being 32°F. on the northeast side and 69°F. on the southwest side at the
same time. On Feb. 10, Mix observed on the southwest side of one tree
a fall from 59° to 27°F. between 2 o'clock and 9, the air temperature
dropping from 28° to 19° F. in the same time, while on the northeast side
the temperature fell from 25° to 19°F. The temperature of the southwest
side dropped 32°F. while that of the northeast side fell 6°F. On another
tree the temperature on the southwest side fell between 5 o'clock and 6
(sunset at 5:30) from —0.3° to — 14.4°C. while on the northeast side it
dropped from —9.4° to — 18.3°C. This, it should be emphasized, was in
1 hour. By morning the temperatures on both sides were frequently
observed to be approximately equal. The southwest side of a tree trunk
is evidently subject to wider fluctuations in temperature and to more

WINTER INJURY

295

Table 33. — Tree Temperatures on Cloudy Days

(After Mia- 135)

Date

Hour

Southwest Northeast

side,

degrees

Centigrade

side,

degrees

Centigrade

Air, degrees
Centigrade

Jan. 15
Jan. 16
Jan. 17
Jan. 19
Jan. 20
Jan. 21
Jan. 23
Jan. 24

11

00

30

30

00

11

40

00

10

10

•6.9
3.3
1.9

■3.9
0.0
0.0

-2.2

-0.5

-7.5

2.8
-3.0
-3.9
0.0
0.0
-2.2
-0.5

-5.5
2.6

-3.9

-2.5
1.1

-2:2
0.0
4.4

Table 34. — Tree Temperatures on Sunny Days

(Data from same tree as Table 33)

(After Mix^^")

Date

Hour

Southwest

side,

degrees

Centigrade

Northeast

side,

degrees

Centigrade

Air, degrees
Centigrade

Jan. 14

Jan. 26

Feb. 2

3:00
3:25
1:30
1:35
1:05
2:10

12:50
1:00
2:50
1:00
1:00

12:55

11:00
1:30

12:50
1:15
1:00

-2.8

1.1

12.2

15.0

12.8

-0.5

-4.4

-6.4

3.9

-6.4

-2.8

1.7

-1.9

20.5

15.0

12.2

11.1

-12.2

-2.8

-1.1

2.8

0.8

-4.4

-9,4

-15.0

-9.4

-11.4

-16.1

-9.7

-10.0

0.0

-3.3

1.7

5.0

-12.2

-1.4

0,5

Feb. 3

Feb. 4

9,4
1 6

Feb. 8

-6.7

Feb. 9

Feb. 13

-8.3
-11.7

Feb. 15

Feb. 23

-12.2
-14 4

Feb. 24

Feb. 25

-5.6

Feb 26

Mar 10

1 1

Mar. 12

-4.4

Mar. 24

3.9

Mar. 25

8.9

sudden falling of temperature after the sun's heat is withdrawn at
sunset. Even more striking temperature differences may occur occasion-
ally. In fact Mix records a temperature of 92°F. on the southwest side
on Feb. 20, while the temperature on the northeast side was 35°F.

296

FUNDAMENTALS OF FRUIT PRODUCTION

The effect of snow in relation to sunscald seems to have escaped the
attention of writers on this subject. Sunhght striking snow is to a large
extent reflected and a late winter snow is bound to have no little influence
in intensifying the heating on the southwest side of tree trunks. If,
as frequently happens in late winter in northern latitudes, a snowfall dur-
ing the night is followed by a clear warm day and a night of considerable
cold the change in temperature of the southwest side must be considerable
and abrupt.

Rapid freezing, especially during the first part of the temperature fall
has been shown by Chandler^* to cause killing at a relatively high point.
These are the very conditions just recorded and seem adequate to explain
killing by sunscald without any assumption that growth has started.
Artificial freezings accompanied by microscopic examination of tissues
made by Mix showed no difference in hardiness on either side when frozen
under identical conditions. Rapid freezing killed at — 20°C. while
slow freezing caused no injury at — 28°C. As spring advances these
tissues become less hardy, but equally on all sides of the trunk. The
conclusion seems inevitable, therefore, that it is rapid freezing after sun-
down that causes winter sunscald.

Preventive Measures. — Prevention of the rapid fall is best effected by
keeping the day temperature down. Anything that will shade the trunk,
as a stake or a bundle of corn stalks, will do this well. Whitewash also,
because of its low heat absorption, may be used to advantage.

Table 35. — Temperatures of Whitewashed, Tarred and Untreated Trees^'

Air, degrees
Centigrade

Untreated

Whitewashed Tarred

Date

Northeast,
degrees
Centi-
grade

South-
west,
degrees
Centi-
grade

Northeast,
degrees
Centi-
grade

South-
west,
degrees
Centi-
grade

Northeast,
degrees
Centi-
grade

South-
west,
degrees
Centi-
grade

Jan. 15

Jan. 30

Feb. 4

Feb. 10

Feb. 19

Feb. 20

Average

3.9
-5.6
0.0
-1.7
3.9
6.1
1.1

1.7

-8.3
-3.3
-3.9
-1.7
0.0
-2.6

11.1

-4.4
7.2
15.0
17.2
21.7
11.3

0.6

-8.9
-4.1
-6.7
-2.2
-0.6
-3.2

2.2

-2.8
1.1

-0.6
5.0
6.1
l.S

3.3
-4.9
-0.6
-1.1
0.0
1.7
-0.3

20.5
13.9
17.8
29.0
31.1
33.3
24.3

Table 35, arranged from data reported by Mix, shows the sharp
contrast in sunny side temperatures between a whitewashed and an
untreated tree, a difference that becomes more marked as the tempera-
tures go higher. The difference appears considerable enough to save
treated trees from sunscald in many cases. The same table suggests
also a reason why gas tar, occasionally applied as a borer repellant, is
said frequently to kill trees. The difi"erence between the temperatures

WINTER INJURY

297

under whitewash and under tar is due apparently to the respective heat
absorptive powers of white and black colors, as their minimum early
morning temperatures were practically the same.

INJURIES DUE TO SUDDEN COLD

Though some types of injury already discussed as associated with
immaturity of tissue might be considered to belong in the category of
injuries due to sudden cold, they may be classed more correctly as due to
untimely cold. Here, too, probably belongs the type known as winter
suriscald which is discussed under late winter injuries but the present
section is limited in its application to injuries occasioned by a sudden
change from moderate cold to intense cold.

General Effects. — Chandler^^ has been quoted earlier as reporting
greater injury to plant tissue attendant upon sudden lowering of
temperature. His statement, however, should be reproduced here : " The
rate of temperature fall is very important indeed, especially in case of
winter buds. In fact, apple buds can be frozen in a chamber surrounded
by salt and ice rapidly enough so that practically all of them will be killed
at a temperature of 0°F., or slightly below, while it is well known that
they may go through a temperature of 20 to 30°F. below zero with but
slight injury where the temperature fall is not so rapid. . . . the
killing temperature of rapidly frozen twigs was 4.5° higher than those of
the more slowly frozen twigs and even then the buds of the rapidly
frozen twigs killed the worst." Table 36, chosen from several reported
by Chandler, shows the difference vividly.

Table 36.

-Effect of Slow and Rapid Temperature Fall on Cherry Fruit

BUDS'«

Variety

Manner of freezing

Date

Number

of

buds

Percent-
age
killed

Montmorency

Montmorency

Early Richmond

Early Richmond

Slowly to -20°C.
Rapidly to -20°C.
Slowly to -20°C.
Rapidly to -20°C.

Mar. 2
Feb. 29
Mar. 9
Mar. 14

163
130
297
263

3.0
96.0

5.0
98.0

However, it should be remembered that Chandler found also a rapid
fall to — 12°C. more injurious than a rapid fall from — 12°C. to the
killing temperature. This is shown strikingly in Table 37, adapted from
a table by Chandler.

No data bearing on this matter drawn from field observations are
available. Fortunately, as Chandler states, ''In this investigation it
was not possible to cause the temperature to fall more slowly than the
most rapid fall to be observed naturally in the climate of this station

298 FUNDAMENTALS OF FRUIT PRODUCTION

Table 37. — Effect of Rapid Fall Early and Late in the Freezing ^s

Variety

Manner of freezing

Date

Number
of buds

Percent-
age
killed

Elberta peach

Elberta peach

Elberta peach

Elberta peach

Montmorency cherry

Montmorency cherry

Montmorency cherry

Montmorency cherry

Slow to -12°; fast

-12° to -16°
Fast to -12°; slow

-12° to -16°
Slow to -17.5°
Fast to -16.0°
Fast to -12°; slow

to -20°
Slow to -12°; fast

to -20°
Fast to -20°
Slow to -20°

Dec. 20

Dec. 20

Dec. 20
Dec. 8
Feb. 24

Feb. 27

Feb. 27
Mar. 2

135

77

129
135
142

136

130
163

3.7

71.4

6.2
98.5
75.0

15.4

96.0
3.0

(Missouri)." Hence, the "slow" of Tables 36 and 37 is the "fast" of
nature. However, it seems quite possible that certain "warm spots"
in an orchard may heat considerably during a clear, cold day only to
have a very rapid drop in temperature following sunset and that some
of the injury attributed to buds "starting growth" during winter is in
reality due to a sudden and considerable drop of this kind. Nevertheless,
in a large number of cases when wholesale destruction of fruit buds occurs
it can be traced to some other cause.

Trunk Splitting. — Trunk splitting is much more common in forest
and shade trees and most of the literature on this type of injury deals
with these trees. Nevertheless, it is by no means unknown in fruit
trees; instances are on record of fruit trees splitting through the trunk. ^^^

Close measurements in Europe have shown that temperatures under
the freezing point induce a contraction in the trunks of various forest
trees which with long continued freezing reaches the magnitude of an
annual ring.^'' Deciduous trees react much more readily than evergreen.
The generally accepted view is that a rapid fall of temperature induces
a considerable contraction of the bark and outer wood while the inner
wood, still at a much higher temperature, does not shrink equally;
hence the splitting. The cracks start generally at the bark and proceed
radially toward the center of the tree or even beyond. Objection has
been raised that clefts extending beyond the center could not be caused
in this way but if it be assumed that the center of the tree is already
frozen, those who have cut frozen wood and know how easily it splits
will have little difficulty in believing that an initial cracking at the
periphery may be transmitted beyond the center because of the glassy
nature of frozen wood and the pull of the contracting bark.

WINTER INJURY 299

Wind may, as has been suggested, ^2 be associated with this type of
injury under certain circumstances but there can be no doubt whatever
that sphtting occurs on absolutely still nights, the sharp, rifle-like
report accompanying the fissure being very noticeable under such con-
ditions. Fisher^^ discusses the subject at some length. He reports that
most frost cracks occur in cold weather between midnight and morning
and may close again with rising temperature; further, that sometimes an
internal frost crack occurs, the sap-wood rending while the bark holds
intact. Hardwoods with large medullary rays are most liable to this
injury, oak, beech, walnut, elm, ash and sweet chestnut being mentioned
as specially susceptible in Europe.

The cracks are said to occur most frequently in the lower part of the
trunk, especially where growth is uneven, as near roots, at knots or where
the stem is eccentric. The south side, the region of most vigorous cir-
cumferential growth, suffers most, according to Fisher. Large old trees
suffer more than young because under conditions inducing this injury
there is in the old trees a greater difference in temperature between center
and periphery. Late winter, when the sap has begun to flow, is said to be
the most favorable time for developments of this kind. Under normal
conditions these cracks close with a rise in temperature and the tissues
in time grow together; this spot is weaker however and subject to a
recurrence of the injury. Repeated splitting and healing may give rise
to a lipped callus.

Observations in America agree generally with Fisher's, adding
the maple to the list of subject trees and finding perhaps more crack-
ing on long, straight-grained, clear boles. Indeed it seems that the two
chief reasons for the comparative resistance of fruit trees lie in their
being low headed, with short areas of trunk free from branches and in
their smaller trunks. Under cultivation they probably do not mature as
early as forest trees and the sappy growth of young trees may be injured
in early winter in contrast with late winter for forest trees. It is stated
that fruit trees growing late and entering the winter with wood not
thoroughly ripened are most subject to frost cracks in Colorado. ^^

On apple limbs an injury similiar in appearance and likely to be
confused with this type, sometimes occurs when there is one sided develop-
ment of the limb so that a heavy load of fruit is borne on one side un-
balanced by any considerable load on the other side, resulting in a fracture
in a vertical plane. Occasionally after a nearly horizontal limb is headed
back to a large branch ascending at about 45° a heavy load on the ascend-
ing branch will cause a splitting of the upper part of the limb from the
lower, the fracture being in this case horizontal. These injuries obvi-
ously occur near harvest and should be differentiated from the true
"frost cracks" without difficulty.

The reverse of the conditions described in connection with radial

300 FUNDAMENTALS OF FRUIT PRODUCTION

clefts, that is to say, the sudden warming of the outer layers of the trunk
while the inside is still cold, is said to produce a different kind of injury,
known to foresters as a ''cup-shake." Here the cleavage instead of
being in a radial direction is along an annual ring, involving a smaller or
greater amount of the circumference. This form may possibly occur in
fruit trees but in most cases of separation along annual rings in such
plants the injury may be traced to direct killing just inside the cambium,
discussed under Black Heart. Even under natural conditions the cup-
shake is far less common than the frost crack.

In connection with trunk splitting, the splitting of the bark while the
wood remains intact should be mentioned. As already indicated this is
generally in immature tissues, produced possibly at times by the same
conditions that induce trunk splitting but more frequently by the con-
ditions commonly associated with crown rot and crotch injury. It
should be understood, also, that splitting of the wood sometimes seems
to be associated to some extent with immaturity^^ and it may possibly,
as for example, when it occurs during protracted and intense cold, be due
to drying out.

Summary. — Winter injury takes many different aspects, 10 more or
less distinct forms being considered in this discussion. Many different
environmental conditions are associated with winter injury, though for
convenience these may be .grouped in three classes : (1) conditions encour-
aging immaturity of tissues, (2) conditions leading to winter drought,
(3) conditions leading to premature quickening in late winter and early
spring. Certain sections or regions are particularly subject to extremes
of one kind or another.

Injuries associated withimmaturity are especially common in the more
humid sections with short growing seasons. Plants adapted to com-
paratively long growing seasons when taken to sections with shorter
growing seasons are particularly subject to injuries of this character.
"Second growth" is hkely to be immature and subject to winter injury.
Cultural practices which encourage late vegetative growth should be
avoided in regions where immaturity is a frequent problem. Crown
injury and crotch injury are in most cases associated with immaturity of
tissues at the affected points. Wind and variation in temperature
between different sides of the limb or trunk may be contributing factors.
Treatment for these localized injuries should be both preventive and
remedial.

Injuries due to winter drought are especially common in sections
like the Dakotas and Wyoming where winter precipitation is low, the
snow covering scanty and the evaporating power of the air high. The
tissues are desiccated by the cold dry winds and recovery of turgidity
is difficult or impossible because of low soil moisture, deep soil freezing
and the inability of the conducting system to function while frozen.

WINTER INJURY 301

Protective measures include the use of winter irrigation, thorough
cultivation, frost-killed cover crops and windbreaks or shelter belts.

Many cases of injury from cold during late winter are associated
with a breaking of the rest period, resulting in some resumption of growth
and an accompanying decrease in resistance to low temperatures. They
are brought on by periods of mild weather during late winter. Fruit
buds particularly are susceptible to injury from this cause. Buds in
certain positions are especially subject to this form of injury. The ending
of the rest period in midwinter or spring is related to some extent to the
time of its inception in the fall. Consequently factors or practices
which delay its beginning tend to protect against the forms of winter
inj ury incident to its breaking. Among such practices may be mentioned :
Moderatel}^ late cultivation, reasonably heavy pruning, applications of
nitrogenous fertilizers and thinning. The end of the dormant period may
be delayed somewhat by whitewashing and shading, which reduce heat
absorption.

Most sunscald is attributable to extreme and rapid fluctuations
in temperature of the affected tissues. Injuries similar in appearance
sometimes are caused by midsummer heat or they may be associated
with immaturity coupled with low temperature.

In general, rapid decreases in temperature are more damaging than
more gradual decreases to the same or even to a lower point. A special
form of injury due to very rapid temperature decline is trunk splitting
or frost crack.

CHAPTER XVII
WINTER INJURY TO THE ROOTS

Root killing is very common in sections where winter precipitation
is light and it is rather common in humid sections where it is not always
recognized. It may occur, regardless of precipitation, at any point
where the soil freezes at all deeply (see Table 38) ; it is characteristically
associated with light and dry soils and with scanty snow cover. If
no part other than the roots is injured the tree may start growth in the
normal way, sending out vegetative shoots and blossoms and perhaps
even setting fruit; some time in the summer, usually with the first warm,
dry weather, it dies. Felled trees will sometimes start growth in a
comparable manner. If only a part of the roots have been injured,
the effect is quite likely to be a slowing in top growth. As the damage
is below ground, it escapes ordinary observation and the slow growth
of the tree may seem quite inexplicable. This condition may last for
several years or until the balance between root and top is more nearly
restored.

Soil Temperatures in Winter. — For a thorough understanding of the
nature of root killing and of the conditions associated with it, some
knowledge of soil conditions during the winter and of the distribution
of roots in the soil is necessary. Table 39, taken from a report covering
12 years of soil temperature observations at Lincoln, Neb.,^^'' shows
quantitatively the effect of depth on soil temperatures.

Table 38. — Mean Soil Temperatures at 6 Inches^^"
(Degrees Fahrenheit)

December

January

February

March

Pennsylvania

Idaho . . .

34.9
35.2

24.1
32.0
33.8
39.5
34.0
34.9
57.0

32.0
32.1
23.0

22.2
28.6
32.0
39.0
27.7
32.7
56.1

31.4
32.1
21.0
22.7
27.8
32.0
39.1
30.4
31.5
57.1

32.9
32 9

Minnesota

38 0

Wyoming

31.0

Nebraska

Michigan

Woburn, England

36.6
33.5
39.9
36.3

Illinois

Alabama

39.3
53.4

302

WINTER INJURY TO THE ROOTS

303

The Pennsylvania figures are for State College, 1892-1896 inclusive; Idaho,
for Moscow, 1903-1904 (Idaho Exp. Sta. Bui. 49); Minnesota, 1889 (a mild
winter); Wyoming, averages for Laramie, 1895, 1898, 1899; Nebraska, from
Table 39; Michigan, selected as typical, from Mich. Agr. Exp. Sta., Tech. Bui.
26, p. 104; Woburn, England, 2d Rept., Woburn Experiment Farms (1900);
Colorado, Fort Colhns; lUinois (Urbana), (1897-1916); from Bui. 208, 111. Agr.
Exp, Sta.; Alabama, from Ala. Agr. Exp. Sta. Bui. 10.

Table 40 is arranged from the same source and is introduced to
show absolute minima at several depths, over a series of years.

Table 39. — Average Soil Temperatures at Lincoln, Neb.is"
(Degrees Fahrenheit)

Depth

January

February

March

April

May

June

Air

6 inches

12 inches

25.2
28.6
31.2
35.4
38.5

24.2
27.8
30.2
33.5
35.5

35.8
36.6
35.4
35.4
35.8

52.1
53.3
49.3
45.6
43.8

61.9
65.1
60.7
56.2
53.5

71.0
75.7
69.9

24 inches

64.6

36 inches

61.3

Depth

July

August

September

October

November

December

.A.ir

6 inches

76.0
81.6
75.7
70.2
67.4

74.5
80.1
75.7
72.2

67.6
72.0
69.2
68.7
67.6

55.5
57.8
57.8
60.0
61.6

38.7
41.5
44.7
49.2
,52. 2

28.3
32.0

35.2

40.1

36 inches

43.3

T.\BLE 40. — Minimum Soil Temperatures at Lincoln, Neb.""
(Degrees Fahrenheit)

Winter

6 inches

12 inches

24 inches

36 inches

1893-1894

19.6

24.5

30.2

34,2

1894-1895

14.9

22.9*

29.2*

29.8

1895-1896

18.0

27.4

35.5

38.0

1896-1897

22.0

27.0

33.0

35.1

1897-1898

20.0

26.5

34.5

36.5

1898-1899

7 0

13 5

24.0

30.5

1899-1900

22.0

28.0

33.0

35.0

1900-1901

24.0

28.0

34.0

36.0

1901-1902

19.0

27.0

33.0

35.0

Data incomplete.

The maximum depth of frost penetration at the same point has been
reported as detailed in Table 41. Recently, however, it has been shown

304 FUNDAMENTALS OF FRUIT PRODUCTION

Table 41. — Maximum Depth of Frost Penetration at Lincoln, Neb.

Date

Depth,
inches

Date

Depth,
inches

Mar 9 1891

30.9

21.9

32.2

29.0

36.0*

18.4

Jan 19 1897

21.2

Jan 19 1892

Feb. 8, 1898

16.8

Feb 12 1893

Feb. 10 to Mar. 28, 1899

Feb. 29, 1900

Feb. 12, 1901

36.0

Feb 27 1894

21.6

Feb 7-27 1895

20.0

Jan 4, 1896

Feb. 9, 1902

21.6

* Not recorded to maximum penetration.

that soil does not freeze until it is cooled several degrees below 32°F.2s
Consequently since these figures were based on the assumption of freezing
at 32° the actual frost penetration was not so great as is indicated.

Critical Temperatures for Tree Roots. — In the section on Water
Relations the extent and the depth of some fruit tree root systems are
indicated. The data there given indicate that in the majority of fruit
growing regions by far the greater part of the feeding roots is in the
surface foot of soil.

The finer roots of beech, oak and ash, trees that are considered
at least fairly hardy, die at temperatures between 8.6° to 3.2°F.i" and the
roots of other hardy plants are reported killed at temperatures from
14° to 5°F.^^ Working with apple roots, under laboratory conditions,
Chandler found that "the killing temperature varies from — 3°C. in
summer to about -12°C. [26.6°F. to 10.4°F.] in late winter with rather
rapid freezing." He remarks further, "They are still very tender in
autumn when tissue above ground has begun to increase rapidly in hardi-
ness ... as the roots extend away from the crown they become more
and more tender and apparently this tenderness is greater on those roots
that extend downward into the soil." It may, then, be concluded that
the roots of most plants are more tender, at a given temperature, than the
parts above ground. Parentheticall,y, though Chandler's statement
as to increasing tenderness with increasing distance from the crown may
be accepted, it should be understood that root killing is frequently
observed at or near the crown and not elsewhere, probably because this
part is nearest the top soil and therefore exposed to colder temperatures,
as shown in Table 39.

Carrick^^ found a marked difference in tenderness of roots at different seasons
in New York. "The material frozen in October and November," he states,
"shows a marked tenderness compared with roots tested in February and March.
The period of maximum resistance seems to end somewhat before the last of
March, tho the date would, of course, vary with the conditions affecting
after-ripening and possibly also with the variety . . . This range of hardiness
indicates a difference in resistance of between 3 and 4 Centigrade degrees.

WINTER INJURY TO THE ROOTS 305

These seasonal differences obtain, not only in the apple seedlings, but in all the
roots reported in this paper."

Another interesting factor in root injury is reported by Carrick, He finds
that, "the resistance is in direct proportion to the diameter of the root," and
suggests that this fact accounts for the occasional observation in laboratory
freezings of root killing at the tips when the roots near the crown are uninjured.

A study of Table 38, with the killing temperatures given above in
mind, shows that the average soil temperatures in the recognized fruit
growing sections noted are substantially above the danger point and
suggests one reason why fruit growing in certain other sections requires
some special precautions. Attention is due, further, to the consideration
that these are average figures in which fluctuations to lower points are
submerged. In Table 40 the actual seasonal minimum temperatures at
one point are segregated. It is particularly significant that the winter of
1898-1899, when the soil temperature at Lincoln, Neb., reached 7°r., was
the winter characterized by an extreme amount of root killing in lowa,^"^
Wisconsin^'' and Ontario."^

Factors Influencing Frost Penetration. — Temperature alone, or air
temperature alone certainly, is not the sole controlling factor in root
killing. A temperature of — 20°F. maintained for several days has
caused extensive root killing in Ontario.^" Goff" in an interesting survey
of an extensive area involved in the freeze of February, 1899, found little
damage in several regions where the unofficial temperatures went as low
as — 50° or even — 52°F., though in no case where root killing occurred
had the temperature gone below — 36°F. A report from Waukee, Iowa,
indicated root killing with a minimum of — 24*'F. ; other localities suffered
severely at — 23°F.

Protection Afforded by Snow. — The principal difference lay in the
fact that in some sections snow lay on the ground while in others there
was none. Goff's analysis showed 34 localities with more or less snow
at the time of the freeze; of these, 20 reported definitely that the chief
injury was in the tops, three reported roots and tops equally damaged,
while in one there was more injury to roots than to tops in apples but
more in the tops of cherries and plums than in the roots. Fifty-seven
localities were without snow at the time of the freeze; definite statements
of comparative injury indicated 43 cases where the principal damage was
in the roots, 3 placed it in the tops and 1 reported roots and tops
equally damaged.

Similar testimonials concerning the value of a snow covering are
common in pomological literature. Quantitative data applicable here
are given by Bouyoucos." Table 42, arranged from his figures taken at a
depth of 3 inches, shows the temperature differences between ground
without snow, ground under compacted snow, under uncompacted snow
and under vegetation plus compacted snow.

306

FUNDAMENTALS OF FRUIT PRODUCTION

Table 42. — Effect of Snow

Cover on Soil. Temperature, January,

1915"

(Degrees Fahrenheit)

Maximum-minimum

Air

Monthly average

Bare

Snow,
compact

Uncom-
pact

Uncom-

pact +

vegetation

Maxi-
mum

Mini-
mum

Average

28.79

24.95

3.84

29.65
28.66
0.99

31.51
31.11
0.40

34.82
34.55
0.27

27.96

13.80

20.64

^ „ / niaxuuum

Jan. 6, <

1 minimum

32.30

32.00

32.00

35.70

32.10

31.80

32.00

35.50

39.00

33.00

36.00

Jan. 29, / m^xunum

' " ' \ minimum

20.00

22.30

29.60

33.00

14.50

20.80

29.00

32.50

13.00

-13.00

0.00

Jan, 30. I"^™"-"

[ minimum

21.20

21. 10

28.80

32.80

7.50

15.60

27.00 ' 32.30

18.00 -13.00

2.00

The minimum for Jan. 30 is certainly at tiie danger point for tree roots
in bare ground, while under compacted snow it is 8.1°F. higher and under
vegetation plus compacted snow it is almost 25° higher. The fruit
grower cannot induce snowfall at his will but he sometimes has a choice
between a slope where snow will remain and one where it will melt away
with a little warm weather. He knows that knolls and wind swept spots
in general are likely to need special care and that cover crops and wind-
breaks tend to hold snow that might otherwise blow away.

Different Systems of Soil Management. — A protective covering of
vegetation can be provided by the grower with more surety than a snow
covering. Table 43, arranged from data by Bouyoucos,^^ shows the
effect of this covering on minimum soil temperatures at 3 inches depth.
The superior protection afforded by cultivated, bare soil as contrasted
with compacted soil is worthy of note.

Table 43. — Average Minimum Soil Temperatures in Uncultivated and Culti-
vated Soil and in Sod^^
(Degrees Fahrenheit)

Month

Uncultivated
(bare)

Cultivated
(bare)

Sod

Dec, 1914

Jan., 1915

Feb. 1915.

31.92
31.11
30.70

33.26
32.59
32.49

35.34
34.55
33.52

Craig^^ in Iowa reported soil temperature at 6 inches depth on a
January day, after hard freezing, two degrees warmer in sod than in
cultivated soil.

Depth of freezing is a fairly good indicator, though indirect, of soil
temperature. Gourley^^ records observations made in New Hampshire

WINTER INJURY TO THE ROOTS 307

in March when freezing was at its greatest depth for the season; these
are shown in Table 44. These figures are of special interest since they
show the protective effect of increased cover-crop growth induced by
fertilizer applications. The "cultivated with cover crop" plot had a
scanty growth.

Table 44. — Depth of Freezing as Affected by Soil Covering

Clean cultivated (no cover crop) 16 inches

Cultivated, with cover crop 15 inches

Sod 12 inches

Fertilizer, cultivation and cover crop 10 inches

Fertilizer (excess nitrogen) cultivation and cover crop. . . 7 inches

Sandsten^^^ made measurements of the depth of frost penetration in
early February under different crops in Wisconsin. Table 45 shows his

Table 45. — Frost Penetration under Different Cover Cropsi^^

Bluegrass sod 18.0 inches

Clean cultivation (no cover crop) 16.0 inches

Rape 15.0 inches

Oats 8.0 inches

Hairy vetch 7.5 inches

data. He interprets these observations to emphasize the protective
value of an uncompacted cover, the bluegrass sod offering httle insulation
because of the lack of dead air spaces. He also considers the lower
amount of moisture in sod land to have an important bearing. In
connection with the data here cited from Gourley and from Sandsten it
should be recalled that the soil does not freeze until its temperature is
several degrees below 32°F.

Oskamp'^2 reports soil temperatures observed in Indiana with differ-
ent soil covers. Table 46 is arranged from his data. It should be noted

Table 46. — Monthly Minimum Soil Temperatures"*
(Degrees Fahrenheit)

Clean cultivation
and cov«r crop

Straw mulch

Jan., 1915

31.0

34.0

Feb., 1915

32.0

34.0

Dec, 1915

32.5

38.0

Jan., 1916

28.5

35.0

Feb., 1916

32.0

35.0

Dec, 1916

33.0

35.0

that this comparison is between straw mulch and land growing a cover
crop, which has been shown to have higher minimum temperatures than

308

FUNDAMENTALS OF FRUIT PRODUCTION

uncultivated or cultivated bare land or sod. A direct comparison of the
extremes is not available, but by comparing minimum temperatures in
bare land with those in sod (Tables 43 and 44), then sod with cover crop
(Tables 44 and 45) and finally cover crop with straw mulch, some idea of
the superior protective qualities of the straw mulch can be formed. As
will appear later, the difference between safe and killing temperatures for
roots is slight and a few degrees are apparently more important below
ground than above.

Soil Type. — Increased injury in sandy soil has been reported so
frequently that the precise temperature conditions existing in the lighter
soils should be examined carefully. Table 47 shows absolute minimum
temperatures for certain months, recorded at a depth of six inches, in
soils of different types.

Table 47. — Absolute Minimum Temperatures in Different Soils

{After Bouyoucos'^^)
(Degrees Fahrenheit)

Gravel

Sand

Loam

Clay

Peat

Dec, 1912

Jan., 1913

Feb., 1913

Dec, 1914

29.0
30.8
21.1
30.0
30.5
32.1

28.9

29.7
29.1
17.3
25.3
27.1
32.4

26.8

30.3
30.9
22 3
31.5
31.4
31.3

29.6

30.2
31.2
23.1
30.3
32.0
31.9

29.8

31.4
31.1
19.1
32.6

Jan., 1915

Feb., 1915

32.4
32.2

Average

29.8

These figures show a sufficient difference to indicate a possible cause
for increased root killing in sandy soils. It should be stated, however,
that Bouyoucos records a very marked tendency for all soils to assume
a uniform temperature if air temperatures remain stable long. The
lower minima in sand are due probably to more rapid conductivity so
that a cold spell of short duration, as most cold waves are, would take
effect here but be over before it would affect some of the other soils to
the same extent. Thus, Bouyoucos states, ''The 12-inch depth of
gravel and sand froze Feb. 3, that of loam, clay and peat on Feb. 5, or
2 days later; while the 18-inch depth of the various soils froze as follows:
gravel, Feb. 6, sand, Feb. 8, clay, Feb. 10, loam, Feb. 1 1 , that of peat did not
completely freeze, its temperature remaining a few tenths of a degree
above 32°F. throughout the rest of the winter." As to the effect of
organic matter in soil, he comments on his investigations as follows:
"The minimum temperature attained was highest in peat, slightly less
and about the same in the various soils treated with peat and lowest in

WINTER INJURY TO THE ROOTS

309

the untreated sand." A continued turning under in the spring of cover
crops tends to raise the soil content of organic matter. The cover crop
protects, then, while above ground by blanketing the soil and when
turned under it affords some protection in the following winter through
the increased amount of organic matter it has supplied.

Soil Moisture. — Another factor, possibly of equal importance, affect-
ing root-killing in sandy soils, is the amount of moisture present. No
evidence need be introduced here as to the comparatively low moisture
content of the average sandy soil. Emerson^^ made some very interest-
ing studies of the effects of moisture on killing, in which lots of 25
young trees each were exposed to a Nebraska winter, in boxes of loam
soil with varying degrees of moisture. His tabular statement of results
is reproduced here as Table 48.

Table 48.— Root-killing of Apple Seedlings as

Related to Soil Moisture

Percent-

Number of roots

Box

Where kept

Soil cover

age of soil

moisture

Uninjured

Injured

Dead

1

Outdoors

None

10.4

0

5

20

2

Outdoors

None

15.2

0

6

10

3

Outdoors

None

19.8

12

10

3

4

Outdoors

None

25.6

13

4

8

5

Outdoors

Straw mulch

16.0

18

7

0

6

Outdoors

Snow occasionally

15.8

10

8

7

7

Cool, dry cave

None

10.0

25

0

0

Emerson comments on his results in part as follows: "That the great injury
to the seedling roots in the drier soils is not due directly to the dryness alone but
to dryness and cold combined, is evident from the fact that the roots were
absolutely unhurt in equally dry soil kept in a cool dry cave. . . . That dry-
ness alone was not responsible is shown by the comparatively slight injury to
roots in rather dry soil which was protected by a 4-inch mulch of straw, while
roots in bare soil of almost the same moisture content were very badly hurt.

"Just why severe freezing should injure roots worse in rather dry than in
moist soil is not shown by the test reported above. On further investigation it
may be found that roots are simply unable to withstand severe freezing or to
recover from it unless surrounded by an abundance of moisture. Be this as it
may, it is quite probable that one cause of the great injury in rather dry soil is
alternate freezing and thawing . . . the more water a soil contains the less
subject it is to frequent alternate freezing and thawing.

"The fact that the apple seedlings were much less seriously injured where
protected by a mulch of straw than they were in bare ground is to be explained
by the effect of mulches on freezing and thawing of the ground. The latter was
tested during the winter of 1901-1902. The mulch protected the soil not only

310

FUNDAMENTALS OF FRUIT PRODUCTION

against severe freezing during cold nights, but also against alternate freezing
and thawing. The temperature changes observed on February 2, 3 and 4,
1902 — a very cold period — are especially interesting. The surface of the bare
ground thawed during the middle of the day and froze severely each night. Two
inches lower, however, the soil did not thaw out during this very cold weather,
though the temperature changes between day and night were great. The
temperature of the mulched ground, both at the surface and 2 inches beneath
it, remained constantly below the freezing point and, moreover, varied but little
during the period."

Recent studies by Bouyoucos^* suggest an interesting possibility in
this connection. He shows that in practically all agricultural soils some
of the moisture remains unfrozen at ordi-
nary temperatures and, indeed, even at

— 78°C. The amount of unfrozen water
varies with the kind of soil, becoming in
general greater as the soils vary from the
simple and non-colloidal to the complex
and colloidal. The amount freezing at

— 78°C. is very little, if any, greater than
that freezing at — 4°C. It seems possible,
then, that the increased amount of root
injury in sandy soils may be due, in ad-
dition to the lower amount of moisture in
such soils, as mentioned above, to the ex-
tremely small amount of water remaining
unfrozen at temperatures only slightly
below 0°C. while the finer soils have a
reserve of capillary adsorbed unfrozen
water under such circumstances.

It should also be recognized that temperatures in the different soils
may have been different. In any case, however, the result is the same;
damage is greater in soils that are dry at the time of freezing.

Relation of Cover Crops to Root Killing. — The effects of single factors
on soil temperatures, and therefore on root killing, have been set forth.
The value of a snow cover has been shown; the increase of soil tempera-
tures with transition from bare ground through sod to cover crops has
been reviewed ; minima varying with the character of the soil have been
indicated and finally dryness of soil has been shown to be associated
with root killing. In orchard practice, however, these factors are rarely
operative singly and some rather complicated interactions may be
expected.

Emerson's^^ studies on depth of freezing under two sets of conditions
are of great importance since they show the interactions referred to above.
Figures 30 and 31, reproduced from his studies, indicate depth of freezing

Fig. 30. — Depth of freezing
under various covers, in absence
of snow. (After Emerson^^)

WINTER INJURY TO THE ROOTS

311

without snow covering and with snow covering respectively. Under both
sets of conditions the clean cultivated land froze deepest. More striking,
however, is the different position occupied by the corn plot under different
conditions. The reason becomes apparent, however, when the depth of
snow covering on the several plots is considered. The close relation
between depth of snow and depth of freezing, shown in all plots, is of
interest.

Fig. 31. — Relation of cover crops to depth of snow and depth of frozen soil.

(After

Emerson's observations furnish more information: "Early in the
winter ... it was noted that soy beans had very few leaves left and
that the plants stood perfectly erect, furnishing almost no protection to
the soil and that cowpeas, tho they still held their leaves, stood too
erect to furnish much protection. The field peas, on the other hand, had
held their leaves well and matted down nicely, forming a very good mulch.
Corn was also found to have remained very erect as was also the case with
cane and millet. Later in winter it was noted that the snow was held
very well by corn, cane, millet, soy beans and cowpeas, while field peas
and rye, the good covers, laid too flat on the ground to catch the
drifting snow. The almost bare stems of such plants as soy beans, which
still stood erect, held the snow much better than a plant like field peas

312 FUNDAMENTALS OF FRUIT PRODUCTION

which retained its leaves but matted down too close upon the ground.
The stalks left standing after a crop of corn grown in the ordinary way has
been harvested make a very efficient snow holder but furnish very little
protection to the ground at times of intense cold unaccompanied by
snow."

The superior snow-retaining qualities mentioned, particularly in the
case of corn, are operative mainly when the snow fall is accompanied by
wind.

Summarizing the requirements for a cover crop under Nebraska
winter conditions, Emerson says: "It should start growth promptly in
order to insure an even stand and to choke out weeds. It should grow
vigorously to insure a heavy winter cover and to dry the ground in case
of late-growing trees so as to hasten their maturity. It should be killed
by the early frosts so that it will stop drying the ground after danger of
late tree growth is passed and help to conserve our light rains so much
needed by the trees in winter. ... A cover crop should be heavy
enough to furnish as good direct protection as possible against freezing
and thawing and it should stand sufficiently erect to hold snow against
the power of strong winds."

Of the crops tried, that which appeared to come nearest meeting these
requirements in Nebraska was German millet.

Root Killing in Different Fruits. — There is less latitude in the root
hardiness of the various species than in the hardiness of their tops.
Nevertheless there are enough differences in many cases to make the
choice of root stocks very important.

The Apple. — Carrick^^ found that the majority of dormant apple roots
were seriously injured at a temperature of — 12°C., with considerable
injury at — 7°C. He reports the cambium as the most tender tissue,
followed closely by the phloem, with the cortex less tender. Under
extreme conditions xylem and pith are said to be killed. French-grown
stocks were found substantially as hardy as the native-grown seedlings.
In all cases there was a considerable variation, as would be expected
among seedling plants. This difference, it may be remarked, is likely
to assume considerable importance under field conditions.

The Pear. — Studies on pear roots by the same investigator indicated
that Kieffer roots were more resistant than the French stock. A tem-
perature of — 11°C. during the dormant period produced extensive injury
in both. In April Kieffer showed only slight injury at — 9°C. while 2-year
French roots were killed. Pear roots seemed to acquire hardiness later
than those of the apple and never become quite so hardy.

The Peach. — The peach root is relatively hardier in the zone of dis-
tribution of this species than is the apple root along the northern border
of apple growing. Occasionally, however, root killing in peaches occurs.
Goff^® records that in the freeze of 1899 peach tops suffei;ed more than the

WINTER INJURY TO THE ROOTS 313

roots; Green and Ballou^^ indicate peach root killing in Ohio. Macoun^^^
reports similar injury to thousands of peach trees in southern Ontario
in the winter of 1898-1899. However, root killing without any appreci-
able amount of injury to the top, as occurs from time to time in the apple,
is extremely rare in the peach; conditions severe enough to injure peach
roots generally will work far greater damage to the tops.

Carrick^^ summarizes the results of laboratory freezing of peach roots as
follows: "As a general rule the order of resistance of the various tissues in the
peach root seems to be as follows: pith, cortex, phloem, cambium, xylem. At
— 18°C. or below, the xylem was usually killed during the hardiest period. In
most cases during February and March the pith is the tissue most easily killed,
but in April the cambium is the least resistant.

"It is not so easy, with the data at hand, to assign an arbitrary hmit within
which the peach root is injured by freezing. This is because of the great varia-
tion in the root tissues. The peach cambium certainly is as hardy as the pear
cambium, tho less so than the apple. Regardless of the size of the root, most
of the peach material tested showed some injury at — 10°C., and, except in
unusual cases, serious injury occurred at —11°. This would then place the
hardiness of the peach root very close to that of either pear seedHng."

The Cherry. — Sour cherries frequently suffer from root killing on the
northern margin of their range, sometimes under conditions such that the
top is uninjured. Hansen*^ states: "One great difficulty in cherry grow-
ing in this state is the tender imported Mahaleb and Mazzard stocks upon
which we are compelled to bud and graft at present. These root-kill in
severe winters." Under some conditions the flower buds of sour cherry
may be more resistant than the roots. Craig^^ reported on damage to
cherry stocks in Iowa in 1898-1.899: "In nursery, the former [Mazzard]
was practically a total loss of 2-year-olds and a complete loss of 1-year-old
in the region of the severe root killing. Mahaleb suffered less, Morello
stock and own-rooted Morello trees generally escaped with slight injury,
except in exposed situations. ... In the college nurseries the practice
of root grafting the cherry received commendation by the fact that the
only trees which escaped were those which were partly on their own roots."
Prunus pennsylva7iica is reported from several sources to be hardy but is
difficult to work commercially.

Carrick^^ places the relative hardiness in cherry stocks in descending
order as follows: Mahaleb, Prunus Besseyi, Prunus yennsylvanica,
Mazzard and he finds the Mahaleb generally much hardier than the apple
roots investigated. "In large Mahaleb roots during their hardiest
period," he states, "little injury is found under — 14°C., while at — 15° the
injury is relatively small. . . . The Mazzard roots in no instance with-
stood — 11°, but the number of tests run at — 10° was insufficient to place
this as its minimum. From these results the Mazzard cherry stock does
not appear hardier than Keiffer pear stock."

314 FUNDAMENTALS OF FRUIT PRODUCTION

The Plum. — Iowa's experience with plums in the winter 1898-1899 is
thus stated by Craig :^^ "Plums, native or European, worked on peach
or Myrobolan killed, on Marianna badly injured, on Americana slightly
injured, but these recovered rapidly except where they were, in a few
instances, permanently inj ured .... Americanas worked on peach roots
escaped where well rooted from the cion. Sand cherry stock (Prunus Bes-
seyi) has been used to some extent in the state. In no case have I found
these roots injured in the slightest degree. In passing I may add that ex-
perience has not yet developed the ultimate effect of this stock upon the cion.
Thus far its dwarfing influence upon varieties of the Americana type is
satisfactorily demonstrated. Domestica plums on own roots fared better
than the same varieties on peach, Myrobolan or Marianna." Elsewhere:
"On the matter of plums the sand cherry {Prunus Besseyi) appears to be
the hardiest form we know anything about. Native plums in the college
orchard on this stock were entirely uninjured last winter, while the same
varieties on Americana stocks alongside were injured or killed." Carrick
places Myrobolan in the same group as Mazzard cherry and pear for
hardiness.

The Grape. — Reports of root killing in grapes are relatively rare. The
comparatively deep-rooting habit, combined with sufficient tenderness of
tops to discourage grape growing in regions where root killing is common,
may account for this apparent resistance. Furthermore, most grapes
of American origin are in fact hardy varieties on their own roots and if it
be safe to reason from the analogy of cion-rooted trees, the roots should
share the hardiness of the tops. Niagara has been reported to be notor-
iously tender in bud and root.^* Hansen^^ reports considerable trouble in
parts of South Dakota from root killing; the New York vineyards suffered
extensive damage in the winter of 1903-1904. Hedrick^- suggests that
the St. George (a variety of rupestris) stock used in some experimental
work at Geneva, N. Y., may be more hardy than certain others and notes
that American varieties on their own roots winter killed extensively.

Carrick made numerous laboratory freezings of six varieties of grapes to
compare their relative hardiness. The varieties studied, representing several
species, fell readily into two classes, viz., Clinton, Concord and Diamond, "rather
resistant to cold" and Cynthiana, Lindley and Norton, "relatively easy to kill
by freezing." Within the groups the differences in hardiness are not striking.
For the hardier group, "Only scattering injury is recorded at —11°, —12°, and
— 13°C. At an exposure of —14.5°, 22 out of 27 Concord roots were uninjured,
and only a trace of cambium and cortex injury was noted in the remainder.
... At —18°, however, the cambium, phloem, and cortex tissues were com-
pletely injured in all roots, with some xylem injury in the Diamond and the
Concord. . . . The limits of this second group (Cynthiana, Lindley and
Norton) he between —10° and — 12°C., the roots usually undergoing con-
siderable injury at —11°. In relative hardiness this places these varieties

WINTER INJURY TO THE ROOTS 315

between the Mazzard cherry and the apple. The Chnton, Concord, and Dia-
mond roots, even excluding the influence of size, are considerably more resistant
than apple roots, and Concord and Clinton seem equal if not superior to the
Mahaleb stock.

" . . . Vitis (Bstivalis, represented by Norton and Cynthiana, is not adapted
to severe cold, and this may account for the fact that its range is limited to the
South. The tenderness of Lindley is probably due in part to the influence of
Vitis vinifera, which, as is well known, will not survive the winter in the latitude
of New York State without much protection. Concord and Diamond represent
Vitis labrusca, the Northern Fox grape, which, while restricted in distribution, is
found in Maine. Vitis vuljmia, represented by Clinton — a variety with extremely
resistant roots — has the greatest range of any American species of grape, it
having been found in Canada north of Quebec. "^^

The Sfnall Fruits. — Among small fruits Carrick found a wide range
in hardiness. The blackberry, dewberry and red raspberry roots tested
appeared to rank with the IMyrobolan plum and the Mazzard cherry.
Eldorado seemed the hardiest of the blackberries under observation, but,
curiously enough the Lucretia dewberry seemed somewhat more hardy
than Eldorado. The roots of the Cuthbert raspberry appeared equal in
hardiness to the Eldorado blackberry. None of the varieties studied
survived a temperature of — 12°C., though many of the larger roots were
uninjured at — 11°C. On the other hand, currant and gooseberry roots
were extremely resistant; a Downing gooseberry root withstanding
— 20.5°C., though this probably would be the limit of hardiness. On the
basis of the material examined Carrick rather provisionally rates the
gooseberry roots as slightly more resistant than the currant.

Preventive and Remedial Treatments. — Danger of root injury may be
permanent or temporary. If the past history of the locality shows
extensive root injury the grower should bear this in mind as a possible
threat. If his site is sandy or chronically dry or wind swept in winter he
is threatened continually and may be justified in accommodating his
orchard practice accordingly. A temporary condition of danger may
occur, such as a dry autumn, in orchards ordinarily safe. Early winter
cold snaps are most to be feared, because the roots are then tender and
there is less likely to be a snow covering. However, it may be February
that brings disaster.

Deep Planting and Mulching. — Preventive methods are more effi-
cacious and generally cheaper than palliative measures. Deeper planting
than usual, if the winter water table is not too high, may protect the
roots, especially in the first winter. Protective soil coverings, either
mulches or cover crops, should be used in very dry locations; the advan-
tage of a snow blanket should be remembered in choice of site or in select-
ing a cover crop.

The tendency of deep planted trees to send out roots from the cion is
well known. Some varieties do this more freely than others. These

316 FUNDAMENTALS OF FRUIT PRODUCTION

roots when they come from cions of extremely hardy varieties are gen-
erally hardier than the stocks commonly used. In those of the northern
sections where root killing is most likely there is a tendency to grow trees
formed by grafting long cions on short pieces of root for the purpose of
inducing cion rooting, thus securing increased hardiness in the roots.
No experimental evidence is available to show clearly whether cion roots
of hardy apple varieties are hardier than those of tender varieties, but
Craig^^ records numerous instances when cion roots proved more hardy
than the stocks on which they were worked. Hansen, ^^ writing in South
Dakota, says: " . . .in ordinary winters the roots emitted by the
scions of hardy varieties are sufficiently hardy but . . . they are not
proof against such winters as that of 1898-1899."

Use of Hardy Stocks. — Top working on stocks of known hardiness is
another method of combating root killing in those sections particularly
subject to it. Pyrus baccata is said by Hansen to succeed in the Trans-
baikal section of Siberia where the mean annual temperature is 27'°F.
and the mean temperature of the coldest month — 18.4°F. and where
the annual rainfall is 11.42 inches. He reports young seedlings of this
species to have wintered perfectly despite a temperature of — 40°F. with
no snow. The "Virginia crab" is also reported to be more hardy than
French crab. However, these have more or less dwarfing effect and do
not make an altogether satisfactory union. '^^^

Pruning. — After the damage has occurred, there is little that can be
done. If the killing is complete or nearly so the trees should be removed.
However, many times the root destruction is incomplete; some of the
roots that start straight down from the crown on old trees will frequently
escape. In many of these cases a heavy pruning back, or, if there is
also injury in the top, a moderate pruning back, will enable the tree to
survive and still have many years of usefulness. Very young trees
that have suffered only partial destruction of the roots can be restored
in many instances by banking the trunks with earth, inducing the for-
mation of additional cion roots.

Handling Nursery Stock in Cold Weather. — One form of root injury
likely to be encountered in regions remote from the territory commonly
subject to killing of this type is that occurring on nursery trees. Root
growth in apple trees in Missouri has been shown to continue long after
the top has assumed a completely dormant appearance, in fact until
winter has well set in. 212. In a growing state, it will be recalled, roots
are damaged by temperatures only a few degrees below freezing and
even in a dormant state they will stand only comparatively high tem-
peratures.^^ Chandler states: "In case of 1-year-old roots of the French
crab, used as stock by most of the nurserymen, about —5 to — 8°C. (23 to
15.8°F.) is as low a temperature as they can be depended upon to with-
stand with no injury." Fall dug trees, necessarily hfted before the

WINTER INJURY TO THE ROOTS 317

ground freezes and often dug rather early must have very tender roots,
so tender in fact that exposure to a sUght frost after digging in this stage
is hkely to have very serious consequences. Extreme care in protecting
tree roots against any freezing from the time they are dug until they
are planted is amply justified.

Summary. — Root killing is particularly common in sections with
low winter temperatures and little snowfall. Minimum soil temperatures
of 24° to 25°F. at a depth of 6 inches are very common in deciduous fruit
sections and soil temperatures of 7°F. have been recorded in Nebraska.
Freezing temperatures are frequently registered to a depth of 2, and occa-
sionally to a depth of 3 feet. The critical temperature for the roots
of most hardy species during their dormant season ranges from about
14° to 5°F. During the growing season it is much higher. Minimum
soil temperature is influenced greatly by soil covering, being distinctly
higher under snow or a mulch formed by some cover crop than under
bare ground. Fertilizers may indirectly protect roots against severe
freezing by promoting the growth of weeds or of cover crops. Frost
penetrates more deeply in light than in heavy soils. Roots are killed
more readily in dry than in moist soils. Considerable differences exist
in the relative resistance of the roots of different species and varieties.
Preventive measures include moderately deep planting, the use of cion-
rooted trees or trees on hardy stocks, the choice of locations not unduly
exposed to the wind, the use of cover crops to hold the snow and thus
both directly and indirectly blanket the soil and in some cases artificial
mulching. Remedial treatment consists chiefly in judicious pruning.
Care should be taken in handling nursery stock that the roots are not
exposed to freezing temperatures in packing, unpacking or heeling in
and they should be protected from freezing while in storage or transit.

CHAPTER XVIII
WINTER INJURY IN RELATION TO SPECIFIC FRUITS

The discussion of winter killing to this point has been general. Any
species furnishing convenient illustrative material has been drawn on
and most of the types considered affect each species more or less; the
prevailing conception has been the tree in general rather than any specific
kind. There are, however, differences in the problem of hardiness as
it relates to the several species and detailed points of adjustment to
these differences. These can be considered more conveniently by dis-
cussing each fruit singly, evaluating for each the different types of injury
to which it is liable and indicating, wherever possible, the best means
of minimizing the difficulties.

The Apple. — The apple is the most widely grown fruit in America
and is, at one point or another, exposed to practically every form which
winter injury can take; it seems, however, practically immune to some
of them. Aside from sunscald there is little or no evidence that the
apple suffers from those types of injury that are characteristic of late
winter, i.e., from warm weather followed by cold. Though killing of
fruit buds sometimes occurs it seems hardly probable that this is a kill-
ing of buds which have broken the rest period. At the time of the
Easter freeze of 1920 in the lower Missouri valley many varieties had
pushed their buds so far along that they showed pink. These varieties
of course suffered more or less but their killing constitutes a case of
damage to succulent tissues rather than of winter injury. Late blossom-
ing varieties, though the buds had swelled noticeably, were not damaged
by the drop to 14°F. Though this is not conclusive evidence it is sugges-
tive. A February freeze of — 7°F. in Georgia when some Japanese plums
were in bloom, worked serious injury to plums and peaches but caused
no damage to the apple. ^^'^

Whipple-"^ introduces clear evidence of fruit bud killing in Montana
and shows that little readily recognized evidence that the buds have been
fruit buds is left after they are killed. If the injury is confined to the
floral parts as Whipple has shown to be the case at times, the vegetative
parts grow and the casual observer concludes that the tree has failed to
form fruit buds and is going through an off year. It is, therefore,
possible that this killing may occur at times when it is not recognized.
Nevertheless it is safe to assume that fruit bud killing is comparatively
rare and that when it does occur it is not necessarily related to the
breaking of the rest period.

318

WINTER INJURY IN RELATION TO SPECIFIC FRUITS

319

Injuries Associated ivith Immaiuritij. — Difficulties due to prolongation
of the growing season are far more common in the apple. Indeed, disre-
garding the winter drought conditions in the north prairie states, which
are not apple growing states in a commercial sense, it is, in one form or
another, the prevailing type of injury. A large proportion of recorded
cases of winter injury may be traced to immatuiity. This probably
accounts for the many cases observed in which the wood is killed while
the buds are not. The various forms of injury associated with imma-
turity have been discussed and require no elaboration here.

There remain for consideration, however, some interesting differences
between varieties in hardiness. Most European varieties were early
found lacking in this respect along the Atlantic coast and the apples
developed in the eastern states in turn proved tender when transplanted
to the northern prairie states. From available data it is not yet possible
to reduce varietal differences from an indefinite empirical status to a
basis capable of quantitative expression. Macoun's statement, quoted
above under Immaturity, that hardiness is merely an expression of
complete maturity, is undoubtedly true in a large measure. The winter
apples of southern latitudes are tender at the north though there are
exceptions, as Ben Davis which is probably hardier than Baldwin, and
the winter apples of the north, hardy there, are summer or fall apples in
the south. The summer apple in the north, finishing its active season
early, has time to develop maturity such that it withstands the winters;
the winter apple must grow longer to complete its cycle and has less oppor-
tunity to acquire the condition that makes it hardy. As an index of
comparative maturity Beach and Allen^^ report observations on the date
of terminal bud formation in several varieties, which are reproduced here,
with some change of arrangement, as Table 49. Despite some incon-

Table 49. — Date of Forming Terminal Buds'^

Variety

Nursery
trees

Orchard
trees

Variety

Nursery
trees

Orchard
trees

Hibernal

Oldenburg. . . . ,

Salome

Soulard

Virginia

Wealthy

Mcintosh

Silken Leaf . . .

Winesap

Anisim

Black Annette.

July 25

.July 1

Aug. 20

July 1

Aug. 20

*

Aug. 20

*

Aug. 20

*

Aug. 20

July 12

Aug. 28

*

Sept. 1

*

Sept. 5

Julv 22

Sept. 5

*

Sept. 20

*

Ben Davis. . .

Gano

Jonathan ....

Patten

Grimes

Delicious

Ingram

Iowa Blush. .
Lansingburg .

M inkier

Roman Stem.

Sept. 27
Sept. 27
Sept. 27

July 1
July 10
July 22
July 1
July 15
July 22

'Terminals not formed at time of first frost, about Oct. 1.

320

FUNDAMENTALS OF FRUIT PRODUCTION

sistencies, as, for example, the relative positions of Winesap, Ben Davis
and Delicious, there is a general correspondence between the date of ter-
minal bud formation and the generally accepted relative hardiness of the
varieties reported upon.

The water content of most tissues may be taken as an index of matur-
ity, diminishing as this condition is approached; the same is true of other
tissues. This being true a study of the moisture contents of different
varieties ought to give an index of their relative maturity.

Shutt^^° reports an interesting set of moisture determinations at Ottawa,
reproduced here as Table 50. These 10 varieties were arranged by Macoun in
groups in decreasing order of hardiness, as follows: Group 1 (hardiest), Olden-
burg, Yellow Transparent, McMahon White; Group II, Wealthy, Scott's Winter;
Group III, Scarlet Pippin, Walworth Pippin; Group IV (least hardy), Hebble
White, Boy's Delight, Blenheim Pippin.

Table 50. — Percentage of Water in Apple Twigs Jan. 23, igOS'^"

Variety

Basal portion

Terminal
portion

Whole twig

Yellow Transparent
McMahon White. . .

Oldenlnirg

Walworth Pippin . . .

Boy's Delight

Wealthy

Scarlet Pippin

Hebble White

Scott's Winter

Blenheim Pippin ...

45.55
45.45
45.02
44.72
44.74
46.82
47.13
49.09
47 . 50
48.93

45.10
46.96
47.51
47,67

44.75
48.72
49.92
48.82
50.36
51.38

45.30
46.14
46.15
46.20
46.25
47.70
48.58
48.91
48.98
50.24

Comparison of Macoun's arrangement with Shutt's figures, considering
in particular the terminal portions of the twigs, shows a correspondence
that at least suggests a relationship. Shutt comments on these figures in
part as follows: . . . "it would seem, therefore, that we have direct
and definite proof that there is a distinct relationship between the mois-
ture content of the twig and its power to resist the action of frost and
that those trees whose new growth contains the largest percentage of
.water, as winter approaches, are in all probability the most tender."

Table 13 shows the moisture content, at different dates, of several
varieties of apples. Of these Hibernal and Wealthy are generally
recognized as the hardiest. It is significant that these two varieties
had the least moisture in July and that in January, after a week of cold
weather, including a minimum of — 15°F., having lost the smallest
amounts of moisture, they had the greatest moisture contents. Winesap,
figures for which were not complete, dropped in water content, between

WINTER INJURY IN RELATION TO SPECIFIC FRUITS 321

July 15 and Dec. 26, from 60.4 to 45.7 per cent., having on that date the
lowest water content. It is also the least hardy of the varieties under
consideration. The hardier varieties were found to lose less water
through the bark in a given time.

Various workers have studied the structure of apple twigs but no one
has been able to correlate definitely any structural differences with hardi-
ness or its lack. There seems some tendency for hardier varieties to
have somewhat thicker bark and more starch in their tissues but these
characters are by no means constant. Were the starch content shown to
be correlated, it could hardly be regarded as a causal agent but more
likely a product of the conditions that make the variety hardy, through
making it mature.

In short, then, the only character that can be linked definitely with
hardiness in the apple is maturity. If one variety is hardier than another
because it matures better, the cultural practices that make the tender
variety mature better make it in effect more hardy. A well matured
tree of a tender variety is undoubtedly more hardy than an immature
tree of a hardy variety. This accounts for many apparent inconsistencies
in field observations.

Control Measures. — Efforts have been made to influence cold resist-
ance by topworking upon stocks of great hardiness. In so far as root
killing is prevented this practice has proved beneficial. It is also a wise
practice if the growing of varieties notoriously subject to crown rot or
crotch injury is to be undertaken. However, that hardiness of stock
increases the hardiness of the cion is not shown conclusively by any
evidence available. It is conceivable that an early maturing stock might
influence the top slightly in the same direction but any influence of this
character is comparatively insignificant. Macoun^^^ reports top grafting
varieties not perfectly hardy on stocks of very hardy varieties at Ottawa,
Ontario; among the cions used were Baldwin, Benoni, Esopus, Fallawater,
King, Newtown, Northern Spy, Ontario, Rhode Island, Rome Beauty,
Sutton, Wagener, Winesap and York Imperial; the stocks used were
McMahon, Gideon, Haas and Hibernal. The grafts endured several
winters, but "the test winter of 1903-1904 killed practically all of them,"
though the stocks survived. It is, however, interesting to note that
Sorauer^^^ considered that grafting of weak growing varieties upon
vigorous stocks results in an increased amount of frost canker, character-
istic of immature tissues.

There is a limit to the effects that can be induced by cultivation.
No amount of cultural manipulations can make a variety mature its
fruit and its wood in a situation where it does not receive sufficient heat
(where the season is too short). It is not without significance that only
one of the important winter apples of the south can be grown to any
advantage in the north. Whether the cause be called failure to mature

21

322 FUNDAMENTALS OF FRUIT PRODUCTION

or lack of constitutional hardiness, there is a northern limit to the culture
of every variety and that limit is reached more quickly for some varieties
than for others.

Varietal Differences. — Out of the vast and costly experiments in hardi-
ness carried on by planting and replanting, the sieve of selection has shown
certain varieties to withstand winter cold in average conditions better than
others. Since Baldwin is perhaps the best known single variety in most
sections where apple hardiness is important it is used as a standard of
reference. Hardier than Baldwin is a quaUty possessed by but few varie-
ties of extensive commercial possibilities though this statement does not
mean that Baldwin is particularly hardy. In the list of varieties recom-
mended by Hedrick, Booth and Taylor^* for the St. Lawrence and
Champlain Valleys, where Baldwin does not succeed, are Fameuse,
Mcintosh, Oldenburg, Wealthy, Blue Pearmain, Jewett Red, St. Lawrence,
Gravenstein, Red Astrachan, Yellow Transparent, Canada Baldwin,
Longfield and numerous crab apples.

For ''the most northerly district" of Quebec, Macoun^^^ recommends
Tetofski, Blushed Calville, Lowland Raspberry, Duchess, Charlamoff,
Antonovka, Wealthy, Hibernal, McMahon, Longfield, Patten Greening,
Mcintosh, Milwaukee, Winter Rose, Stone, Scott Winter and Malinda.
It is stated that the summer and autumn varieties are the hardiest.

At the Northwest Experiment Farm, in Minnesota, where winter con-
ditions are probably as severe as at any point where apples can be
expected to grow% the list of approved varieties is limited, aside from
certain crab apples, to four: Hibernal, Oldenburg, Okabena and Patten
Greening. ^^^

If one variety were to be picked as the hardiest of all cultivated
varieties of the apple grown in America it would probably be Hibernal.

The Pear. — The pear is like the apple in its reactions to winter con-
ditions. It is somewhat less hardy than the apple. Though apples are
grown at points where the mean temperature of December, January and
February is 13°F., the northern limit of the pear follows in general the
mean temperature line of 20°F.'^^ Nevertheless certain varieties possess
considerable hardiness. Though evidence as to actual hardiness in the
northern Mississippi valley is not available because of the complications
introduced by fire blight prevalence, some information may be secured
from experience in certain eastern states where blight is not so serious.

Pears suffered extensive injuries in New York during the extremely
severe winter of 1903-1904.^^ Young trees, though the bark and wood
were discolored, made good recovery, in one case forming a layer of 5
millimeters over the old sap wood in the first summer. Trees that had
been injured by psylla were killed outright in many cases. Dehorning
old trees that were injured aggravated their poor condition.

Waite'^^ reports extensive damage to pears in the Hudson River

WINTER INJURY IN RELATION TO SPECIFIC FRUITS 323

valley during the same winter. Pointing out that pear orchards are
planted customarily in low rich ground, in other words, on sites more
inviting to winter injury than those ordinarily chosen for peaches, he
states that pears were as severely injured as peaches and do not possess the
recuperative powers of the peach. Elevation made great difference in
the amount of damage. "The young pear trees are rather less hurt than
the older trees, as in the case of the peach, but it should be noted in this
connection that young pear trees having the wood blackened, although
they will push out their wood and make a start, are very apt to decline or
else maintain their life in a very feeble manner as a result of the dead
wood at the heart. They have not the ability to recover by depositing a
thrifty layer of sap-wood. Pear trees under 3 or 4 years of age which are
badly frozen and which show blackened or discolored wood, even though
the bark may look normal from the outside and may appear to be alive
and quite fresh when cut into, should be cut off below the snow hne
and allowed to sprout."

Injury to pears occurred in the localized Michigan freeze of October,
1906.^^2 Though peaches were killed, it was only in low places and in
vigorously growing trees that pears were seriously injured. Blackening
of the wood was found. Apples were very little injured under the same
conditions. In parts of Washington an early winter freeze caused split-
ting of trunks on the south side and blackening in the wood of the fruit spurs
down to the limbs, with damage in some sections to the blossom buds.^^
Bailey* reports killing of fruit buds at Ithaca, N. Y., with no injury to
wood, during a dry cold winter. Injury to wood occurred elsewhere, he
states, at the same time, but evidently he does not consider this severe.

The following varieties have been reported suitable for culture in
Vermont and hence presumably hardy : Vermont Beauty, Flemish Beauty,
Anjou, Winter Nelis, Onondaga, Tyson, Lawrence and Sheldon. ^^s As
"succeeding in many gardens" Angouleme, Bartlett, Buffum, Seckel,
Louise Bonne de Jersey are mentioned. At Orono, Maine, a little beyond
the northern limit of the Baldwin apple, the hardier varieties have been
found to be Clapp Favorite, Flemish Beauty, Howell, Lawrence, Sheldon
and Winter NeUs.^^' Chandler states that Anjou is one of the hardiest
varieties at Ithaca, N. Y., probably a little more so than Clapp Favorite
and Sheldon, certainly less than Flemish Beauty. Bartlett is generally
conceded to be rather tender.

Flemish Beauty has proved the hardiest variety of the better class of
pears tested at Ottawa, Ont."^ Evidence elsewhere corroborates this
selection, though even this varietj^ is by no means immune to winter
injury in regions of commercial fruit growing.^"^

The Peach. — The difference in the hardiness problem in peaches
north and south has been discussed, maturity being stated as the leading
factor in the north, the rest period in the south. Root killing has been

324 FUNDAMENTALS OF FRUIT PRODUCTION

shown to be of relatively small importance in the peach, though it is by-
no means unknown. Extensive killing occurred in the Michigan peach sec-
tion in a freeze on Oct. 10, 1906, while the trees were still in full foliage. ^^^
At South Haven the temperature fell to 17°F., and some unofficial ther-
mometers registered 6°F. Cambium and sap-wood injuries extending to
the snow line were common. Frost cankers on peach trunks and crotches
are found sometimes, following winters of extreme cold or a late growing
season. ^^ "Gum pockets usually form under the flattened areas and the
gum often oozes out during periods of wet weather. The injured area is
usually rather indefinite about the margin and the formation of a healthy
roll of callus is thereby much retarded."

It has been shown earlier that no stated temperature can be assumed
as fatal. However, fruit buds are generally more tender than wood.
When, therefore, there occur cases in which the wood is killed and the
buds survive, they may be considered good evidence of lack of maturity.
There is hardly a winter without some killing back of young twigs which
may be interpreted as indicating a lack of maturity. The care generally
exercised in selecting sites for peach orchards to secure freedom from
spring frosts fortunately has another equally desirable, though seldom
recognized, effect in that it secures greater maturity. There is a remark-
able uniformity, throughout reports of various freezes in northern
states, in locating the greatest injury in trees growing in moist, rich soil
and receiving late cultivation. Another point of agreement is the ascrib-
ing of great injury to trees low in vitality from various causes such as
San Jose scale, leaf curl, low fertility, borers and poor drainage. Green
and Ballou^i mention an orchard in which the San Jose scale spray was
omitted in 1902 on three rows running through the middle. In the
severe winter of 1903-1904 these three rows were killed while the rest
were uninjured. Whether the greater injury to weak trees is actual and
due to some specific condition characteristic of weakness or whether it is
apparent and due to their inferior recuperative powers is not clear. A
given degree of injury would be more evident, certainly, on a weak than
on a strong tree.

Waite,^^^ reporting on the January, 1904, freeze in New York, dis-
tinguished three classes of injury: " (1) In bearing peaches the trees most
injured by freezing show the bark entirely blackened and dead, more or
less separated from the trunk and the wood turned a very dark brown
color. The injury extends far up onto the limbs although the bark
usually has not separated on the branches. Such trees are dead beyond
all question. The bark on such trees still retained its vitality. Some-
times a rise of 10 or 15 feet resulted in trees being less seriously
injured. (2) With many peach trees the bark is lightly separated from
the wood which is of a dark-walnut color next to the cambium and brown
throughout. Though still alive the bark is somewhat browned and

WINTER rXJURY IX RELATION TO SPECIFIC FRUITS 325

discolored, the youngest or outer layer of wood has been frozen until it is
now of a dark-walnut color and the wood is blackened throughout.
Many of these trees are of doubtful vitality and will probably succumb.
Others have enough vitality to enable them to pull through. Where
bark is adhering or only partially separated from the trunk the chances
for recovery are good. The tops of such trees are usually found in fair
condition, the wood brownish, but the white cambium layer uninjured
though lying immediately in contact with brown, dead wood. The
twigs, especially the 1-year wood, sometimes have been frozen so badly
that they will not be able to push out the leaf buds. In severe cases the
leaf buds themselves are killed, but, as a rule, they are still alive. Of
course on all such trees the fruit buds are killed. The most injured part
is the trunk just above the snow line. ... (3) The third class, which
may be described as the moderately frozen trees, in which the wood above
the snow line is blackened but the bark not separated from the wood and
with the cambium still apparently alive, although water-soaked and
injured, frequently has minute brown streaks in the bark immediately
in contact with the cambium. Such trees will almost invariably
recover. . . . Nearly every tree in the entire Michigan fruit belt
was frozen in February, 1899, so that the wood was blackened and dead
clear to the bark. A new layer of live white wood formed inward from
the white bark, the trees made a fairly good growth, having no fruit crop
to carry, and bore the year following a record fruit crop."

As in the apple, the bark on the trunk near the ground seems to
mature late and is particularly liable to injury. After seasons favoring
late growth mounding of earth to cover this region somewhat has been
found very profitable insurance. In several instances in Ohio in 19G3-
1904 a few shovelfuls of earth at the crown made the difference between
dead trees and uninjured trees. ^^

Chandler^^ records an interesting case of mild injury associated with
immaturity. After a very rainy August in 1914 the minimum for
the winter, — 9°F., occurred late in December. In the following spring
the blossoms of several varieties were at least three weeks late in opening.
Examination disclosed injury to the pith of the bud, extending even as far
as the pith of the twig. There was very little injiny elsewhere. Usually
the flower parts are less resistant than the pith of the bud and of the
twig. The temperature evidently was not low enough to kill matured
buds but it did damage the immature tissues. The trees in question bore
a normal crop that season. Similar cases have been observed at other
times. ^*

Treatment of damaged trees consists of the ordinary prophylactic
measures and a moderate pruning. Very heavy heading back, or
dehorning, has proved decidedly injurious when the bark or the wood is
damaged; a fair amount of pruning is, however, beneficial.*^ This

326 FUNDAMENTALS OF FRUIT PRODUCTION

should be done before growth starts. There is a. general tendency to
overestimate damage and immediately after a freeze many orchards
have been taken out which would have recovered in time had they been
allowed to remain. Trees with any considerable injury to the trunk
should by no means be allowed to bear fruit in the season following the
injury."

Observations by Mer^^^ on oaks may explain the injurious effects
of very heavy pruning. Investigating old winter injuries of the "black
heart" type, he found considerable starch still in the injured wood but
little in the wood subsequently laid down, indicating that the tree was
unable to withdraw starch from the injured tissue. This suggests that
if the injury is extensive the tree will have difficulty the following spring
in securing sufficient carbohydrates to sustain growth until a supply can
be secured from the new leaves. If the pruning is heavy enough to
remove all the buds which make new growth most readily the difficulty
must be increased. If, however, no buds are removed the scanty carbo-
hydrate supply is apportioned to so many growing points that none
receives enough to sustain growth until it can become self-supporting and
the tree dies of carbohydrate starvation.

Hardiness in wood and in bud are not always combined in the same
variety. Elberta, generally considered hardy in wood, seems tender in
the fruit buds. Hedrick,^^ reporting a questionnaire of New York and
Michigan peach growers, states their selections for wood hardiness as
follows: For New York in order named, Crosby, Hill's Chili, Stevens'
Rareripe, Gold Drop and Elberta; for Michigan, Hill's ChiH, Crosby,
Gold Drop, Kalamazoo and Barnard. Jaques Rareripe, Wager, Carman,
Belle of Georgia, Hale's Early, Champion and Greensboro are listed as
hardier than the average in this respect. Early Crawford, Late Craw-
ford, Chair's Choice, St. John and Niagara are rated as the five most
tender in wood of the varieties commonly grown in New York. Salway
is listed as tender in Michigan.

In fruit buds. New York growers find greater hardiness in Crosby,
Hill's Chili, Triumph, Gold Drop, Stevens' Rareripe and Kalamazoo;
Michigan growers find Hill's Chili, Gold Drop, Crosby, Kalamazoo and
Barnard hardiest. Concerning the five most tender varieties in bud
there is entire agreement in New York and Michigan as to the order of
their tenderness: Early Crawford, Late Crawford, Chair's Choice,
Reeves' Favorite and Elberta. The Peento group is extremely tender.

The Cherry. — Sweet cherries are generally known to be far more tender
than the Dukes, Amarelles and Morellos. As outlined by Finch'^'* the
northern range of cherries is marked by the mean winter temperature of
about 16°F. For the three coldest of the pomological districts into
which the United States is divided in the fruit catalog of the American
Pomological Society only one variety of sweet cherry, Black Tartarian

WINTER INJURY IN RELATION TO SPECIFIC FRUITS 327

is recommended and that recommendation is confined to one district.
For the same districts 13 varieties of Duke and Morello cherries are
recommended. ^^^ Of 26 varieties in the catalog, 13 are recommended
for District 1 and of these, 10 evidently are considered worth growing in
District 2 which includes most of the northeastern fruit growing sections.
The three leading commercial varieties, Early Richmond, Montmorency
and English Morello, are considerably hardier than the Baldwin apple.
However, some of the hardiest apples appear to be hardier than the hard-
iest cherries. Hansen*^ states that root killing is the one great difficulty
in cherry growing in South Dakota. Following the February, 1899, freeze,
with a minimum of -27.5°F., at Madison, Wis., some root killing was rep-
orted, but most varieties brought their fruit buds through, Large Morello,
Late Morello, Shadow Amarelle, Dyehouse and Ostheim having over
90 per cent, live buds.^^ Curiously enough many varieties undamaged
in the 1899 freeze had their buds killed in the winter of 1896-1897 with a
minimum of — 23°F. During the summer of 1896 the trees had been in
sod and there was much dry weather. Considerable variation in the
hardiness of the embryo flowers, not alone between varieties, but on the
same tree and even within the same bud, has been reported. ^^ Careful
study showed a strong inclination toward tenderness in varieties having
the greater number of flowers per bud and a similar susceptibility in
individual buds within the variety. The periphery of the tree had 39.9
per cent, live buds while the central part had 69.9 per cent, alive. Goff
did not regard this difference as due alone to the greater number of flowers
in the peripheral buds but suggested that it might be due to the protection
afforded by the branches and to conduction of heat along the trunk from
the soil. Roberts, ^^^ also working in Wisconsin, reported that though
winter injury to cherry buds is frequent in that state, it is rarely severe
enough to affect seriously the yield of fruit. Frequently only one or two
of the four or five blossoms within the bud are killed. Studies made in
the spring of 1917 are interesting in several respects. All injury had been
confined to blossom buds. Older trees showed more injury than young
and the exposure appeared to have little relation to the amount of injury
during that winter. Trees which had been partly defoliated by the shot
hole fungus the previous season received less bud injury than normal trees.
The shortest and the longest spurs were less injured than spurs of medium
length and on terminal shoots there was less injury in the buds at the
base and at the tip than along the central portion of the shoot. Larger
buds were most frequently injured.

The injury occurred early in December following a temperature of
-12°F. and could not have been due to development excited by warm
winter weather. Microscopic study showed that the buds most
damaged were the most advanced in their development. Late maturity
could not have been the factor involved as the trees and parts of trees

328 FUNDAMENTALS OF FRUIT PRODUCTION

growing latest were the least injured. This finding is in agreement with
Goff's earlier report of greater tenderness in the winter of 1896-1897 when
the trees stood in sod and the weather was dry, both of which conditions
favor early formation and rapid development of fruit buds. It appears,
then, that cultural practices tending to promote vigorous growth and
fairly late maturity would have some effect in reducing injury of this sort,
though Roberts states that it could not be eliminated altogether.

In a general way, it may be said that the cherry is not very liable to
injuries associated with immaturity. Some varieties of sweet cherries
were shghtly injured in Michigan in October, 1906, when peach trees were
killed and pears considerably injured in some places. ^^^ Cherries, how-
ever, showed considerable injury in Washington in late November,
1896, at a temperature somewhat below 0°F.^2

Bessarabian, Brusseler Braun, Lutovka, English Morello and Early
Richmond appear, from the scant data available, to be the hardiest of
the commonly grown varieties.

The Plum. — Perhaps because of the number of botanical species from
which the cultivated varieties have sprung, plums show a wide range in
hardiness; though some are more tender than the majority of peaches,
others are hardier than the hardiest apples. Hedrick^^ states that the
Nigra plums are the hardiest of our tree fruits and are able to resist
nearly as much cold as any cultivated plant. Only a little less hardy are
the Americanas. The relative hardiness of the other groups is thus
summarized by Hedrick: "Insititias as represented by Damsons come
next with varieties of Domestica as Arctic, Lombard and Voronesh
nearly as hardy. The Domesticas are less hardy than the apple, ranking
in this respect with the pear. Of Domesticas the Reine Claude plums
are as tender to cold as any though some consider Bradshaw more tender.
. . . The Triflora (Japanese) plums vary more in hardiness than any
other of the cultivated species. Speaking very generally they are less
hardy than Domesticas, the hardiest sorts, Burbank and Abundance, being
somewhat hardier than the peach, while the tenderest varieties, of which
Kelsey is probably the most tender, are distinctly less hardy than the
peach. Of the remaining plums, the Hortulana, Munsoniana and
Watsoni groups, there are great diversities in opinion as to hardiness.
Probably all the varieties in these last groups are as hardy as the peach
with a few sorts in each more hardy than the peach. It is to be expected
from the more northern range of the wild prototypes that the Hortulana
and Watsoni plums are somewhat hardier than Primus Munsoniana.''

Waugh^o-* indicates distinct varietal ranges, within the species:
" The tenderness of Bradshaw seems to belong more to the fruit buds than
to the wood and correspondents do not seem to agree in their reports;
but upon the basis of statistics received, we may trace the northern limit
of the Bradshaw . . . which runs from 100 to 300 miles south of the

WINTER INJURY IN RELATION TO SPECIFIC FRUITS 329

line traced for Lombard. . . . In fact a majority of the standard varie-
ties, such as Coe Golden Drop, Italian Prune, Jefferson, Lincoln, Moore
Arctic, Pond, Shippers' Pride and Washington, would probably be found
to conform fairly well to the same limits as Lombard." Of the Japanese
plums, "Abundance, Chabot (Chase, Yellow Japan), Hale, Red June,
Willard and Ogon seem to be about as hardy as Burbank. Satsuma
stands about midway between Burbank and Kelsey."

In North Dakota, Waldron-°^ states: "Only one species of plum
(Americana) can be grown with any success in the State. So far as
tried here they are all hardy though some ripen late and most of them
are vigorous and productive. . . . All things considered they are the
easiest and most profitable fruit to grow in North Dakota. . . . For
general cultivation the following varieties will be likely to succeed: De
Soto, Forest Garden, Weaver, Cheney, Wolf, Rolling Stone, and Wyatt. "
In parts of Minnesota RoUing Stone, De Soto, and Surprise are too late in
ripening their fruit to be satisfactory in cultivation, though they are not
stated to lack hardiness." For the colder parts of Vermont several
varieties have been reported to be as hardy as the sugar maple : Stoddard,
Hawkeye, Quaker, Aitkin, Surprise, Cheney, De Soto, Forest Garden,
Wolf, Wyant and Weaver, ^os

In Wisconsin many varieties have brought their buds through a tem-
perature of — 38°F. in one winter, though they succumbed to — 23° in
another, ^^ indicating that the condition of the tree makes a considerable
difference in the amount of cold that can be endured. In view of the work
of Chandler with peaches and Roberts with cherries it seems possible that
the advancement of the buds when they enter the resting stage may
have much to do with their hardiness. No definite data are available,
unfortunately, on this point, but the superior hardiness of the Americana
group, which is late in maturing, appears to justif.y investigation. It
would seem, since plum blossoms are injured more frequently than the
woody parts, that maturity might be delayed safely to some extent
without unduly increasing liability to injury in other ways.'*^

Recent investigations in Minnesota indicate that some of the injury to plum
blossoms is associated with early breaking of the rest period. Treatment to
increase hardiness by retarding blossom formation and development would tend
also to delay the breaking of the rest period.

The Grape. — Winter killing is not so prominent a factor in grape
growing as it is with some of the tree fruits. Two reasons may be assigned
for this comparative freedom from injury. First, varieties grown com-
mercially in the majority of sections subject to winter killing are de-
scended, at least in part, from the native species and therefore profit
from the adjustment of the native species to their environments. Second,
the difficulty ox seeming satisfactory ripening of the fruit, because of

330 FUNDAMENTALS OF FRUIT PRODUCTION

the shorter growing season, tends to hmit the northward spread of grape
culture to points with winter extremes well within the adaptation of
the vine.

Nevertheless, the grape is far from immune to winter injury. Varie-
ties with Vinifera qualities predominating or from species native to
regions of mild winters have distinct climatic limitations and even
the so-called hardy varieties frequently suffer. There is little evidence
to connect winter drought with winter injury except in so far as a dry
soil freezes deeper. Heavy winter irrigation has proved of no value
with Viniferas in New Mexico. '^^ Under very severe conditions root
killing may occur; at times the vines are killed to the ground and there
are frequent instances of killing of fruit buds because of imperfect matu-
rity. Gladwin''^ records three seasons out of eight at Fredonia, N. Y.,
when the vines did not reach proper maturity. Sometimes heavy rains
late in the growing season bring about this condition; again it may
be due to the ripening of a heavy crop. The light crop usually following
a heavy fruiting is commonly ascribed to exhaustion of the vines but
it may be due also, at least in part, to the killing of a large number of
imperfectly matured buds. Since the grape bud is compound and mixed,
the primary floral parts may be killed and only the secondary shoot
develop the following spring. This tends to obscure the kilhng and the
sterility of the shoot is attributed to exhaustion following the heavy
crop of the preceding season. Gladwin shows that the three lightest
crops of the period studied followed the seasons when the sugar content
of the grapes (an index of maturity) was lowest. However, since vines
which have not borne are affected also much of the immaturity must
come from other causes. Indeed, Budd-^ considered immaturity and
tenderness to result from the lack of a crop and remarked that the wood
of Rogers' hybrids ripened well when bearing a crop but without a crop
did not mature. Much greater injury has been reported in low ground,
particularly in ground with poor drainage.

At times very low temperatures, even when the vines are mature,
will cause a discoloration of the wood without actually killing the vine.

Anthony^ reports recent investigations of the practicability of
growing certain Vinifera varieties in the eastern United States. When
a moderate amount of winter protection is given, by bending the vines
down and covering with a few inches of earth, very satisfactory results
are obtained. Indeed, with the varieties tested, the hmiting factor
seemed to be the heat and length of the growing season rather than tender-
ness to winter cold. Anthony states: "A well matured Vinifera is seldom
killed outright by the winter even if given no protection, but the effect of
the first winter is usually to decrease the plant's vitahty to such an
extent that it is unable to reach proper maturity the next season and so
is usually killed the second winter. "

WINTER INJURY IN RELATION TO SPECIFIC FRUITS 331

Mounding has been effective in protecting Vinifera grapes in New
Mexico" and hardy grapes in Iowa were satisfactorily wintered by a
sUght mounding about the trunks and a slight covering of the tips of
the canes with soil.-' Straw protection has been less satisfactory on
Viniferas in New York than laying the vines down and giving a slight
earth covering. Vines treated in this last manner have proved hardy
in very trying climates.

Severe freezes in grape growing regions damage all varieties so that
a close estimate of hardiness in such places is difhcult. However, as
the culture extends into colder regions varietal differences become more
evident. The American Pomological Society's catalog highly commends:
for Section I, Brighton, Cottage, Diamond, Herbert, Lady, Lindley,
Moore Early, Moyer, Niagara (?), Victor, Winchell (Green Mountain),
Woodbury and Worden; for Section II, Janesville and Winchell; for
Section XIV, Diamond is the only variety to receive even a qualified
recommendation. ^^^

For Vermont, Waugh^o^ recommends Moore Early, Worden, Moyer,
Brighton, Wyoming Red and Green Mountain. The Northwest Minne-
sota Experiment Station for a more trying situation recommends Beta,
Janesville and Campbell Early. ^^^ Hansen in South Dakota expresses
preference for Worden, Concord and Moore Early in favorable situations
and for unfavorable locations, Janesville. ^^ The difficulty with Concord
in Vermont appears to arise, not from its lack of hardiness but rather
from the brevity of the growing season.

THE SMALL FRUITS

Though winter killing in cane fruits is common, more common,
perhaps, than it is among tree fruits, conditions of plant and environ-
ment favoring or reducing injury are far less understood. This is due,
in part to the large number of units involved so that the loss of a few
plants is hardly noticed, in part to the short normal life of a cane fruit
plantation so that even an extensive loss is not as calamitous as that of
an orchard and in part to the quick recovery of the plants from the com-
mon forms of winter injury. When a tree trunk is severely injured
recovery is a matter of several years, if indeed it is ever complete.
Raspberry or blackberry canes, on the other hand, may kill to the ground
but only one crop is lost and the following autumn generally finds the
plants in as good condition as ever.

The growing of small fruits has, in most of the northern sections,
because of these conditions, developed along two lines; in some cases only
hardy varieties are grown and no winter protection is given and in others
protection is given and desirable varieties grown regardless of their
hardiness. Hence inquiry into hardiness as it relates to small fruits
generally has taken the form of variety testing for this quality; related

332 FUNDAMENTALS OF FRUIT PRODUCTION

experimental data are very meager. Field observations as recorded are
frequently contradictory and puzzling. A certain variety, for example,
half hardy in New York would be expected to be wholly adapted to
Georgia; actually it may prove fully as tender in the south as in the north.
The red raspberry as a group is generally conceded in northern regions to
be hardier than the blackcap group yet the reverse condition obtains over
wide areas. ^^ Though loganberry and other western dewberries are very
tender, in one winter at Corvallis, Ore., with a minimum of 20°F., when
Cuthbert raspberries were killed at the collar the loganberry was un-
harmed. Furthermore, cane fruits frequently suffer from drought injury
which is doubtless sometimes confused with winter injury and so reported.

Winter injury to cane fruits may take one of several forms. Root kill-
ing occasionally occurs, especially in dry, cold climates with little snow.
Where this occurs, covering the canes is of no avail unless the roots
also are covered. In other cases the canes may kill to the ground, or
they may kill part way back, or the laterals may kill. Immature canes
appear to kill more easily at the tips and close to the ground and would
sometimes be benefited by mounding. The canes may be weakened only
and blossom but fail to mature the crop. Under exceptional conditions
currant and gooseberry fruit buds may be killed while the stems live.

Immaturity Most Important.— It is a generally accepted principle in
the growing of cane fruits that maturity is important to hardiness. Imma-
ture tips, laterals on canes pinched back and suckers that develop late are
sometimes injured by comparatively mild freezing; a temperature of 12°F.
in November has caused extensive damage to raspberry tissues of this
sort in Missouri. Even in Virginia caution about late cultivation,
inducing an immature and tender growth, appears necessary.^ That the
degree of maturity attained at the onset of cold weather can be modified
by cultivation, irrigation and fertilization is obvious.

Relation of Summer Pinching to Maturity. — The effect of pinching
on raspberries in northern sections where maturity is clearly a factor
with tree fruits is well illustrated by Table 51, which shows the resistance
to winter killing of different varieties pinched at 15 to 20 inches and of the
same varieties unpruned. It is evident that the lateral growth induced
by pinching is not so hardy as the unbranched canes; presumably this is
due to immaturity.

A statement of Michigan experience is not without interest. ^^^
"Hansell, King, Miller [red raspberries] seldom branch and should not
be pinched back. When allowed to grow naturally the canes form strong
buds from which the fruiting branches will be developed the following
season while if the ends are pinched the buds will develop the first year
into slender shoots upon which the fruit buds will be weak, . . . [with
an] increased tendency toward winter-killing. Hence, for non-branching
varieties pinching back is not to be recommended." However, Card*^

WINTER INJURY IN RELATION TO SPECIFIC FRUITS 333

Table 51.— Winter Resistance of Pruned and Unpruned Raspberries"
(10 = no injury)

Pruned

Unpruned

Protected

Unprotected

Protected

Unprotected

9.0
9.0
2.0
7.0
8.0
7.0
8.0
5.0
8.0
8.0
7.0
7.0
8.0
7.0
7.0
9.0
8.0

7.3

4.0
7.0
2 0
5.0
7.0
4.0
4.0
5.0
4.0
6.0
4.0
4.0
6.0
5.0
4.0
6.0
6.0

4.9

10.0
9.0
4.0
9.0
9.0
9.0
8.0
8.0
8.0
9.0
9.0
9.0

10.0
8.0
9.0
9.0
9.0

8.6

5.0

Springfield

7.0

Royal Church

Carman

5.0

8.0

Thompson Early Prolific . . .

Herstine

Parnell

7.0
6.0
5.0

Golden Queen

Reider

5.0
4.0

Brandy wine

7.0
6.0

Marlboro

5.0

Hansen

7.0

Clarke

5.0

Cuthbert

7.0

Turner . . .

6.0

Caroline

7.0

6.0

Average pruned, 6 . 08
Average unpruned, 7 . 29

reports instances in which canes growing fairly late in the season have
been hardier because they were smaller and of more compact growth and
in reality better matured. It is worthy of note, also, that it is a common
practice among dewberry growers in the South Atlantic states, where
winter injury to cane fruits is by no means unknown, to mow all canes
after the fruit has been picked; evidently no serious winter killing to the
late growing shoots results.

Varietal Differences from Year to Year. — Phenological notes on
cane fruits are not sufficiently extensive to indicate whether there is any
correlation between varietal behavior in regard to maturity and resistance
to cold weather. Comparison of the dates of ripening of fruit with the
recorded degree of winter killing fails to establish any connection; the
same is true with regard to the date of blossoming. There is, furthermore,
some inconsistency in varietal behavior. Table 52, arranged from reports
on variety tests of blackberry in Massachusetts, shows a considerable
fluctuation in the percentage of canes killed in successive winters, with a
considerable difference in varieties. Thus Agawam's record is 30-0-0
while Erie's is 20-20-80. This indicates that more than one factor must.

334 FUNDAMENTALS OF FRUIT PRODUCTION

be operative in determining hardiness and that though maturity is

frequently very important, it is by no means to be considered the sole

factor.

Table 52. — Percentage of Blackberry Canes Killed in Successive Winters'^^

1890 1891 1892

Agawam 30 0 0

Early King 10 12 8

Erie 20 20 80

Minnewaski 0 8 5

Snyder 10 0 0

Wachusett, 20 0 10

Western Triumph 30 8 3

Wilson 20 5 40

Injuries from Drought not Uncommon. — Any variety may be weak-
ened from drought or fungous diseases and suffer unduly the following
winter. It is well known that large amounts of moisture in the soil
induce winter killing and that accumulation of ice on the surface of
the soil has the same effect. The relation of winter drought to winter
killing is perhaps less appreciated. Some unpublished investigations
by Emerson in Nebraska on this matter are of great importance,
pointing as they do to the conclusion that "injury to raspberries
in that locality was apparently almost wholly a matter of winter
drying."" Canes coated with paraffin suffered no appreciable injury
while untreated canes on the same stools were killed to the ground or to
the snow line. Observing that when the snow cover was deep enough
to keep the soil from freezing the canes were not injured, even in the
parts that projected above the snow, Emerson tried to secure the same
results by mulching. Various mulches were tried and the ground was
in many cases kept from freezing but the canes were killed down to the
mulch. "Temperature readings taken at various depths in the mulch
indicated that for a period of some weeks a portion of the mulch was
continuously below the freezing point. Of course, the water absorbed by
the roots from the unfrozen ground could not pass through the frozen
part of the cane. Other studies suggested, though I perhaps did not
have sufficient data to prove it, that the canes are not frozen for any
length of time when surrounded by snow."^^

Card^'^ remarks that though in Nebraska covering of raspberries
and blackberries is necessary the same varieties are commonly grown in
New York without protection, despite the fact that the winters in
Nebraska are no colder. He reports that during one winter in Nebraska
when the mercury fell below zero (Fahrenheit) but once, with —5° as the
minimum, unprotected canes were killed. Plants in adjoining rows
exactly alike, except that they were laid down and covered, were entirely
uninjured. The following winter was much colder but the soil was moist

WINTER INJURY IN RELATION TO SPECIFIC FRUITS 335

from autumn rains and both raspberries and blackberries came through
in good condition without protection. Growers of raspberries in Wyom-
ing are advised to stop irrigation about Aug. 1 but to give a heavy late
fall irrigation, besides covering the plants. ^^ There is general agreement
that cane fruits suffer more in seasons and in sections with little snow.

It is possible that much of the benefit attendant upon covering canes
comes from the reduced drying out rather than from actual protection
from cold. Even a trivial protection seems sufficient, sometimes just
enough to hold the canes down. Lying prostrate without covering they
escape most of the drying effect of the wind; when covered with earth
or snow they will resist extreme cold. Such protection is essential in
some sections, in others the profit in the operation depends on the
variety grown. Thus, in some experiments at Ottawa it was found that
the increased yield resulting from protection of the hardiest varieties
did not repay the cost of the operation though other less hardy varieties
thus treated gave 16 to 22 per cent, greater yields or enough to leave a
profit for the work.*^ Incidentally, it was reported that the plants thus
protected ripened their crops 5 to 8 days ahead of those not protected.
In Colorado minimum temperatures around zero ordinarily do not neces-
sitate covering raspberry canes ;^^ in New York unprotected raspberry
plantations stand considerably lower temperatures without material
injury.

Group and Varietal Characteristics. — The small fruits as a class
exhibit a rather wide range of hardiness. Currants probably are to be
regarded as the hardiest of all cultivated fruits, with gooseberries only
slightly less so. Next in order, in the north at least, come the red rasp-
berries descended from native species — those of Europe are tender —
followed by the blackcap raspberries which in turn are hardier than the
blackberries. There is some overlapping; the hardier black raspberries
are hardier than the more tender of the red raspberries and some black-
berries in turn are hardier than certain of the raspberries. Least hardy
of all are the dewberries, which are really tender though their trailing
habit makes possible their culture much farther north than their upright
hybrids with the blackberry can be grown without protection. The
dewberry and the blackberry, like the plum, are derived from several
native species and their range in hardiness is correspondingly wide. The
loganberry. Phenomenal berry and allied forms are tender to tempera-
tures below 15°F. and the Himalaya and Evergreen blackberries are
very little, if any, hardier. On the one hand, then, is the currant, hardier
without protection than the apple or the plum; on the other is the dew-
berry, rather less hardy than the peach though it is sometimes grown
where the peach is not grown, because it is more easily protected.

Among currants the smaller Red Dutch and Raby Castle types are
considerably hardier than the large-fruited varieties, the Fay and Cherry

336 FUNDAMENTALS OF FRUIT PRODUCTION

types. 12^ Gooseberries rarely suffer from winter killing but where
comparison has been possible Houghton seems the hardiest, with Down-
ing and Industry only slightly less resistant. Turner seems for a long
time to have been considered generally the hardiest of the older red
raspberries; though the newer Sunbeam and Ohta appear even hardier,
a large number of varieties, such as Hansell, Marlboro and Herbert,
are hardy enough for all but the most trying climates. Hardier than
many of the red raspberries, particularly those with European ancestry,
are the hardiest blackcaps, including Plum Farmer and Older. Of the
blackberries, Snyder is generally the hardiest, with Eldorado and Agawam
ranking close to it. Lucretia is perhaps the most widely grown dewberry
in the northern states, being grown successfully in Iowa and Minnesota
when covered with soil through the winter.

Summary. — Though winter injury from other causes sometimes
occurs, both the apple and the pear suffer most from those forms asso-
ciated with immaturity. Certain cultural practices encourage earlier
maturity, but in these fruits protection against winter injury is most
readily secured by a judicious selection of varieties. The peach, plum
and cherry suffer from injuries associated with immaturity and with
an early breaking of the rest period, the latter being the most important
with the peach and certain plums and the former with other plum groups
and the cherry. Protective measures lie principally in controlling season
and degree of maturity, though something can be accomplished by selec-
tion of varieties. Grapes suffer mainly from those forms of winter
injurj^ associated with immaturity. Varieties show great differences
in their hardiness. In addition to the protective measures adapted to
the tree fruits protection by artificial covering of the canes during the
winter is sometimes practicable with this fruit. The small fruits show
a wide range in hardiness, some of them, as the currant and gooseberry
being among the hardiest and others, as the western dewberries, being
very tender. The bramble fruits, in addition to being subject to a
general killing back, are particularly susceptible to injury at the crown.

CHAPTER XIX

THE OCCURRENCE OF FROST

Though spring and autumn frosts determine the geographic Hmits
of certain fruits less frequently than minimum winter temperatures,
they are nevertheless of no small importance in fruit production. There
are some whole sections of the country, as for instance the high table
lands of eastern Oregon, where fruit growing is very uncertain because
frost may occur at almost any time during the growing season. There
are many other sections or areas where spring frosts frequently occur
so late that certain fruits such as the apricot or the almond cannot be
successfully, or where autumn frosts are so early that late maturing
fruits such as the grape do not ripen properly and consequently are not
grown. Furthermore, within regions or sections that are suitable for
fruit culture there are many sites or locations which, because of their
susceptibility to frost, are unsuited for orchard purposes or where, if
fruit is planted, it requires expensive artificial protection from frost.
Finally, there come years when untimely frosts levy a heavy toll on
the fruit crop in isolated places or over wide areas generally considered
to be favorably located for fruit production. Early autumnal frosts
seldom cause concern so far as the season's crop is concerned, though in
grapes and some of the late maturing or everbearing types of small
fruits they may be responsible for considerable damage. On the other
hand, comparatively few and exceptionally fortunate are the fruit growers
who are entirely free, year after year, from concern about possible spring
frosts. The cost of full protection from spring frosts of certain pear
orchards in the Rogue River valley has amounted sometimes to $40
per acre. It is quite likely, however, that many crop failures arising from
other causes are attributed to frost damage and it is certain that much
can be done to lessen this injury by the careful selection of kinds and
varieties of fruit adapted to the particular situation or by selecting
a situation suitable to the kinds or varieties of fruit that it is desired to
grow. Furthermore, under favorable circumstances much can be accom-
plished by palliative methods, such as heating the orchard.

FROST FORMATION

Though discussion of the nature, occurrence and prediction of frosts

belongs properly in treatises on meteorology, a brief outline of the

more important facts concerning frost formation, so far as they concern

the fruit grower, seems necessary here because this subject is not studied

22 337

338 FUNDAMENTALS OF FRUIT PRODUCTION

SO widely as is warranted. It should be understood, however,
that cold weather aside from frosts may damage fruit crops and it is
not always necessary that the temperatures go below the freezing point.
Dorsey shows that cold weather, though the temperature remains above
freezing, immediately following the pollination of certain plum varieties,
results in such a slow growth of the pollen tube that abscission of the
style often takes place before fertilization, the result being as complete
failure to set fruit as though frost had actually occurred during the
blossoming period. Low temperatures also prevent the bees from
effecting pollination.

Frosts and Freezes Distinguished. — Furthermore, not all freezing
temperatures are due to frosts. English writers use the term "frost"
to designate freezing temperature of any kind but usage in the United
States restricts ''frost" to a kind of cooling well recognized and limited
in its scope. A "freeze," as distinguished from a frost, is due to the
importation of cold air from other regions and may be accompanied by
a high wind; a frost is due to a local cooling of air and occurs during
calm weather. A frost may take the form called a "hoar" frost, with
a visible deposit of frozen moisture, or it may be a "dry" or "black frost"
with freezing temperatures but with no deposit. Freezing temperatures
may accompany snow squalls. All of these may injure orchard fruits.
Against freezes the fruit grower is generally unable to contend by
palliative methods; against frost much effort has been expended and it
is upon frost that much horticultural thought has been centered.

Relation of Radiation to Frost. — Some knowledge of the nature of radiation
is necessary to a proper understanding of the nature of frost. It is generally
considered by physicists that all substances are constantly receiving and emanat-
ing heat. This radiation heat travels in straight lines through ether and through
air, being absorbed by them little or none. Striking a solid substance it is in
part reflected and in part absorbed, the amounts of reflection and of absorption
varying with the substance. During a clear day the heat received by any sub-
stance through radiation from the sun and from other substances is in excess of
the amount emitted through radiation; during a clear night the heat lost by
radiation exceeds that gained. On a cloudy day the sunlight is cut off to a
great extent and the substance is warmed less than on a clear day; during a
cloudy night much of the heat lost by radiation is reflected by the clouds and the
substance is cooled less than on a clear night. There is some absorption of
radiant heat by the atmosphere. Radiant heat from the earth is absorbed by
water vapor, carbon dioxide and ozone.

Radiation is proportional to the exposed surface, and the amount of heat
stored and available for radiation is to a large extent proportional to the volume
of the radiating substance. Therefore vegetation, which has a large surface in
proportion to its volume, cools by radiation with relative rapidity.

Though air freely permits the passage of radiation heat, it radiates little
itself in comparison with other substances. There is, it is true, an appreciable

THE OCCURRENCE OF FROST 339

amount of radiation from the air. The rapid cooling of air after sunset is largely
a radiation effect, especially if the air at higher elevations is rather free from
water vapor as is usually the case with a high barometer. However, in compari-
son with radiation from the earth's surface that from the air is small. Coming
in contact with radiating and therefore cooler substances, air loses heat to them
by conduction and is thereby cooled. If the air is in motion, the cooled air and
the warmer air form a mixture which is constantly coming in contact with the
radiating substances bringing to them fresh supplies of heat. If, on the other
hand, the air is calm, the cooling of the radiating substances and therefore of the
adjacent air continues as long as conditions remain stable, frequently till the
sun rises.

Temperature Inversion. — Evidently the nocturnal cooling of the
air is largely dependent on the cooling of the earth's surface by radia-
tion. The cooling effect is, therefore, most marked near the surface,
but since on even the stillest night the air becomes somewhat mixed its
temperature may be affected for from 200 to 600 feet above the surface,
the effect becoming less with increasing height. ^^^ During the day the
temperature decreases at the normal adiabatic rate with increasing
distance from the earth. This relation is unchanged at night except in
so far as it is disturbed, as shown above, by radiation up to a height of
200 to 600 feet. There is, then, at night, first an increase in temperature
with distance above the earth, followed by the normal adiabatic decrease.
This phenomenon is known to meteorologists as the temperature inversion.

The extent of the temperature inversion is indicated by Table 53, showing the
averages of observations made throughout the year at varying heights above a
thermometer placed on grass and fully exposed to the sky, expressed in relation
to the readings of this thermometer. The steepness of the inversion varies from
night to night and it is more marked in some localities than in others but it

Table 53. — Average Temperatures at Different Heights Compared to that

IN Grass"!

Distance above Grass Increase (Degrees Fahrenheit)

1 inch 3

6 inches 6

1 foot 7

12 feet 8

50 feet 10

150 feet 12

necessarily exists whenever frost occurs. This temperature inversion causes
frost but it also makes possible the combatting of frosts by orchard heating as
shown later. Humphreys^^ points out another interesting relation of this in-
version to frost damage: " . . . it is obvious that the tops of open and sparsely
foliaged trees, especially if rather tall, often are less subject to frost and more
easily protected than are the lower limbs. On the other hand, when the tree is
low and its outer foliage sufficiently dense to produce a protecting canopy over
the under and inner branches, as is generally the case with orchard trees, the

340 FUNDAMENTALS OF FRUIT PRODUCTION

difference between the free radiation from the exposed fruit and the restricted
radiation from that which is covered may usually be sufficient, even when there
is a marked temperature inversion, to subject the former and not the latter to the
greatest danger from frost and freeze."

Radiation and Thermometer Readings. — The full importance of radia-
tion to the horticulturist needs emphasis. Lack of recognition of this
factor has diminished the value of much investigational work. A ther-
mometer exposed to the open air is radiating and receiving heat. During
a clear night the outgoing exceeds the incoming heat and the thermometer
registers a lower temperature than that of the air. Inside a shelter prac-
tically all the outgoing radiation heat is reflected to the thermometer
which consequently registers very close to the actual air temperature.
During May in cranberry marshes in Wisconsin there were found differ-
ences between sheltered and exposed thermometers over bare soil averaging
2.3°F. for all nights of record, including nights not clear. Occasionally
the exposed thermometers recorded as much as 5.7 and 6.4° lower than
the thermometers in shelters.*^ Inasmuch as these temperatures were
taken near the ground it is possible that they represented extreme con-
ditions and would be of direct importance only to the cranberry and
strawberry grower. Sheltered and unsheltered thermometers at a
height of 5.5 feet from the ground at Williamstown, Mass., showed dif-
ferences at the time of the minimum temperature averaging 1.6° and
a maximum difference of 4°F.^^^ It is evident, then, that the exposed and
sheltered, thermometers do not check and that the differences are not
constant.

Radiation and Plant Temperatures. — Plants as well as thermometers
lose heat by radiation, Seeley^^^ working with strawberries found con-
siderable difference between plant temperatures and air temperatures.

He reports in part on his results as follows: "The plant thermometer readings
were usually lower than the air temperature in the early morning, the minimum
usually being about 3 or 4°[F]. lower than the air, the difference being greater,
of course, when the weather was clear with but httle wind velocity. The plant
cooled off more rapidly than the air in the early evening so that at 7 p. m. it was
usually 3 or 4°[F.] lower in temperature than the surrounding air." At times
the temperature of the plant may fall to 8°C. below that of the surrounding air
and plants may be frozen stiff though the thermometer indicates one or two
degrees above zero (C.),i" and there are records showing that occasionally plants
are cooled by radiation to a temperature 12 to 15°F. below that of the surrounding
air."2 Tomato vines under apple trees sometimes escape frost when those
exposed to radiation are killed and the temperature on a lawn under a tree may
be 5° higher than in the open.i^'^

Observations, predictions and conclusions, then, must be made with
three standards in mind: the air temperature, the exposed thermometer
temperature and the plant temperature. Though the exposed ther-

THE OCCURRENCE OF FROST 341

mometer doubtless registers closer to the plant temperature than the
sheltered thermometer, it must be remembered that predictions
are based on and apply to sheltered thermometer readings. The dif-
ferences between the three temperatures maj^ not be great but they are at
times great enough to vitiate conclusions drawn from observations and
they may conceivably become at times great enough to have material
effects.

Dewpoint and Its Relation to Frost. — Air is commonly known to
contain more or less water vapor. Other things equal, the higher its
temperature the more vapor it can contain and conversely the lower its
temperature the less moisture it can hold. If, therefore, any sample of air
be cooled enough it will reach the point where it can no longer hold as
vapor all the moisture it contains and some of it is deposited. Obviously
the drier the air at a given temperature the farther must its temperature
fall before the moisture is condensed. The dewpoint, or temperature
at which condensation occurs, varies, then, with the absolute amount of
moisture present in the air.

As radiation proceeds from soil, vegetation and other substances
it has been shown that the temperature of the air in the immediate
neighborhood of these substances falls. In a calm this cooling frequently
proceeds to the point at which moisture is condensed; if this point is above
the freezing point dew is formed; if below, frost is formed directly. It
should be observed that frost is but an index of a low temperature and is
not of itself injurious. It should be observed further that radiating sub-
stances, particularly in a dry atmosphere, may cool the air several
degrees below the freezing point without any deposit of frost. This is
the black or dry frost. It is possible, too, for cooling to be extremely
localized so that frost forms when the free air temperature is several
degrees above freezing; frosts have occurred with a free air temperature of
40°F.

The condensation of moisture from the air sets free a certain amount
of heat and retards the further fall in temperature. To that extent dew
or even frost formation is beneficial as compared with low temperature
without moisture condensation. It was formerly assumed that the
liberation of heat from condensation would check any further tempera-
ture fall and that because of this the dewpoint as determined the previous
evening would forecast the minimum temperature of the night. Later
investigations have shown this view to be unwarranted.

Relation of Clouds and Wind to Frost Occurrence. — Evidently con-
ditions favoring loss of heat by radiation and a calm condition of the air
combine to produce dew or frost. Clouds reflect the heat lost by radiation
and even radiate some of their own heat so that the passage of a cloud may
for a short time raise the temperature a degree or two. Therefore cloudy
nights, though still, are not very likely to be frosty. A fair breeze does

342

FUNDAMENTALS OF FRUIT PRODUCTION

not prevent radiation but it mixes the air and prevents excessive cooling
of any small portion of it; therefore, windy nights are not likely to be
frosty. It is the nights which combine good radiation conditions with
still air that the fruit grower should watch when his trees are in bloom.

INFLUENCE OF LOCATION ON DANGER FROM FROST

It has been shown that in the northern hemisphere the blossoming of
fruit trees begins early in the south and, subject of course to minor dif-
ferences, moves northward at a rate of 4 or 5 days for each degree of lati-
tude, though somewhat more rapidly to the west of a given point than to
the east. If the date of the last killing frost in the spring moved north-
ward at the same rate, the calculation of the chances of a given fruit's
escaping frost at any location would be a simple matter. Unfortunately

Fig. 32. — The blossoming season of Wildgoose plum for 1898. (After Waugh'^^*)

conditions are much more complicated. Dates of blossoming and of
last frosts fluctuate from year to year. There are local variations
particularly in the occurrence and severity of frosts; these are considered
later. The present phase of the discussion is intended to point out that
certain regions are more subject, perhaps, to late frosts at critical times
for the fruit grower than other localities.

The Blossoming Season and Latitude. — Figure 32 shows the dates of
blossoming for the Wildgoose plum at various points in the United States
for 1898, a season that was, on the whole, rather earlier than the average. ^"^
Unfortunately not enough data are available for the construction of a
map showing average blossoming seasons for any particular variety of
fruit and minor fluctuations due to varying weather in different sections

THE OCCURRENCE OF FROST

343

might change in another season the hnes shown in the figure. However,
the figure shows in a general way tlie northward progress of the blossom-
ing season.

Unpublished figures compiled by Phillips give average data for several
kinds and varieties of fruits and show that the blossoming season moves
northward more rapidly in the Mississippi valley than along the Atlantic
seaboard (c/. Table 54). Philhps finds the rate for each degree of lati-
tude to be: along the Atlantic coast, 5.7 days; in the Mississippi valley,
4.8 days and for the Pacific region, 3.4 days. Somewhat similar relative
progress has been found for certain phases of insect life.^^ These differ-
ences between sections assume importance in connection with the dates
of the last killing frosts.

Table 54. — Avekage Date of P'ull Bloom for Several Fruits at Different

Latitudes

{After Phillips^'-^)

Latitude

Pacific

Mississippi

Atlantic

section

valley

section

35°

Mar. 11

Mar. 16

Mar. 19

36°

Mar. 14

Mar. 16

Mar. 24

38°

Mar. 19

Mar. 30

Apr. 10

40°

Mar. 18

Apr. 11

Apr. 19

41°

Mar. 22

Apr. 19

Apr. 26

42°
)aralIol,s

Mar. 27

Apr. 27

May 5

Average all ]

Mar. 19

Apr. 4

Apr. 11

Avei^age Date of Last Spring Frost and Latitude. — The average dates
of the last killing spring frosts are shown in Fig. 33. Though there is
a general northward recession, local conditions evidently complicate
this process in the extreme so that latitude alone is not a safe guide in
determining the date of the last frost. The date lines of last frosts are
obviously not parallel. As an example, the last-frost date line for
June 1 is worth consideration. Barely dipping below the forty-fifth
parallel in New England it leaves the United States to reappear in
Minnesota where it remains well above the forty-fifth parallel until it
leaves the states at the Canadian boundary. Entering the United
States again in Montana it moves southward to New Mexico, almost
to the thirty-fifth parallel, embracing a wide range of territory until it
leaves Idaho, reappearing again in Washington.

Average Dates and Frost Danger. — An average date, if the data on
which it is based be suflficient to give it validity, means that approximately
50 per cent, of the occurrences are prior to this date and 50 per cent.

344

FUNDAMENTALS OF FRUIT PRODUCTION

follow it. If the average date of blossoming and the average date of
the last frost for a given locality coincide there are possible four combi-
nations of events: (1) blossoming before the average and frost before
the average, a condition which may or may not be disastrous to fruit
at that point; (2) blossoming before the average and frost later than
the average, very likely to be a disastrous combination; (3) blossoming
after the average date and frost before the average date, a safe condition,
and (4) blossoming later than the average and frost after the average,
unsafe. In cases 1 and 4 the last frost may or may not precede the
blossoming, with chances balancing. Cases 2 and 3 balance each other.

Fig. 33. — Average dates of last killing frost in spring. (After ReecP^^)

It appears, therefore, that locations where the average blossoming date
and average last frost date coincide have an even chance of escaping
frost, a margin of safety that is rather small for growing of the fruit
in question.

Determining Frost Risks in Different Sections a7id Localities. — Averages,
of course, do not indicate the range of the figures that they represent.
The range of last frost dates may be considerable at one point and limited
at another, with the averages identical. Table 55 shows variations in
the last frost dates on record for several stations with identical average
date for this event. Such averages have only a limited significance for
the fruit grower, unless the fruit he grows generally blossoms consider-
ably later than the average date of the last frost.

The last column in Table 55 records standard deviations from the
average date of the last frost, Apr. 15 in each case. This standard
deviation means, taking Roseburg for example, that over a considerable

THE OCCURRENCE OF FROST 345

Table 55. — Spring Frost Data for Selected Stations^^"

Station

Average
date

Last in
9 to 10 years

Last in
1895 to 1914

Standard
deviation

Keokuk, Iowa

Cumberland Md . . .

Apr. 15
Apr. 15
Apr. 15
Apr. 15

Apr. 30
May 2
Apr. 28
Apr. 15
May 10

May 4
May 12
May 2
May 1
May 10

11.7
13.0

New Bedford, Mass

10.0
12.4

Roseburg, Ore

Apr. 15

19.7

period, in approximately half the years the last frost will occur between
20 days before Apr. 15 and 20 days after, or between Mar. 27 and May
5; in approximately one-fourth of these years it will occur before Mar. 27
and in approximately one-fourth of the years it will occur after May 5.
The record shows that the latest date of last frost for this station is
May 10. Figure 34 shows the rather considerable range of standard
deviations in dates of last frosts at various points in the United States.

Fig. 34. — Standard de%'iations of dates of last killing frosts in spring. {After Reed^^^)

Of greater immediate value to the fruit grower is Fig. 35, showing
dates " when the chance of killing frost falls to 1 in 10. "^^^ If the average
date of blossoming at a given point is identical with the date of the 1:10
chance for that point the probability of damage is slight, being in fact
3^ X Ko = Ho, or one chance in 20. This may happen very frequently
in cane fruits and grapes, though in most cases the average date for
orchard fruits would precede that of the 1:10 chance. Comparison of
such average blossoming dates as are available and of real validity shows

346

FUNDAMENTALS OF FRUIT PRODUCTION

that very few orchard fruits have less than one chance in 10 of encoun-
tering frost.

The data here presented arc introduced as suggestive rather than
for their absohite value. As pointed out elsewhere, a frost recorded as
"killing," though damaging to tender vegetation, may do little or no
damage to fruit blossoms; similar data based on the last occurrence of
30° or 29°F. would be of more direct value to the fruit grower. Neverthe-
less the general liability of certain regions to frosts damaging to fruits
holds true, whatever criterion be adopted, and though it would be hazard-
ous to apply the present data unreservedly to any one point they serve

Fig. 35. — Computed dates when the chance of killing frost falls to 1 in 10. After these
dates killing frost will occur only 10 years in a century. {After Reed^^^)

adequately for comparison between different points. Arranged on a
slightly different basis and in conjunction with accurate blossoming
charts, which are not available, they would have even greater value.
At present only generalizations are possible. The tendency of blossoming
to advance more rapidly in the central than in the Atlantic states and the
irregularity in the recession of last frosts, with a general tendency toward
faster recession on the Atlantic seaboard, makes a given fruit more
liable to frost damage in the Mississippi valley region than on the
Atlantic coast, if local variations do not intervene.

INFLUENCE OF SITE ON MINIMUM TEMPERATURES

The air in the neighborhood of radiating surfaces has been shown to be
cooled by conduction and the air temperature on a still night to increase
with distance from the surface. As the air in contact with radiating

THE OCCURRENCE OF FROST 347

surfaces cools it becomes more dense and tends to sink. It is then
replaced by air somewhat warmer, probably for the most part flowing in
from the same level, which air in turn cools and sinks. If the supply of
relatively warm air be extensive enough and warm enough, the radiating
surfaces may be kept from reaching the freezing point. This frequently
happens on hillsides where the coolest air is continuously being pushed
downward by air nearly as cool and warmer air is flowing in from the side.
So much cool air may accumulate, however, that it fills a depression com-
pletely and raises the level of warm air. The warm air may be raised
so high above a given object that, as radiation proceeds, the replacing
air has little heat to give up. It therefore fails to warm the surface
sufficiently to prevent freezing. ^^2 Little replacement can be expected
by warm au from above since it is lighter.

However, other things being equal, the wider a valley the greater
its area in proportion to its circumference; consequently the reservoir
of free warmer air at any level is greater in proportion to the radiating
shorehne at that level. The higher levels, in a given valley, therefore,
in addition to having better "drainage facilities" for removal of cold
air have larger reservoirs of warm air on which they can draw. For
the same reasons a slight elevation above a wide valley may be con-
siderably freer from frost than a higher elevation above a more restricted
valley.

The term "air drainage," used to signify the resemblance of the
flow of cold air to the flow of water, is more or less unscientific and
inexact. ^^^ Nevertheless it is a convenient term; it suffices for practical
purposes and doubtless will continue in use. In many cases there is
an actual flow of air, closely comparable to the flow of water. This
flow of air is frequently the salvation of orchards in narrow valleys
which otherwise would fill quickly with cold air.

In the discussion of Sites the statement is made that air drainage
insuring as much freedom from spring frosts as possible is one of the
most important considerations in picking the site for an orchard. It
should be stated here conversely that the best method of insuring against
frost and against the continual tax of frost-fighting is the proper selec-
tion of a site. There are certain sections where to secure proper soil
or plentiful moisture it becomes necessary for the prospective fruit
grower to locate on low sites that are subject to frost. He should recog-
nize clearly that he is exchanging relative immunity from frost for other
advantages; the exchange may be profitable if the frosts are not too
numerous and too severe. Over a large part of the country, however,
a considerable latitude in choice is available and intelligent discrimi-
nation in the choice of site may very easily make the difference between
considerable profit and heavy loss. The grower who is forced to protect
his orchard may make a profit in spite of his heavy overhead expense

348

FUNDAMENTALS OF FRUIT PRODUCTION

and annual tax; the grower whose location is such that he is comparatively
immune from spring frosts is more likely to be commercially successful.
Sometimes the line that divides desirable and undesirable locations is very
finely drawn. Table 56 shows minimum temperatures during the blossoming
season at two locations not far apart and with only 25 feet difference in elevation.
The dissimilarities in average minima are at once obvious.

Table 56. — Minimum Temperatures at State College, New Mexico

(After Garcia''^)

(Station A 25 feet higher than Station B)

March

1

April

Day

1912

1913

1912

1913

A B

A

B

A

B

A

B

1

32.0

24.5

45.0

42.0

2

38.0

26.0

40.0

35.0

3

38.0

33.0

40.0

36.5

4

49.0

46.5

34.0

31.5

5

44.0

45.0

35.0

31.5

6

39.0

34,0

51.0

40.0

7

39.0

36.0

38.0

36.0

8

40.0

37.5

36.0

33.5

9

37,0

34.5

33.0

30.5

10

52.0

45.0

38.0

36.5

11

39.0

34.0

36.0

35.5

12

41.0

40.0

29.0

25.5

13

36.0

33.0

30.0

27.0

14

32.0

29.0

31.0

28.0

15

39.0

34.0

39.0

35.0

16

1

8.0

13.0

40.0

35.5

38.0

35.0

17

2

0.0

16.5

38.0

32.5

44.0

40.0

18

2

5.0

20.5

39.0

33.0

49.0

44.0

19

4

1.0

35.0

40.0

34.0

39,0

35.0

20

4

2.0

38.5

49.0

40.0

59.0

45.0

21

3

0.0

27.0

40.0

35.0

46.0

44.0

22

3

6.0

31.0

31.0

29.0

53.0

43.5

23

3

2.0

26.5

38.0

33.0

43.0

42.0

24 3

0.0 25

.0 1

9.0

17.0

51.0

45.0

31.0

27,0

25 3

6.0 33

.0 2

1.0

19.0

43.0

39.0

32.0

29.0

26 4

5.0 39

.0 3

1.0

26.5

34.0

28.5

36.0

33.0

27 3

5.0 32

.5 3

5.0

31.5

49.0

40.0

39.0

35.0

28 3

5.0 29

.0

44.0

39.0

40.0

36.0

29 3

4.0 29

.0

40.0

35.5

44.0

40.0

30 3

3.0 26

.5

48.0

39.0

44.0

40.0

31 4

1.0 30

.0

Average. . 3

6.1 30

.5 2

9.1

25.2

40.6

35.7

39.7

35.7

THE OCCURRENCE OF FROST 349

More important, however, is the consideration that Station B during the
time covered by these data registered temperatures below freezing 28 times as
compared with 13 for Station A; Station B registered temperatures 28°F. or
less 14 times while this point was reached at Station A, only five times. Ana-
lyzing the figures in another way: in the spring of 1912 Station B had a minimum
of practically 28°F. as late as Apr. 26 though .Station A did not reach this figure
during the season. In 1913 the last minimum of 28°F. or less for Station A
occurred on Mar. 26 and for Station B the date was Apr. 14.

Similar variations were found in Nevada between two points 190 feet apart
and differing in elevation by 13.5 feet.*^ The average April and May minimum
for the higher station was 42.7°F.; for the lower jt was 39.5.° On selected single
nights paired observations were 29-22, 34-31, 32-24, 39-31, 37-30. The diver-
sity in the amount of fruit grown in 2 years on sites such as these, other
things being equal, must necessarily be great and the difference in expense of
orchard heating in the two cases would be well worth considering.

In some cases this effect is said to be somewhat neutralized by the
increased earliness of higher elevations. As a rule vegetation is later at
high altitudes, but this condition is reversed frequently between points
differing in altitude only a few hundred feet. An interval of 2 weeks
between the first blossoming dates has been reported at points in Utah
2 miles apart and with 200 feet difference in elevation. ^ It is not, how-
ever, clear that this was due wholly to the elevation since slopes and
condition of soil and of trees were not stated and the variations reported
are certainly much more marked than is ordinarily the case, making 1
day's difference for each 14 feet in elevation. Were the air constantly
still, during the whole season up to blossoming, the moderately high
elevations might indeed accumulate enough excess of heat to make con-
siderable difference but in nature this condition obtains only during a
very small portion of the time and such differences as do occur generally
may be attributed to other effects.

The steepness of slope necessary to effective freedom from frost varies
with the local topography. Young^i^ states: "From observations in
the Pomona Valley, California, it appears that there is little if any advan-
tage to be gained by locating on orchard in the upper portion of a long
uniform slope of 150 feet or less to the mile. However, in even slight
depressions of whatever shape or direction on this slope the frost hazard
is likely to be considerably greater."

MINOR FACTORS AFFECTING TEMPERATURE
Of interest chiefly to growers of strawberries and cranberries are
certain differences in narrowly restricted limits, differences usually small
but frequently important. Included among these are those due to
elevation, to the character of the soil covering and to the state of the soil.
Minor Differences in Elevation. — Observations on three sets of ther-
mometers at several points in Williamstown, Mass., with the upper

350

FUNDAMENTALS OF FRUIT PRODUCTION

thermometers exposed at a height of 5.5 feet, the lower at 0.5 feet, show
differences tabulated in Table 57, from which it appears that a strawberry
plant may be exposed to considerably lower temperatures on a frosty
night than the trees above it or than the thermometer in the ordinary
shelter. Milham points out that the differences are greatest at the
time of the minimum temperature and at the coldest station, in other
words when conditions for frost are most favorable. Strawberry growers
should bear this in mind in interpreting for their own use forecasts issued
by the Weather Bureau.

Table 57. — Temperature Differences with Height"''
(Degrees Fahrenheit)

Station 8
(8 p.m.)

station 7 Station 1 (St-,f°"J, Station 7

Average difference .
Largest difference.

0.5
2.0

1.5
4.0

2.1

5.0

0.5
2.0

2.0
4.0

2.9
5.0

On the other hand Cox^^ found temperatures at 5 inches above the
soil lower than those at the surface, particularly on nights with good
radiation conditions.

"The average depression of temperature," he writes, "at the 5-inch height
below that at the surface for the season of 1907 (May to October inclusive) was
1°[F.]. The average depression on clear cool nights probably reached 4°. There
were several instances of differences exceeding 6°." Cox evidently was not
entirely satisfied with the possible explanations he advanced for this difference
though they doubtless explain it in part. He states, "In a marsh grasses and
uprights from the vines interfere slightly with radiation from the thermometers
placed on the surface and it is probable that a thermometer or leaf exposed at an
elevation above the surface loses its heat more rapidly by radiation than if it
rested upon the surface because the upper one is not shielded in any way and
while the radiation is going on from the lower one, at the same time heat is being
conducted to it from the ground beneath. A thermometer resting upon the
surface of the bog becomes a part of the soil or vegetation upon which it rests,
as it were, and is benefited by the free conduction of heat to it from the ground,
while the conduction to and through the air is very slight in comparison ; because
of these differences in radiation and conduction, the surface thermometer usually
registers a higher temperature than the instrument a few inches above. For
the same reason, the temperature of the vegetation at the surface and 5 inches
above would vary as these temperatures have varied, especially when the surface
vegetation is shielded above. It is a matter of common knowledge that in the
bogs the cranberries growing at the tops of the uprights a few inches above the
ground are often damaged by frost while those lying on or near the ground escape
injury."

Cox reports also two series of observations on temperatures at various
heights up to 36 inches above the surface. On the bog the 5-inch height had

THE OCCURRENCE OF FROST

351

the lowest average minimum temperature, the surface averaging 1.7° higher than
the 5-inch level and 1.4° lower than the 36-inch level. In a garden on upland
the differences were less. Cox summarizes his observations on this point as
follows: "The temperature at 2.5 inches averaged lowest, 44.5°[F.], instead of at
5 inches, as on the bog, but the difference was very slight between these two
elevations — 0.1°. The surface thermometer averaged highest, 45.5° but there
was only 1° difference on an average between the two extremes while the average
surface reading was 0.6° higher than at 36 inches. The average for the entire
season fairly represents the conditions prevailing each month, the highest in
each case occurring at the surface and the lowest at 2.5 inches." Table 58,
compiled from Cox's report, shows minima for nights selected because of the
low temperatures and indicates no substantial variation from his averages.^®

Table 58.

-Minimum Temperatures in Open Over Sandy Loam
(Degrees Fahrenheit)

Date

Sur-

2.5

5

7.5

10

12

15

36

(1907)

face

inches

inches

inches

inches

inches

inches

inches

May 20

24.9

23.7

23.8

24.0

24.8

24.9

25.0

25.9

May 21

24.9

22.9

23.0

23.1

23.1

23.1

23.0

23.8

June 6

34.7

31.4

31.5

31.7

31.7

31.7

31.2

31.4

Sept. 22

28.0

27.8

27.8

28.1

28.3

28.0

28.2

28.6

Sept. 30

25 . 0

24.6

24.7

25.0

25.2

25.1

25.2

25.4

It is evident that these differences are not constant. Some light is
thrown on the effect of radiation by data compiled from Greenwich
observations showing that a thermometer on grass fully exposed to the
sk}^ registered lower than a thermometer suspended 4 feet from the
ground :'^^

Degrees
fahrenheit

On cloudless nights 9.3

Half cloudy 7.3

Principally cloudy 6.8

Entirely cloudy 3.4

Influence of Soil. — Reference is made again to Cox's work for data
concerning the minimum temperatures over two different soils. Table
59 shows minima for selected nights with the average for the month.
The difference, striking at the surface, becomes very slight at 3 feet. The
differences up to 5 inches are, however, of no little significance to the
strawberry grower. They are to be regarded as due to character of the
soils, since other conditions were uniform. Incidentally it may be stated
that Cox considers it possible for identical atmospheric conditions to
cause a light frost in the spring and not in the fall because of the difference
in soil temperatures at the two seasons. To the extent that a high day
temperature indicates considerable heat furnished the soil, it diminishes

23

352

FUNDAMENTALS OF FRUIT PRODUCTION

Table

59. — Minimum

Temperatures in Open over Two Soils''^

(September, 1906)

Day of month

Over peat

Over sand

Differences between peat
and sand

Surface

5
inches

36
inches

Surface

5
inches

36
inches

Surface

5
inches

36

inches

5

38.4

33.1

34.8

45.0

35.9

35.9

-6.6

-2.8

-1.1

14

35.6

33.0

34.7

43.9

35.0

35.1

-8.3

-2.0

-0.4

24

35.7

32.5

33.4

41.0

34.0

33.5

-5.3

-1.5

-0. 1

27

33.9

31.0

30.4

40.3

30.8

30.3

-6.4

+ 0.2

+ 0.1

28

39.8

31.9

35.7

43.0

35.7

36.1

-3.2

-3.8

-0.4

30

34.0

28.8

31.4

39.6

31.0

33.0

-5.6

-2.2

-1.6

Monthly mean..

50.6

47.0

48.7

53.6

48.6

49.0

-3.0

-1.6

-0.3

the probability of frost the following morning. Furthermore Cox states,
"It is practically impossible for frost to occur in the bogs on the first cool
night following a warm spell, but it is likely, if conditions are favorable,
on the second night after the soil has become cold."

The difference in temperature over the two soils is due probably to
their difference in radiating and conducting powers. Peat absorbs and
radiates heat readily but of course the heat lost by radiation warms the
air exceedingly little; peat is a poor conductor and cannot warm the air
greatly by conduction. The sand, though not as good an absorber of
heat is a better conductor and warms the air above it at night.

Influence of Soil Covering, — A thick mat of vegetation covering the
soil prevents much heating during sunshine. At night, though it pre-
vents conduction of heat from the soil, it radiates heat and thus tends to
lower the air temperature further. It is not strange therefore that lower
temperatures are found over vegetation than over bare ground. Table

Table 60. — Temperatures Over Sod and Over Bare Ground

(After Seeley^'"')

(Degrees Fahrenheit)

p.m.

a.m.

Loss

Surface, bare piround . . .

45.0
43.0
46.2
43.0

27.3
23.9
30.1
23.9

,7 7

Surface, sod

19.1

Half inch below surface, bare ground

16.1

11.7

60, giving the means of observations on 18 morning at Peoria, III., shows
the increase in difference of surface temperatures between sod and bare
ground from afternoon to morning. The sod surface is 2° cooler in the

THE OCCURRENCE OF FROST

353

afternoon and 3.4° cooler in the morning. Below the surface, however,
the sod loses less.

In minimum temperatures 5 inches above the surface on cranberry-
bogs considerable difference, according to the density of the vegetation,
is reported by Cox,'*^ from observations made in September, 1906. Table
61, which records his observations for the coldest nights, shows the magni-
tude of these variations attributable to the difference in the amount of
vegetation and the effect it has on soil temperature. Similar inequalities
may be expected in very weedy and dense strawberry beds. More frost
damage has been observed in weed-infested German vineyards than in
those kept clean. '^^

Table 61. — Minimum Temperatures with Thick and with Thin Vegetation

(After Cox''')
(Degrees Fahrenheit)

Day of month

Thinly vined

Thickly vined

Difference

5

33.1

28.3

-4.8

14

33.0

28.8

-4.2

24

32.5

28.9

-3.6

27

31.0

24.4

-6.6

28

31.9

28.0

-3.9

30

28.8

23.0

-5.8

Monthly mean

47.0

43.6

-3.4

The effect of mulching, a common practice in strawberry growing,
should be mentioned at this point. As a winter protection the value
of a mulch is indubitable. In early spring a mulch tends to retard
blossoming, an effect which may or may not be desirable. Once the
plants are in blossom, however, a mulch may invite frost damage.

Lazenby'O' reported observations to this effect: "To compare temperatures
over mulched and unmulched ground I took 16 observations with a self-registering
minimum thermometer daily between May 17 and June 1 of last year. The
average minimum over straw was 43.2°; over bare ground 46.4.° The greatest
difference was 7°. This year the average minimum over straw was 32.3°; over
bare ground 34° with a maximum difference of 3.5°."

This effect is due probably to the exclusion of sunshine from the
soil during the day and to increased radiation at night. If the mulch
is used to cover the plants during frost, its effect is, of course, totally
different.

Influence of Soil Moisture. — Observations on surface temperatures
in wet and in dry sanded bogs at Berlin, Wis., in 1906, indicated a
consistent and at times considerable, difference. Table 62, compiled

354

FUNDAMENTALS OF FRUIT PRODUCTION

Table 62. — Surface Minimum Temperatures on Dry and on Wet Sanded Bogs
{Adapted from Cox*^)
(Degrees Fahrenheit)

Date

ry sand

Wet sand

Difference

43.9

37.7

-6.2

41.0

37.4

-3.6

40.3

33.1

-7.2

43.0

38.0

-5.0

39.6

32.3

-7.3

35.8

27.3

-8.5

53.6

51.2

-2.4

Sept. 14

Sept. 24

Sept. 27

Sept. 28

Sept. 30

Oct. 1

September mean

by the selection of the coldest nights, shows that at the very time when
these differences are most important they are greatest. It might be
argued that the wet sand was coldest because it had given up more
heat; however it is stated that on Oct. 1 cranberries in this bog were
frozen, except in the dry sanded section. The lower minimum on the
wet sand is attributed to the heat lost in evaporation at the surface.
It should be remarked that irrigation with relatively warm water
at the time of frost apparently has proved of considerable value occa-
sionally but irrigation that merely wets the soil and keeps it cold is
probably injurious. An experimental investigation in Wisconsin showed
very little difference in temperature over irrigated and over unirrigated
blocks.

King,io2 commenting on the results, stated: "Not only did frost form after
the water was brought to the areas but some of the rape leaves became stiff
with streams of water flowing both sides of the row. It is true, however, that a
very perceptible difference could be noted in the degree of stiffness which foliage
took on above and close to the water, and that which was more distant. For
close to the water the leaves did not become so rigid as to break in the hand while
at a distance from the water they did.

"It is quite possible that were broad areas irrigated at such times the pro-
tection would be more marked, but it does not look very hopeful for the protec-
tion against night frosts by this method, especially where the temperature falls
3 or 4° below freezing."

It seems evident from the data above that evaporation does not
interfere with radiation sufficiently to offset its cooling effect and that
unless the water actually imparts heat it is deleterious. A thoroughly
saturated soil is, however, likely to retard frost formation.

Cox"^ states: "The explanation is found in the high specific heat of water.
A certain quantity of heat lost during the night time from relatively dry ground
and its vegetable cover cools the exposed portions of these poor heat-conducting

THE OCCURRENCE OF FROST

355

objects to a very low temperature. An equal loss of heat from the same sub-
stances when they are loaded with moisture results in only a small lowering of the
temperature not only because the water must now be cooled in addition to the
ground and vegetation but, as we know, water requires the removal of consider-
able heat to cool it sUghtly. The radiation losses from the saturated surfaces
may also be less than from the dry surfaces."

Evidently looseness in application of terms "wet" and "dry" has
led to some apparently conflicting results. Petit^*^ records observations
that at first seem contradictory to those of Cox, since they indicate
higher temperatures over the wetter soil (c/. Tables, 63 and 64). Petit

Table 63. — Temperatures in Moist and Dry Soils

{After Petit'^'>)
(Degrees Centigrade)

Date and time

Saturated soil

Apr. 23, 4.00 p.m
Apr. 23, 7.15 p.m
Apr. 24, 5.20 p.m

21.6
16.1
6.5

states that the chief cooling influence in wet soil, evaporation, is inactive
at night, that the moist soil conducts heat more rapidly than the dry
and therefore can receive more heat from below; he evidently considers
that these factors offset the greater radiation he ascribes to wet soil and
the lower heat storage during the day. Curiously enough he finds
that dew forms earlier and is more abundant on the moist soil. It is
possible, however, that Cox and Petit worked with soils of different
texture and moisture content and that their results are not necessarily
conflicting.

Table 64. — Surface Temperatures Over Wet and Over Dry Soils

(After Petit^'^)
(Degrees Centigrade)

Date

Time

Not watered

4.30 p.m.

18.2

6.00 p.m.

14.0

10.00 p.m.

6.9

5.00 a.m.

2.3

5.15 p.m.

10.6

9.25 p.m.

5.6

5.55 a.m.

4.0

Watered

Sept. 23
Sept. 23
Sept. 23
Sept. 24
Sept. 28
Sept. 28
Sept. 29

15.6
12.4
7.3
3.2
10.6
6.9
5.2

Efifect of Cultivation. — In a series of- observations on the minimum
temperatures over cultivated and uncultivated soils at Peoria, 111., it

356

FUNDAMENTALS OF FRUIT PRODUCTION

was found that cultivation apparently increased the temperature about
2°.^^^ Cox states: "It is as important to cultivate as it is to practice
drainage," but adds that "it is impossible to determine absolutely the
advantage in exact degrees gained by cultivation, draining or sanding. "
It is evident that his statement refers to any attempt to make the
observed differences fit all cases.

Cultivation is said by Petit to increase the loss from the surface of
the soil b}^ radiation, diminishing heat conduction from below; tamping
the soil is stated to lessen this danger. It should be observed that the
temperatures recorded are those of the surface and not of the air above.

Table 65. — Temperatures at Surface of Cultivated and Packed Soils

{After PetiP^^)

(Degrees Centigrade)

Date and time

Packed

Stirred

Lumps

July 15, 1898—4 30 p.m

16.8

37.9
17.8
14.2

37.4

July 15, 1898— 8. 15 p.m

15.8

Aug. 4, 1898 — 8.00 p.m

12.6

Increased surface of the loosened soil would tend to increase the loss
of heat by conduction and might easily raise the temperature of the air
immediately above it, though the surface itself be cooled.

Significance — Particularly in Small Fruit Culture. — A saving of
2° or 3° may or may not be an important matter according to circum-
stances and consequently any one of the factors affecting temperature
may in itself be important. However, it is frequently the case that
several of them are operative at once and their combined effect is likely
to be considerable, particularly on nights when these differences are
most important.

Cox expresses this aptly: "While there is an average difference of 3.4° . . .
between the minimum thermometers in the thinly vined and the heavily vined
sections, a difference of 2.4° . . . between the minimum thermometers on
peat and sanded bogs, both thinly vined, and a difference of 2.2° between the
surface and 5 inches, it is obvious why an average difference of 10° . . . can
exist between a minimum thermometer exposed at the most favorable location
as far as drainage and sanding and cultivating are concerned and another in a
most unfavorable location, an unsanded peat section with a very dense growth
of vegetation, and poor drainage. [The greatest difference observed by Cox
was 17.1°F.] It is not strange therefore that in a bog where there is a variation
in the conditions of sanding, draining, and cultivation, the range in minimum
temperatures is considerable, and that a portion of a bog is seriously injured by
frost while another portion completely escapes. "*«

These inequalities are extremely localized; probably none of them is

THE OCCURRENCE OF FROST 357

effective at the height of trees and they are of little importance to the
orchardist. They are, however, of extreme importance to the grower of
small fruits. His is the most difficult problem in heating his fruit planta-
tion but, on the other hand, he can do more than any other fruit grower to
prevent frost. Generally he has the same freedom as the orchardist in
the selection of site; in addition he can take advantage of minor localized
variations. In aiming to profit by them he is following cultural prac-
tices that are beneficial to his fruit plants in other ways.

Summary. — Spring frost is important in setting geographic limits to
the commercial culture of fruits of some kinds and in determining the
regularity of crops, yields and profits in practically all deciduous fruit
growing sections. Frost formation depends to a considerable extent on
the radiation of heat by exposed surfaces during the night. Because of
radiation on still clear nights, temperatures close to the earth are lower
than those at somewhat greater elevations, giving rise to the condition
known as temperature inversion. On account of radiation the real tem-
peratures of plants may be several degrees lower than those registered by
sheltered thermometers. When the dewpoint is very low, freezing will
occur without frost formation. Clouds and wind both protect against
frost, the former by reducing the total effect of radiation, the latter by
mixing warm air with that which has been cooled. In a general way
both the blossoming dates of fruits and the average dates of the last
killing frosts range later with each increase in latitude, though the prog-
ress of the two is not always parallel. Study of Weather Bureau records
showing average last dates of killing frosts, together with the standard
deviations therefrom, will make possible an accurate determination of
frost danger beyond any particular date for any given locality, though not
for any site. Air drainage secured by suitable elevation is of considerable
importance in determining danger from frost in particular sites. Minor
differences in temperature within narrow limits in space are occasioned by
minor differences in elevation, amount of soil moisture, character of the
soil covering, type of soil and system of cultivation. These are seldom
important in influencing frost injury to tree fruits; however, they may be
of considerable importance in small fruit culture.

CHAPTER XX

PROTECTION AGAINST FROST

The fruit grower should have, not only knowledge of the conditions
under which frost occurs, but information as to the exact danger points for
his various fruits and as to the value of different protective measures that
may be at his disposal.

CRITICAL TEMPERATURES

If heating is to be done it should be delayed until the temperature is
near the critical point to save expense and exhaustion of the fuel in the
heaters before morning. If it is known that the blossoms of one variety
or of one species are more tender than others protective effort may be
concentrated more or less on the tender plants. At times it has been
assumed arbitrarily that a certain temperature is fatal and that because
certain orchards had been exposed to that temperature they would bear
no crop. Accordingly the calyx spray was omitted, to save labor and
expense, only to have it appear later that a fair crop had survived the freeze
but had become thoroughly infested by codling moth, scab and other
pests. If, then, there is a certain temperature that is universally fatal
to the blossoms of all fruits or of one kind of fruit it should be known.

A compilation of temperatures stated as dangerous to blossoms of
various fruits is reproduced here as Table 66.

The considerable difference in the damaging points as stated by these
various writers is significant and it seems probable that the range of
killing temperatures is as great if not greater than indicated by the table;
West and Edlefsen state that there is sometimes a spread of 5°''. The
variations in temperatures between sheltered thermometers, exposed
thermometers and plant tissues make field observations of only limited
value. Variations in radiation conditions make the correction of ther-
mometer readings to plant temperatures uncertain. Furthermore,
different blossoms must be exposed to radiation in varying degrees because
of diversity in their positions in the cluster and on the branch.

Assuming, however, that temperatures can be measured accurately,
as doubtless has been done in closely controlled work such as that of
Chandler and of West and Edlefsen, the final result is still a complex
involving several factors whose separate measurement is difficult.
Several blossoms, alike in development, will show differences in their

35S

PROTECTION AGAINST FROST

359

Table 66. — A List of "Danger Points" as Given by Different Authors

Degrees Fahrenheit

{After West and Edlefsen,-'^'' with additions)

Closed but

Fruits

showing
color

In blossom

Setting

Authority

Apples

27

29

30

1

27

29

30

2

27

29

30

3

25

28

28

4

25

28

28

5

25

28

29

6

Peaches

20

25

28

1

29

30

30

3

29

30

30

2

22

28

28

4

25

27

27

5

25

26

28

6

Cherries

22

28

29

1

29

30

30

2

22

28

28

4

25

28

30

6

Pears

27

29

29

1

29

29

29

2

28

29

29

3

25

28

28

4

25

28

30

6

Plums

30

31

31

1

30

30

31

2

30

31

31

3

22

28

28

4

25

28

30

6

Apricots

30

31

32

2

30

31

32

3

22

28

28

4

25

27

30

6

Prunes

30

31

31

2

30

31

31

3

28

29

30

6

Almonds

20

27

30

7

Grapes

30

31

31

7

Authorities: (1) Wilson, W. M.=
(4) Paddock and Whipple. "^ (5)
(7) Young, Floyd D.^is

" (2) O'Gara, P. J.i
W. H. Chandler. =8

1 (3) W. H. Hainmon. ^1
(6) Garcia and Rigney.^^

resistance to the same freezing; different trees of the same variety will
set materially different crops; finally, varieties are unequally susceptible.
It is impossible at present to state to what extent fruit blossoms are

360 FUNDAMENTALS OF FRUIT PRODUCTION

or can be supercooled, at what temperature ice formation occurs or at
what temperature damage results. General sudden freezing following
supercooling is considered in itself injurious. ^^^ To what extent this
applies to fruit blossoms cannot be stated at present. Indeed it is possible
that under natural conditions supercooling as ordinarily understood
does not occur in fruit blossoms. The influence of capillarity on freezing
in these tissues cannot be stated now. It is, however, safe to conclude
that critical temperatures as determined by laboratory methods would
be somewhat lower than would appear from field observations with ordi-
nary thermometer exposures, because of the differences between air
temperatures and plant temperatures under the radiation conditions
accompanying most frosts. For the same reason precise determination
of killing points would not be of direct application in the orchard. Paren-
thetically it may be remarked that the insufficient recognition of radia-
tion effects on plant tissues in horticultural investigation may account
for many of the conflicting results secured.

However, studies in artificial freezing are interesting, though the
high degree of humidity that accompanies them is not invariably present
in nature. This high humidity may serve conceivably to inoculate
the plants with freezing nuclei and cause freezing at higher temperature
than would be required in a drier atmosphere. Despite limitations,
however, the tests by artificial freezing possess considerable significance.
West and Edlefsen have reported some rather extended investigations
of this sort.

In part, they summarize their results as follows: "Ben Davis apple buds in
full bloom have experienced temperatures of 25, 26, and 27°F. without injury,
but 28° usually killed about one-fifth. Twenty-nine degrees or above are safe
temperatures. Twenty-five degrees kills about one-half and 22° about nine-
tenths. On several occasions, however, apples matured on branches that experi-
enced 20° when the buds were in full bloom.

"With Elberta peach buds in full bloom, 29°F. or above are the safe tem-
peratures, because even though occasionally 26, 27, and 28° do no damage, yet
on most occasions 28° will kill from one-fourth to one-half. Twenty-six degrees
kills about one-half of them and 22° about nine-tenths. Temperatures as low
as 18° have failed to kill all of them.

"With sweet cherry buds in full bloom, 30°F. is the safe temperature; 25, 26,
27, 28° have done no damage, but 29° usually kills about one-fifth. Twenty-
five degrees usually kills about one-half, and when the buds were showing color
22° killed only two-fifths of the buds.

"Sour cherries are hardier than the sweet varieties. When the buds were
showing color 23°F. did not harm them, and when they were in full bloom 26°
killed about one-fifth and 22° only two-fifths of them.

"With apricots, 29°F. is the safe temperature; 26 and 27° killed about one-
fifth and 22° killed one-half. . . .

"The foregoing figures refer to the buds when in full bloom. Starting from

PROTECTION AGAINST FROST

361

this stage, the earlier the stage of development the hardier the buds are; and in
general, when the fruit is setting the injury is from 5 to 10 per cent, more than
when they are in full bloom.

"Sour cherries are the hardiest, and then follow in order apples, peaches,
apricots, and sweet cherries. "2°'*

Field observations sometimes indicate that open peach blossoms are
more resistant than apple blossoms at the same stage.

At Different Stages of Blossom Development. — Table 66 indicates
that the difference in tenderness of blossoms at various stages in their
development is well recognized. Table 67, arranged from a similar table
by West and Edlefsen, shows experimental data that are, in general,
confirmatory.

Table 67.— Hardiness of Jonathan Apple Buds
ficial cooling^o^

TO Various Degrees of Arti-

Date

Stage of
blossom

Duration of
freezing,
miimtes

Temperature,

degrees

Fahrenheit

Percentage
damaged

April 25

Full bloom
Full bloom
Full bloom
Full bloom
Fruit setting
Fruit setting
Fruit setting
Fruit setting
Fruit setting
Fruit setting
F'ruit setting

10

5

45

5

25

5

5

20

30

15

5

24.5
26.5
27.5
28.5
28.0
25.5
26.5
26.5
27.5
27.5
27.5

52 0

Apra29

36 0

April 25

54 0

4pril 29

0 0

May 9

46 0

May 9

Mav 9

93.0
40 0

May 10

May 10

May 9

May 9

22.5
21.0
59.0
62.0

It should be remembered that not all the blossoms on a tree are going
through the same stage of development at any given time and the amount
of damage done by a light to moderate frost will depend to a considerable
extent on the number of opened and of unopened buds. This is shown
in Table 68.

Strawberries that are half grown, however, appear able to stand
more freezing than the blossoms.

Coit" reports on this fruit: "Blossoms are injured by temperatures below
30° at the ground but young fruit endures temperatures as low as 24° at the
ground and 28° in a government shelter without injury and green fruit protected
by foliage endures temperatures several degrees below this. Ripening fruit
endures less cold, being injured by temperatures below 25° at the ground. A
good picking was taken from Excelsior plants Dec. 24, 1903, although the mercury
had fallen at the ground to 22 to 26° during 10 nights of the month. Some

362

FUNDAMENTALS OF FRUIT PRODUCTION

Table 68. — Percentage of Open and of Unopened Blossoms Killed by the

Freeze of Apr. 4, 1908 (24°F.)

(After Chandler^^)

Variety

Buds open

Buds unopened

Oldmixon Free

Oldmixon Free

Elberta

69.9
25.4
24.4
51.1

36.6

15.3

7.1

Elberta

11

green fruit well protected with foliage survived January, 1904, the mercury falling
to 14 at the ground one night, 16 one night, 17 two nights, 18 one night and 19
three nights; and a few berries ripened during the early part of the month."

Varietal Differences. — Varietal differences in hardiness are sometimes
apparent in apples.

In one case in Missouri the greatest injury in Jonathan seemed to be in the
stamens while in Oldenburg the pistil was damaged. It may be suggested that
this type of injury might have some interesting bearing on the pollination of
mixed orchards.

In Iowa many of the Russian varieties were hardier in blossom than standard
varieties in better locations. Similarly among the native plums a freeze that
killed the ovaries of several varieties such as Rollingstone which, incidentally,
is very resistant to winter cold, injured only a part of the blossoms of De Soto,
Cheney and other varieties. These in turn were surpassed in resistance by the
Russian plums which were said to have been "less exposed than our native
plums. "28 The Bosc pear has been reported as more tender in blossom than the
other pears. 2*^ Chandler states that among peaches " the large flowered varieties
seemed uniformly to be the most hardy, probably because the petals remained
closed over the pistils longer."^' This statement was in reference to resistance
to frosts at blossoming time; after that period no determining factor could be
found. Elberta, tender at some other stages, seemed to resist very late frosts as
well as most varieties.

Some varieties of strawberry are more susceptible to frost injury
than others because their flower stalks are longer and more inclined to
raise the blossoms above the protection of the leaves.^

Schuster"'* reports on the Ettersburg No. 121 strawberry: "The first blos-
soms being below the foliage are quite well protected from ordinary frost. Foli-
age protection is quite a factor when comparing this variety with other varieties
of hght fohage, as the primary blossoms are very apt to be fully protected during
the frost, while the secondary blossoms that extend beyond the foliage will
usually be frosted. Due to the extended blossoming period, it will take repeated
frosts to destroy the crop unless there is a heavy freeze."

Some interesting studies have been made in an attempt to correlate
varietal morphological peculiarities with differences in hardiness.

PROTECTION AGAINST FROST 363

Emery ,^2 in Montana, found injury in strawberry varieties ranging from 12
per cent, to zero. Tlie date of bloom in this case seems to have had little effect,
since Warfield, one of the earhest blossoming of the 58 varieties under observa-
tion, escaped all injury. Wilcox^i^ at the same station found the anthers of
certain varieties injured by frost; the tissue in which the pollen grains were
embedded ruptured and a small proportion of the pollen grains were killed. Some
injury was observed in styles and stigmas, probably enough to interfere with
their functioning. In blossoms which had been fertilized the injury was confined
to the akenes; in no case was the receptacle injured. The akenes became dis-
colored rapidly. In resistant varieties they were so deeply imbedded in their
pits as to be practically surrounded by the pulp. Tender varieties had their
akenes most exposed or in very shallow depressions. Between these extremes
there was a regular gradation. It thus seems possible that a variety may be
resistant at one stage — before fertihzation, for example — and yet be tender at
another stage, say, after fertilization.

Vigor and Recuperative Ability. — The vigor of the tree is stated
frequently to be a factor in the damage produced by frost. This opinion
may be founded on observations of the crop the weak trees bear and in
failure to recognize that, frost or no frost, such trees fail often to set a
large percentage of fruit. A series of freezings of blossoms from strong
and from weak Gano apple trees indicated no superior hardiness in blos-
soms from the more vigorous; in fact the average of the various tests
was very slightly in favor of the weak trees.^^ In herbaceous plants,
injury sometimes appears more pronounced in those making a less
vigorous growth, but in all probability the observed difference is due
to the superior recuperative powers of the more vigorous plants. There
is some indication that plants treated with nitrate of soda recover from
frost damage better than others. This recovery is, however, in the vege-
tative portions. There is, occasionally, a fairly large second bloom on
apple and pear trees following a frost, but this is the exception and ap-
parently it is not related to vegetative vigor. Recuperative power is of
little immediate benefit to the grower once the blossoms are killed.

Weather Conditions Before and After Freezing. — The weather pre-
ceding and immediately following the freeze may be factors of some
little impoi'tance.

Pf offer'", speaking of plant tissues in general, says: "The resistance to
cold depends to a certain extent upon the present and previous external
conditions. Thus Haberlandt found that seedUngs grown at 18° to 20°C.
froze more readily than those grown at 8°C." Rosa^'^^ found that cabbage
grown in a greenhouse at 20°C. killed when exposed to -4°C. for 1 hour
while plants grown in a cold frame were uninjured by exposure to _the same
temperature for over 2 hours. It seems reasonable to suppose that the
same principle applies to fruit blossoms. Garcia''^ records that a temperature
of 24.75°F. at 2 a.m. followed by a rise to 31° at 5:30 caused less than 3 per
cent, injury to Alexander peach blossoms which were in full bloom at the time,

364 FUNDAMENTALS OF FRUIT PRODUCTION

though in other instances considerable damage followed a temperature of 25.5°.
It should be recalled that there is practical unanimity among investigators that
rapid thawing is not in itself injurious, but there is no evidence as to the effects
of Hght on frozen tissue. Light is known to increase permeability and may well
be conceived to prevent the return to the cells of water which has been withdrawn
upon freezing, thus causing injury to tissues which otherwise would recover
their normal state. The common conviction among practical horticulturists
that rapid thawing is injurious may be founded on observations of the effect
of light on frozen tissue. Furthermore, the effects of the duration of exposure to
a given temperature have not been established definitely.

Signs of Damage. — The thermometer, evidently, frequently fails to
give close or reliable indication of the amount of damage a frost has
inflicted. A fairly close estimate may be made, ordinarily, late in the
forenoon following a freeze, by an examination of the buds themselves.

The pistils are the parts most readily affected in the blossom, becoming, when
damaged, wilted and discolored, though the bud may unfold its petals and
stamens. Curiously, in April, 1920, at Columbia, Mo., a temperature of 14°F.
when Jonathan apple blossoms were fairly well advanced seemed to damage, not
the pistils, but the stamens which turned orange in color, and the effects also be-
came evident on the stems near the purse. A similar condition, though less
pronounced, has been observed in the Willamette valley in Oregon. Sometimes
the petals are dwarfed but the bud otherwise uninjured. In peaches advanced
beyond the blossoming stage. Chandler^* states that the veins surrounding the
seed are the most tender, followed in order by the kernel and the flesh. Chandler
suggests that the greater tenderness of the seed may be correlated with the differ-
ence in sap density. The young seeds of the apple seem particularly tender and
after a frost they frequently are brown while the flesh is apparently undamaged.

Paddock and Whipple^^^ state that after fertihzation has occurred apple
blossoms may survive some injury to the seeds though blossoms of the stone
fruits frozen to the extent that the basal part of the pistil is damaged rarely set
fruit. When interior apple tissues outside the seed cavities are damaged the
fruit does not mature. In this particular case, they say, the injury becomes
apparent early, in a yellowing of the tissues around the stem end of the fruit.
Seedless apples, particularly of some varieties, frequently develop to maturity
but generally are somewhat smaller than those with seeds. The same writers
state that the pear will mature fruit after showing still more injury than the
apple. In the young fruit they find much the same conditions holding, though
the stone fruits are said not to show injury which is confined to the seed cavity
until the time of the final swelling just before ripening, when the injured fruit
will show gummy exudations and ripen abnormally or it may drop before ripen-
ing. When the injury ismoreextensivethey drop shortly after blossoming. Apples
and pears survive injury to the seeds alone and in most cases with no other visible
evidence of damage. Apples injured outside the seed cavity do not mature but
pears so injured develop abnormally through enlargement of what would ordi-
narily be the neck of the fruit. This enlargement, together with the retarded
development of the parts surrounding the core, results in the familiar " bullneck."

PROTECTION AGAINST FROST 365

Injury to pear flesh apparently must extend well away from the core to prevent
the development of the fruit, though it conceivably may interfere to some extent
with the so-called "secondary effect" of pollination.

Impaired germination of pollen of pear, plum, cherry and peach on
exposure for 6 hours to a temperature of — 1.5°C. has been reported. ^^^
Chandler^* found that pollen of the Jonathan apple after exposure to
— 3°C. showed a germination of 33 per cent, as compared with 84 per
cent, for unfrozen pollen, and pollen of the Cillagos apple frozen for
30 minutes at — 8°C. germinated 25 per cent, as compared with 67 per
cent, for unfrozen.

Frost Injury and the Size of the Crop. — Finally it must be considered
that the damage from a given frost is a varying quantity. Some peach
trees on which 1,000 peaches would be a good crop bear 20,000 or more
fruit buds. Obviously, with other conditions favorable, a loss of 80
per cent of the buds would not interfere with the production of a full
crop and in a commercial sense this frost would not prove damaging.
If, however, the same trees were bearing only 8,000 buds a loss of 80 per
cent might become a serious matter.

It should be apparent that no set rules of procedure as governed by
observed temperatures can be given. Probably the safest course for the
grower when freezing occurs is to try to keep the temperature above
29°F. if he is heating his orchard and after a frost it is best to proceed on
the assumption of a full crop unless the evidence to the contrary is
convincing.

AVOIDING FROST THROUGH LATE BLOSSOMING VARIETIES

The relatively wide range in blossoming dates of the many kinds and
varieties of fruits is often important in determining the relative danger
from frost to an orchard on a given site. Conversely, the blossoming
dates should have bearing on the decision as to the type of fruit to be
planted. On a very large scale the limiting factor in the growth of
apricots and almonds is not their lack of hardiness to winter cold, since
some varieties are probably as hardy as, or even hardier than, the peach,
but rather their extremely early blooming.

Blossoming Range Varies with Earliness. — The earlier the average
date of blossoming in any section the longer is the spread of the ordinary
season of bloom. In the north the time between the first peach and the
last apple to blossom is frequently shorter than the interval in the south
between the first and the last peach. Consequently the relative earliness
or lateness in blossoming of a variety may be more important in some
regions than in others. Table 69 shows the difference between peaches
and apples in the number of times heating might be necessary at various
places in Utah. The difference between a total of 263 heatings for the

366

FUNDAMENTALS OF FRUIT PRODUCTION

Table 69. — Number of Heatings Necessary to Protect Utah Orchards
{After West and Edlefsen'^°'')

County

Number
of years

Peach

Apple

Apricot

Cherry

Utah (Prove)

16
16
14
16
13
16

93.0
28.0
32.0
36.0
66.0
8.0

46.0

13.0

8.0

15.0

4.0

3.0

45.0

45.0
3.2

Provo Bench

Box Elder (Corinne)

Salt Lake (Salt Lake)....
Weber

21.0

Cache

Totals

263.0
2.9

89.0
0.97

21.0

Average per year

1.5

peaches and 89 for the apples would make a considerable item in the
cost of production. In addition, the later blooming fruit is not only-
likely to encounter fewer frosts but such as it does encounter are likely
to be less severe. Finally, it should be recalled that the later stages of a
blossom's development are the most tender; for this reason also a given
frost is likely to damage the early variety more. This double effect is
well shown in Table 70.

Table 70. — Percentage op Peach Blossoms Killed by Temperature of 28°F.
(After Garcia''^)

Varieties

Fruits just
setting

Freshly opened
flowers

Buds about to
open

Elberta

Crothers

Salway

Texas King ....
Hynes' Surprise
Alexander

This table shows that for blossoms just setting fruit there was not
enough difference to indicate any varietal superiority in hardiness. How-
ever, Elberta, Crothers and Salway blossoms were all at the most ad-
vanced stage which is very tender. The three other varieties had a
considerable number of blossoms less advanced at the time of the freeze
so that, despite a rather large percentage of killing, the fruit of these
varieties had to be thinned, while the first three varieties bore very little,
Elberta in fact bearing none at all.

Table 71is based on the Mikesell data,"^ with additions. Though computed
rather arbitrarily it shows in a general way the relative susceptibility to frost

PROTECTION AGAINST FROST

367

Table 71. — Date of First Blossoms Relative to Last Minimum of 29°F. at
Wauseon, Ohio, for 30 Years

Blossoming relative
to frost

Apple.

Pear.

Peach,

Plum,

Cherry,

Grape,

Straw-
berry,
years

years

years

years

years

years

years

8

13

12

14

0

10

22

19

14

17

15

26

16

10

13

13

15

15

0

20

17

14

14

14

26

5

12

12

11

14

0

25

18

15

18

15

26

Red
rasp-
berry,
years

Type variety:

Before

After

Early variety:

Before

After

Late variety:

Before

After

at Wauseon of the fruits under observation there (see Tj'pe fruits). In addition
an attempt is made to show how earher or later blossoming varieties of the respec-
tive fruits would have been affected. A somewhat artificial method was
necessary. Taking as guide the average blossoming dates of various fruits at
Geneva, N. Y.,^° the varieties studied in Table 70 were interpolated and the
differences between their average dates of blossoming at Geneva and that of the
earliest and latest blossoming common varieties grown there were used in the
Wauseon figures. Thus the apple was figured on the basis of Gravenstein being
2 days earUer in blossoming than the type variety (King). The Bartlett pear
was fitted into the New York tables on the assumption that it blossomed with
Clapp Favorite and Angouleme; Anjou and Vermont Beauty were the extremes,
2 days earUer and later respectively. The plum (variety not stated) was placed
in the middle of the Domestica group.

The table should not be taken too literally as it is constructed on such arbi-
trary assumptions (including the temperature selected as injurious). Neverthe-
less it shows quite clearly the respective chances of frost damage to different
fruits at a given spot in northern latitudes and in a measure the relative import-
ance of early and late blossoming varieties which is much greater in some fruits
than in others. Furthermore, it should be understood clearly that the blossoming
dates of all kinds and varieties of fruits have a much wider spread in milder
cUmates than that of the northeast and these differences are much greater and
more important in these regions.

Figure 36 shows the blossoming dates of certain fruits in relation to
the last spring temperature of 27°F. at a point in southern Utah. In no
year did the apricot or the almond blossom after the last temperature of
27°, and in no case did the Yellow Transparent, generally a rather early
blossoming apple, bloom before. Between these extremes lie the Elberta
peach, which blossomed after the last 27° temperature in 2 years out of
the 8 represented, and the German prune which preceded it in 1 year
out of 6 recorded. The likelihood of damage or safety from frost is this
locality quite evidently depends on the kind of fruit chosen, more so

368

FUNDAMENTALS OF FRUIT PRODUCTION

than in sections where the blossoming season has less spread. At Geneva,
N. Y., the average interval from the first peach blossom to the last
apple tree's first bloom is 15 days. However, there are unquestionably
years in almost any fruit growing region when the blossoming period
actually determines the difference between a full or a partial crop — or a
crop failure.

Fig. 36. — Frost susceptibility of several fruits as determined by date of blossoming.
{After Ballantyne^^)

Blossoming Period and Fruit Bud Position. — In addition to varietal
difference in blossoming season there is occasionally some diversity within
the variety. There is a tendency, though it is by no means constant, for
vigorous trees to blossom somewhat later; sometimes the interval
between vigorous and weak trees is 2 to 3 clays. Terminal and lateral fruit
buds of apple frequently are several days behind the spur fruit buds in
opening; in at least one instance Jonathan trees have lost practically all
the spur blossoms from frost and still returned a partial crop from
their terminal buds. The outer buds on long twigs and all buds on short
twigs in peaches are the first to open and the slight difference in develop-
ment of these and the basal blossoms on the same trees has made at times
a vast difference in the crop borne in respective zones. ^^

Retarding Blossoming. — Attempts at retarding fruit blossoms so they
will escape a certain amount of exposure to frost have not proved success-
ful on a commercial scale. Whitewashing the branches to reduce the
amount of heat absorbed from sunlight has been discussed previously;
shading has been shown to have only a very limited application. Despite
abundant evidence to the contrary the notion persists that mulching
retards the opening of fruit buds. Except for fruits whose tops are
covered, as strawberries, it is of no value.

PROTECTION AGAINST FROST

369

If late blooming is urgently needed it is best secured by selecting late
blossoming varieties, planting them on a north slope and keeping them
growing vigorously. The last two measures are effective only within
comparatively narrow limits, leaving the first as the best method of
evading frost damage. In certain fruits the present varietal range in
blossoming season is hardly sufficient to secure protection through the
selection of the later blooming sorts, but in others practical immunity
from damage may be obtained in that way. There is reason to believe
that late blooming varieties of many fruits may be bred and the ultimate
solution of the frost problem lies in that direction.

Indices to Blossoming Periods in New Location. — Sometimes in
considering locations where fruit has not been grown it is desirable to
know at what time the trees may be expected to bloom. It is possible
that phonological observations on native plants in different sections
would show a degree of correspondence with the various fruits so that
certain native plants might serve as indicators of what fruit trees would
do in the same locality.

Figure 37, arranged from the Mikesell Records, '^^ shows the overlapping of
the King apple in the stage from first blossom to full bloom with poison ivy, a

1884.

"IT

_■_

"_.

TIT

13=

E^

^^

:^T^=

1886

_•=:

=-=:

.

._-

_

3^;

l»8g

—

■"

—

1890

_

__

— ;

rzir"

r:_

1

loyi!

--

■=-=

■=—

;rr:

IB 94

_

IBSfa

__

.

^

_

_ _

1

_ -

—

—

1898

'-^-z

-:3d

1 —

poisoh/iv

Y

1893

-T-

\-~.

—

r

—A

PP

-F-

?0 IZ 24 Z6 ?8 JO 2 4 6 8 10 \Z 14 IG IS 20 22
April f^ a y

Fig. 37. — Comparable phenological stages in apple and poison ivy. (Apple from first
blossom to full bloom; poison ivy from starting of buds to first fully formed leaf).

fairly common wild plant, in the stage from buds starting to the first fully formed
leaf. It will be observed that the correspondence, though not invariable, is
rather close. Some plants show better correspondence with the King apple than
others; several recorded in the Mikesell records show less than the poison ivy.
This instance is but suggestive of many other parallels or overlappings in
blossoming seasons that may be estabhshed— parallels that in many cases would
repay careful study.

FROST PREDICTION

It is frequently important to know a few hours in advance whether
or not a frost will occur, so that final preparations for protection against

24

370 FUNDAMENTALS OF FRUIT PRODUCTION

its effects may be made. In a general way frost may be looked for on a
clear, still night; clear, because it favors radiation, still, because the cooled
air is not mixed with the warmer air. These conditions are associated
with high barometric pressure. However, they do not always produce
frost and a closer estimate is desirable.

Relation of Dewpoint to Minimum Temperature. — Until recently the
dewpoint as determined in late afternoon or early evening has been
considered to mark the minimum temperature for the following morning.
Air contains varying percentages of moisture; the higher the tempera-
ture the more it can carry as vapor. If any given sample of air is cooled
the point is reached ultimately where some of the moisture is deposited.
This is the dewpoint. The condensation of moisture releases heat to the
air and it was thought that the heat thus released was sufficient to prevent
any further drop in temperature and that the evening dewpoint therefore
marked the minimum for the following morning.

Careful comparison of indicated and actual temperatures has shown,
however, that the afternoon or evening dewpoint alone is not a suffi-
ciently reliable indicator to be of any great value in predicting the
minimum for the following morning. In fact Cox^^ records a slight degree
of frost with the humidity at 100 per cent. Ordinarily, however, it may
be assumed that when the evening relative humidity is from 40 to 50
per cent., the ensuing minimum temperature on a characteristic radiation
night will be very close to the evening dewpoint; when the evening relative
humidity is below 40 per cent the minimum will average 5° above the
evening dewpoint; with evening relative humidities above 50 per cent
the minimum temperatures will be below the evening dewpoint.

Little reliance can be placed on the afternoon maximum alone as an
indicator unless it is very high indeed. No maximum below 75 or
76°F. should be regarded as a guarantee against frost the following morning.

Weather Bureau Methods. — At present no one method of predicting
minimum temperatures is in use by Weather Bureau officials throughout
the country. Local conditions apparently make a certain method fit
closely at one point while at another point it gives less satisfactory results.
It seems probable that observations extending over at least 2 years for
each section should be accumulated and the data studied to determine
which method will give the closest approximation in future predictions.

Smith^*- has devised several methods and applied them to data from different
points. The simplest, perhaps, is the so-called median temperature method.
This is based on the assumption that, in weather characteristic of most spring
frosts, the "radiation nights," clear and rather still, the temperature falls practi-
cally at a uniform rate from a maximum in the afternoon to a minimum in the
morning and that the times of maximum and minimum temperatures will be
the same for all such days. The average time of the median, half way between
the times of the maximum and of the minimum, is ascertained from previous

PROTECTION AGAINST FROST 371

records of the particular station. A thermometer reading at this median time,
subtracted from the afternoon maximum, gives, presumably, half the total
fall in temperature to be expected. Thus if the maximum were 70°F., the
median temperature 50°, the difference, 20°, taken from the median temperature,
would indicate the expected minimum to be 30°. Under conditions obtaining
at some stations this method seems the most reliable that has been tried.
In general it seems to give closer approximations to actual temperatures in
regions of very low humidity, not, perhaps, because the method works better
there than elsewhere, but possibly because the other methods do not work so
well. As indicated by Hallinbeck, with certain precautions in its application
it seems to work well at Roswell, New Mexico. Wherever compared with
the older method of assuming identity between evening dewpoint and morning
minimum it has proved superior.

Still more accurate predictions were found possible in Ohio by Smith, using
the equation y = a -\- bR, where R is the evening relative humidity, y the varia-
tion of the morning minimum temperature from the evening dewpoint, while a
and b are constants derived from previous data accumulated at points with like
conditions. This linear equation, when plotted, fitted the Ohio data very satis-
factorily, but charts from certain other points were fitted more closely by a
parabola whose equation was modified by Smith to read v = x + by -\- cz in
which X, y and z are coefficients to be determined from previous data, b the eve-
ning relative humidity, c the square of the relative humidity and v the variation
of the minimum temperature of the following morning from the evening dew-
point. The value found for v is added to or subtracted from the evening dew-
point and the minimum temperature indicated.

The method of obtaining the constants is explained in detail in Supplement
16 of the Monthly Weather Review. As has been suggested above, the constants
vary with the locality. As samples, the following may be cited: for the y = a
+ bR equation, at Lansing, Mich., a = —11.2, b = 0.727, at Grand Junction,
Col., a = —7.01, b = 0.53; for the v = x -\- cz -\- by equation, Modena, Utah
(all nights, radiation or otherwise), x = 7.3, y = 0.18, z = 0.0057; for Montrose,
Col, X = -22.0, y = 0.383, z = 0.01167.

The first equation has been found to give satisfactory results at some places,
the second has proved preferable at others; as stated above, the median tempera-
ture method seems best here and there, while in some cases still other me'thods
are used. Sometimes a mean between results secured by two methods has
proved more nearly accurate than either singly. One disadvantage of the
median temperature method as compared with the others outlined here lies in
the fact that the forecast cannot be made until several hours later than is possible
from the metheds based on hygrometric data. The fact that different methods
fit various places is probably an expression of the differences in topography and
in humidity, relation to centers of high pressure and other factors somewhat
pecuhar to particular locaUties but all combining in frost production.

It should be borne in mind also that the methods outlined fit only
radiation nights and that occasionally fruit blossoms are damaged by
cold in other ways such as high cold winds or cold snow squalls. To
forecast these, reliance must be placed in the weather map. The problem

372

FUNDAMENTALS OF FRUIT PRODUCTION

is, in any case, sufficiently complex to warrant the grower who wishes
reliable forecasts in trying to secure them from the nearest station of the
Weather Bureau, either directly or by corrections from forecasts made
for some noar])y point.

Local Interpretation of "Key Station" Predictions. — It will be under-
stood, considering the local differences in temperature, that the general
forecast may require correction for the grower's own site. The forecast,
as issued, is based upon observations from sheltered instruments at
a certain spot; yet it is given out necessarily to cover a wide radius of
territory where local differences may be considerable. Districts that
are well organized for frost fighting have several "key stations" for which
the forecasts are corrected individually. Even in such cases, however, it
may be necessary to make discriminating corrections if the probable
minimum for a given spot is to be determined.

Table 72 shows minimum temperatures on cold spring mornings at 5.5
feet and 0.5 foot elevations at three spots in the village of Williamstown, Mass.
Station A is a shelter thermometer and may be considered the "key station."
It is of interest to see how predictions for the key station would apply to straw-
berries at Station 7. As is shown in the last column of the table the difference is
variable but always considerable, under conditions favorable to frost. As
Milham,!^^ from whose data the table is taken, states, it is not a difference due
to site alone; in adapting the forecast for Station A to vegetation at Station
7 allowances must be made as follows: 2° for the deviation between sheltered
and exposed thermometers, 3° for the inequality in height of the two thermome-
ters above ground and 6° for the difference in site. These together indicate a

Table 72. — Minimum Temperatures at

Williamstown

, Mass.

134

Date

Station A
(.shelter)

Station 1

Station 8

Station 7

Difference,
Station A
and lower 7

Upper

Lower

Upper

Lower

Upper

Lower

1907
April 27

32
33
38
27
42
37
39
33
37

40
39
3.5
42
46
39
42
40

29
36
25
41
35
38
31
36

38
37
33
30
45
39
40
39

30
28
34
24
40
35
38
30
36

38
36
33
30
44
39
40
39

30
28
32

39
34
36

34

37
35
31
28
43
38
38
39

27
25
32

36
32
34

32

36
32
30
27
39
37
36
37

27
25
31
18
33
34
36
25
31

35
31
31

28
40
38
36
36

23
21
27
15
31
31
33
20
31

34
28
27
24
35
38
34
34

9

May 1

May 5

May 11

May 12

May 20

12
11
12

6

May 21

6

May 24

13

May 28

6

1908
April 29

6

May 1

May 3

11
8

May 4

May 5

May 9 ....

18
11
1

May 10

May 14

8
6

PROTECTION AGAINST FROST 373

total of 11° which, it is evident from the table, was realized frequently. Though
it is unsafe to generalize from a few observations, it is interesting to note that
for the lower temperatures at Station A the departures for Station 7 averaged
greater than they did for the higher temperatures at Station A ; in other words it
would seem that as the temperature at Station A came nearer to the freezing
point the temperature at Station 7 was in even greater measure more likely
to drop below that point. Evidently a strawberrj^ grower at Station 7 should
deduct at least 11° from the minimum indicated for Station A to forecast the
probable temperature at his own place; if apples were the crop at the same point
the deduction would be somewhat less.

Even greater differences are reported by Cox''" between minima on the bog
at Mather, Wis., and the minima at the "key station" La Crosse, 55 miles away.
Shelter minimum temperatures on the upland at Mather for May, 1907, averaged
3.8° below those at La Crosse with ranges from —14° to +8°; minima at 5
inches above the bog at Mather averaged —8.5° below those for La Crosse,
with ranges from —20° to +5°. Cox states that the average difference when the
weather is clear and the pressure high is about 18°, so that in such weather a
minimum of 50° for La Crosse signifies a bog minimum at Mather of about 32°.

The grower who wishes to prophesy with accuracy what the minimum
will be in his own orchard, bog or field must rely on the Weather Bureau
to furnish information as to the probable minimum at some fixed point
and he must rely on himself to adapt these indications to the spot where
his own crop is located. To do this it will be necessary to keep accurate
records of minima at his own orchard on all clear nights during the spring
for 2 or 3 years, to compare them with the records of the Weather Bureau
and from these data to determine the probable and the safe corrections
to be made.

FROST FIGHTING

The data already discussed show that much can be accomplished in
combatting frost by selection of site, fruit and variety and in some cases
by cultural practices. All these measures may be regarded as preventive.
There remain for consideration the palliative measures.

Smoke Screens to Reduce Radiation. — In view of the emphasis placed
on radiation as a factor under frost conditions, efforts to prevent heat
loss through radiation might be expected to be fruitful. In fact it is
rather generally assmned that a dense smoke will so retard radiation
losses that frost damage will be checked or prevented. Such cases have
been recorded. However, quantitative data available for comparison of
temperatures in smudged areas where the heating factor is eliminated
with those in unsmudged and unheated areas do not indicate a sufficient
saving of heat to make the smudge in itself of any great value. Table 73
shows temperatures in a smudged area and in an unsmudged area adja-
cent, in a German vineyard. The averages include some figures not
presented here.

374

FUNDAMENTALS OF FRUIT PRODUCTION

Table 73. — Temperatures in Smudged and Unsmudged Areas^^s
(Degrees Centigrade)

Hour

Temperature

Smudged

Unsmudged

10:30

+2.01

+ 1.87

11:30

+ 1.53

+ 1.40

12:30

+0.78

+0.62

1:30

+0.13

+0.07

2:30 *

-0,73

-0.50

3:30

-0.90

-0.95

4:30

-1.14

-1.25

5:30

-0,05

-0.03

0,098

0.042

The differences are at the most too small to be of practical impor-
tance. It was suggested that the small difference was due to air move-
ment and the investigator appears not to have been convinced that
greater differences might not be found under other conditions.

Kimball and Young/"^ using a pja-ogeometer, measured the radiation
in smudged and in unsmudged areas in California and Oregon, finding
decreases by smudging from 0.110 and 0.115 calories per minute per
square centimeter to averages of 0.098 and 0.103 respectively in Cali-
fornia and in Medford, Oregon, from 0.109 to an average of 0.099. Con-
siderable fluctuation under the smoke occurred, the maximum decrease
amounting to 28 per cent, with averages respectively of 11, 10 and 9
per cent. They conclude from their investigations that "the retardation
of nocturnal radiation by the smoke cloud plays an insignificant part in
frost protection."

The reflection of heat from smoke clouds is evidently very small.
Miiller-Thurgau^^^ points out that smoke differs in its composition from
clouds. It should be recalled that radiation is constantly occurring,
clouds or no clouds, and that they do not prevent radiation but only
reflect heat, and since outgoing and incoming heat approach equal value
on cloudy nights the net loss by radiation is small. Smoke differs from
water vapor in being relatively transparent to long heat waves. There
is a relatively large difference in the way violet (or blue) and yellow (or
red) are transmitted through dust in the air^ — for example, the sun is
yellow or red at horizon, the short waves not being transmitted as readily
as the longer yellow and red waves. The sun looks red through smoke,
showing the same effect. The smoke screen appears opaque because the
eye uses the shorter waves but it must be very much less opaque to the
long waves which the earth radiates.

PROTECTION AGAINST FROST 375

Covering and Spraying. — The protection of plants from frost by-
covering tliem with paper or cloth is of course effected through saving
of the heat otherwise lost through radiation. The efficacy of this
method is well known though it is not practicable in the orchard. ^^^ An
experiment in California showed that with an outside minimum of 19°
the lowest temperature under a paper covering spread over an almond
tree was 24°, a saving equal to the raise in temperature secured in many
instances by orchard heating.

The protective effects of water spray were investigated in Utah by
keeping a block of apricots under a continuous fine spray during a frost. ^°^
Ice formed on the blossoms and it finally appeared that only the sprayed
trees were damaged. The injury was not a mere failure to set fruit;
there was actual killing. In view of the work of Harvey^'' it seems prob-
able that in this case the ice formation on the surfaces of the blossoms
inoculated the inside tissues with ice crystals and actually hastened their
freezing.

Orchard Heating. — The most successful results so far achieved in pre-
venting low temperatures have been realized by the use of large numbers
of small heaters, warming the air itself. This practice has become a
settled part of orchard routine in some sections; in others it has been in
extensive use but is now almost obsolete. There can be no doubt of
its efficacy in some cases. Frequently, however, it has been considered
too expensive insurance. The heating capacity of a set of heaters is
limited and sometimes in a severe freeze the temperature sinks so low
they are unable to maintain a protecting temperature, or in some cases
a high cold wind renders them useless. On the other hand, a few degrees
of freezing rarely destroys a whole crop. The full value of these heaters
is, then, realized only with minima in a certain narrow range; with
minima outside, they are either unnecessary or useless.

It is probable that failure to realize these limitations led to the instal-
lation, during the greatest vogue, of orchard heating equipment in many
places where its true usefulness is rarely available and that failure to
realize its limitations at the outset caused unjustifiable expectations of
its value. In either case the reaction was bound to cloud the instances
and circumstances in which it can be of real worth.

Furthermore, orchard heating has been invoked at times when the
difficulty, supposedly frost, was in reality something entirely different.
At one time many cherry growers at The Dalles, in Oregon, installed
extensive heating equipment to induce a proper setting of fruit when
their orchards were of self sterile and inter-sterile varieties and what
they actually needed was provision for proper cross pollination. Orchard
heating cannot make weak trees set heavy crops. In view of the equal
influence of freezing on blossoms of weak and of strong trees, as cited
previously in this section, the increases sometimes reported in fruit set

376 FUNDAMENTALS OF FRUIT PRODUCTION

after frost on nitrate-fertilized trees may constitute a splendid testimonial
for nitrate fertilization but they do not in themselves indicate that
orchard heating without fertilization would have been beneficial.

Heat Units in the Fuel. — Limits must be recognized to the amount of
actual heating any ordinary equipment can secure.

McAdie^^^ indicates this in some interesting calculations. "At the present
time," he states, "with a hundred burners to the acre, using a gallon each of oil,
something Hke 15,000,000 British thermal units or 3,760,000 [kilogram] calories
would be given off, provided the combustion was perfect, which of course is never
true. Now, to raise the temperature of the air 1°F. over an acre to a height of 15
feet is practically heating 653,400 cubic feet of air. In practice it is found that to
maintain the temperature on a still night 1° above the freezing temperature
requires 0.252 calories per hour per cubic foot. Therefore for a period of 7
hours, which is about the average duration of a low temperature [McAdie wrote
in California], although 10 hours is a safer period, there will be required 1,138,200
calories. And if a raise of 5° is required it is evident that more than 5,500,000
calories are needed or more than the full number of heat units in the fuel under
perfect combustion."

In practice oil is burned generally at a faster rate than that used in
IVIcAdie's calculations, but the pubhshed results of careful experiments
indicate that the actual heating achieved rarely exceeds 5° and that 4°
is a liberal estimate of what may be expected with ordinarily favorable
conditions. A breeze of 6 miles an hour materially lowers the net gain
of heat; any movement lowers it somewhat and dead calms are rare.
According to Young, in the lard-pail type of heaters only about 40 per
cent of the heat in the oil is actually- realized in combustion and even
in the high stack type it is doubtful if more than 70 or 80 per cent of
its fuel value is attained. A still further loss is caused by the height of
the "ceiling layer" of air which, though variable, permits in any case
the accumulation of heat at a height above the trees.

Height of the ''Ceiling Layer." — The holding of heated air within a
few feet of the ground appears mysterious unless the inversion of tem-
perature be considered. Data introduced previously have shown that
the normal adiabatic cooling of the air upward from the earth, charac-
teristic of daytime, is modified during radiation nights and that the air
only a few feet above the ground is distinctly warmer than that at or
near the surface. It is this layer of warm air, acting as a roof or ceiling,
that makes possible the warming of the air at the level of the trees.
As the warmed air ascends from the heaters it mixes with other some-
what cooler air and the mixture finally reaches a layer of the same tem-
perature; it then has no impulse to rise further.

Figure 38, by Humphreys," shows a typical frosty morning tempera-
ture gradient and is used by him to indicate how heat may be wasted.
He shows that under the given conditions any portion of the surface

PROTECTION AGAINST FROST

377

air warmed from 32 to 34°F. would rise to about 30 feet only, as shown
by the adiabatic curve from 34°, until it would reach the layer of air
having a temperature equal to its own. If it were warmed to 40°,
however, it must rise over 250 feet, cooling somewhat by diminished
pressure, until it reaches air with an equal temperature. Thus in one
case the ceiling is about 30 feet high, in the other it is 250 feet high. When
the gradient begins at, say, 24° instead of 32°, in other words when the

900

.£ 500
c
o

P 400

300

200

100

\

\

\

\

\

7->

TEM

'PICA
°ERA1

L HO
URE 1

RNIh]
NVER.

G
SION

/

\

/

J

k

,«9

,^

f

■?

k

\
\

\

^

Mti^

%

ZZ 33 34

35

36 2.T

Temp era+u re,d eg.fohr.

Fig. 38. — Illustrating the physical possibility of protecting outdoors from frost by artificial
heating. (After Humphreys^'')

outside unheated surface air is at 24°, whether or not the gradient is
affected at 500 feet, the ceiling above the 34° mark is raised, meaning
that not only must the air now be heated from 24 to 34°, 10 degrees
instead of 2, but a greater amount of air must be heated. The increasing
difficulty of heating toward morning is due evidently to other factors
besides the heaters themselves.

If a few large fires are employed the body of warmed air rising from
them is so great that it does not become mixed readily and rises farther

378 FUNDAMENTALS OF FRUIT PRODUCTION

than the heat from the small fires, being thus rendered ineffective in
warming the air at lower levels. Large fires of course emit a considerable
amount of radiation heat which warms the surfaces exposed, but since
the intensity of heating by radiation diminishes as the square of the
distance from the source of heat it soon becomes ineffective. In addi-
tion the current set up above the large fire draws in the colder surface
air to replace the warmed air driven high aloft and it is easy to conceive
that it may disturb ceiling layers considerably.

Effect of Wind. — Winds, besides carrying heat away directly, break
up the "ceiling layer" of warm air and unless the heated areas are very
large and the wind such that the warmed air is "blown down," they
make heating efforts of little avail. Windbreaks, therefore, though at
times they may invite frost conditions, may render heating more effec-
tive, though they cannot preserve tjie ceiling layer which is necessary
for full realization of its possibilities.

Humphreys, ^^ assuming a radiation per minute per square centimeter of
0.1 calorie and evidently basing his calculations on soil surface area alone,
disregarding vegetative surfaces, concluded that for each plot of ground 10
meters by 10 meters there would be needed per hour 6,000,000 calories, which,
assigning a value of 8,500 calories per gram of petroleum, indicates the need of
approximately a pint and a half of oil per hour to offset radiation or to hold the
temperature from falling. If a moderate air movement occur, new air must be
warmed constantly. Humphreys, assuming the dewpoint below 32°, land sur-
face horizontal, temperature of air 32° and a wind of 2K miles per hour (approxi-
mately 1 meter per second), with air weight 1,290 grams per cubic meter, makes
an interesting calculation of the amount of heat necessarj'- to warm the entering
air 2°C. to an elevation of 12 meters. He states: "Now the specific heat of the
atmosphere is very approximately 0.24. Hence to warm 1 cubic meter of the
given air 1°C. requires about 310 calories. Hence, to warm the air 2°C. to an
elevation of 12 meters, as it enters the given area with the given velocity of 1
meter per second, will require, per linear meter at right angles to its direction,
approximately 2 X 12 X 310 X 7,440 calories per second, or the consumption of,
roughly, 3.7 liters or 6.5 pints of oil per hour."

A considerable amount of the heat imparted to the air as it enters is retained
while the air drifts through the orchard; therefore, though radiation must be
fought equally at all points the raising of air temperature itself is moit jt^roperly
done on the windward edge. With the somewhat idealized conditions enumer-
ated above, assuming an orchard 1 kilometer square (about 247 acres) with the
breeze at right angles to one side the oil requirements are stated by Humphreys :
to counteract radiation 8,600 liters; to warm the entering air 3,700 liters. A rec-
tangular orchard might require more or less oil to warm the entering air, accord-
ing to the direction of the breeze and if the breeze is quartering two sides must be
warmed, but the amount to offset radiation alone is constant. In other words
the oil necessary to offset radiation is determined by area alone ; the amount nec-
essary to warm entering air is determined by the outline of the orchard and by
the direction and velocity of the wind.

PROTECTION AGAINST FROST 379

Concerning the influence of wind velocity Humphreys says: "Of course a
greater wind velocity than 2K miles per hour, the velocity above assumed, would
appear to necessitate a correspondingly larger consumption of fuel for the border
or entrance heating. But this, presumably, is not true in practice, since probably
even this velocity, certainly a greater one, would considerably mix the surface-
cooled air with the warmer air above, and thereby decrease the amount of
necessary heating. During a perfect calm the required border heating is zero;
it is also zero when there is a fairly good breeze and hence has its maximum value
at some quite moderate intermediate velocity."

It should be noted that Humphreys is stating that the higher the
velocity of the air movement the higher the air temperature is likely to be.
This is quite different from the case of high wind at a dangerous tem-
perature, for here the heating required increases with the wind velocity
and too many times becomes impossible.

The choice of heater types depends on the nature of the service
required. In some sections where dangerous temperatures are of
short duration the simple 1-gallon heaters will be adequate; in other
sections longer burning may be required. Young- '^ points out that the
size of the temperature inversion characteristic of many of the California
frosts permits the use of stack heaters which, perhaps, could not be
employed in sections where the temperature inversion is weaker. No
one type is best for all sections or for all occasions in one section.

Conditions Determining Practicability. — No general discussion can
decide the question whether orchard heating is profitable. The con-
tinuance of the practice in certain sections over a long period is rather
good evidence that with conditions as they are in those sections it is
either profitable or necessary or both. The necessity of the practice,
if fruit is to be grown in a certain spot, may mean that it is desirable or it
may mean that the spot should be devoted to some other crop. If the
value per acre of the crop is high, as with oranges, heating may be
economically sound; if the value per acre of the crop is low, heating is
of doubtful wisdom. If a given spot is exposed to several frosts a year
heating is likely to pay as compared with no heating but it may be that
fruit growing should be abandoned at that spot.

The installation of an orchard heating equipment involves a heavy
overhead expense. Each year heaters and fuel must be distributed and
made ready. The chief difference in expense between a frosty and a
frostless spring so far as heating is concerned is in the oil consumed and a
reduction or increase in the labor charge. The profits of the frostless
season are taxed only somewhat less than those of the frosty season.
Frequently the yearlj^ expense has amounted to $20 per acre; it has
reached $40. In many, if not in most, fruit growing sections, $40 per
acre added to the initial price of the land will secure sites located advan-
tageously enough to escape this tax.

380 FUNDAMENTALS OF FRUIT PRODUCTION

Orchard heating is not so common as it was some years ago. Certain
sections have abandoned it altogether, in others only a few growers
continue it. In some instances too much has been expected of it; in
others the falling in fruit prices from an artificial level has been a con-
tributing cause, but probably in the majority of cases it has been aban-
doned for the excellent reason that it has not paid.

It will be seen from the Wauseon figures that heating at that point
would be an expensive insurance considering the number of times it
would be useful. If, in addition, the orchards are, as is the case fre-
quently, bearing chiefly in alternate years, the likelihood of heating being
profitable over a long term is further reduced. Assuming a damaging
frost in half the blossoming seasons, a ratio far greater than that for the
largest apple growing sections, and assuming a crop in alternate years,
the chance of heating being required to save a crop is 3^^ X M or 1 in
4. If damaging frost occurs once in 3 years the chance is 3^^ X li or
1 in 6. At Wauseon, with very liberal allowance, it is, for the King
apple, 2 in 15. It is significant that much of the experimental work on
orchard heating has been done at temperatures above freezing because
there was not enough frosty weather for all the tests. There are, too,
in almost all sections, springs when the crop is damaged by high cold
winds, under such conditions that heating fails to protect it sufficiently.
If a season of this kind is added to seasons when heating is unnecessary
the number of years when it really pays is still further reduced.

The fruit grower is forced, sooner or later, consciously or uncon-
sciously, to consider the economic doctrine of marginal utility. This
means, as applied to the topic under discussion, that until all the land
otherwise well adapted to fruit growing and free from frost danger in a
given area is in use for that purpose it is of doubtful expediency to attempt
fruit growing on land that will require heating. It means, too, that in
seasons when profits in general run low they are, other things equal,
wiped out first on the land that requires heating.

In addition to the doctrine of marginal utility the grower should
apply to his analysis the law of the minimum. Orchard heating is
not hkely to be profitable to him if his spraying is defective, his pruning
poorly done, his land lacking in drainage or irrigation, his trees weak or
if his fruit is not marketed to advantage. "When he is satisfied that he has
developed these essentials so that none of them is hmiting his profits and
that frost is the limiting factor he can consider orchard heating. In some
cases it will be profitable; in more cases it will not.

FROST EFFECTS
Manifestations of frost injury aside from the dropping of the fruit
are sometimes found. The so-called bull-necked pears previously men-
tioned are rather common and are sometimes confused with seedless

PROTECTION AGAINST FROST 381

fruit, particularly with that arising from late bloom. Russet bands,
generally extending more or less completely around the middle of the
fruit, though sometimes near the calyx end, occur on pears and occasion-
ally on apples. Similar russeted areas, frequently somewhat raised, but
less regular in location, are found on plums. Apples and pears with this
form of injury are said to wilt rather rapidly.^"*"*

In the apple the outside leaves of a cluster sometimes show a form
of injury called "frost-blister."^'*^ As observed in New Hampshire and
Missouri, this injury does not appear to reduce the size of the affected
leaves which are normally small and it apparently does not extend beyond
the first two or three leaves to unfold. The injury evidently may occur
when the buds are still verj^ little advanced. The appearance is suffi-
ciently described by the name; the "blisters" are caused by the separa-
tion of the upper and the lower surfaces. The leaves tend to curl and
in many cases drop off. Inasmuch as those most affected are of doubtful
importance to the growing spur this type of injury is probably
unimportant.

Another interesting consequence of frost injury is the so-called
"secondary bloom." When there is extensive killing of fruit buds the
spurs which have bloomed may form new blossoms, which in some cases
have been observed to mature fruit, sometimes with and sometimes
without seeds. The same phenomenon may occur independently of any
frost. It is discussed more fully under Fruiting Habit.

Summary. — The critical temperature for opening flower buds varies
greatly with their stage of development and somewhat with species and
variety. Some of the fully expanded flowers of many fruit varieties
will withstand an apparent temperature of 25°F. without injury, though
some will be killed at or above this point. Unopened flower buds are
considerably more frost resistant. Plants in a vigorous condition are
apparently no more resistant to frost, but they possess greater recupera-
tive ability. Often trees losing a considerable percentage of their blos-
soms from frost still have enough good buds to bear a full crop. In
many cases danger from frost can be avoided to a great extent by the
selection of late blossoming varieties. Relatively greater immunity from
frost danger can be secured in this way with those fruits and in those
sections showing a considerable range in blossoming. The blossom-
ing season of many fruits may be slightly retarded by certain cultural
practices, but, except in the case of fruits like the strawberry that can
be entirely covered, such methods of frost protection are of secondary
importance. In new sections the probable blossoming dates of certain
varieties of fruit may be foretold with considerable accuracy by com-
parison with the blossoming season of native plants. The probability
of frost occurring on any particular night can be foretold fairly accurately
by the middle of the preceding afternoon. Several methods are employed,

382 FUNDAMENTALS OF FRUIT PRODUCTION

some of them being more reliable in certain districts than others. The pre-
dictions for regular Weather Bureau "key" stations, corrected to apply to
local conditions are of greatest general use. Several distinct methods of
preventing frost have been used in fruit growing sections. The use of
smoke screens is of little value in checking the radiation of heat at night.
Orchard heating is practicable under certain conditions. However, only a
limited protection is afforded by orchard heaters, the exact amount de-
pending on the height of the "ceiling layer" of the air, on the number and
kind of heaters and on the amount of wind. A protection of 4 or 5°F. on
typical frosty nights is all that can be expected under average conditions.
Before the installation of orchard heating equipment is warranted there
should be reasonable assurance that growing conditions during the average
season and the average margin of profit warrant it. Frost occurring
after the time of fruit setting may occasionally arrest the further develop-
ment of seeds and still permit the fleshy tissues to develop and mature,
giving rise to fruits abnormal in size and shape. It may also cause the
appearance of "frost rings" or bands of russet around the apical end of
the fruit. It occasionally leads to certain other pathological conditions
in fruit or foliage.

Suggested Collateral Reading

Schimper, A. F. W. Plant Geography upon a Physiological Basis. Pp. 35-51;

241-259. Oxford, 1903.
Chandler, W. H. Hardiness of Peach Buds, Blossoms and Young Fruit as Influenced

by the Care of the Orchard. Mo. Agr. Exp. Sta. Cir. 31. 1908.
Emerson, R. A. Cover Crops for Young Orchards. Nebr. Agr. Exp. Sta. Bui. 92.

1903.
Gladwin, F. E. Winter Injury in Grapes. N. Y. Agr. Exp. Sta. Bui. 433. 1917.
Harvey, R. B. Hardening Processes in Plants. Jour. Agr. Res. 15: 2, 1918.
Hooker, H. D., Jr. Pentosan Content in Relation to Winter Hardiness. Proc. Am.

See. Hort. Sci. 17: 204-207. 1920.
Macoun, W. T. Overcoming Winter Injury. Proc. Am. Soc. Hort. Sci. Pp. 15-27.

1908-9.
Rosa, J. T., Jr. The Hardening Process in Vegetable Plants. Mo. Agr. Exp. Sta.

Research Bui. 48. 1921.
Selby, A. D. Fall and Early Winter Injuries to Orchard Trees and Shrubbery by

Freezing. Ohio Agr. Exp. Sta. Bui. 192. 1908.
Waite, M. B. Fruit Trees Frozen in 1904. U. S. D. A., Bur. PI. Ind. Bui. 51 (part

3). 1905.
Wiegand, K. M. The Biology of Twigs in Winter. Bot. Gaz. 41: 373. 1906.

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51. Craig, J. la. Agr. Exp. Sta. Bui. 44. 1900.

52. Crandall, C. S. Col. Agr. Exp. Sta. Bui. 41. 1898.

53. DeCandolle, A. Geog. bot. raison. Paris, 1855.

54. Downing, A. J. Horticulturist. 1 : 58. 1846.

384 FUNDAMENTALS OF FRUIT PRODUCTION

55. Ibid. 2: 339. 1847.

56. Ibid. 2:416. 1847..

57. Duchartre, P. Compt. rend. 60: 754. 1865.

58. Emerson, R. A. Nebr. Agr. Exp. Sta. Bui. 79. 1903.

59. Emerson, R. A. Nebr. Agr. Exp. Sta. Bui. 92. 1906.

60. Emerson, R. A. Nebr. Agr. Exp. Sta. Ann. Rept. 19: 101. 1906.

61. Emerson, R. A. Correspondence, Dec. 14, 1920.

62. Emery, S. M. Mont. Agr. Exp. Sta. Bui. 16. 1898.

63. Emery, S. M. Mont. Agr. Exp. Sta. Bui. 24. 1899.

64. Eustace, H. J. N. Y. Agr. Exp. Sta. Bui. 269. 1905.

65. Fernow, B. E. U.S.D.A., Forestry Div. Bui. 7. 1893.

66. Finch, V. C, and Baker, D. O. Geography of the World's Agriculture. P. 77.

Washington, 1917.

67. Fisher, W. R. Schlich's Manual of Forestry. 4: 505. 1907.

68. Ibid. 4: 522.

69. Frank, A. B. Die Krankheiten der Pflanzen. 2: 204. Breslau, 1895.

70. Friedrich, J. Ueber den Einfluss der Witterung auf den Baumwachs. P. 155.

Vienna, 1897.

71. Garcia, F., and Rigney, J. W. N: Mex. Agr. Exp. Sta. Bui. 89. 1914.

72. Ibid. Bui. 100. 1916.

73. Gladwin, F. E. N. Y. Agr. Exp. Sta. Bui. 433. 1917.

74. Goff, E. S. Wis. Agr. Exp. Sta. Ann. Rept. 15: 220. 1898.

75. Ibid. 16: 283. 1899.

76. Goff, E. S. Wis. Agr. Exp. Sta. Bui. 77. 1899.

77. Gould, H. P. Peach Growing. P. 354. New York, 1918.

78. Gourley, J. H. N. H. Agr. Exp. Sta. Tech. Bui. 12. 1917.

79. Greene, L. Purdue Univ. Agr. Exp. Sta. Ann. Rept. 31: 46. 1918.

80. Green, S. B. Minn. Agr. Exp. Sta. Bui. 32. 1893.

81. Green, W. J., and Ballou, F. H. Ohio Agr. Exp. Sta. Bui. 157. 1904.

82. Grossenbacher, J. G. N. Y. Agr. Exp. Sta. Tech. Bui. 23. 1912.

83. Gunderson, A. J. 111. Agr. Exp. Sta. Bui. 218. 1919.

84. Hammon, W. H. Cited by 71.

85. Hansen, N. E. S. D. Agr. Exp. Sta. Bui. 50. 1897.

86. Ibid. Bui. 65. 1899.

87. Harvey, R. B. J. Agr. Res. 15: 2. 1918.

88. Hedrick, U. P., Booth, N. O., and Taylor, O. M. N. Y. Agr. Exp. Sta. Bui. 275.

1906.

89. Hedrick, U. P. Hort. Soc. of N. Y. Mem. 2: 119. 1907.

90. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 299. 1908.

91. Hedrick, U. P. Plums of New York. P. 103. Albany, 1911.

92. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 355. 1912.

93. Herrick, R. S., and Bennett, E. R. Col. Agr. Exp. Sta. Bui. 171. 1910.

94. Hooker, H. D., Jr. Proc. Am. Soc. Hort. Sci. 17: 204-207. 1920.

95. Hopkins, A. D. U.S.D.A., Mo. Weather Rev. Sup. 9. 1918.

96. Howard, A., and Howard, G. L. C. Sci. Rept. Agr. Inst. Pusa. 48. 1916-1917.

97. Humphreys, W. J. U.S.D.A, Mo. Weather Rev. 42: 562. 1914.

98. Jehle, R. A. Cornell Univ. Agr. Exp. Sta. Cir. 26. 1914.

99. Johnston, E. S. Am. J. Bot. 6: 373-379. 1919.

100. Jones, C. H., Edson, A. W., and Morse, W. J. Vt. Agr. Exp. Sta. Bui. 103.

1903.

101. Kimball, H. K., and Young, F. D. U.S.D.A., Mo. Weather Rev. 48: 461.

1920.

102. King, F. H. Wis. Agr. Exp. Sta. Ann. Rept. 13: 207. 1896.

TEMPERATURE RELATIONS 385

103. Lazenby, W. R. Proc. Am. Pom. Soc. P. 54. 1885.

104. Lindley, J. The Theory and Practice of Horticulture. P. 150. London, 1855.

105. Ibid. P. 155.

106. Linsser, C. Cited by Bailey, L. H. Survival of the Unlike. P. 292. New

York, 1901.

107. Lippincott, J. B. U.S.D.A., Ann. Rept. P. 200. 1862.

108. Livingston, B. E. Physiol. Res. 1:8. 1916.

109. Livingston, B. E., and Livingston, G. J. Bot. Gaz. 56: 5. 1913.

110. Lloyd, F. E. Plant World. 20: 121. 1917.

111. Loomis, E. Treatise on Meteorology. P. 91. New York, 1892.

112. Ibid. P. 93.

113. MacDougal, D. T. Hydration and Growth, ('arn. Inst. Wash. Publ. 297.

P. 167. 1920.

114. Macoun, W. T. Rept. Cent. (Can.) Exp. Farms. 12: 99. 1899.

115. Ibid. 13: 73. 1900.

116. Ibid. 13: 92. 1900.

117. Macoun, W. T. Cent. (Can.) Exp. Farms Bui. 38. 1901.

118. Macoun, W. T. Proc. Am. Soc. Hort. Sci. 3: 7. 1906.

119. Macoun, W. T. Cent. (Can.) Exp. Farms Bui. 38. 2d ed. 1907.

120. Macoun, W. T. Proc. Am. Soc. Hort. Sci. 6: 15. 1909.

121. Macoun, W. T. Trans. Mass. Hort. Soc. Pt. 1. P. 39. 1916.

122. Marvin, C. F. U.S.D.A., Mo. Weather Rev. 42: 583. 1914.

123. Mason, S. C. U.S.D.A., Bur. PI. Ind. Bui. 192. 1911.

124. Maynard, S. T. Agriculture of Massachusetts. P. 348. Boston, 1884.

125. Maynard, S. T. Mass. Agr. Exp. Sta. Buls. 10. 1890; 15. 1891; 21. 1893.

126. McAdie, G. U.S.D.A, Mo. Weather Rev. 40: 282. 1912.

127. Ibid. 40: 618.

128. McCall, F. E. Amer. Fruit Grower. 39: 7. July, 1920.

129. McLean, F. T. Physiol. Res. 2: 129. 1917.

130. Mell, P. H. Ala. Agr. Exp. Sta. Bui. 8. 1890.

131. Mer, E. Compt. rend. 114:242. 1892.

132. Ibid. 124: nil. 1897.

133. Mikesell, T. U.S.D.A., Mo. Weather Rev. Sup. 2. 1915.

134. Milham, W. I. U.S.D.A., Mo. Weather Rev. 36: 250. 1908.

135. MLx, A. J. Cornell Univ. Agr. Exp. Sta. Bui. 382. 1916.

136. Moore, W. L. Descriptive Meteorology. P. 82. New York, 1911.

137. Mosier, J. G. 111. Agr. Exp. Sta. Bui. 208. 1918.

138. MuUer-Thurgau, H. Landw. Jahrb. 45: 453. 1886.

139. Munson, W. M. Me. Agr. Exp. Sta. Ann. Rept. 7: 96. 1893.

140. N. Y. Agr. Exp. Sta. Ann. Rept. 37: 468. 1919.

141. O'Gara, P. J. U.S.D.A., Farmers' Bui. 401. 1910.

142. Oskamp, J. Proc. Am. Soc. Hort. Sci. 14: 118. 1917.

143. Paddock, W., and Whipple, O. B. Fruit Growing in Arid Regions. P. 325.

New York, 1911.

144. Ibid. P. 326.

145. Ibid. P. 327.

146. Ibid. P. 353.

147. Pantanelli, E. Atti. accad. Lincei. 27(1): 126-130; 148-153. 1918.

148. Pa. Agr. Exp. Sta. Ann. Repts. 1892, 1893, 1894, 1895, 1896.

149. Petit, A. Rev. hort. 13(N.S.): 206. 1913.

150. Pfeffer, W. Physiology of Plants. Transl. by Ewart. 2: 236. Oxford, 1903.

151. Ibid. 2: 237.

152. Ibid. 2: 246.

25

386 FUNDAMENTALS OF FRUIT PRODUCTION

153. Philips, H. A. Thesis. Cornell Univ. 1920.

154. Porter, E. D. Minn. Agr. Exp. Sta. Bui. 7. 1889.

155. Price, H. L. Va. Agr. Exp. Sta. Ann. Rept. P. 206. 1909-1910.

156. Prillieux, E. Compt. rend. 74: 1344. 1872.

157. Quaintance, A. L. Ga. Agr. Exp. Sta. Ann. Rept. 11: 123. 1899.

158. Ragan, W. H. U.S.D.A., Div. Pom. Bui. 8. 1899.

159. Reed, W. G. Proc. 2d Pan-Amer. Sci. Cong. P. 625. 1917.

160. Reed, W. G., and ToUey, H. R. U.S.D.A., Mo. Weather Rev. 44: 354.

1916.

161. Roberts, R. H. Proc. Am. Soc. Hort. Sci. 14: 105. 1917.

162. Rosa, J. T. Jr. Proc. Am. Soc. Hort. Sci. 16: 190. 1919.

163. Ibid. 17: 207-210. 1920.

164. Rosa, J. T. Jr. Mo. Agr. Exp. Sta. Res. Bui. 48. 1921.

165. Sandsten, E. P. Wis. Agr. Exp. Sta. Ann. Rept. 21:258. 1904.

166. Sandsten, E. P. Wis. Agr. Exp. Sta. Bui. 137. 1906.

167. Sandsten, E. P. Wis. Agr. Exp. Sta. Res. Bui. 4. 1910.

168. Schimper, A. F. W. Plant Geography upon a Physiological Basis. P. 34.

Oxford, 1903.

169. Ibid. P. 37.

170. Ibid. P. 45.

171. Ibid. P. 47.

172. Schneider, Numa. Rev. hort. 11(N.S.): 21. 1911.

173. Schubler, G. Poggendorf's Annal. Phys. u. Chem. 10: 581. 1827.

174. Schuster, C. E. Ore. Agr. Exp. Sta. Bien. Crop Pest and Hort. Rept. 3: 44.

1920.

175. Seeley, D. A. U.S.D.A., Mo. Weather Rev. 36: 259. 1908.

176. Ibid. 45: 354. 1917.

177. Selby, A. D. Ohio Agr. Exp. Sta. Bui. 192. 1908.

178. Selvig, C. G. Rept. Exp. Farm, Crookston, Minn. 1917-18.

179. Shaw, J. K. Mass. Agr. Exp. Sta. Ann. Rept. 23: 177. 1911.

180. Shutt, F. T. Trans. Roy. Soc. Can. (Ser. 2.) 9(4): 149. 1903.

181. Smith, A. M. Ann. Roy. Bot. Gar. Peradeniya. (Abs. in Bot. Gaz. 44: 6.

1917.)

182. Smith, J. W. U.S.D.A, Mo. Weather Rev. Sup. 16. 1920.

183. Sorauer, P. Schutz der Obstbatime gegen Krankheiten. P. 42. Stuttgart,

1900.

184. Ibid. P. 46.

185. Squires, R. W. Minn. Bot. Studies. 1 : 452. 1894-8.

186. Stevens, N. E. Am. J. Bot. 4: 1. 1917.

187. Ibid. 4: 112.

188. Stockman, W. B. U.S.D.A., Mo. Weather Rev. 32: 125. 1904.

189. Strausbaugh, P. D. Bot. Gaz. 71: 337. 1921.

190. Swezey, G. D. Nebr. Agr. Exp. Sta. Ann. Rept. 16: 95. 1903.

191. Swingle, W. T. U.S.D.A., Bur. PL Ind. Bui. 53. 1904.

192. Taft, L. R. Mich. Agr. Exp. Sta. Sp. Bui. 11. 1898.

193. Ibid. Sp. Bui. 40. 1907.

194. Ibid. Sp. Bui. 46. 1908.

195. Taft, L. R., and Lyon, T. T. Mich. Agr. Exp. Sta. Bui. 169. 1899.

196. Tufts, W. P. Correspondence, 1921.

197. Von Mohl, C. Bot. Ztg. 6: 6. 1848

198. Waite, M. B. U.S.D.A., Bur. PI. Ind. Bui. 51. 1905.

199. Waldron, C. B. N. D. Agr. Exp. Sta. Bui. 25. 1896.

200. Ibid. Bui. 49. 1901.

TEMPERATURE RELATIONS 387

201. Ward, H. W. The Book of the Peach. P. 27. London, 1903.

202. Waugh, F. A. Vt. Agr. Exp. Sta. Bui. 62. 1898.

203. Waugh, F. A. Vt. Agr. Exp. Sta. Ann. Kept. 11:270. 1898.

204. Ibid. 11: 273.

205. Waugh, F. A. Vt. Agr. Exp. Sta. Bui. 74. 1899.

206. Webber, H. J. et al. Cal. Agr. Exp. Sta. Bui. 304. 1919.

207. West, F. L., and Edlefsen, N. E. Utah Agr. Exp. Sta. Bui. 151. 1917.

208. West, F. L., and Edlefsen, N. E. J. Agr. Res. 20: 8. 1921.

209. Whipple, O. B. Mont. Agr. Exp. Sta. Bui. 91. 1912.

210. Whitten, J. C. Mo. Agr. Exp. Sta. Bui. 38. 1897

211. Ibid. Bui. 49. 1900.

212. Whitten, J. C. Mo. Agr. Exp. Sta. Res. Bui. 33. 1919.

213. Wiegand, K. M. Bot. Gaz. 41:373. 1906.

214. Wiegand, K. M. Plant World. 9: 2. 1906.

215. Wilcox, E. V. Mont. Agr. Exp. Sta. Bui. 22. 1899.

216. Wilson, W. M. Standard Cyclopedia of Horticulture. 3: 1282. 1915.

217. Winkler, H. Jahrb. f. Wiss. Bot. 52: 467. 1913.

218. Young, F. D. U.S.D.A., Farmers' Bui. 1096. 1920.

219. Young, F. D. U.S.D.A., Mo. Weather Rev. 48: 463. 1920.

SECTION IV
PRUNING

Fruit production by the trees, shrubs and vines that yield edible
fruits is dependent on (1) the possession of the mechanism or machinery
for fruit production that is characteristic of the species or variety in
question and (2) its proper and more or less efficient functioning. Thus
it is characteristic of most varieties of the brambles to bear fruit clusters
terminally on short shoots developing from lateral buds on year-old
canes. If the plant is so handled as to prevent or reduce the formation
of lateral shoots of this type, fruiting is correspondingly limited. It is
characteristic of certain varieties of the walnut to bear terminally only
on short shoots developing from terminal buds on the growth of the previ-
ous season. Obviously then the production and preservation of terminal
buds is a prerequisite to fruit production in those varieties. The peach
bears fruit on shoots of the past season but only at nodes from which no
lateral branches arise.

However, some of the lateral buds on last year's raspberry and black-
berry canes do not produce fruiting shoots; some of the shoots from ter-
minal buds of the walnut are barren and many nodes on the unbranched
primary peach shoot do not have fruit buds. The framework, the
machinery, for fruit bud formation is apparently there, but no fruit buds
are formed. The mechanism does not function in the way it is desired.
This functioning or non-functioning of the fruiting machinery is to be
regarded as a definite response to varying conditions within the tree —
primarily conditions of nutrition, which in turn may be influenced by
age, vigor, food supply, temperature, humidity and many other factors.

In some cases production is limited by the amount of fruiting machin-
ery, or, as the grower would say, the amount of bearing surface. In
others the limiting factor to production is the irregular, imperfect or
inefficient functioning of the fruiting mechanism. For the grower the
ideal condition is to have the plant well equipped with fruit producing
machinery and to have that machinery working efficiently. One or two
further parallels may be drawn at this point between the living plant and
the hypothetical manufacturing establishment with which it has been
compared. Good equipment with fruit producing machinery does not
mean the maximum amount that can be crowded into the available room
any more than an amount plainly inadequate for the establishment. Too
much fruiting wood unduly taxes the tree for its maintenance. On the

388

PRUNING 389

other hand maximum production cannot be expected from a half-equipped
plant. An efficiently working machine is not one that is carrying an over-
load any more than it is one carrying half or a third of a load. Regular,
steady, annual production of large but not maximum amounts is desirable.

Perhaps in certain species the problem of securing heavy and regular fruit
production is somewhat simpler than has been indicated. In the jaboticaba
whose blossoms and fruits come out indiscriminately anywhere on the bark,
from the crown or even exposed roots to the tips of the youngest branches, the
question of developing a special fruit producing mechanism never arises. The
plant cannot grow without developing its fruit machinery and it is only the
proper functioning of this bark that is a limiting factor to production. Certain
other tropical and subtropical fruits present other apparent exceptions to the
general statements that have been made, but they need not be given serious con-
sideration here, for they do not alter materially the general principles involved
or their application in deciduous fruit production.

Therefore it is desirable to determine as nearly as possible the exact
nature of the fruiting habits of the different species and the methods by
which they can be modified and controlled. What is the fruiting mechan-
ism of the various fruits? What constitutes an adequate equipment for
plants of different sizes or ages? How can the amount best be increased
or limited? How does it usually function under varying conditions?
What methods can be employed to make it work at full efficiency, carry a
full load, year after year? How long does the machinery last? What are
the best means of getting rid of useless or inefficient machinery and of
securing new equipment? When is it best to attempt to repair and speed
up equipment that is working poorly and when is it best to discard it and
obtain new? The answers to these and many other related questions are
of first importance to the grower, for profitable production depends on
them to no small degree.

CHAPTER XXI
GROWING AND FRUITING HABITS

Left to themselves the plants of each species, or even of each variety
show more or less distinctive growing and fruiting characteristics. The
former are partly under the control of the grower, so that it is possible
for him to make plants of quite different growing habits assume a nearly
uniform shape in the orchard or to train two of the same kind so that they
appear very unlike. His control over bearing habits is less complete
though much can be done to modify them in certain directions. Both are
influenced directly or indirectly by nearly every cultural practice. Prun-
ing, however, using that term in its broader sense, is the most direct and
most important of these practices.

Some growers prune their trees; some do not. Others prune some of
their fruit trees, but leave other kinds unpruned. The trees or plants of
certain species are quite generally given some kind of pruning treatment ;
those of certain other species are almost as generally let alone. In some
orchards pruning is a regular annual operation; in others it is done bienni-
ally or at long irregular intervals. There is no horticultural practice con-
cerning which there is a greater diversity of opinion or in the application
of which there is a greater diversity of procedure. If the average grower
is asked why he prunes or why he does not his answer is likely to be that he
believes it is good for the tree or that it is not good for it. Seldom does he
give specific objects that he has in mind or that he beheves may be accom-
plished by means of pruning. If specific objects are mentioned they are
likely to be among the following: (1) to open the tree so that the fruit
will color more satisfactorily, (2) to train it to some desired form, (3) to
remove dead or diseased limbs, (4) to remove water sprouts, (5) to thin
the fruit.

All of these are accomplished by pruning if the work is done properly;
nevertheless they are not its primary objects. Fundamentally, pruning,
in common with other cultural practices, should be directed to encourage
the production of larger quantities of fruit, the production of fruit of
better grade, or to lower the cost of production ; its value, like that of
any other orchard operation, may be determined by the extent to which
it contributes in any one or more of these three directions.

Pruning may be considered from many points of view and subdivided
in many ways. In the following discussion it is considered briefly as a

390

GROWING AND FRUITING HABITS 391

means of modifying shape and in more detail as it influences development,
location and functioning of the fruiting machinerj^ of the tree.

PRUNING FOR FORM— TRAINING

There is frequent failure to distinguish clearly between pruning and
training. The two practices are often regarded as one and the same or
at least as inseparable. Training concerns form primarily; pruning
affects function primarily. Training determines the general character
and even the details of the plant's outline and of its branching and frame-
work; pruning is meant to assist more in determining what the tree
does in respect to fruiting. Training may be illustrated by reference
to what may be done easily with the grape. Without cutting off or
cutting back a single cane, it is possible to train a vine on a one-wire
trellis, a two-wire trellis, a three-wire vertical trellis, a three-wire hori-
zontal trellis, an arbor, or in any one of a dozen other ways. The
training simply gives the vine its form and has comparatively little to
do with the number or size of the bunches of fruit it produces. Similarly,
fruit trees are made to assume one form or another — for example, high-
headed or low-headed, open-centered or closed-centered, flat-topped or
pyramidal — and production is influenced comparatively little by these
shapes. It is true that the pruning saw and shears are generally used in
forcing the trees into the one shape or the other, and hence, perhaps the
operation should be spoken of as "pruning for form." Nevertheless
the operation affects form principally and consequently is here discussed
under the heading of training, even though strictly speaking the use of
that term should be limited to such changes in form as are effected with-
out the removal of parts. If parts are removed at such a time and in
such a way as to modify materially the functioning of the whole tree or of
some of its parts, even though its general shape is left unchanged, the
operation should be considered pruning. Many times both shape and
function are modified by a single operation, which then is to be regarded
as both pruning and training; often, however, it is chiefly one feature of
the tree's growth that is influenced.

General Objects. — In general, training has little direct effect on
the amount of fruit borne. Some of the pruning practices that accom-
pany certain methods of training may affect yields profoundly, but the
training in itself is of only secondary importance in this connection. On
the other hand training may be a factor in determining grade, or what
is frequently referred to as " quality. " Its influence on grade is produced
largely through making it difficult or easy to spray thoroughly and
consequently in aiding or hindering the control of insects and diseases.
Standard control measures for certain pests may lose half of their effi-
ciency if the plants have been untrained or poorly trained. This influ-
ence is distinct from and additional to the direct control of certain pests

392 FUNDAMENTALS OF FRUIT PRODUCTION

by cutting out and destroying infected parts. In certain fruits the
shape and openness of the tree is important in influencing the colora-
tion. Training is important also in reducing certain production costs.
Tillage and other soil treatments, spraying, thinning, propping, trellising
and harvesting all may be greatly facilitated by proper training.

In a general way training should tend so to distribute the fruiting
wood and the fruit that all orchard or vineyard operations may be con-
ducted with greatest facility and lowest cost. It should eliminate or
minimize the necessity and cost of trellising, propping, or artificially
supporting the plant and its fruit. It should provide the leaves and
developing fruits with as nearly as possible optimum conditions for
coloration without danger from sunscald and, wherever feasible, it
should aim to provide those conditions least favorable for the work of
injurious insects and diseases. In view of all these possible effects of
training and of the widely varying conditions under which plants of even
the same variety are grown, it is evident that the best method of training
a plant in one situation may be quite distinct from what is best in
another and it often happens that two fruits or two varieties of the same
fruit should be trained differently when grown in the same environment.

Since the training of trees presents certain problems quite distinct
from those of pruning it seems desirable to consider them separately
from their possible influence on function.

Details in Training. — A comparatively large part of the training
that trees are to receive should be given during the first few years of
their growth. It is during this period that they are building their frame-
work and taking on the general form that the grower has decided shall
be theirs during the rest of their lives. During later years efforts are
directed mainly to preserve the form already given the tree and attention
is given to its pruning as distinguished from training.

Height of Head. — By height of head is meant the distance from the
ground at which the main or scaffold limbs branch from the trunk.
Trees in which the scaffold limbs come out within 23^^ or 3 feet from the
ground are spoken of as low-headed; those in which they come out from
the trunk 4 feet or more from the ground are high-headed. The height
of head generally is established at the time of setting by the distance
from the ground at which the top is cut off though it is possible to raise
the head or sometimes to lower it by later treatment. In the older
orchards high-headed trees are the rule. It was thought that high-
heading facihtated cultivation and other orchard operations and perhaps
was better for the tree. More recent tendencies have been in the
direction of lower heads. If properly handled it is no more difficult to
cultivate around and under such trees and pruning, spraying, thinning
and picking are greatly facilitated. Furthermore, low-headed trees are
less subject to sunscald and suffer less from high winds.

GROWING AND FRUITING HABITS 393

Number of Scaffold Limbs. — The number of scaffold limbs found in
orchard trees varies from 2 to 15 or 20. Neither extreme is desirable.
If there are only two or three main scaffold limbs they are almost certain
to form crotches that are likely to split and allow one or both parts to
break down. A large percentage of the injury resulting from trees break-
ing when heavily loaded with fruit or when subjected to severe winds
is due indirectly to sharp crotches that could have been avoided by the
use of more and better spaced scaffold limbs. Should one limb of a
group of three split down, a third of the tree is gone; should one of eight
be lost, most of the tree still remains and the injury, which is much less
likely to happen, is more readily repaired. On the other hand too many
scaffold limbs, as 10 to 12, give rise to thick, brushy tops that make
work in them difficult. A moderate number, five to eight, makes a
tree that is mechanically strong and at the same time open enough to
facilitate necessary orchard operations.

Distribution of Scaffold Limbs. — Of still greater importance than the
number of scaffold limbs is their distribution. When they come out from
the trunk at points close together, as for instance, when the upper one of
five is onl}^ 8 or 10 inches above the lowest they form bad crotches much
sooner than if they are distributed over a longer distance on the trunk.
When they are distributed over 11^ or 2 feet of the trunk each limb has
a chance to make more or less " shoulder;" weak crotches with subsequent
splitting are avoided. It may require a little attention to select and
develop scaffold limbs that are separated well from one another, on
account of the tendencj^ of the tree to make its most vigorous growth
from buds near the end of the trunk or near the extremities of its branches
but it is well worth while. Furthermore, it should be remembered that
the distribution of these limbs is determined once and for all by the first
two or three prunings and no amount of later work will entirely correct
a mistake made then. If a tree is headed at a height of 33 to 36 inches
it is possible to have a good number of well-distributed limbs and at the
same time have a low-headed tree. One of the main advantages of the
"modified leader" type of training is the opportunity for a wide spacing
of the scaffold limbs.

Ope7i and Closed-centered Trees. — There has been much discussion over
the relative merits of open-centered or vase-shaped and close-centered
or leader trees. Both forms have their advocates. Both are extensively
used and both are successful — good evidence that the exact form in which
trees are trained is a matter of secondary importance from the standpoint
of production. Theoretically at least, the open-centered method of
training admits more sunlight and thus enables the fruit to attain a
higher color than is possible in the closed-centered tree, though in reality
the tree that is started with the open center is often allowed to become
more thick-topped than many "leader" trees. Obviously, this is a

394 FUNDAMENTALS OF FRUIT PRODUCTION

matter that can be of no real importance in fruits where coloration does
not depend on the light reaching the fruit itself. From the very nature of
the case the central-leader type of tree forms more scaffold limbs than the
open-centered tree and consequently it is less likely to split at the crotches.
It is often more bushy-topped but this condition is not necessary.

It has become a generally accepted practice to train certain fruits in
certain styles. For instance, peaches are almost always grown in the
vase form and pears are trained with a central leader. In some cases
whole sections use a certain style for practically all their tree fruits. To
what extent these practices are based on careful comparisons of different
methods of training for the fruit or the locality in question and to what
extent they are followed simply because the custom has become estab-
lished is often difficult to say. A careful study of training methods might
lead in many cases to some change that would be of considerable com-
mercial importance to the particular district or for the particular variety.

The general method of procedure in training a tree to the central-
leader type is each year to prune back the central and upper shoot or
leader less severely than the lateral shoots or hmbs surrounding it. If an
open-centered tree is desired the opposite method should be followed.
It is a mistake in attempting to train a tree to the open-centered type
to cut out entirely the interior and central limbs. This merely provokes
the production of water sprouts to take their place and more cutting out
must be done. By cutting back the interior and upper shoots and limbs
more severely than the outer, the former are subordinated and the latter
are made the dominant limbs in the tree. In other words, it is easier
and better to grow an open-centered tree with a comparatively open
center — with only a few, small, subordinate, fruiting branches in the
interior — than one with a completely open or hollow center.

A different type of training that is coming into favor is known as
the "modified leader." As the name suggests, it is intermediate between
the open-centered and the leader tree. It is developed by training to the
leader type for the first 4 or 5 years and from then on as an open-centered
tree. This results in a tree with a central leader extending some 3 to 5
feet above the point where it was originally headed and then an open
center above that. It possesses practically all the advantages of the two
other types and few or none of their disadvantages.

Trees of Different Shape. — Less attention need be devoted to the
general shape of the tree than to certain other features of its training.
Nevertheless, there are occasional arguments for flat-topped or round-
topped trees or other forms. In general, little emphasis should be placed
on these particular shapes. It is not a bad plan to allow the tree con-
siderable freedom in assuming the general shape that is natural. Training
for form should be limited to correcting minor defects rather than altering
profoundly the shape.

GBOWING AND FRUITING HABITS 395

Lowering the Tops of Trees. — In the course of time the trees of many
species become so tall that the added cost of gathering the fruit from the
topmost branches reduces the margin of profit to the vanishing point.
Furthermore the higher branches shade the lower and reduce their effi-
ciency as fruit producers. The increased difficulty in controlling insects
and diseases in the tops of very tall trees, even with the aid of the best of
the present power spraying outfits, makes those portions of doubtful
value to the grower even though it should be possible to harvest the
fruit economically. One investigator sets 25 feet as about the limit
in height for profitable apple production '^ ^nd with the smaller spraying
outfits the limit is probably well below that figure. The problem of
controlling the height of trees and keeping their lower branches actively
producing a good grade of fruit is thus very real.

Many growers wait until the trees get much too tall for profit and then
"dehorn;" that is, they cut back the limbs severely, leaving large stubs
that promptly send out an abundance of strong vigorous watersprouts.
Eventually new fruiting wood is developed from this new growth, but in
the meantime crowding is likely to force this new growth up, so that by
the time the top has been bearing a few years it is too high again and
another dehorning becomes necessary.

A much better method of lowering the tops of tall trees is to cut back
into 2-, 3-, or 4-year-old wood, always to a lateral branch. The more
nearly horizontal this side limb, the better. By thus cutting to a lateral
the flow of sap is utilized in a somewhat increased growth and few or no
watersprouts develop. A year or two later this lateral can be cut back
to one of its side branches, or perhaps the whole structure can be removed,
the cut being to a still lower side limb on the main branch that in the mean-
time has been strengthened by the heading back of the season before.

This, it will be recognized, is a procedure aiming constantly to keep
the tree within bounds rather than permitting it first to become far too
tall and then greatly reducing its height. To be most successful it
should begin when the tree reaches about the desired height and from
then on it should constitute a part of the regular annual treatment that
the tree receives. It will not be necessary to lower every part or limb
of every tree each year; only the tallest, those getting too high, need be
cut back. This practice not onlj^ results in the production of fewer
watersprouts but it keeps the lower part of the tree in a better producing
condition than is possible with occasional dehorning. It is a heading
back in name mainly — really resulting in more thinning than cutting
back — and is followed by the kind of a response that attends thinning
out.

Eliminating and Subordinating Limbs. — It has just been stated that
in the training of open-centered trees it is usually better to suppress or
subordinate the interior limbs than to attempt their total elimination.

396 FUNDAMENTALS OF FRUIT PRODUCTION

This last can be done by cutting them out and then repeatedly removing
watersprouts that take their place, but this involves much labor. If
they are subordinated the water sprout problem is largely eliminated
and they may serve as fruit-producing branches for many years. In
apples, pears and other spur-bearing fruits, their retention may also aid
materially in bringing the trees into bearing earlier, because if properly
handled they develop fruit spurs and fruit buds freely at a period when
heavy pruning back for proper form may prevent to a great extent
formation of spurs on the more permanent framework of the tree. Often
one of the best ways to subordinate and make fruiting branches from
these interior limbs is to let them remain with no heading back at the
beginning of their second season. They then produce short vegetative
growths from their terminal buds, with few or no lateral shoots but with
many lateral spurs. After their second season's growth they are headed
back into 2-year-old wood. Treated in this way they make but little
further shoot growth and little difficulty is experienced in keeping them
as subordinate fruit-bearing limbs.

Preventing the Formation of Crotches. — It is a principle of rather gen-
eral application that the unequal cutting back of two parts in the same
tree or plant tends to subordinate that part pruned more severely and
to give the advantage to the other. Equal cutting of two shoots or
limbs of about the same length results in their equal subsequent develop-
ment into a fork or crotch that is a point of weakness in the framework of
the tree. Crotches can be largely avoided and the framework corre-
spondingly strengthened by pruning with the idea of making one of two
equal branches a leader and the other a lateral subordinate to it.

BEARING HABITS

There is reason to believe that with proper nutritive conditions in the
plant, particularly with an accumulation of certain carbohydrates, any
partly developed bud may undergo differentiation, form flower parts
and develop as a fruit bud. This assumes that other limiting factors,
such as moisture and temperature, are favorable. It is conceivable that
in the developing buds of some plants a stage is finally reached when
such a differentiation cannot take place except by the unfolding of the
bud into a leafy structure and the subsequent formation of the fruit bud
at a new growing point. In general, though, every bud is to be regarded
as a potential flower bud. In every kind of plant, however, most of the
flower buds are formed in certain definite positions, probably because it
is only in those positions that nutritive and other conditions favorable
for flower bud formation ordinarily occur. It is therefore possible to
speak of the bearing or fruiting habit of a plant, though the use of this
term does not mean that other types of bearing, other fruiting habits,
may not be found on the same plant under unusual conditions. Not

GROWING AND FRUITING HABITS 397

infrequently the crop borne from flowers appearing in such an unusual
place exceeds that produced by those considered characteristic. For
instance, the nectarine would be classed generally as a tree bearing its
fruit buds laterally on shoots, but the Stanwick variety is as typical a
spur bearer as the Montmorency cherry.

Since all buds are to be regarded as potential flower buds, flowers or
inflorescences and hence fruits, may be borne wherever buds are borne —
usually (1) terminally on long or short growths, or (2) laterally in the
axils of the current or past season's leaves and now and then (3) adven-
titiously from any point on the exposed bark of limbs, trunks or roots.
As a rule the position of the flower or inflorescence on the shoot relative
to the growth of the current season is characteristic of the species or
variety and is subject to but little change. The inflorescences of the
raspberry and blackberry are always terminal to the growth of the current
season and the flowers or inflorescences of the persimmon are always
lateral. Flower-bearing shoots may arise from either terminal or lateral
buds on either long or short growths (spurs), or they may arise from
adventitious buds. There is often considerable variation within the
species, variety, or even individual plant in this respect.

Relation of Growth Habits to Position of Fruit Buds. — Within limits
certain habits of growth are necessitated by or at least are associated with,
particular fruiting habits. In general, plants with terminal fruit buds
have a somewhat restricted habit of growth. Terminal bearing tends to
promote greater compactness of tree or plant than bearing from lateral
fruit buds, because it forces the development of laterals from below,
rather than beyond, the flowers or flower clusters. Plants whose fruit
buds are borne either terminally (apple) or laterally (sweet cherry) on
short growths or spurs are generally more compact than those like the
peach or grape whose fruit buds are borne on long shoots and the problem
of preventing their bearing areas from getting too far away from the
trunk or head of the plant is less serious. If fruit buds are borne later-
ally on long shoots there may be a distinct difference in the general man-
ner of growth, depending on whether they are found principally on the
basal, median or distal portion and the grower will employ a "short,"
"medium" or "long" pruning system, as the case may be.

Different Kinds of Flower-bearing Shoots. — Regardless of the location
of the fruit bud — that is, whether terminal or lateral — when it unfolds it
may give rise to any one of three distinct types of flower-bearing struc-
tures: (1) it may contain flower parts only and develop a single flower
(as in the peach) or a flower cluster (as in the cherry) without leaves, (2)
it may be a mixed bud and develop a short or long leafy shoot terminating
in an inflorescence (as in the apple), (3) it may be mixed and develop a
short or long leafy shoot bearing flowers or flower clusters in some of its
leaf axils (as in the persimmon).

398 FUNDAMENTALS OF FRUIT PRODUCTION

Classification of Fruits According to Fruiting Habits

Fruit buds terminal

Fruit buds lateral

I

IV

Flower bud containing

Loquat

Peach

flower parts only

Mango

Plum

Apricot

Cherry

Almond

Plumcot

Currant

Gooseberry

Kumquat

Northern papaw

Walnut (staminate catkins)

Hickory (staminate catkins)

Pecan (staminate catkins)

II

V

Flower bud mixed

Apple (principally)

Blackberry

Flowering shoot with

Pear (principally)

Raspberry

terminal inflorescences

Quince

Dewberry

Medlar

Grape

Hawthorn

Filbert

Haw

Blueberry

Elder

Cranberry (European)

Juneberry

Cashew nut

Walnut (pistillate flowers)

Brazil nut

Hickory (pistillate flowers)

Pond-apple (and various

Pecan (pistillate flowers)

other anonaceous fruits)
Apple (occasionally)
Pear (occasionally)

III

VI

Flower bud mixed

Guava

Persimmon

Flowering shoot with

Tropical almond

Mulberry

lateral inflorescences

Rose-apple (.and other species

Fig

of Eugenia)

Cranberry (American)

Olive (partly)

Chestnut

Chinquapin

Oak

Beech

Pistachio

Star-apple

Jujube

Avocado

Olive (partly)

GROWING AND FRUITING HABITS 399

A Classification of Plants According to Bearing Habits. — Since the
flower bud itself is either terminal or lateral, there are six main types of
fruiting, six distinct bearing habits, the classification being based upon
the location of the fruit buds and the type of flower-bearing structure to
which they give rise. These six main groups together with the more
important of the fruits they include are shown in the accompanying
diagram.

There are endless variations within these main groups; certain
species or varieties sometimes bear in one way and sometimes in another,
or in two or more ways at the same time.

The following discussion points out some of the peculiarities of the
more important fruits. Several special groups also are included to bring
together those fruits having in their bearing habits certain peculiarities
that make it desirable to consider them separately from the main groups
to which they might be referred.

Group I. — Fruit buds borne terminally, containing flower parts only
and giving rise to inflorescences without leaves.

None of the common deciduous fruits has this bearing habit. It is best
illustrated perhaps by the loquat and the mango (see Fig. 39). Growth is con-
tinued by branches rising from lateral buds below the inflorescence; some of these
branches form terminal buds for a succeeding crop. The indications are that in
the mango fruit bud differentiation does not take place long before the flowering
season and sometimes two, three or even four crops of flowers are formed during
the year, though this is not hkely if there is a good set of fruit which is carried
through to maturity. In case some accident happens to the terminal flower bud
of the mango, some of the a.xillary buds may differentiate flower parts and thus
form fruit buds.

Group II. — Fruit buds borne terminally, unfolding to produce
leafy shoots that terminate in flower clusters.

This bearing habit is characteristic of most of the pome fruits and is
found likewise in a few others of minor economic importance.

In the apple and pear most of the terminal fruit buds are on spurs,
(see Fig. 40) though in young vigorous trees of certain varieties many
of the long shoots form terminal flower buds. Seldom, however, is any
considerable percentage of the crop borne in this latter way. The fruit
buds of these plants are mixed and invariably give rise to very short
growths with a few short internodes, leaves of ordinary size and a lateral
branch (sometimes two or more) arising in the axil of one of the leaves; this
branch may bear fruit the following season, though usually fruit bud
formation is delayed a year or more. The spur may live a great many
years and bear repeatedly. The actual records of individual spurs
generally show an irregularly alternate bearing habit. New spurs origi-
nate from lateral buds on shoots of the preceding season and occasionally
from latent or adventitious buds on the trunk or older limbs. The

400 FUNDAMENTALS OF FRUIT PRODUCTION

continued bearing of the individual spurs makes for a comparatively
compact type of tree growth.

The juneberrj^ or shadbush (Amelanchier) and hawthorn or azarole {Cratoe-
gus) have bearing habits practically identical with those of the apple and pear
just described.

Mention should be made that both the apple and pear occasionally bear
lateral fruit buds on long shoots. Certain varieties, like Wagener, are particu-
larly given to this habit. It is found more frequently in young vigorous trees
than in those with a settled bearing habit. However, the fact that it may occur
on almost any variety and that occasionally a considerable percentage of the
crop may be borne in this way, is evidence that this habit is a response to unusual
nutritive conditions. The special treatment that should be accorded trees
fruiting in this manner is discussed under Pruning of the Apple and Pear.

/
Figs. 39-42. — Diagrams showing (from left to right) bearing habits of loquat, apple
olive and peach. F equals fruit; B equals flower bud; L equals leaf bud. One-year-old
wood shown by solid line, two-year-old wood by broken line.

The bearing habit of the quince and the medlar is similar to that of the
apple and pear, except that when the terminal (mixed) fruit bud unfolds
it gives rise to a leafy shoot of medium length, with medium long instead
of short internodes and the flowers are borne terminally on this shoot.
Fruit buds for the following season's production are borne terminally on
shoots springing from lateral buds on either flowering or non-flowering
shoots, or from terminal buds on older shoots that the year before did not
differentiate flower buds. These fruits consequently are not such com-
pact growers as the apple or pear, though the shorter growth of their
purely vegetative shoots and the greater tendency for their lateral buds to
grow rather than remain latent may give them a very thick and brushy
appearance.

The haw {Viburnum), elder (Sambunis), and clove (Caryophyllus aromaticus)
have bearing habits similar to the quince and medlar, though occasionally they
differentiate flower buds terminally, like the apple and pear on short growths,
which are essentially spurs. All these fruits are opposite-leaved and it fre-
quently happens that the lateral buds in the axils of the upper leaves differenti-
ate flower parts. This is more likely to happen if the terminal bud is injured or
destroved.

GROWING AND FRUITING HABITS 401

Group III. — Fruit buds borne terminally, unfolding to produce
leafy shoots with flowers or flower clusters in the leaf axils.

This might be called an incomplete terminal bearing habit, for the
fruit itself is not borne terminally, but is lateral to the growths upon which
it appears. However, the flower buds are terminal. The terminal buds
of the flowering shoots may differentiate flower parts for the following
year's production or new buds may develop from lateral leaf buds.

None of the common deciduous fruits has this bearing habit. It is found in
the pomegranate, the tropical ahnond {Terminalia catappa), the guavas {Psidium
spp.), the olive, and in a number of the species of Eugenia. In the pomegranate,
guava and in the Eugenias the fruit buds are formed on short shoots or spurs
and the flowers and fruits in the axils of the outermost leaves. In the oUve the
inflorescences are generaUy found in the axils of the shoot's lower leaves and
flowering shoots sometimes spring from lateral as well as terminal buds (see Fig.
41). The tropical almond {Terminalia) has a somewhat })eculiar growing and
fruiting habit, the terminal mixed flower buds being formed on the ends of long
shoots. When these unfold they give rise to short growths or spurs, in the axils
of whose upper leaves flowers and fruits are borne. The long growths or shoots
originate from lateral buds.

Group IV. — Fruit buds borne laterally, containing flower parts only
and giving rise to inflorescences without leaves or if leaves are present
they are much reduced in size.

In the peach, lateral fruit buds are formed on the long shoots (see
Fig. 42). Two additional or supernumerary leaves commonly appear
at many nodes as the season progresses and fruit buds develop in their
axils. The bud in the axil of the original leaf generally remains a leaf
bud; rarely it too differentiates flower parts. This whole structure may
possibly be considered a much reduced secondary growth. Often only a
single extra leaf develops at the node, in which case only one fruit bud
forms at that point, that in the axil of the supernumerary leaf. The
peach also forms fruit buds on secondary or even on tertiary lateral
branches. As a rule when the fruit buds occur on the upper or outer
portions of secondary shoots and sometimes on the primary shoots, they
are single, being differentiated from the bud in the axil of the single leaf.
They are quite likely to be in pairs at the more basal nodes. As already
stated, the flower buds of the peach are usuallj^ produced on what would
be called long growths or shoots, though under certain cultural and prun-
ing treatments many varieties form short laterals that are comparable
to spurs in every way. The flower bud of the peach produces only one
flower. Growth is continued b}^ terminal or by lateral leaf buds.

The sweet cherries and the Domestica and Insititia groups of plums
form their flower buds for the most part laterally on spurs (see Fig.
43). These come from lateral buds on the shoots of the preceding season

402 FUNDAMENTALS OF FRUIT PRODUCTION

and their new shoots form both terminal and lateral buds on shoots or on
older wood.

The almond, apricot, plumcot, the Japanese and American plums, the
sour cherry, the currant and the gooseberry have a fruiting habit which is
a combination of that of the peach on the one hand and the sweet cherry
on the other. They bear in both ways, though certain varieties may
show a greater tendency in the one direction or the other. As a rule,
frmt-bud production on shoots gradually gives way to production on
spurs as the plants become older and less vigorous. Supernumerary fruit
buds are produced freely at the nodes of the long vigorous shoots of Japanese
and American plums and in the currant and gooseberry.

•a

ti^

Figs. 43-45. — Diagrams showing (from left to right) bearing habits of sweet cherry,
raspberry and grape.

The kumquat (Citrus Japonica) and the northern pawpaw (Asimina triloba)
differentiate their flower buds in the axils of the leaves on long shoots of the
current season and the following season these buds give rise to leafless inflores-
cences. This bearing habit corresponds to that of the sweet cherry, except that
production of the flower buds is on long rather than on short growths.

Group V. — Fruit buds borne laterally, unfolding to produce leafy
shoots that terminate in flower clusters.

The blackberry, raspberry, dewberry and their hybrids form fruit
buds either on primary shoots that come up from their crowns or roots
each year, or on their secondary lateral shoots (see Fig. 44). These
flower buds develop into leafy shoots with terminal inflorescences and
individual flowers or flower clusters in the leaf axils. In most varieties
the entire cane dies after bearing and growth is continued by the forma-
tion of new canes springing from the crown or roots.

In the unopened flower bud of the grape (see Fig. 45), the inflores-
cence is terminal to a leafy shoot also within the bud, like that of the
raspberry and blackberry. As the bud opens, however, the bud in the
axil of the topmost leaf of this developing shoot unfolds and continues
the growth of the shoot. This results in pushing the flower cluster to
one side so that the inflorescence appears lateral and opposite a leaf.
Several flower clusters are formed terminally at successive intervals on

GROWING AND FRUITING HABITS

403

the same shoot and in turn are crowded to one side and hence to appar-
ently lateral positions. As a rule only certain branches or canes of the
grape bear lateral buds that differentiate flower parts. These branches
or canes usually arise from buds near the base or in the median portion
of bearing shoots. What appears to be the bud or "eye" of the grape
really consists of two or three buds within the one; a well developed
central shoot and one or two less highly developed lateral growing points.
In case the central bud develops prematurely and is killed by frost, its
place may be taken by another of the group. Occasionally the grape
produces flowering shoots from latent or adventitious buds.

In the filbert, which has no ti-ue terminal buds, some of the more
apical lateral buds develop into short leafy shoots ending in clusters of
pistillate flowers (see Fig. 46). Other lateral buds grow out into dwarf
shoots, which are without normal-sized leaves, are branched and really
constitute the male inflorescences. These remain dormant until winter
or early spring when they open to discharge their pollen. At the base

Figs. 46-48. — Diagrams showing (from left to right) bearing habits of filbert, chestnut
and walnut. In filbert and walnut B equals pistillate flower buds, C equals staminate
flower buds; M equals male catkins.

they may have resting buds which give rise to vegetative or pistillate
flower-bearing shoots the following year.

The cashew nut {Anacardium) and the Brazil nut (Bertholletia) also bear
terminally on shoots from lateral buds.

In the cherimoya, pond-apple, sour-sop, sugar-apple and various other
Anonaceous fruits the fruit buds are borne laterally and the inflorescences
terminally, with the growth of the flowering shoots proceeding much as in the
grape. Here the flowers and fruits appear to be between nodes, or extra-axillary.
Not infrequently they develop on short spur-like branches.

In the blueberries the inflorescences develop both terminally and in
the axils of leaves on new shoots springing from lateral buds. This bear-
ing habit is a combination of the typical concHtions found in Groups V
and VI as here classified. Ordinarily there are no true terminal buds in
this group but if terminal buds are formed they are usuallj^ fruit buds.
In Vaccinimn atrococcum the flowering shoot has no foliage. Fruit bud
differentiation apparently takes place in late fall in the axils of leaves
near the end of the shoot.

404 FUNDAMENTALS OF FRUIT PRODUCTION

The European cranberry {Vaccinium oxycoccus), litchi {Nephelium litchi)
and sea-grape {Coccoloba iwifera) have similar bearing habits.

Group VI. — Fruit buds borne laterall}^ (or pseudoterminally), unfold-
ing to produce leafy shoots with flower clusters in the leaf axils.

In the persimmon any lateral bud and not infrequently adventitious
or dormant buds on 2-year-old or older wood, may become a fruit bud.
The following year these unfold and form leafy shoots with solitary
pistillate or with clusters of staminate flowers in the axils of the more
basal leaves. The male and female flowers may be borne on the same
tree or on different trees.

The mulberry has a similar bearing habit, except that both pistillate
and staminate flowers are usually borne on the same flowering shoot.
The male flowers are formed in the axils of the more basal leaves and the
pistillate flowers in the axils of higher leaves.

In the American cranberry {Vaccinium macrocar'pon) the flowering
shoots arise from lateral buds on the creeping vegetative branches. The
flowers are borne singly in the leaf axils.

The chestnut, chinquapin, oak and beech have very similar bearing
habits (see Fig. 47). The pseudoterminal or more apical lateral
buds, when they differentiate flower parts, give rise to shoots in the axils
of the leaves. Male catkins appear in the lower axils and female, or
mixed male and female, clusters above them. Sometimes dwarf shoots
arise from the basal buds in the chestnut and produce male catkins only
in the leaf axils. True terminal buds are sometimes formed in the oak
and beech and these may be fruit buds. In the beech there are short
spur-like growths which have no lateral buds except a single pseudo-
terminal bud. This is never a flower bud.

The fig bears lateral fruit buds. Its pseudoterminal bud, which is usually
larger than the others, is generally vegetative. Frequently more than one
bud is formed in a leaf axil and they appear in pairs, side by side. The fruits are
formed singly in the leaf axils. The fig can bear three (or more, according to
some authorities) distinct crops in a year.

In the avocado the lateral flower buds give rise to flowering shoots in which
the inflorescences are in the axils of the more basal leaves.

The pistachio {Pistacia vera) and star apple {Chrijsophyllum) have a similar
bearing habit and the olive, which has been mentioned as belonging in Group
III, might as readily be included here, since it produces lateral as well as terminal
flower buds.

In the jujube {Zizyphus jujube) several flowering branches may arise at a
single node. Solitary flowers are borne in the leaf axils of these branches. After
the ripening of the fruit the leaves and fruit fall off and finally the entire branch
falls. Buds for the following crop are differentiated on strictly vegetative
branches. There is thus a definite dimorphism of branches in this species, the
fruiting branches being deciduous and not forming a part of the permanent
framework of the tree.

GROWING AND FRUITING HABITS 405

Group VII. — Fruit buds borne both terminally and laterally, inflo-
rescences generally terminal. The fruits that are discussed here might
be included with those of Groups II and IV for they represent a combi-
nation of those two fruiting habits, but for convenience they are con-
sidered separatel.y.

In the walnut, hickory and pecan the terminal bud may give rise to
a short leafy shoot ending in a female inflorescence (see Figure 48). The
male flowers are borne on leafless inflorescences arising from lateral
buds not far below the terminal. In the walnut there are two superposed
buds in each leaf axil, the upper being usually the first to open. At a
single node two male inflorescences may appear simultaneously from the
two buds, or a leafy shoot may come from the upper and an inflorescence
from the lower. In the hickory the male catkins are sometimes borne
in the axils of the basal leaves on the terminal shoot, resulting in the pro-
duction of male and female flowers on the same shoot.

Group VIII. — Fruit buds adventitious. Since adventitious fruit
buds are necessarily lateral, the plants included here might readily be
classed with those of Groups IV, V or VI. However, this bearing habit
is more or less distinct and these fruits may well be placed in a separate
class.

The jaboticaba and cambuca form adventitious flower buds on their trunks,
main and smaller limbs and even on their exposed roots. These produce no
leaves when they open.

The cacao bears in the same way, though the flower buds appear first on the
trunk and as the trees grow older, on the whorled branches.

The coffee produces fruiting branches from adventitious buds at the nodes.
The upper bud becomes a horizontal fruit-bearing branch, the lower an upright
vegetative shoot.

Group IX. — There is another group of plants which have fruit buds
in the axils of the leaves and in which these buds unfold and develop
their flowers and fruits very soon after the flower parts are differentiated.
However, it is not possible to draw a clear line between this fruiting
habit and that described for Group IV.

This group includes the passion fruit (Passiflora), the papaya (Carica papaya)
and many others with a more or less herbaceous type of growth. In culture,
as well as in growing and fruiting habits, these plants resemble certain vegetables
more closely than deciduous fruits.

The Relation of Fruiting Habit to Alternate Bearing.— Terminal
fruit bud formation often has been regarded as an explanation of the
alternate bearing frequently occurring in species or varieties with
this fruiting habit. However, not all the terminal buds on shoots and
spurs of plants with a terminal-fruit-bud-bearing habit develop into
fruit buds at one time. Many are leaf buds and unfold Icafv non-

406 FUNDAMENTALS OF FRUIT PRODUCTION

flowering shoots or spurs. Fruit bud differentiation depends on
nutritive conditions in and about the terminal bud at such time or times
when differentiation can take place. Terminal bearing involves a definite
limitation to shoot or spur extension in a straight line. New vegetative
extension must be from lateral buds if all terminals form fruit buds in
one season, but this seldom occurs and those buds that do not become
fruit buds one year may therefore become differentiated into fruit buds
the next season. In this way regular annual bearing is possible if nutri-
tive conditions within the plant remain such that fruit bud differentia-
tion can occur each year. Even if all terminals were to differentiate
fruit buds one season and to flower and fruit the next, there would still
be opportunity for the formation of another set of fruit buds terminally
on the new shoots or new spurs. Therefore regular annual bearing would
still be possible provided nutritive conditions were favorable. The
terminal fruiting habit does not in itself lead to alternate bearing except
in the event that practically every terminal forms a fruit bud one season
and sets fruit the next while at the same time growing conditions this
second season prevent fruit bud differentiation on the new shoots or
spurs developed from lateral buds. When this extreme is encountered
it should be handled as a problem in nutritive conditions to be corrected
by the control of environmental factors. In other words, though many
varieties of plants which bear fruit buds terminally are much inclined
to alternate bearing, that tendency is not a necessary product or accom-
paniment of terminal fruit bud formation.

Obviously the production of fruit buds laterally on either spurs or
shoots makes every provision for regular annual bearing, not only of
the plant as a whole, but of the individual part, if conditions within the
plant are favorable for fruit bud differentiation.

Regularity of bearing, therefore, is a cultural problem, to be dealt
with by influencing nutritive conditions. Attention is given to this
phase of the question in the section on Nutrition.

Possible Causes of Different Bearing Habits. — Knowledge of bearing
habits is decidedly fragmentary and little is known concerning the factors
which may control it or influence it in any way. However, it is known
that the apple with its characteristic terminal fruit bearing habit stores
the bulk of its starch in the pith while the peach with its characteristic
lateral fruit bearing habit stores the bulk of its starch in the leaf gaps.
Since carbohydrate, and particularly starch, accumulation is so closely
associated with fruit bud differentiation, at least in the apple, it is
possible that anatomical structure may have much to do with the region
of starch storage and that this in its turn may be an important factor
determining the bearing habit.

Summary. — The general purpose of all pruning is to increase yields,
improve grades and reduce production costs. These objects may be

GROWING AND FRUITING HABITS 407

attained either through modifying the form or through influencing the
functioning of the tree as a whole or of its individual parts. Pruning
for form is essentially training. Training seeks directly to secure the
distribution of the fruit bearing parts that is most advantageous for
economy of production, disease and insect control, for minimum loss
from breaking of limbs and for proper coloration. These ends are fur-
thered by (1) heading the tree properly, (2) providing a reasonable
number of well-spaced scaffold limbs, (3) preventing the formation of
weak crotches, and (4) keeping the tops of the trees from growing too
high or spreading too far. Pursuant to these aims the plants are generally
trained in one or another of several' standard shapes. Thus training
results in a certain degree of uniformity of appearance in the orchard.
The bearing habits of most species and varieties are fairly well fixed,
though they are subject to some modification by pruning and other
cultural treatment. Fruit buds are differentiated either terminally or
laterally and when they open they may give rise to (1) leafless flower
clusters, (2) leafy growths with terminal flower clusters, or (3) leafy
growths with lateral flower clusters. There are thus six distinct bearing
habits and in addition a number of combinations between these types.
The more common fruits are classified in respect to their bearing habits.
Alternate bearing is not a necessary product of any type of bearing. If
nutritive conditions within the tree are favorable fruit buds may be
formed every year. Consequently alternate bearing is a problem in
nutrition. Different bearing habits are probably associated with differ-
ent methods or places of food storage.

CHAPTER XXII
PRUNING— THE AMOUNT OR SEVERITY

Pruning can vary in three major respects and in three only. It can
vary: (1) in amount or severity, (2) in kind or distribution and (3) in the
season at which it is done. Characteristic responses by the plant are
to be expected not only as the pruning varies in any of these three respects
but according to fruiting habit and as the plant itself varies in age, vigor
and nutritive condition. These three major aspects of pruning are dis-
cussed in the order in which they have been mentioned.

A search through horticultural literature reveals a great diversity of
opinion as to the influence of varying amounts of pruning on growth and
productiveness. Some have considered heavy pruning a great stimulant
to vegetate growth especially, though perhaps having the opposite effect
on fruit production. This idea is reflected in the phrase "prune in the
winter for wood." Others have regarded pruning of any kind and more
particularly, pruning in any amount, as a harmful practice because it has
been thought to check growth. Most of these partly accepted ideas have
been based upon theoretical considerations or field observations, of which
some have been sound and accurate but many have been either fallacious
or inaccurate or have failed to consider other important facts. Not until
comparatively recent years have exact and pertinent experimental data
been available.

Influence on Size of Tree. — Bedford and Pickering^ were among the
first to make a careful study of the different effects of various amounts of
dormant season pruning on the apple. Table 1 shows the mean tree
size and weight for all varieties studied and given different pruning treat-
ments covering a period of ten years. The figures for tree size take into
consideration spread and height and trunk circumference. Clearly these
show that the unpruned tree increases in size and weight more rapidly

Table 1. — Influence of Amount of Pruning on Tree Size in the Apple

(After Bedford and Pickering*)

Very Little or no Pruning Moderate Pruning Hard Pruning

Tree size relative. . 106 100 82

Tree weight relativel20 100 84

than the pruned tree and that the heavier the pruning the more pro-
nounced is the check upon growth. In commenting on the somewhat
greater influence of pruning on weight than on size revealed by the figures
in the table Bedford and Pickering remark, ''This increase in weight
must be due to an increase in weight of the stem and main branches, for it

408

PRUNING— THE AMOUNT OR SEVERITY

409

cannot be accounted for merely by the weight of wood removed during
pruning: the prunings would, on an average, have amounted to 27
pounds per tree during the ten years in the case of the moderately pruned
trees, whereas these trees at the end of this time showed a deficit of 49
pounds as compared with the unpruned ones." Gardner'^ in Oregon and
Alderman and Auchter^ in West Virginia (see Table 2), both working
with young apple trees, obtained results leading to the same conclusions.
The unpruned tree increases in size more rapidly than the moderately
or heavily pruned tree, not because it produces more new shoot growth
each year, but because it losses none by pruning. Tufts, ^^ in California,
studying the influence of varying amounts of pruning on newly set
apricots, sweet cherries, peaches, pears and European and Japanese
plums found, in every instance, less rapid increases in trunk circumference
with each increase in the severity of the pruning (see Table 3). Since
he found correlation coefficients ranging from 0.83 to 0.92 for trunk cir-
cumferences and weights of top and coefficients ranging from 0.76 to
0.84 for trunk circumferences and weights of root, depending on the
species, it is evident that trunk circumferences may be taken, other
things equal, as fairly accurate indices to tree size. Consequently his
data, together with those of the investigators already cited, are evidence
that, in general, pruning results in a check to increase in size. At least
it may be considered established that this holds for deciduous tree fruits.

Table 2.

-Influence of Amount of Pruning on Size of Young Apple Trees
(After Alderman and Auchter'^)

Variety

Type of
pruning

Number
of trees

Height
(in feet)

Spread
(in feet)

Stayman

Stayman

Stayman

Rome

Rome

Rome

Gravenstein

Gravenstein

Gravenstein

Stark

Stark

York, Grimes and Rome
York, Grimes and Rome
York, Grimes and Rome

Heavy

Moderate

Light

Heavj'

Moderate

Light

Heavy

Moderate

Light

Heavy

Light

Heavy

Moderate

Light

7.32
7.89
9.50

7.45
8.18
9.16

7.43
6.83
8.94

7.57
10.79

9.55
9.73
10.50

5.29
5.52
5.75

3.68
4.17
4.23

4.05
4.19
4.34

5.17
6.85

4.83
6.17
7 10

410

FUNDAMENTALS OF FRUIT PRODUCTION

Table 3. — Increase in Trunk Circumference under Varying Pruning

Treatments
{After Tufts''')

Kind of fruit

Pruned

severely

(centimeters)

Pruned •
moderately
(centimeters)

Pruned

lightly

(centimeters)

Apricot (Royal) . . .
Cherry (Napoleon)
Peach (Elberta) . . .
Pear (Bartlett) . . . .
Plum (Climax) . . . .

Plum (Pond)

Prune (French) ...

Average

11.7
10.0
12.0

8.7
6.3
7.2
6.2

8.9

12.6
11.2
16.9
9.1
10.4
8.8
7.1

10.9

15.3

12.3

19.4

9.7

11.3

9.4

8.4

12.3

Amount and Character of New Shoot Growth. — The framework of the
tree is developed from its shoots of the preceding or earlier years. Since
the general influence of pruning is to check increase in size, it might be
reasoned that it results in a corresponding decrease in the amount of new
shoot growth produced each year. On the other hand it is possible that
the check to increase in size might be due largely, or even entirely, to the
annual removal of wood. Experimental data on this question were
obtained by Bedford and Pickering.^ They selected a number of shoots
in a tree, all as nearly as possible of uniform length (about 36 inches) and
thickness. Some were pruned back to a length of 6 inches, some to
12 inches, some to 24 and some had only their terminal buds removed.
Table 4 shows the relative numbers, lengths and weights of the new side
shoots that were formed and also the influence of these treatments on the
parent branch. Heavy pruning back resulted in fewer side shoots with
less total length and less weight than lighter pruning or than none at
all. The greatest decrease was in the number of new shoots, from
which it may be inferred that individually these shoots were somewhat
longer and stronger than those on the lighter pruned limbs. The differ-

Table 4. — Effects of Pruning Back Individual Shoots Varying Amounts
(After Bedford and Pickering'^)

Length of shoot after pruning, in inches 6 12 24 36

Weight of original shoot and laterals (relative) 100 179 310 562

Thickening of the original shoot (relative) 100 114 117 129

New shoots formed:

Number (relative) 100 116 198 292

Length (relative) 100 113 145 183

Weight (relative) 100 108 123 142

ence in weight of old wood after a year's growth is particularly striking,
the unpruned trees having over five times the amount of those pruned

PRUNING— THE AMOUNT OR SEVERITY

411

heavily. These same investigators found, however, that in mature
trees that had been bearing for a number of years heavy pruning resulted
in almost twice as much new shoot growth as was produced by unpruned
trees.

On the other hand Blake and Connors,^ in New Jersey, found that
pruned peach trees produced in the first year somewhat more new shoot
growth than unpruned trees. The average for the latter in their Vineland
experiment was 695 inches and for the pruned trees (all treatments)
753 inches. In West Virginia, Alderman and Auchter^ report that heavy
pruning of the apple resulted in somewhat greater new shoot growth for
the first 2 or 3 years, but that greater shoot development accompanied
lighter pruning as the tree became older (see Table 5). Gardner^^
in Oregon, likewise working with young apple trees, found that different

T.iBLE 5. — Effect of Light and Heavy Pruning on New Shoot Growth in
Apples of Different Ages
(After Alderman and Auchter^)

Pruned heavily

Pruned lightly

Season

Average total
length, feet

Average total
removed, feet

Average total
length, feet

Average total
removed, feet

pruning (feet)

1911

4.41

3.30

5.58

3.44

1912

16.25

12.91

15.51

4.78

-0.74

1913

41.53

33.16

34.33

13.89

-7.20

1914

84.08

49.17

99.39

22.12

15.31

1915

161.74

224.89

63.15

varieties respond in a quite dissimilar manner to pruning of the same
severity. His data, some of which are summarized in Table 6, show that
lightly or moderately pruned Grimes produced more shoot growth
annually than unpruned trees, but those heavily pruned produced dis-
tinctly less than the check trees. On the other hand the heavily pruned
Romes produced more shoot growth annually than those pruned moder-
ately or not at all, while on the whole the severity of annual j^runing
seemed to make but little difference in the amount of new shoot growth
in Gano and Esopus. At first these data may seem so contradictory
that no conclusion or interpretation is possible. However, attention
may be called to the great variations shown by young apple trees of
different varieties in their growing habits and to the change in these
differences with age. Thus there is a great dissimilarity between young
trees of Rome and Grimes in the number of spurs and the peach usually
produces no true spurs. When these peculiarities of age and variety are
considered along with the data that follow on the influence of various
pruning treatments on fruit spur and fruit bud production the contradic-
tions that have been noted do not appear so puzzling.

412

FUNDAMENTALS OF FRUIT PRODUCTION

Table 6. — Effect of Light and Heavy Pruning on New Shoot Growth in

Young Apples op Different Varieties

(After Gardner^'^)

Number of
trees aver-
aged

Severity of
annual prun-
ing, per
cent.

Average 1914

shoot growth,

centimeters

Average 1915

shoot growth,

centimeters

Average 1916

shoot growth,

centimeters

Average

number fruit

spurs in fall

of 1916

Grime.s.
Grimes.
Grimes.
Grimes.
Gano. .
Gano. .
Rome. .
Rome . .
Rome. .
Esopus.
Esopus.

none
0-25
26-50
51-75
26-50
51-75
none
26-50
51-75
none
46-76

492
675
714
378
456
561
629
508
845
583
453

1762
2251
2401
1339
2493
2464
2051
1973
2541
2121
1736

3852
4713
4913
2818
5435
5459
3520
3634
4630
2287
3077

402
457
341
116
158
111
142
34
31
505
134

In recapitulation it may be said that different species and varieties
show great variations in their response by new shoot production to prun-
ings of like severity. These differences are due primarily to growing
and fruiting habits and secondarily to age, vigor and nutritive conditions,
as well as to environmental conditions with which they may happen to be
associated at the time.

Leaf Surface and Root System. — Any practice that would effect a
reduction in the amount of new shoot growth and perhaps of spurs as
well, would be expected to result in a corresponding decrease in leaf
area and in root development. Chandler's^ ^ investigations of the rela-
tion of certain pruning practices to subsequent root development show
this reduction. Some of his data are summarized in Tables 7 and 8.

Table 7. — Influence of Varying Amounts of Pruning on Subsequent Leaf

AND Root Development

{After Chandler'')

Treatment

Number of
trees

Average leaf
surface be-
fore pruning,

May 23,

1918 (square

inches)

Average leaf
surface after

1918 (square
inches)

Average leaf
surface,
Sept. 17,

1918 (square
inches)

Average root

weight

May 19,

1919 (grams)

Average top
weight.
May 19,
1919 in-
cluding prun-
ings (grams)

Unpruned

Little pruning . .
Much pruning . .

41
33
39

756.48
819.14
775.70

756.48
470 . 27
291.61

1737.94
1219.80
895.96

208.5
166.9
126.3

684.0
558.3
494.3

In commenting on the data presented in Table 8, Chandler" says:

"It will be seen that in all cases the leaf surface has been rather markedly
reduced. On the other hand except in case of the summer-pruned trees, when

PRUNING— THE AMOUNT OR SEVERITY

413

Table 8. — Effect of Pruning on Leaf Surface and Top and Root Growth of

Peach Trees 4 Years Old at Beginning of Experiment

(After Chandler^')

Average

leaf sur-

Average leaf sur-

face in 1916

face in 1917

Tree.

Root

Treatment

June,

Sep-

June,

Sep-

weight.

weight.

square
inches

tcmber,
square
inches

square
inches

tember,
square
inches

pounds

pounds

pounds

Elberta:

Pruned 1910 and 1917

14,239

80,659

31,209

59,579

90.3

11G.4

27.4

Unpruned

24,771

97 , 8oO

98,169

116,344

116.3

110.3

37.3

Crawford Early:

Pruned summer 1910, spring

1917

2,202

50,034

18,904

68,070

75.8

97.4

20.9

Unpruned

17,886

85,721

74,389

142,920

111.9

111.9

34.6

Pruned spring 1917

40,681

79 , 563

120. 3

134.7

34.9

114,516

144,911

131.7

131.7

the weight of the prunings has been added to that of tlie tree, the t(jtal weight
of pruned and unpruned trees is practically the same. The root growth, how-
ever, has been greatly reduced. When it is considered that this reduction in
growth has occurred during the last 2 years of the 6 years during which the trees
have been in the orchard, it will be realized how striking the reduction is. Thus
if at the beginning of 1916 the roots weighed 15 pounds, then the root growth
on the unpruned trees since that time has been nearly twice that on the pruned
tree. Unfortunately we have no records as to the root weight of trees 4 years
old, but it must have been 10 pounds or more, since by records that we have the
tops would then have weighed from 30 to 35 pounds. If the root weight at the
beginning was 10 pounds, then the root growth in the pruned trees since that
time has been but 65 per cent, of that made by the unpruned trees."

In effect the influence of a heavy top pruning on the subsequent
development of the tree is more or less comparable to that of a root
pruning.

Presumably, pruning practices which do not reduce top growth in
trees of other kinds or of greater age than those studied would not have
such an influence on root growth; exact data, however, are lacking. It
is significant, nevertheless, that in young trees pruning of the top has
been found greatly to influence the extent of root development the
following season. This suggests one of the indirect ways through which
pruning one season may influence growth and development 2 or 3 years
later.

Influence on Fruit Spur and Fruit-bud Formation. — In Table 6
are presented data on the influence of varying amounts of pruning on
fruit spur formation in young apple trees. The less the pruning the larger
is the number of fruit spurs formed. With very severe pruning there is a

414 FUNDAMENTALS OF FRUIT PRODUCTION

great reduction, the checking influence differing greatly with the variety,
however. Varieties Hke Esopus and Grimes, that are much inclined to
develop spurs at an early age, show a relatively greater check in this
respect than those like Rome and Gano that as young trees produce
comparatively few spurs. In any case, however, pruning tends to reduce
their number. Data are presented showing also that severe pruning acts
in a similar manner in decreasing the numbers of fruit buds that form
on the spurs. ^^ Similar data on fruit bud formation in young apple
trees have been obtained in West Virginia^ and in England.'* The ratio
of flower clusters for the years 1909-1914 obtained by the English
investigators in one of their experiments was 52 for hard pruning, 100
for moderate pruning and 180 for no pruning. There were corresponding
differences in total yield. All these investigators show that heavily
pruned trees may be expected to come into bearing more slowly than
those pruned moderately, lightly or not at all.

On the other hand, heavy pruning does not always result in decreased
yields. Data obtained in an experiment with Arkansas and York
Imperial apple trees that had been bearing for a number of years and
were somewhat lacking in vigor, summarized in Table 9, show steady
increments in yield with each increase in the severity of the pruning. ^

Table 9. — Influence of Pruning on Yields in a Declining Apple Orchard
{After Alderman and Auchter"^)

AFKaiisas, iwit-ivdo i orK, lyit crop

crops (bushels per tree) (bushels per tree)

Arkansas, 1914-1915

York, 1914 crop

Heavy pruning . . . .
Moderate pruning .
Light pruning

14.02

11.94

9.15

The heavy pruning must have had the effect of reducing somewhat the
total number of fruit spurs, at least in comparison with the trees pruned
more lightly. Consequently the increased yields must have been due
either to the formation of a larger number of fruit buds or to the better
setting of the blossoms. This is an influence not unlike that already
pointed out as very frequently attending the judicious use of nitrogenous
fertihzers.

Influence on Leaf Area and Fruit Size. — In Table 10 are presented data
on the influence of varying amounts of pruning on average size of leaf
and total leaf area in apple trees. Not only are the individual leaves of
the heavily pruned trees larger than those of the unpruned or lightly
pruned trees, but there are more of them. Consequently such trees
have a materially increased leaf surface. This in turn creates a greater
requirement for nutrients and for moisture; if this requirement is met, an
increased production of elaborated foods may be expected.

PRUNING— THE AMOUNT OR SEVERITY

415

Table 10. — Influence of Pruning on Leaf Size Area
(After Alderman and Auchter^)

I'uf area (s<iuare
inches)

Lupton
orchard

Grimes
orchard

Total leaf area per tree
(.square feet)

Lupton Grimes

orchard orchard

Heavy pruning. . .
Moderate pruning
Light pruning. . . .

2.77
2.37
2.10

4.99
4.18
3.52

610.8
432.2
418.7

1143.8
911.5
659.6

The decrease in size of fruit recorded by Bedford and Pickering*
as accompanying severe pruning probably is explained by the increased
leaf area of the trees and the consequently greater requirement of this
foliage for water — a requirement that under the conditions of the experi-
ment the roots were unable to supply. Experience and observation
generally indicate that pruning does not decrease size of fruit. As
a matter of fact it often has the opposite effect. Perhaps this tendency
is most clearly shown in such fruits as the raspberry, blackberry and grape
which in the absence of pruning are inclined to set more fruit than they
can mature properly, especially when supporting the large amount of
barren wood which unpruned plants of these species characteristically
bear. Within certain rather wide limits the general influence of pruning
is to reduce, through the removal of actual or potential bearing wood,
the amount of fruit that can set. It tends also to enlarge leaf area
and thus, though its effects are concentrating, it at the same time increases
the requirement for nutrients and moisture. If these are available in ample
quantities pruning may result in an increase in size of fruit; if they are
lacking it may result in a reduction. Though the general tendency of
pruning, as of fertilization, is to increase the size of the fruit, its influence
in this regard is not direct. Nevertheless it is one of the most important
means at the grower's disposal for this purpose. This is particularly
true for those species or varieties with which thinning of the fruit is
impracticable.

Pruning as a Cause of Abnormal Structures. — In the sections on
Water Relations and Nutrition attention is directed to certain patho-
logical conditions that may result from extremes of moisture or from an
unbalanced nutrient supply. Pruning may disturb both the water and
food relations of the plant; hence certain pathological conditions may
follow, particularly from heavy pruning. Daniel,'* who has given this
question considerable attention, enumerates a rather large number of
monstrosities more or less directly attributable to pruning. Among the
more important of these maybe mentioned the forcing out of the so-called
"second-bloom" from the limbs and trunks of pear trees, marked

416 FUNDAMENTALS OF FRUIT PRODUCTION

increases in size and changes in the form of leaves, fasciation and the
metamorphosis of the glands of apricot leaves into small leaflets. He
considers these abnormalities to be due to an upsetting of the balance
normally existing between transpiration and assimilation. It should be
remembered, however, that in many instances these abnormal structures
arise independent of any pruning.

Amount of Pruning Varying with Fruiting Habit. — The facts just
presented on the results to be expected from light, moderate, heavy
or no pruning, show clearly that no rigid rules can be stated as to the
amount of pruning best suited to orchard trees even of a single age or of a
single kind. However, if certain other pertinent facts and principles
be considered, the amount to be given orchard trees becomes somewhat
more easilj^ determined.

The fruit grower wishes to produce as soon as possible a tree, shrub,
or vine sufficiently large to bear crops of at least moderate size. It is
necessary, furthermore, that the plant have a strong framework for the
support of the smaller branches and their fruiting wood and that it be
adequately equipped with the spurs or shoots that bear fruit buds. For
the first year or several years, in many species, fruit production is neither
expected nor desired. The maturing of fruit and to a certain extent even
the formation of fruit buds and potential fruiting wood might tax the
energies of the plant so that increase in size would be checked seriously.
A little later, however, when the tree approaches such age and size that it
can begin production without injury to its general welfare the grower
desires it to develop gradually (or sometimes quickly) fruit-producing
growth and he wishes to keep this growth actively at work. As the
tree becomes still older its natural growing habits are very Hkely to
encumber it with too much fruiting wood, more than its roots and leaves
can supply with food materials for heavy and regular production. The
grower's aim then should be to get rid of the old unproductive wood
or to invigorate it or to limit the formation of new wood. His problem
is first that of building the plant; then it is equipping it and providing
for such extensions and new equipment as space and conditions permit
and finally it becomes a problem of maintenance at maximum efficiency.

When these general principles are considered in their relation to the
varying results attending pruning in different amounts, it is evident that,
in general, tree, bush and vine fruits should be pruned heavily when young
to secure a strong, stocky framework with well spaced limbs and — of
equal importance — to prevent the production of fruit and even of fruiting
wood As the plant approaches bearing age and size, pruning should be
less severe, to permit or encourage the production of fruiting wood.
Perhaps in extreme cases it may be desirable at this stage to do no pruning
at all. As the plant becomes still older, pruning is again increased in
severity, thus limiting or sometimes reducing the amount of fruiting

PRUNING— THE AMOUNT OR SEVERITY

417

wood and in this way concentrating the energies of the tree upon a better
support of what is left. The lower line shown in Fig. 49 gives graphically
some idea of the manner in which the amount of pruning should vary with
age in the average apple, pear, plum or cherry tree which is rather slow
growing at first and bears principally on spurs. Of course as the trees
vary in vigor, rapidity of growth, fruiting habits and in other respects
there should be accompanying changes in the severity of the annual
pruning. Thus the peach ordinarily begins bearing at an earlier age
than the apple or cherry. Consequently it should be pruned to leave
fruiting wood and permit bearing earlier. Furthermore, since it bears
fruit only on shoots of the preceding year, regular production depends
on annual provision for a good supply of new shoots. If these are to be
produced on the lower part of the tree where the weight of the fruit will
not place an excessively severe strain upon the crotches comparatively
heavy annual pruning is necessary. At no stage in the life of the peach

Age

Fig. 49. — Graphs showing relative amounts of pruning required for the peach and apple at

different ages.

tree is it necessary practically to discontinue pruning in order to develop
fruiting wood and bring it into bearing. The upper line in Fig. 49
shows roughly how the amount of pruning desirable for trees of this kind
varies with age. Similarly it is possible to draw graphs for the amounts
of pruning required by trees of other kinds. It should be emphasized,
however, that these will vary in details not only with different kinds of
fruits, but with varieties of the same kind and for the same variety
from place to place and under varying soil and environmental conditions.
Summary. — By and large, unpruned trees increase in size more rapidly
than pruned trees of the same kinds and the dwarfing effect of pruning
is more or less directly proportional to its severity. This dwarfing
effect is a result not so much of the production of less new shoot growth
each year as of the amounts of wood removed. The dwarfing effect
of top pruning extends to the root system because of the reduction in
total leaf area. Pruning generally results also in a diminution in

418 FUNDAMENTALS OF FRUIT PRODUCTION

the number of fruit spurs in spur producing species, though there may
or may not be a corresponding reduction in number of fruit buds and
in the resulting yield. Within certain limits it tends to increase the
size of the fruit. Extremely heavy pruning may occasionally result
in different types of abnormal growth, such as fasciation. The severity
of pruning that is desirable depends on many conditions, the age of
the tree and its bearing habit being among the more important.

CHAPTER XXIII
PRUNING— THE METHOD

It seems strange that a horticultural practice as old as pruning should
have come down to the present with so little realization that it includes
questions of kind as well as of amount and of season. Nevertheless, most
of the literature is silent on this matter, as though all pruning were
necessarily the same in kind, except perhaps for the innumerable detailed
ways of cutting to certain buds or of leaving certain spurs or shoots for
replacement purposes. The fundamental differences between essen-
tially distinct practices have not been generally recognized. Instead,
attention has been focused upon the minute and less important details
of procedure. Without doubt this lack of realization that pruning may
vary greatly in kind and that entirely different results attend distinct
kinds or types of pruning has been responsible for much of the confusion
and apparent contradiction that is evident on comparison of the reports
of various writers and investigators.

Heading Back and Thinning Out. — A number of classifications of
pruning as to kind are possible. However, none is more serviceable than
one which recognizes the difference between heading back and thin-
ning out. It is difficult, if not impossible, to differentiate absolutely
between the two for sometimes the removal of a branch or part of a
branch is at the same time a thinning out and a heading back. In
general, however, the differences between the two are clear and evident
even to a casual observer. Thinning out removes entirely a shoot, spur,
cane, branch, limb, or whatever the part may be; heading back removes
only a portion, leaving another portion from which new growths can
develop.

Influence on New Shoot and New Spur Formation. — Theoretically a
heading back that is equal in severity to a certain thinning out removes
approximately the same amount of wood and the same number of buds.
In practice however, there is a considerable difference. A thinning out
that removes 50 per cent of the shoots, gets rid of just half the amount
of wood of the past season and just half of the total number of buds,
both lateral and terminal. On the other hand a 50 per cent heading
back removes somewhat less than half the weight of woody tissue formed
the past season and somewhat more than half the total number of new
buds, for it removes an equal number of the lateral buds and all the
terminals. A heading back that is equal in severity to a certain thinning

419

420

FUNDAMENTALS OF FRUIT PRODUCTION

out is therefore more severe in one respect and less severe in another.
If the pruning is comparatively heavy the difference is slight, but if the
pruning is light the difference is correspondingly greater.

Observation shows that when growth begins the terminal and sub-
terminal buds are usually the first to start and in the majority of decidu-
ous trees and vines (less frequently in shrubs) they produce the longest
and strongest shoots, though shoots may grow from many of the lower
buds. However, seldom do all the lateral buds start and as a rule the

Fig. 50. — Grimes apple tree, showing a typical response to heading back. Compare with

Fig. 51

largest percentage of those that remain dormant are on the basal portion
of the shoot. Those species that bear principally on spurs form these
spurs mainly from buds on the median and terminal portions of the
shoot. Heading back, therefore, limits fruit spur formation to a greater
extent than a correspondingly heavy thinning out. This is obvious
from the data presented in Table 11, showing the amounts of shoot
growth and the numbers of spurs formed by vigorous 5-year-old apple
trees of different varieties that had been headed back or thinned out

PRUNING— THE METHOD

421

with equal severity. However, the influence on fruit-spur formation
of heading as compared with thinning out is much more pronounced in
some varieties than in others. Gano, for instance, showed practically
no difference in this respect.

Even more striking than the inequality in numbers of spurs from the
two kinds of pruning was that in the amount of new shoot growth.
Heading back invariably led to greater shoot production than a corre-
sponding amount of thinning out (see Table 11). In Esopus the amount

Fig. 51. — Grimes apple tree, showing a typical response to thinning out. Compare with

Fig. 50.

of new shoot growth was almost double that in the thinned trees. Appar-
ently thinning out some of the shoots in a tree does not result in diverting
the same amount of food and moisture they would have used into the
remaining unpruned shoots. Certainly it does not result in a suffi-
ciently increased new shoot growth from them to compensate for that
which would ordinarily have grown from the portion of the top that
has been pruned away. It has some stimulating influence of
this kind but it also results in a reduction in the total new growth formed.

422

FUNDAMENTALS OF FRUIT PRODUCTION

On the other hand heading back has a more stimulating influence and
the pruned shoots tend to give rise to as much (often more) new shoot
growth as would have arisen from the unpruned tree. This is well
illustrated by Figs. 50 and 51 which show the response of two trees of
Grimes to the same amount of pruning, the tree on the left having been
headed back and that on the right having been thinned out.

Table 11. — Influence of Heading Back and Thinning Out on Shoot and
Spur Formation in Young Apple Trees

{After Gardner^'')

o a

« M 6

e-^2

Grimes
Grimes
Grimes
Grimes
Gano . .
Gano . .
Gano. .
Gano. .
Rome.
Rome.
Rome.
Rome.
Esopus
Esopus

26-50
2&-50
51-75
51-75
26-50
26-50
51-75
51-75
26-50
26-50
51-75
51-75
46-76
4fr-76

697
731

450
462
560
562
507
508
1007
682
444
461

2297

82

2495

83

1315

22

1362

23

2376

15

2609

14

2493

15

2435

15

1990

9

1956

10

2851

9

2230

8

1659

28

1813

28

Thinning
Heading
Thinning
Heading
Thinning
Heading
Thinning
Heading
Thinning
Heading
Thinning
Heading
Thinning
Heading

4123
5703
2308
3328
4577
6293
5072
5846
3352
3915
4785
4474
2122
4031

360

322

130

101

158

158

110

111

43

25

54

25

180

144

Influence on General Shape and Habit. — Incident to quite different
effects of heading and of thinning upon the amount of new shoot growth
and the number of new spurs are the influences of these practices on gen-
eral shape and growth habit. Thinning out places no check on the
natural tendency to grow principally from the terminal and subterminal
buds. Consequently plants pruned exclusively in this way grow tall
and wide spreading and they gradually develop a more open, "rangy"
habit than they would otherwise. This may be advantageous or dis-
advantageous to the grower, depending on a number of conditions. On
the other hand constant heading checks this tendency to extend out and
up and results in a plant compact in habit and often very dense in growth.
The average well kept hedge furnishes an extreme example of the direc-
tion in which all heading tends. Indeed much of the usual pruning of
the bramble fruits, which consists largely in heading back both leaders
and laterals and the pruning that frequently is afforded other deciduous
fruits — especially when they are young — results in a type of growth and

PRUNING— THE METHOD 423

a condition of tree in many ways closely comparable to that of the privet
or osage orange hedge.

Influence on Fruit-hud Formation and Fruitfulness . — The orchard
is grown and maintained not primarily for its shoot growth or for its
spurs, but for fruit. The grower therefore wishes to know the influence
of different pruning practices on fruit-bud formation. It has been
shown previously that this occurs at varying times in diverse plants
and that different species present entirely unlike fruit bearing habits.
That is to say, some bear on spurs, some on shoots; some bear terminally,
some laterally. If, then, pruning practices differ greatly in their influ-
ences on spur formation and shoot formation, corresponding, perhaps
greater, differences may be expected in their influences on fruit-bud
formation and fruiting. The practice that leads to greater fruitfulness
in one species may tend in the opposite direction in another. Thus
heading back may be a good practice in growing the peach because it
encourages new shoot formation on which the fruit buds are borne and
on the other hand, heading back may be a bad practice for the pear,
because it generally limits the formation of fruit spurs on which most of
the fruit of this species is borne.

In contrast to thinning out, heading back generally tends not only to
reduce the number of spurs in spur bearing species but also to lower the
percentage that differentiate fruit buds. In these same species, thinning
out, though it may reduce somewhat the total number* of fruit spurs, has
been shown under some conditions to lead to the formation of fruit buds
and to the maturing of fruit on a larger percentage of those remaining.
Data on this question obtained from pruning experiments with j^oung
apple trees in Oregon are furnished in Table 12. The figures presented
in the last three columns of this table also show something of the influence
of these two pruning practices on fruit-bud formation on shoots. Though
the apple is not generally considered a shoot bearer, where this investiga-
tion was carried out, two of the varieties studied, Rome and Gano, bear
principally on shoots for the first few seasons. Thinning out generally
encouraged terminal and lateral fruit-bud formation on shoots more
than a corresponding heading back, though there were some exceptions.
In commenting on these data Gardner^- says:

"The moderately thinned Grimes trees were somewhat more than twice as
productive of fruit buds as the correspondingly headed trees; the heavily thinned
Grimes trees were 10 times as productive of fruit buds as correspondingly headed
trees. The moderately thinned Rome trees were nearly twice and the heavily
thinned, nearly five times as productive of fruit buds as those correspondingly
headed. On the other hand, moderately thinned Gano trees produced but
slightly more fruit buds than those moderately headed, and heavily thinned
trees of this variety averaged distinctly fewer buds than those heavily headed.
The last statement also holds true of the heavily pruned Esopus trees. A more

424

FUNDAMENTALS OF FRUIT PRODUCTION

Table 12. — Influence of Thinning Out and Heading Back Shoots on Fruit-
bud Formation in the Apple
(After Gardner'^-)

•SS2

i ^

■3 c_

I&2

III

Us

2; '^

29.5

2.7

5.0

24.8

3.9

4.6

31.7

2.6

10,0

8.9

7.4

2.2

18.0

0.9

6.2

0.1

1.3

1,0

12.9

59.3

31.6

14.8

65.0

16.4

8.5

43.5

15.0

14.6

53.6

13.7

31.6

3.5

72.4

5.6

1.3

47.5

5.2

5.3

21.9

5.0

2.6

51.7

3.5

2.8

6.4

41.9

0.3

10.4

17.2

0.1

7.2

11,4

2.1

17.6

Grimes
Grimes
Grimes
Grimes
Grimes
Grimes
Gano. .
Gano . .
Gano . .
Gano . .
Rome. ,
Rome. ,
Rome . ,
Rome . .
Rome. .
Esopus
Esopus
Esopus

No pruning
Thinning
Thinning
Heading
Thinning
Heading
Thinning
Heading
Thinning
Heading
No pruning
Thinning
Heading
Thinning
Heading
No pruning
•Thinning
Heading

1-25
26-50
26-50
51-75
51-75
26-50
26-50
51-75
51-75

26-50
26-50
51-75
51-76

41-76
41-76

402

457

360

322

130

101

158

158

110

111

142

43

25

54

25

635

180

144

37.2
33.3
44.3
18.5
25.1
2.4

103.8
96.
67.
81,

107.
54.
32.
59.

12,7
52.6
24.5
31.1

detailed study of the table brings out a number of additional points. In the
first place, it is noted that thinning, as compared with an equally severe heading,
almost invariably led to an increased production of fruit buds upon fruit spurs.
The one exception to this statement is furnished by the heavily headed Gano
tree, a variety in which severe heading of short shoots in the interior seems often
to have the effect of forcing the development of strong fruit spurs from the remain-
ing lateral buds. The short interior shoots of other varieties do not show such a
tendency to respond to severe heading in this way. Heading-back was invariably
accompanied by a greater development of terminal fruit buds on shoots than
thinning out. In the case of a variety like Gano, that when young bears a
large percentage of its fruit buds in this way, this effect may be sufficient to give
the tree a larger total number of fruit buds than correspondingly thinned trees.
Attention is called, however, to the fact that a continuation of the winter heading
year after year would remove the fruit buds on all the shoots headed and thus
actually result in decreased flower and fruit production as compared with thinning.

"Another point worth noting, but not brought out in the table is the fact
that the shoots bearing terminally average much shorter in the thinned than in
the headed trees. They are generally so placed, moreover, that in the thinning
of shoots they can be left to advantage while sterile ones are taken out.

"Except for Esopus, winter thinning of shoots, as compared with heading,
led to greatly increased production of lateral fruit buds on shoots. In the case

PRUNING— THE METHOD 425

of the heavily pruned Rome trees, the proportion of such lateral fruit buds was
8 to 1 under the two pruning treatments. Furthermore, the distribution of these
lateral fruit buds is such that a given heading-back (for instance, 50 per cent)
would remove a much larger percentage than an equall}^ severe thinning out.
This percentage, in the case of Esopus, would be enough greater more than to
counterbalance the effect upon total fruit production of larger numbers of such
lateral fruit buds.

"Taking all these facts into consideration, it is evident that the effect of
thinning-out and likewise of heading back upon fruit-bud formation varies
greatly with the variety. The pruning practice that will lead to the largest
fruit-bud production in one variety will not necessarily lead to it in another.
Thus it becomes important for the grower to become- better acquainted with
the exact fruiting habits of his varieties under his conditions as well as to the
response that these varieties make to various pruning practices."

Thinning and Heading Lead to Different Nutritive Conditions. — The
explanation of the varying effects of thinning out and of heading back
on fruit-bud formation is not found exclusviely in the different fruiting
habits of the several species and varieties. New growth is made chiefly
at the expense of stored foods, particularly carbohydrates. In the section
on Nutrition data are presented showing that the younger wood is
comparatively richer in food reserves than older tissues. Heading back,
therefore, removes a larger amount of the tree reserves than a correspond-
ingly severe thinning out and leaves it less able to recuperate, especially
if the pruning has been severe.

It is also pointed out in the section on Nutrition that the initiation
of the fruitful condition, or in other words fruit-bud formation, is associ-
ated with an accumulation of carbohydrates in the regions where fruit
buds can be formed. Carbohydrate accumulation in turn depends on
carbohydrate manufacture on the one hand and on carbohydrate utiliza-
tion on the other. When the latter process lags behind the former, oppor-
tunity is finally afforded for the laying-down of fruit buds. In the last
analysis, therefore, pruning influences fruit -bud formation to the extent
that it influences carbohydrate accumulation or carbohydrate utilization
or the status of the ever changing ratio between them.

Thinning out not only removes less stored food than a corresponding
heading back, but, as just pointed out, it also leads to increased fruit-
spur formation and decreased shoot growth. This means decreased
carbohydrate utilization and increased carbohydrate manufacture,
because spurs are short growths with relatively large leaf surfaces. Their
growth is made very early in the season and from then on they are manu-
facturing and accumulating rather than spending or dissipating organs.
On the other hand heading back produces fewer of these short growths
and more of the longer and stronger shoots that complete their growth
much later. Consequently they more nearly exhaust the plant's re-

426 FUNDAMENTALS OF FRUIT PRODUCTION

serves than the shoots and spurs of thinned trees and their carbohydrate
contributions to the tree as a whole come later and may amount to less.

Furthermore the thinned is more open than the headed tree. Its
leaves are better exposed to light and presumably they are for that reason
somewhat more effective manufacturing organs. The more common
formation of fruit buds in the better exposed parts of the tree is evidence
on this point. The rather general production of fewer and smaller leaves
on spurs in the interior shaded portions of compact headed trees, in
contrast to the larger and more numerous leaves on the spurs of open
thinned trees, is another fact pointing to material differences in the rate
of carbohydrate accumulation in their fruiting wood.

Still another reason for the difference in response from heading back
and from thinning out lies in a disturbance of an equilibrium within the
branch itself induced by heading back. Each branch, as it grows, may
be regarded as a system in equilibrium, comparable to that in the plant
as a whole. That is, there is a balance between part and part. If a
portion of the branch is removed this balance is disturbed. Equilibrium
is reestablished by regeneration of the part pruned away. Apparently
little readjustment is necessary after thinning out, because the equihb-
rium of the remaining branches is not disturbed. The adjoining parts
will function more nearly as they would, had no pruning been done.

The Places of Thinning and of Heading in Pruning Practice. — The
preceding discussion shows that no rules can.be laid down as to the relative
amomits of heading and of thinning that should be given trees of a certain
kind or of a certain age. Rather is it necessary to study carefully each
problem as it arises, to interpret and to apply the general principles that
have been pointed out. In a general way, however, it may be stated that
both the development of a more extensive fruiting system and more
especially the better and more efficient functioning of that system are
favored more by thinning than by heading. There are notable instances
of other effects, however, e.g. in the bramble fruits, in which the heading
back of the canes or other growth limits the energies of the plant to pro-
duction on the remaining shoots or spurs and causes them to produce
larger, if not more, fruits. In the section on Fruit Setting it is pointed
out that pinching back the growing shoots of the grape before blossoming
sometimes leads to a better setting. In most species continued thinning
out leads eventually to tall or wide spreading and "rangy" plants, plants
that require wider spacing in the orchard, that often make undue expense
in pruning, spraying and other care and that are unable to mature their
crops without a great number of mechanical supports. Judicious heading
back corrects these tendencies and promotes a compact type of growth
that, in these respects, is much more satisfactory. In fact it may be
stated that in general the main purpose of heading back is to control the
form of the tree, bush or vine — to train it. In practice this means that

PRUNING— THE METHOD 427

while the trees are young they should receive relatively more heading back
and less thinning out, because they are then being trained. As they
grow older they should receive relatively less heading and more thinning,
because they will require less and less training for shape and more atten-
tion to the proper functioning of their fruit-producing wood. Species like
the peach and grape, which, because of their growing habits, continually
require considerable training for compactness and shape, should receive
correspondingly more heading when mature than certain other species
like the apple or walnut that have entirely different growing habits.

Fine, as Compared with Bulk Pruning. — In pruning practice and in the
consideration of pruning problems aside from those dealing with the heal-
ing of wounds, pruning is generall}^ regarded as something directly affect-
ing the tree as a whole. It is common to speak of pruning this tree heavily
and that one lightly, of heading back one and thinning out another, of
winter pruning in one instance and summer pruning in another. A certain
tree having been neglected for a number of years is said to require a heavy
pruning to bring it back to a vigorous productive condition. Such
sweeping statements disregard frequent cases in which though possibly
certain parts of the tree should be pruned heavily, certain other parts
should be pruned lightly, if at all. If a heavily pruned tree fails to attain
quickly a vigorous productive condition there is query why the result has
not been satisfactory. When it is decided that another tree requires
only a light pruning, only a very few branches are removed. If such
pruning is attended by some of the results usually accompanying heavy
pruning there is speculation regarding the reason. These statements,
which will be recognized as based upon very general experience, show that
pruning is regarded somewhat as a bulk problem — as something which
is decided on for the tree as a whole, done to the tree as a whole and to
which the tree as a whole responds. Yet the results frequently obtained
indicate nothing more clearly than that pruning is not exactly a problem
of bulk.

Results Following "Dehorning." — The sucker type of growth that
almost invariably follows very severe cutting back or "dehorning" is
well known. If the dehorning has been done in winter or early spring,
numerous comparatively upright shoots are produced during the following
summer. The usual practice is to thin these out and head back those
that are left, in order to develop as quickly as possible new fruiting
branches. Thus is the tree "rejuvenated." So well is this procedure
understood that the question as to when and how to rejuvenate trees has
been considered practically settled. However, even a cursory examination
of a tree that has recently received such a treatment shows that only a
part has responded. Undisturbed branches in the lower part of the
dehorned tree usually continue to grow in the ordinary way. Their
spurs bear flowers and fruit but little more regularly and yield a product

428

FUNDAMENTALS OF FRUIT PRODUCTION

of but little better grade than before. There is nearly the same tendency
for their older spurs and smaller fruiting branches to become gradually
weaker and die. Apparently neither as whole units nor in their separate
parts have these lower branches been accelerated or retarded in growth.
In many cases they do not even produce watersprouts, such as develop so
abundantly on the dehorned branches above them. In other words, an

Fig. 52. — A Bartlett pear tree, three years after a heading back of the main upright
limbs. Notice that the response to this pruning has been principally close to where the
cuts were made.

important — often the most important — portion of the tree, apparently
has not been affected in any way by the dehorning. This is brought out
clearly in Fig. 52. The treatment has resulted merely in the production
of new wood to replace a portion of the old top.

Even more striking evidence on this question of the distance to which
the influence of pruning extends is furnished by trees that have been
partly dehorned, that is, have had a portion of their branches cut back

PRUNING— THE METHOD

429

very severely and others of equal size and reaching to an equal height
left untouched. In such instances those responses, commonly regarded
as characteristic of dehorning, usually are limited to the branches that
have been cut back. These branches produce watersprouts in abun-
dance, but the unpruned branch continues to grow and function as though
nothing had been done to upset the usual conditions in the tree.

Fig. 53. — An old Italian prune tree. All of the main limbs but one were cut back four
years before this picture was taken. The unheadcd limb in the center shows little response
to the pruning.

Examples of this occur in old trees of many species that are being top-
worked, when the process is being distributed over a period of several
years. The influence of the heavy pruning, incident to the top working
process, usually is not reflected to any appreciable extent in a changed
manner of growth in the ungrafted limbs (see Fig. 53).

Results Attending the Removal of a Few Large Limbs. — The entire
removal of one or more comparatively large limbs, the majority being
left unpruned, is a type of pruning in more or less sharp contrast to the
bulk heading back just discussed. It may be considered a kind of bulk
thinning. Many fruit growers prune in this manner, which possesses

430 FUNDAMENTALS OF FRUIT PRODUCTION

at least the advantage of requiring little labor. Experience shows that
when a single large limb is removed from almost any part of a tree, water-
sprouts develop to take its place and the rest of the top continues to grow
as before. The watersprouts arise, for the most part, not from limbs far
removed from the pruning wound, but close to the point where the cut
was made. There is an unmistakable response to the pruning, but that
response is evident within a very limited area. The tree as a whole does
not show it.

Those who, after permitting a leader to develop for a number of years
and to form a close centered tree, have finally tried to train to an open
center or vase shape can furnish abundant evidence on the question under
discussion. The removal of the central leader from trees of this kind
(bulk heading back or bulk thinning out, depending on the form of the
tree and where the cut is made), is almost always followed by the pro-
duction of a number of watersprouts that tend to take its place. The
subsequent removal of these watersprouts is followed by the production
of still others, nearly always at points near the wound left by the removal
of the leader. The unpruned branches seem little influenced by the
cutting out of the leader.

In attempting to train young Yellow Newtown apple or Bartlett or
Anjou pear trees to an open center, or the Mcintosh apple or Winter
Nelis pear to a closed center, there is difficulty in keeping these trees
from growing dense in the center in the first instance and from spreading
out or even growing down in the second, though the shoots are cut out or
off. Furthermore — a matter of equal or greater importance — there is
difficulty in making the other shoots and limbs of these same trees spread
out or grow upright, as the case may be and thus profit by the nutrient
materials that it is desired to divert from the closely pruned parts. In
fact so persistently do the watersprouts tend to replace removed limbs,
that the easiest way to develop an open centered tree is not to cut out all
of the growth in the center, but rather to suppress it by pruning it a little
more severely than the surrounding branches that are desired for the
main framework. Even then it is doubtful if the usual characteristic
growth of the remaining branches is materially changed. Similarly, when
young trees are lightly, or even heavily, headed back new shoots are sent
out, but mainly from points where some of them can easily replace the
portion removed. It is not common for distant untouched portions of the
tree to show a well defined response to pruning.

Results Attending Spur Pruning. — As they become older, some
varieties of apple and pear trees develop large numbers of fruit spurs,
which often branch and rebranch until they become fruit spur clusters.
Usually when there are such large numbers of fruit spurs only a com-
paratively small percentage can flower and fruit in any single season and
the record of any single spur, or even spur cluster, especially in an older

PRUNING— THE METHOD 431

part of the tree, would show very irregular fruiting. In such trees,
though there is little vegetative growth in the general acceptation of the
term, nearlj^ all the energies of the tree are really being absorbed in a
slow vegetative growth of the spurs. The recognition of this condition
leads the grower to try dehorning or some other type of bulk pruning as a
remedial measure. That bulk pruning is only a partial remedy has
already been shown. Occasionally a grower tries the removal of a part
of the spurs from such trees. As the spurs possess a very large percentage
of the growing points and bear practically all of the leaf system of a tree
in such condition, a thinning of spurs is in one sense the equivalent of a
heavy pruning though the total weight of the wood removed may be
negligible. When treated in this way trees produce few or no water-
sprouts, though the removal of a few large branches with an equivalent
number of growing points leads to their formation. However, the re-
maining spurs grow more vigorously and the new shoots developing from
lateral and terminal buds are much larger and stronger. As a net result
though the tree is changed httle, if at all, in general form, the rate of
growth of nearly all its individual parts is accelerated and the ways in
which they function are materially changed. The tree as a whole has
been affected because nearly all its individual parts have been affected.

Application to Practice. — A consideration of the points that have been
made leads unmistakably to at least one conclusion: namely, that the
radius of influence within the tree of any pruning (that is, the cutting
out or cutting back of any particular shoot or branch) is comparatively
small. Parts close to the pruning wound, or perhaps close to a space
left by the removal of a branch, respond to the pruning treatment. Gen-
erally speaking, other parts of the tree do not. In other words, pruning
does not appreciably affect the tree as an entity; it affects the whole tree
only indirectly through its effect on limited portions. To stimulate the
formation of fruit spurs pruning must be done close to the point where
they are desired and to increase the productivity of spurs already present
pruning must be done in their immediate neighborhood. This in turn
means light, or rather fine, as opposed to coarse, pruning. It is neces-
sary to avoid bulk pruning and give greater attention to detail. Theoret-
ically pruning should concern itself mainly with shoots, spurs and the
smaller branches rather than with older and larger wood. Practically
some exceptions must be made, particularly in trees that have been
neglected for several years, because the operation must be conducted with
due regard to economy. The finer and the more evenly distributed the
pruning the more expensive it is and the net returns become subject to
the law of diminishing returns. Therefore in practice the most profitable
kind of pruning is always a compromise between the type which is best
for the tree and the type which can be done most cheaply.

Most of the trouble from fungous or bacterial infection comes from

432 FUNDAMENTALS OF FRUIT PRODUCTION

the large wounds, those made in bulk pruning. This is not an important
factor in the culture of the bush or vine fruits but it is usually of consider-
able importance in the tree fruit plantation. Indeed it is not too much
to say that the life of the average orchard tree is reduced by one-third
through the work of wound fungi and bacteria. Fine, as opposed to
coarse or bulk, pruning is the most practicable way of preventing losses
of this sort.

Carrying the line of reasoning a step further it becomes evident that
pruning should be regular and frequent. This is a statement which most
growers know to be true from observation and experience, though the
reasons may not always be clearly understood. However, the points
that have been brought out furnish an explanation of some of the charac-
teristic results following irregular pruning. Trees left unpruned for
several years usually seem to require the removal of some of the larger
branches or limbs. This approaches the bulk type of pruning and stimu-
lates new vegetative growth more than it invigorates the older fruiting
wood; new vegetative growth of this sort is as likely to increase as to
diminish difficulties.

What has been stated should not be construed as condemnation of
occasional heavy pruning, that is, the removal of a considerable amount
of growth. Though heavy pruning as commonly done is bulk pruning,
it is not necessarily so. It may consist in the removal of a large amount
of shoot growth and small branches and instead of giving rise to water-
sprouts, it may stimulate the normal vegetative growth and the fruit
spur system. The spur pruning to which reference has been made is
evidence to this effect.

Even bulk pruning is not always harmful. There are occasions when
a growth of strong vigorous shoots or watersprouts is desired in some part
of the tree. Particularly is this true in trees that have suffered from win-
ter injury or some other form of dieback. Then too, it should be remem-
bered that many species do not bear on fruit spurs or on short growths of
any other kind. Their flower buds are formed freely upon their longest
and strongest shoots and bulk pruning which leads to this type of vege-
tative growth may increase rather than check fruitfulness.

Root Pruning. — Root pruning has long been a recognized practice
among many European fruit growers, particularly those of the British
Isles and the adjacent continental countries and for many years it was
generally recommended (but rarely done) in the United States. Though
its use has not been limited to trees grown as dwarfs it has been employed
much less commonly with standards. In this country particularly, as the
culture of dwarf fruit trees has become relatively less important, root
pruning has all but disappeared from the list of cultural operations.
However, a certain amount of root pruning is almost always accomplished
in the regular cultivation of standard orchard trees. For this reason,

PRUNING— THE METHOD 433

though tillage is thought to effect a root pruning seldom, some of the
more important effects of severing a portion of the tree's roots at different
seasons may well be noted.

In the culture of dwarf trees of almost any kind, Rivers,^^ one of the
leading exponents of the practice, recommended an annual, or at least a
biennial, shortening of all the roots. In describing the operation he said:
"Open a circular trench 18 inches deep around the tree, 18 inches from
the stem, and cut off every root and fibre with a sharp knife. When
the roots are so pruned, introduce a spade under one side of the tree, and
heave it over so as not to leave a single tap-root; fill in your mould, give a
top dressing of manure, and it is finished. The diameter of your circular
trench must be slowly increased as years roll on; for you must, each year,
prune to within 1}^4 or 2 inches of the stumps of the former year. Your
circular mass of fibrous roots will thus slowly increase, your tree will
make short and well-ripened shoots, and bear abundantly." It is gen-
erally recommended that this root pruning be done in the late fall. The
major repsonse will then be evident the following spring and summer in a
reduced vegetative growth and an increased formation of fruit buds.

Some conception of the dwarfing influence of continued root pruning
on apples grown on Paradise stocks is afforded by an investigation con-
ducted at the Woburn Experiment Station in England. In summa-
rizing their results, Bedford and Pickering^ state: "In one series the
trees were root-pruned every year, in another every other year, and in
a third every fourth year; actual lifting from the ground being adopted,
till they became too large for this to be done without excessive injury.
The check caused to the growth of the trees was apparent from every
point of view, and its extent may be gathered from the weights of the
trees when they were ultimately removed. Thus with the Cox, which
were removed after 15 years, the weights of those trees which had been
root-pruned every fourth year were only 43 per cent of those which had
not been root-pruned; where the operation had been performed every
other year, the weights were 7 per cent of the non-treated trees,
and with the yearly operation, 3 per cent; indeed, in the last case, the
trees had scarcely increased in weight since they had been planted, and
had been dead for several years before they were removed." These
investigators then state that root pruning is followed by increased crop
production, though usually this is not evident until the second season
after the operation. However, repeated root pruning so weakens the
trees that they soon fall behind non-treated trees in yield. Bedford
and Pickering conclude that "root-pruning is an operation which should
be practiced with extreme moderation, and only in those cases where
excessive branch-growth calls for stringent measures." The root
pruning investigations of Drinkard^® in Virginia led to practically the
same conclusions. He reported a greatly reduced shoot growth, with

434 FUNDAMENTALS OF FRUIT PRODUCTION

leaf areas on the root pruned trees only 5 to 20 per cent of those on the
checks. Furthermore the leaves of the treated trees were smaller and
paler than those of the untreated trees. This check in vegetative
growth was accompanied by an increased formation of fruit buds; these,
however, were so weak that comparatively few set fruit and yields were
less than those obtained from trees not root pruned.

The experimental results of these and of other recent investigators
do not, on the surface, agree with the opinions of many of the earlier
writers regarding the desirability of root pruning. The quotation
from Rivers, however, included with the recommendations for annual
or biennial root pruning one for liberal applications of manure and a
study of the earlier literature dealing with this subject shows that arti-
ficial feeding and often artificial watering was assumed for practically
all root pruned trees. The relatively great productivity of the root
pruned dwarfs of European and other gardens therefore should be re-
garded as due only partly to root pruning, some of the other attendant
practices being perhaps more responsible.

Seldom, if ever, would the operations incident to clean culture or
any other system of soil management result in a root pruning as severe
as that contemplated in the regular practice that goes by that name.
Nevertheless the deep plowing of trees growing in a shallow soil or in
a soil that compels shallow rooting actually effects a considerable, and
occasionally a very severe, root pruning. This may be expected to
afford a temporary stimulus to fruit-bud production and at the same time
to check vegetative growth more or less, though either or both of these
direct effects may be masked by the indirect influence that the tillage
exerts.

Special Pruning Practices. — Stripping, notching, ringing and girdling
may be considered together as a group of special orchard practices rather
closely related to pruning. The names used to designate them are suffi-
ciently descriptive to make unnecessary any further explanation of the
procedure involved. They are all performed with the aim of so control-
ling the translocation of elaborated foods that their accumulation in
certain parts may lead to increased fruit-bud formation and hence to
greater fruitfulness or to a better setting of the flowers or to a better
development of the fruit itself.

The upward movement of water in the tree, of the transpiration stream,
is commonly thought to occur in the outer layers of the wood. Knowl-
edge of the translocation of elaborated foods is rather fragmentary,
though it is rather generally agreed that their downward movement
is through the phloem. Recent investigations of Curtis^* indicate that
no appreciable quantities of carbohydrates move upward through the
xylem and that such elaborated food materials as are stored in the xylem
move only radially in the wood. Their upward transfer is limited mainly

PRUNING—THE METHOD 435

to the tissues of the bark, except for a limited translocation by means of
_ diffusion. Consequently those portions of shoots or branches above the
point where the flow of elaborated foods has been checked by girdling
or ringing depend on their own resources in so far as elaborated foods
are concerned. That is, they cannot receive foods manufactured else-
where in the plant and foods that they manufacture must be stored
within their tissues or utilized by them. If the operation is performed
during the dormant season or very early during the growing season,
vegetative growth above the ringed or girdled point will be checked
because of the early exhaustion of the stored carbohydrates and the
reduced leaf area will limit the synthesis of a new supply. On the other
hand, this new supply that is synthesized cannot be translocated to
the roots or other parts of the tree and must be stored or utilized in
close proximity to its point of manufacture. Girdling or ringing after
the first flush would permit a greater amount of growth beyond the
point of operation because food stored elsewhere would be to some extent
available for this new growth and following the ringing there would be
opportunity for a correspondingly greater accumulation of foods. The
general influence of notching and stripping is in the same direction as
that of ringing, but is less pronounced because the operations themselves
only partl}^ stop translocation through the phloem.

It is evident that the effect of any of these special practices on
accumulation and concentration of food materials is almost certain to
be more pronounced in the summer than it is during the spring months.
This explains why they so often fail to encourage the formation of fruit
buds and greater fruitfulness for which they have been so frequently
recommended, the period of fruit-bud differentiation having passed before
their concentrating effects are realized.

The following quotation from Drinkard's'* summary of his work in Virginia
bears on this point: "Ringing at different seasons when accompanied by or
preceded by spring pruning, of the branches produced no noticeable stimulation
of fruit bud formation. Ringing at the time growth was resumed in the absence
of spring pruning did not stimulate fruit bud formation. The treatment was
given too early. Ringing at the time the foliage was fully developed in the
absence of spring pruning gave the best results ; however, when the treatment was
given at the time the fruit buds began to become differentiated there was some
stimulation to fruit bud development. Stripping at different seasons when
accompanied by or preceded by spring pruning, had no stimulative effect on
fruit bud formation. The effects of stripping were offset by those of spring
pruning. Stripping at the three seasons ah-eady mentioned, in the absence of
spring pruning, stimulated fruit bud formation uniformly."

The facts relating to food translocation and manufacture may also
partly explain why ringing so frequently results in an increase in size or
in some modifications of the texture or composition of the fruit that

436 FUNDAMENTALS OF FRUIT PRODUCTION

matures during late summer or in early fall. Thus DanieP^ reports
a marked increase in size of the fruits of the tomato and egg-plant from
ringing; Paddock,^" Bioletti*^ and Husman-'* have reported a similar
increase in grapes. On the other hand Howe^^ found no increase in
size of fruit in ringed apples, pears, cherries and plums, though he reports
other late-season effects in the earlier maturity of fruit and a much
earlier dropping of the foliage Paddock^^ likewise has reported an
earlier maturity of grapes borne on ringed shoots, an earliness sometimes
amounting to as much as two weeks. It has been noted frequently
that grapes borne on ringed shoots contain relatively less sugar and more
acid^^ or are somewhat poorer in quality^ ^ than those borne on untreated
shoots.

In the section on Fruit Setting ringed shoots of the grape and of
certain other fruits are mentioned as setting in many cases a larger per-
centage of their blossoms than those not treated in this way, if the opera-
tion is performed just previous to the opening of the flowers. Seldom is
the difference great enough to make the operation worth while for this
purpose. A few varieties of the grape, however, without such treatment
grow so vigorously that they set but little fruit and with them the opera-
tion should be performed annually. Thus in the Fresno (California)
Experiment Vineyard 12-year-old ringed Panariti grafts on 10 different
resistant stocks averaged 7.5 tons per acre during 1917 and 1918, while
unringed vines on the same stocks and under the same conditions aver-
aged 2.3 tons per acre.^^

From the data presented here and in the section on Nutrition it
is evident that the concentrating influence of ringing, stripping and
related practices depends not alone on their effects on new vegetative
growth, leaf area and food manufacture, but also on food utilization.
In turn the utilization of the elaborated foods that are synthesized in the
shoot beyond the point of ringing depends on the available water and
nutrient supply. If the soil is comparatively dry and low in nitrates, the
effect of ringing or related practices may be quite different than with an
abundant supply of both moisture and nutrients, because the products
of synthesis beyond the ringed point may be utihzed in an entirely
different manner. This factor has received very little consideration and
it must be properly evaluated before any ringing operation can be per-
formed with certainty of its effects on either fruit bud formation or on the
development of fruit. Inadequate consideration of this factor has caused
much apparent contradiction and uncertainty in the results attending this
group of practices.

In at least one respect there is general agreement among those who have
employed ringing, stripping or other operations to check the transfer of
food. They all report a tendency to check the growth of the plant during
later years and thus have a dwarfing influence. This is proportional to

PRUNING—THE METHOD 437

the degree of starvation of the roots through separation from their supply
of elaborated foods and its ultimate effect on growth and development is
in every way comparable to the results attending root pruning. It
should be mentioned also that ringing inflicts mechanical injuries that
sometimes heal slowly and for this reason alone it should be used with
great caution, if at all, on certain fruits like the plum and cherry. Appar-
ently with the grape alone, among the connnon deciduous fruits, should
this group of practices be a regular cultural treatment and even in the
grape only a very few of the most vigorously growing varieties can be
ringed with profit. Other cultural treatments may be combined and
employed to better advantage to bring about the same conditions that
these special practices induce and with far less danger of undesirable
after-effects.

Summary. — In kind all top pruning may be considered either as
heading back or as thinning out. These two kinds produce quite differ-
ent results, particularly as the pruning increases in severity. In general,
thinning out is accompanied by less new shoot growth but more new spur
and fruit-bud formation than correspondingly severe heading back.
Heading back tends to make trees more, and thinning out less, compact
in habit. The different responses from the two methods of pruning are
due probably in large part to the distinct nutritive conditions to which
the practices give rise. Both methods have their places in orchard man-
agement, heading l)ack being more viseful in keeping the tree well shaped
and thinning out in developing its fruiting wood and in keeping that wood
in good working order. As most trees grow older they should receive
relatively more thinning out and less heading back.

In kind, pruning may be coarse or fine with essential differences
in the attendant responses. Coarse or bulk pruning tends to disturb
seriously the equilibrium within the plant and generally results in the
production of watersprouts. Careful fine pruning, on the other hand,
evokes a much more general response. The ideal pruning is fine, as
opposed to coarse or bulk; however in practice a compromise must gen-
erally be made between the kind which is best for the tree and the kind
which is most economical.

Root pruning has a dwarfing influence and its greatest use is in the
culture of dwarf trees. The supposed influence of root pruning in pro-
moting fruitfulness is due probably in part, if not largely, to other prac-
tices such as irrigation and fertilization which generally accompany the
culture of dwarfs.

Girdling, notching, ringing and stripping are special practices, related
to pruning, which have for their object the promotion of fruitfulness
through interrupting the translocation of foods. Their use is attended
by uncertain results and they are not to be recommended under average
conditions.

CHAPTER XXIV

PRUNING— THE SEASON

The subject of pruning has been shown to present three major aspects,
one of which is a consideration of the varying response from pruning at
different seasons. Theoretically at least this involves a study of the
different effects from pruning each successive month, or perhaps at more
frequent intervals. Practically the question is much less complicated,
involving principally a comparison of the effects attending pruning during
the growing season with those following winter pruning.

Pruning at Different Times During the Dormant Season. — Prun-
ing at different times during the dormant period may, however, re-
ceive brief consideration. Dormant or winter pruning is generally
understood to mean late winter or early spring pruning, since it is usually
done then. Winter pruning, however, may begin as soon as the plants
become more or less dormant in the fall and may continue into the spring
until vegetation is starting actively. The supposed advantages and
disadvantages of pruning at different times during the dormant period
have been long discussed. Apparently so far as any effect on the amount
and character of subsequent growth is concerned there is little or no
difference. This is brought out clearly by experimental work with apples
in England* and in Minnesota^ and with grapes in New York.^* On the
other hand since there is a gradual translocation of food materials from the
canes to the trunk and roots of the grape during a 3- or 4-weeks period
following leaf fall,"*^ pruning before this translocation is complete or after
the reverse movement has begun in the spring should result in a some-
what greater check to vigorous growth of the vine than a corresponding
pruning during the period between these extremes. This effect has
been noted both in France*" and in California.^

In California the time of winter pruning has been found to be impor-
tant in determining when grape vines of. the Vinifera group start growth.
Vines pruned immediately after the fall of the leaves started earliest;
those pruned in midwinter started about 4 days later and those pruned
considerably later, when bleeding commenced, were delayed about 6 days.
"Pruning when the terminal buds commenced to swell retarded the
lower buds 11 days, and, when the terminal buds had grown 2 or 3 inches,
20 days."^ In other words the lateness of starting of the buds was in
the order of the lateness of the pruning.

In commenting on some of the practical applications of these facts in grape
culture in California Bioletti'' remarks: "The retardation of the starting of the

438

PRUNING— THE SEASON 439

shoots in the spring may be a valuable means of escaping the injurious effects of
spring frosts. In one of our tests, the crop on nine rows pruned Mar. 13, was
saved, while that of 12 rows pruned Nov. 19, and Dec. 21, was completely
ruined by a frost on Apr. 21. Late pruning also retards the blossoming though
somewhat less than it does the starting. Pruning as late as March may retard
the blossoming 10 days. The time of ripening is also influenced slightly in the
same direction. When spring frosts occur, this influence appears to be reversed.
The vines pruned early may blossom and ripen their fruit later. This is because
the frost having destroyed the first shoots, the only flowers and fruit which
appear are on buds which have started after the frost . . .

"Pruning may be done, therefore, in frostless locations and with varieties
which set their fruit well, at any time when the vines are without leaves. Where
spring frosts are common the pruning should be as near the time of the swelling
of the buds as possible. The benefits of late pruning without its inconveniences
can be obtained by the system of 'double' or (clean) pruning practiced in some
regions. This may be applied in various ways. The simplest is to shear off all
the canes to a length of 15 to 18 inches at any time during the winter that is
convenient. This permits plowing and other cultural operations, and the final
pruning is done in April. A better method is to prune the vine as usual but to
leave the spurs with four or five e.xtra buds. These spurs we then shortened
back to the proper length as late as practicable. In some cases the method
practiced in the Medoc may be used. This consists in leaving a foot or 15 inches
of cane beyond the last bud needed and removing all the extra buds at the time
of pruning. The base buds are said to be retarded by the length of cane above
them the presence of buds on the cane having no effect."

Pruning late in the dormant season is quite likely to be attended by
more or less bleeding. Seldom is the amount great enough to be harm-
ful though many growers prefer to avoid any. In a few species,
as for example, the English walnut, late pruned trees may bleed very
profusely and the moist exposed surfaces offer an excellent opportunity
for infection. For this reason, if for no other, fall pruning may occa-
sionally be preferable to spring pruning.

Summer Pruning. — In the discussion of the effects attending various
amounts of winter pruning there was shown to be a slower net increase in
size with pruned than with unpruned trees and the more severe pruning
was shown to have the more pronounced retarding influence. Similar
results generally follow summer pruning and for about the same reasons.
The real question is whether or not summer pruning has a greater retard-
ing effect than a correspondingly severe winter pruning of the same kind.

Influence on Vegetative Growth. — The new shoots and leaves in the
spring are built chiefly at the expense of food materials formed the
preceding season and stored through the winter. After the leaves are
fully expanded they become manufacturing organs and eventually return
to the plant a supply of elaborated foods equal to or in excess of that
consumed in their development. At first, however, their growth is

440

FUNDAMENTALS OF FRUIT PRODUCTION

in effect parasitic and it is not until they have been active for some time
that they have fully replaced the materials used in their growth. Sum-
mer pruning removes them after they have levied their tax on the
tree's reserve foods and often before they have contributed much to its
welfare. It must have, generally, a greater retarding influence on net
increase in size than a correspondingly heavy winter pruning. This
devitalizing effect of summer pruning has been noted by many observers
and recently has been the subject of a number of experimental studies.
Alderman and Auchter^ found that young summer pruned apple trees
averaged only 120 feet of new shoot growth in 1915 while winter pruned
trees of the same age and of the same varieties averaged 188 to 216,
according to the severity of the pruning. The summer pruned trees
increased in spread, height and circumference more rapidly than trees
pruned very severely in the winter, but much less rapidly than those
pruned moderately or lightly in the winter. Apple trees just coming into
bearing produced, after winter pruning, shoots that were 20 to 50 per
cent longer and 10 to 20 per cent thicker than those on summer pruned
trees. In one orchard under investigation they found that the total leaf
area of summer pruned trees averaged only from 299 to 459 square feet,
that of trees pruned both summer and winter averaged from 527 to 794
square feet and that of trees pruned only during the winter averaged
from 660 to 1144 square feet. Not only were there fewer leaves on the
summer pruned trees, but these leaves averaged smaller in size. The
leaves of the summer pruned trees were paler and yellowish, suggesting
an additional reduction in their photosynthetic abilities. Arkansas and
York Imperial trees in full bearing, on the other hand, showed practically
no difference in the responses to summer and to winter pruning. In
fact the summer pruned trees of middle age produced more terminal
shoot growth than those pruned lightly during the dormant season,
though somewhat less than those pruned heavily. Table 13 presents
data obtained in England from pruning back weak declining plum trees at
various seasons. The figures show the relative lengths of the new
shoot growth. In this case the July pruning was little short of disastrous
to the trees. Certain experimental results obtained in Virginia from
various summer and winter prunings combined with special practices

Table 13. — Relative Length of New Shoots of the Plum, Cut Back at
Different Dates
{After Bedford and Pickering'^)

May 27

July 14

Nov. 2

Mar. 16

May 15

July 14

Not cut
back

1905

1905

1905

1906

1906

1906

125

75

100

• 100

65

18

67

PRUNING— THE SEASON

441

such as ringing, stripping and root pruning, show, despite some apparent
inconsistencies, that pruning during the growing season checks new shoot
formation and increment in trunk circumference more than does winter
pruning. 19 Batchelor and Goodspeed,^ reporting an experiment with
young bearing Jonathan and Gano apple trees in Utah, state that summer
pruning caused reduced vitaHty, though their figures show that the
average length of the new shoots under both pruning treatments was
practically the same during the 3 years for which the data are given.
Summer pruning, however, does not always retard growth more than
winter pruning. Experiments in New Jersey showed that peach trees

Table 14. — Influence ok Early Summer Pruning on Shoot Development
IN Young Apple Trees
(After Gardner-^)

Average

Average

Average

total

shoot

growth for

season,
centimeters

Average

shoot

shoot

net gain of

growth re-

growth re-

tree in

Variety

Pruning treatment

moved by

moved by

shoot

winter

pruning,

centimeters

summer

pruning,

centimeters

length for

season,
centimeters

Wagener

Winter pruned only

538

2690

2152

Wagener

Winter and sum-

mer pruned

.533

1611

4250

2106

Yellow Newtown

Unpruned

2720

2720

Yellow Newtown

Winter pruned only

826

3460

2634

Yellow Newtwon

Winter and sum-

mer pruned

488

1904

4930

2548

Jonathan

Unpruned

3576

3576

Jonathan

Winter pruned only

967

5165

4198

Jonathan

Winter and sum-

mer pruned

941

3837

7430

2652

Grimes

Unpruned

2270

2770

Grimes

Winter pruned only

988

2965

1977

Grimes

Winter and sum-

mer pruned. ....

rm

1603

4360

2256

pruned during the dormant season averaged 3,821 inches of new shoot
growth in 1916, while those pruned in the summer averaged 4,227.^
Though this difference is perhaps not much above experimental error,
it at least indicates that summer pruning does not always have a dwarfing
influence. In Table 14 are presented data obtained in Oregon showing
the influence on shoot development in young apples of rather severe
early summer pruning. In kind and in severity the summer pruning
treatment was practically identical with that given in the winter. In
every instance the summer pruned trees produced more total shoot

442 FUNDAMENTALS OF FRUIT PRODUCTION

growth — 58 per cent, in the Wagener trees, 44 per cent, in Yellow Newtown,
44 per cent, in Jonathan and 47 per cent, in Grimes — than those that
were pruned during the dormant season only. A part of this increased
growth came before the time of summer pruning (about July 1), but the
larger part of it was produced during the summer months following the
pruning. The growth produced before the time of summer pruning is to
be regarded as the consequence of a summer pruning treatment of the same
kind the preceding season; the growth after the pruning was a direct
response to that pruning. There was practically no difference between
the summer and winter pruned trees in their net increase in size, except
in Jonathan. The winter pruned trees of that variety showed a greater
net growth, principally on account of the great amount of wood removed by
the summer treatment. Vincenf*^ in Idaho has reported the 11-year
record of an apple orchard of Jonathan, Rome, Grimes and Wagener a
part of which received only winter pruning from the start while the other
part received only summer pruning (Aug. 6 to Sept. 6). In kind and
amount the pruning of the two portions was as nearly as possible. Table
15 summarizes some of the growth records of these trees. For the most
part the average heights, widths and trunk circumferences were slightly
greater in the winter pruned than in the summer pruned trees, while the
reverse was true in regard to average shoot lengths. In no case, how-
ever, were the differences large enough to be significant. Clearly,
summer pruning exerted no dwarfing influence in this orchard.

These almost diametrically opposite results attending summer pruning
in carefully controlled experimental work can be harmonized. The
tree is to be regarded as a system in mobile equilibrium. This equili-
brium involves a condition of balance between part and part and between
constituent and constituent within the plant and a condition of adjust-
ment to the environment without. Chief among these factors of environ-
ment are temperature, light, moisture and food supply. Growth of any
kind is a response to the condition of the equilibrium within and of
the adjustment without. Pruning, at any time — and more especially
summer pruning — disturbs both the adjustment to the environment
without and the balance within. The immediate effect on the tree as a
whole of any summer pruning is to reduce the carbohydrate supply
and the rate of carbohydrate manufacture and at the same time to
increase the supply of water and other nutrients, particularly nitrates,
that is available to the rest of the plant. The size or amount of this
influence depends on: (1) the severity, (2) the kind and (3) the time of
the pruning and on (4) the moisture and (5) the nutrient supply available
in the soil. Its general effect on growth therefore may be expected to
correspond closely to that of fertilization and irrigation at that particular
time. If the pruning is not severe enough to reduce carbohydrate sup-
ply and carbohydrate manufacture to the point where they limit new

PRUNING— THE SEASON

443

Table 15. — Growth Records of Summer and Winter-pruned Apple Trees in

Idaho

(After VincenV^)

Variety

Pruning

Average

shoot

length

eleventh

year, inches

Average

height

eleventh

vear, feet

Average

width
eleventh
year, feet

Average

diameter

eleventh

year, inches

Jonathan

Jonathan

Winter

Summer

Winter

Summer

Winter

Summer

Winter

Summer

16.1
18.2
15.4
14.8
12.7
16.2
11.9
12.4

17.24
15.98
15.88
15.75
16.00
15.38
14.65
14.30

19.51
17.71
14.35
13.60
15.30
14.67
12.25
12.95

7.43
7 35

Rome

6.58
6 56

Grimes

Grimes

6.71
6 32

Wagener

Wagener

5.82
5.61

tissue formation, active growth ensues. This apparently is the explana-
tion of the results obtained with young peach trees in New Jersey^ and
with young apple trees in Oregon, ^i Soil conditions were such and the
pruning was such, in time, kind and severity, that a vigorous new vegeta-
tive growth was promoted following the pruning and terminal bud forma-
tion was completed at a considerably later date. This condition may
frequently result in an actual increase of food reserves at the time of leaf
abscission, especially in sections with a late growing season, because of the
greatly increased leaf surface. On the other hand if the pruning is of
such character that carbohydrates and other elaborated foods are re-
moved in considerable quantity and if it is done at a time when soil and
tree conditions do not stimulate later growth the same season, there is
not only an immediate reduction in size but reserves for the following
season are depleted and growth the next year will be correspondingly
restricted. Summer pruning under such conditions has a distinct
dwarfing influence.

In conclusion, then, it may be stated that summer pruning does not
necessarily have either a dwarfing or an invigorating influence. It
may have the one or the other, depending on the severity, kind and
time of pruning (as related to the state of development of the plant,
rather than to the exact date on which the pruning may be done).
Environmental conditions also, particularly nutrient supply, soil moisture
and light, influence greatly the nature of the response from summer
pruning. Consequently it should be employed as an orchard practice
only when due consideration is given the several factors on which its
results depend. The amateur or the careless grower cannot use it safely.
The careful student of fruit growing can often employ it with reasonable

444 FUNDAMENTALS OF FRUIT PRODUCTION

certainty of the results and frequently will find it of great value. The
results attending summer pruning in some of the best managed cane
fruit plantations furnish ample evidence to this effect.

Influence on Production. — The grower, however, is interested par-
ticularly in knowing whether or not certain specific objects can be accom-
plished— or accomplished more readily — by doing the work at one season
rather than at another. This really is the question leading to most of
the discussion over summer pruning.

The opinion receiving general acceptance is expressed in the proverb,
"prune in winter for wood and in summer for fruit." Quintinye^^
states that summer pruning leads to the formation of fruit buds for the
following crop. Hovey,^^ referring particularly to the apple and pear,
states that it leads to the formation of fruit spurs and thus indirectly
aids in fruit production. Quinn^* recommends pinching back in summer
to promote fruitfulness in the pear and Barry'^ recommends this practice
even more generally for the same purpose. Waugh^^ states that summer
pruning tends to promote fruit-bud formation. Cole,^^ Downing^^ and
many others recommend summer pruning in preference to winter pruning,
but because wounds made at that time heal more readily than those
made at other seasons. On the other hand Pearson^'' states that summer
pruning may either promote or repress fruitfulness, depending on how
it is done. The general idea is that fruitfulness is promoted by summer
pruning through checking growth or weakening the plant.

Though the majority of the opinions just cited are from American writers,
it should perhaps be stated that it is in European countries that the practice is
most commonly employed and that it is in those countries that it is generally
believed to be of particular value in promoting fruitfulness. In America there
is a much greater diversity of opinion. Much of the apparent difference in
results attending summer pruning in this country and in Europe is to be explained
through the difference in the methods employed. The growers of this country
mean by the term summer pruning a pruning similar in kind and in amount to
that ordinarily done during the dormant season. On the other hand, summer
pruning to the European fruit grower means something entirely different — for
the most pai't a pinching or at least a pruning that can be done largely "with
the thumb and forefinger." This type of pruning is employed in America neither
in summer nor in winter. As explained later under Pinching the practice of
summer pruning commonly employed in Europe is hardly applicable here be-
cause of economic considerations and consequently the extensive European
literature on summer pruning is only of incidental interest to most American
fruit growers.

In the section on Nutrition, data are presented showing that vigor
of growth and productiveness are not necessarily antagonistic qualities.
Indeed, the largest yields are always obtained from rather vigorous plants.
The belief that increased fruitfulness should follow summer pruning as

PRUNING— THE SEASON

445

generally practiced in America, is therefore based on two assumptions,
both of which are fundamentally wrong. This is shown by some of
the more recent investigations in this particular field — notably those
in Virginia, 1^ West Virginia' and Utah.^' All these showed decreased
production of flower clusters or decreased yields of fruit following the
summer pruning of young trees just coming into bearing or with their
bearing habits not yet well established and all report an accompanying
decrease in vegetative growth. In one of the West Virginia experi-
ments the yield of the summer pruned trees averaged barely a third of
the yield from those receiving winter pruning. On the other hand
Bedford and Pickering^ in one series of experiments found flower-bud
formation following summer pruning greater by 13 to 41 per cent, than
following winter pruning, depending on the time of operation. Alderman
and Auchter,' who found summer pruning a considerable check to fruit
production in apple trees just coming into bearing, report no such general
influence on mature trees. Table 16 summarizes the yields obtained in
Idaho over a 7-year period from winter and from summer pruned plots.
In every variety under trial summer pruning resulted in an increased
yield.

Table 16. — Average Yields in Pounds per Tree From Winter and yuMMER-
PRUNED Trees

{After Vincent'^^)

Variety

Pruning

1910, 1911,
pounds pounds

1912,
pounds

1913,
pounds

1914,
pounds

1915,
pounds

1916,
pounds

Total,
pounds

Jonathan. . . .

Winter

Jonathan. . . .

Summer

Rome

Winter

Rome

Summer

Grimes

Winter

Grimes

Summer

Wagener ....

Winter

Wagener ....

Summer

29.0
33.9
13.9
13.9
13.2
20.0
29.0
.54 . 3

95.5
95.5
52.5
58.5
85.1
99.5
67.0
123.2

127.8
144.3
58.8
85.0
101.6
195.5
22.0
50.8

257.4
252.1
76.8
80.0

128.7
88.5
83.7

1.59.0

50.3
51.7
18.7
23.0
102.1
155. 6
6.2
27.2

2.39. 4
272.1
105.7
160.4
197.3
108.3
177.4
215.5

834.7
870.9
391.6
450.8
689.0
738.4
402.5
689.4

In commenting on these increases Vincent^^ says: "If the entire orchard had
been summer-pruned there would have been an increase per acre during the 7
years as follows: Jonathan, 30.02 boxes or an increase of 4.28 boxes per year;
Rome, 49.7 boxes, or an increase of 7.1 boxes per year; Grimes, 50.6 boxes or an
increase of 6.07 boxes, per year; Wagener, 240.9 boxes or an increase of 34.4
boxes per year. Summer pruning therefore has increased crop production on all
the plats and quite substantially on the Wagener."

In neither the mature West Virginia trees nor the Idaho trees was
summer pruning attended by an appreciably decreased vegetative
growth.

446 FUNDAMENTALS OF FRUIT PRODUCTION

At first glance these records of yields from summer and winter pruned
trees seem contradictory. As is the case with the corresponding records
of shoot growth, however, they can be reconciled. It has been pointed
out that fruit production depends on (1) the formation of fruit-producing
wood and (2) on the proper functioning of that wood. Furthermore,
different kinds of fruits have quite unlike fruiting habits and the processes
culminating in fruit production may be quite different in one from those
in another. The effect of summer pruning on fruitfulness, therefore,
is not a simple question, but rather a series of questions each of which
must be answered in turn.

Among the major aspects of the summer pruning problem may be
stated the following: (1) The concentrating effects of different kinds and
amounts of pruning at various times during the growing season, (2)
The relation of diverse summer pruning treatments to shoot growth
both of the current and of the following season. (3) The influence on new
spur formation. (4) The effect on fruit bud formation — on spurs and
on shoots. (5) The relation to the intake of nutrients and to the manu-
facture, translocation, storage and utilization of elaborated foods. (6)
The influence on color and size of fruit. These questions are not entirely
distinct; they are inter-related and inter-dependent. Since few data are
available concerning some of them, any discussion at this time must of
necessity be incomplete. It is attempted here on a few aspects only of
the general problem, those which have more or less immediate practical
bearing and on which the evidence seems reliable.

Summer Pruning to Develop Framework. — Data have been presented
concerning the influences of summer pruning on vegetative growth in
general and on new shoot formation in particular. No further attention
is devoted here to this problem except to indicate a rather special use
of early summer pruning in developing the framework of young, strong,
vigorously growing trees.

Trees of many kinds growing under favorable conditions often develop
shoots 23^^ or 3 feet — and sometimes more — in length during their second,
third and fourth seasons in the orchard. Occasionally they make such
growth their first season and shoots of this character are not at all
uncommon as the trees grow older. Ordinarily most of this shoot growth
is cut away in the annual dormant season pruning, some being taken out
entirely and the terminal half or even three-fourths of each remaining
shoot generally being removed. This heavy cutting back is necessary
for securing a strong framework and a compact type of growth. The
question naturally arises whether these trees can be pruned in mid-
summer shortly after the shoots have attained a length equaling that to
which they would be cut back at the usual winter pruning. This would
then be followed by the production of secondary lateral shoots, many of
which could be saved with little or no heading back at the following

PRUNING— THE SEASON 447

winter pruning. In this way two steps in the construction of the franie-
work of the tree would be taken in one season and theoretically a year
would be saved in growing the tree to producing size and in bringing it
into bearing. This type of summer pruning, which includes both thin-
ning and heading early in the summer (about July 1) was studied with
apples in Oregon.-^ Though such varieties as Jonathan, Grimes, Yellow
Newtown and Wagener summer pruned in this way did not make the
equivalent of two seasons' ordinary growth in one summer, three success-
ive years of such treatment resulted in trees comparable in size, fruit
spur development and productiveness to winter pruned trees a year
older. In other words a j^ear had been gained in developing their frame-
work and in bringing them into bearing. Observation led to the belief
that this method of pruning is equally valuable in forcing the early de-
velopment of both pears and sweet cherries. This special pruning prac-
tice is desirable with young trees only under favorable growing conditions
when they are making new shoots at least 2}^ feet in length and where
the growing season is long enough to permit a proper maturity of the
late secondary shoots.

Summer Pruning as a Conservation Measure. — It has been stated
before that the removal of any living portion of the top of a plant at any
time deprives the plant of a certain amount of elaborated food material.
This is true particularly of pruning in summer when the storage tissues
have been depleted for the building of new structures. However, the
removal of any portion of the top reduces somewhat the demand on the
root system for nutrients and moisture; under certain conditions this
reduction may enable the roots to supply the remaining parts with
amounts nearer their requirements for growth. In this way pruning
can be said to have a stimulating influence. In other words, it may be
regarded as a conservation measure, making given amounts of moisture
and nutrients go further; because these larger amounts of materials are
available, certain parts may manufacture and store more elaborated
foods than they could otherwise. This may be considered a concentra-
tion effect. The concentration is limited to certain parts and in some
instances other parts may suffer and perhaps the plant as a whole may be
weakened. Apparently one of the more important objects that may be
accomplished by pruning during the growing season is due to this in-
fluence.

This effect of summer pruning depends on many factors. Among the
more important are: (1) the severity of the pruning, (2) its kind, (3) the
exact stage of development of the plant at the time the pruning is done
and (4) the soil conditions before, at the time of and after the operation.

Independent of the other factors, it is evident that, within certain
limits, the more severe the pruning the greater will be its effect in diverting
into the remaining parts nutrients and moisture. However, a point is

448 FUNDAMENTALS OF FRUIT PRODUCTION

always reached, unless the operation is performed shortly before the begin-
ning of the dormant season, when an increase in the severity of the pruning
results in forcing into growth buds that otherwise would remain dormant
until the following spring. At this point its general effect changes from
conservation to dissipation since the new tissues demand not only soil
nutrients and moisture but elaborated foods as well. The branches,
canes or shoots remaining and perhaps the whole plant, are left weaker
in that they are likely to enter the dormant season less richly supplied
with elaborated food materials. In general the conservation effects of
any pruning cease when it promotes greater utilization of reserve foods
in the building of new tissue. Were these effects (that is, the ratio that
they bear to the total effects) of summer pruning plotted in a curve as
they vary with the severity of the pruning this curve would start close to
the 100 per cent value with very light pruning and fall steadily with each
increase in severity until the zero point is reached. Furthermore this
general situation would obtain regardless of the kind of the pruning or of
the exact time of the operation, though in no two cases could the curves
be expected to be exactly parallel.

Closely related to the stimulating effect of varying amounts of summer
pruning is the influence of the stage of seasonal development at which it
is done. In general a very early summer pruning, particularly if it
consists in thinning out, is most effective in diverting the energies of
the plant into other developing or already developed tissues. It may
lead to greater elongation of shoots, to shorter internodes and more
leaves, possibly to the formation of side branches or to several other
growth responses or it may simply result in a more efficient functioning
of the remaining tissues. This, for instance, is the general effect of the
prompt removal of watersprouts, suckers or other shoots just as they are
starting. If the pruning is done a little later, during the period of most
rapid vegetative growth, it may have a concentrating effect (that is,
lead to the greater accumulation of elaborated foods) or it may have the
opposite effect and force out a crop of secondary shoots, the kind of the
response varying with the severity and kind of the pruning. Pruning
late in the growing season, if not too severe, is almost sure to have a
concentrating effect (for the particular parts affected), since no new
growth will take place to utilize the stored foods and there will be still
further accumulations resulting from the increased supply of nutrients
and of light.

Of the two kinds of summer pruning, thinning out generally has a
much greater concentrating effect than heading back. The latter
practice, unless it consists in a mere pinching out of the terminals or
unless it comes very late in the season, results immediately in the forma-
tion of numerous secondary lateral branches. Their development
consumes food materials that have been, or are being, manufactured and

PRUNING—THE SEASON 449

results in a shading of leaves lower in the tree and possibly in reduced
rates of photosynthesis and of food manufacture. However, a light
heading back or pinching of the terminals of the grape early in the season,
thus temporarily checking new shoot growth, is said to aid materially
the setting of fruit in certain varieties.^ This is a concentration effect,
though the practice is of special rather than general application. On the
other hand thinning out has no such tendency to encourage the develop-
ment of secondary; shoots certainly they are not formed to anything
like the same extent as with summer heading. More light is admitted to
the interior of the plant which is better supplied with nutrients and
moisture and the result is an increased accumulation of elaborated foods.
The results attending a well distributed thinning of the shoots and smaller
branches would be more pronounced in this direction than those following
a coarse or bulk thinning.

When soil conditions, particularly^ moisture and nutrient supply,
encourage new vegetative growth, summer pnming is much less likely to
exert concentrating effects than it is when less moisture and less nitrogen
are available. Indeed its influence may be the reverse, particularly if the
summer pruning has been mainly heading back. Generally speaking, it is
easier to secure the concentration effects of summer pruning when the
available soil moisture and nitrates are not too high and when atmospheric
conditions favor a high transpiration rate. These, it will be recognized,
are the conditions under which it has been suggested by Chandler'" that
summer pruning can be employed advantageously as a moisture-
conserving measure to prevent the wilting of partly grown fruits on
heavily laden and vigorously growing trees. The influence of certain
summer pruning practices on the formation of fruit buds, discussed a
little later, is probably due to their concentrating effect.

In a general way it may be stated that summer pruning is often
very useful because of its influence in diverting the energies of the plant
into other channels. In the average plant most of the watersprouts and
suckers (except those used for renewal purposes) are worse than useless.
They dissipate- energies and yield little in return. Their prompt
removal is a conservation measure and is particularly important in
certain fruits like the grape and in nearly all young trees. The longer
the delay in cutting them out the less is gained by removing them.
Practically the same statement holds for the early summer removal of a
portion of the barren shoots in the grape and certain other plants.
Midsummer or late summer pruning may be desirable occasionally, in
so far as it reduces transpiration losses and indirectly aids in the sizing
and coloration of the fruit.

It should be reiterated that the concentrating effect of pruning does
not necessarily invigorate the plant as a whole. In fact it may have
exactly the opposite influence, though certain parts are favored by the

450 FUNDAMENTALS OF FRUIT PRODUCTION

process. Thus a heavily laden peach tree pruned in late July as a protec-
tion against drought is probably weakened by the operation and may
show the effects in the new growth put out the following spring, though
the pruning operation enabled the fruit to mature properly. The
situation is simply another aspect of a problem constantly encountered
in pruning practice — that of subordinating or even eliminating one part
in the interest of another.

Influence on New Spur Formation. — The influence of summer pruning
on new shoot formation and consequently on the fruit-producing wood
in plants bearing on shoots or canes has been discussed. There
remains consideration of its influence on new spur formation. Spurs are
generally formed from lateral buds on the long growths of the current
or of the preceding season. Only a certain percentage of these grow out
into spurs, the number depending on many factors, among the more
important of which are (1) the supply of nutrients and elaborated food
materials available for their growth and (2) the relative stage of develop-
ment or the size of the buds themselves. The influence of summer
pruning on the supply of available foods has just been considered under
the head of Concentration; consequently that aspect of the question
need not be discussed further.

Observation shows that in almost all species there are considerable
differences in the size of the lateral buds on the long growths or shoots.
Usually those on the basal portion are small and inclined to remain
dormant unless stimulated into growth by some special pruning or
other treatment; the buds on the median and terminal portions of the
shoot are better developed and grow out readily, to form either shoots or
spurs. Apparently their greater size and development is due largely to
the better light supply and to the more favorable location for food manu-
facture, of the leaves that subtended them. Obviously almost any
pruning and particularly any summer pruning will influence the amount
of light reaching the leaves on the remaining shoots. In many fruits sum-
mer heading back, unless very light and done comparatively late in
the season, encourages the formation of laterals or secondary shoots and
consequently produces poorer conditions for photosynthesis in the lower
parts of the plant. At the same time, as shown later under Pinching,
it results in thickening the bark on the lower portion of the shoot and
therefore in different food storage conditions that are associated with the
change in the relative proportions of the several tissues. These effects
may outweigh in importance those occasioned by greater shading. There
is reason to believe that in at least some fruits summer heading acts as a
stimulus to fruit-bud formation on the current season's shoots. On the
other hand thinning out admits more light to the leaves on the lower
part of the shoots and thus encourages the elaboration of foods and the
formation of larger and stronger buds. Summer thinning therefore

PRUNING— THE SEASON 451

tends to encourage fruit-spur formation. This is in a sense another
concentrating effect of summer pruning. It is evident from what has
been said that the earlier in the season the pruning is done the greater is
its influence in this direction.

Gardner 21 has reported that in young apple trees not yet in bearing
greatly increased fruit-spur formation follows early summer pruning
in addition to winter pruning. This is not so much because of the better
spur production from the buds left on the primary shoots after the
summer pruning as because after the pruning many secondary shoots are
produced on which the buds grow out readily to form new spurs the
following season. In apples nearly all the buds on these late summer
secondary shoots enter the winter in practically the same condition as, and
are comparable in every way to, the buds on the median and terminal por-
tions of the primary shoots. ^^ j^ f^g^ ^^e of the most useful purposes
served by the early summer pruning of young vigorously growing spur
bearing trees Hke the apple is to increase the number of spurs over that
secured by winter pruning alone. It is worthy of mention that spurs
developing from these secondary late summer shoots are as a rule
especially strong, vigorous and likely to produce fruit buds.

Influence on Fruit-hud Formation. — In the section on Nutrition
it is shown that, in all cases studied, fruit-bud differentiation is associated
with carbohydrate accumulation in the immediate vicinity of the buds
concerned. The work of Magness^^ on young apple trees indicates that
this accumulation takes place principally where there is the greatest
effective leaf area. In other words, within certain limits those spurs
that have the largest and best lighted leaves accumulate the largest
reserves of carbohydrates and differentiate the most fruit buds. He
found that by partial or complete defoliation of spurs well supplied with
leaves, fruit-bud formation on these spurs could be entirely prevented,
even though adjacent spurs retaining their full complements of leaves
formed fruit buds freely. Similarly he found that the formation of
lateral fruit buds took place only in the axils of good sized, well lighted
leaves.

Magness^^ summarizes his results as follows: "Fruit-bud initiation will not
take place, and fruit buds will not form in most varieties in the absence of a fair
amount of leaf area in the tree.

"Food material stored in the tree through the dormant season is apparently
stored largely in the tissue adjacent to the leaves in which it was manufactured.
This is shown by the fact that the defoliated portion does not develop as strongly
and well during the spring following the treatment, as does the undefoliated
portion.

"Leaf area in one part of the tree will usually not supply food material to
the buds in another part to the extent necessary to cause them to become fruit
buds. DefoHating one-half of a tree has Uttle influence upon the undefoliated

452 FUNDAMENTALS OF FRUIT PRODUCTION

portion, but that part which is defoliated functions as it would if all the leaves
had been removed from the whole tree.

"Removing the same number of leaves, without any pruning, has practically
the same effect upon the fruit-bud formation for the immediate year following
that a summer pruning, removing leaves from the same position, would have.

"Buds on 1-year wood, in areas from which the leaves have been removed
are slower in starting out into growth, and make a weaker growth the following
spring than do other buds on the same shoots not defoliated. This is more
noticeable in some varieties than in others.

"One shoot seems to be very largely independent of other shoots about it so
far as fruit-bud formation is concerned. It is apparently largely dependent upon
its own leaves for nourishment.

"Removing leaves from individual spurs tends to prevent the formation of
fruit buds upon those spurs, although it does not entirely check the development
of flower parts.

"On those spurs which form fruit buds, notwithstanding defoliation, the
blossoms are, on the average, considerably later in opening in the spring.

"Axillary buds of the Wagener seem to be almost entirely dependent upon
the immediate subtending leaf for the carbohydrate supply with which they are
nourished. Removing the subtending leaf entirely prevents fruit-bud formation.
Buds so treated either remained entirely dormant during the following growing
season or pushed out into very weak growth. Very few of them showed a
development approaching normal."

Magness' work may explain incidentally why the basal portions of
shoots often produce relatively fewer fruit buds than the median and
terminal portions. The basal portions are poorly lighted and, assuming
leaves of equal size, they would manufacture smaller amounts of elabo-
rated foods. Neither spurs nor shoots can be expected to differentiate
fruit buds freely if they are heavily shaded. Summer pruning, however,
naay admit more light both to the spurs and to the basal portions of
the shoots at the same time it concentrates the supply of nutrients.
This direct influence on the factors associated with fruit-bud formation
could hardly help but influence more or less directly the relative number
of fruit buds. Obviously early summer pruning comprising thinning
out instead of heading back would have the greatest influence of this
kind. No pruning practice after fruit-bud formation for the season
is completed could conceivably have any influence in this direction and
heading back with the formation of many secondary lateral branches
would cause still heavier shading and reduce rather than increase fruit-
bud formation. Doubtless many of the cases in which summer pruning
has failed to produce an increased number of fruit buds have been due
to its consisting mainly in heading back or being done too late to
have any important influence in this direction. Experience shows that
a light or moderate early summer thinning of the shoots of those trees
such as the peach that bear laterally on shoots aids greatly in the forma-

PRUNING—THE SEASON 453

tion of fruit buds on the basal and median portions of those shoots.
Though such summer pruning may not result in any considerable increase
in the total number of fruit buds, it does favor fruit-bud formation
in more desirable places and is well worth while.

Influence on Fruit Color. — In the apple, peach and certain other
fruits the development of the red colors in the skin of the fruit depends
mainly on sunlight. With those fruits summer pruning naturally
influences their coloration, particularly if the pruning consists mainly
in thinning out. Vincent*'' reports that summer, as compared with
winter, pruning the apple in Idaho resulted in an increase of 33 per cent,
of extra fancy apples in Jonathan, 32 per cent in Rome and 5 per cent
in Wagener, the grading being mainly on the basis of standard commercial
color requirements. The coloring of certain other fruits, as plums and
grapes, does not depend on light reaching the fruit itself, though pig-
ment formation depends on carbohydrate manufacture in near by
leaves. Consequently summer pruning is of less direct aid in the colora-
tion of these fruits. Bioletti,^ however, states that judicious summer
pruning may occasionally favor the coloring of the fruit in certain grape
varieties. Presumably this influence is exercised through the better
lighting of the foliage near the fruit clusters.

Most fruits develop their color late in the growing season or shortly
before ripening. Consequently summer pruning to promote a better
coloring of the fruit may be done comparatively late. In pruning for
this purpose caution should be exercised; too severe or too early summer
pruning is likely to result in more or less sunburn of the fruit.

Summer Pinching. — It is impossible to distinguish clearly between
what is termed pinching and what is usually termed topping or heading
back. The difference between the operations is siniplj' in the maturity of
the tissues at the time the operation is performed and in the relative
amount of new growth removed. In some species, as for example the
rambles, pinching leads to considerable branching of the pinched shoots;
in many others it may be attended by very little branching, one or two of
the subterminal buds promptly growing out to replace the leader. Conse-
quently its general effect may be concentration or dissipation and dilution,
depending on the species and on conditions. Summer pinching has been
much used in European fruit growing and in the growing of fruits under
glass. In this country it has been used mainly with the brambles and with
grapes, though occasionally it is helpful in checking or directing growth
in some of the other fruits.

There seems to be much difference of opinion among growers and
investigators as to the wisdom of summer pinching of brambles. Both
satisfactory and unsatisfactory results have been reported. Apparently
much depends on the time of the operation; furthermore varieties respond
quite differently to the same treatment. Macoun^' has reported that at

454 FUNDAMENTALS OF FRUIT PRODUCTION

Ottawa, Canada, red raspberries pinched back in early summer and thus
forced to branch, generally yield less than untreated plants. Since
Kenyon, Loudon, King, Hansell and Miller (red raspberries) do not branch
freely, they should never be summer pinched.*^ The main advantage
claimed for summer pinching is that it results in a lower, more compact,
bushy plant with mechanically stronger canes than those that are un-
headed and unbranched. Consequently they hold up their fruit better
and require less trellising. Dewberries which usually require trellising
are seldom summer pinched. It is generally agreed that if raspberries or
blackberries are to be summer pinched the operation should be performed
early, when the shoots are only 18 to 24 inches high or perhaps even
before this.^ Pinching higher or cutting back to this point at a later date
is likely to result in weak, late-maturing laterals that are especially sub-
ject to winter injury and are less likely to give rise the following year to
good fruiting shoots. Blackberries and black raspberries generally
respond better than red raspberries to summer pinching. Pinching the
ends of the growing shoots just before blossoming has been stated
to aid sometimes in the setting of fruit in the grape; it is thus a partial
remedy for "coulure."^ Bioletti*' mentions pinching as sometimes useful
also in protecting grapes from sunburn by causing the shoots, through
more rapid lignification, to remain more upright and to furnish more shade
for the fruit clusters. But little evidence is available concerning the
influence of summer pinching on fruit-bud formation in the grape and at
present it cannot be recommended confidently for any effect of this sort.
The early and repeated pinching back of shoots of the apple and pear
to stimulate the development of fruit spurs and fruit buds has been dis-
cussed freely. Thomas^^ states that " by pinching off the soft ends of the
side-shoots after they have made a few inches of growth — the sap imme-
diately accumulates, and the young buds upon the remainder of these
shoots, which otherwise would produce leaves, are gradually changed into
fruit buds. To prevent the breaking of these buds into new shoots by too
great an accumulation of the sap, partial outlet is left for its escape
through the leading shoot of the branch, which at the same time is effect-
ing the desired enlargement of the tree. ... It often happens, and espe-
cially when the pinching is done too early, that the new buds send out
shoots a second time the same season. When this occurs, these second
shoots are to be pinched in the same manner as the first, but shorter; and
third ones, should they start, are to besimilarly treated." Barry, ^Rivers^^
and others recommend the same treatment for the same purpose and these
early authorities have been followed by many later writers. Recently
Ballard and Volck^" in California have shown that, by two or three repeated
summer pinchings, fruit spurs bearing fruit buds can be developed from
watersprouts of the apple in one season. They found also that normal
shoots throughout the tree respond in the same way to similar treatment.

PRUNING— THE SEASON

455

Gaucher^s recommends early summer pinching in spurs which are growing
out into vegetative shoots. He states this pinching usually stops further
growth from the terminal bud and forces out at lower points on the spur
lateral buds that otherwise would remain latent. These then develop
into branch spurs that often form fruit buds the first season. If a single
pinching does not result in fruit-spur and fruit-bud formation, a second
pinching is recommended,

Goumy^s studied the influence of summer pinching on the subsequent
development of bark and wood; some of his results are summarized in
Table 17. Pinching obviously has led to a proportionally greater
development of the bark. Goumy found also some difference between the
relative amounts of bark and of wood in the spurs on the year old growth
of pinched and unpinched spurs. The determination of just what these
differences in relative amounts of bark and wood signify in terms of nutri-

Table 17. — Influence of Summer Pinching on Relative Thickness of Bark
AND Wood in the Pinched Shoot of the Pear

(After Goumy^^)

Tissue

Shoot not pinched

Shoot pinched

Pith

2.3
5.5
2.25

1.0

2.2
0.6
1.6
0.6

2 8

Wood

3 7

Bark

Bark tissues in particular:

Epidermis

Cortical parenchyma

3.4

1.0

4 4

Sclerenchyma

Cortex

0.5
3.0

0.6

tive conditions and food reserves is difficult, but presumably they favor
fruit-bud formation in the pinched shoots.

However, summer pinching has been practiced frequently for the
purpose of promoting fruit spur and fruit-bud formation and has not
secured the expected response. In general it may be stated that, though
the practice may produce satisfactory results if followed properly by succes-
sive pinching of secondary and tertiary shoots, the amount and kind of
labor involved are such as to make it of doubtful value in the commercial
fruit plantation in America. When trees are grown as standards other
measures or practices that are available will call forth more of a mass
response and will provide at much less expense the requisite number of
fruit spurs and fruit buds.

The early summer pinching of shoots in young trees for the purpose
of subordinating those that are not wanted for permanent framework is
only occasionally employed but is frequently to be recommended. In

456 FUNDAMENTALS OF FRUIT PRODUCTION

newly planted trees the buds within a short distance from the ground
often start to grow. Generally the resulting shoots are promptly rubbed
off or they are pruned away after they have been allowed to grow a year.
In either case the growth of the upper branches is very likely to be checked.
If these lower shoots are promptly pinched back so as to leave three or
four leaves apiece the upper shoots are not checked in their development,
the trunk is shaded and the food materials that their leaves manufacture
will be of considerable value in promoting a vigorous growth the following
season, after which they can be removed. Similarly in trees that have
been growing in the orchard for 1, 2 or 3 years, are formed many shoots
that ordinarily are removed at the following dormant-season pruning.
Their growth reduces somewhat the development of those desired for the
permanent framework. Pinching them back early in the season sup-
presses them and the nutrients and moisture are largely diverted into other
parts, but at the same time their leaf surface serves to manufacture
elaborated foods for the current and the following seasons.

Summary. — On the whole but little difference is likely to result from
pruning at different times during the dormant season, though in certain
fruits early pruning is followed by earlier foliation in the spring. This is
a factor of commercial importance in grape culture. Very late pruning
generally leads to more bleeding than earlier pruning. Bleeding from
pruning wounds seldom harms the plant.

Summer pruning may have a dwarfing or an invigorating influence
(as compared with a corresponding winter pruning), depending on its
severity, kind, the stage of development of the plant and on environ-
mental conditions — particularly nutrient supply, soil moisture and light.
A light summer thinning encourages fruit-spur formation through favor-
ing the development of larger and stronger lateral buds from which spurs
are formed. The same practice promotes fruit-bud formation also if the
work is done early enough in the season. Heading back tends to stimu-
late purely vegetative growth. Judicious summer pruning is more or
less a conservation measure. This applies particularly to the removal
of watersprouts and other superfluous growth. In very strong vigorously
growing trees 2 to 5 years old early summer pruning results in encouraging
a late secondary growth and this may be a means of hastening the general
development of the tree if there is a long growing season and other condi-
tions are favorable. A light summer pruning may aid materially the
coloration of fruit in certain species.

Summer pinching in general encourages the development of sec-
ondary shoots. This is often desirable in the culture of the bramble
fruits. Pinching may be used also to subordinate individual shoots and,
in the spur-bearing species, it may result in their developing into spurs.
This practice is of doubtful utility, however, in the culture of standard
trees.

CHAPTER XXV
PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS

In a preceding chapter were discussed some of the more important
general or mass effects of pruning. • Mention was made also of the more
specific influence of certain practices on fruit-spur, shoot or fruit-bud
formation in particular parts of the tree, though this concerned the
general aspects of those questions rather than the particular applications
presented by different fruit plants. Another chapter attempts to explain
in some detail the fruit bearing habits of the more connnon fruits. There
remains for discussion the adaptation of pruning practices to plants hav-
ing these different methods of bearing so that maximum annual produc-
tion may be obtained along with the form of tree or plant most conducive
to long hfe and economy in production. It should not be inferred,
however, that all fruit plants with the same fruiting habit should be
pruned alike. Their general growing habits, that is, the amount and
character of their new vegetative growth, may be quite different and
necessitate equally diverse pruning treatments. Though the Winter
Nelis pear has essentially the same bearing habit as the Maiden Blush
apple, the two must be pruned quite differently because they are so
unlike in their vegetative growth and the red raspberry with essentially
the same fruiting habit as the black raspberry should be pruned more
sevei'ely because of its great tendency to sucker; many other instances
might be cited.

Broadly speaking, pruning may be said to influence fruit-bud and
fruit formation — bearing habit — in two ways, directly and indirectly.
Its most important direct influence is to thin the crop through the removal
of actual or potential fruit-bearing wood. Another rather direct influence
is its effect on the location or distribution of fruiting wood, both spurs
and shoots. Its indirect influence is effected mainly through changing
nutritive conditions within the tree and consequently limiting or encour-
aging fruit-spur or fruit-bud formation. As these indirect effects have
been considered rather fully in the preceding chapters but little attention
is given them here. Furthermore no attempt is made to discuss the
influence of different pruning treatments on the fruiting habits of any of
the tropical or subtropical fruits or of a number of the less common and
less important deciduous fruits.

Pruning the Apple and the Pear. — As has been pointed out, apple and
pear flowers are for the most part borne terminally on short growths

457

458 FUNDAMENTALS OF FRUIT PRODUCTION

springing from terminal buds on other short growths, or spurs. Indi-
vidual spurs are wont to bear only every other year, though annual
bearing spurs are not rare and are common in trees of certain varieties.
More frequently, however, individual spurs fail to produce even every
other year, bearing perhaps only once in 3 or 4 years, or very irregularly.
These spurs may live many years and there is nothing in their manner of
growth to necessitate a deterioration in efficiency as they grow older. In
reality, however, they flower and, more particularly, set and mature
fruit, much less regularly as they increase in age.^^ Without doubt this is
due to unfavorable nutritive conditions induced by crowding and compe-
tition with other parts of the tree for food, moisture and light. Records
show, nevertheless, that even very old spurs may bear good fruits and that
when strong and vigorous they are more efficient fruit producers than
those that are much younger but lacking in vigor. ^^ Roberts^" has
reported a marked correlation between the vigor of spurs, as measured
by the length of each year's growth and by the number and area of their
leaves and performance in flower-bud formation. Spurs of medium
length with relatively large leaf areas and consequently with the means
of accumulating reserves of elaborated foods are more likely to form
fruit-buds.

Heavy annual production, then, would seem among other things
to depend on (1) the formation of an adequate supply of fruit spurs,
(2) the retention of those already formed and (3) maintaining all of
them in a vigorous condition so that they may flower and fruit regularly.
These requirements plainly cannot be met or supplied by any single
pruning practice or by any combination of pruning practices. They
depend on many factors, chief among which are nutritive conditions
within the plant, which, in turn, are influenced most readily by ferti-
Uzers and various systems of soil management. Pruning, however,
is important in this connection.

The Formation of Fruit Spurs. — As pointed out elsewhere, maximum
fruit-spur formation is encouraged by leaving the trees unpruned or by
pruning them very lightly. Such treatment or lack of treatment leaves
the largest possible number of buds from which spm-s may develop;
consequently an approach to this treatment is recommended to induce
bearing in a short time. Formerly the artificial bending of long shoots
was quite generally recommended to make them more fruitful through
the formation of fruit spurs. However, recent investigation indicates
that this practice is of doubtful value and certainly is not to be recom-
mended under average field conditions. ^^ Experimental work at the
Oregon Station has shown that when certain shoots are selected for
removal in young apple trees, new fruit-spur formation is favored by
leaving those that are vigorous and comparatively upright. ^^ As the
trees become older and possess fruit spurs in numbers sufficient to pro-

PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 459

vide full crops less attention need be given to obtaining new spurs. Some
of the old spurs die out or are lost through accident and new spurs are
needed tore place them and of course the numbers increase as the tree
grows older. Usually, however, more spurs form than the tree can
support to advantage and it is only in the tree between 4 and 6 or 8 years
of age that there is need of definite effort to encourage their development.

Very rarely do new spurs form directly on the old wood from either
latent or adventitious buds. In case the spurs in the lower-interior part
of the tree die out or are destroyed the only way to develop new spurs in
that region is to prune back the top of the tree somewhat heavily. This
will force out watersprouts from latent or adventitious buds. At the
same time there should be enough thinning out to permit free access
of sunlight and thus promote the development of large leaves and large
lateral buds which a year later may develop into fruit spurs. These
watersprouts are then treated in very much the same way as the tops of
trees just coming into bearing; the same may be recommended for the
strong vigorous growth in trees recently "dehorned" or recently
top worked.

Retaining Spurs Already Established. — Since the spurs of the apple
and pear bear fruit repeatedly they should obviously be retained as
long as they remain efficient producers. Yet many growers remove
them unnecessarily at the time of pruning or permit their useless destruc-
tion by careless pickers. In some varieties particularly, as for example
the Esopus (Spitzenburg) apple, new spurs do not readily develop to
replace the old, because of the difficulty in obtaining sucker growth in
the interior of the tree; hence the loss of any considerable number of
spurs is likely to render those portions of the tree permanently barren.
There is often occasion for prmiing out some of the fruiting wood of the
apple and pear; however, this should be done with caution and with a
clear understanding of the problems involved in replacing it. The
advisability of much thinning of the crop by means of pruning is ques-
tionable in these fruits. The ultimate result of the loss of spurs from
the interior and lower portions of the tree is the forcing out and up of
its bearing surface. Eventually the active fruiting wood will be around
the outside and in the top of the tree with the major portion of the interior
unproductive. When a crop is so distributed, its weight places the
greatest possible strain upon the crotches and the tree is subject to
greatest injury from storms and winds. Much of the breakage in the
older orchards is associated with this condition, which can be largely
avoided by thinning out which limits the formation of new fruit spurs and
at the same time keeps the older spurs productive.

Keeping Spurs Strong and Vigorous. — The superiority of vigorous
fruit spurs over those that are weak has been mentioned repeatedly.
They flower and set fruit more frequently and are much more likely to

460 FUNDAMENTALS OF FRUIT PRODUCTION

bring their fruits to maturity. Indeed, some question may be raised
as to whether the very weak spurs, those that annually push out only
two or three small leaves and rarely or never form fruit buds, are of any
real benefit to the tree. They draw on the supply of moisture and
nutrients obtained from the soil and they can yield but little elaborated
food in return. Furthermore, observation indicates that forcing such
spurs into vigorous growth, once they become weakened, is extremely
difficult. Heavy pruning, alone or combined with certain cultural
treatments, may force them to grow out into new shoots and later these
shoots may give rise to fruit spurs; however, to reinvigorate them and
make them form fruit buds without an intervening shoot growth is
very difficult after they have ceased to function satisfactorily for several
years. Therefore keeping fruit spurs in a vigorous condition from the
start is doubly desirable.

The vigor and growth of individual spurs depends on (1) the supply
of moisture and nutrients from the roots and (2) the supply of elaborated
foods stored more or less locally. This locally stored supply in turn
depends largely on manufacture at or very near the point in question.
Both of these factors are influenced by many cultural practices. Pruning
may be a means of modifying, at least temporarily, the supply of moisture
and nutrients available for the spurs that are left, through diverting
to them large amounts before intake is correspondingly reduced. This
effect of pruning can be obtained more readily by fertilizing, tillage,
irrigation, mulching or other soil treatments. It may be pointed out,
however, that though the effects attending these other cultural opera-
tions and those attending pruning are quite similar, in the one instance
there is a general influence on the vegetative activities of the tree while
pruning has a more specific influence on certain of its parts or local
regions.

Pruning is a more important means of influencing the accumulation
of elaborated foods, through admitting more or less light to the spurs.
As has been pointed out, the general effect of heading back is to thicken
the top, cause more shading and thus probably decreased carbohydrate
manufacture in the lower and interior parts of the tree. On the other
hand thinning out tends to have the opposite effect. Since the removal
of spurs by thinning (either the removal of individual spurs or small
spur-bearing branches) has as great a concentrating effect on nutrients
as an equivalent heading back, it is to be regarded as the most important
pruning practice in this respect. Indeed it is about the only pruning
practice that always tends to increase longevity and regularity of bearing
in fruit spurs. Consequently the heading back that is done in bearing
apple and pear trees should be hmited to that required to keep the tree
from becoming too tall and too spreading for the mechanical support
of its crop and for convenience in various orchard operations. In

PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 461

other words heading back should be done principally for the purpose
of training, thinning out serving principally to affect its bearing habits.

Suminarij of Usual Pruning Treatment. — Briefly, the general pruning
treatment recommended for the apple and the pear, considering their
growing and bearing habits and their I'csponses to different types of prun-
ing, may be stated as follows: During the first few years in the orchard,
assuming at least a moderately strong growth, the tree should be pruned
rather severely (beginning with perhaps a 75 per cent pruning) and this
should consist in both thinning out and heading back, with the emphasis
perhaps on heading back. This heavy pruning is for the purpose of
properly developing the framework of the tree. If it has made a weak
growth, pruning should be correspondingly lighter. As the tree becomes
older, pruning gradually decreases in severity until at 6 or 7 years, when it
reaches bearing age and size, very little is done. As pruning slowly
lessens in severity it gradually changes in kind, consisting less in heading
back and more and more in thinning out. This general procedure devel-
ops a fruit-spur system and brings it into bearing. After the tree is once
in bearing, pruning slowly increases in amount but continues to be
mainly a thinning out; this thinning should comprise the removal of small
limbs throughout the top rather than the cutting of a few large limbs.
When this plan is followed there is some thinning of fruit spurs and of the
fruit crop, overbearing is prevented and the length of life, regularity of
bearing and efficiency of individual spurs are promoted.

Special Suggestions for Unusual Fruiting Habits. — Certain varieties
of the apple and the pear have been said to bear many fruit buds termi-
nall}' or laterally on long shoots. This is particularly common during
the period when they are just coming into bearing. Under these cir-
cumstances greater care must be exercised against the unnecessary removal
of any new shoots and heading back should be reduced to a minimum
until the trees have a better developed fruit spur-system and are bearing
a considerable percentage of their crop on it. The production of lateral
fruit buds on long shoots, it should be noted, presents a case quite similar
to that of the peach and consequently the pruning of such trees should
resemble that ordinarily given peach trees as much as it does that of the
average apple or pear variety. However, most of these lateral fruit buds
in the apple are borne on the terminal half or even third of the shoot,
while a considerable percentage of those of the peach are found on the
basal half. This necessitates much more care in heading back the fruit
bearing shoots in these particular varieties than is requisite in the peach.
Pruning the Peach. — The peach is perhaps the best known repre-
sentative of that group of fruits which "bear lateral fruit buds on long
growths or shoots. These buds contain flowers only and with their
falling, or with the maturing of the fruits which develop from them, that
portion of the branch to which they were attached becomes barren.

462 FUNDAMENTALS OF FRUIT PRODUCTION

Neither fruits nor flowers are again borne upon it. New growth develops
from the terminal bud or from lateral leaf buds at some of the non-flower-
ing nodes or in some instances from adventitious or latent buds lower in
the tree. It is therefore characteristic of the peach to have its fruiting
wood carried a foot or two further out and up each year, leaving long
stretches of non-fruiting wood that serves only as a connecting link
between the fruiting periphery of the tree and its root system.

Seldom does the peach tree of bearing age fail to differentiate enough
fruit buds for a heavy crop. In fact it commonly produces many more
than are desired, so that some pruning is advisable for the purpose of
thinning the crop. Furthermore, since the fruit buds are produced each
year on the new wood of the current season there is no danger of rendering
the tree unproductive for a period of several years, as in the apple or the
pear, by cutting away its fruiting wood. Therefore the two main prob-
lems in pruning this fruit are to thin the crop and to "keep the tree within
bounds," that is, to prevent its fruiting wood from developing so far away
from the trunk that propping, picking, spraying and fruit thinning involve
too much expense. Almost any kind of pruning serves the latter purpose
if it is severe enough; on the other hand the location of the new fruiting
wood and the distribution of its fruit buds depend very considerably on
the type of pruning that is employed. In fact it would not be far from
correct to say that in the bearing peach tree the severity of pruning
should be governed largely by the amount of crop thinning required and
its kind should be determined by the desired distribution of the following
season's fruiting branches and fruit buds.

When and How Severely. — The bearing peach tree should be pruned
lightly or heavily, depending on whether it gives promise of bearing just
enough or too much, if little or no pruning is done. As a rule prospects
cannot be estimated accurately until the trees are in bloom or even until
the fruit has set, on account of danger from late spring frosts. Conse-
quently it is wise to wait until that time and then to prune with the aim
of providing as nearly as possible a full crop but still of reducing the labor
of fruit thinning to a minimum. If crop prospects are ruined by a late
frost the trees can be dehorned advantageously, because this heavy
pruning will not result in any loss of fruit and since new growth for the
following season's production will be forced to develop from the main
scaffold limbs, the bearing surface will be lowered and made more com-
pact. If midwinter or late winter freezing destroys the fruit buds this
same type of pruning can be done earlier.

Pruning to Secure Most Favorable Location of Fruiting Surface. —
The usual method of pruning the bearing peach tree comprises such thin-
ning out as seems necessary, this thinning consisting generally in the
removal of wood from the center of the tree so as to provide an extreme
open center. In fact the average peach tree as found in the commercial

PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 463

orchard illustrates more nearly the vase or goblet shaped form than almost
any other species. This thinning out is then followed by as severe head-
ing back of the shoots as is compatible with leaving enough good fruit
buds — or flowers if the operation has been delayed until the blooming
season — to provide for a full crop. If the number and distribution of
buds is such that the heading back can be rather severe the new shoot
growth will be forced to come out rather low and the tree will be kept
relatively compact, though the fruiting wood of the following season will
be necessarily somewhat farther out from the trunk than that of the
current season.

One result of the heading back will be a crowding of the new shoot
growth; this will increase with the severity of the heading back. The
result is comparatively long slender shoots, from whose nodes the leaves
soon fall because they are shaded. Only leaf buds will be formed in
their axils; these will be small and quite likely to remain latent the
following year. Fruit buds are formed chiefly on the median or apical
portions of these crowding shoots or on their secondary lateral branches.
This necessitates a less severe heading back the following spring if fruit
buds sufficient in number for a good crop are to be left and the bearing
portion of the tree is pushed farther away from the trunk. Some shoots
will probably develop in the interior of the tree from latent or adven-
titious buds on the main limbs. These should be saved for renewal
purposes, though usually it is only a matter of time before a general
"dehorning" becomes necessary in order to lower the top and make
the tree sufficiently compact for economical production.

A practice seldom employed, but frequently desirable, is an early
summer thinning out of the new shoots. Ordinarily this should be done
in late June or early July, considerably before terminal bud formation
is under way. It reduces crowding and the remaining shoots are less
likely to become long because their internodes remain shorter. Their
leaves are better lighted and those at the basal nodes persist through the
season instead of falling prematurely. Consequently fruit buds form at
these basal nodes as well as at the median or distal. This makes it
possible to head back much more severely the following spring and still
leave provision for a full crop. The fruiting zone is not carried so
far from the trunk each year and dehorning is not so frequently necessary.
Furthermore, the fruit buds at the more basal nodes enter the dormant
period at a relatively less advanced stage of development than those
farther out on the shoots. This makes them somewhat more resistant
to winter cold and a httle slower in opening the following spring. The
practice also results in the development of many very short shoots that
amount almost to fruit spurs bearing lateral fruit buds — a fruiting habit
closely resembling that of the apricot or almond. This means in effect
a tree that mechanically is much stronger than the average. The summer

464 FUNDAMENTALS OF FRUIT PRODUCTION

pruning here suggested could easily be overdone. It should not remove
so much new growth that the developing fruit is subjected to danger
from sunscald or that the formation of secondary shoots is stimulated.
It should be well distributed through the top and outer portions of the
tree, as its effectiveness depends on making possible a better distribution
of sunlight to the leaves on the lower portions of the new shoots. If
carefully done it reduces greatly the amount of shoot thinning that will
be required the following spring and the yearly pruning treatment really
becomes a summer thinning out and a winter heading back. Inci-
dentally it is of considerable aid in promoting coloration of the fruit.

Pruning the Sweet Cherry. — Typical of that group of fruits whose
flower buds are borne laterally on short spurs and give rise to an inflores-
cence only is the sweet cherry. The terminal of the sweet cherry spur is
always a leaf bud by which the growth of the spur is continued each year.
New spurs originate from some of the lateral leaf buds on the shoots of the
preceding season and new shoot growth proceeds from other lateral buds,
from terminal buds on shoots, from latent or adventitious buds on the
older wood and occasionally from the terminal buds of spurs. However,
comparatively few shoots arise from buds of the last two classes in the
sweet cherry. The lateral buds on the year-old shoots of young vigor-
ously growing trees are little inclined to produce spurs, but either grow
out into new shoots or remain dormant. Consequently the young trees
of this species are thick brushy growers, strongly vegetative in character
and often slow in coming into bearing. Old trees of the same species
present a rather sharp contrast to this condition. Most of the lateral
buds on their shoots produce spurs or remain dormant. Often new shoot
growth is produced mainly from the terminal buds of the last year's
shoots, the result being a tree that is markedly reproductive and often
lacking in vigor.

As the problem in the young tree is first to secure a strong framework
and then a good equipment of fruit spurs, much as in the apple and
pear and as its shoots and spurs originate from buds in the same locations,
its pruning treatment the first few years should correspond closely to
that of those fruits. In other words pruning should be fairly heavy at
first, gradually decreasing in amount till at 6 or 7 years little is
done. At the same time it should change gradually from a treatment
which consists largely in heading back to one which consists almost
entirely in thinning out.

As the tree becomes older, however, its pruning treatment should div-
erge gradually from that customarily given the apple or pear. Its natural
tendency to produce large numbers of fruit spurs obviates the necessity
of employing any treatment to encourage greater spur and fruit bud
production. At the same time this growing habit results in a fairly
open top in which the foliage is well exposed to light. On the other

PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 465

hand measures should be taken to promote a greater vegetative growth,
particularly in those varieties or under those conditions that tend toward
the development of new shoots from terminal buds only. Otherwise
long pole-like fruiting branches, subject to much injury from the wind
when heavily loaded with fruit, will develop. Heading back to promote
branching, however, must be done with considerable care. If the
heading is into 2-year, 3-year, or older wood new side branches are not
likely to form and the limbs in question are subordinated to an unim-
portant position in the tree. Heading back to near the base of the one-
3^ear old shoots is much more likely to induce the branching desired,
though this alone is often rather ineffective in large trees somewhat
lacking in vigor. A certain amount of pruning back to 2-year, 3-year
or older laterals is often effective in keeping the tree within bounds.
There is little occasion to do much thinning out in the sweet cherry tree
that is well in bearing and the heading back is mainly for the purpose of
lowering the top and correcting form. Dehorning is seldom resorted to
because of the poor response in new shoot growth that often follows this
operation and because of the time required for the formation of a good
supply of new spurs before the tree can again come into heavy bearing.

Generally speaking, then, the pruning of the bearing sweet cherry
should be light in amount and for correcting and improving shape. On
account of the growing habit this means that it will consist largely in
heading back. Other orchard practices, such as cultivation, irrigation
and fertilization, should be counted on to encourage a strong new shoot
growth which can be headed back to promote branching and compactness
of tree.

Pruning the Almond, Apricot, Plum, and Sour Cherry. — As has been
stated in the classification of fruiting habits, the almond, apricot, plum
and sour cherry form a series intermediate in their habits of bearing
between the peach on the one hand and the sweet cherry on the other.
That is, all of these fruits bear fruit-buds laterallj^ on both long and short
growths. Some of them, as certain of the almonds and Japanese plums,
approach the peach more closely; others, as the Insititia plums, approach
the sweet cherry more closely. The age and vigor of the trees and the
cultural conditions under which they are grown influence the relative
distribution of fruit buds on spurs and on shoots. Roberts*^ states that
weak or moderately vigorous sour cherry trees bear a much larger per-
centage of their fruit buds on medium to short shoots than do the vigorous
trees of the same varieties. The reverse is likely to hold in certain varie-
ties of the Japanese plum.

Since the bearing habits of these fruits are intermediate between
those of the peach and of the sweet cherry, it follows that their pruning
treatments should likewise be intermediate between those given typical
bearing trees of those species. If the bearing habit is more like that

466 FUNDAMENTALS OF FRUIT PRODUCTION

of the peach the pruning treatment should be correspondingly severe;
if it is more like that of the sweet cherry it should be correspondingly light.
In kind, likewise, it should resemble that of the fruit whose bearing habit
it most closely resembles. Furthermore, with a change in the bearing
habit as the tree grows older or as its environment varies there should be a
corresponding change in the amount and kind of pruning.

In general with these fruits it is usually desirable to employ those
cultural and pruning practices that encourage the spur-bearing, rather
than the shoot-bearing, habit. The production of fruits on spurs means
compactness of trees, less danger from the breaking of limbs and lighter
and less expensive pruning. There is not the necessity of constant prun-
ing for "renewal" purposes. It has been found in the sour cherry at
least that spur-borne fruit buds are hardier than those borne on shoots. ^^
Pruning the Currant and Gooseberry. — The fruiting habits of the
currant and the gooseberry resemble that of the apricot more closely than
those. of any of the other tree fruits. Within certain limits their pruning
treatment should follow closely that found best suited to the apricot.
Since the currant and gooseberry are bush, rather than tree, fruits, they
have a marked tendency to throw out strong vigorous new shoots from
the crown or from the base of the old canes. The growth of this wood,
together with fruiting of the older wood, weakens the latter and a point
is soon reached where its retention is no longer profitable. Experience
has demonstrated that canes more than four years old should be removed
to make room for the younger and more vigorous growth. As a rule more
new shoots form each season than can be retained without undue crowd-
ing. Consequently they are thinned each spring to from 3 to 6 of the
strongest and best distributed; these are headed back to a height of
2 or 3 feet to keep the bush more compact. Thus, when the currant
or gooseberry plantation once becomes well established, its annual
pruning actually comprises a removal of the old canes that are becoming
weak and a thinning of the new shoots to make provision for the replacing
of the old wood that is discarded. Injured or diseased canes are of
course removed and some attention should be devoted to training.

Certain varieties or types that have growing or fruiting habits
different from those described as typical should receive a correspondingly
different pruning treatment. The wood of the black currant loses its
vigor and becomes relatively unproductive at an earlier age than that of
the red currant or the gooseberry. Consequently the old canes are
removed after they have fruited 1 or 2 years and a correspondingly larger
number of new shoots are retained each season for replacement purposes.

Both currants and gooseberries may be trained in either the bush or
the tree form. In America the bush form is preferable, both because
less labor is required in training and because it lends itself more readily
to an economical control of the currant borer.

PRUNING WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 467

Pruning the Brambles. — Most of the bramble fruits are perennials,
with biennial canes. The dying of the canes at the end of their fruiting
season the second year necessitates their removal. Experience demon-
strates that it is good practice to cut out and destroy the old canes
promptly after the fruiting season. Their retention until the following
fall or spring can serve no useful purpose and they prove a source for the
spread of diseases and insects to the new growth if they are allowed to
remain.

The early spring pruning of this group usually consists in some thin-
ning out of the cane growth that is to bear fruit during the following
summer and at the same time a heading back of the main canes or of their
laterals, or perhaps of both. This pruning is done almost exclusively for
the purpose of thinning the crop. If done properly it reduces the number
of fruit buds but results in little or no reduction in the total yield. Natur-
ally its severity varies greatly with variety and with the environmental
conditions. The moisture supply during the ripening season limits yield
in the bramble fruits probably more frequently than any other single
factor. Consequently the severity of the pruning should be influenced by
the prospect for available water during and just before harvesting.
Under conditions of ample rainfall or abundant irrigation water and of
relatively high atmospheric humidity this pruning may be much less
severe than when summer drought is likely. The bulk of this spring
pruning of dormant or nearly dormant canes should consist in heading
back rather than in thinning out. The laterals from the median and
more basal fruit buds generally produce larger clusters and their indi-
vidual berries are larger than those from the more apical buds. It is a
good plan to delay this pruning until the buds are swelling in the spring so
that the winter-injured ends of the canes may be removed without extra
labor.

The summer pinching of the bramble fruits has been discussed under
the heading of Pinching and need not be treated at this point.

Few or no data are available showing the best methods of pruning
certain types of the blackberry that have perennial canes. However,
observation indicates that they can be handled best by treating them as
ordinary varieties with biennial canes. That is, their canes are pruned
out as soon as they have fruited once, even though they would bear a
second crop were they allowed to remain.

The so-called everbearing or fall-bearing raspberries produce their
late summer crop terminally on the main shoot or on sub-terminal laterals
of shoots of the current season. The following main-season crop is
borne on laterals coming from lower parts of the same canes. They
should be winter pruned in the same way as related mid-season varieties.

Pruning the Grape. — More has been written about pruning and
training the grape than any other fruit. Many different systems or

4.68 FUNDAMENTALS OF FRUIT PRODUCTION

methods have been worked out and described in detail and an examina-
tion of any considerable part of this literature is as likely to be confusing
as it is enlightening. This is not because the several practices differ so
much in the principles involved, but because there is so great diversity in
the methods of their application that the principles themselves are
likely to remain hidden.

As pointed out in the classification of bearing habits, the grape pro-
duces its fruit buds laterally on shoots, which at the close of the growing
season and for a year thereafter are called canes. These fruit buds give
rise to flower-bearing or fruiting shoots on which the inflorescences appear
to be lateral. However, many shoots form few or no fruit buds, particu-
larly those springing from latent or adventitious buds on 2-year-old
or older wood — in Other words, those arising from the arms, head, trunk
or crown of the plant. Only those shoots (canes, when a year old) coming
from lateral buds on the canes of the preceding season are sure to form
fruit buds, though under some conditions those coming from the older
wood differentiate a limited number. Furthermore not all buds on shoots
springing from the preceding year's canes contain flower parts. Those
at the basal one to four or five nodes, depending largely on variety, seldom
do. Though it is difficult, and often impossible, to distinguish the fruit
buds from the leaf or wood buds by their external appearance, their
position on the plant offers a rather accurate index to their character
and the grower or student, once he becomes well acquainted with the
characteristics of the individual variety, will have little difficulty in telling
which are of the one kind and which of the other.

Severity of Pruning. — Practically all grape vines differentiate each
year more fruit buds than can grow into fruiting shoots and set and mature
grapes the following season. It is therefore unnecessary in pruning the
grape to give thought to securing larger numbers of fruit buds. The real
problem is that of reducing to just the right number those that are already
formed and normally would or could produce fruiting shoots the following
season. Furthermore, this must be done in such a way that the fruit
will be well distributed and that the new shoots on which fruit buds for a
succeeding crop are differentiated will be so located as to preserve the
compactness and established form of the vine.

The reduction of fruit buds to just the right number is often difficult
and always requires an accurate knowledge of fruit-bud location in the
particular variety and good judgment as to how much fruit the vine
should bear. Overpruning reduces the crop and diverts the energies of
the plant into excessive wood growth. This is well illustrated by the
work of Maney^"* in Iowa. Underpruning permits the plant to overbear,
resulting in too many clusters, undersized berries of inferior quality and a
weakening of the vine itself so that succeeding crops will be reduced in
size and the life of the plant shortened. These statements, of course,

PRUNINd WITH SPECIAL REFERENCE TO PARTICULAR FRUITS 469

apply to the priming of many other fruit phmts, but not to the same
extent that they do to the grape. In practice perhaps the best way of
determining the severity of pruning is, following a suggestion of Hed-
rick,2^ to figure the problem for each vine on a mathematical basis. He
says in reference to varieties of the Labrusca and Labrusca-hybrid types:
"A thrifty grape-vine should yield, let us say, 15 pounds of grapes, a
fair average for the mainstay varieties. Each bunch will weigh from
a quarter to a half pound. To produce 15 pounds on a vine, therefore,
will require from 30 to GO ])unches. As each shoot will bear two or three
bunches, from 15 to 30 buds must be left on the canes of the preceding
year. . . . Pruning, then, consists in calculating the number of bunches
and buds necessary and removing the remainder." As some of the fruit-
ing shoots may be broken off incident to the work of cultivation, spraying
or other vineyard operations, it may be well to leave a few extra fruit
buds; this matter, however, can be overdone easily.

Special mention should be made of the variation in the relative
amounts of pruning to be given vines of any given variety, not only with
their age and the conditions of soil moisture and fertility but, in grafted
vines, with the stocks on which they are grown. Certain stocks have the
reputation of producing shy-bearing vines, though actually they are
unproductive only when pruned too closely.

Another point already mentioned is the provision that should be made
for the production of properly placed new shoots on which fruit buds for
the following crop can form. In practice this "proper distribution"
generally involves their location as near the head of the vine as possible,
so that the fruiting wood is not pushed out unnecessarily each season;
thus the plant is kept compact. In many varieties this is secured by
retaining the lowest or basal cane (fruiting shoot of the preceding season)
on each arm or spur and pruning away those originating farther from the
head. In certain other varieties, however, the fruiting shoots develop
only from buds at nodes some distance from the base of the canes and the
more basal buds remain dormant when the heading back is light enough
to permit the development of fruiting shoots. Pruning varieties with
such growing and fruiting habits in the way just described would quickly
carry the bearing surface of the vine far from its head and necessitate
frequent resort to pi-uning like that called dehorning in tree fruits. The
usual method of handling vines of this type is each year to prune lightly
or moderately certain canes for fruit production, leaving them with the
requisite number of fruit buds and to prune severely other canes so that
all their fruit buds are removed and they are forced to develop vegetative
shoots from their basal buds. These vegetative shoots then become the
fruiting canes of the following year, while those that have borne fruit
are entirely removed. These much shortened canes are spoken of as
"renewal spurs."

470 FUNDAMENTALS OF FRUIT PRODUCTION

Kind of Pruning. — Pruning the grape, like the pruning of most other
fruits, includes some thinning out and some heading back. The relative
amounts of these two types desirable in any given case depend largely on
the style of training employed. Invariably all the past season's shoots
are removed except those retained for their fruit buds or for "renewal"
or "replacement." This is a thinning out process. If the style of train-
ing calls for pruning to spurs, more of last season's shoots must be
retained ; consequently there can be less thinning out than if the vines are
pruned to canes. As the pruning should leave a fairly definite number of
fruit buds, the amount of heading back of the canes left after thinning
varies inversely with their number. Thus there is much less severe
heading with a two-wire Kniffin system of training than with pruning
back to spurs. Little need be said at this point regarding the summer
pruning of the grape, as the more important features are discussed in
Chap. XXIV.

Methods of Training. — As already indicated, there is almost endless
variety in methods of training the vine. A description of each, even of
those that are fairly distinct, would require many pages and probably
would be of little real use. The fundamental objects of all these methods
differ little from those governing the training of other fruit-producing
species. Training should increase yields, improve grades or quality and
reduce production costs through facilitating other vineyard operations.
In this fruit the usual training methods, at least those employed in
America, have little influence on total yields. ^^ They do, however, affect
quality and production costs. No one method of training is necessary
for the production of fruit of the highest grade or quality. Thus in New
York, vines of the Concord have been found to mature their fruit better
when trained to the umbrella Kniffin system than when trained in any of
the other ways standard in that state. ^^ Husmann and Bearing^" report
that in Muscadine grapes the upright system permits the fruit to ripen
more evenly than does the overhead system. Only after a careful study
of the growing and fruiting characteristics of the different varieties in
various sections and soils and on different stocks can the best system
of training be selected and the best system for one variety may not be best
for another in the same vineyard.

In general those systems of training in which the new shoots are
allowed to droop are much less costly than those in which they are tied
in horizontal or vertical positions; consequently it is only under special
conditions that these latter methods of training are to be recommended.
Along the northern limits of outdoor grape culture some of the low renewal
systems of training greatly facilitate the work incident to artificial
winter protection and are quite generally employed. Those varieties
whose canes bear fruit buds almost to the very base, are naturally better
suited to Spur renewal than those whose canes habitually form only

PRUNING 471

wood buds in the same regions. With these latter cane renewal or a
combination of long and short spur renewal is more practicable. Only
those varieties (particularly of the Vinifera group) with comparatively
stocky and rigid trunks that require no artificial supports can be trained
to the tree form advantageously. Other varieties require trellising.

Suggested Collateral Readings

Howe, G. H. The Effect of Various Dressings on Pruning Wounds of Fruit Trees.

N. Y. Agr. Exp. Sta. Bui. 396. 1915.
Roberts, R. H. Prune the Cherry Trees. Wis. Agr. Exp. Sta. Bui. 298. 1919.
Tufts, W. P. Pruning Young Deciduous Fruit Trees. Cal. Agr. Exp. Sta. Bui. 313.

1919.
Alderman, W. H., and Auchter, C. E. The Apple as Affected by Varying Degrees of

Dormant and Seasonal Pruning. W. Va. Agr. Exp. Sta. Bui. 158. 1916.
Gardner, V. R., Magness, J. R., and Yeager, A. F. Pruning Investigations. Ore.

Agr. Exp. Sta. Bui. 139. 1916.
Magness, J. R., Edminster, A. F., and Gardner, V. R. Pruning Investigations.

Ore. Agr. Exp. Sta. Bui. 146. 1917.
Bioletti, F. T. Vine Pruning in California. Cal. Agr. Exp. Sta. Bui. 241. Part 1.

(No date.)
Drinkard, A. W. Fruit Bud Formation and Development. Ann. Rept. Va. Agr.

Exp. Sta. Pp. 159-205. 1909-10.
Sorauer, P. A Popular Treatise on the Physiology of Plants. Transl. by F. E.

Weiss. Pp. 134-168. London, 1895.
Bioletti, F. T. Vine Pruning in California. Cal. Agr. Exp. Sta. Bui. 246. Part 2.

1914.

Literature Cited

1. Alderman, W. H., and Auchter, E. C. \Y. Va. Agr. Exp. Sta. Bui. 158. 1916.

2. Barry, P. The Fruit Garden. Pp. 94-95. Detroit, 1853.

3. Batchelor, L. D., and Goodspeed, W. E. Utah Agr. Exp. Sta. Bui. 140. 1915.

4. Bedford, H. A. R., and Pickering, S. U. Science and Fruit Growing. Pp. 57-80.

London, 1919.

5. Ibid. P. 46.

6. Bioletti, F. T. Cal. Agr. Exp. Sta. Bui. 241. 1913.

7. Blake, M. A., and Connors, C. H. N. J. Agr. Exp. Sta. Bui. 326. 1917.

8. Brierley, W. G. Proc. Am. Soc. Hort. Sci. 16: 102-104. 1919.

9. Card, F. W. Bush Fruits. Pp. 48-51; 70-73. New York, 1917.

10. Chandler, W. H. Mo. Agr. Exp. Sta. Res. Bui. 14. 1914.

11. Chandler, W. H. Proc. Am. Soc. Hort. Sci. 16: 88-101. 1919.

12. Childs, L. Ore. Agr. Exp. Sta. Bui. 171. 1920.

13. Cole, S. W. The American Fruit Book. P. 57. Boston, 1850.

14. Curtis, O. F. Am. J. Bot. 7: 101-124. 1920.

15. Daniel, L. Compt. rend. 131:1253-1255. 1900.

16. Daniel, L. Trav. scient. Univ. de Rennes. 6 (2) : 22-72. 1907.

17. Do\Aaiing, A. J. The Fruits and Fruit Trees of America. P. 31. New York,

1856.

18. Drinkard, A. W. Va. Agr. Exp. Sta. Ann. Rept. Pp. 96-120. 1913-1194.

19. Drinkard, A. W. Va. Agr. Exp. Sta. Tech. Bui. 17. 1917.

472 FUNDAMENTALS OF FRUIT PRODUCTION

20. Edminster, A. F. Ore. Agr. Exp. Sta. Bui. 146. 1917.

21. Gardner, V. R., et al. Ore. Agr. Exp. Sta. Bui. 139. 1916.

22. Gardner, V. R. Ore. Agr. Exp. Sta. Bui. 146. 1917.

23. Gaucher, N. Handb. der Obstkultur. Pp. 602-644. Berlin, 1902.

24. Gladwin, F. E. N. Y. Agr. Exp. Sta. Bui. 464. 1919.

25. Goumy, E. Thesis Presented to the Faculty of Science of the University of Paris.

1905.

26. Hedrick, U. P. Manual of American Grape Growing. P. 114. New York,

1919.

27. Hovey, C. M. Hovey's Mag. of Hort. 15: 301. 1849.

28. Howe, G. H. N. Y. Agr. Exp. Sta. Bui. 391. 1914.

29. Husmann, G. C. U. S. D. A. Bui. 856. 1920.

30. Husmann, G. C., and Bearing, C. U. S. D. A., Bur. Pi. Ind. Bui. 273. 1913.

31. Macoun, W. T. Can. Dept. Agr. Bui. 56. 1907.

32. Magness, J. R. Ore. Agr. Exp. Sta. Bid. 139. 1916.

33. Magness, J. R. et al. Ore. Agr. Exp. Sta. Bui. 146. 1917.

34. Maney, T. J. la. Agr. Exp. Sta. Bui. 160. 1915.

35. Paddock, W. N. Y. Agr. Exp. Sta. Bui. 151. 1898.

36. Paddock, W., and Whipple, O. B. Fruit Growing in Arid Regions. P. 112.

New York, 1910.

37. Pearson, A. H. J. Roy. Hort. Soc. 29: 274. 1896.

38. Quinn, P. T. Pear Culture for Profit. P. 72. New York, 1889.

39. Quintinye, J. de la. Instructions pour les jardins fruitiers et potagers. 2: 579.

Paris, 1746.

40. Ravaz, L. Taille hative ou taille tardive. 1912. (Cited by Bioletti, F. T.,

Cal. Agr. Exp. Sta. Bui. 241. 1913.)

41. Rivers, T. The Miniature Fruit Garden. P. 8. New York, 1866.

42. Ibid. Pp. 12, 82.

43. Roberts, R. H. Wis. Agr. Exp. Sta. Bui. 298. 1919.

44. Roberts, R. H. Wis. Agr. Exp. Sta. Bui. 317. 1920.

45. Taft, L. R., and Lyon, T. T. Mich. Agr. Exp. Sta. Bui. 169. 1899.

46. Thomas, J. J. American Fruit Culturist. P. 82. New York, 1867.

47. Tufts, W. P. Cal. Agr. Exp. Sta. Bui. 313. 1919.

48. Vidal, J. L. Rev. de Viticulture. 1:895-903. 1894.

49. Vincent, C. C. Ida. Agr. Exp. Sta. Bui. 98. 1917.

50. Volck, W. H. Mo. Bui. Cal. St. Com. Hort. 6: 80-89. 1917.

51. Waugh, F. A. The American Apple Orchard. P. 90. New York, 1912.

52. Yeager, A. F. Ore. Agr. Exp. Sta. Bui. 139. 1916.

SECTION V
FRUIT SETTING

It is customary to speak of the reproductive activities of the plant
as distinct from its vegetative activities. That use of terms is accepted
and followed here, though it is not always an easy matter to define the
two. The woody tissues of the shoot and spur may by common consent
be considered vegetative in character. Likewise, it is generally agreed
that the ovarian tissues of the fruit may be classed as reproductive,
being more intimately associated with reproduction than with vegetative
growth. On the other hand, there might easily be some difference in
opinion regarding the tissues composing the peduncle or central axis of the
inflorescence. In many plants these structures differ but little from
other stem structures and they are vegetative in character. On the
other hand, when these tissues become fleshy and form an integral part
of the developing fruit, as they do in the pineapple, fig and many other
fruits, they would as naturally be considered along with the ovarian
tissues with which they are so closely associated. Mention is made of
these points to emphasize the fact that the problem of fruit setting is not
necessarily limited to a consideration of strictly reproductive tissues
and reproductive activities. Indeed, the formation of an abscission layer
at the base of the ovary, the pedicel or the peduncle is a function of the
sporophytic tissue at that point. Consequently it is subject to the same
influences, though perhaps not to the same extent or in exactly the same
way, as abscission layers developed in other places. However, fruit
setting and fruit formation depend on the initiation and successful
completion of at least some of the reproductory processes. Therefore,
the more important of the processes more or less directly concerned with
the setting of fruit are outlined briefly.

In the great majority of higher plants, fruit and seed formation are
conditioned on the bringing together and fusion of two specialized cells
known as gametes. The larger of these cells is called the egg and is
borne in the embryo sac. The smaller gametes are formed by a divi-
sion of the generative nucleus of the pollen grain. The flower is the
special organ of the plant for the production of these gametes. More
specifically the stamen or microsporangium is the organ for the pro-
duction of the male gametes and the ovule or macrosporangium the
organ for the production of the female gametes. The great diversity

473

474

FUNDAMENTALS OF FRUIT PRODUCTION

in the size, form, color and odor of flowers docs not modify the funda-
mental processes which take place, following pollination, in the growth of
the pollen tube or in fertilization. In this discussion, therefore, but
little attention need be given to the structure of the so-called non-
essential flower organs.

r^^

Plate I.— Successive stages in the development of the ovule of the orange. In Figure
1, mm = macrospore, u = inner integument, and oi = outer integument. Figs. 2 and 3,
later stages in which the integument more nearly encloses the nucellus. Fig. 4, the fully
developed embryo sac, showing the egg apparatus at the upper end, the polar bodies near
the center, the antipodals at the bottom. Fig. 5, the embryo sac after fertilization, one
of the synergids (pO disintegrating, the egg cell at oo, and 8 endosperm nuclei (e7i)- {After

CHAPTER XXVI

THE STRUCTURES AND PROCESSES CONCERNED IN FRUIT
FORMATION

The entire flower may be regarded as a specialized branch, consisting
of a central axis to which are attached several whorls or sets of organs
that bear a certain resemblance to leaves. The two outer or lower
whorls, the calyx and corolla, take no direct part in reproduction and
are spoken of as non-essential organs, though after fertilization the
calyx may undergo considerable differentiation and form a considerable
part of the mature fruit. As stated before, the stamens bear the male
gametes. In the higher plants, exclusive of the gymnosperms, the female
gametes are developed inside an enclosed structure, the ovary. This
last may consist of a single carpel (or modified leaf, to follow the concep-
tion of one school of botanists) or of several that are more or less com-
pletely united. In the latter case the ovary and the fruit which develops
from it, may be several-loculed. That portion of the central axis of the
flower to which the several sets of floral organs are attached is the recep-
tacle or torus.

A fruit may be defined as a ripened ovary together with whatever
may be intimately attached to it at maturity. If it consists of a ripened
ovary only, as in the peach or tomato, it is a simple fruit; if it includes
additional structures it is spoken of as an accessory fruit. Sometimes
the accessory structure may be the torus, as in the apple; sometimes
the torus and the calyx, as in the cranberry and sometimes a part of
the peduncle or pedicel, as in some varieties of the pear. The developing
ovaries of certain fruits grow together and give rise (1) to aggregate
fruits, if they all belonged to the same flower, as in the raspberry, or
(2) to multiple fruits if they belonged to different flowers, as in the
mulberry. In the latter the mature fruit includes ovarian, toral and
stem tissues. Not infrequently the ovarian tissues constitute only a
small part of the mature fruit and as a rule it is the accessory tissues
(when they are present) in which the pomologist is mainly interested,
for they are likely to constitute most of its edible portion. However,
it is the ovary with its enclosed ovules on which fruit formation
depends; consequently a discussion of fruit setting and fruit formation
must start with the ovary and its ovules.

The Ovule. — The ovule arises as a protuberance from the inner wall
of the ovary. The particular points, lines or surfaces from which it

475

476

FUNDAMENTALS OF FRUIT PRODUCTION

/^.^

Plate II. — Successive stages in the development of tlie pollen grain of the grape.
Fig. 1, section of anther showing epidermal, middle, tapetal and mother-cell layers. Figs.
2 and 3, later stages in these same layers. Fig. 4, a pollen-mother-cell. Fig. 5, the tetrad
stage in the pollen-mother-cell. Fig. 6, a microspore or pollen grain, before its liberation
from the pollen-mother-cell. Fig. 7, a pollen grain of the Concord grape. Fig. 8, the genera-
tive cell in a mature pollen grain. Figs. 9-12, various stages in the development of the
generative and vegetative nuclei, but in each instance one or both nuclei are undergoing
degeneration. Fig. 13, the normal generative cell and vegetative nucleus of a pollen grain.
(After Dorsey.^^)

FRUIT FORMATION 477

springs are known as the placentae. Successive stages in the develop-
ment of a typical ovule are shown in Figs. 1 to 3 of Plate I. The ovules
of different species vary greatly in size, shape and degree of development
and differentiation. However, practically all differentiate into a central
portion and one or two enveloping layers. The central portion is known
as the nucellus, the enveloping layers as the outer and inner integuments.
These several structures are clearly shown in Figs. 2 and 3 of Plate I.
The integuments never completely enclose the nucellus but leave an
opening of varying size, the micropyle, through which the pollen tube
usually passes to effect fertilization. The stalk or filament by which the
ovule is attached to the ovarian wall is known as the funicle. Through
it the ovule and later the developing seed receives its supply of food
material. In many species the funicle is fused with the outer integument
for a short distance, giving rise to a ridge known as the raphe. The
point where the nucellar and integumental tissues are continuous and
grown together is the chalaza.

The Embryo Sac. — At an early stage in the development of the
nucellus, one of its cells, the macrospore, becomes differentiated from
the others. This cell enlarges and divides first into two and then into
four cells forming the axial row. The first division of the macrospore
mother cell is the reduction division, which means that the number
of chromosomes in the nucleus of each of these four cells is half of the
number in the mother cell from which they were derived. Ordinarily
only one of these four cells develops and this becomes the embryo sac,
shown in Fig. 3 of Plate I. Its nucleus divides into two, then four and
finally eight, presenting the condition shown in Fig. 4 of Plate I. At this
stage the protoplasm of the embryo sac is highly vacuolated. At one
end, three of the nuclei are visible, constituting the egg apparatus. Only
one is capable of being fertilized. The other two are called synergids;
their exact function is not known. At the opposite end of the embryo sac
are three nuclei called antipodals which are separated at an early stage
from the rest of the sac contents by the formation of cell walls. These
cells do not take any direct part in the process of fertihzation and they
do not influence the development of the fruit so far as known. Sooner
or later they, like the synergids, disintegrate. Near the center of the
embryo sac are the other two nuclei called polar bodies because each has
come from the group of nuclei at the extreme ends or poles of the embryo
sac. These nuclei fuse and divide rapidly, forming the endosperm; in
many instances one of the male gametes unites with the fusion nucleus
bringing about double fertilization.

Pollen. — Stamens originate as small protuberances at their points
of insertion on the axis of the flower. At first these projections consist
of homogeneous tissue, but differentiation soon occurs and it becomes
possible to recognize filament and anther. The anther increases in

478 FUNDAMENTALS OF FRUIT PRODUCTION

size more rapidly than the filament and gives rise to a structm^e that is
generally grooved longitudinally on the outside and four-loculed in
cross section. Figures 1 to 8 of Plate II show successive stages in the
development of the male reproductive cell, or pollen grain, from the
tissues of the anther in the grape. At a comparatively early stage there
is a differentiation between the cells of its outer layers and those in the
interior. This differentiation has progressed rather far in the section
shown in Fig. 1, Plate II, the epidermal, middle, tapetal and mother-
cell layers being clearly distinguishable. Eventually the epidermal
and sub-epidermal layers undergo a series of changes which lead to
their separation from the sporogenous tissue within and to their assuming
the role of a simple protective shell or covering. Some idea of these
changes is afforded by Figs. 2 and 3 of Plate II. Figure 4 of Plate II
shows a single large pollen-mother-cell just previous to the reduction
division, which gives rise to four daughter cells, each of which is sur-
rounded by a membrane or cell wall. This is the so-called tetrad stage,
shown in Fig. 5, Plate II, though only three of the four microspores are
shown in the plane in which that figure was drawn. Shortly after the
formation of these tetrads the mother-cell wall breaks down and liberates
the microspores. Figure 6 of Plate II shows one of the microspores of the
Brighton grape just previous to its liberation and Fig. 7 of Plate II shows
one of the Concord variety a short time after its liberation. Its thick
wall, large nucleus and vacuole are prominent. Usually some time
before, though sometimes after, the dehiscence of the anther and the
dispersal of the pollen there are further changes within the pollen grain.
The nucleus divides giving rise to two daughter nuclei. One is called the
generative nucleus, because it alone gives rise to the gametes. This
generative nucleus becomes surrounded by a cell wall and is then called
the generative cell of the pollen grain. The other is called the vegetative
nucleus, because its function is more closely associated with germination
and because it functions as the nucleus of the pollen tube. Figures 9
and 12 of Plate II show two stages in the development of these two nuclei,
though both cases are somewhat abnormal because they show the initial
stages of a degeneration that leads to impotency. Figure 14 of Plate II
shows the generative cell and vegetative nucleus of a mature pollen grain
of the Concord grape before dehiscence.

Pollination. — In the ordinary course of events the maturing of the
ovules and of the pollen grains is followed by a transfer of pollen from
stamen to stigma. If the transfer is from stamen to stigma of the same
flower or to the stigma of another flower on the same plant, or, in the
case of pomological varieties, to the stigma of a flower on any plant of
the same variety, the process is self pollination. If the transfer is to
the flower of another individual, or, in the case of pomological varieties,
to the flower of another variety, the process in cross pollination. When

FRUIT FORMATION

479

Plate III. — Fig. 1, an early stage in the development of the normal orange embryo,
showing the so-called suspensor. Figs. 2-4. stages in the development of the ovule of the
orange showing various degenerative changes which result in embryo abortion; should the
fruit mature it would be seedless. {After Osawa.^"")

480 FUNDAMENTALS OF FRUIT PRODUCTION

self pollination is effected without the aid of any outside agency, such
as wind or insects, the process is known as autogamy. Many of the
peculiarities of form, structure, color and odor of flowers are closely
associated with means for securing proper self or cross pollination.
Some of the factors which are of importance in aiding or preventing
pollination are discussed later.

Germination of the Pollen Grain. — Pollination is usually followed
promptly by the germination of the pollen grain. This is brought
about by the absorption of water and various substances in the stigmatie
fluid. The grain swells and a tube is pushed out through one of the
pores in the outer covering or extine. The tube is formed by the intine
or inner covering which pushes out through the germ pore. As it elongates
it penetrates the tissues of the style by growing between the cells and as it
advances toward the ovarian cavity its rate of growth may increase. The
styles of the flowers of many species contain rows of cells that may be
looked upon as specialized conducting tissue for the purpose of guiding and
facilitating the growth of the pollen tubes. In other species there is
no evidence of such tissue. For the most part pollen tubes digest their
way as they go, by the secretion of a pectin-digesting enzyme. This
dissolves the middle lamella which is composed of pectin-like substances
that hold adjoining cells together and thus permits the insertion of the
pollen tube between them.^"^ Green^^ has shown that the pollen
of many kinds of plants contains diastase and some kinds were found to
contain invertase as well ; during the process of germination these enzymes
increase in amount. Presumably they are effective in rendering available,
for the nutrition of the pollen tube, food materials stored in either pollen
grain or style. This assumption is supported by work which showed that
pollination produces a rapid rise of respiratory activity in the gynaeceum. ^*^

In Pelargonium zonale the amount of carbon dioxide produced by
the pollinated flowers is 5.8 times greater than that produced by the
unpollinated flowers, though most other cases studied were somewhat
less extreme. It was also found that in every case pollination resulted
in some change in the respiratory coefficient — the ratio of oxygen taken
in to the carbon dioxide given off.

Course of the Pollen Tube. — For the most part, the growth of the pollen
tube is- directed by chemotropic influences supplied by the tissues of
the ovary, the ovules and by the style and stigma. Miyoshi^* sowed
pollen grains on agar in which were imbedded pieces of stigma, ovary
and ovules of different degrees of development. The pollen tubes grew
toward the pieces from the vicinity of the stigma, but they were attracted
most strongly by ovules ready for fertilization, growing into the micropyle
in each instance. In other investigations pieces of stigmatie tissue were
observed to influence the direction of pollen tube growth at distances
up to 70 times the diameter of the poUen grain. ^*^ Pollen tubes are

FRUIT FORMATION 481

especially sensitive to sugar solutions, growing toward them readily.
They tend to grow away from dry air and "show a preference for spaces
saturated with aqueous vapour to such as are less humid. "^^ Investi-
gations of the mode of growth of the pollen tube in Houstonia led to the
conclusion that the tissues of the style influence its direction only in a
passive manner but that "a chemotactic stimulus originating in the
egg-apparatus, or the egg itself, is the chief directive influence, "^^
Dorsey, however, has found tubes growing in plum styles with aborted
ovules; therefore it is possible that growth often depends less on a
normal egg-apparatus than the work with Houstonia would indicate.
Dorsey found also that in the apple the pollen tube may grow beyond
the ovule and down into the stem. Kerner and Oliver^^ state that
ovules ready for fertilization "attract not onlj^ pollen-tubes from pollen
of the same species, but of others far removed from it in point of affinity.
The delicate hyphae of several mould-fungi are similarly attracted."

Time for Pollen Tube Growth. — Ordinarily germination of the pollen
grain occurs promptly after pollination, the pollen tube grows fairly
rapidly and fertilization occurs within a period of 1 or 2 days, though
the time may be expected to vary with temperature and other environ-
mental factors. Under favorable conditions there is an interval of from
9 to 120 hours between pollination and fertilization in apples, plums
and cherries."'*'**^ The very much slower growth of Rome pollen tubes in
Rome styles as compared with that of the tubes of other apple varieties
found by one investigator^^ is interesting and may offer an explanation of
some cases of self sterility. A period of from 26 to 41 hours has been re-
ported in the case of certain cucurbitaceous plants, ^^ 4 days in one of the
species of Gastrodia,^"^ one month in Betula, ^ several months in H amamelis^^^
and approximately a year in certain of the oaks.-^ That there may be
a great variation in this respect between closely related plants is evident
from the behavior of the Satsuma orange in which about 30 hours have
been found to elapse • between pollination and fertilization,^^ while a
corresponding period of 4 weeks has been reported in Citrus trifoliata.^°°

Fertilization. — In Fig. 13 of Plate II are shown the vegetative
nucleus and the generative cell of the mature pollen grain. During the
growth of the pollen tube the nucleus of the generative cell divides, giving
rise to two male gametes, each consisting of a nucleus and a small portion
of stainable material. The pollen tube, after entering the micropyle,
penetrates the intervening tissue of the nucellus and then enters the
embryo sac. The following account of fertilization is adapted from
Mottier's^^ description of the process: The end of the tube may enter
the sac at one side of the synergids, in which case only one of these cells
is at once disorganized, the other retaining its normal structure for some
time. This condition is illustrated in Fig. 5, Plate I. Often it enters
between the two synergids, in which case both cells disintegrate almost

482 FUNDAMENTALS OF FRUIT PRODUCTION

immediately, ''As soon as the end of the pollen tube enters the embryo-
sac it opens, discharging the two male gametes and other contents. One
of the male nuclei enters the egg-cell and applies itself to the nucleus of
the egg, while the other passes into the cavity of the sac. ... It is pre-
sumably the first male nucleus which escapes from the pollen tube that
unites with the nucleus of the egg, but positive proof on this point is
wanting. ... As fusion progresses, the nuclei become quite alike in
shape, size and structure. Their membranes gradually disappear at the
place of contact, their cavities become one, and the resulting fusion
nucleus, which is in the resting condition, can scarcely be distinguished
from the nucleus of an unfecundated egg. The nucleoli finally unite
also." The fertilized egg cell becomes the embryo cell, the antecedent
of the embryo.

Secondary Fertilization. — Attention has been called to the presence
of two nuclei, the so-called polar nuclei, near the center of the mature
embryo sac. These are shown clearly in Fig. 4 of Plate I. Usually these
two fuse with the second sperm nucleus and the nucleus resulting from
this triple fusion divides repeatedly giving rise to many daughter nuclei,
shown in Fig. 5 of Plate I. Soon these daughter nuclei are separated by
the formation of cell walls, the resulting tissue being the antecedent of the
seed endosperm.

Sometimes the second sperm nucleus fuses with but one of the polar
nuclei^^^ and sometimes it degenerates in the cytoplasm of the embryo
sac. In the former case, the endosperm is of the same parentage as the
embryo beside which it develops; in the latter case it is built from
maternal tissue alone. In plants with albuminous seeds, this results in
the condition known as xenia.

Development of the Embryo and Endosperm. — Following the process
of fertilization the embryo cell "divides by a transverse wall into two
cells, one directed towards the micropyle, the other towards the base of
the embryo sac. The upper of these two cells stretches, and is repeatedly
segmented; thus a string of cells is formed, known as the suspensor, bear-
ing at its lower extremity the embryo-cell, which gives rise to the greater
portion of the young plant. "^'^ This stage is shown in Fig. 1, Plate III.

Coordinate with the development of the embryo is that of the
endosperm. To be exact, in most developing seeds the growth of the endo-
sperm is at first more rapid than that of the embryo. In many exal-
buminous seeds there is a period of very rapid growth of the endosperm
during which the young embryo either grows very slowly or persists in
a practically resting stage. This is followed by a period of rapid embryo
development, which occurs largely at the expense of the materials accu-
mulated in the endosperm. The initiation of this period of rapid growth
in the slow growing or resting embryos is apparently one of the "sticking
points" in the process of seed formation and in many species it is very

FRUIT FORMATION 483

important in determining whether or not the fruit shall matm-e or fall
prematurely.

In the developing seeds of most species the tissues of the nucellus
disintegrate and their substance is used by the growing endosperm or
embryo. In some species, however, the nucellar tissues persist and develop
into a storage tissue that can hardly be distinguished from endosperm.
Storage tissue of such origin is known as pcrisperm.

THE SETTING OF THE FRUIT

The fertilization process and the following segmentation and growth of
the embryo and endosperm within the ovule are accompanied b}^ changes
in the surrounding ovary wall and often in the torus and other adjoining
tissues. Most noticeable among these changes is a thickening and an
increase in size, perhaps with some change in color, shape and position,
so that it is evident very soon after blossoming that the fruit has or has
not "set," or that there is or is not a possibihty of its maturing properly
in due time.

However, some blossoms do not set fruit and sometimes the percentage
that sets is extremely small. Nothing is of greater importance to the
fruit grower than having a reasonable percentage of the blossoms set.
Yield, income and profits are all absolutely dependent on what the tree
does in this respect at and just after the time of blossoming. Of course
accidents or unfavorable conditions later in the season may injure or
destroy the crop, but they are contingencies with which the grower has
greater confidence in dealing than the accidents that may befall at the
time of fruit setting.

The term "fruit setting" is used here to refer to the initial and appreciable
swelling of the ovary occurring shortly after the period of petal fall. It is gener-
ally accompanied by some thickening of the pedicel or of the peduncle. Meanwhile,
flowers that have not " set " are turning yellow or withering and faUing off. After
this stage is passed accidents may happen and the "June drop" or some other
"drop" or some environmental factor may cause abscission; nevertheless, at
least for the time being, it appears as though fertilization had taken place and
the chances are good for the fruit maturing.

What Constitutes a Normal Set of Fruit. — It is not to be expected that
all the blossoms will set fruit, even though conditions are ideal. In most
species and varieties they are produced in such profusion that a total set
would be little short of calamitous for the grower. He is more interested
in obtaining a reasonable number of specimens of good marketable size
than a much larger number of a size for which there is little demand.
Furthermore, he prefers a crop such as the trees can mature without
undue exhaustion, for then he is surer of crops the following years.

484 FUNDAMENTALS OF FRUIT PRODUCTION

The set that the grower would call perfect varies greatly with species,
variety and with conditions. In 1899, Fletcher'*'' counted 4725 blossoms
of the apple, pear, plum and apricot; from these 617 fruits developed what
was considered a full crop for the branches on which they were borne.
It would be called a perfect set by the grower, yet the percentage actually
setting was 13. The setting of 20 to 30 per cent of the blossoms of the
Muscadine grape would give a full crop.^* If, however, the setting of 10
per cent of the blossoms provides for a full crop, a 5 per cent set will
provide only half a crop, though proportionally but a few more blossoms
drop. In terms of the percentage of blossoms setting, then, a difference
of a few per cent may have a great effect on the size of the crop so that
it becomes important to ascertain the causes of these slight differences and
the methods of controlling them.

The usual failure of many blossoms to set and mature fruit is due to
many factors, the more important of which are discussed later. It
should be understood, however, that many cultivated varieties char-
acteristically produce more blossoms than possibly can mature into fruits
and that consequently a certain amount of dropping is to be expected.
This may be regarded in the same light as the nearly universal abortion
of one of the two ovules in the ovaries of most stone fruit varieties
or two of the three ovaries in the flower of the date palm — phenomena
due to deep-seated hereditary causes that are quite beyond control by
any cultural means.

The June Drop and Other Drops. — All of the flowers that fail to
mature fruit do not drop at one time and a continuous dropping from
the flowering stage up to the time of maturity is not common. Instead
there are more or less definite periods or stages when extensive dropping
occurs. The loss comes in a series of waves, varying with the different
fruits in number and in the length of time between them. There appear
to be certain "sticking points," critical periods, through which each
fruit must proceed to reach full maturity. When one of these stick-
ing points is safely passed there is comparatively little danger of the fruit
falling before the next critical period arrives. Apparently these sticking
points for fruit setting are closely correlated with definite changes in
the development taking place in the embryo and in the endosperm of the

Dorsey^^ has made a careful study of dropping of blossoms and newly-set
fruits in the plum and the following account, adapted from his report, illustrates
the phenomenon as it occurs in fruits in general :

The First Drop. — The first drop takes place very soon after blossoming.
Examination of the pistils of the flowers dropping at this time shows that they
are defective. In some, pistil abortion has occurred at an earlier stage than in
others though the stage at which it occurs is quite constant for each variety.
Pistils show all degrees of development, ranging from mere rudiments up to those

FRUIT FORMATION 485

that are nearly perfectly formed. The more defective pistils drop earliest, but
all flowers come into full bloom. Flowers with defective pistils always drop at
the pedicel base and neither the calyx tube nor the style is shed by abscission
because growth is not carried far enough. The immediate cause of the dropping
is the abortion of pistils that are structurally defective and cannot function.

The Second Drop. — "The first drop is followed 2 weeks or so after bloom by
another distinct wave of falling pistils. While there are a few intergrading
forms between these two drops, certain features of the second drop separate it
distinctly from the first. Unlike the pistils of the first drop, those of the second
have every external appearance of being normal. Enlargement up to a certain
point takes place and in most cases the calyx tube breaks away at least in part
even though there is insufficient growth in the young plum to throw it off. The
style is not deciduous in the earliest pistils to fall, but, like the calyx tube, drops
in those which fall later. . . . Pistils which fall in the second drop, as in the
first, absciss at the pedicel base while the pistil is still green, although the pedicel
has become light yellow. Yet in the last pistils of the second drop to fall the
abscission layer is formed at the base of the ovary and in some instances can
be easily broken off at this point. . . .

"Emphasis is placed upon the following points. . . : (a) the period of
abscission of the second drop extended from 17 to 30 days after bloom; (b)
beginning with the first pistils to fall, size differences between those persisting and
those which fell, gradually increased with time; (c) pistils which fell within the
above-mentioned time limit enlarged only up to a certain point ; ((/) those pistils
with the stigmas snipped before pollination, enlarged before falling, to a size
comparable with that of those not so treated; and (e) in each variety there was
a gradual increase in the size of the pistils which fell off. . . .

"The condition found in the unfertilized series is in marked contrast with
that found when fertilization takes place. As early as 18 days after bloom the
embryo sac in which the egg has been fertilized extends the entire length of the
nucellus to the chalaza, and a jacket of endosperm, usually only one cell thick,
covers the entire area of the 'dumb-bell-shaped' sac. With the completion of
these changes in the embryo sac the embryo may be no larger than four cells
across. . . .

"It will be seen from the above observations that all the evidence shows that
fertihzation has not occurred in the pistils which fall at the second drop. . . .
Pollination may have taken place, but tube growth was retarded to such an
extent that fertilization was prevented probably by the abscission of the style."

The Third Drop or June Drop. — "Following the second drop there is still
another — the so-called 'June drop.' In popular usage the term June drop
applies primarily to the third drop of large plums because they are much more
conspicuous, but does not include the relatively few which fall from time to time,
even up to maturity ... It has been shown that time and size of dropping draw
a relatively sharp line between the first and the second waves of dropping. Like-
wise these two factors separate the second drop from the third. . . . When
fertilization does not take place enlargement reaches only a certain point, the
maximum recorded being in the 5.6 to 6.0 milUmeter class, while the mode is
near 3.0 millimeters. Among the last of the second drop an occasional ovule is
found with slight embryo development, which shows that there are connecting

486 FUNDAMENTALS OF FRUIT PRODUCTION

forms between the second and third drops as well as between the first and second.
In approximately one month the second drop is over, and those setting have so
increased in size as to place them in a distinct size class from those which have
fallen. . . .

"Sections have been made of the embryos of a large number of plums which
fell at the June drop. Dissections were also made of ovules at various stages to
determine the amount of growth in the embryo. The general condition found
may be summarized as follows: (a) embryo development started but growth
stopped at any time from the stage when the embryo was a few cells across to
the time at which it had reached nearly the mature size; (b) endosperm had partly
formed, but the embryo gained the ascendency to such an extent that it was
often found naked in the nucellus ; (c) enlargement in the seed could reach nearly
the mature size when fertilization had once occurred, accompanied by only a
sUght growth of the embryo. . . .

"The status of development in the ovule in the third drop shows marked
differences from that in the second. Firstly, greater size is attained than is ever
found in the second drop, and secondly, instead of there being disintegrating
nuclei within a slightly elongated embryo sac, tissues cease growing at various
stages rather than disintegrating. This latter fact alone suggests an additional
stimulus absent in the second drop. ..."

It is not known exactly how many other fruits have three distinct
periods in which blossoms and developing fruits drop. However, the
sweet cherry has three such periods; some varieties, at least, of the apple
and pear have corresponding periods and presumably they are to be found
in a number of other fruits, though in some of these species or varieties
they may be associated with other internal and environmental condi-
tions. Certain other fruits, such as the currant and the raspberry
show quite different characteristics in their fruit setting and fruit drop-
ping. In some, as the strawberry, the flowers either set fruit or fail to set
and there is no later dropping or abortion. However, the so-called "June
drop," which may or may not occur in June and may correspond either to
the second or the third drop of the plum is important in determining the
size of the crop with most deciduous tree fruits.

Usually, though not always, the relation between the losses incident
to the successive drops varies with the severity of any one of them.
Heinicke''^ points out that when the "first" drop in the apple is relatively
large the June drop is relatively small; on the other hand the June drop
is heavy if a comparatively large proportion of the flowers begin to form
fruits. This may vary according to variety or with the conditions under
which it is grown. Comparable to this is the condition pointed out by
Reed^*" in certain lemon varieties, in which an individual flower bud on
a small inflorescence has a greater chance to set and develop into a mature
fruit than one on a large inflorescence. Napoleon is an example of a
sweet cherry variety that, as grown in the Pacific northwest, almost
invariably shows a heavy first drop, a light to heavy second drop.

FRUIT FORMATION 487

depending on conditions, and an almost negligible June drop. When
Llewelling is grown under similar conditions it usually shows a fairly-
heavy first drop, a light second drop and a very heavy June drop.

It is interesting in this connection that occasionally certain flowers
of the cluster do not set well, while others set fruit perfectly. Schuster^^^
has called attention to this peculiarity in the flower clusters of Ettersburg
121, a strawberry variety. The primary flowers of the cluster, those com-
ing from the forks, set freely; only a small percentage of the secondaries,
those coming from the lateral branches of the peduncle, set fruit. The
case is not exactly one of blossom dropping, for the flowers do not drop
off; but it is at least in certain respects comparable to the first drop
described by Dorsey for the plum, though the pistils do not appear to be
defective. Valleau^^^ found in some species and in certain varieties of the
strawberry that the later flowers to open may have sterile pistils. He
ascribes this to a tendency toward dioeciousness.

Another interesting case of the June drop or of a pheuomenon comparable
to it is found in the date pahn. Ordinarily by the end of June three partly
grown fruits of approximately equal size have developed from the three ovaries
of each pistillate flower. If pollination and fertilization have taken place two of
these developing fruits drop off, leaving a single one to mature. On the other
hand, if the flowers have not been pollinated, all three may persist and continue
to grow slowly; they never reach full edible maturity and are without value.
They are seedless, closely crowded together and generally somewhat deformed. ^^"^

Fruit Setting, Fruitfulness and Fertility Distinguished. — In the

preceding discussion the term "fruit setting" has been used to refer both
to the initial setting of the fruit at or just after the time of blossoming
and to its remaining on the plant until maturity. The term is used often
in a somewhat narrower sense to indicate whether or not it remains
attached to the plant for any considerable time after flowering and whether
any enlargement of the ovary takes place. Probably in the case of the
plum just described in detail few would regard the fruit as having
set if it did not siyvive the second drop, but many would consider it as
having set if it remained through this period, even though abscission
took place at the time of the third or June drop. There are reasons for
refraining from an attempt to limit too closely the meaning and use of the
term. However, it is desirable to be able to refer to definite conditions
that are exemplified in many different species. By common consent the
term "fruitful" is used to describe the plant that not only blossoms and
sets fruit, but carries it through to maturity. The plant that is unable to
do this, or that does not do it, is "unfruitful" or "barren." "Fertihty"
indicates ability not only to set and mature fruit but to develop viable
seeds. Inability to do this is described by the terms "infertility" and
"sterility." Fruitfulness and fertility are not synonymous, for manj^

488 FUNDAMENTALS OF FRUIT PRODUCTION

fruits, like the banana, mature their fruits though they bear no mature
seeds. This should be emphasized because fruitful plants are often
spoken of as being fertile, when, as a matter of fact, they may or may not
be. Fertile plants are necessarily fruitful. Self fruitfulness, therefore,
refers to the ability of the plant to mature fruit without the aid of pollen
from some other flower, plant or variety, as the case may be ; self fertility
indicates a similar ability to mature viable seed without the aid of pollen
from some other flower, plant or variety.

Sterility and Unfruitfulness Classified. — In a general way the causes
of sterility, unfruitfulness and of the failure of the fruit to set may be
grouped in two main classes — those internal to the plant and those ex-
ternal, that concern more directly its environment. Frequently it is
difficult, if not impossible, to differentiate between these groups of
factors, for they are interdependent to an important extent; nevertheless
it is convenient to make such a grouping.

Summary. — The essential organs of the flower as they concern fruit
setting and fruit production are the pistils and stamens, though other
parts may enter into the structure of the fruit. The changes taking
place in the ovule and anther just previous to the time of pollination and
fertilization are described in detail. Pollination is followed by the germi-
nation of the pollen grain and the growth of the pollen tube, under the
influence of chemotropic factors, down the style. With the penetration
of the nucellus by the pollen tube and the fusion of one of the generative
nuclei of the latter with the egg cell, fertilization is complete, though a
secondary fertilization of one of the polar nuclei by the second generative
nucleus occurs frequently. The embryo results from the segmentation
and growth of the embryo cell and the endosperm is the tissue developing
from the polar nuclei. Fertilization is usually followed by a growth of
the surrounding ovarian tissues, resulting in a "setting" of the fruit.
As a rule only a small percentage of the flowers of most deciduous fruits
"set" and many of those that remain fall before the fruit reaches
maturity. In many fruits there are several distinct periods of dropping,
these distinct waves being referred to as the first, second and June drops.
These periods of dropping generally are closely associated with definite
stages in the development of the tissues of the ovule. Fruit setting,
fruitfulness and fertility are distinguished. The factors responsible for
unfruitfulness may be classified for convenience into those which are
external and those which are internal to the plant.

CHAPTER XXVII
UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS

Stout^^" recognizes three types of sterility that are to be attributed
mainly to internal factors: (1) sterility from impotence, (2) sterility from
incompatibility, (3) sterility from embryo abortion. Sterility from impo-
tence arises when one or both of the sex organs fails to develop. This may
be complete, in which case either no flowers or no sex organs are formed, or
it may be partial, in which case either stamens or pistils are abortive.
Sterility from incompatibility arises when, though the sex organs are
completely formed, they fail to function properly. In the last type of
sterility the gametes are formed and apparently function but abortion
of the developing embryo takes place before maturity is reached.- The
same classification may hold for the internally controlled factors with
which unfruitfulness and the failure to set fruit are associated. It may
be observed that the sterility due to impotence represents an evolutionary
tendency in the group or species — an evolutionary tendency that finds
immediate expression in a distribution of the two sexes between different
flowers or branches on the same plant or between different plants. The
distinction between sterility due to incompatibility and that due to
embryo abortion is drawn in recognition of the time or stage of develop-
ment at which the male and female gametes, both structurally and func-
tionally perfect, show their incompatibihty — their inability to unite or
develop together to form a mature embryo.

Perhaps a classification of the causes of sterility associated with
internal factors and based upon more fundamental processes would recog-
nize: (1) those due to evolutionary tendencies, mentioned above; (2)
those due to genetic influences, regardless of the exact time or stage of
development when the two kinds of gametes show their mutual aversion
and (3) those due to physiological factors, in which case there is not true
incompatibility but a failure of the plant to provide nutritive conditions
suitable for continued growth. This last type of sterility cannot always
be differentiated clearly from that due to environmental factors.

DUE PRINCIPALLY TO EVOLUTIONARY TENDENCIES

In nature the advantage of cross fertilization in maintaining the vigor
of the species has resulted in many cases in the development of certain
characteristics which make self fertilization difficult, if not impossible.
These factors, so favorable to the maintenance of the species, may, in

489

490 FUNDAMENTALS OF FRUIT PRODUCTION

cultivation, limit its usefulness and range. The more important of
these characteristics, as they concern the fruit grower, are mentioned
here.

Imperfect Flowers: Dicecious and MoncEcious Plants. — Most
fruit-producing species bear perfect flowers. There are some, however,
in which the sexes are separated. In certain species, such as the walnut
and pecan, they are found in different flowers on the same tree or plant;
in others, such as the papaya and sometimes the strawberry, they are
found on different plants.

Monoecious plants bear the pistillate and staminate flowers on the
same individual and are always fruitful — at least theoretically — and rather
frequently they are self fruitful. Certainly the segregation of the sexes
to separate flowers of the plant does not in itself interfere with pollination,
fruit setting and fruitfulness. Among the more common fruits that are
monoecious are the walnut, pecan, filbert and chestnut. The members of
the Cucurbitacese also are for most part monoecious.

Probably the strawberry is the most widely grown of the dioecious
fruits. A comparatively large percentage of its varieties bear perfect
flowers, but some of the best are pistillate. For many years after
the strawberry was introduced into cultivation no attention was paid to
the matter of planting so as to secure pollination of the pistillate varieties,
hence much of the failure of the fruit to set properly in the plantations of
a century ago. It was not until the observations of Nicholas Longworth
of Cincinnati were brought to the attention of horticulturists generally
in the fifties that the unisexuality shown by plants of this species attained
recognition and planting practices were modified accordingly. Experi-
ence has taught long since that these pistillate sorts should be interplanted
with perfect flowering varieties. There are many strawberry varieties
classified as perfect flowering that produce only small amounts of pollen.
These, as well as the imperfect sorts, should be interplanted with good
pollen producers.

The Japanese persimmon or kaki presents a very interesting case of
sex distribution. Many of its varieties, such as Tanenashi, Hyakume,
Hachiya and Costata, produce only pistillate flowers year after year.
These are called "pistiUate constants" by Hume.^" Certain other varie-
ties bear each year pistillate flowers and also some staminate flowers;
these he designates as "staminate constants." Still other varieties bear
only pistillate flowers some seasons and in other seasons both pistillate
and staminate. These are called "staminate sporadics." Hume'^^ also
records the occasional appearance of perfect flowers on trees that regularly
or occasionally bear staminate flowers, though they have not been
found on plants of the pistillate constant type. In other words, certain
varieties are monoecious, others dioecious; still others vary from the one'
condition to the other and occasionally a variety becomes temporarily

UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 491

perfect flowering. The study of these flowering characteristics of the
persimmon and the ehissification of the more important of its varieties
has done much to explain the rather erratic behavior of this plant in
fruit setting and the maturing of seed-bearing or seedless fruits.

Even more variable is the distribution of tlie sexes between different flowers
and different plants in the papaya. Higgins and Holf^" recognize 13 classes of
trees, depending on the combination or separation of stamens and pistils and on
form of the flower clusters, corolla and fruit. Independent of the classes based
on features other than sex distribution, these types are:

1. Pure pistillate flowering plants.

2. Pure staminate flowering plants.

3. Plants producing both staminate and perfect flowers.

4. Plants producing both staminate and perfect flowers, but with sterile
pollen. These might be called pseudo-hermaphrodite plants.

5. Plants producing staminate and perfect flowers in which neither pistils
nor pollen are fertile. The plants might be called sterile hermaphrodites.

G. Plants producing staminate, pistillate and perfect flowers.

7. Plants producing pistillate and perfect flowers.

8. Plants producing staminate and pistillate flowers.

Tj^pes 2 and 5 are necessarily unfruitful, though type 5 is unfruitful appar-
ently because of incompatibiUty rather than impotence, for the sex organs are
developed but non-functioning. Types 1 and 4 are self unfruitful, though it is
possible that 4 is self barren because of incompatibility rather than impotence.
The other types are self fruitful; at least fruitfulness is not impossible because
of impotence. Some of these self fruitful types are dioecious, some are poly-
gamo-dicecious. Types 1 and 2 are by far the most common; that is, the papaya
is for the most part unisexual. Consequently in the average planting of that
fruit it is customary to retain a few of the staminate trees in order to insure a
good set of fruit on those bearing pistillate flowers. Of course staminate trees
remain barren, but if there should be only relatively few of them, they probably
would be valued more highly than an equal number of the fruit producers.

The fig shows a distribution of its sexes somewhat less complicated than
the papaya; nevertheless this distribution should often be given careful
attention at the time of planting. Two kinds of flower clusters are borne
by fig trees. Certain bear pistillate flowers only. The standard fig
varieties include trees of this type exclusively. Certain other trees,
called "caprifigs, " produce both pistillate and staminate flowers within
the same cluster. As a rule, the staminate flowers are borne near the
"eye" of the fig and the pistillate flowers near its base. Fig trees may
thus be placed in two classes in respect to sex distribution, dioecious or
unisexual trees and monoecious trees. The pistillate flowering trees
alone produce the figs of commerce. The monoecious trees or caprifigs
are planted only for the purpose of furnishing pollen for the pistillate sorts.
Some authorities would take exception to certain of the statements just made
about the nature of fig flowers. Eisen^" states that there are three kinds of

492 FUNDAMENTALS OF FRUIT PRODUCTION

flowers on trees of the caprifig class — pistillate, staminate and gall. The gall
flower is regarded as a specialized pistillate that can harbor the pollen-carrying
Blastophaga wasp but cannot develop seed. Rixford,"^ on the other hand, holds
that all so-called gall flowers are in reality simple pistillates, not structurally
different from other pistillate caprifig flowers that occasionally are pollenized,
set fruit and form seed. Usually they do not have the opportunity to set
and develop seed because they are not pollinated or because they are stung by
the Blastophaga and subsequently become galls.

Eisen^o and many others recognize a third kind of pistillate flower which
they call ''mule" flowers. These are produced by most of those cultivated
varieties which yield seedless fruits. They are held to be somewhat different
in structure from the pistillates of such varieties as the Smyrna, that are capable
of setting seed. However, Rixford"^ has shown that these so-called mule
flowers do set and mature seed when properly pollinated and consequently
considers them true pistillates.

Heterostyly. — It has been stated that the flowers of many species present
peculiarities of form and structure, the main function of wliich is to aid in bringing
together the male and female gametes so that fertilization may take place and
reproduction be insured. However, many of these peculiarities of form and
structure are of such a nature as to prevent self pollination and make cross
pollination more certain. If cross pollination does »ot occur, the plant is very
likely to remain unfruitful even though perfect sex organs have been developed.

One of these diversities of form is heterostyly, a type of dimorphism in which
some of the flowers have short styles and long filaments and other flowers of the
same species or variety have long styles and short filaments. The structure
and arrangement is such that when these flowers are visited by pollen-carrying
insects no self pollination takes place but pollen from short stamens is deposited
upon the stigmas of the short pistils and pollen from the long stamens is carried
to the stigmas of the long pistils. Cross pollination between two flowers of the
same form on a single plant may occur, but the arrangement assures a consider-
able amount of crossing between plants. It has been shown that when the pistils
of heterostyled plants are pollenized with pollen from the same flowers or from
other flowers containing stamens of an equal height the union may be fruitful
but is likely to be attended by varying degrees of sterility. ^^ This, however,
introduces the factor of incompatibility, about which more is said later.
Apparently heterostyly is relatively unimportant in determining setting in
deciduous fruits.

Dichogamy : Protandry and Protogyny. — It has just been pointed out
that in heterostyled plants the sexes are nearly as completely separated
and self pollination as completely prevented as in monoecious plants.
Likewise there may be more or less separation of the sexes and a pre-
vention of self pollination in perfect flowered plants through the maturing
of the two sex elements at different times. This behavior of the plant
is known as dichogamy. If the stamens ripen before the pistil is ready
to receive pollen the flower is protogynous; if the reverse condition
holds it is protandrous. Dichogamy is incomplete when there is an

UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 493

overlapping in the seasons of maturity of the two sex elements; otherwise
it is complete. Complete dichogamy insures pollination with some other
flower and perhaps with another plant. Incomplete dichogamy tends
in that direction, but still allows opportunity for a certain amount of
selfing.

The frequent occurrence of dichogamy and consequently its impor-
tance in influencing the setting of fruit is not generally appreciated.
Kerner and Oliver^* state: " . . . It appears that all species of plants
whose hermaphrodite flowers are adapted to cross-fertilization by the
relative position of anthers and stigmas are, moreover, dichogamous,
although this dichogamy may be of slight duration. Plants with hetero-
styled flowers are also dichogamous, since those with short-styled and
those with long-styled flowers develop at different times. . . . As far as
we can tell at present all monoecious plants are protogynous. . . .
Alders and Birches, Walnuts, and Planes, Elms and Oaks, Hazels and
Beeches are all markedly protogynous. In most of these plants . . . the
dust-like pollen is not shed from the anthers until the stigmas on the
same plant have been matured 2 to 3 days. Sometimes the interval
between the ripening of the sexes is still greater. The majority of
dioecious plants are also protogynous." Both Waugh^^* and Dorsey^^
call attention to the existence of dichogamy in the plum. Pecan varieties
have been classified in two main groups, those exhibiting dichogamy and
those which mature their stamens and pistils simultaneously. ^-''

Interesting as illustrating the influence of dichogamy on fruit setting are
certain experiments of Wester ^^^ with Anonas. Flowers of the cherimoya
(Anona cherimolia) and of the custard apple {A. reticulata) were found to shed
their pollen iu the afternoon from about 3:30 to 6:00. Flowers of the sugar
apple (.4. squamosa) discharge their pollen from sunrise to about 9:00 a. m.
A few trees of this latter species were found to shed their pollen in the afternoon
and these same trees did not shed any pollen in the morning. Many pollina-
tions were made, the results of all pointing to the same general conclusion. The
follo^^^ng account of one of his experiments illustrates the results obtained:
"... 1-43 flowers on one sugar apple tree were, in April and May, 1908, pol-
linated with their own pollen or that of flowers of other plants of the same
species, 41 with pollen of the cherimoya, 31 with pollen of the pond apple, and,
51 flowers with pollen of the custard apple. In no instance did fruit set where
the pollen was applied to the stigma simultaneously with the discharge of its
pollen; practicallj'' all responded where it was applied 15 to 48 hours previous to
this act, though here, as in the case of the cherimoya, the tree shed much of the
fruit before it matured OA\'ing to its inability to carry it all."

The flower clusters of the caprifig, the dioecious form of the fig tree, afford
an extreme and very interesting instance of dichogamy.^" The stamens and
their pollen do not mature until shortly before the ripening of the fig, when the
wasps have attained their maturity in the gall flowers of the same flower clusters
and are ready to emerge and enter other fruits to which they carry pollen. On

494 FUNDAMENTALS OF FRUIT PRODUCTION

the other hand the pistillate flowers of the fig are receptive weeks, or even months,
earlier. In this way the wasps, carrying the pollen from one crop {e.g., the pro-
fichi) of the fig, enter the flowers of the following crop (mammoni) at a time when
their stigmas are receptive. It is possible for self pollination to take place within
the tree, but there is at least a crossing between two successive crops of the
caprifig and there is often actual cross pollination between trees or varieties.

Commenting on the significance of dichogamy Kerner and Oliver^^ remark:
" From these facts we may infer that every dichogamous plant has an opportunity
for illegitimate crossing or hybridization at the beginning or end of its flowering,
and that dichogamy — especially incomplete dichogamy — is the most important
factor in its production. Of course this does not exclude dichogamy from playing
an important part in legitimate crossing as well. On the whole, however, we
can maintain the view that the separation of the sexes by the maturation of the
sexual organs at different times leads to hybridization, while their separation
in space promotes legitimate crossing. The fact that the separation of the sexes
in time and space usually occur in conjunction harmonizes with this conclusion,
i.e., that the dioecious, monoecious, and pseudo-hermaphrodite flowers, as well
as those hermaphrodite flowers whose sexual organs are separated by some little
distance, are in addition incompletely dichogamous, because by this contrivance
the flowers of any species obtain (1) the possibility of hybridization at the begin-
ning or end of their flowering period, and (2) of legitimate crossing during the
rest of that time. This also explains why incomplete dichogamy is so much more
frequent than complete dichogamy ; why there are no dioecious species of plants
with completely dichogamous flowers; and why, if one ever should occur, it
would of necessity soon disappear. Let us suppose that somewhere or other
there grows a species of Willow with completely protogynous dioecious flowers,
that is to say, a species in which the female flowers mature first, and have ceased
to be receptive before the male flowers in the same region discharge their pollen.
Hybridization only could occur in it, and the young Willow plants resulting from
it would all be hybrids whose form would no longer agree absolutely with that
of the pistiUiferous plant. The species would therefore not be able to reproduce
its own kind by its seed, and it would leave no descendants of similar form; in
other words, it would die out."

Data are not available as to the exact degree of dichogamy char-
acteristic of different species and varieties of the deciduous fruits ; therefore
it is impossible to state accurately the extent to which it interferes with
their self pollination or to what extent it is a factor in determining their
fruit setting. Furthermore, as is shown later, the completeness of
dichogamy varies considerably with environmental conditions. There
can be no question, however, but that in many varieties it explains the
failure of numerous blossoms to set.

Impotence from Degenerating or Aborted Pistils or Ovules. — It is
obvious that, if the setting and maturing of fruit usually depend on the
union of two properly formed sex cells, anything which occurs to interfere
with the development and proper functioning of either gamete probably
will result in unfruitfulness or at least in sterility. This occurs in the

UNFRUITFVLNESS ASSOCIATED WITH INTERNAL FACTORS 495

developing pistils and stamens of manj^ species and is responsible for
many failures in fruit setting.

Sometimes degeneration takes the form of an abortion of the entire
pistil. This may occur early or comparatively late in the course of its
development; consequently in certain species there are pistils in all
stages from those very rudimentary and plainly not functioning to those
that apparently are perfect in structure and ready for fertilization.
Goff^' records this condition as very common in many varieties of our
native plun>s, and Hodgson^^ states that the same thing is found in the
pomegranate. It occurs more frequently in the ornamental types of the
pomegranate than in those varieties cultivated primarily for their fruit;
in either case it is one of the main causes of the failure of the fruit to set.
Waugh/^* in a rather extended study of the occurrence of defective
pistils in plums, found striking differences in various groups. His
findings are summarized in Table 1.

Table 1. — Percentage of Defective Pistils in Different Groups of Plums
{After Waugh'^*)

Domestica group 4.3 Wayland group 10.5

Japanese group 11.2 Wildgoose group 19 . 8

Americana group 21 . 2 Chicasaw group 10. 5

Nigra group 17.0 Hybrids group 18.1

Miner group 1.9

In a number of species and varieties the pistils attain their usual size
and they contain ovules that to the unaided eye appear entirely normal.
However, examination shows partial or complete degeneration in the
embryo sac just prior to its maturing; therefore fertilization is impossible.
Embryo sacs of the orange showing degeneration at various stages in
their development are pictured in Figs. 2 to 4 of Plate III. Sometimes
these degenerative processes set in early in the development of the ovules
and their abortion is so complete that it is evident to the unaided eye
at the time for fertilization. In the Unshu and Washington Navel
oranges, however, the fruits may develop in spite of that defect, though
they are seedless. Embryo sac abortion thus becomes in certain instances
a cause of seedlessness rather than unfruitfulness. Pistil abortion,
apparently at a comparatively late stage in development, has been found
to explain the failure of many strawberry blossoms to set fruit and the
production of "nubbins" from many others. ^^^ One of the two ovules
in the ovary of the plum" and other stone fruits is often much sma^er
than the other at the time of flowering, showing that at least a part of the
almost universal failure of one of the ovules to develop into a seed is
due to processes operating before the time of fertilization. It should be
noted in this case, as in many other fruits, that the abortion of a part
of the ovules of the flower does not lead necessarily to unfruitfulness.

496 FUNDAMENTALS OF FRUIT PRODUCTION

The relation of number or proportion of seeds to the holding of the fruit
is discussed in another connection.

Impotence of Pollen. — It has long been known that many apparently
perfect flowered plants produce only small amounts of pollen and that
occasionally a considerable portion of that which is borne is non-viable.
In fact it is unusual to find pollen that is 100 per cent viable. However,
few data have been available as to the proportion of the pollen produced
by ordinary fruits under varying conditions that is defective and until
recently there has been little realization of the importance of this factor
in determining fruit setting and fruitfulness.

Beach, ^> ^> * was one of the first to investigate this subject carefully
as it pertains to deciduous fruits. He found that varieties of American
grapes fall readily into three classes in respect to fruitfulness when de-
pendent on their own pollen for fertilization. These he called self
fertile, self sterile and partly self sterile. The varieties of the partly
self sterile group varied from vineyard to vineyard and from season to
season in their degree of self sterility, but those of the self fertile group
remained completely self fertile; likewise those of the self sterile group
remained completely self sterile. Controlled cross pollination experi-
ments led to the conclusion that the partial or complete self sterility of
those two groups was not due to any defect in the pistils but to impotence
in their pollen, though an abundance of it was formed. The stamens of
the self fertile varieties were erect, while those of the self sterile sorts were
reflexed. A detailed study of the pollen of these different classes showed
marked differences in the shape and appearance of the grains.^ Those
of the self fertile varieties were oblong, blunt at the ends and quite sym-
metrical and they germinated well ; those of self sterile sorts were irregular
in shape and did not germinate well. Stamens of the partly self sterile
varieties were found to contain some good and some poor pollen.

A little later Reimer and Detjen^'" reported that all the varieties of
the Muscadine grape bear reflexed stamens only and that all their pollen
is defective. Their flowers are pseudo-hermaphrodites rather than true
hermaphrodites. For fruit to set the pistils must receive pollen from
male or staminate vines. The plants of this species are essentially dioe-
cious. Failure to recognize this fact has been responsible for much of
the unfruitfulness previously encountered in the culture of this group of
grapes. Among the plants growing wild about three-fourths are stami-
nate and one-fourth pseudo-hermaphroditic with functional pistils.^*
More recently there have been found ^^ ' '^^ several plants of this species
producing true hermaphrodite flowers; these have afforded a starting
point for the breeding of a new and perfect flowered race of Muscadine
grapes.

Apparently the failure properly to set and mature fruit occasionally
found in European varieties of grapes is likewise due at least partly to

UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 497

defective pollen.'' This dropping of grape blossoms or of the partly
developed berries in those of the Vinifera varieties is commonly known
as "coukire."

Dorsey^*^ has made a study of the cj^tological changes within the
developing pollen grain of the grape leading to, or associated with,
its impotence. Figm-es 9 to 11 in Plate II show something of the nature
of these degenerative changes. He distinguishes between what he terms
sterile pollen and aborted pollen. In the former after true pollen grains
are formed degeneration occurs in cither their generative or vegetative
nuclei or in both. Aborted pollen results from a development arrested
at an earlier stage. The following quotation from his report brings out
the more important details of his investigations:

"In the formation of the sterile and fertile pollen of the grape the hetero-
typic and homotypic divisions and the divisions of the microspore nucleus take
place normally. Sterile pollen in the grape results from degeneration processes
in the generative nucleus or arrested development previous to mitosis in the
microspore nucleus. Where degeneration begins early after the division of the
microspore nucleus, both the generative and vegetative nucleus may be affected.
If the generative cell is well organized before disintegration begins the vegetative
nucleus may remain normal. . . .

"Aborted microspores occur in various percentages in the native forms, as
well as in the cultivated varieties. While in the end the result is the same, a
distinction should be made between aborted and sterile pollen. The former occurs
in both sterile and fertile forms and seems to be due to arrested development soon
after being Uberated from the tetrad, while the latter results from disintegration
processes subsequent to mitosis in the microspore nucleus, and occurs associated
with the reflex type of stamen and the absence of the germ pore. . . .

"The amount of aborted pollen which occurs in the grape varies much in
different vines. In the 52 cultivated varieties the average per cent, of aborted
pollen is 22.83, compared with 4.08 in 121 wild staminate vines of V. vulpina
and 3.70 in 50 wild pistillate. ... Of the 52 cultivated varieties only 10
have less than 5 per cent, of aborted pollen. . . .

"The difference between the percentage of aborted pollen in known hybrids
and the pure forms, among the cultivated varieties, is only slight. The average
percent of aborted pollen from 10 vines, of varieties generally regarded to be
pure V. labrusca, is 23.10, while that for 38 of the hybrid varieties is 24.60.
There are some instances, however, among the hybrids, as in Black Eagle, where
the amount of aborted pollen is small. . . .

"Since aborted pollen occurs in much the same relative amounts in the self
fertile and self sterile varieties, from the standpoint of fertilization and the setting
of fruit it would seem that the aborted pollen is unimportant in the grape, be-
cause in the fertile forms there is still an abundance of potent pollen.'"'^

It should not be inferred, because the discussion thus far has been
limited to the grape, that sterility or unfruitfulness due to pollen abortion
does not occur in other fruits. Pollen abortion is a common occurrence

32

498 FUNDAMENTALS OF FRUIT PRODUCTION

and a frequent cause of unfruitfulness. Osawa^"^ reports irregular
development of the pollen mother cells and much defective pollen in
Daphne odora. Two to 10 per cent of the pollen of the mango is regu-
larly defective, i"*^ Dorsey^^ finds pollen abortion common in the plum,
noting that in that fruit the disintegration processes usually occur after
the liberation of the tetrad from the pollen mother cell. If distinction
is to be made between pollen sterility and pollen abortion, in this case
as in the grape, the defective pollen of the plum is sterile rather than
aborted. In neither the plum nor the mango, however, is the percentage
of defective pollen high enough to interfere seriously with the setting of the
fruit. Pollen abortion has been reported as a practically constant char-
acteristic of blackberries in New England. ^^ Furthermore it has been
found to vary greatly with the variety and species. For instance Ruhus
allegheniefisis was found to have about 96 per cent, while R. hispidus
had less than 10 per cent, morphologically perfect pollen. Between these
extremes were all gradations. The higher percentages of defectiveness
were enough to reduce very materially the set of fruit. A similar condi-
tion is reported in the strawberry. ^^^

Degeneration occurs in nearly all the pollen mother cells of the
Washington Navel orange. ^^^ ^<"' Consequently practically no mature
and perfect pollen grains are formed. In the Unshu variety ^°° degen-
eration is not so general; nevertheless it affects a large number of the
pollen mother cells. In these two varieties, as in certain others, pollen
abortion is not accompanied by unfruitfulness because the fruits are
capable of parthenocarpic development, but it is responsible for partial or
complete suppression of their seeds.

DUE PRINCIPALLY TO GENETIC INFLUENCES
The forms of self sterility and self unfruitfulness discussed up to this
point are due plainly to factors associated with the fundamental constitu-
tion of the protoplasm. It is also clear that sterility due to these factors
is inherited, though the underlying causal agents are evolutionary
tendencies within the species. Self sterility and self unfruitfulness that
are to be attributed more directly to genetic factors, to the inheritance
received, are here discussed under the headings of hybridity and incom-
patibility. However, it is impossible to differentiate sharply between
these two types of sterility.

East and Park^^ remark: "Self-sterility is a condition determined
by the inheritance received, but can develop to its full perfection only
under a favorable environment." In his study of fertility in chicory
Stout^^^ found that out of a total of 101 plants in one crop which came
from three generations of known self sterile ancestry 11 were self fertile
and 90 were self sterile. From his data he was able to conclude not only
that self sterility is inherited but that in this species narrow breeding

UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 499

is more likely to give rise to self sterile plants than is broad breeding.
Detjen^^ concluded from his studies with the Southern dewberry {Rubus
trivialis) that not only is self sterility in that species transmitted to its
pure offspring, but frequently to its hybrid progeny.

Sterility and Unfruitfulness Due to Hybridity. — Unfruitfulness and
sterility have long been recognized as conditions frequently associated
with hyl)ridity. Generally the wider the crossing the greater is the degree
of sterility encountered. Many instances might be cited; a few will
suffice. Waugh^^^ describes a hybrid between the Troth Early peach and
the Wildgoose plum that has been named the IVIule. It bears an abun-
dance of flowers but they are without pistils or petals. The stamens are
numerous, but malformed, assuming something of the shape and appear-
ance of pistils. The variety is fairly constant in its flower characteristics,
completely sterile and also barren. He mentions another peach-plum
hybrid, known as the Blackman, with similar characteristics. A hybrid
between the pear and the quince, described under the name Pyronia,
flowers and fruits freely but is always seedless. ^^7 jj^ ^]^jg ^g^gg hybridity
is responsible for sterility alone, instead of sterility and barrenness, as in
the peach-plum hybrids. The Royal and Paradox walnuts, hybrids
between the Persian and the California and Eastern Black respectively,
are almost barren. In these cases, as in many other hybrids, barrenness
due to hybridity is associated with great vegetative vigor. The high
percentage of aborted pollen found in wild and cultivated blackberries in
New England is to be attributed mainly to a condition of hybridity. ^^
A number of hybrids between Vitis rotundifolia and various species of the
Euvitis group have been found almost completely sterile; this is attributed
mainly to their hybrid condition. ^^ In describing one of these V. vinifera

"Flowers perfect hermaphroditic and imperfect hermaphroditic; stamens
upright and pistils medium large in the perfect hermaphroditic ; stamens reflexed
and pistils well developed in the imperfect hermaphroditic flowers. . . . The
pollen in the perfect hermaphroditic flowers is a mixture of shriveled and plump,
sterile and fertile grains. The fertihty of these plump grains has been demon-
strated in actual hand-made cross poUinations, also by selfing some of the flowers.
The pollen in the imperfect hermaphroditic flowers is all shriveled and impotent.
The pistils in both types of flowers are mostly sterile, only two from 17 perfect
hermaphroditic flower-clusters having developed into berries in 1918. The
perfect hermaphroditic flowers are sterile because of hybridization, while the
imperfect hermaphroditic flowers are sterile due to the double phenomenon of
hybridization and intersexualism with attendant impotence."

However, abortion of pollen and of pistils cannot always or entirely
be attributed to hybridity; and, conversely, hybridity is not always a
cause of unfruitfulness or even of sterility. Many of the cultivated
American varieties of the grape that are probably pure species bear some

500 FUNDAMENTALS OF FRUIT PRODUCTION

aborted pollen and, furthermore, many varieties of known hybrid origin
are highly self fertile. In discussing this matter Dorsey^** says: "Since
both fertile and sterile hybrids occur among the cultivated varieties of
American grapes, hybridity is not necessarily a cause of sterility. The
relation of the sterile pollen to the absence of the germ pore, the reflexed
type of stamen, and the tendency toward diceciousness, suggest that
pollen sterility in the grape is only a step toward functional dicliny."
The same investigator^^ reports somewhat more aborted pollen in some
of the hybrid plum varieties than in some of those of pure species and also
a tendency for the degeneration processes to start earlier in the hybrids.

All the available evidence warrants the conclusion that the highest
fertility is correlated with neither the narrowest nor the broadest breeding
possible.

Incompatibility. — One of the most common causes of self unfruit-
fulness and self sterility is incompatibility between the pollen and the
ovules of the same plant or of the same variety. That is, both the ovules
and the pollen of the plant are fertile in themselves, but they fail to
effect conjugation. Miiller found self incompatibility in Oncidium flexuo-
sum and a number of other species of orchids. ^^ In some instances not
only did the pollen fail to impregnate the ovule but its action was injurious
or poisonous to the stigmas, causing them to turn brown and to decay
prematurely. At the same time unpollinated stigmas remained fresh.
Those that were pollinated with pollen from other plants showed no signs
of injury; fertilization took place and fruit set; the pollen that acted so
injuriously upon the stigmas of its own flowers functioned perfectly on
other plants. The same condition has been reported in Lobelia^^ and as
not uncommon in Cichorium intybus.'^^'^

The self sterility or self unfruitfulness that has been reported in the
apple, 88, 107 in pears,^^; "^ [^ ^^^ sweet cherry,^"; ^^s j^ the plum,^^; i^"
in dewberries and blackberries^^ and in the almond^^^ is probably in large
part attributable to incompatibility. In practically all of the instances
cited the varieties set fruit properly when cross pollinated, showing that
the pistils were perfectly developed and functional. Furthermore the
pollen from these same varieties proved viable and capable of taking part
in the fertilization process and in yielding mature fruits and seeds when
it was applied to other varieties of the same species. Nevertheless,
barrenness followed self pollination. However, in most cases data
are lacking to show whether or not pollination was followed by fertiliza-
tion. It is possible that in many instances fecundation took place and the
immediate cause of the failure of the fruit to set or mature was embryo
abortion at a later stage. This has been mentioned as a distinct cause
of fruit dropping. It is, however, in most cases very closely related to,
if it is not actually one aspect of, incompatibility. Therefore the self
sterility and self unfruitfulness of these common fruits may be considered

UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 501

as due to incompatibility, using that term in its broader sense signifying
that the normal processes of fertilization fail somewhere between the
production of functional gametes and the fusion of the sex cells.

I nterfruitf Illness and Inter fertility. — Just as the terms self fruitfulness
and self fertility refer to the ability of a plant or a variety to mature
fruits or seed with pollen from its own flowers, so interfruitfulness
and interfertility indicate the abihty of two plants or two varieties to
mature fruits and seed with each other's pollen. Varieties that are
self unfruitful because of dioecism, such as for instance pistillate flowered
strawberries, figs of the Smyrna type and the date palm, have long been
known to be interbarren as well. Other fruit varieties, such as many
of the grapes, that are self barren, or partly so, because of impotent
pollen, have been recognized as interbarren for the same reason. ^^ Until
comparatively recently, however, it has been the rather general belief
that most fruit varieties are interfertile, or at least interfruitful, even
though they might be self sterile, provided that they bear good pollen.
That is, it was assumed that any variety of apple can successfully
pollenize and fecundate any other apple variety, the only precaution
necessary in planting being to choose varieties blossoming at approxi-
mately the same season. .Occasional instances of interunfruitfulness
were encountered in experimental studies^"^ but later work with the same
varieties in the same or in a different place often proved them interfruitful
and the first results were regarded as due to accident or experimental
error. However, Whitaker and Milton, which are open pollinated
seedlings of the Wildgoose plum, have been reported intersterile and
though both are fertile when pollinated with Sophie, that variety is
sterile to their pollen.^"

In 1913, Gardner^'' reported the three leading varieties of the sweet
cherry grown on the Pacific Coast as intersterile and interunfruitful
in Oregon and a little later the same condition was reported for two of
these varieties in California. '^^ At the same time all three varieties
were found to have perfectly good pistils and potent pollen. This is
clearly an instance of intersterility due to incompatibility. More
recently several varieties of the almond have been shown to be inter-
sterile in California. ^-^ Stout^-" has found cross incompatibility occurring
sporadically in his pedigree cultures of chicory and it has been recorded
in tobacco. ^^ In summarizing their observations on cross incompati-
bihty in tobacco. East and Parks state :^^ "Cross-sterility in its nature
identical with self-sterility was found in every population of self-sterile
plants tested. The percentage of cross-sterility in different populations,
based in each case on numerous cross matings, varied from 2.4 per cent,
to 100 per cent. "

Cross-stei'ility is much less common than self-sterility but apparently
is to be expected in all those groups in which self-sterility exists. Data

502 FUNDAMENTALS OF FRUIT PRODUCTION

are not available to show to what extent, if at all, the degree of inter-
unfruitfulness can be modified by environmental conditions and it is
not possible to tell, without trial, which varieties are and which are not
interfruitful.

In Reciprocal Crossings. — In the investigations with tobacco to which
reference has just been made, there was found a uniformity of behavior
between reciprocal crossings. ^^ That is, if a certain crossing proved
sterile, its reciprocal was likewise sterile and if one variety proved incom-
patible with two others, those two were likewise sterile to each other.
On the other hand, all grades of opposite results in interfertility have
been obtained in Verhascum phceniceum when reciprocal crossings were
made.^^^ In some instances when one plant was used as the male and
the other as the female parent there was complete compatibility and
when the reverse combination was attempted there was complete incom-
patibility. A similar condition has been reported in chicory. ^^^ Vitis
vinifera, V. bourquiniana, V. labrusca and V. cordijolia hybridize freely
with V. routundifolia and V. munsoniana when the latter two are used
as the pollen parent, but they hybridize much less freely when the re-
ciprocal crossing is made.^^

An interesting case of interf ruitf ulness of a reciprocal crossing but of intersteril-
ity when the crossing was made one way and interfertility when made the other
appeared in work done at the Georgia Experiment Station. ^^ Flowers of the
upland cotton, Gossypiiwi Barbadense, were crossed with pollen of the okra.
Hibiscus esculentns. Perfect cotton bolls were produced but the seeds were non-
viable. The reciprocal crossing resulted in normal appearing okra fruits and in
viable seeds. WeUington^'''^ secured seedless tomatoes by using pollen of the
Jerusalem cherry, Solanum pseudocapsicum, but no fruit was formed when the
reciprocal crossing was made.

DUE PRINCIPALLY TO PHYSIOLOGICAL INFLUENCES

Besides the effects of evolutionary and genetic influences in hmiting
the set of fruit there are a number of others that can be conveniently
grouped as physiological, though exact demarcation is impossible.

Unfruitfulness Due to Slow Growth of the Pollen Tube. — Closely
related to the unfruitfulness and the sterility due to incompatibility is
that caused by the very slow growth of the pollen tubes in the style.
Indeed, this may be considered one type of incompatibility, due to
chemotropic influences.

Darwin^^ made many crossings between different forms of heterostyled
dimorphic and trimorphic plants. He found that when pistils were
pollinated with pollen from stamens of corresponding height there was
a high degree of fertility; when pollinated from stamens of a different
height there were varying degrees of sterility. This sterility ranged
from slight to absolute. Pollen from stamens of a height corresponding

UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 503

to that of the stigma (legitimate polHnation) placed on stigmas 24 hours
after pollination from stamens of anothcn- height (illegitimate pollination)
was found to effect fertilization, the earlier applied pollen still remaining
ungerminated. Plants raised from the few seeds obtained from illegiti-
mate pollinations showed many of the characteristics of hybrids between
species, being few flowered, weak or perhaps profuse flowered and partly
sterile. Practically the same has been found in the heterostyled flowers
of buckwheat. ^^^ In the legitimate pollinations less than 18 hours
was required for the growth of the pollen tube and the fusion of its
generative cell with the egg cell of the embryo sac. In the illegitimate
pollinations more than 72 hours were necessary for the same series of
events. Discussing the cause of self-sterility in Nicotiana East and Parks
say:^^ "... The immediate difference between a fertile and a sterile
combination is in the rate of pollen tube growth. If at the height of the
season a series of self pollinations and a series of cross pollinations are made
on a single plant and the pistils fixed, sectioned and stained at intervals of
12 hours, it is found by plotting the average length of the pollen tubes
in each pistil against time in 12-hour periods that the growth curve of
selfed pollen tubes is a straight line which reaches less than half the
distance to the ovary during the life of the flower, while the curve of
crossed pollen tubes resembles that of an autocatalysis and reaches the
ovary in less than 96 hours." Similar differences have been found in the
rate of pollen tube growth in selfed and crossed apples.*^

Obviously, slow pollen tube growth alone cannot be responsible for
a failure of the fruit to set, for eventually the tubes would reach the
ovules. However, flowers do not remain attached to the flower cluster
or to the stem indefinitely when fertilization does not occur. Unless it
occurs within a fairly short time, varying with species, variety and
environmental conditions, abscission takes place at the base of the style,
ovary, pedicel or peduncle and fruit setting is prevented.

The failure of the flowers to set fruit through the retarding of pollen
tube growth by low temperature is discussed in another connection.

Premature or Delayed Pollination. — Hartley^^ has found that the
flowers of tobacco are very susceptible to injury from premature pollina-
tion. When mature pollen grains are applied to immature pistils they
germinate, penetrate the styles and enter the ovules and if the ovules are
not ready for fertilization the flowers soon fall. In cases of this kind
"the separation of the flower from the plant was rapid and complete and
not accompanied by any previous wilting of the flower, but invariably
occurred at a j oint situated at the base of the peduncle. ' ' This is somewhat
different from the falling of flowers from other causes. Table 2 shows the
results of one series of pollinations at various stages of pistil maturity.
Hartley did not find any injurious results from pollinating orange blossoms
nine days before opening and but little injury from premature polhnation

504

FUNDAMENTALS OF FRUIT PRODUCTION

in the tomato. To what extent premature pollination interferes with
the set of fruit in the orchard is unknown.

Table 2. — Influence op Premature Pollination on Setting in Tobacco
{After Hartleif^)

Number flowers

Time pollinated

Per cent set

20

4

days before opening

5

40

3

days before opening

5

20

2

days before opening

0

40

1

day before opening

77

20

]/2 day before opening

95

20

When fully receptive

95

It is well known that if pollination is long delayed the blossoms fall without
setting. Kusano/'' working with orchids belonging to the genus Gastrodia, found
that when pollination was delayed for 2 to 3 days fertilization took place in an
almost normal manner. When it was delayed 4 days it was rather ineffective
and when it was effective the resulting fruit varied in size "according to the
number of embryogenic seeds." He also made the interesting observation that
when pollination was delayed 3 to 4 days a comparatively large percentage of
the seeds formed were poly embryonic, while seeds resulting from earlier pollina-
tion seldom contained more than one embryo.

Nutritive Conditions Within the Plant. — There is abundance of
both circumstantial and experimental evidence to show that the nutri-
tive conditions within the plant at and just after the time of blossoming
are important in determining the percentage of the blossoms that will set
and also the percentage that will finally reach maturity.

Effect on Pollen Viability. — Sandsten"* collected pollen from old
apple trees in a poor state of vigor and at the same time from strong young
trees of the same varieties in an adjoining orchard. The average percent-
age germination of the first lot was 39.8 while that of the second lot was
56.5. The average number of hours required for germination of the pollen
from the strong trees was 19.8 ; for that from the weak trees, 28.7. Though
these differences may not be great enough under average conditions to
account for much failure to set fruit, it is conceivable that they may
be of real importance under some conditions. Furthermore, it is possible
that greater differences frequently exist between the pollen of strong and
weak blossoms of other varieties and of other fruits.

Effect on Defectiveness of Pistils. — Goff^^ reported the percentage
of defective pistils borne by trees of the American varieties of plums and
consequently their fruitfulness to be closely correlated with nutritive
conditions within the tree. Exhaustion or weakening one season by
overbearing, drought or poverty of soil was found to induce the production
of many defective pistils the following spring. He suggested thinning as

UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 505

a preventive. Dorsey^^ has observed the same occurrence in the plum
group in Minnesota. He mentions two cases 'in particular: "One
variety, Wickson, bore two heavy crops of crossed plums in the greenhouse
and the following year all pistils were aborted. In the second instance,
Wolf under orchard conditions bore heavily in 1914, and for three con-
secutive seasons afterward produced less than 1 per cent of normal
pistils." Hendrickson^^ mentions two French prune trees in California,
one of which bore a heavy and the other a hght crop in 1916. In 1917 the
conditions of these two trees were reversed. Paralleling these alter-
nations in crop yields were differences in the actual percentage of blossoms
setting and maturing fruit. In each case the light crop was due partly
to a poorer setting of the blossoms through exhaustion from heavy bearing
the previous season.

Fruit Setting of Flowers in Different Positions. — Some fruits, like the
plum and cherry, bear on both shoots and spurs and it is to be
expected that slightly different nutritive conditions obtain in these diff-
erent tissues. Dorsey" studied fruit setting of the plum in these positions
and found a distinctly heavier June drop in the shoot-borne fruits. Some
of his observations are particularly interesting:

"In the varieties available in this investigation^"" there was a pronounced
June drop in the plums borne on the terminal wood. In fact, on the older trees
fruit seldom matured in this position. The dropping of fruit from the terminal
growths can be partly accounted for on the basis of the competition from a
thorn or branch which is developed between the lateral fruit buds on the terminal
twigs the second season. This condition occurs over the entire outer area of the
tree. . . . Under favorable conditions fruit matures on the terminal shoots,
but the percentage to set is small considering the mass of bloom, and even the
small setting noted above is far in excess of the usual condition when there is a full
crop on the remainder of the tree. It is apparent that in this position competi-
tion takes place between fruit and branch as well as between different fruits."^'

Strong and Weak Spurs. — A number of important correlations have
been reported between fruit setting in the apple and nutritive conditions
in the spurs or limb upon which the blossoms are borne. ^^ As between
limbs from the same trees, on those with a light bloom 73.8 per cent of
the spurs set fruit, while on those with a heavy bloom only 14.1 per cent
set fruit. Of the spurs on vigorous limbs with large leaves 41.6 per cent
set fruit; 15.7 per cent set on weak limbs with small leaves. Spurs that
lost all their flowers and fruit at the time of the first drop had the smallest
average number of flowers (4.45) and those that flnally set had the largest
average (5.74). Furthermore, a slightly higher percentage of the flowers
borne on spurs with many flowers actually developed into fruits than of
those borne on spurs with few flowers. Of 2066 spurs making more than
1 centimeter growth in length in 1915, 791, or 38.3 per cent, set fruit
in 1916; of 3,171 spurs making less than 1 centimeter of growth in length

506

FUNDAMENTALS OF FRUIT PRODUCTION

in 1915 only 561, or 17.7 per cent, set fruit in 1916. Five hundred
ninety-five flower-bearing spurs of several varieties that set fruit
averaged 2.55 grams in weight; 760 flower-bearing non-setting spurs
of the same varieties averaged only 1.50 grams in weight. Table 3 shows
stiU more clearly the influence of weight of spur on its fruitfulness. In
a series of defoliation experiments Heinicke found that though 50.6 per
cent of the check spurs set fruit, only 47.6 per cent of those partly defoli-
ated and 20.2 per cent of those completely defoliated set.

Table 3. — Weight op Baldwin Apple Spurs Holding Fruits Varying Lengths

OF Time

(After Heinicke^^)

Time spur held fruit

Number of spurs

Average weight
in grams

Until first drop ...

30

28
30

2 94

Until June drop

3 29

4 27

Evidence Jrom Ringing Experiments. — Certain plants which under
ordinary circumstances would not set and develop fruit partheno-
carpically have been made to do so by ringing or girdling and thus leading
to the accumulation of an extra store of food materials above the injury.
Instances of this kind have been recorded in the gooseberry''^ and grape.'*
That ringing often does not have such an influence on fruit setting is
indicated by certain experiments with Nicotiana.^^^ It is probable how-
ever that ringing has quite different effects on various plants and broad
generalizations cannot be made from the available data.

Evidence from Starvation Experiments. — Kusano^^ produced experi-
mentally a series of extreme nutritive conditions in an orchid belonging to
Gastrodia, at the time of fertilization and during the period of develop-
ment of the fruit by partly or completely separating the ovaries from their
source of food. Though the results he obtained probably would not
apply generally to the developing fruits of other species treated similarly,
they are instructive in pointing out some of the relations existing between
fruitfulness, sterility and nutritive conditions. The following quotations
from Kusano's report summarizes his findings:

"Imperfect or almost no fruit, but normal seed with embryo: where the
normally fertilized flower is separated from its nutritive connection.

"Imperfect or almost no fruit, and nearly normal but embryoless seed:
when the unpoUinated flower is parted from its nutritive connection ; the number
of seeds is exceedingly diminished.

"Imperfect or almost no fruit and seed, but almost normal embryo: when
the fertilized flower is subjected to an extremely unfavorable condition of nutri-

UNFRUITFULNESS ASSOCIATED WITH INTERNAL FACTORS 507

tion. In this case the typical integument is quite suppressed in development
and the ovular tissue developed previous to the fertilization stage partakes of the
formation of the imperfect seed-coat. . . .

"From the above we see that the embryo does not require during its develop-
ment the accompaniment of the normal development of the ovarial wall and
the sporophytic ovular tissue and that the seed-coat alone can develop com-
pletely, independent of the formation of the embryo, or of the normal develop-
ment of the fruit-wall. But it must be remembered that a nutritive condition
which renders the development of the fruit-wall unfavorable may bring about a
small amount of embryoless seed.

"In the process of fruitification the embryo is placed in the first rank for
development; if the nutritive condition is favorable, it accompanies the develop-
ment of the seed-coat and fruit- wall; if not, only the latter portions are in high
degree retarded in development. A similar relation may exist between the
fruit- wall and the embryoless seed; under the condition which induces most
ovules to develop into embryoless seeds the fruit-wall develops most vigorously;
under an insufficient supply of nutritive substances the number- of the seed-
forming ovules is diminished, and in this case the fruit-wall is sacrificed for
development; in the extreme case of an insufficient nutrition both the fruit-wall
and a larger number of ovules are suppressed in development, thereby supplying
limited nutritive material to a few ovules, enabling them to form seed. . . .
The development of the fruit-wall alone under entire suppression of the ovular
development is found in some instances of the habitual parthenocarpy."

It may be noted in passing that the influences of the nutritive condi-
tion of the plant upon fruit setting, fruitfulness and fertility that have
been pointed out have been in part upon pistil or pollen abortion and thus
more or less indirect and they have been in part direct in apparently
affecting the ability of the developing seeds or fruits to complete their
maturing processes. No direct or indirect influence on compatibility
has been noted. On the other hand, experimental studies with chicory
have led to the conclusion that, at least in that species, "self compati-
bility and self incompatibility operate independently of the purely
nutritive relations of the embryos to their parent plants." ^^^

Summary. — The individual plants of many species and likewise many
bud-propagated varieties are self unfruitful because their flowers are
unisexual and flowers of but one sex occur on a single plant. Among
deciduous fruits often self unfruitful from this cause the kaki or Japanese
persimmon and the strawberry are the most familiar. Of more general
occurrence among fruits is dichogamy. Though seldom complete,
it accounts for the failure of many individual blossoms to set fruit and
emphasizes the importance of planting with cross pollination in mind,
even though the varieties in question are partly self fertile. Heterostyly
is not important in limiting the "set" of deciduous fruits. Impotence
(partial or complete) resulting from the degeneration of pistils or ovules
is very common among certain deciduous fruits. Many varieties,

508 FUNDAMENTALS OF FRUIT PRODUCTION

particularly of grapes, produce large numbers of impotent pollen grains
and they have all the appearance of perfect-flowering sorts, though
in reality they are pseudo-hermaphrodites. If the embryo sacs degen-
erate and fruit still forms, seedless specimens are produced. The self
sterility of many varieties is associated with the hybrid condition of
the plant. Hybrids between rather distantly related forms are likely
to be self sterile and often self unfruitful as well. On the other hand,
there is some evidence that very narrowly bred varieties or strains are
rather inclined to sterility. When sterility is due to hybridity it is
likely to be associated with pollen or embryo sac degeneration. Incom-
patibility is another cause of much self unfruitfulness. This is par-
ticularly important in the apple, pear, plum and cherry. Not only are
some varieties self unfruitful but incompatibility exists between them and
certain other varieties. This characteristic has immediate importance
in the sweet cherry and almond. In some cases failure to set fruit
properly is due to premature or delayed pollination or to a slow growth of
the pollen tube. Unfavorable nutritive conditions within the plant are
responsible for much failure in fruit setting. Trees that have been
weakened by overbearing or other causes are very likely to produce
pistils which are defective or pollen that is low in vitality. There is often
considerable difference between flowers borne in various positions, or
between those borne on strong and weak limbs, in their abilities to set
fruit.

CHAPTER XXVIII
UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS

Practically every phase of the environment to which the plant is
subject just before, at and shortly after the time of blossoming has
some effect on fruit setting. The influence may make itself felt through
rendering the plant or the variety more or less completely dichogamous,
through the production of more or less defective pistils, ovules, embryo
sacs or pollen grains, through affecting compatibility, indirectly through
aiding or interfering with pollen transfer or in a number of other ways.

Nutrient Supply. — It is often impossible to distinguish clearly between
the influence of nutritive conditions within the plant and of conditions
of nutrient supply without upon fruit setting, fruitfulness and fertility.
Though the nutrient supply available to the plant probably acts upon
fruit setting and development largely through first influencing nutritive
conditions within, there are so many cases in which the association
between the two is so evident that the intervening effect of the environ-
ment upon nutritive condition within is overlooked. Furthermore,
nutritive conditions within the plant are controlled more readily by
affording or withholding certain nutrients than by most other means.
It is therefore desirable to give some attention to nutrient supply as it
influences fruit setting and fruitfulness.

. Darwin" states that much manure renders many kinds of plants
completely sterile. He cites Gartner as authority for the statement that
sterility from overfeeding is very characteristic in certain families,
Gramineae, Cruciferse and Leguminosae being mentioned specially. In
India Agave vivipara is said invariably to produce bulbs but no seeds when
grown in a rich soil, though when it is grown in a poor soil without too
much moisture the converse condition holds. ^s On the other hand
extreme poverty of soil often leads to dwarfing and sterility, certain spe-
cies of clover being mentioned particularly in this connection." Sand-
sten^^^ found that excessive feeding of tomatoes caused abnormal flowers.
In some instances the stamens almost aborted; in others the pistils were
greatly thickened and overgrown. There was a general tendency for the
overfed plants to produce fruits with fewer seeds. Two plants produced
seedless fruits of normal size. Though these two plants produced many
flowers they set fruit poorly. The Jonathan apple, which is usually self
sterile or nearly so on rich land in Victoria (Australia) , becomes self
fruitful when grown on land of low productivity." The Hope grape,

509

510 FUNDAMENTALS OF FRUIT PRODUCTION

which is classified as a perfect flowered variety of the Muscadine group,
produces true hermaphrodite flowers only when given proper cultivation
and care.^^ Under neglect "its pistils gradually cease to function and
the vine assumes the general role of one that is staminate." This is just
the reverse of the condition found in the Hautbois race of strawberries,
which is reported as perfect flowered and productive when grown under
ordinary culture, though in a rich soil the stamens develop poorly and
produce little good pollen, the result being a poor setting of fruit. ^*

The data presented in Table 69 of the section on Nutrition are
particularly pertinent. Applications of nitrate of soda to the trees a week
or 10 days before blossoming increased the set of fruit by as much as 300
per cent in some instances. Data are not available to show just how the
fertilizer applications increase fruit setting, though recent investigations
indicate that a high nitrogen content in the spur itself favors that
process.^^ The results of these and similar experiments in other parts of
the country and with other fruits are of far reaching practical importance,
for they indicate that fruit setting may be much more completely and
directly under control than has been realized.

Pruning and Grafting. — Pruning and grafting result in a changed
environment for at least portions of the plant and in changed nutritive
conditions within the entire plant or within certain parts. The general
influence of these practices on vegetative growth and fruitfulness is
discussed in some detail in the sections on Propagation and on Prun-
ing. In addition to those indirect influences on fruit production, how-
ever, they often have a more direct influence on fruit setting. Thus
Darwin^^ states that plants of Passiflora alata as grown in England are
generally self sterile. However, at Taymouth Castle one plant of this
species grafted on an unknown variety became entirely self fertile.
Pinching the growing tips of the shoots of certain European grape varie-
ties when they are 18 to 24 inches long and the blossom bunch is well
formed helps materially in the setting of the fruit. ^ Pruning, along with
other practices, is reported to be one of the means of keeping the Hope
grape (one of the Muscadine group) in a true hermaphrodite condition. ^^
If this is neglected the variety tends to sterihty through a weakening and
an abortion of its pistils. The Malta orange grafted on rough lemon or
"khatti" stock in Baluchistan produces fruits averaging 16 to 17 seeds;
when grafted on the sweet lime the fruits of the same variety average
but seven seeds. ^^ In this case the trees have remained fruitful, but
fecundity has been modified. Though data on this question as it pertains
to deciduous fruits are almost lacking, there is reason to believe that the
subject is often of real importance in commercial production.

Locality. — Fruit setting on trees of the same variety is often much
better in one locality than in another. It might be possible to segre-
gate the various factors of soil, temperature, humidity, light, etc.,

UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 511

that constitute what is termed locality and to assign to each its portion of
the total influence on fruit setting. This, however, is often difficult and
from the grower's standpoint it is only the environmental complex and
the plant's response to it that are discernible. Therefore it is suitable
to make some mention of the influence of localitj^ in fruit setting, without
attempting a detailed analysis.

The common lilac is said to bear seeds moderately well in England
but in parts of Germany its capsules never contain seed.^^ The America
grape has been found self sterile in the Experiment Station grounds at
Columbia, Mo., though it has been reported perfectly self fertile farther
south. "2 Since the immediate cause of self sterility in the American
varieties of grape is of two general types — pollen abortion and degeneration
in the generative nucleus — locality may be considered to have an influence
on pollen development. Acoinis calmnus, when grown in certain parts
of Europe, becomes sterile through the degeneration of both pollen grains
and embrj^o sacs.^*^ The Jonathan apple is often self sterile in Victoria
( Australia), ^^ though in the United States it is almost invariably self
fertile. As self sterility in the apple is due usually to incompatibility or

Table 4. — Pekcentace of Defective Pistils i\ Burbank P
{After Waugh''*)

LUM

Source of flowers

Per cent
defective

Source of flowers

Per cent
defective

Denison, Tex

Santa Rosa, Cal

Stark ville Miss

27
0
9

36

Phoenix, Ariz

Manhattan, Kan

Parry, N.J

5

21
0

Auburn, Ala

embryo abortion, the conclusion seems warranted that it is in one of
these ways that the difference between the localities produces this dis-
tinctive effect on fruitfulness.

Still another way in which the factors characteristic of locality influ-
ence fruitfulness is in the production of defective pistils. Waugh^'*
obtained flowers of the Burbank plum from different sources and found
the percentages of defective pistils to be as shown in Table 4. He found
all the pistils of Rollingstone defective in flowers obtained from Minnesota
City, Minn., and none in a lot obtained from Lafayette, Ind. He
observed also that in some seasons certain plum varieties were protogyn-
ous in one locality and protandrous in another.

A case in which self fertilitj^ and fruitfulness vary according to locality,
apparently through some influence on compatibility, was mentioned by
Darwin. ^'^ He stated that " Escholtzia is completely self sterile in the
hot climate of Brazil, but is perfectly fertile there with the pollen of any

512 FUNDAMENTALS OF FRUIT PRODUCTION

other individual. The offspring of Brazihan plants became in England
in a single generation partially self fertile, and still more so in the second
generation. Conversely, the offspring of English plants, after growing
for two seasons in Brazil, became in the first generation quite self sterile."

Season. — Just as it is almost impossible to separate the influence on
fruit setting of nutritive conditions within the plant from those of nutrient
supply without, so it is almost impossible to distinguish the influence of
locality from that of season. Seasonal variations at the same place may
give rise to practically the same changes in environment as are occasioned
by differences in localities during a single season. When this is true
approximately the same responses to the changed conditions would be
expected. Darwin^^ stated that Kolreuter had several plants of Verhas-
cum phoeniceum that for 2 years flowered freely and, though self sterile,
were interfertile with other plants, but that later "assumed a strangely
fluctuating condition, being temporarily sterile on the male or female
side, or on both sides, and sometimes fertile on both sides; but two of the
plants were perfectly fertile throughout the summer." Trees of the
native plum varieties have been found to vary greatly in fertility from
season to season^^ and a plum variety that is protandrous one season
may be protogynous the next."*

An interesting case of a return of the potato to the fertile condition
through seasonal influences has been observed in the Greeley district of
Colorado.*^ The Pearl variety as grown in that section usually pro-
duces no flowers. During seasons that are unfavorable for the normal
development of the plant and its tubers, however, flowers are formed on
the late branches. Though ordinarily the blossom buds of the potato
fall off, in this case they opened but no pollen was produced. Thus the
degeneracy from the standpoint of the potato grower is accompanied by
some added development in the direction of fruitfulness. A ''bastard"
type is described as occurring sometimes in the Greeley fields of this
variety; in this there is still further degeneration of the tuber-bearing
habit, but an abundance of potent pollen is produced.

End-season Fertility. — End-season fertility of normally self sterile
plants is rather common. Whitten^^^ reports that, "during 1897, Ideal,
a hybrid (grape) variety, proved to be self impotent early in the season
but self potent later on, the season being favorable to a succession of
bloom throughout the summer." He states that since the vine had
little fruit to carry, it made a vigorous growth and bore a succession of
flowers. The appearance of the self fertile condition late in the season
was accompanied by an increasing uprightness of the stamens and pre-
sumably with the formation of good instead of sterile pollen. A gradual
decrease in the percentage of defective mango pollen has been noted as
the season advanced. ^''^ East and Park^^ found end-season fertility
developing in their self sterile Nicotiana plants. In this case the imme-

UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 513

diate cause of the normal self sterility was a slow growth of the pollen
tubes, presumably a result of chemotropic influences; the appearance
of the self fertile condition followed an acceleration in pollen growth.
These investigators remark: "Since we have reason to believe that the
difference between a sterile and a fertile combination in these plants is the
ability of the pollen grain through something inherent in its constitution
to call forth in the tissue of the style in the former and not
in the latter case a secretion which accelerates pollen-tube growth, it
follows that in weakened style tissue some change has occurred that renders
this secretion more easily produced." They report that self sterility can
be restored in these weakened plants by allowing them to go through a
period of rest and then forcing them into vigorous growth. Their sugges-
tion that "truly self fertile plants cannot be forced into self sterility by
any treatment" obviously holds if self fertility is defined to agree with that
concept. However, if that is to be the concept of self fertility it may be
questioned whether any of our cultivated fruits be self fertile. In the
fruit plantation there are fruit setting, fruitf ulness and fecundity conditions
which vary with environment.

Contrasting sharply with the end-season fertility that has just been
mentioned as sometimes occurring in the grape, mango and tobacco is an
end-season sterility found by Valleau^^'^ to be quite common in the
strawberry.

A striking example of seasonal influence on fruit setting and fruitful-
ness occurs in figs of the San Pedro class. -^ In varieties of this group the
early crop, or brebas, set freely without pollination, developing seedless
fruits. The later main or summer crop will not set and mature without
caprification. This, like the strawberry, is particularly interesting both
because it is an instance of early season rather than late season fruitful-
ness and because it is a constant characteristic of these varieties.

Change of Sex with Season. — Related to the influences of season on
fruit setting, fruitfulness and fertihty, or, more accurately, to be mentioned
as the immediate explanation of some of those influences, are the occa-
sional effects of season upon the complete suppression of one or the other
of the two sex organs, its effect upon their development when normally
they are undeveloped or non-functional and its effect upon change of
sex. The sweet gale or bog myrtle {Myrica gale) is a small shrub which
grows abundantly in the swamps of Europe, Asia and North America.
It is described by many authorities as strictly dioecious. However, it has
been found that intersexes or mixed plants of many gradations are present
everywhere in the peat moors of England. ^^ Furthermore, a .study of
individual plants for a series of years showed that changes of sex occurred
from year to year. Plants entirely female in 1913 were entirely male in
1914. Plants female in 1913 were mixed in 1914, entirely male or nearly
all male in 1915 and again female in 1916. There is a record of a hybrid

514 FUNDAMENTALS OF FRUIT PRODUCTION

grape vine (F. riparia X V. labrusca) which fruited only twice during a
30-ycar period, "the pistils evidently varying in strength but being gener-
ally too weak to produce fruit. "^ Though the date palm is usually
monoecious, still a tree that ordinarily produces pistillate flowers only may
develop occasionally a cluster of staminate flowers, or perhaps one year
produce a few hermaphrodite flowers and never do so again. ^^^ Certain
varieties of the Japanese persimmon show great variation in the kinds
of flowers they bear from year to year. 2"; ^o jj^ some seasons they
produce pistillate flowers only and in other seasons they produce a num-
ber of staminate flowers along with the pistillates. "Seedling (per-
simmon) trees are very unreliable in the production of blossoms, bearing
male flowers during the first few years, then a small proportion of female
flowers, while later the appearance of male flowers is sporadic on some
trees and regular on others. "2"

Age and Vigor of Plant. — Practically inseparable from the influences
on fruit setting of nutritive conditions within the plant, of nutrient
supply without, of locality and of season, is that of age and vigor. The
change from the production of staminate flowers only to that of some
staminate and some pistillate flowers and later of pistillate flowers only,
mentioned in a preceding paragraph as common in seedlings of the
Japanese persimmon, is a case in point. Young vigorous apple trees
often fail to set fruit under controfled cross pollinations, when older and
less vigorous trees of the same varieties set freely. ^"'^ Waugh^^* found on
the average a higher percentage of defective pistils in young and vigorous
plum trees than in older trees of the same kinds. The Muscat of Alex-
andria grape is reported to show marked susceptibility to "coulure" or
dropping for the year or two after starting to bear, but later this trouble
is much less serious.^ Young grape vines have been found to produce
less pollen than mature vines of the same variety.^

In the instances cited, age of plant has been the factor apparently
associated with the degree or percentage of fruit setting. It is probable,
however, that age is effective through its influence on vigor and the
internal conditions of nutrition or hybridity with which vigor is asso-
ciated. It is interesting that Stout found self compatibility in chicory
entirely independent of differences in vegetative vigor, thus suggesting
that some of the internal factors controlling fruit setting and fertility are
not influenced by vigor. As in the cases where fruitfulness is influenced
by variations in nutritive conditions, nutrient supply, locality and season,
most of the influence of varying age and vigor seems to be through
effects on impotence preceding fertilization and embryo abortion at a
later stage and not on compatibility, using that term in its narrower
sense.

Temperature. — The general effect on the setting of fruit of tempera-
tures slightly below freezing just before, at or shortly after blossoming is

UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 515

well known and in the section on Temperature Relations is a some-
what detailed account of the more important factors in frost occurrence
and their bearing upon fruit production. However, temperatures well
above the freezing point often are important in determining the setting
of fruit. Darwin^s calls attention to the rather common failure of
European vegetables to develop fruits and seeds when grown in India and
attributes this failure to the hot climate of that country. In some of
these instances the influence of temperature may be more directly upon
the formation of flower buds and flower parts than upon the processes of
fruit setting.

Goff^^ has shown that though pollen of most deciduous "fruits, like
the plum, cherry, apple and pear, germinates freely at temperatures of
50°F. or above, the process is practically inhibited by temperatures of
40°F. or lower. In a number of plums the stigma is receptive for a
period of only 4 to 6 days. The abscission of the style occurs in from
8 to 12 days after bloom and it is not influenced to any great extent by
temperature.^^ On the other hand, the period required for the germina-
tion of the pollen grain and its penetration of the style may depend on
temperature and may be as short as 4 days and as long as 12. A period
of cool, but frostless, weather during blossoming, therefore, may prac-
tically prevent fertilization and thus very materially limit the set of fruit.
Presumably similar conditions are found in many other fruits, though
the relative importance of this factor varies greatly with different
species and varieties.

In this connection mention should be made of the indirect influence
of temperature on fruit setting through its effect on the activity of pollen-
carrying insects. Evidently the temperature at which bees and other
pollen-carrying insects will work depends on conditions, for 40°F. has
been given as the lowest temperature at which the honey bee will take
flight^^ though normally they do not leave the hive until the temperature
reaches about 60°F., except after a considerable period of confinement.
Whatever the exact temperature may be, it is evident that should all
other conditions be favorable a continued period during blossoming well
above freezing but still too low for much activity of the pollen-carrying
insects may account for many failures in fruit setting.

An interesting example of the influence of temperature on fruit setting is
furnished by the papaya. Though usually a strictly monoecious plant, the
"male" form sometimes bears fruit in cool climates. In commenting on the
change of sex here involved Higgins and Holt remark: ^^ "This 'fruiting of the
male papaya' takes place most freely in cool climates outside the tropics or at
high altitudes. In Hawaii it may be seen that these trees fruit more abund-
antly on the mountains than near the sea level. Information received by cor-
respondence with experiment stations and botanic gardens in many parts of the
world, in reply to direct inquiry, have confirmed this conclusion. In torrid cli-

516 FUNDAMENTALS OF FRUIT PRODUCTION

mates the fruiting of the male is rare. It is to be remembered in this connection
that all the staminate flowers of the male trees possess an undeveloped or an
abortive pistil. The only change in the cases mentioned consists in the develop-
ment of this pistil."

Light. — It is doubtful if variations in light supply are important
with deciduous fruits. However, it is of some interest that the willow-
herb (Epilobiu7n angustifolium) develops its flowers normally and sets
fruit and seed freely in open sunny situations but when shaded its flower
buds abort and fall off before opening. ^^ In fact, this is true of many
plants.

Disturbed Water Relations. — In the section on Water Relations
it is shown that conditions of low atmospheric humidity, high tempera-
ture, exposure to high winds and a limited supply of soil moisture some-
times induce in trees moisture deficits that lead to the formation of an
abscission layer and the dropping of the blossoms or fruits. The water
loss in developing Washington Navel orange fruits at and shortly after
midday has been shown to be as much as 30 per cent.^^ Practically the
same conditions have been found responsible for much of the shedding
of the developing bolls in cotton.*^ Studies of boll abscission in cotton,
however, led to the conclusion that the water deficit in the leaves and
stems was only indirectly the cause of abscission since the water deficit
produced in the tissues a rise in temperature which was "the stimulus
which directly leads to abscission."

The dropping of flowers or partly developed fruits that is due to
water deficits is partly under control. Irrigation, tillage, the use of
certain cover crops and windbreaks are among the more important
means that tend to lessen the difference between absorption and trans-
piration in times of stress.

Discussing the shedding of cotton balls because of water deficits Floyd ex-
plains how a surplus of water may act in the same way. He says:

"If the general conclusion that the grand march of shedding is due to the
depletion of moisture in the deeper soil be true, irrigation and better soil manipu-
lation are indicated as remedies. It has been shown experimentally by Barre,
in South Carolina, that irrigation has the effect of inhibiting shedding. The
observations of Balls that the rise of the water table in Egypt due to the Nile
floods, by asphyxiating the deeper roots and so limiting the water supply, causes
severe shedding, are quite in harmony with the above findings, since too much
water may have quite the same effect as too little, and suitable drainage is thereby
indicated as surely as irrigation. "^^

Not only may a water deficit lead to the dropping of flowers and newly
set fruits, but it has been shown experimentally that very high atmos-
pheric humidity tends to cause the abscission of partly developed apples.^'

Rain at Blossoming. — Rain at blossoming is recognized generally
as one of the most important factors Umiting the set of fruit.

UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 517

The following regarding weather conditions at blossoming time in New
York verifies this statement;*" "Wet weather almost wholly prevented the
setting of fruit in New York in the years 1881, 1882, 1883, 1886, 1890, 1892 and
1901. Rain is mentioned as one of the causes of a poor setting of fruit in the
years 1888, 1889, 1891, 1893, 1894, 1898, 1905. . . . Rain and the cold
and wind that usually accompanj' it at blossoming time cause the loss of more
fruit than any other cUmatal agencies. The damage is done in several ways.
The most obvious injury is the washing of the pollen from the anthers. The
secretion on the stigmas also is often washed away or becomes so diluted that the
pollen does not germinate. It is probable that the chill of rainy weather decreases
the vitaHty of the pollen and an excess of moisture often causes pollen grains to
swell and burst."

Experimental evidence on the damaging influence of rain on fruit
setting is furnished by an experiment in which a Mount Vernon pear
tree was sprayed continuously for 219 hours while in bloom. ^^ This
tree set very little fruit while a tree of the same variety standing nearby
and not subjected to such treatment set a good crop. Similar results
were obtained with two Duchess grape vines.

However, plants possess many protective devices which serve to
reduce injury to their blossoms from rain. Thus in Vaccinium and
many other genera the flower is pendent and the essential organs are
protected by a bell-shaped corolla; in Opuntia and many others the
petals close over stamens and stigma during damp weather; the male
racemes of the Juglandacese and Cupuliferse are pendulous and shed
water almost perfectly when mature and in Vitis anthers that have
dehisced and shed part of their pollen close and shut out water upon the
advent of rain." In the investigation just citied, it was found that
pollen of the Duchess grape when examined under the microscope
after 11 days of continuous spraying was apparently uninjured.'*^ Work
with the plum has shown conclusively that after pollination the pollen
is washed from the stigmas only with great difficulty and that stigmas
will secrete their fluid a second time if rain removes that first secreted. ^^
Rain, however, is usually accompanied by temperatm-es below those
characterizing fair weather at the same season. Thus Hedrick in the
report just cited states that "rainfall came in periods of prolonged cold
weather in the years 1881, 1882, 1883, 1886, 1888, 1889, 1891, 1892, 1894,
1898, 1905. Frosts and cold weather accompanied the rains in 1888, 1889,
1890, 1891, and 1892." In the light of these and many other observa-
tions and findings as to the distinctly different effects of low temperature
on rate of pollen tube growth and time of style abscission, it may be
questioned if rain at blossoming is in itself a very important factor in
limiting the set of fruit. Other conditions, particularly lower tempera-
tures, with which rain is generally associated, and interference with the
work of pollen-carrying insects, are more important. This statement

518 FUNDAMENTALS OF FRUIT PRODUCTION

is not made for the purpose of minimizing the importance of "rainy
weather" at blossoming in reducing the fruit crop. It is desirable,
however, that there be a correct understanding of the relative importance
of the different factors that usually constitute "rainy weather" and that
there be a realization that even a hard rain, if of short duration and not
accompanied by very low temperatures, is not ordinarily a serious limit-
ing factor in this connection.

Wind. — The average fruit grower regards wind as one of the most
important agents in the transfer of pollen from stamen to stigma. Many
plants, such as the walnuts, oaks, hickories and hazels, are wind-polli-
nated and with these a reasonable amount of wind at blossoming is a
distinct aid in securing a good set of fruit. However, the majority of
the deciduous fruit crops are insect-pollinated. With these, wind hinders
rather than helps pollination, since bees and other pollen-carrying insects
work most effectively in a still atmosphere and in a strong wind they
refuse to work at all. Abundant evidence on this point may be found
in orchards with some exposed and some protected situations. Other con-
ditions equal, there will be a much better set of fruit where the trees are
protected from the full sweep of the wind and in exposed places there is often
a much better set on the leeward than on the windward side of the trees.
In addition to the indirect effect of wind through interfering with
the work of pollen-carrjdng insects, it may operate more directly in whip-
ping about the flowers and causing mechanical injuries. It may also cause
the stigmatic fluid to dry prematurely and thus prevent the germination
of the pollen grains. In some species at least, the action of wind is more
pronounced early in the usual period of pistil maturity than later. ^^

There are many cases in which the protection afforded the fruit
plantation at the time of blossoming is of greater importance than any
other service rendered by a windbreak.

Fungous and Bacterial Diseases. — The flowers of many species are
subject to the attacks of various fungous and bacterial diseases and often
their work at this time is serious enough greatly to reduce the set of
fruit. Thus fire blight is generally recognized as one of the most impor-
tant factors in limiting the set of fruit in pears; the apple and the pear
scab are responsible for the falling of many flowers of those fruits at or
shortly after blossoming; brown rot attacks the blossoms of practically
all the stone fruits; black rot works on grape blossoms, causing many
to drop; the flowers of the mango^"® are attacked frequently by an
anthracnose; the list might be extended almost indefinitely. Naturally
the losses occasioned by these fungous and bacterial attacks at the time
of fruit setting vary greatly with locality, variety and seasonal conditions.
For instance, there are certain restricted areas where fire blight of the
pear and apple is not found, though the disease may levy a very heavy
toll on pear blossoms a hundred miles distant. The Grimes apple is but

UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 519

little subject to the scab fungus and ordinarily its setting of fruit will not
be materially reduced by it, though a Winesap crop in the same orchard
may be practically ruined by its work upon the blossoms. In California
brown rot is a serious disease on the blossoms of the apricot only in
"regions exposed to ocean influences and does not develop except in
times of unusually moist weather.""^

Fortunately most of the fungous and bacterial diseases that attack
the blossoms of fruit trees can be controlled by spraying or other preven-
tive measures; consequently losses due to these factors are avoidable in
many cases.

Spraying Trees When in Bloom. — Though spraying trees with the
proper materials may be effective in preventing the attacks of certain
diseases that otherwise would seriously reduce the set of fruit, it is not
necessary or desirable to spray during blossoming. Spray applications
at that time are seldom recommended and are generally regarded as
undesirable. They may reduce the set of fruit either directly through
injuring the pollen or stigma or indirectly through interfering with the
work of bees and other pollen-carrying insects.

Beach* made a number of laboratory cultures of pollen grains in
media to which varying amounts of Bordeaux mixture alone and Bor-
deaux mixture with an arsenical poison had been added. He found
that 200 parts of Bordeaux mixture to 10,000 parts of his culture media
practically prevented the germination of pollen and that much smaller
amounts had a distinct inhibiting influence. On the other hand in one
experiment sprajdng apricots when in bloom with the regular summer
strength of the lime-sulfur mixture and with a weak Bordeaux mixture
caused no injury to the flowers and no interference with fruit setting. ^^
This suggests at least that in actual field practice no great injury in
fruit setting is likely to result from the use of fungicides alone when trees
are in bloom.

Apparently the indirect effects on fruit setting of spraying with
arsenical poisons when trees are in bloom are much more serious. It
has been shown that a very small amount of arsenic — less than 0.0000005
gram of arsenious trioxide — is a fatal dose for a bee and most bees die
within a few hours after being poisoned. ^"^ Bees work as freely upon
sprayed as upon adjacent unsprayed trees. Price ^"^ found that the mor-
tahty of bees in a check cage was only 19 per cent., as compared with 69
per cent, in a lime-sulfur-arsenate of lead sprayed cage and as compared
with 49 per cent, in a sulfur-arsenate of lead dusted cage.

The suggestion is made that if it has been impossible to spray before
blossoming for the control of fungi which interfere with fruit setting and
such fungi are known to be present to a serious extent, spraying may con-
tinue into, or even through, the blossoming season, but a fungicide alone
should be used at that time.

520 FUNDAMENTALS OF FRUIT PRODUCTION

Other Factors that Cause the Dropping of Fruit and Flowers. — Many
other agencies besides those mentioned may occasionally cause flowers or
developing fruits to drop prematurely. Among these may be mentioned
the presence of small amounts of illuminating gas in the atmosphere.^*

BushnelP^ has found that fruit setting in certain cucurbitaceous
plants is characterized by a distinct periodicity. That is, flowers
opening during a 2- or 3-day period may set freely, those opening
during the next 2 or 3 days set poorly, then there is another period of
good setting and so on.

Summary. — The most important of the direct effects of the environ-
ment through the plant itself is in influencing nutritive conditions.
Soil type, water supply, fertilizers, cultivation and pruning are more
or less important in this connection. Low temperature and rain are the
two most important of the environmental factors indirectly affecting
fruit setting through affording or preventing the opportunity for pollina-
tion, the germination of the pollen grain and fertilization.

It is evident from the subject matter presented in this and the two
preceding chapters that the whole subject of fruit setting is complex.
In the first place it depends on a number of internal factors, many of
which are entirely beyond any direct or indirect control. Secondly,
blossoming generally comes at a season when great fluctuations in
temperature, humidity and the other features of environment are likely.
It is therefore not surprising that the response of the tree to the combina-
tion of all these interrelated factors and conditions varies from year
to year, from orchard to orchard and even from tree to tree. It is
fortunate indeed for the grower that the most important of the limiting
factors to fruit setting — both those internal and those external to the
plant — are within the grower's control by either direct or indirect means.

CHAPTER XXIX

FACTORS MORE DIRECTLY CONCERNED IN THE DEVELOP-
MENT OF THE FRUIT

The discussion thus far has been hmited mainly to a consideration of
the primary results of fertilization. From the grower's standpoint, how-
ever, the nature and extent of its indirect effects are often of equal or greater
importance.

The immediate or primary result of fertilization is the initiation of the
series of changes in the mature embryo sac leading to the development
of the embryo and endosperm. The changes subsequently occurring
in the ovarian wall and oftentimes in attached tissues result in the setting
and development of the fruit. These are the indirect or secondary
effects of fertilization.

Stunulating Effects of Pollen on Ovarian and Other Tissues. — Before
fertihzation takes place, the pollen often has an important influence on
the development of ovarian and other tissues connected with the fruit.
This effect is independent of the process of fertilization and may be exer-
cised though fertilization never occurs. For example, Wcllington^^^
secured fruits of the Seckel pear by applying to its stigmas pollen of the
Yellow Transparent apple, and Millardet^^ obtained fruits of certain va-
rieties of the European grape by employing pollen oi A^npelopsishederacea.
Presumably in neither case could fertilization occur, though the pollen
tubes may have entered the embryo sacs. Tritm-ated pollen applied
to the stigmas of certain curcurbits has induced a partial development of
their fruits ^° and fully formed but seedless fruits of certain species
have been obtained by applying to their stigmas spores of Lycopodium^^
In both of these cases fruit development must be attributed to the stimu-
lating influence of the pollen or spores. Goodspeed''^ reports that emas-
culated but unpoUinated flowers of the Thompson Seedless grape do not
set fruit; however, emasculated and pollinated flowers set freely, though
the resulting fruits are seedless because of embryo sac degeneration.

Some of the most interesting, and perhaps among the most striking,
cases of response to the stimulus of pollination are found among the
orchids.^' In most species of this family the ovule is in a very rudimen-
tary stage of development at the time of pollination. In some of these
if pollination is not effected the ovules never reach the stage at which
fertilization can take place, but immediately after pollination the tissues
of the ovule proceed to complete their development and finally reach the

521

522 FUNDAMENTALS OF FRUIT PRODUCTION

stage for fertilization. In many cases several weeks between the time of
pollination and fertilization are required for the ovules to reach maturity.

Kusano,^^ who studied the influence of pollination in stimulating the develop-
ment of the ovary and fruit in Gastrodia, found that many fruits would develop
in this genus when no pollination occurred. These parthenocarpic fruits were
normal in appearance, .though somewhat below the average in size. Seeds were
formed but they were without embryos and the number of these imperfectly
formed seeds was usually below that in fruits resulting from ordinary pollination.
When Gastrodia flowers are poUinated with pollen of Bletia, another orchid,
fruits likewise developed but they were much larger than the parthenocarpic
fruits developing without pollination, though they too were without embryo-
containing seeds and presumably no fertilization had occurred. Fruits of the
first category, that is, those developing without the stimulus of pollination, were
classed as instances of vegetative or autonomic parthenocarpy; those of the
second class were considered instances of stimulative or aitionomic partheno-
carpy. Commenting upon the results of some of his experiments, Kusano*^
remarks: "As regards the parthenocarpic development by the foreign pollen
two points may be worthy of consideration. First, the size of the resulting
fruit may depend on the intensity of the stimulus. This is evidenced by the
experiment with the Bletia-poUinium; pollinated the day of bloom, the poUin-
ium sends out massive tubes, leading the fruit to maximal growth, but the
delayed pollination brings about a feebler development of the tube, perhaps
owing to a certain modified condition of the stigma, and consequently smaller
fruits result. Further, the poUinia of other orchids yield smaller fruits than the
Bletia-pollinium, in conformity with the feeble development of the pollen-tubes.
Secondly, it may be most probable that the size of the fruit correlates with the
duration of the stimulus acted upon. The product of the normal-sized fruit by
crossing Bletia appears to be due to the longevity of activity of the pollen-tube,
remaining alive and vigorous far beyond the period of maturation of the fruit,
and thus exerting the stimulus unceasingly upon the ovules and ovary throughout
the interval of their complete development. ... As far as observed in
Gastrodia, we are led to the view that the ovarial development is correlated
with the embryogenic development of the ovules when the tube of its own
pollinium is concerned, but when it is induced by the foreign pollen tube, it is
likely comparable to the gall formation by the action of fungi or insects. So that,
though the kind of the stimulus is unknown, whether chemical or mechanical,
we may ascribe the resulting effect to an incessant stimulus of suflScient intensity."

The Effect of Certain Stimulating Agents on Fruit Setting. — It
has long been known that the fruits of certain species which seldom or
never develop parthenocarpically can be made to set occasionally by
treating the stigmas with certain stimulating agents other than pollen.
Indeed the use of Lycopodium spores, mentioned in a preceding paragraph,
may be regarded as a stimulating agent of this character. Hartley^^
secured a partial set of fruit in tobacco by treating receptive stigmas with
magnesium sulfate and other chemicals. The seeds of these fruits
were poorly developed and without embryos. Wellington, ^^'^ working
with the same species, obtained some fruits, likewise without good seeds,

THE DEVELOPMENT OF THE FRUIT

523

by "singeing young buds with a hot platinum wire, by exposure of young
plants to chloroform gas, and by cutting away a portion of the pistil and
pollinating the stub both with and without the accompaniment of a
germinative fluid." The ovaries of certain orchids can be made to
develop into fruits by the mechanical irritation of the stigmas. ^^

Closely related to the effects of mechanical irritation and of various
chemicals on fruit setting are those of the presence or the stings of
certain insects. Miiller-Thurgau" stated that the presence of a certain
gall insect would cause the setting of pear flowers and a brief rapid
growth of the fruit, though these insect-infested specimens fell before
reaching maturity. Figure 54 shows a flower cluster of the LeBrun pear
shortly after petal fall. The outside flowers had been pollinated, had
set fruit, and were developing normally; of
the two center specimens one had not been
pollinated and was about to drop; the other,
infested with the gall insect, had not only
set but was enlarging much more rapidly
than fruits developing normally. Kraus^^
reports that no.t only fruits but embryo-
containing seeds often develop from the
flower clusters of self sterile and self barren
apple varieties when those flower clusters
are attacked by aphids. The same devel-
opment has been recorded in the sweet
cherry.^" In such instances the resulting
fruits are generally much dwarfed and mal-
formed and seldom can the seeds be made
to germinate; as a rule the fruits contain
fewer and smaller seeds than normally devel-
oped specimens of the same varieties. ^"^

Some observations of Johnson"^ on this point are very interesting. Several
species of cacti often retain their fruits long after maturity. They may persist
for months or in some cases for years. Johnson, examining a large number of
plants of Opuntia versicolor in April and May, found only about 25 per cent,
bearing persistent fruits. However, about 9 out of 10 of those plants which did
bear apparently normal persistent fruits bore also abnormal gall fruits, the
result of the stings of one of the gall insects. This led Johnson to suggest,
"that the cause of the persistence of the normal fruits may be the same as the
cause of the abnormality as well as of the persistence of the far more common
gall fruits."

One of the most interesting cases of the influence of the presence
of insects, independent of their pollen-carrying activities, on fruit
setting is found in the male fig, or caprifig.2i)*0;ii2 These are not in
fact male trees; their flower clusters contain both staminate and pistillate

Fig. 54. — Fruit cluster of the
LeBrun pear. The central fruit
has been parasitized. The outer
two have set and are developing
normally. The other one is about
to fall off. In the cross section,
larvse are shown at g. {After
Midler-Thurgau.^'')

524 FUNDAMENTALS OF FRUIT PRODUCTION

flowers. Occasionally some of the pistillate flowers of these clusters are
pollinated and develop seeds, but as a rule if the Blastophaga wasps enter
the cluster they oviposit in the pistillate flowers and so-called gall flowers
result. While the larvae of the Blastophaga are developing in the gall
flowers the staminate blossoms of the cluster mature so that their pollen
is shed when the mature wasps are ready to emerge. Such flower
clusters on the caprifig are known as insectiferous figs. If, however, the
Blastophaga wasps do not enter these clusters at the stage when their
pistillate flowers are ready for pollination or oviposition, the cluster
may or may not persist until its staminate flowers mature their pollen.
(From a practical standpoint their remaining and maturing is of no
value, since no wasps are in them to emerge and carry pollen to the
flowers of pistillate trees.) Such clusters are known as polliniferous figs.
In any case they drop off before the insectiferous figs reach full maturity
and the dropping is in a way comparable to the June drop of many other
fruits. Since pollination is unnecessary for the setting and persistence
of the insectiferous fig it must be concluded that the mechanical or chem-
ical stimulus resulting from the insect's presence is the real cause of
setting. The growth stimulus changes the twigs and branches^" bearing
insectiferous figs so that they may be told readily from those bearing
only polliniferous figs by their thickness, length and general vigorous
appearance. This response, not unlike that frequently attending the
injection of some chemical substance into vegetative tissue, is at least
suggestive of the complexities involved in fruit setting.

Seedlessness and Parthenocarpy. — Seedless fruits are found in
practically all fruit-producing species. In some cases they are of rather
infrequent occurrence, their production apparently depending on unusual
conditions of culture or environment. In others they appear frequently
and many seedless strains or varieties have been established and are
propagated extensively by vegetative means. In such cases the seed-
lessness is due primarily to internal causes that are usually but little
influenced by changes in environment.

Investigations with the grape by Stout^^^ have led to this conclusion: "The
most effective course in breeding for the development of seedless sorts is suggested
by the conditions of intersexualism. Most individuals and varieties producing
seedless or near-seedless fruits are strongly staminate. The former can be used
as male parents on the latter, which do produce a few viable seeds. Plants
strongly male and seedless can be crossed with plants strongly male but weakly
female and near-seedless and, also, the self-fertilized progeny of the latter may
be obtained. In this way families weak in femaleness may undoubtedly be
obtained in which a considerable number of individuals will produce seedless
fruits."

Parthenocarpy refers to the ability of a plant to develop its fruit (1)
without fertilization or even (2) without the stimulus that comes from

THE DEVELOPMENT OF THE FRUIT 525

pollination. In other words, the growth of the ovarian and other
tissues of the fruit can occur without any stimulus from the accom-
panying development of the ovules into seeds, Parthenocarpic fruits are
usually, but not always, seedless. In some species fruits will develop
and viable seeds will be formed even if no pollination takes place. Such
plants are parthenocarpic and parthenogenetic at the same time. (Par-
thenogenesis is common in certain strawberry varieties.) Furthermore,
many parthenocarpic fruits contain aborted or partly developed seeds,
or seeds that, though normal in appearance, are incapable of germination.
On the other hand, not all seedless fruits are parthenocarpic. In some
cases seedlessness is due to embryo abortion some time after fertilization;
unless pollen had been available to furnish the stimulus for fruit setting
no later development of the fruit would have been possible.

It is evident therefore that seedlessness and parthenocarpy are
rather distinct phenomena though it frequently happens that the two
are associated.

Seedlessness of N on-'parthenocarpic Fruits. — The immediate cause
of seedlessness in fruits that have not developed parthenocarpically is
embryo abortion. This in turn may be due either to internal or to exter-
nal factors. Frost or freezing temperature after the fruit has set is
perhaps one of the most common of the environmental factors leading to
this condition; it has been observed repeatedly in pears, apples and
peaches. The developing embryo of the seed seems for some reason
more tender to low temperatures than the ovarian and other tissues
surrounding it. Consequently embryo development is arrested; how-
ever, if the growth of the fruit has proceeded far enough it will continue
through to maturity, though such fruits are often materially smaller
than those containing seeds. In many pear varieties, particularly
those that normally are either elongated or pyriform, the seedless speci-
mens are generally quite distinct in shape. ^^ Each has a shorter trans-
verse diameter through the core, but is much thickened at the basal end.
Sandsten^i^ has produced seedless tomatoes by excessive feeding.
Though no statement is made as to whether or not these fruits developed
parthenocarpically, it is presumable that pollination at least and prob-
ably fertilization took place and that seedlessness was due to embryo
abortion.

In a preceding paragraph it was shown that full matm'ity of the fruits
on a caprifig tree is usually attained only when some of its pistillate
flowers are inhabited by the developing Blastophaga wasp. Ordinarily
these fruits matm-e no seeds because few or none of the pistillate flowers
are pollinated. In this fruit, then, embryo abortion and seedlessness are
associated with a stimulus resulting from the attack of a certain insect.

Embryo abortion, resulting in seedlessness, is not, however, always
due to external factors. For instance, according to one investigator only

526 FUNDAMENTALS OF FRUIT PRODUCTION

about 25 per cent, of the fruits of the Blue Damson plums contained good
plump seeds. ^^ The remaining 75 per cent, were seedless or their seeds
were only half grown and non-viable. Many other plum varieties were
found to bear a large percentage of seedless fruits. Nevertheless, none
of these varieties developed fruit parthenocarpically and in some of them
cross pollination was necessary for any set at all. " The kind of pollen used
seems to have had little bearing upon the relationship of fruit production
to seed production, as the percentage of seeds developed in any variety
seems to be rather constant regardless of the kind of pollen used."^^
The same type of seedlessness has been observed in many sweet cherry
varieties, in the May Duke cherry reaching sometimes over 95 per cent,
of the fruits. Seedlessness that is not associated with parthenocarpy is
likewise frequent in some of the cultivated varieties of the filbert, where
it is a serious matter since seeds constitute the crop. A thorough study
would undoubtedly show that seedlessness is frequently associated
with embryo abortion in the developing seeds of many cultivated fruits.
Though in many varieties if seed abortion takes place at any stage
the fruit drops prematurely, in many others it can occur at a late, and
still others at an early, stage and still the fruit will persist and mature
properly. Evidently seedlessness from this cause depends on the
varying requirements of the ovarian tissues of different fruits for the
stimulus imparted to them by the growth of the partly developed
seeds within. Instances of this kind, however, probably always follow
fertilization.

Vegetative and Stimulative Parthenocarpy. — Distinction has been
made between vegetative or autonomic and stimulative or aitionomic
parthenocarpy. In certain species parthenocarpic development is
vegetative; in other species it is stimulative; in still others both kinds
occur. The cases of parthenocarpy that have been reported for a number
of species have not been studied carefully enough to make possible
their classification. Among the fruits reported as vegetatively partheno-
carpic may be mentioned the banana,^ many varieties of the Japanese
persimmon, ''°' ^^ certain mulberries, ^^ certain peach varieties, ^^^ the
medlar, ^2 i\yQ papaya,*^^ the egg plant, summer squash and the English
cucumber, ^^ a number of varieties of the orange^^*' and many varieties
of the fig.'*'' These fruits, or certain of their varieties, either occasionally
or regularly set and mature fruit without the stimulus even of pollination.
Among those that have been reported parthenocarpic when subjected to
certain stimuli, usually the stimulus of pollination, are the pepino,'*^
tobacco, *^^ pear^^^ and Jerusalem cherry. ^^^ Many varieties of Musca-
dine^^" and of Labrusca and Labrusca-hybrid grapes^ have been reported
as occasionally or sparingly parthenocarpic when subjected to the stimu-
lus of pollination with impotent pollen, and the Thompson Seedless^^ grape
is regularly parthenocarpic under similiar conditions.

THE DEVELOPMENT OF THE FRUIT

527

In discussing the influence of nutritive conditions within the plant
on fruit setting attention has been directed to their influence on
parthenocarpy. Apparently unusual accumulation of elaborated foods
in proximity to flowers in the receptive stage often acts as a stimulus to
further growth and development and in this way inhibits the formation
of an abscission layer much as would the stimulus occasioned by the
stings of certain insects or by developing seeds.

Relation of Anatomical Structure of Fruit to Parthenocarpy. — As
has been pointed out, seedlessness is to be expected at least occasionally
in almost every species and variety and it is probable that the same may
be said of parthenocarpy. It may be noted, however, that it is more
frequent in species whose fruits the botanist classifies as inferior, those
into whose structure tissues other than the ovary enter. Though this
may be a mere coincidence, it at least suggests that the greater stem-like
character of such fruits imparts to them a stronger tendency to persist

Fig. 55.

-Developing fruits of the LeBrun pear; a and d normal seed-containing
fruits; b, c, e and / seedless. (After Muller-Thurgau.^'')

than there is in those whose tissues when mature are entirely carpellary
in nature. They seem to be less in need of the stimulus of fertilization.
In Fig. 55 are shown pears of the LeBrun variety, one of which is develop-
ing as a result of the stimulus afforded by pollination and fertilization.
The other two are developing parthenocarpically. The greater develop-
ment of the stem tissues in the latter case is very suggestive.

Suggestive also in this connection are the following statements by Johnson^*
on the perennation and proliferation of the fruits of Opuntia fulgida. "It is
true that the vegetative joints and both the fertile and sterile fruits resemble
each other greatly in their capacity for proliferation. There seems no adequate
reason, however, for assuming that either the proUferating habit or the fimda-
mental structure of the fruit is a secondary thing in the evolution of the opuntias.
On the contrary, it is natural that the thick-skinned, water-stored joints of
these cacti should have proved capable of persisting on moderately moist soil
until rooted deeply enough to secure a water-supply adequate for the starting
of a young plant. The fruit being . . . really a stem in organization, up to

528 FUNDAMENTALS OF FRUIT PRODUCTION

the latest phase of its development, it is also very naturally capable of prolifera-
tion to root and shoot. The capacity of joint and fruit for persistence and pro-
liferation is probably as old as the fleshy character of the family. The persistence
of the sterile fruits, at least to maturity, is not a really surprising thing, in view
of the preponderatingly vegetative and stem-like character of the bulk of the
wall of the ovary. Sterile ovaries occur in many species of angiosperms, but in
most of these the carpels constitute the bulk of the fruit. Therefore, when the
seeds are wanting in these forms, and the carpels as usual fail to develop, no
fruit is formed and the flower bud soon withers and drops off. In Opuntia, on
the contrary, even if the seeds and carpellary portion of the fruit do fail to develop,
the basal stem-like part may go on, practically unhindered in its vegetative
growth, and mature quite normally."

Between the conditions represented by autonomic parthenocarpy
on the one hand and varietal interunfruitfulness on the other there is a
series exhibiting practically all possible expressions of the tendency to set
and mature fruit. Only a little less extreme than the tendency to fruit-
fulness shown by plants vegetatively parthenocarpic is that of plants
aitionomically parthenocarpic. Next in the series are the plants that
can set and mature fruit if self pollinated and fertilized, though embryo
abortion takes place almost at once. These in turn are followed by
plants which require varying degrees of development in the seeds that
they may properly mature their fruit. Finally there are those that
require the maturing of viable seeds along with the developement of their
fruits else premature dropping will occur.

The Value of Seedless and Parthenocarpic Fruits. — Seedlessness in
edible fruits is generally regarded as a valuable variety characteristic
for commercial purposes. In many cases at least the market is willing to
pay a premium for it. Mention of the regard in which seedless grapes and
oranges are held is ample evidence. Bananas and pineapples containing
seeds would probably find a very limited market. Even a material
reduction in the number of seeds would be a great asset in the blueberry,
the blackberry, the watermelon, the sugar apple and in many other
fruits. On the other hand, in many fruits seedlessness would not be an
asset. There would be little advantage in seedless apples or pears, if the
carpels remained. It has been pointed out that many fruits of our
ordinary plum and cherry varieties are seedless, but this condition is not
generally known or even suspected because the bony endocarp (stone)
remains unchanged.

For the grower, parthenocarpy probably is a more valuable variety
characteristic than seedlessness. If his fruits are parthenocarpic he is
insured against crop failure from self and cross unfruitfulness and, if
their parthenocarpy is autonomic, through failures resulting from lack
of pollinating agents or pollinating weather, his setting of fruit is more or
less guaranteed. It should not be inferred, however, that all the flowers
of parthenocarpic varieties set fruit and that aU these fruits mature.

THE DEVELOPMENT OF THE FRUIT 529

Mention has been made of the relation of water deficiencies at blossoming
or shortly thereafter to dropping in the Washington Navel orange.'*
]\Iany other agencies that Hmit fruit setting in non-parthenocarpic
varieties cause the dropping of those varieties that develop partheno-
carpically. In other words, the parthenocarpic condition is only a partial
and not a complete insurance against crop failure from premature
dropping.

From a practical standpoint seedlessness and parthenocarpy are to be
considered more as varietal characteristics to be sought when breeding
or originating new varieties or strains, rather than as conditions to be
produced by cultural means.

The Relation of Seed Formation to Fruit Development. — It has just
been pointed out that in some species or varieties ovarian and other
tissues of the fruit may develop independently of those of the enclosed
ovules. This condition, however, is by no means universal and such
parthenocarpic fruits are usually somewhat different in size, shape or
other characteristics frcm seed-containing specimens of the same kinds.
Furthermore, in the seed-containing specimens important differences in
development are often associated with varying seed number and
distribution.

Structure of Fruit. — Evidence that certain tissues of the pear undergo
a proportionally greater development in seedless than in seed-containing
specimens is presented in Fig. 55. That this is very common in other
fruits is indicated by the work of many investigators. Thus in seedless
eggplants the outer portions of the fruit grow more rapidly than the inner
portions, "the placentae evidently requiring the stimulus of the growing
ovules to induce development."^^ In seedless fruits of the eggplant and
in those in which the development of the ovary is arrested at an early
stage there is sometimes a very marked and abnormal development of
the subtending calyx. "Usually the most prominent indication that
impregnation has taken place, in the eggplant, is the rapid growth
of the calyx. Many times, however, the calyx becomes much enlarged
while for some reason the ovary fails to develop. I have frequently
seen examples of this, in which the calyx was fully 6 inches long."**
Ewerf*2 studied the structure of seedless and seed-bearing gooseberry
fruits and found striking differences in their cell size and structure. The
cells of the placentae and inner ovarian wall of seed-containing fruits
averaged 45-90/i^ in diameter, while many of those in the seedless speci-
mens were seven or eight times as large.

Form. — The pears sho^vn in Fig. 55 are illustrations of changes in form
accompanjdng changes in internal structure due to seedlessness. Mun-
son*^ observed that the parthenocarpic seedless fruits of English cucum-
bers were cylindrical in shape, but that when they were pollinated and
seeds developed the apical one-third of each fruit was much enlarged.

530

FUNDAMENTALS OF FRUIT PRODUCTION

owing to the location of the seeds in that end and not in the basal portion.
Seedless or nearly seedless specimens of Taber No. 129, a variety of
Japanese persimmon, are almost conical and distinctly pointed, while
seed-bearing specimens of the same variety are oblate. Furthermore,
"Taber No. 23 when seedy is oblate-rounded, but when seedless it
assumes an almost quadrangular form with very blunt or rounded corners.
Zengi is oblate-rounded when seedy, but approximates a truncated cone
in shape, or is distinctly oblong when seedless. "^*^

Size. — Perhaps an even more striking influence of seed formation
on the development of the fruit is in size. Seedless grapes are much
smaller than seed-containing berries of the same variety and berries
containing aborted seeds are intermediate between those that are seed-
containing and those that are seedless.* Seed- containing gooseberries
have been found to average 5 grams in weight, while seedless berries of
the same variety averaged only 3 grams, ^^ Seedless apples and pears
are often, though not always, smaller than seed-containing specimens.
In the date palm the seedless fruits maturing from unpollinated flowers
are only one-third to half the size of normal seed-containing fruits of the
same varieties.'"^

Furthermore in fruits normally containing a number of seeds consid-
erable correlation is likely between the size of the fruit and the number of
seeds developing. Munson^^ found this true in the tomato and he
observed that the locules were well developed only on the side of the fruit
containing a considerable number of good seed. The influence of seed

Table 5. — Number of Seeds in Fruits That Drop and in Fruits That Remain

(on the Apple Tree)

(After Heinicke^^)

Number of

Baldwin

Rhode Island

Maiden Blush

seeds to
the fruit

Attached
fruit

Drop
fruit

Attached
fruit

Drop

fruit

Attached
fruit

Drop
fruit

1

2

6

1

3

2

5

16

13

4

17

3

9

12

4

18

9

17

4

9

7

1

9

7

8

5

14

4

5

15

4

6

6

6

6

5

2

10

7

7

3

5

1

10

3

8

1

1

6

2

11

4

9

1

6

10

1

2

11

1

12

1

13

1

THE DEVELOPMENT OF THE FRUIT

531

number on the premature dropping of apples is shown by data summarized
in Table 5. Though the possession of a certain number of developing
seeds did not insure the fruit against dropping and though some of the
few-seeded fruits persisted and matured, there was a well-marked tend-
ency for the latter to fall prematurely and an equally distinct tendency
for the several-seeded fruits to persist. In a previous paragraph it was
pointed out that the setting and maturing of apples is favored by the size,
strength and vigor of the limbs and spurs on which they are borne. Table
6 presents further data which show the varying seed numbers in fruits
of approximatel}^ the same size but borne on spurs of varying weights.
It is noticeable that with fruit weights remaining constant the number
of seeds they contain varies inversely as the weights of the spurs. In
other words, the poorer development of fruit generally found on weak
spurs is offset if the fruits have enough seeds. This has led to the sugges-
tion that developing seeds have a pulling power for water and sap,
enabling the fruits of which they form a part to develop more or less at
the expense of other fruits with presumably smaller food-attracting
abilities. ^^

Table 6. — Seed Number Compensating for Spur Weight in the Apple

{After Heinicke^^)

(Weight of fruit constant, number of seeds and weight of spurs varying)

Lot

Variety

Fruit
weight
(grams)

Number
of seeds
per fruit

Spur
weight
(grams)

Tompkins King

Tompkins King
Tompkins King
Tompkins King
Rhode Island. . .
Westfield

5.54
5.05
2.31
1.98
3.97
1.45
6.09
3.75
5.05
2.40
4.86
2.28
2.33
1.31

Experimental evidence in corroboration of this suggestion was obtained
by coating with vaseline partly grown apples on spurs removed from trees
and exposed to a drying atmosphere. It was found that the leaves on the spurs
were able to withdraw less water from many-seeded than from few-seeded fruits
and more from the side of a fruit having no seeds than from the side where the
locules contamed a number.*^

532

FUNDAMENTALS OF FRUIT PRODUCTION

Muller-Thurgau" found a similar correlation between fruit size
and number of seeds in grapes, as is shown in Table 7, and Valleau^^^
found the size of strawberry fruits closely correlated with the number
of their akenes.

Table 7. — Relation of Seed Number to Fruit Size in Grapes

{After Mailer- Th urgau « ^)

Seedless

1 seed

2 seeds

3 seeds

4 seeds

Variety

Flesh,
grams

Flesh,
grams

Seeds,
grams

Flesh,
grams

Seeds,
grams

Flesh,
grams

Seeds,
grams

Flesh,
grams

Seeds,
grams

Riesling

Early Burgundy

25.0
27.9
23.7
58.7
60 3

58.2
52.9
81.6
135.8
112 6

2.1
1.8
2.14
2.4
3 1

77.2
92.4
116.7
196.6
202.0

3.9

3.7

4.12

5.0

7.4

89.0
110.5
140.8
232.7
244.4

5.2
5.2
5.9
7.4
10.9

112.0
140.0
155.8

258.8

6.0
7.3

White Gutedel

Orleans

14 9

It should not be inferred, however, that seedless fruits are always
smaller than seed-containing fruits of the same varieties or that fruits
containing many seeds are larger than those containing but few. For
instance, in his pollination work with plums, MarshalP^ found that
many varieties mature a large precentage of seedless fruits. These
cannot be distinguished from those containing seeds by their size or any
other external characteristic. The same is true of fruits of the sweet
cherry. Furthermore it has been found that seed-bearing fruits of the
Japanese persimmon are uniformly smaller than seedless specimens
of the same varieties.''''

Composition and Quality. — Associated usually with differences in
the structure of fruits are variations in composition and quality. This
holds true for the structural changes associated with varying seed number,
and indeed the differences in composition are often greater than would
be expected from observation of the variations in structure. Table 8
shows the sugar content and acidity of seedless and normal pears and
Table 9 shows differences in composition between caprified and un-
caprified figs of several varieties. The difference in acidity between
the seedless and seed-containing pears is striking and is sufficient to
make a considerable variation in quality. Though the distinctions
between the caprified and the uncaprified figs are on the whole less
prominent they are great enough to be of commercial importance in
such varieties as the Dottato. There are differences also in color of
flesh between caprified and uncaprified figs of the same variety. ^^^

Perhaps the most striking dissimilarities in composition and quality
between seedless and seed-bearing fruits are found in certain varieties
of the kaki or Japanese persimmon. Zengi, Hyakume and certain other-
sorts are always solid, dark fleshed when they have a good supply of

THE DEVELOPMENT OF THE FRUIT

533

Table 8. — Influence of Seed Number on Sugar Content and Acidity in

Pears

{After Ewert'-)

Grams of reducing sugar in 100
cubic centimeters of sap

Grams of acid, calculated as malic

acid, in 1000 cubic centimeters of

sap

Fruits seedless j

Fruits 1-seeded I

Frui.ts 2-seeded .• . .

5.81
8,33
9.26

0.98
1.61
1.79

Table 9. — Analyses of Caprified and Uncaprified Figs
(After CoruUr-^)

Variety I Analysis by

I

Fig d'Or, caprified Du Sablon

Fig d'Or, uncaprified j Du Sablon

Fig Datte, caprified | Du Sablon

Fig Datte, uncaprified j Du Sablon

Bourjassotte, caprified Du Sablon

Bourjassotte, uncaprified j Du Sablon

Adriatic, caprified W. V. Cruess

Adriatic, uncaprified W. V. Cruess

Dottato, caprified (Kadota) W. V. Cruess

Dottato, uncaprified (Kadota) W. V. Cruess

Dottato (dried), caprified F. W. Albro

Dottato (dried), uncaprified F. W. Albro

Adriatic (half dried), caprified F. E. Twinning

Adriatic (half dried), uncaprified F. E. Twinning

Adriatic (fresh), uncaprified M. E. Jaffa

Adriatic (fresh), caprified M. E. Jaffa

Adriatic (dry), uncaprified M. E. Jaffa

Adriatic (dry), caprified ' M. E. Jaffa

Per cent

Per cent

water

sugar

80.00

11.20

74.00

12.60

71.00

14.30

71.00

18.70

70.00

3.50

76.00

6.20

19.05

18.00

35.20

28,40

22.57

75.36

25.75

68.16

27.05

34.80

28.70

35.50

70.70

18.78

74.70

13.00

18.00

51.50

16.00

48.50

seeds, or when there are only three or four seeds and these are well
distributed.'" When there is only a single seed, or two or three seeds
in adjacent locules, the flesh surrounding these is dark while that some
distance away is light colored. When these varieties produce seedless
fruits all of their flesh is hght colored. O'kame and Yemon, possessing
full complements of seeds, have dark colored flesh immediately surround-
ing the seeds, but light colored flesh next to the skin. Tsuru, Costata,
Triumph and some others are light fleshed whether seeds are present
or not. The dark flesh of persimmons is edible while stiU hard and flrm,
but the light flesh remains astringent untfl it softens. Hume'" states
that no variety is known which is dark fleshed when seedless, but Condit^"
reports an apparent exception to this rule.

Variation in seed number is accompanied by differences in composi-

534 FUNDAMENTALS OF FRUIT PRODUCTION

tion in many other fruits. In most grape varieties, for instance, seedless
fruits are much sweeter than seed-containing berries of the same kinds.
On the other hand, the differences in composition are often negligible.
There is no general rule that can be laid down stating that seedlessness
tends either to improve or to detract from quality.

Seaso7i of Maturity. — There is often a considerable difference in the
time intervals between fruit setting and maturing of seedless and seed-
containing fruits of the same variety. As a rule the parthenocarpic or
seedless fruits are slower in reaching maturity than the seed-bearing
specimens. Munson^^ mentions several instances in which flowers of the
cucumber, pumpkin and summer squash were induced to set fruit by
applying to their stigmas pollen of certain other species of cucurbits. The
resulting fruits which were seedless required over 2 months longer for
maturity in some cases and in all cases a somewhat longer period than was
necessary for the development of normal fruits from intra-specific polli-
nation. The so-called "second bloom" fruits of the apple and pear that
set 2 to 4 weeks after the usual blossoming period and are very often
seedless frequently never mature properly and such maturity as they do
attain is reached only after they have persisted on the trees much longer
than the extra 2 to 4 weeks that would compensate for their late setting.
Caprified figs of the Smyrna type drop from the trees at full maturity;
uncaprified figs tend to persist and usually must be cut or pulled from the
trees, as they will fall only when past their prime. '**^ In the Japanese
persimmon seed-containing fruits usually ripen earlier. Zengi commonly
matures its seed-bearing fruits in late July, while its seedless fruits may
not be ready for harvest untilDecember.^" In other varieties there may
be less difference in ripening periods, though they are often quite distinct.
Fruits bearing only one or two seeds show a tendency to ripen with the
seedless, while those with a greater number show a tendency to ripen with
the normal fruits. ''''

In almost all cases the relation of seed number to season of maturity
is of very secondary importance.

Specific Influence of Pollen on Resulting Fruit.- — Much has been
said on the supposed specific influence of the pollen on the characteristics
of the fruit resulting from the pollination. For instance, it has been
claimed that the red color of striped apple varieties is intensified after
pollenizing with a dark red sort. The pollination of varieties with
an acid flesh with pollen from a sweet or subacid variety has been said to
result in fruit less acid in character. Early maturing sorts are claimed
to mature their fruits somewhat later if pollinated by late ripening kinds.
These conceptions are based on a misunderstanding of the processes
actually involved in pollination, fertilization and fruit development, or
on faulty observations, or on a wrong interpretation of field observations
that may have been accurate.

THE DEVELOPMENT OF THE FRUIT

535

There is no evidence to indicate any immediate influence of pollen
on the color of the resulting fruit, or any direct effect on its composition,
flavor, quality, shape, season of maturity or keeping quality. This
statement is borne out by a number of extensive cross and self pollination
experiments^^' ^^^ as well as by a theoretical consideration of the nature
of the tissues and processes involved in fruit setting and maturing. Of
course if in a series of pollination experiments some pollen is used on a
certain variety and normal seed-containing fruits result and then pollen
of some other kind is used on other flowers stimulating them to set and
mature seedless fruit, differences in size, shape, composition and season of
maturity may be obtained. However, these are diversities associated
more directly with the relationship existing between seed formation and
fruit development and not directly between kind of pollen and fruit
development. In the same way the pollination of pistils of a given
sort with pollen of half a dozen other varieties with which it is inter-
fruitful may result in one crossing in fruits averaging say two seeds, in
another crossing in fruits averaging four seeds, and so on. Under these
conditions minor differences in size, composition, shape and even flesh
color and season of maturity may follow. Differences of this kind
probably account for such inequalities in fruit size in the pear as were
found by Waite^^^ when he used pollen of several kinds on Bartlett or
Kieffer pistils (see Table 10).

Table 10. — Influence of Kind of Pollen on Fruit Size and Seed Weight

IN Pears
{After Waite "2)

Cross

Average weight
of fruit, grams

Average weight
of seeds, grams

Bartlett X Bartlett

100.4
116.1
167.7
133.6
89.4
114 2

0 07

Bartlett X Anjou

0.38

Bartlett X Easter

0 38

Bartlett X Angouleme.

Bartlett X White Dovenne

0.30
0 27

Bartlett X Clapp Favorite

0.32

The limited data available indicate that these variations are relatively
unimportant except in comparing cross pollinations with self pollinations.
That is to say, many varieties that will set and mature fruit when self
pollinated will set and mature distinctly larger fruits when cross pollinated,
regardless of the kind of pollen used if only it is from a compatible variety.
The explanation of the smaller fruits resulting from self pollination
is that though selfing often results in fruitf ulness the fruits bear few or no
perfect seeds, while the cross pollinated fruits have the usual number of

536 FUNDAMENTALS OF FRUIT PRODUCTION

good seeds. In other words, it is crossing so as to secure a good comple-
ment of seeds, rather than crossing with some particular variety, that is
responsible for the difference in size and is consequently important in the
orchard. Investigations conducted with many fruits indicate that the
number or percentage of seeds developing in the fruits of different kinds
is to a considerable extent a varietal characteristic or at least it is
more dependent on the variety and the condition of the tree or plant
than on the kind of pollen, assuming that an adequate supply of good
pollen is available.

Kraus^^ has pointed out that the occasional striping of self colored
fruits of the apple, so often cited as proof of an immediate influence of the
pollen on the character of the resulting fruit, is in reality a special form of
bud mutation. Bud mutations of this kind may in many cases be propa-
gated vegetatively and striped varieties obtained.

What appears at first as an exception to some of the preceding statements
has been recorded for the developing fruits of the vanilla. McClelland'^ crossed
two types of this plant — Vanilla planifolia and the "vanillon" type. "The
typical well-developed fruit of V. planifolia from a close-fertilized blossom is a
long slender capsule tapering at the stem end but carrjdng its fullness well down
toward the blossom end. It contains thousands of tiny, oily, black seeds.
. . . The fruits [of the vanillon type] are much thicker and shorter . . .
and differ in being of a more uniform thickness near the two ends, the blossom
end frequently being rather tapering. Where to either the V. planifolia or the
vaniUon stigma pollen of the other has been applied a very marked modification in
the form of the fruit has resulted." These differences in shape apparently are
associated with the location within the capsule of the ovules that were fertilized
and develop into seeds. When V. pla^iifolia pollen is used on vanillon
stigmas, fertilization takes place mainly toward the apical end of the ovary and
not toward the basal end, while in self pollenized vanillon stigmas fertiliza-
tion occurs clear to the bottom of the ovarian cavity. On the other hand, the
pollen tubes of the vanillon type seek the basal ovules in the ovaries of the
V. planifolia type when that crossing is made. In reality, instead of being an
exception to the statement that crossing with a particular kind of pollen affords
no direct influence on the character of the resulting fruit, this is but another
instance of an indirect effect on shape, the direct relationship being between
kind of pollen and seed number in the one case and seed number and location
and shape of fruit in the other.

Summary. — Ordinarily the development of the carpellary and other
tissues of the fruit depends on fertilization and the consequent develop-
ment of seeds from the ovules. In some cases, however, the development
of the fruit may proceed without an accompanying growth of seeds, or
even without the stimulus of fertilization. In still other cases develop-
ment may occur in the absen.ce of pollination. Parthenocarpy is a term
used to cove-r those cases of f-ruit development in the absence of fertiliza-

THE DEVELOPMENT OF THE FRUIT 537

tion. Parthenocarpic fruits are usually seedless, though seeds may de-
velop in them parthenogenetically. Some seedlessness is due to embryo
abortion after fertilization and therefore is not associated with partheno-
carpy. Fruits which the botanist classifies as accessory are somewhat
more inclined to parthenocarpic development than those consisting of
ovarian tissues only. Parthenocarpy is no insurance, however, against
loss of crop from excessive dropping of blossoms under certain condi-
tions. In general, seedlessness is valuable from the commercial stand-
point. In most instances there is a distinct correlation between the
formation of seeds and the development of the fleshy tissues of the fruit —
the greater the seed number, the larger the fruit. Other limiting factors,
however, may destroy this correlation. Between seed-containing and
seedless fruits of the same varieties, there are often distinct differences
in form, composition and ripening period. However, there is no good
evidence that the specific qualities or characteristics of the pollen variety
are in any way stamped upon the resulting fruit.

CHAPTER XXX
FRUIT SETTING AS AN ORCHARD PROBLEM

The preceding discussion has shown that certain fruit varieties are
completely self fruitful, others are partly self fruitful and still others are
self barren. With varieties definitely known to be self fruitful it is safe
to plant solid blocks to a single variety without making any provision
for cross pollination. The heavy production that characterizes large
plantations of the Concord grape, the Baldwin apple, the Montmorency
cherry, the Cuthbert raspberry and many other fruits is sufficient evi-
dence on this point. On the other hand many varieties that are often
considered self fruitful because in the average season they set a full crop
without the aid of any foreign pollen, are often greatly benefitted by
cross pollination. Thus though the French prune is generally considered
self fruitful and there are many large orchards consisting exclusively of
that variety, a higher percentage of its blossoms set when cross pollin-
ated with Imperial than when selfed.^^ In general it is good practice
always to make provision for cross pollination when planting the orchard,
unless there is definite knowledge that this is not needed for the variety
when grown under the conditions in question. Even though a variety
is entirely self fruitful under a given set of conditions the evidence shows
that in many cases the increase in the size of fruit resulting from the
stimulus of cross fertilization is sufficient to warrant planting together
two or more varieties which bloom at the same time.

Fortunately the selection of varieties to secure effective cross pollina-
tion does not usually add many complications to the problem of variety
selection. In most fruits the grower prefers to raise two or more varieties
rather than a single sort. By choosing those that ripen at different
seasons the harvesting problem is usually greatly simplified and often
problems of tillage and spraying as well. When the orchard is to be
planted to two or more varieties for reasons other than cross pollination,
it is necessary only to make a selection such that their blossoming seasons
overlap to a considerable extent. When it seems best to have as large
a part of the orchard as possible consist of a single variety, the problem
of selecting one for cross pollination purposes is not materially different
than before. First and foremost, its blossoming season should overlap
that of the main sort. Then, questions of its maturing season, produc-
tiveness, market value and so on, should receive due consideration.
Another point that should receive attention in the selection of a pollenizer

538

FRUIT SETTING AS AN ORCHARD PROBLEM 539

to be planted in limited numbers for the benefit of a main sort is its
pollen -bearing qualities. Some varieties are heavy pollen producers;
others bear only limited amounts. Thus IVIeylan is one of the best varie-
ties of the Enghsh walnut and Glen Mary one of the poorest strawberries
to plant for pollinating other varieties.

The Number of Pollenizers. — The question often is raised as to the
number or percentage of pollenizers necessarj^ when business considera-
tions make it desirable to limit them as much as possible. No very
definite rule can be given. In most deciduous tree fruits every third
tree in every third row will furnish all the pollen necessary for the remain-
ing 89 per cent. This proportion, however, would not be practicable in
the strawberry plantation when it is desired to grow pistillate varieties
mainly. Much depends on the provision for cross pollinating agents.
If it is an insect-pollinated plant and pollen-carrying insects are numerous
(say amounting to one swarm of bees for each 1 or 2 acres of fruit trees)
fewer trees of the less valuable pollenizers are necessary than if the bees
are few.

In cases where large blocks of a single self unfruitful variety have been
planted and the trees have been in the orchard for a number of years
much quicker results can be obtained by grafting over some of them than
by removal and replanting. Occasionally growers solve the difficulty
by grafting over a limb or two in each tree, but this usually complicates
the problem of harvesting and from an economic standpoint is less satis-
factory than changing the entire tops of certain trees.

Temporary Expedients. — Immediate results are often obtainable in
self unfruitful orchards through securing from trees of other varieties large
branches containing nvmierous flower buds and placing them here and there
in the self barren orchard. This permits pollen-carrying insects to effect
a transfer of pollen from these branches to the pistils of the orchard trees.
Such branches should be cut just as their flowers are starting to open and
stood in buckets of water so that they will keep fresh while their flowers
are opening and shedding pollen. This is only a temporary expedient,
for it is troublesome and often rather expensive ; however, it has been the
means of insuring a good set of fruit in many cases when there would have
been a crop failure otherwise. It really is a kind of artificial pollination,
comparable to practices in vogue for thousands of years in the produc-
tion of dates and many varieties of figs.

Pollinating Agents. — Wind and insects have been mentioned as the
chief pollen -carrying agencies for deciduous fruits. Of the two, insects
are by far the more important except in some of the nut crops. In fact
the amount of cross pollination effected through the agency of the wind
in apples, pears, peaches and other insect-pollinated fruits is practically
negligible. This has been shown experimentally for the plum by
Waugh^^*^ and for other fruits by other investigators. Among pollen-

540 FUNDAMENTALS OF FRUIT PRODUCTION

carrying insects the common honey bee is probably the most important
for the fruit grower. Its importance is such that the presence of an
ample number should be insured during the blossoming season. In
some of the cherry growing sections of the Pacific Northwest growers
make a practice of securing colonies of bees from apiarists to place in
their orchards during blossoming and they find that the rental they
pay yields them a higher rate of interest on their investment than any
other item in their cost of production. No hard and fast rules can be
laid down regarding the number of colonies necessary for effective pol-
lination in an orchard of a given size. Much depends on the size of the
trees, their profusion of bloom and the number of hours of favorable
weather for pollination during their flowering season and the presence
or absence of other pollen-carrying agents. Ordinarily one colony of
bees to each 1 or 2 acres of orchard, depending on conditions, will
produce satisfactory results and sometimes they will take care of a
considerably larger acreage.

It is often assumed that perfect flowered and self fruitful varieties
require no outside agent for the transfer of pollen from stamen to stigma.
In other words, the self fruitful variety is assumed to be autogamous.
This is often the case, at least to a certain extent, However, it has
been found in California that Imperial prune trees from which bees were
excluded during the blossoming season set only 0.34 per cent, of their
blossoms, while trees of the same variety accessible to bees but protected
from cross pollination from other varieties set 3.02 per cent.''^ In
the French prune 19 per cent, of the blossoms matured fruit where bees
visited them, while only 0.43 per cent, matured fruit where the bees were
excluded. Conditions may be quite different in other fruits or in other
self fruitful varieties of the plum, but in the absence of definite knowl-
edge that the varieties he is growing are both self fruitful and autogamous
the grower should make adequate provision for pollen transfer.

The Fruit Setting Habits of Different Fruits. — In the preceding
discussion of the factors influencing the setting of fruit most deciduous
fruit species have been mentioned along with certain others. Following
are summarized statements of the more important fruit setting character-
istics of the common fruits.

Apple. — The flowers of the apple are true hermaphrodites. Occa-
sionally defective pistils are found and generally a portion of the pollen
grains are defective, though apparently all varieties mature a certain
amount of good pollen. i° The percentage, however, varies with environ-
mental conditions. Many varieties are self fruitful, many others are
self barren or partly so. Lewis and Vincent^^ reported about 70 per cent,
of the varieties studied as self barren in Oregon; Gowen^^ found about
63 per cent, completely self barren and only 13 per cent, completely self
fruitful in Maine and Hooper^^ reported about two-thirds of the varieties

FRUIT SETTING AS AN ORCHARD PROBLEM 541

he worked with in England to be self sterile. The degree of self fruitful-
ness in the apple varies greatly with the age and vigor of the trees, the
season, locality and many other factors. Thus the Jonathan, which is
self fruitful in many parts of the United States, is self fruitful in Victoria
(Australia) when grown on soils of medium productivity, but self barren
when grown on rich soils. '*^ Among the prominent commercial varieties
that are classed as comparatively self fruitful, at least in a number of
sections, are: Baldwin, Ben Davis, Gano, Jonathan, Oldenburg, Yellow
Newtown, Grimes, Wagener, Yellow Transparent, Willow Twig, Esopus,
Stark, On the other hand, nearly all of these varieties have been reported
partly or completely self barren in certain localities or at certain times.
Among those classed as partly or completely self barren are: Arkansas
Black, Gravenstein, King, Arkansas, Maiden Blush, Missouri Pippin,
Rome, Ralls, Rhode Island, Salome, Tolnian, Wealthy, Winesap and
York. These varieties, however, may frequently prove self fruitful.

Young vigorous trees just coming into bearing have been observed
repeatedly to be much more likely to drop their fruit than trees of the
same varieties somewhat older and having the bearing habit well estab-
lished. On the other hand old weak trees frequently bloom verj'- heavily
but set little or no fruit. Often this situation can be remedied by liberal
applications of nitrate of soda or some other quickly available nitrogenous
fertilizer shortly before blossoming.

Apple scab and fire blight frequently attack the blossoms or the newly
set fruits and are responsible for much dropping at an early stage. These
diseases can be controlled by proper spraying and sanitary measures
respectively.

Inter-unfruitfulness has been reported for a few varieties,^^' ^"^
particularly some of those of the Winesap group; but a large body of
data indicates that cross sterility is of very little importance in apple
production. With perhaps the exceptions just noted the grower may
consider it safe to interplant any one variety with any other for purposes
of cross pollination, provided they bloom at the same time.

Parthenocarpy occurs rather frequently, but true parthenocarpic
varieties are rare.

Pear. — The flowers of the pear, like those of the apple, are true her-
maphrodites. So far as known, all varieties produce at least a certain
amount of good pollen. However, many pear varieties are self barren
because of self incompatibility. Waite^^- reported 22 out of 36 varieties
as self unfruitful. Among the more prominent of this group are: Anjou,
Bartlett, Clairgeau, Clapp Favorite, Columbia, Easter, Howell, Louise
and Winter Nelis. Among the more important of the self fruitful
varieties are: Angouleme, Bosc, Flemish Beauty, Kieffer, LeConte,
Seckel, Tyson and White Doyenne. However, Kieffer has been reported
practically self sterile in Virginia'*^ and Bartlett has been found partly

542 FUNDAMENTALS OF FRUIT PRODUCTION

self fruitful in certain localities in California. ^^"^ It has been found
that most sparingly self fruitful pear varieties generally mature fruits
with few or no good seeds and that these fruits are distinctly inferior
in size to those of seed-bearing fruits of the same varieties resulting
from cross pollination. Pears generally should be so planted as to
secure the benefits from crossing.

So far as known the more common pear varieties are interfruitful
and one variety is as good as another in cross polhnation if it blossoms
at the right period.

Parthenocarpy is not uncommon in pears but none of the varieties
of commercial importance in America is parthenocarpic regularly.

Quince. — Circumstantial evidence points clearly to the conclusion
that the commonly cultivated varieties of the quince are self fruitful.
This is supported by the results of investigations of Dorsey in New York
(data unpublished).

Peach. — Experimental work with the peach at the Missouri/^^
Delaware, ^^ and Virginia^^ Stations indicates that practically all the
commonly grown varieties are self fruitful. Furthermore there is no
evidence of any gain in size of fruit from cross pollination. The grower
is safe, therefore, in planting entire orchards to a single variety.

Almond. — The work of Tufts ^^g ^^s shown that all almond varieties
that were tested are generally self sterile under California conditions,
though in occasional seasons certain varieties will set a fairly good crop
with their own pollen. This self unfruitfulness is due to incompatibility
rather than to imperfect pollen, for the pollen proves satisfactory on the
pistils of certain other varieties. Certain varieties were found also to be
interbarren; I.X.L. and Nonpareil will set practically no fruit when
interplanted and the same is true for plantings of Languedoc and Texas.
Plum. — Plum varieties vary greatly in their abilities to mature fruit
without the aid of cross pollination. Waugh^^^' ^^^> ^^'^> i" reported
practically all the commonly cultivated varieties of the Japanese and
American species to be self sterile; this -has been confirmed by the inves-
igations of others.^^' ®^' ®*' ^^' ^^^ On the other hand, a considerable
number of European varieties, including Giant, Green Gage, Italian,
French and Blue Damson have been found partly or completely self
fruitful in Oregon, ^^ and Sutton^^^ reported 18 out of 39 varieties to be
fully self fruitful and five more partly self fruitful in England.

Hendrickson^^ and MarshalP^ reported all Japanese varieties tested
as interfruitful and Waugh^^^ found both Japanese and American varieties
generally interfertile. Some exceptions, however, have been recorded.
Thus Whitaker and Milton, both seedlings of Wildgoose, are interbarren
and, curiously enough, both are fertile with Sophie; however, Sophie
used as the pistil parent is fertile with neither. ^^^ Dorsey" obtained
only eight mature fruits from 1327 flowers of the Compass pollinated

FRUIT SETTING AS AN ORCHARD PROBLEM 543

with Yellow Egg, while 114 flowers set and matured fruit when polli-
nated with Burbank. Though both crosses evidently may be classed
as interfertile, there is a great difference in the degree of fertility exhibited.
Marshall, ^° working with varieties of P.domestica, iound anyone combina-
tion to give as good set of fruit as any other; Sutton, ^^^ working with other
varieties of the same species, reached the same conclusion, except that
intersterility appeared in three varieties. However, two of these three
varieties originated as bud sports from the third. The European plums
are not interfruitful to any considerable degree with those of either the
Japanese or American groups.

Except for certain varieties of the several European groups known to
be self fruitful, plums always should be planted so they will secure the
advantages of cross pollination.

Apparently both self and cross unfruitfulness in the plum is due to
incompatibilities and not to degeneration of the pollen or of the embryo
sacs.

Apricot. — Experimental data are not available on the pollination
responses of the apricot; however, circumstantial evidence indicates
that at least a number of the leading varieties grown in America are
self fruitful.

Cherry. — Until a comparatively recent time cherries have been
assumed to be self fruitful. In 1915, Gardner^" reported several varieties
of the sweet cherry, all that were tested, as self unfruitful under Oregon
conditions and a little later Tufts^^^ reported a number of the same
varieties self barren in California. All the sweet cherries tested have been
reported self barren in' England. ^^^ The conclusion seems warranted
therefore that self barrenness is the general rule in this group. Gardner*"
also found May Duke self unfruitful in Oregon, but Sutton^^^ found
both May Duke and Archduke partly self fertile and Late Duke fully
self fertile in England. Experimental data on the sour cherries are not
available but Hedrick*'^ concludes from his observations that self fruit-
fulness is the general rule in that group.

, Inter-unfruitfulness has been found among some of the varieties of
the sweet cherry- — notably Napoleon, Lambert and Bing — in both
Oregon*" and California, ^^s

Self unfruitfulness and cross unfruitfulness in the cherry are due to
incompatibilities rather than to any structural defects of pollen or ovules.

Grape. — As mentioned already, conditions in the grape range all the
way from complete self fruitfulness to complete barrenness. Varieties
of hybrid origin particularly are likely to be self barren, though this
condition is found in many varieties descended from a single species.^*' ^^
Among some of the more common self fruitful varieties may be men-
tioned: Clinton, Champion, Concord, Isabella, Moore Early, Niagara,
Worden, Agawam, Catawba, Delaware, Diamond and Norton. Among

544 FUNDAMENTALS OF FRUIT PRODUCTION

those that are self unfruitful are: Salem, Barry, Brighton and the follow-
ing are among those often at least partly self fruitful : Lindley, Vergennes,
Wyoming.^

Practically all the varieties of the Muscadine group bear pseudo-
hermaphroditic flowers and should have staminate vines interplanted
with them.

The immediate factor responsible for self barrenness in the grape is the
production of impotent or sterile pollen which is incapable of fertilizing
the ovules of the same or of any other variety.^' ^^ Consequently self
barren varieties are interbarren and partly self barren sorts are partly
interbarren. Self fertile varieties should be interplanted with the self
barren or partly self barren kinds. The production of impotent or
sterile pollen is associated almost invariably with curved or reflexed
stamens; good pollen is produced in erect stamens. This flower character
therefore affords an accurate index to the degree of self fruitfulness that
may be anticipated, except in the comparatively few parthenocarpic
varieties.

Many grape varieties occasionally produce a few seedless berries
when not polhnated or when pollinated with impotent pollen. This
characteristic apparently is aided by certain practices such as ringing or
girdhng. In a few varieties, such as Thompson's Seedless, this occurs
regularly .^^ According to Stout, ^^^ seedless American grape varieties
generally produce good pollen, but since their "femaleness" is not
strongly developed they are not able to mature good seeds.

Strawberry. — Strawberry varieties are generally classed as pistillate
flowering and perfect flowering. Apparently all the perfect flowering
sorts produce good pollen and all are self fruitful and apparently any
perfect flowering variety may be planted with any pistillate flowering
sort for purposes of cross pollination. Since, however, some of the per-
fect flowering varieties produce only small amounts of pollen, they are
not ideal pollenizers for pistillate sorts. In general the later maturing
flowers of the inflorescence, particularly in the perfect flowering varieties,
are less fertile than earlier flowers of the same cluster and this pistil
sterility is "expressed in the production of irregularly shaped berries or
entirely sterile flowers." ^^^

Currant and Gooseberry. — Few exact data are available on the polli-
nation requirements of the currant and the gooseberry. However, field
observation indicates clearly that the varieties commonly grown in this
country are self fruitful and hence no provision need be made for cross
poflination. Hooper^^ has reported all the varieties of the English goose-
berry which he tested to be self fertile.

The Brambles. — Until comparatively recent date the bramble fruits
have generally been considered self fruitful. Hooper,''^ working with a
number of varieties of the raspberry and with the loganberry in England,

FRUIT SETTING AS AN ORCHARD PROBLEM 545

found all that he tested self fertile but reported some increase in size
of fruit resulting from cross pollination. In North Carolina 11 out of
15 varieties of dewberries were found self barren and 12 out of 16 varieties
of blackberries self fruitful. The varieties of Ruhus villosus generally
were self fruitful, those of R. trivialis self barren. There was no increase
in size of fruit from cross pollination in those varieties maturing fruit
when selfed. The Vineland (Ontario) Horticultural Experiment Sta-
tion* ^^ has reported that a number of the seedlings of the raspberry which
they have obtained in their breeding work are self sterile. Others are
self fruitful or partly so. A number of the blackberry-dewberry hybrid
varieties are partly or wholly self barren.

The Nuts. — Data are not available on the degree of self fruitfulness
characteristic of different varieties of the walnut, pecan, hickory, chest-
nut and filbert. All are monoecious and a large majority are characterized
by partial dichogamy. In some the dichogamy is almost complete,
rendering the tree or variety self unfruitful to a marked degree. To
what extent, if at all, individual trees or varieties are self unfruitful because
of incompatibility is not known. On account of the partial dichogamy
that is generally found it is always a good plan to interplant two or more
varieties having approximately the same blossoming seasons.

Persimmon. — The kaki, or Japanese persimmon, includes varieties
bearing pistillate flowers only and those bearing both pistillate and stami-
nate flowers. Of the varieties in the latter class some bear staminate
flowers regularly, others bear them sporadically. The names pistillate
constants, staminate constants and staminate sporadics have been applied
to these several groups.

Some varieties set fruit freely without pollination and they mature
seedless fruits. Others require pollination and their fruits usually con-
tain one or more seeds. Apparently pollination is not so essential to the
securing of a good persimmon crop in California as in Florida. ^^

The differences in the size, shape, color, flavor and season of maturity
of seed-bearing and seedless persimmons have been discussed previously.

There is reason to believe that most pistillate flowers of the native
American persimmon (Diospyros virginiana) require pollination from
staminate trees of the same species in order to set and mature a good crop.
The Japanese and American varieties of persimmon are not interfruitful.^^

Summary. — In the absence of definite knowledge that the variety
being planted is self fruitful under local conditions provision should
always be made for cross pollination. Even when varieties are self
fruitful the increase in size often obtained as a result of cross pollination
warrants the use of other pollenizers. In most tree fruits one of the
pollenizing variety is sufficient for 8 or 10 trees of the leading sort.
Top grafting and the use of flowering branches of other varieties at the
blossoming season are the most satisfactory methods of providing for

546 FUNDAMENTALS OF FRUIT PRODUCTION

cross pollination in established self unfruitful or inter-unfruitful orchards.
Insects, particularly the honey bee, are the most effective pollinating
agents in the deciduous fruit plantation. There should be ample provi-
sion for pollen transfer, even in orchards of self fruitful varieties. The
fruit setting habits and polHnation requirements of different deciduous
fruits are discussed.

Suggested Collateral Readings

Waite, M. B. Pollination of Pear Flowers. U. S. D. A. Div. Pom., Bui. 5. 1895.
Hedrick, U. P. Relation of Weather to the Setting of Fruit. N. Y. Agr. Exp. Sta.

Bui. 299. 1908.
Valleau, W. D. A Study of Sterility in the Strawberry. Jour. Agr. Res. 12:613-

670. 1918.
Dorsey, M. J. Pollen Development of the Grape with Special Reference to Sterility.

Minn. Agr. Exp. Sta. Bui. 144. 1914.
Eisen, G. The Fig. U. S. D. A. Div. Pom., Bui. 9. Pp. 74-128. 1901.

Literature Cited

1. d'Angremond, A. Flora. 107: 57. 1914.

2. Beach, S. A. N. Y. Agr. Exp. Sta. Bui. 157. 1898.

3. Beach, S. A. N. Y. Agr. Exp. Sta. Bui. 169. 1900.

4. Beach, S. A. N. Y. Agr. Exp. Sta. Bui. 223. 1902.

5. Beach, S. A. Proc. Am. Pom. Soc. P. 72. 1901.

6. Benson, M. F. Trans. Linn. Soc. IL Bot. 3: 409-424. 1894.

7. Bioletti, F. T, Cal. Agr. Exp. Sta. Bui. 197. 1908. (P. Viala and P. Pacottel

cited as authority.)

8. Bioletti, F. T. Cal. Agr. Exp. Sta. Cir. 191. 1918.

9. Booth, N. O. N. Y. Agr. Exp. Sta. Bui. 224. 1902.

10. Booth, N. O. Proc. Am. Soc. Hort. Sci. P. 25. 1906.

11. Brainerd, E., and Peitersen, A. K. Vt. Agr. Exp. Sta. Bui. 217. 1920.

12. Brown, F. R. First Bienn. Crop Pest and Hort. Rept. Ore. Agr. Exp. Sta.

Pp. 41-43. 1911-12.

13. Brown, W. R. Agr. Res. Inst. Pusa Bui. 93. 1920.

14. Burbidge, F. W. Cultivated Plants; Their Propagation and Improvement.

P. 472. Edinburgh and London, 1877.

15. Bushnell, J. W. Proc. Am. Soc. Hort. Sci. 17: 47-52. 1920.

16. Claypole, E. W. Rept. U. S. Com. Agr. Pp. 318-321. 1887.

17. Close, C. P. Del. Agr. Exp. Sta. Rept. 14: 99-102. 1902.

18. Coit, J. E. Cal. Agr. Exp. Sta. Ann. Rept. P. 105. 1914.

19. Coit, J. E., and Hodgson, R. W. Cal. Agr. Exp. Sta. Bui. 290. 1918.

20. Condit, I. J. Cal. Agr. Exp. Sta. Bui. 316. 1919.

21. Condit, I. J. Cal. Agr. Exp. Sta. Bui. 319. 1920.

22. Conrad, A. H. Bot. Gaz. 24: 408-418. 1900.

23. Darwin, C. The Variation of Animals and Plants under Domestication.

2d Edition. 1:434. New York, 1894.

24. Ibid. 2: 113. (Cited on authority of Hildebrand.)

25. Ibid. 2: 115-117.

26. Ibid. 2: 119.

27. Ibid. 2: 147.

FRUIT SETTING 547

28. Ibid. 2: 152-153.

29. Ibid. 2: 165-169.

30. Darwin, C. Cross and Self Fertilization in the Vegetable Kingdom. Pp. 343-4.

1895.

31. Davey, A. J., and Gibson, C. M. New Phytol. 16: 147-151. 1917.

32. Detjen, L. R. N. C. Agr. Exp. Sta. Tech. Bui. 11. 1916.

33. Detjen, L. R. N. C. Agr. Exp. Sta. Tech. Bui. 12. 1917.

34. Detjen, L. R. N. C. Agr. Exp. Sta. Tech. Bui. 17. 1919.

35. Detjen, L. R. N. C. Agr. Exp. Sta. Tech. Bui. 18. 1919.

36. Dorsey, M. J. Minn. Agr. Exp. Sta. Bui. 144. 1914.

37. Dorsey, M. J. Genetics. 4: 417-488. 1919.

38. Dorsey, M. J. Jour. Agr. Res. 17: 103-126. 1919.

39. East, E. M., and Park, 'J. B. Genetics. 2: 505-609. 1917.

40. Eisen, G. U. S. D. A., Div. Pom. Bui. 9. 1901.

41. Exp. Sta. Rec. 3: 135. 1892.

42. Ewert, R. Landw. Jahrb. 39: 463-470. 1910.

43. Fairchild, D. G., and Beach, S. A. N. Y. Agr. Exp. Sta. Rept. 11: 607-611.

1892.

44. Farrell, J. Jour. Agr. Victoria. 15: 142. 1917.

45. Fitch, C. L. Proc. Am. Soc. Hort. Sci. 11: 100. 1913.

46. Fletcher, S. W. Cornell Univ. Agr. Exp. Sta. Bui. 181. 1900.

47. Fletcher, S. W. Va. Agr. Exp. Sta. Rept. Pp. 213-224. 1909-10.

48. Floyd, F. E. Trans. Roy. Soc. Canada. (Ser. 3) 10: (Sec. 4) 55-61. 1916.

49. Gaertner, K. F. Versuche und Beobachtungen iiber die Bastardzeugung im

Pflanzenreich. Stuttgart. 1849.

50. Gardner, V. R. Ore. Agr. Exp. Sta. Bui. 116. 1913.

51. Goff, E. S. Wis. Agr. Exp. Sta. Bui. 63. 1897.

52. Goff, E. S. Wis. Agr. Exp. Sta. Bui. 87. 1901.

53. Goff, E. S. Wis. Agr. Exp. Sta. Ann. Rept. 18: 289-303. 1901.

54. Goodspeed, T. H., McGee, J. M., and Hodgson, R. W. Univ. Cal. Publ. Bot.

5: 439-450. 1918.

55. Goodspeed, T. H. Address before General Session Bot. Soc. Am. Chicago,

Dec. 28, 1920.

56. Gowen, J. W. Me. Agr. Exp. Sta. Bui. 287. 1920.

57. Green, J. R. Phil. Trans. Roy. Soc. 185 B: 385-409. 1894.

58. Hartley, C. P. U. S. D. A., Bur. PI. Ind. Bui. 22. 1902.

59. Harvey, E. M., and Murneek, A. E. Ore. Agr. Exp. Sta. Bul. 176. 1921.

60. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bul. 299. 1908.

61. Hedrick, U. P. Cherries of New York. P. 83. Albany, 1915.

62. Heideman, C. W. H. Ann. Rept. Minn. State Hort. Soc. 23: 187-195. 1895.

63. Heinicke, A. J. Cornell Univ. Agr. Exp. Sta. Bul. 393. 1917.

64. Hendrickson, A. H. Cal. Agr. Exp. Sta. Ann. Rept. P. 45. 1916.

65. Hendrickson, A. H. Cal. Agr. Exp. Sta. Bul. 291. 1918.

66. Higgins, J. E., and Holt, V. S. Hawaii Agr. Exp. Sta. Bul. 32. 1914.

67. Hodgson, R. W. Cal. Exp. Sta. Bul. 276. 1917.

68. Hooper, C. H. Jour. Royal Hort. Soc. 37: 531-535. 1912.

69. Howard, W. L., and Home, W. T. Cal. Agr. Exp. Sta. Bul. 326. 1921.

70. Hume, H. H. Proc. Am. Soc. Hort. Sci. Pp. 88-93. 1913.

71. Hume, H. H. Trans. St. Louis Acad. Sci. 22: 125-135. 1913.

72. Hume, H. H. Jour. Heredity. 5: 131. 1914.

73. Husmann, G. C, and Dearing, C. U. S. D. A., Bur. PI. Ind. Bul. 273. 1913.

74. Husmann, G. C, and Dearing, C. U. S. D. A. Farmers' Bul. 709. 1916.

548 FUNDAMENTALS OF FRUIT PRODUCTION

75. Johnson, D. S. Carnegie Inst, of Wash. Pub. 269. 1918.

76. Kerner, A., and Oliver, F. W. Natural History of Plants. 2(1): 407-414.

New York, 1895.

77. Ibid. Pp. 104-129.

78. Ibid. Pp. 312-313.

79. Ibid. P. 317.

80. Ibid. P. 420.

81. Ibid. P. 453.

82. Ivirchner, O. Jahreshefte Ver. f. vaterl. Naturk. in Wiirtemburg. 1900.

83. Kirkwood, J. E. Torrey Bui. 33: 327-341. 1906.

84. Knight, L. I. Proc. Am. Soc. Hort. Sci. 14: 101-105. 1917.

85. Kraus, E. J. Bienn. Crop Pest and Hort. Rept. Ore. Agr. Exp. Sta. 1 : 71-78.

1913.

86. Kraus, E. J. Jour. Heredity. 6: 549-557. 1915.

87. Kusano, S. Jour. Coll. Agr. Imp. Univ. Tokio. 6: 7-120. 1915.

88. Lewis, C. I., and Vincent, C. C. Ore. Agr. Exp. Sta. Bui. 104. 1909.

89. Marshall, R. E. Proc. Am. Soc. Hort. Sci. 16: 42-49. 1919.

90. Massart, J. Bui. Jard. Bot. Brux. 1: 85-95. 1902.

91. Mathewson, C. A. Torrey Bui. 33: 487-493. 1906.

92. McClelland. Jour. Agr. Res. 16: 245-251. 1919.

93. Millardet, A. Rev. de Viticulture. 16: 677-680. 1901.

94. Miyoshi, M. Bot. Zeit. 52: 1-28. 1894.

95. Mottier, D. M. Carnegie Inst. Wash. Pub. 15: 174-180. 1904.

96. Miicke, M. Bot. Ztg. 66: 1-23. 1908.

97. Miiller-Thurgau, H. Landw. Jahrb. Schweiz. 22: 564-597. 1908.

98. Munson, W. M. Me. Agr. Exp. Sta. Ann. Rept. Pp. 29-58. 1892.

99. Ibid. Pp. 218-229. 1898.

100. Osawa, I. Jour. Coll. Agr. Imp. Univ. Tokio. 4: 83-116. 1912.

101. Ibid. 4: 237-264. 1913.

102. Parrott, P. J., Hodgkiss, H. E., and Hartzell, F. Z. N. Y. Agr. Exp. Sta. Tech.

Bui. 66. 1919.

103. Baton, J. B. Doctor's Dissertation. Yale University. 1920.

104. Popenoe, P. B. Date Growing. P. 113. Altadena, Cal. 1913.

105. Ibid. P. 105.

106. Popenoe, W. U. S. D. A. Bui. 542. 1917.

107. Powell, G. H. Del. Agr. Exp. Sta. Ann. Rept. 12: 129-139. 1900.

108. Price, W. A. Purdue Univ. Agr. Exp. Sta. Bui. 247. 1920.

109. Reed, H. S. Jour. Agr. Res. 17: 153-165. 1919.

110. Reimer, F. C, and Detjen, L. R. N. C. Agr. Exp. Sta. Bui. 209. 1910.

111. Rept. Vineland (Ont.) Hort. Exp. Sta. P. 17. 1919.

112. Rixford, G. P. U. S. D. A. Bui. 732. 1918.

113. Sandsten, E. P. Wis. Agr. Exp. Sta. Ann. Rept. 22: 300-314. 1905.

114. Sandsten, E. P. Wis. Agr. Exp. Sta. Res. Bui. 4. 1909.

115. Schuster, C. E. Bienn. Crop Pest and Hort. Rept. Ore Agr. Exp. Sta. 3: 44-46.

1921.

116. Shoemaker, D. M. Johns Hopkins Univ. Circ. 21: 86-87. 1902.

117. Sirks, M. J. Arch. Neerland. Sci. Ex. et Nat. (Ser. B). 3: 20.5-234. 1917.

118. Stevens, N. E. Bot. Gaz. 53: 277-308. 1912.

119. Stewart, F. C, and Eustace, H. J. N. Y. Agr. Exp. Sta. Bui. 200. 1901.

120. Stout, A. B. Mem. N. Y. Bot. Garden. 6: 333-454. 1916.

121. Stout, A. B. Am. Jour. Bot. 4: 375-395. 1917.

122. Stout, A. B. Jour. Genetics. "7: 71-103. 1918.

FRUIT SETTING 549

123. Stout, A. B. N. Y. Agr. Exp. Sta. Tech. Bui. 82. 1921.

124. Stuckey, H. P. Ga. Agr. Exp. Sta. Bui. 124. 191(1

125. Sutton, I. Jour. Genetics. 7: 281-300. 1917-18.

126. Swingle, W. T. U. S. D. A., Bur. PI. Ind. Bui. 53. 1904.

127. Trabut, L. Jour. Heredity. 7:416. 1916.

128. Tufts, W. P. Cal. Agr. Exp. Sta. Ann. Kept. P. 46. 1916.

129. Tufts, W. P. Cal. Agr. Exp. Sta. Bui. 306. 1919.

130. Tufts, W. P. Cal. Agr. Exp. Sta. Bui. 307. 1919.

131. Valleau, W. D. Jour. Agr. Res. 12: 613-670. 1918.

132. Waite, M. B. . U. S. D. A., Div. Pom. Bui. 5. 1895.

133. Waite, M. B. Amer. Agric. 75: 112. 1905.

134. Waugh, F. A. Vt. Agr. Exp. Sta. Ann. Kept. 10: 87-93. 1896-1897.

135. Ibid. 11:245. 1897-1898.

136. Ibid. 13:358. 1899-1900.

137. Waugh, F. A. Plums and Plum Culture. Pp. 282-307. New York, 1901.

138. Webber, H. J. U. S. D. A., Div. Veg. Phys. and Path. Bui. 22. 1900.

139. Wellington, R. Am. Nat. 47: 279-306. 1913.

140. Wester, P. J. Torrey Bui. 37: 529-539. 1910.

141. White, J. Ann. Bot. 21: 487-499. 1907.

142. Whitten, J. C. Mo. Agr. Exp. Sta. Bui. 46. 1899.

143. Whitten, J. C. Mo. Agr. Exp. Sta. Bui. 117. 1914.

144. Wicks, W. H. Ark. Agr. Exp. Sta. Bui. 143. 1918.

SECTION VI
PROPAGATION

The universality of variation in plants when propagated sexually is well
known. Comparatively few are the fruit plants which reproduce their
like by seed with any great degree of certainty. Though this condition
has certain disadvantages it is, on the whole, fortunate. The animal
breeder or the breeder of seed propagated plants, when he has obtained a
desirable individual, confronts the problem of reproducing its like, of
fixing the strain. The propagator of fruit plants facing the same prob-
lem has a different solution ; from the parent plant he cuts pieces each of
which produces a plant practically the same as the original. The problem
of propagation of fruit plants is essentially making these pieces of the
parent plant live. Sometimes they grow if thrust into earth; hence,
propagation by cuttings. Again, they must be placed on rooted plants
with which they can unite; hence, budding and grafting, which is in reality
the placing of cuttings is another medium.

Though the conception is simple, actual practice involves a seemingly
interminable variety of refinements and detail, varying with the climate,
the species, even the variety and with economic conditions. The mere
feasibility of a given process does not demonstrate its expediency and
though the process is expedient it does not necessarily follow that the
product is of lasting value. A certain stock may be desirable to the
nurseryman because it is cheapest, or most easily worked or makes the
best initial growth and still it may not be well suited to the orchard.
This condition may be reversed. Again, a given stock may be entirely
satisfactory if the trees are planted in one section or in one soil and totally
unsuited to another section or to another soil.

Though the art of grafting (the term as used in this discussion in-
cludes budding) apparently antedates the art of writing, many questions
growing out of its application are far from answered, at least so far as
American practice is concerned. In the early days of standardized apple
production, when the seedling orchards were newly topworked to named
varieties, there was much discussion of the effect of stock on cion and of
related questions, but attention was soon diverted to the protection of
fruit and trees from pests and for many years little notice has been given
the underground parts of the trees, except when it was forced upon
growers in some sections. With the rise of commercial nurseries the

550

PROPAGATION 551

newer generation of fruit growers know little about the propagation of the
trees they grow ; many do not know on what stocks their trees have been
worked.

Similarly, scientific investigation has devoted little attention to these
matters, being concerned with perhaps more pressing problems. For
most of the precise study in this field indebtedness must be acknowledged
to European workers.

CHAPTER XXXI
THE RECIPROCAL INFLUENCES OF STOCK AND CION

Grafts between certain plants are successful; in many other cases the
results range from partial success to utter failure. Sometimes there is
immediate failure to unite; sometimes the grafts unite but the death of
either cion or stock — generally the cion — occurs in a short time; again
the grafted parts may unite but there will be an ultimate failure in stock
or in cion. On the other hand, as with apricot on plum and on peach in
New York, plants may live a considerable time and function fairly well,
under favorable conditions, without a very successful union of stock and
cion and it is only an untoward incident, such as a high wind, that reveals
the defective union. Sometimes a certain combination can be made
with one kind of graft and not with others — the approach graft frequently
succeeds when others fail. Finally, though a certain combination of
stock and cion may be successful it is not inevitable that a reciprocal
combination will succeed.

The capricious occurrence of successful and of unsuccessful combina-
tions in grafting follows no well defined law. Jost^^ states the cases
must be accepted as they occur; they are not to be explained. DanieP"
explains most of them by the degree of correspondence of "functional
capacity" of stock and cion, i.e., that there must be, for a successful
graft, a certain relative similarity, qualitatively and quantitatively, in
their requirements for water and food and in their general habits of
growth.

Botanical relationship, as understood by closeness in the system of
classification, is a fair guide to probable congeniality but it is by no means
infallible. Horticultural varieties of exogenous plants generally may be
intergrafted freely, species somewhat less so, genera only occasionally
and families only rarely. Nevertheless, the pear and the apple form a.
less congenial combination than the pear and the quince though the
pear is more closely related to the apple than to the quince. Sahut^^^
states that the pear works on quince more readily than Portugal quince
on quince.

THE CONGENIALITY OF GRAFTS

Shoots of potato succeed better on Datura and Physalis than on
many species of the genus Solarium. According to Sahut^^s Carriere
grafted Garrya elUptica Dougl. on Aucuha japonica, thus uniting members

552

THE RECIPROCAL INFLUENCES OF STOCK AND CI ON 553

of different families. Biffen^^ succeeded in grafting Trifolium pratense
on Anthyllis vulneraria, of a different genus.

Dawson^^ cited some interesting cases: "The Photinia allied to the
beam tree (Pyrus Aria) and the Eriobotrya [loquat], allied to the medlar,
both evergreens, will graft on the medlar and not on the hawthorn.
Cotoneasters, amelanchiers and Pyrus Aria all do well on hawthorn and
last longer but make slower growth than on mountain ash. Pyrus
arbutifolia grafts well as a standard on mountain ash. ; . . Pyrus
Toringo . . . will grow on seedlings but are better on Pyrus haccata."

Manning^°^ listed several cases of incompatibility in close relatives.
The laburnum, he stated, would not take on locust. Flowering dogwood
on cornelian cherry (both in the genus Cornus) made only short-lived
unions. The Josika lilac was said to succeed on the ash while the Persian
lilac failed, though it grew on the common lilac. Coulter'*^ states that
Prumis Padus and P. Laurocerasus show a lack of affinity. Native, Japa-
nese and European plums take readily on western sand cherry, though
sweet and sour cherries unite with it much less readily."

The gooseberry will grow on Ribes aureum but not on the cultivated
edible currants. ^^ Some varieties of pears unite readily with quince
stocks, but others are so conspicuously defective in uniting that they
necessitate a resort to double working.

Berckmanns^" reported that Labrusca and Aestivalis grapes inter-
worked readily but that, apparently because of the difference in the
texture of the wood, Labrusca varieties would not take on Vulpina.
Bioletti^^ recognizes certain of the Vinifera group of grapes as having
"defective affinity" in that they do not unite at all well with the stocks in
common use; he recommends a special stock for these varieties because it
makes an excellent union with them. Among these varieties he lists
Emperor, Ferrara, Cornichon, Muscat, Mataro, Folle Blanche, Pinot,
Gamay, Gutedel; the stock recommended for them is known as 1202.

Brown^s cites a case in California in which both cion and stock grew
larger than their customary size. "Almonds grafted on peaches," he
states, "have developed a circumference of a little less than 10 feet, while
the maximum size of either, growing alone, would be scarcely 5 feet.
Where almonds are grafted on plum stock, the reverse is true." Measure-
ments are cited showing, in the almond on peach, a circumference of 9
feet 1 inch above the graft and 10 feet 4 inches below, while the almond
on plum, of equal age with the first combination, measured 4 feet below
the union and 4 feet 10 inches above.

Other stone fruits exhibit similar capriciousness. In Vermont the
Newman plum seemed to have much greater affinity for peach roots than
did Green Gage, Stoddard, Chabot or Milton; in fact the last three did
very poorly on peach stock. ^^^ In California certain prunes, including
Robe de Sargent, Imperial Epineuse and Sugar, lack affinity for the

554 FUNDAMENTALS OF FRUIT PRODUCTION

peach root; on the ahnond the last two take well but the first is again
refractory. '24 'pj^g Yellow Egg, Jefferson and Washington plums also
lack affinity for peach roots. 1^4 Wiskeri^^ g^^j^g Diamond and Grand
Duke to this list. Sugar, mentioned above as failing on peach, succeeds
on apricot, while the French prune fails on the latter stock. ^^

Swingle'^" calls attention to the lack of compatibility between the
Satsuma orange and the sour orange stock. On the sweet orange, growth
is satisfactory but the fruit is poor; by far the best results are secured on
trifoliate stock. The kumquat unites with the sour orange but dies
after starting growth, though on trifoliate stock it gives very satis-
factory results. Bonns^'' reported the trifoliate to be distinctly dwarfing
for lemon, much more so than for orange.

Apple varieties show various degrees of congeniality with dwarfing
stocks. Hedrick^^ reported Mcintosh, Wealthy and Lady to be the most
congenial of a large number of varieties tested, and Jonathan, Esopus,
Grimes, Alexander, Wagener, Boiken and Bismark as "very satisfactory."
Baldwin, Rhode Island, Rome, Ben Davis and Northern Spy were uncon-
genial and Twenty Ounce gave the poorest results.

Mclntosh^^^ is said to make a strong growth as a young tree on cion-
rooted Transcendent Crab, though Red Astrachan is markedly dwarfed
on the same stock.

Maynard'"^ described a case which may be considered to have a
bearing on the present question. It was reported as follows: "About
10 years ago six small trees of yellow Siberian crab and three of Williams'
Favorite were planted as represented in the following diagram, S indicat-
ing Siberian crab, S.B. the same budded and W Williams' Favorite;

S W S.B. S W S.B. S W S.B.

"The trees were all of the same size as nearly as could be selected
and every third tree in the row was top-budded with the Williams'
Favorite. The buds all grew well the first season, but the subsequent
growth was very little and at the end of 10 years all were dead. The
diameters of the three Siberian crabs were 4, 4}-^ and 6 inches, of the three
Williams' Favorite 3%, 3 and 3 inches, while none of the budded trees
reached over % of an inch." It is difficult to decide whether this is a
case where the cion influences stock or stock influences cion but the fact
is worthy of record here.

Reciprocal or inverse grafts are not always equally successful. This
may be due in part to lack of adaptability rather than to a lack of affinity,
but there appears at times to be a real lack of congeniality in a graft
whose opposite is congenial. In some of Daniel's work the grafts of
pimento on tomato seemed rather less successful than those of tomato on
pimento.^^ Sahut'^'' states that the Mahaleb succeeds as a cion on no
other cherry though it is the standard stock for the sour cherry in America

THE RECIPROCAL INFLUENCES OF STOCK AND CI ON 555

and that the pear does better on the apple than the apple on the pear.
Baltet states that medlar does well on quince but the quince fails on
medlar; the same holds true with quince on hawthorn and vice versa.
Sweet cherry on sour cherry is more successful than the reverse
combination.^^

Tufts states: " . . .it has been the experience of certain growers
in the Vacaville section, California, that practically all the varieties of
Japanese plums will work satisfactorilj'- with domestica varieties. How-
ever . . . the insertion of European plum scions on Japanese plums
does not always result in a satisfactory union. It has been found that
plum orchards, where worked over to Japanese varieties, could not be
worked back to European varieties unless all the Japanese wood was
taken from the tree."^*^

Similar contrasts in reciprocal grafts occur in the combination of
various evergreen on deciduous plants. There are numerous instances
of at least passable success in grafts of this sort, but the inverse combina-
tion, deciduous on evergreen, is almost invariably a failure.

Congeniality and Adaptability Distinguished. — Distinction should be
made between congeniality and adaptability. The former term refers
to the degree of success of the union between stock and cion; the latter
term to the relation of the combined parts to environment, most often
to soil and climate. Husmann's conception of perfect congeniality
in grapes is a condition in which "a variety grafted on another behaves as
if the stock were grafted with a scion of itself, the union being perfect and
the behavior of the vine the same as that of an entire ungrafted plant. "^*
He states also, "When both stock and scion are suited to the conditions,
but will not thrive when grafted, congeniality is lacking." Further:
"The adaptability of varieties to soil, climates and other conditions can
often be closely forecasted, but congeniality has to be determined by
actual test."

Congeniality and adaptability are sometimes differentiated only
with difficulty, as is shown by the following quotation from Blunno:^^
"In France, however, it was found that the yield of the French vines
grafted on du Lot was low; our experience is exactly the same at the
Viticultural Station, Howlong [New South Wales] — the wine-grape
varieties grafted on this stock are the poorest croppers of all. In Sicily,
however, the affinity between the native European vines and the Rupe-
stris du Lot seems to be perfect and the yield is heavy. In this state the
principal wine-grapes are French varieties and this explains how our ex-
perience with vines on Rupestris du Lot as poor croppers is similar to
that in France."

The most congenial combination is not necessarily the most successful,
as is shown by an experience in New York, citied by Bailey.^ Plum
and peach stocks failed to make satisfactory unions with the apricot

556

FUNDAMENTALS OF FRUIT PRODUCTION

and sometimes the trees were broken at the union by high winds. Worked
on apricot roots, the apricot made a better union and few trees were
lost through breaking off; nevertheless in spite of the congeniality of this

combination, the death rate of these trees was higher than that of apricots
on other stocks. This evidently is a case of a lack of adaptability being
the limiting factor. Budd^^ reported similar lack of adaptability between
Russian apricots and plums. In this case some of the trees died without

THE RECIPROCAL INFLUENCES OF STOCK AND CION 557

breaking off, death being due to the failure of the roots to receive enough
elaborated food from above, though the tops seemed not to suffer greatly
till the root systems collapsed. Paul C. Stark reports the peach a much
better stock for apricot than plum. In California there appears to be
little difficulty in effecting union between apricot cion and peach or plum
stock, but the almond stock proves recalcitrant.^^* In France certain
plum stocks are used in the north but farther south success is attained
with ahftond, apricot and peach stocks as well as plums. Evidently
the same difficulty is experienced with almond stock near the Mediter-
ranean, for Baltet described a double working when this stock was
used.i"

From India is reported an interesting case. Brown, ^^ trying
numerous stocks for Malta and Satsuma oranges, found extraordinary
differences in the behavior of the sam'e variety on different stocks and
of the same stock worked to different variaties. For the Malta orange
the "rough lemon" gave greatest vigor and fruitfulness, the "sweet
lime" was suitable only to amateur growing, producing a small tree with
a few oranges of high quality, while the citron and sour orange were
unsuitable. On the other hand the Satsuma orange gave best results
on the sweet lime; the rough lemon and citron proved unsuitable.
Figures 56, 57 and 58 show clearly differences associated with the influ-
ence of stock on cion and of cion on stock. It is noted by Brown that
his results are not in accord with American experience, particularly in
the poor growth with the sour orange as a stock for the Malta orange.
The Satsuma on the same stock was satisfactory, completely reversing
the results obtained in California.

This situation seems analagous to that just outlined for grapes and
suggests that adaptability and possibly congeniality may be operative
in producing these striking differences and contradictions.

THE INFLUENCE OF STOCK ON CION

The recognition of dwarfing stocks is assertion of the effects of the
stock on the cion; the recognition of the utility of grafting is acquies-
cence in the independence of the cion. At first glance the question
seems to hang on both horns of the dilemma.

Stature. — At the outset the dwarfing effects of certain stocks, such
as the quince on the pear, the Paradise and Doucin apples on the standard
apples, the Sand Cherry on plums and sundry others must be conceded
as evidence of the effect of the stock on the cion.

Parenthetically it may be stated that much of the conflicting evidence con-
cerning quince stock is due to the different kinds of quince used. Barry, as
early as 1848, noted a mixing of quince stocks as received from French nurseries. ^^
Apparently in England at present the situation is very much confused.^^

558

FUNDAMENTALS OF FRUIT PRODUCTION

Dwarfing effects are most evident and best known, but others occur.
In general the top of a grafted tree tends to assume a size equal to that
of the top which the stock would have formed if ungrafted. There are,

■> So

however, exceptions and qualifications. Northern Spy, itself a vigorous
grower, tends somewhat to dwarf many other varieties worked on its
roots. 13* Some varieties of apple form characteristically small trees,

THE RECIPROCAL INFLUENCES OF STOCK AND CI ON

559

while others assume large stature, both worked on similar stock. Certain
dwarf varieties of peach remain dwarfed regardless of the stock on which
they are worked.

On the other hand, some plants attain greater size on roots other
than their own. The common lilac is said to be greatly increased in
stature on the ash, though this is a short lived graft. Similar increases
are said to obtain when Pinus Gerardiana is worked on P. sylvestris,
incense cedar on common cedar^'*^ and in herbaceous grafts, as in
Phy salts on potato, Arabis alhida (rock cress) on Brassica oleracea
(cabbage, etc.,) and Solanum dulcamara (bitter-sweet) on S. ly coper sicum.

Rose acacia is considered to grow larger on Eobinia viscosa; likewise

iiitii

\\ ih

iiiLM' Mil f 1 ('/// '//(, sour
oraMgc (," kluUt;i " ul India) ; ii;:ihl, saiuu on (.'. LitiLumnn, lough lenioa (, khaiiia ' uf India).
Twenty-seven months planted. (After W . Robertson Brown.^^)

the dwarf double-flowering almond on peach. ^"^ Magnolia glauca
(swamp bay) is reported to attain three times its normal size when
grafted on M. acuminata (cucumber tree), though this has been suggested
as due to the lack of adaptation to ordinary soil in the root of the former,
which is a bog plant.

It is stated that Grimes and Winesap apples increase in vigor when
worked on vigorous stocks."^ A similar influence is exercised by
American persimmon on Japanese persimmon cions.*^ Prunus pumila
(sand cherry) makes an increased growth on plum stock. ^^ Among
growers of Vinifera grapes the Rupestris St. George (du Lot) stock is
generally known to induce unusually vigorous growth in varieties worked
upon it and skilful vignerons recognize this difference when pruning.

Hedrick^^ reports an experiment in which a number of grape
varieties more or less grown in the grape regions of New York were studied

560

FUNDAMENTALS OF FRUIT PRODUCTION

on three stocks; Clevener, a Labrusca-Riparia hybrid, grown in New
York as a direct producing wine grape, Rupestris St. George (or du Lot), a
stock obtained through Cahfornia from France and Riparia Gloire, also
a repatriated American. It should be borne in mind that all the cion
varieties are commonly grown in this section as direct producers, i.e.,
on their own roots. In almost every case at least one of the stocks used
caused a marked increase in vigor over that of the cion variety on its
own roots. Table 1, condensed from Hedrick's data, shows the growth
ratings of several varieties as direct producers and on the various stocks.
This growth rating should be distinguished from total growth since
Hedrick states distinctly that the grafted made less wood growth than
the ungrafted vines.

Table 1. — Relative Growth Rating of Grape Varieties on Different Stocks

IN 1910

(After Hedrick-'^)

Variety

Own roots St. George

Gloire

Clevener

Brighton

Campbell ,

Catawba

Concord

Delaware

Herbert

lona

Niagara ,

Vergennes

Worden

Average 20 varieties

55.0
17.3
40.0
46.0
46.0
64.6
26.8
53.9
44.1
26.1

40.0

56.0
62.1
74.0
94.0
60.0
87.5
45.6
84.5
77.8
36.0

63.2

73.7
54.6
70.0
90.7
68.7
87.1
43.0
57.5
69.2
61.6

65.2

75.0
35.0
81.6

81.6

56.4
90.3
38.1

67.9

In general, when a symbiotic relation between stock and cion exists at
all, there is apparently a tendency toward a balance between the two.
The influence is relative. A dwarfing stock is dwarfing because of the
limitations on its development relative to the top. There is nothing
inherent which impels it to dwarf all tops worked on it. As an example
the quince may be considered. It obviously dwarfs pears in general,
yet it is said to increase the vigor of Cratcegus glabra Thunb.^^* while its
dwarfing effect on the loquat is slight or absent. ^^

Form. — Closely related to vigor of growth, possibly interwoven with
it, is form or habit of growth. According to Loudon, ^°^ "Cerasus canaden-
sis," naturally a rambling shrub, assumes an upright habit when grafted
on the common plum, while Tecoma radica7is on catalpa forms a round
head with pendent branches. Garry a elliptica, Sahut states, '^° grafted
on Aucuha branches less. Chamcecyparis obtusa pygmcea, according to

THE RECIPROCAL INFLUENCES OF STOCK AND CION 561

Burbidge,^® worked on C. Boursieri, grows erect, while on Biota or Thuya,
or if grown from cuttings, it spreads horizontally on the ground. The
same writer quotes Briot to the effect that the Lihocedrus tetragona is
changed from a narrow cyUndrical column to a wide-spreading form by
working on Saxegothcea.

Among fruit plants, the plum and peach have been cited as showing
in the habit of their tops the influence of the stocks on which they are
growing.

Knight**^ described this influence: "The form and habit which a
peach tree of any given variety is disposed to assume, I find to be very
much influenced by the kind of stock on which it has been budded; if
upon a plum or apricot stock, its stem will increase in size considerably,
as its base approaches the stock, and it will be much disposed to emit
many lateral shoots, as always occurs in trees whose stem tapers consider-
ably upwards: and, consequently, such a tree will be more disposed to
spread itself horizontally, than to ascend to the top of the wall, even when
a single stem is suffered to stand perpendicularly upwards. When,
on the contrary, a peach is budded upon the stock of a cultivated variety
of its own species, the stock and the budded stem remain very nearly
of the same size at, as well as above and below, the point of their junction.
No obstacle is presented to the ascent, or descent, of the sap, which
appears to ascend more abundantly to the summit of the tree. It also
appears to flow more freely into the slender branches, which have been
the bearing wood of preceding years; and these extend themselves very
widely, comparatively with the bulk of the stock and large branches."

Comparing the growth of the Milton plum on various stocks, Waugh^^^
reported: "The trees of this variety growing on Wayland roots are
upright narrowly vase-form, with relatively few large branches. They
are almost as narrow headed as typical trees of Abundance or Chabot.
On Marianna roots, in the very next row, the trees of Milton are low,
round-headed, bushy, with thick-spreading, drooping tops, much Hke
trees of Marianna. If anything, they exaggerate the typical character
of the Marianna head. Moreover, the leaves are several shades darker
and glossier and the twigs are dark red instead of being green as in trees
of the same variety growing on Wayland roots. On Americana Milton
has almost the same characters as on Wayland."

Somewhat later Stewart,^^^ describing these same trees, wrote: "At the
present time the differences in color of foHage and bark of young twigs are not
noticeable, neither is the ' upright narrowly vase-form ' head of Milton on Way-
land anywhere near so pronounced. Notwithstanding these modifications, how-
ever, there is still a marked difference in the habit of growth of the trees upon
Wayland and Marianna stocks. On Wayland the habit of growth is more or
less upright, whereas on Marianna the head is low, bushy and spreading. Doubt-
less, as the trees grow older, these differences will tend to become less marked."

562 FUNDAMENTALS OF FRUIT PRODUCTION

Rough lemon stock is said to produce tall upright trees of the varieties
worked on it.-*^

Seasonal Changes. — In the orchard or vineyard, cultural practices
have, in the majority of cases, no very obvious influence on the time of
starting growth, but the effect on ripening and maturity is more marked.
The classical experiment of introducing a vine or a branch of a tree into
a warmed room during the winter, keeping its connection with the parent
stock and observing it start growth while the remainder of the plant is still
dormant, would lead to the inference that the cion is practically indepen-
dent of the stock in the spring flush of growth. So it proves in most cases.

End-season Effects. Ripening of Fruit. — Concerning effects at the
other end of the growing season there is some conflict of evidence. It is
rather well known that some of the annual species of Convolvulacese
become perennial when grafted on perennial species." Daniel reports
that by grafting the annual parts of certain perennials on certain other
perennial plants he has succeeded in prolonging the life of the cions.*^
Conversely, in some instances, cions of perennials grafted on annual
stocks have died at the usual time for the stocks, though Lindemuth^^ has
shown a case where the plant lived longer. Such instances as these are
more striking than those observed in fruit plants, where the possibility of
change is necessarily more limited. It is sometimes claimed that grafting
in itself hastens maturity in grapes by a few days. Cole^" states that
several growers in Victoria claim a few days earlier ripening in peaches
worked on almond than on peach stock, while in France Sahut^^" claims
that the Myrobolan plum induces earlier ripening in peaches than does
almond stock. Sahut states also that cherries ripen earlier on Laurocera-
sus than on ordinary cherry seedlings and the Reine Claude plum on
Damas is said to be somewhat earlier than on St. Julien. Cole reports
that heavy autumnal rains in Victoria are not so likely to induce second
growth or fall blossoming in plums worked on Marianna roots as in those
worked on Myrobolan and attributes this to the early dormancy of the
former stock.

In America topworked trees were more common formerly, propor-
tionately at least, than they are now and discussions of mutual influences
were correspondingly more frequent. These discussions show a sur-
prising variety of experience and opinion, particularly in the effect of the
stock on the time of ripening of fruit in the autumn. Diametrically
opposite results apparently come from identical combinations of stock
and cion. Hovey recounted extensive combinations of early pears on
late and vice versa in Massachusetts, without any change from the usual
season of ripening. There was, however, rather good evidence that
plums on Myrobolan ripened earlier than on late plums. In apples,
Shaw states that "particularly with Rhode Island Greening the season of
ripening is influenced by the stock." ^^^

THE RECIPROCAL INFLUENCES OF STOCK AND CI ON

563

The trifoliate stock is generally conceded to secure early ripening in
oranges. Florida experience seems to indicate that oranges on rough lemon
stock cannot be held on the trees as long as when grafted on sour orange.^"

The grape, however, supplies the best examples of stock influence on
fruit ripening. Wickson states that the Riparias Gloire and Grand Glabra
induce ripening one to two weeks ahead of Rupestris St. George. Hed-
rick found that many American grapes on Gloire and Clevener stocks
consistently ripen their fruit ahead of the same varieties on their own
roots. In the St. George there was less uniformity of effect; in fact this
stock seemed to retard the ripening of some varieties. This difference of
a few days is likely to assume considerable practical importance with
late varieties in regions where autumnal frosts come early or where
autumnal rains are frequent.

Husmann^^ considers that the degree of congeniality between cion and
stock influences the time of ripening. From this point of view it may be
inferred that the same stock may have a retarding effect on one variety
and hasten the ripening of another. Much conflicting evidence, in other
fruits besides grapes, may be reconciled in this way.

Table 2, including data taken more or less at random from Husmann's
figures, indicates that this possibility may be realized. Taking Lenoir as
the standard, grapes on St. George have ripened, in one case 4 days ahead, in
another case 9 days after, Lenoir. Dog Ridge has ripened fruit on its
cion varieties 2 days ahead and 13 days after the same varieties on Lenoir.

Table 2. — Ripening Dates of Grape Varieties on Different Stocks
{After Husmanrfi^)

Stock

Variety

Dog Ridge

Lenoir

Rupestris St.
George

Aramon

Sept. 29

Sept. 27
Sept. 20
Sept. 28
Sept. 23
Sept. 10
Sept. 15
Sept. 28

Sept. 28

Bastardo

Sept. 23
Sept. 28
Sept. 23
Sept. 23
Sept. 28
Sept. 26

Sept. 25
Sept. 26

Bicane

Blauer Portucieser

Sept. 24
Sept. 15

Boal de Maderc

Sept. 24

Sept. 24

Data introduced later to show differences in the composition of fruit
on several stocks may be anticipated here. Those differences that are
found can be considered to represent such as might occur in separate
specimens on the same tree or vine. Much of the available data is from
European sources, or, if from America, it concerns such plants as are

564 FUNDAMENTALS OF FRUIT PRODUCTION

shown elsewhere to be rather sensitive to temperature conditions during
the growing season. In other words, nearly all the available data con-
cern plants or situations such that the difference between heat required
and heat available is small. The grape in the northeastern states is
near the limit of its summer heat requirements; the pear and the apple
are not.

The evident readiness of European authorities to recognize small
differences in ripening according to the stocks used and the preponderance
of American opinion — aside from a few instances — to the contrary can be
reconciled if the climatic differences are considered. Just as a few days of
unusual heat in the spring will force into simultaneous bloom varieties
that blossom at different times in a cooler season, the greater heat at
harvest in America probably obscures small differences that would be
apparent in a cool region or in a cool season.

End-season Effects. Maturity of Wood. — Evidence of the effect of the
stock on the maturity of the wood, on the contrary, seems brought out
more clearly in America than in Europe because of the different winter
climates and the intimate relation of maturity to hardiness. There is,
however, some mention of these effects in parts of France. Baco reports
considerable difference in the time of ripening of the wood in grapes,
stating: "In recapitulation, the grafted vines ripened their canes less
than vines on their own roots. In this respect many grafts have appeared
to us to be influenced by the stock about as they would be by nitrogen-
ous fertilizers or by a mellow deep and fertile soil if one had not grafted
them,"* Since these differences have most intimate relation to hardiness,
they are discussed under the effects of the stock on hardiness.

The fall of leaves from a deciduous stock does not cause the fall of
leaves on an evergreen cion. Though the trifoliate orange is deciduous,
other varieties worked on it are not; though the quince is deciduous, a
grafted loquat top is evergreen. This holds true in other cases. How-
ever, despite this retention of foliage, it is probable that the deciduous
stock has some effect tending toward a partial dormancy. Evidence of
this lies in the smaller injury at a given temperature to orange on trifoliate
than on evergreen stocks and in the possibility of transplanting the
loquat on quince without "balling" of the roots, provided the leaves are
stripped, though this cannot be done if it is on its own roots.

Spring Effects. — Returning, for the sake of completeness, to the effect
of stock on spring growth, the behavior of cherries on Chicksaw plum
may be cited as typical. The stock starts much earlier and throws out
leaves and shoots while the cherry grafts remain dormant until their
customary season of growth. "^^ However, Brown^^ recognizes a delay
in blossoming of plums and almonds on certain varieties of plums. He
states: "Blossoms appear on plums from 1 to 2 weeeks later than the
almond. Where the plum stock has been tried the delay has been about

THE RECIPROCAL INFLUENCES OF STOCK AND CION 565

one-half the difference between the two blooming periods." It seems
quite possible that this difference can exist in one climate and not in
another. A retarded entrance into the rest period in the autmnn is
shown elsewhere to delay the opening of peach blossoms in the spring. If
the plum stock prolongs growth in the fall, it will evidently have a re-
tarding effect on blossoming in the spring. However, the rest period is a
retarding factor only in climates with mild winters and early springs and
it is only in such climates that the retarding influence of plum stocks would
become obvious. In the north the rest period ends before the dormant
period and no retarding influence from the stock would be expected.

Baco^ recorded considerably more copious bleeding in Baroque and
Tannat grapes grafted on various American and hybrid stocks than on
their own roots. He also reported differences in the time of breaking of
the buds ; those on the own-rooted vines opened much more regularly and
somewhat earlier than those on the grafted vines. As a rule the vines
on hybrid stocks blossomed later and more irregularly. ■■*

Here again, as in the ripening of fruits, it is in Europe and particularly
with grapes that more attention is given to slight differences due to stocks
and here again climatic factors explain the few differences observed.

Several European commentators are inchned to emphasize the need
of substantially the same seasons of growth inception in stock and cion
to insure compatibihty. Lindemuth states that his investigations have
led him to the same conclusion in this respect as that of Lucas, to wit : a
graft of an early starting kind on a late starting kind is never successful:
" . . . late starting kinds grafted on early starting stocks, very fre-
quently become sick, since they are not able to take up the quantity of
sap which the early-starting seedling offers. Canker injuries at the point
of grafting are very often the consequences of defective grafts of this
kind. Less easily does the early starting cion become sick on late starting
sorts. The more nearly equal in time and strength the growth of the
cion and stock are, the better, according to the opinion of Dr. Lucas, is
the success of the graft." ^''-

An expression of the same influence in the apple in Brittany is fur-
nished by Duplessix;^^ "... if one inserts a cion of Doux Normandie
[blossoming in June] on a stock from seed of Launette [blossoming late
in April], the sap will ascend in the trunk 6 weeks before the graft is
ready to receive it. The tree may die. If it lives the sap will accumulate
in the swelling at the base of the graft and this swelling . . . can
become in its turn a cause of death. ... If the reverse be tried, the
cion of Launette will require sap when the Doux Normandie trunk is
not ready to provide it and the cion of Launette will perish or it will grow
slowly for want of feeding at a useful time.

"... A stock starting earlier than the graft is preferable to one
starting later."

566 FUNDAMENTALS OF FRUIT PRODUCTION

Though these two views differ in details, they agree in the general
harmfulness of great differences in the starting season between stock and
cion. The very fact that these differences can become harmful is evi-
dence against any considerable modification of either stock or cion in
season of growth inception.

In brief, then, the influence of the stock on the season of the cion may
be stated, for spring manifestations, in Knight's words: "The graft, or
bud, whenever it has become firmly united to the stock, wholly regulates
the season and temperature, in which the sap is to be put in motion, in
perfect independence of the habits of the stock, whether these be late
or early." Concerning the effects on autumnal processes, it may be said
that some influences exist but may be obscured by the climate and that
they are not necessarily parallel to the nature of the stock.

Hardiness. — As to the effects of the stock on the hardiness of the cion
there is considerable conflict of evidence, due in part, perhaps, to lack
of precise definitions. It is frequently stated in European pomological
literature that pears on quince stock are much freer from canker than on
pear stock. Elsewhere in this work rather strong evidence is cited to
show that the common frost canker of Europe is associated with lack of
maturity. Evidence presented earlier in this section suggests that cer-
tain stocks may affect the season of maturity of the tops.

Hardiness has been shown to be involved to a great extent with water-
retaining capacity which in turn appears to depend in no little degree on
maturity. It may be affected by cultural practices and in some cases,
apparently, by the stocks used. The stock may, to this extent, be con-
sidered to induce hardiness in the top. If, however, the conception of
hardiness be that of a specific property which is present or absent there
is no evidence that it is transmitted from stock to cion. It is conceivable
that a stock may in itself be hardy but through the congeniality of the
graft it may actually diminish the hardiness of the cion.

Fruit growers of the upper Mississippi Valley have a well defined
belief that such varieties as Jonathan and Grimes are rendered hardier
by topworking on Haas, Oldenburg and similar hardy varieties. It
seems plausible that with some varieties there is a certain increase in
hardiness due to a slightly earlier maturity; more important, however,
is the consideration that the cases under examination are not so much
cases of increasing hardiness as they are of substituting a hardy variety
in those parts of the tree that are particularly susceptible to winter injury.
Even though the hardiness of the cion were not increased in the least, a
tree of Jonathan topworked into Oldenburg framework could not help
but be hardier, though only within limits. Macoun,^''^ in Canada, top-
working such varieties as Baldwin into hardy stocks, was unable to
increase the hardiness sufficiently to stand a test winter.

Hedrick^^ reports that Mahaleb stock makes hardier tops in cherries,

rUE RECIPROCAL INFLUENCES OF STOCK AND CION 567

both in nursery and in orchard, because of the earher ripening of the wood.
Prunus lusitanica is said to ripen its wood earher on Prunus Padus stock
than on its own roots and to withstand cold weather better, probably
on that account.^"* Budd^^ reports the Jonathan apple ripening its
terminal shoots better on Gros Pomniier "than on its own roots" and
states that "the hardiness of a variety is increased by the influence of a
stock with a determinate habit of growth. ... In our own State
[Iowa] we have evidence that by the selection of proper stock we can
grow Jonathan or Dominie on low, wet soils where they would not reach
bearing size, root-grafted . . . the main utility with us of top-working
on such prepotent stocks as Gros Pomier, Duchess, Wealthy, Wolf River,
etc., is in the way of fitting the less hardy scion for enduring the tempera-
ture of our test winters."

Experience with grafted grapes in regions where winter killing is
important was more extensive in an earlier generation than in the present.
The literature of the times shows a tendency to agreement in the increased
hardiness of certain varieties such as lona and Adirondac on hardy stocks
such as Concord. Precise observations as to the reason for this were
not common, but the suggestion was made that lona roots were tender."^
The increased hardiness was secured, if this be true, by the substitution
of a hardy variety in a tender part and not by changing the nature of the
cion. Here again, roots inducing early maturity appear to increase
hardiness. Nicholas Longworth,^^ after extensive trials, reported,
"Foreign vines grafted on our natives are equally tender as on their own
stock and are, with me, often killed down to the native stock."

It is not, it should be noted, invariably the stocks inducing early
maturity that are hardiest. St. George stocks, as reported by Hedrick,
induced late growing in many cases; however, they suffered rather less
from winter killing than the other stocks tested. Hedrick suggested that
the deep rooting habit of this variety may be connected with its hardiness.

Onderdonk^i^ and Vosbury^*^ reported that in the Gulf States the
trifoliate orange increased the hardiness of the varieties worked upon it
and attributed the hardiness to the deciduous habit of the trifoliate,
inducing a degree of dormancy in the cion varieties and thereby making
them more cold resistant. In the freeze of 1913 in Cahfornia lemons
worked on orange trunks proved more hardy than those on their own
trunks, hardier not only in the orange trunks but in the lemon tops. It
was suggested ^^^ that in some way the trunks of the trees modified the dor-
mancy of the tops. This condition was more apparent in young trees
than in those of bearing age. As in the Gulf States, trees on trifoliate
were somewhat hardier than those on other stocks. In cases of severe
injury, however, when the entire top has been killed, the trifohate
is unable to send up any sprouts and dies, though it has not itself suffered
any direct injury from the cold weather.

568 FUNDAMENTALS OF FRUIT PRODUCTION

Disease Resistance. — Cole'*'' recommends the "Kentish sucker as a
cherry stock for fruit growers in Victoria because many varieties are
less likely to gum when worked upon this stock than on Mazzard seed-
lings." Presumably the gumming to which Cole refers is the physiologi-
cal type. Barss,^* in Oregon, recommends the genuine Mazzard stock
as freer from bacterial gumming than miscellaneous seedlings from the
ordinary sweet varieties. This, however, is another case of substitution
in part of the tree rather than of change in the part grafted in, since to
secure the greater freedom from the disease it is necessary to grow the
tree two or three seasons in the nursery or the orchard and then graft
it over in the limbs.

Sometimes increased resistance to fungous diseases is claimed from
top working, as in the gooseberry on Ribes aureum, but no evidence is
available of any direct influence. In the case just cited any increased
resistance is due probably to the changed habit of the plant, the increased
height securing better aeration.

In California the black walnut is used as a stock for the English
walnut {Juglans regia), in large part because of its resistance to a soil
fungus, the mushroom root rot {Armillaria mellea), to which the English
walnut roots are very susceptible. This is, again, a case of substitution
and not an influence of stock on cion.

The claim is sometimes made that certain stocks make the top more
or less resistant to insect or fungous attack. Since vigorously growing
trees are more subject to aphis or to fire blight and perhaps less subject
to certain cankers, it is quite conceivable that a stock affecting growth
may indirectly have such an influence. The same effect, however, can
be secured by cultvu^al practice and no available evidence indicates
any modification of a specific nature in the cion by the stock making it
more or less liable to insect or fungus attack.

Physiological Diseases. — Diseases of a mosaic nature are, of course,
transmitted in either direction by grafting. DanieP^ states that some
cases of court noue in the grape can be traced to grafting and expresses
the belief that it is due to "a kind of physiological trouble induced by
osmotic changes caused by the union of plants of different chemical
functional capacities." Daniel's statement that the characteristic
shortened internode appears also on shoots from the stock suggests a
condition similar to the transmission of pathological variegation rather
than a specific change due to grafting. Daniel states that grafted beans
grown in nutrient solution were free from chlorosis longer than check
plants which had absorbed more of the solution. ''Since the chlorosis
could not be attributed," he states, "to anything but the presence of
an excess of a salt (carbonate of lime, or another), it is necessary to
admit that this salt has passed in less quantity because of the different
osmosis and because of its utilization at the graft-union to neutralize the

THE RECIPROCAL INFLUENCES OF STOCK AND CION 569

acidity of the wound surface. In a word, these results show very clearly
that the graft, considered by itself, modifies the regimen of water and
of soluble salts, that is to say, of the functional capacities of the grafted
plants."

In support of this view he cites Viala and Ravaz to the effect that the
Herbemont grape was free from chlorosis on Clairette; likewise Merlot
on Viala. It seems possible that these last instances may be due to a
high degree of congeniality between the varieties mentioned. Blunno^*
states that many resistant stocks are without chlorosis until they are
grafted, but become so afterward, explaining this through the weakening
of the plants by grafting. Susceptibility is greater, he reports, when the
graft is not well healed and any weakening influence such as a fungus or
insect pest, even on a resistant variety, favors infestation by phylloxera.

Since John Lawrence, ^^ in 1717, noted the transmission from the cion
to the stock of variegation in leaves, this fact and its converse have been
cited as standard evidence of the influence of stock on cion or of cion on
stock or both. Numerous instances of such transmission are easily found,
but have lost much of their significance through the view that in many
cases variegation is a pathological condition and that grafting is in such a
case also an inoculation. Variegation arising from other than patho-
logical causes seems not to be transmitted from stock to cion or from cion
to stock.

Yield. — Some commentators are disposed to believe that grafting
per se disposes the plant to fruitfulness. This is well expressed in this
statement: "Seedling apples, especially those which are of a vigorous
nature, run to wood and produce few fruits, or begin very late to produce
them. Grafted apples, on the contrary, begin earlier to fruit." ''^ . . .
Undoubtedly early bearing is favored by grafts which have not united
perfectly, just as it is by ringing or by any influence obstructing trans-
location. Whether grafts which unite readily have the same effect is
not so clear. Precocity of bearing is necessary to the success of any
variety in cultivation; deficiency in this respect is the chief objection
to the Northern Spy apple and the chief reason that it is now so little
planted. Naturally, then, grafted trees of cultivated varieties tend to
come into bearing early; otherwise the varieties would not be in culti-
vation. Some varieties come into bearing at an earlier age than others,
though all are grafted presumably on the same stocks. This time can
be hastened or retarded by cultural means. Vigorous seedlings are
late in bearing; so are vigorous grafted trees. There seems no clear
evidence that grafting in itself, as commonly practiced in fruit trees,
hastens the time of bearing.

The influence of different stocks on the functioning of the cion is
shown neatly by experiments such as those of Lindemuth'-** on potatoes.
This investigator found that the potato on Datura, a vigorous growing

570 FUNDAMENTALS OF FRUIT PRODUCTION

stock, forms aerial stolons freely. The combination plant grows vigorously
and manufactures much starch which cannot go into tuber formation as
it would in an ordinary potato plant. It is, therefore, because of the
vigor of the stock, utilized in the conversion of the potato stolons into
leafy shoots. On a weakly growing stock, however, such as Capsicum
annuum, starch accumulation exceeds utilization and tuber formation
ensues from the buds which on Datura stocks give rise to shoots.

Fruit-bud Formation. — Voechting^^^ "has shown that buds which grew
from the base of the inflorescence of a beet in the second year came out as
leafy shoots supplied with large leaves, if they were grafted on a 1-year
beet; on the contrary, they infloresced if they were placed on a stock
already in its second year."

Leclerc du Sablon^^ shows differences in total carbohydrates in
the tops of Angouleme 2 years grafted on pear and on quince stocks.
Except in May the carbohydrate content of the pear on quince is higher
than that of the pear on pear. In view of the importance of carbohy-
drate content to fruitfulness this difference seems of possible signifi-
cance, though it is comparatively slight at the ordinary time of fruit
bud formation.

Table 3. — Total Carbohydrates in Tops of Angouleme Pears Grafted on Pear

AND on Quince

(After Leclerc du Sahlon^'^)

(Per cent, on dry weight basis)

On Pear On Quince

Jan. 19 23.7 25.9

Feb. 26 21.7 25.4

Mar. 28 24.3 27.9

May 9 21.6 21.3

June 17 22.2 22.6

July 22 22.6 22.9

Sept. 7 24.5 25.8

Oct. 16 23.4 25.4

Nov. 22 23.4 25.3

Dec. 26 23.4 25.5

Specific citations are hardly necessary to show the influence of
certain stocks on fruit-bud formation. The dwarfing stocks, through
limiting growth and therefore carbohydrate utilization, have a general
tendency to permit sufficient carbohydrate accumulation for free forma-
tion of fruit buds. European and Japanese chestnuts, for example,
worked into chinquapin, bear in 1 or 2 years. ^^ It should be remem-
bered, however, that the total framework on which fruit buds can be
formed is smaller and the total production of fruit buds on a given area
of ground is not necessarily greater and may even be smaller, when
dwarfing stocks are used. In some cases certain stocks not dwarfing
in themselves make poor unions with cions set in them and exercise a

THE RECIPROCAL INFLUENCES OF STOCK AND CI ON

571

dwarfing effect. Some Wildgoose plums are said to be more fruitful
on peach roots. '^'*

These instances are introduced here, not as showing a general tend-
ency toward any marked influence of stock on cion, but rather the
dearth of more positive evidence. Considering the amount of top-
working that has been done, little evidence of a change of practical im-
portance has been accumulated. There has been a general tendency
to assume that if there is any influence on the size of fruit the dwarfing
stocks tend to produce larger fruit. Most of the instances just cited
fail to bear out this idea.

In Victoria Cole"*" reports that many varieties of plums which are
shy bearers on Myrobalan stock are prolific on Marianna. "Although
some varieties . . . somewhat overgrow this stock it is no great fault
but an improvement — it influences the bearing qualities of varieties so
inclined to overgrow."

In France some years ago, according to Pepin, ^''^ there was a dwarf-
ing apple stock, neither Paradise nor Doucin, known as the Pommier
hybride or batard; grafts on this grew vigorously but bore little fruit
and that little was inferior.

Bioletti,^^ reporting on the St. George grape stock, states: "In some
cases the vines grow well but the crops are unsatisfactory. This has

Table 4. — Product of Panariti Grapes on Different Stocks at Fresno, Cal.
{After Husmann^*)

Stock

Yield (in pounds
per vine)

1917

1918

Sugar content
(Balling scale)

1917

1918

Acid as tartaric

(grams per 100

cubic centimeters)

1917

1918

Adobe Giant

Aramon X Rupestris Gan-

zin No. 1

Dog Ridge

Lenoir

Mourvedre X Rupestris

No. 1202

Riparia Gloire

Riparia X Rupestris No.

3309

Rupestris St. George

Salt Creek

Solonis X Riparia No.

1616

Average

21.0
3.0
1.5

8.0
5.0

17.0
6.5
8.0

24.5

10.2

7.5

11.0
3.0
2 0

1.5
2.0

20.0
2,0
1.5

19.0

6.95

30.5

28.0
26.5
28,0

23.5
23.5

28.5
28.5
28,0

29.0

27.4

27.0

26,0
28.0
26.0

28.0
30.0

26.0
26.0
26,0

26.0

26.9

0.9675

0.7650
0.8300
0.6450

0.8700
0.8850

0.8650
0.7800
0.7800

0.6900

0.80775

0.8770

0.8255
0.8250
0.7500

0.7575
0.9450

0.8250
0.8550
0.8175

0.8325

0.8310

572 FUNDAMENTALS OF FRUIT PRODUCTION

been noted only in rich valley soil of the coast counties and only with
certain varieties. A similar condition has often been noted in Europe,
but it is usually easily overcome by longer pruning and diminishes with
age. "

Husmann^^ shows very striking differences in the product of the
Panariti or currant grape on various stocks in California, as shown in
Table 4.

Rolfs^-^ suggests a difference in the value of different stocks for the
mango. The kumquat on sour orange roots grows a vigorous tree but
it is practically barren.

Fruit Setting. — A casual survey of European literature shows a con-
siderable body of opinion to the effect that the setting of fruit is influenced
sometimes by the stock on which the fruiting wood is worked. Par-
ticularly does this appear in grapes. Ravaz is quoted to the effect that in
sandy soils strong growing stocks fail to set fruit and for this reason many
of the Riparia and Rupestris hybrids are not well suited to such soils. ^*^
Baco^ found the short and reflexed stamens characteristic of many hybrid
stocks, but very rare in the pure Vinifera, produced in Baroque grafted on
1202. These characters have been shown in the section on Fruit Setting
to be associated with lack of viability in the pollen. Though it is not
clear from Baco's account whether this condition was universal on this
stock, he recorded it on other stocks also, including the Rupestris du Lot
(St. George). Consequent upon this condition was a considerable
amount of couture and of miller andage. Nevertheless, he recorded a
general increase in production on these same stocks.*^

Rupestris du Lot stock is reported to cause poor setting of fruit in
many Victorian vineyards ;^^ the vigorous growth of this same stock
produces coulure in some varieties in California. ^^^ Odart, writing before
the days of phylloxera in Europe, stated that the Raisin des Dames set
fruit much better when grafted on the common white Muscat;''^ Bur-
bidge^^ cites similar cases from the experience of forcing house grape
growers. Baltet'^ states that the Cabernet grape when grafted is exempt
from coulure beside own-rooted plants that are badly affected and quotes
Hardy: "Graft the Chasselas Gros-Coulard, even on itself, and you will be
resisting coulure." In Australia when the Kieffer pear is grown on wet
soils better setting occurs if quince roots are used."*^ Sahut'^" states that
Chionanthus virginica, grafted on ash, flowers abundantly but never
fruits, while as a seedling it bears.

Size of Fruit. — So many factors affect the size of fruit that it is difficult
to find clear evidence of any considerable influence on size that can be
attributed to the stock. Sometimes grape growers imagine an increase
in the size of the individual berries when certain stocks are used. Bur-
bidge,'^ for example, cited an instance in which the Gross Guillaume grape
was considered to form larger berries on Muscat of Alexandria than

THE RECIPROCAL INFLUENCES OF STOCK AND CION

573

on Black Hamburg. Pepin '^'^ stated that certain almonds grafted on
bitter almond or on St. Jiilien plum stocks bore smaller fruit. His
statement of a stock which produced small fruit in the apple has been
mentioned earlier. Daniel^^ found that tomato grafts on pimento pro-
duced less fruit than on their own roots and that the fruit was generally
smaller. The Golden Pippin in England when worked on free growing
stock was said to l)c larger, mealy and poorer in keeping quality than
on less vigorous stock. "^^ In America some of the older generation of
pear growers thought that small fruited varieties, such as Dana's Hovey,
bore larger fruits when worked on vigorously growing stocks. The sand
cherry has been said to produce larger fruits on Prunus americana than
on its own roots."^ IVIany California growers believe that peach roots
induce larger fruit in both European and Japanese plums than plum or
almond roots. ^^^ Hedrick,''^ however, reported no difference in numerous
varieties of apples grown on Doucin, Paradise and standard stocks.

Reference has been made to the greater growth of American grapes
on certain stocks in an experimental planting in New York.''^ The same
investigation showed much greater productivity in the grafted vines.
Typical comparisons are shown in Table 5, condensed from Hedrick's
results. Summarizing, on an acre-yield basis, the results for all varieties,
including many not listed in the table just given, the yields by stocks for
that year were, in tons per acre: on own roots, 4.39; on St. George,
5.36; on Gloire, 5.32 and on Clevener, 5.62. Averages for 3 years were in
the same order of magnitude.

Table 5. — Average Yield per Vine of Own Root and Grafted Grape Varieties,

1911

(After Hedrick-'^)

Variety

Ovvn roots,
pounds

St. George,
pounds

Gloire,
pounds

Clevener,
pounds

Campbell .
Concord. .
Vergennes
Herbert. .

lona

Niagara . .
Catawba . .
Delaware .
Brighton . ,
Worden . .

16.00
16.20
17.36
12.21
15.17
20.51
15.37
12.75
14.43
10.37

23.69
16.93
22.13
11.89
16.42
22.55
12.95
24.25
15.56
16.47

20.41
16.95
24.52
14.95
17.68
24.57
16.41
14.25
13.06
15.95

18.35
21.17

21.79
21.94
17.75
17.40
15.71

"The crop on the grafted vines was increased," Hedrick states,
"through the setting of more bunches and the growth of larger bunches
and berries. The increase in the number of bunches was easily deter-

574 FUNDAMENTALS OF FRUIT PRODUCTION

mined by actual count but for the statement regarding size we have only
the fact that the proportion of unmarketable grapes was greater on the
ungrafted than on the topworked vines. The greater fertility of the
varieties on other than their own roots cannot be ascribed to larger vines.
No data are available as to size of vines but judging by the eye alone the
grafted vines do not make as much wood as do the varieties on their own
roots."

It should be stated that there is by no means a unanimity of opinion
as to the effect of dwarfing stocks on the size of the individual fruit, even
in Europe.

Quality. — Practically all the older authorities were agreed that in
some cases the stock influences the quality of the fruit borne by the cion;
as to the extent of this influence there was more diversity of opinion.

Downing,^" writing in 1845, stated: "A slight effect is sometimes produced
by the stock on the quality of the fruit. A few sorts of pear are superior in
flavour but many are also inferiour, when grafted on the Quince, while they are
more gritty on the thorn. The Green Gage, a plum of great delicacy of flavour
varies considerably upon different stocks; and Apples raised on the crab, and
Pears on the Mountain Ash, are said to keep longer than when grown on their
own roots."

Barry^^ spoke of the Beurre Diel pear as, "Sometimes gritty at the core on
pear stock; invariably first rate on the quince." Again, of the Glout Morceau:
"like the Duchesse d'Angouleme, Louise Bonne and some others, it is decidedly
superior on the quince."^*

Lindley^^ wrote: "It is not merely upon the productiveness or vigour of the
scion that the stock exercises an influence; its effects have been found to extend
to the quality of the fruit. This may be conceived to happen in two ways —
either by the ascending sap carrying up with it into the scion a part of the secre-
tions of the stock, or by the difference induced in the general health of a scion by
the manner in which the flow of ascending and descending sap is promoted or
retarded by the stock. In the Pear, the fruit becomes higher coloured and smaller
on the Quince stock than on the wild Pear, still more so on the Medlar. . . .
Mr. Knight mentions such differences in the quality of his Peaches. . . . Since
the quality of fruit is thus affected by the stock, it seems allowable to infer that
the goodness of cultivated fruits is deteriorated by their being uniformly worked
upon stocks whose fruit is worthless; for example, the Almond or the austere
Plum can only injure the Peaches they are made to bear, the Crab the Apple,
and so on." Lindley cites with apparent approval numerous other instances
of the sort.

A generation later the grape growers of France were forced by the
ravages of the phylloxera to confront this question in connection with the
grafting of their Vinifera varieties on American vines whose fruit was,
at the best, of indifferent quahty. Much misgiving was felt lest the
quality of the wines made from the new combination plants should be
inferior to that of the older vines on their own roots. This great experi-

THE RECIPROCAL INFLUENCES OF STOCK AND CION 575

ment, one of the greatest pomological experiments the world has seen,
has failed to show any consistent deterioration in the quality of the prod-
uct that could be attributed to the use of American stocks. In fact, at
times wine from grafted vines has brought higher prices than that from
the same varieties on their own roots. >^

Sahut cites among instances where the quality is not injured by the stock,
Vinifera grapes on American stocks, cherry on Mahaleb, almond on bitter almond,
apricot on the common plum. In some cases, he states, more, larger and better
fruits are secured by particular stocks, as in pears on the quince, apples on the
Paradise, peach on the almond. The loquat on hawthorn, he states, is more
perfumed and less acid than on its own or on quince roots, while of pears on haw-
thorn some retain and some lose their quality.

Some years ago California citrus growers hesitated to use sour orange
stock through fear of spoiling the quality of their fruit, but extensive
tests have shown no differences induced by either sour or sweet stock. ^^°

Swingle^^'' reports that the Satsuma orange on sweet orange stock
bears fruit that is coarse, dry and insipid, as well as being later in ripening
than on trifoliate stock, while on the latter the fruit is much improved in
quality. Elsewhere the incompatibility between this orange and all
stocks except trifoliate is discussed.

In Pomaceous Fruits. — Riviere and Bailhache^^^ present 3 years'
average analyses of Triomphe de Jodoigne pears from trees of equal age,
standing side by side, one on quince, the other on pear roots. The
fruits on the standard tree averaged 280 grams in weight, those on the
dwarf, 406 grams; total sugars per liter of juice: in the standard, 93.4
grams, in the dwarf, 102.3 grams. The investigators calculate that a
crop of 300 fruits would produce on the standard tree 7 kilograms of
sugar and on the dwarf, 11. Two years' investigations on Doyenne
d'hiver showed: On quince stocks, average weight of fruit, 435 grams,
sugar percentage in juice, 11.59; on standard, average weight of fruit,
230 grams, sugar percentage in juice, 9.04.

Commenting on some experimental tests of dwarf apples in New
York, Hedrick^'^ states: "It is a common claim that dwarf apple trees
produce larger, handsomer and better flavored fruits than standard trees.
There is little in these three orchards to substantiate these claims. There
are differences between trees on the three stocks but they are as often as
not in favor of standards as of dwarfs."

In Stone Fruits. — For the stone fruits Knight ^° may be quoted:
"But I have subsequently planted two trees (of Moorpark apricot)
growing upon plum stocks, and two upon apricot stocks, upon the same
aspects, and in a similar soil, giving those upon the plum stocks the advan-
tage of some superiority in age, and I have found the produce of the
apricot stocks to be in every respect greatly the best. It is much more

576

FUNDAMENTALS OF FRUIT PRODUCTION

succulent and melting, and differs so widely from the fruit of the other trees
that I have heard many gardeners, who were not acquainted with the
circumstances under which the fruit was produced, contend against the
identity of the variety. The buds were, however, taken from the same
tree.

"I have also some reasons for believing that the quality of the fruit
of the peach tree is, in some cases at least, much deteriorated by the oper-
ation of the plum stock."

In Grapes. — CurteP^ reported a difference in must from Pinot grapes
on their own roots and on Riparia roots. More careful studies in 1903
are recorded in Table 6. In his discussion Curtel stated that there were
differences according to the variety and the stock and that since the
amount of organic nitrogen was thought to explain the observed differ-
ences in susceptibility to wild yeasts the matter might assume considerable
practical importance.

Table 6. — Analyses op Juice Extracted from Grapes

{After Curtel*^)
(Parts in 1000)

Pinot

on

Riparia

Pinot

Gamay

on
Solonis

Gamay

on

own roots

Dextrose

Levulose

Total acidity

Bitartrate of potassium

Phosphoric acid

Organic nitrogen

Ash

Tannin

Coloring matter

87.30
102 . 05
9.20
8.47
0.46
4.02
5.15
1.05
100.00

81.07
98.05
8.54
8.51
0.61
3.17
5.45
1.85
126.00

153 . 50

10.43
9.41

1.04
100.00

158.70

8.60
10.43

1.10
106.00

Bioletti compares grapes grown on certain stocks r^^ "The quahty
of the grapes was in nearly all cases, where a comparison was possible,
better on Riparia stock than on St. George. The grapes were larger and
sweeter. The higher sugar content was, moreover, usually accom-
panied by higher acidity, showing that the grapes were better developed."
Quantitative data are shown in Table 7.

Husmann^^ uses sugar and acid determinations of grapes as a test of
the congeniality of the graft. Extensive determinations were made to
test the effects of various stocks on the quality of the fruit. "These
tests," Husmann states, "have yielded very interesting and suggestive

THE RECIPROCAL INFLUENCES OF STOCK AND CION

577

T.\BLE 7. — Comparison of Composition op Grapes on Riparia and on St. George

(After BiolettP^)

Variety

Stock

Riparia Gloire

Sugar Acid

Riparia Grande
Glabre

Sugar Acid

St. George

Sugar Acid

Valdepenas . . .

Zinfandel

Gros Mansene

Fresa

Vernaccia. . . .
Marsanne. . . .
Chardonay. . .

Sultana

Cornichon. . . .

Moan

27.5
26.5
24.1
25.6
27.5
23.3
25.0
24.0

0.65
0.92
1.20
0.92
0.84
0.50
0.60
0.75

26.7
24.0
27.6
25.0

22.8

20.3

0.77

0.80

24.4

0.86

23.5
24.0

24.2
21.6

22.7

0.56
0.85

0.61
0.62

0.75
0.65

0.67

(lata which, when contrasted with the growth ratings of the same vines
based on observations and measurements of growth during the same
growing seasons, indicate that there is a close correspondence between
these important chemical constituents of the fruit and the congeniality
of graft and stock as determined by observation of growth. Similar rat-
ings of the growth of a variety grafted on various stocks are found to be
accompanied by fairly definite percentages of sugar and acid. Under
like conditions of growth the sweetness and acidity of the fruit, as well as
its time of ripening, are evidently materially influenced by the congeni-
ality of the graft and stock."

This is of considerable importance. It indicates that the congeniality
of the graft is influential rather than the stock and that the same stock
may with one variety increase the sugar content and with another
decrease it.

Qualitative Differences and Quantitative Variations. — Since com-
position, ripening and keeping quality of fruits are more or less related,
an effect produced on one of these implies an effect on the others. It
was stated, many years ago, that there was a month's difference in the
keeping quality of Hubbardston apples grown on Hightop Sweet and on
Roxbur}' Russet in the same soil and with the same culture. Rhode
Island Greening on Hightop Sweet was said to be only a fall variety. The
crab stock of England made the Golden Pippin keep longer than did
the free stock. Daniel,^* who states that Labrusca stock has a rather

578 FUNDAMENTALS OF FRUIT PRODUCTION

unfavorable action on the table and wine qualities of certain white
grapes, does not specify the nature of the action.

These differences are quantitative rather than qualitative. No
evidence is available showing a qualitative change in fruits, in the sense
of an introduction or a manufacture of entirely different compounds,
emanating from the stocks used. Furthermore, accepting all the cases
alleged, there is still no clear evidence of any change beyond such differ-
ences as could be effected by changes in maturity. A reference to Ravaz
appears to show a possible relation of the stock to quality in fruit. It
is stated 1^^ that, "to secure high gravity must in his opinion it is stocks
with Riparia-like behavior which should be selected — one requires vines
with slow and regular vegetation, the activity of which ceases early in
the season. In a word, the vines should behave in as nearly as possible
the same way as though they were growing on a dry hillside."

Apparently, then, the nature of the fruit the stock bears is a matter
of indifference; the two possibly important factors are (1) the vegetative
habits of the stock, (2) the congeniality of stock and cion. In the light
of present knowledge of the formation and ripening of fruit, it would be
difficult to arrive at any other conclusion. An apple is sweet or sour
according as it contains more or less sugar; the acid content is fairly
uniform. This is determined largely in the spur or the neighboring
branch; the trunk or roots cannot have much effect on it. The roots
may keep the tree growing late and so influence the ripening, but the
quality of the fruit the stock bears cannot be expected to influence the
top. A stock with good fruit but unsuitable vegetative habits might
influence the cion to produce inferior fruit and vice versa; a stock of a
sweet variety may make the fruit of a cion sweeter or more acid.

Longevity. — It is the generally accepted view that processes greatly
increasing fruitfulness tend to hasten the ultimate death of the plant.
This opinion has ample corroboration in the dwarf apples and pears and
in recent years has been a very real problem to grape growers. Blunno^^
mentions some instances that have a bearing here.

"The Riparias, which are considered excellent stocks for loose, rich, deep
soils such as are found on river flats, have given some disappointment in a few
places in Sicily and Algiers," he states. "For the first few years vines grafted
on them are loaded with fruit, which over-production seems to exhaust the
plant. . . .

"Similarly the Riparia X Rupestris No. 3306, which is generally planted in
practically the same classes of soil as the Riparias and the R X R No. 3309, in
soils a little stiff er, have gradually given signs of exhaustion in various localities.
. . . Wherever the Riparia and Riparia X Rupestris hybrids failed it was
always noticed that the exhaustion followed several years of very heavy crops;
those vignerons who managed, by a skilful pruning, to keep the vines from yield-
ing so heavily, have these vines still in bearing."

THE RECIPROCAL INFLUENCES OF STOCK AND CION 579

Sometimes grafting has opposite effects. Without specifying as to
the effect on fruitfulness, Jost records that Pistacia vera (the pistachio
nut) as a seedUng Uves at the most 150 years, on P. lentiscus only 40, while
on P. terehenthinus it reaches 200 years.

General Influence of Stock on Cion. — Such evidence as is available
on the influence of stock on cion has been presented. This influence
wherever it is positive, is, almost without exception, quantitative. There
is no doubt of the influence of stock on vigor and form of growth; there
seems httle reason to doubt some influence of the stock on the termination
of the growing season, which is, after all, only a phase of vigor. If, now,
the effect of stock on vigor be accepted, all other influences of stock on
cion can be explained through that one influence. None of these influ-
ences differs from effects that might be secured from so manipulating
cultural conditions as to modify vigor. Cultural conditions can be
changed to induce early fruiting or late growth or earlier ripening or
hardiness or disease resistance or increased fruit-bud formation or better
setting of fruit or larger or better ripened fruits. Girdling the grape
will increase the sugar content and size of the fruit. The dwarfed trees
of China that bear inferior undeveloped fruit are on their own roots j^""
the inferiority of the fruit is brought about by manipulation, not by any
influence of stock on cion.

The influence of the stock on cion is not to be minimized; much
harm has come from ignoring it. Frequently it is of extreme importance.
However, it is important to the cion only as its vigor is important to the
cion and as the graft union is satisfactory; the cion, for adjustment to one
locality or purpose, may require a vigorous stock; for adjustment to
another locality or purpose it may require a less vigorous stock or one
that thrives in a soil of peculiar character. Adjustment of stock to cion,
then, should be made with these factors in mind. In addition, the choice
of stock should, where choice is possible, be made with soil, pests and
cultural practices in view; conversely these should be considered in their
relation to the stock as well as to the top.

INFLUENCE OF CION ON STOCK

Instances of apparent influence of cion on stock are more striking in
plants other than those grown for their fruit, possibly because the
interest of the fruit grower is centered chiefly in the cion and minor influ-
ences on the stock are less likely to attract attention. Furthermore, an
influence of cion on stock might involve a reaction on the cion and so
be attributed to the effect of stock on cion. However, a few cases, some
undoubted and some less clearly defined, are available for consideration.

Just as among the influences of the stock on the cion, the effect on
vigor and form of the cion are the most obvious, possibly because most

580 FUNDAMENTALS OF FRUIT PRODUCTION

readily observed, so among the effects of the cion on the stock those on
vigor and form of the stock are most conspicuous.

Size and Number of Roots. — Daniel/^ working with various Cruciferse,
found that in some cases when the cion belonged to a species of greater
height than that of the stock it accelerated the growth of the latter and
that, when conditions were reversed, an inhibiting effect was exercised.
Sahut^^^ stated : "If the cion belongs to a more vigorous species or variety-
it stimulates the vigor of the stock. The common hawthorn, grafted
with hawthorn bearing double pink flowers, with Sorbier des oiseleurs,
Azerolier d'ltalie and the common Rohinia grafted with R. decaisneana,
develops much more rapidly. It is the same with the majority of Euro-
pean vines [grapes] when grafted on American York Madeira or Rupestris
stocks which are less vigorous. If the cion is less vigorous it restrains
the vegetation of the stock. The Dwarf peach of Orleans, grafted on
peach or almond, and Chinese plums on Damascene or St. Julien [are
examples]. It is the same with the majority of European grapes on
Riparia or Jacquez."

Instances drawn from American experience are not lacking. Swin-
gle ^'*° states: "Although the Trifoliate is naturally a small tree and of slow
growth, when used as a stock its growth is so stimulated that its diameter
always continues greater than that of the scion. . . . This form of
union wherein the stock slightly outgrows the scion has been noticed also
in the case of the loquat grafted on the quince growing at Eustis, Fla.
In this case, also, the variety so grafted began to bear when still very
young and has borne abundant crops since." Bonns^" confirms the
large growth of the trifoliate stock, even while it is exercising a dwarfing
effect on the lemon tops worked on it.

Brown^^ states that the Myrobalan root system is larger than usual
if it is worked with peach tops.

Bioletti and dal Piaz^^ compare Zinfandel and Tokay grapes growing
on Rupestris St. George stocks. Here the stocks are cuttings and there-
fore even more comparable than most seedling stocks. The greater
growth of the Zinfandel top is balanced by a corresponding development
of the root system.

Whether the cause be incompatibility, poor graft union or something
else, there is apparently sufficient evidence to warrant the statement
that in some cases the cion does influence the stock. Since pruning
the top of any tree, regardless of the stock, tends to reduce the root
system and since some dwarf trees are kept so only by heading back,
the necessity for seeking a mysterious influence is not apparent. A
top which will not grow vigorously may be expected to act on the stock
as would a heavy pruning; a top which is able to supply the roots with
abundant food may be expected to increase their growth. Nevertheless,
caution should be exercised against ascribing too much to this effect.

THE RECIPROCAL INFLUENCES OF STOCK AND CION 581

Some grape stocks cannot grow fast enough to supply some cions; the
sand cherry cannot be developed by a vigorous top to the size necessary
for the successful support of a rapidly growing plum. If the implied
effect of stock on cion be admitted, limitation in that of cion on stock is
obvious.

Distribution and Character of Roots. — Possibly because the root
systems of nursery plants come under observation much more than
those of the same plants once they are set in orchard or vineyard, there
is considerable evidence of an effect of cion on stock in young fruit plants.
Nurserymen frequently identify certain pear or apple trees by their
root systems, though all are on seedling stocks. Hovey,'"" however,
himself a nurseryman, indicated that this could not be done in all cases;
some strong growing varieties, he stated, would have strong, and weak
growers such as Winter Nelis would have correspondingly weak, root
systems. It is stated that the roots of trees grafted with Siberian Crab
" generally run down more than those of other trees. " ^''*'

Murneek^^^ states: "Upright growing varieties of apples of the
Russian type, for instance, will form a correspondingly deep growing
root system while those of the Winesap type will be flat and shallow.
This can be extended even to particular varieties. The Red Astrachan,
Oldenburg, Fameuse, for example, form each a characteristic root system
of its own. In this connection, Shaw believes 'that the size or stoutness
of the main branches is positively correlated with the size of the main
roots and angle of the branch with the angle of the main roots and the
axis of the tree. In many individual cases this correlation is obscure,
yet careful observations with large numbers of trees will reveal it.' "
Bailey^ stated that Northern Spy and Whitney tops make the roots
of the stock grow deeper than usual.

Waugh,!^^ discussing plum propagation, reported:". . . Stoddard
tops seem to give some of the curved tap-root character of the Americanas
to all the stocks on which they grow. . . . One interesting point was in
the way in which Stoddard tops induced a conspicuous branching of the
root system when worked on peach. With other varieties the peach
gave almost always a clean, unbranched tap-root. The weak growth
of Green Gage naturally served to induce only a weak growth in most
of the stocks on which it was worked; while the rampant growth of
Chabot had exactly the opposite effect. The strongly branching root
systems found on Chabot trees were probably due in part to the energetic
way in which the foliage acted during the growing season. Marianna
stocks, which seemed to be uncongenial to Milton, giving only a poor
union, made very little growth when grafted with Milton scions. No
other case was observed in which Milton appeared to have any influence
on its stock. Newman seemed to influence all stocks in the way of
giving off more secondary roots. Nearly all stocks when grafted with

582 FUNDAMENTALS OF FRUIT PRODUCTION

Newman gave a strong, vigorous growth, considerably above the average,
tending at the same time to produce more both of secondary roots and
of fibers." In the following year he reported: "No case was observed
this year in which the scion showed any marked effect on the stock. "^^^

Baco^ cites numerous grape stocks in which the roots grow more
spreading when grafted with Baroque; among these are: Riparia
Gloire, Rupestris du Lot and Riparia X Rupestris 3306. On the other
hand, Chasselas X Berlandieri 41 5 becomes deeper rooted when grafted
with the same cion variety. This last stock, it is said, succeeds best in
warm, dry seasons and the deeper penetration of the roots is held to be
disadvantageous in many locations and seasons.

Longevity, Growing Season and Hardiness. — Some rather spectacu-
lar instances of modification in growing habits of stocks are reported.

Linderauth^^ grafted an Abutilon cion on the roots of an annual plant, Modiola
caroliniana, and thereby kept the combination plant alive 3 years and 5 months.
Althcea narhonnensis has tops which die to the ground every winter. Grafted
with Abutilon Thompsoni, a plant of Althcea with no other top could not secure
the proper materials for forming winter buds and died. Another specimen,
similarly grafted, but sending out a sucker from the root, lived and kept the
cion living over a year. DanieP' obtained similar results with Solanum
puhigerum on Giant tobacco, which is an annual in Brittany.

Sahut^^^ cites numerous instances of evergreen cions, as Cratcegus glabra
and Raphiolepis on the common quince, etc., succeeding on deciduous stocks.
However, these cases lose some of their significance in the light of present knowl-
edge of winter processes in deciduous plants. The same writer states that when
the late opening St. Jean walnut is grafted on the common walnut the stock "is
obliged to hold back a month or more. Deciduous cherries," he states, "on
the Laurier-Amande (evergreen) make the stock rest almost absolutely. The
varieties of grape which push out late, Carignane, for example, grafted on Riparia
or other American species which start sensibly earlier, hold the stock back. The
European early starting grapes, as Aramon, when on late American stocks, as
York Madeira, force the stock to earlier growth."

Perhaps more definite information may be secured from certain
instances where the cion appears to have an effect on hardiness.
Since this is in many cases a matter of maturity the effects recorded may
be considered equally as effects on maturity.

Vard^'*^ in an extensive survey following the severe winter of 1890-1891 in
France found that rose stocks which had supported cions of Tea and Bourbon
roses had not only lost their cions but were themselves killed back to the ground.
Unbudded stocks or those which had supported hardy varieties suffered Uttle.

Following the cold whiter of 1913 in Cahfornia Webber and others found some
apparent cases of "a definite influence of the tops upon the stocks. In one case,"
they report, "in the spring of 1912 a nursery of gour seedlings was budded to
Eureka lemons. Many of these buds did not take, so that during the freeze of

THE RECIPROCAL INFLUENCES OF STOCK AND CION 583

January, 1913, there were in this nursery, at the same elevation and under the
same conditions, yearling lemon tops on sour stock (buds had been inserted
several inches above the ground) alongside of sour seedlings. While a shght
injury to the foliage was the only harm experienced by the latter, the lemon
tops were killed, and the frozen wood extended 3 to 4 inches down on the sour
stock. Similar conditions were found on pomelo stock while the pomelo seedlings
were scarcely touched. "^^^

Other Influences. — Sahut states that quince roots topworked to pear
are more particular in their soil requirements than those not worked over;
they require a more fertile soil. However, as he indicates, the general
rule is to the contrary; otherwise the selection of lime resistant, drought
resistant and moisture resistant stocks would be to no point. The cion
itself does not render the stock subject to phylloxera or immune to
woolly aphis, though a lack of congeniality may induce weakness and
hence a lack of recuperative power. The transmission from cion to stock
of variegation has been discussed previously; it cannot be regarded as an
instance of true influence exerted on the stock by the cion.

In General. — Just as in the case of stock on cion, in considering the
influence of cion on stock it is not necessary, so far as fruit plants are
concerned, to predicate any direct effect other than on vigor. Every
other influence that has been established or attributed can be explained
as exercised indirectly through vigor and can be placedoon a quantitative
basis. This action on vigor may be direct when the two parts to the
graft are congenial and make a good union, or it may be indirect when
there is apparent uncongeniality and the union is poor. Qualitative
influences, such as the passage of alkaloids across the graft, or the barring
of inulin by the graft, are not necessary to explain any observed phe-
nomena resulting from grafting in fruit plants.

CHAPTER XXXII

THE ROOT SYSTEMS OF FRUIT PLANTS

The choice of stocks for the various fruits, where any considerable
latitude is possible, is frequently rather complex. First, two economic
interests are concerned, the grower's and the nurseryman's; second,
several natural factors, the congeniality of the union involved, the
relation of the stock to the soil, to the climate and to the variety. Rarely
is it possible to secure a stock that meets all requirements in all situations;
the result is generally a compromise.

CONFLICTING INTERESTS OF NURSERYMAN AND FRUIT GROWER

The nursery business, like most businesses, is competitive. The
individual nurseryman is, therefore, sometimes compelled to adopt
certain alternative choices which may not be to the best interest of the
grower or, ultimately, of the nursery business itself. The responsibility
for this situation rests not with the nurseryman alone, for as long as
growers will buy cheap trees, ignoring their real value for the conditions
under which they are to be grown, all nurseries are more or less forced
to offer cheap trees and often find difficulty in selling better. The
nurseryman's immediate interest, then, rests in securing stock that
is cheap, that makes a good union, with a high percentage of successful
grafts, and that makes a marketable tree quickly.

The plums, with the multiplicity of species cultivated for fruit and of
species available for stocks, serve as an excellent illustration of con-
flicting interests and factors. Some years ago it became evident that for
successful plum culture in the north central states a very hardy stock
was necessary. The Americana stocks met the growers' requirements
very well in nearly all respects. However, seed for growing the stocks
in large quantities was not readily available. The Marianna stock,
rooting readily from cuttings in the south, was much cheaper. Trees
on Marianna roots could be produced at little expense and were sold at a
price which virtually precluded competition from the better suited, but
higher priced, trees on Americana roots. Want of discrimination on the
part of buyers of nursery stock made this situation possible. Waugh
furnishes another illustration. The St. Julien plum, he states, is the
best stock for Domestica plums, making ''a better, stronger, longer-lived
tree than Myrobolan." He proceeds to quote a nurseryman's letter,
in part, as follows: "St. Julien stocks are much preferred by the orchard-

584

THE ROOT SYSTEMS OF FRUIT PLANTS 585

ists in this locality, because trees certainly do better in every way on that
stock. They sprout less from the root, are longer-lived, and generally
more vigorous than when on Myrobolan stocks. We occasionally plant
some St. Julien seedlings, but do not make a practice of it, because
in the first place St. Julien seedlings cost more than double the price of
Myrobolans, and they are not as thrifty the first year they are trans-
planted. They also are attacked by a fungus which causes them to lose
their leaves early in the summer, thus preventing the budding of the
stocks altogether, or a partial failure in the buds when this leaf fungus is
not corrected. Of course, when taken in time we can in a large measure
prevent this falling of the leaves by spraying with Bordeaux mixture, but
taking all things into consideration, it is quite a bit more expensive to
raise plums on St. Julien stock, and we find that we cannot get any more
for them in the open market, so that we have become discouraged growing
stocks on the St. Julien root." Hedrick quotes J. W. Kerr of Maryland
to the effect that though for that section he prefers the peach as a stock
for the Domestica plums, there are many varieties of this species that
will not form a good union with the peach and in these cases he is forced
to use Marianna or Myrobolan stock.

Growers of Vinifera grapes have found that no one stock is suitable
to all conditions. Cuttings of a given species may not root freely and
it is eliminated from the list of available stocks, no matter how resistant
it may be to phylloxera or how desirable in other respects. Another
species or variety may not give a large percentage of successes in bench
grafting and the establishment of a vineyard on this stock becomes a
matter of more labor and greater expense.

Dawson^^ gives the scarcity of seed as the chief reason against the
employment of Pyrus hetulafolia which he states would be a very satisfac-
tory stock for pears on dry soil.

The Mazzard stock for cherries is preferred by growers in some sec-
tions, but nurserymen have rather forced the use of Mahaleb. The
Mazzard has several features which make it rather unsatisfactory for the
nurseryman; one of these is its sensitiveness to weather conditions in
the nursery row so that though buds may take readily one season the
following year may give entirely unsatisfactory results, or the budding
season may close abruptly before the work is complete. ^^

Enough evidence" has been introduced to show that the best stock for
the nurseryman, under existing circumstances, is not always best for the
grower. The responsibility, however, rests with the grower. When he
is so convinced of the superiority of a given stock that he is willing to pay
the price for it, the nurseryman will produce trees on that stock. Until
the grower realizes that the best stock in the orchard may not be the
best stock in the nursery or vice versa the nurseryman can do only as he
has been doing.

586 FUNDAMENTALS OF FRUIT PRODUCTION

ADAPTATION OF STOCKS TO PARTICULAR CONDITIONS

Further, it must be remembered that a plant that is valuable to the
grower in one location may prove otherwise in another. Climatic condi-
tions may simplify the choice for a certain grower by eliminating all
but the most hardy stocks, but they may complicate matters for the
nurseryman who is selling to a wide territory.

Adaptation to Soil Temperatures. — A grower ordering stock from a
nursery in a milder climate should consider that he may be getting trees
with stocks not adapted to his conditions. A northern grower, for exam-
ple, securing plum trees from the south, would do well to make sure that
they are not on peach or Marianna roots, though some of the leading
nurseries no longer use these stocks. The southern grower may be more
interested in securing a stock that will not sucker or in extreme cases, as
cited by the Howards,^" he may even require a stock that is able to endure
high soil temperature. These investigators found that in Baluchistan
the peach and plum stocks commonly used in Great Britian would not
succeed, but by using stocks which they considered better adapted to hot,
dry soils, such as Marianna, Myrobolan and Mahaleb, they secured much
better results.

Adaptation to Soil Texture and Composition.^ — Prune trees in the Paci-
fic northwest have been planted in many cases without much regard to the
stock on which they were worked. In numerous instances prunes with
peach roots have been planted in rather heavy, poorly drained land in
which the planting of peach trees would not be considered.

French horticulturists had not solved the problem presented by phyl-
loxera when they had isolated certain varieties of American grapes that
were resistant to this pest, that lent themselves to making good cuttings
and satisfactory graft unions with the Vinifera cions. Many of the
French vineyard soils are strongly calcareous; in these soils only compara-
tively few of the American vines flourish. Hence, ability to withstand
calcareous soils must be considered in any choice of stocks for rather wide
use in France. When California vineyards were invaded by phylloxera
the stocks tried and approved in France were naturally given early
consideration. However, lime tolerance is not so important in California
since comparatively little vineyard soil is calcareous; of much greater
importance, in some localities in this state, is ability to withstand di'ought,
in others ability to flourish in soils with a high water table for part of the
year. Rupestris St. George (du Lot), because of its deep roots, with-
stands drought better but suffers severely when the water table stands
near the surface for long; the shallow rooted Riparia Gloire and certain
Berlandieri hybrids meet requirements here. Most Vinifera-American
hybrids adapt themselves to these conditions. The Muscadine grapes
also are adapted to moist soils and hot climates."^ In California, as in

THE ROOT SYSTEMS OF FRUIT PLANTS 587

France, ignorance of local conditions and of the stocks suited to them may
indeed lead to utter failure.

Other plants than the grape prove refractory on calcareous soils in
France and in many cases recourse to a lime resistant stock has proved
successful. DentaP^ furnishes an instance in the Australian Acacia
dealbata which grows freely in calcareous soils on A . floribunda though on
its own roots it will not grow in such soils. A similar expedient is neces-
sary for the growth of certain pines in these soils. Some Australian exper-
ience seems to indicate that sour orange is the best stock for orange and
lemon in sections where the irrigation water is likely to contain alkali
in considerable quantities. '^^ California experience indicates that lemon
is unusually susceptible to alkali.^'' On the other hand, lemon roots are
stated to be the best foragers in poor soils in this section. Primus davi-
diana is now under trial in Cahfornia as an almond stock; the particular
quality commending it is its ability to grow in more alkaline soils than
other commonly used almond stocks.^*- Two successive plantings of
peaches in one California orchard were killed by alkali; following this
peaches on Davidiana roots have proved successful in the same soil.^^'
Cock^^ states that the trifoliate orange, though it is too dwarfing in its
effects to be a commercial success, may be used to advantage in very wet
soils. In the Gulf States the trifoliate succeeds in rich, moist soils and is
unsuited to light, dry soil.^^^ Pomelo in California appears to suffer
most from drought.-*^ Sahut^^'^ states that in wet soils the peach and
apricot grow better on plum roots than on their own or on almond roots
and that the cherry on Mahaleb grows in poor soils where it would not
grow on its own roots.

The degree of refinement to which adaptation of stocks can be carried is shown
by Bioletti's tentative recommendations of stocks for Vinifera grapes in Cali-
fornia :-^

"The Rupestris St. George has given its best results in the hot, dry interior on
deep soils. . . .

"For a great majority of our soils and varieties the two Riparia X Rupestris
hybrids 3306 and 3309 promise to be superior in every way to the St. George.
The former for the moister soils and the latter for the drier. . . .

"For the wettest locations in which vines are planted — in places where the
water stands for many weeks during the winter, or where the bottom water rises
too near the surface during the summer— the most promising stock is Solonis X
Riparia 1616.

"For moist, rich, deep, well-drained soils, especially in the coast counties and
on northerly slopes, the St. George is utterly unsuited. The crops on this stock,
in such locations, are apt to be small, and the sugar content of the grapes defec-
tive. In these locations the Riparia Gloire is much to be preferred, and will
undoubtedly give larger crops of better ripened grapes.

"None of the above stocks give good results, as a rule, in very compact soils.

588 FUNDAMENTALS OF FRUIT PRODUCTION

For such soils the most promising varieties are 106^ in the drier and Aramon X
Rupestris No. 1 or 202^ in the wetter locations. In dry, shallow soils 420A
and 157^^ give promise of being excellent stocks."

Some stocks show such cathohcity in taste that it is safe to grow trees
on them for planting in all locations that are at all suited. The Cah-
fornia black walnut, for example, adapts itself to so many soils that it is
almost universally used in California as stock for the English (or Persian)
walnut, though its resistance to root rot {Armillaria mellea) is also an
important factor.

Sorauer^^* quotes Lieb to the effect that Pyrus mains prunifolia
major and P. m. baccata cerasiformis have been found valuable as stocks
for apple in very exposed or dry positions.

Immunity or Resistance to Soil Parasites. — Adaptation to soil must
be paralleled at times by adjustment to diseases. The Damson plum
seems rather resistant to crown gall and in special cases might be given
preference for this reason. Shaw has found that cion-rooted apple trees
show crown gall in different forms according to variety. "Thus," he
states, "the Jewett apple shows usually if not always the hard form of the
gall, the Red Astrachan the simple form of the hairy root and the Olden-
burg the woolly knot form with many soft fleshy root growths. Other
varieties show the brown root form and still others often the aerial
form. . . .

"Some varieties on their own roots seem to be largely if not entirely
immune to this disease. If this proves to be really the case, here may lie
the solution of the problem of the prevention of crown gall. . . . Prob-
ably the economic advantage would warrant the extra effort necessary to
propagate such trees, only under conditions where the crown gall was
especially troublesome.

"There are other root diseases which are injurious, especially through
the southern part of the apple belt, that might possibly be avoided in a
similar fashion." '^^

The pear affords an interesting example. The so-called Japanese
pear (Pyrus serotina) is more resistant to blight than the French stock, but
seems rather susceptible to mushroom root rot and is sensitive to soil
moisture. Choice between the two may at times involve nice discrimi-
nation. In some soils the lemon suffers from root rot to such an extent
that other stocks are substituted. In Florida the sweet orange roots
formerly used as stocks were so badly attacked by root rot that this
stock has been superseded. Similar susceptibility is found in California.
In regions subject to pear blight the displacement of French seedling
pear stock by other stocks, such as Pyrus serotina, P. ussuriensis and
P. calleryana, that are resistant or immune can be forecasted, except as
other troubles may develop.

THE ROOT SYSTEMS OF FRUIT PLANTS 589

PROPAGATION BY CUTTINGS

Under this head are considered the various forms of cuttings, layers,
stools and the like which depend on the formation of roots from the wood
of the variety to he cultivated, without the intervention of grafting or bud-
ing. All plants thus propagated are on their own roots. The list of fruit
plants so propagated commonly, includes the fig, olive, grape, currant,
gooseberry, mulberry, filbert and pomegranate from hardwood cuttings;
the various dwarfing apple stocks and quince from mound layers or stools;
the strawberry by rooted "runners;" the black raspberry, loganberry and
dewberry by rooted tips of canes, the red raspberry and blackberry by
suckers; the cranberry and blueberry by hard or soft wood cuttings or
by "tubering" or "stumping" as the case may be. If pomological
literature be searched at all carefully there appear some rather sur-
prising additions to the list of plants that can be propagated by cuttings,
particularly by hardwood cuttings, including frequently the citrus fruits,
plums, pears and apples.

"Some of the plums grow well from cuttings. This is especially true of
Marianna, and millions of Marianna cuttings are made every year in this coun-
try, mostly for stocks. . . . The St. Julien plum grows fairly well from cut-
tings, and nearly all the Myrobolan varieties may be propagated this way. Some
of the Japanese varieties, especially Satsuma, have been grown from cuttings
in the southern states. Practically, however, propagation by cuttings is con-
fined to the Marianna. "^^"^

That the apple may be propagated by cuttings is indicated by quota-
tions from Knight, though possibly he is describing what is now known to
be a rather common pathological condition in the apple.

"There are several varieties of apple tree, the trunks and branches of which
are almost covered with rough excrescences, formed by congeries of points which
would have become roots under favorable circumstances; and such varieties are
always very readily propagated by cuttings."*^ The Paradise and Doucin
stocks root more or less readily from cuttings.

Darwin^^ cites Tennent as saying, "in the Botanic Gardens of Ceylon the
apple tree sends out numerous underground runners which continually rise into
small stems, and form a growth around the parent tree."

Ribston Pippin is said in England to grow readily from cuttings.

Again quoting Knight: "Peach and Nectarine trees, particularly
of those varieties which have been recently obtained from seed, may be
propagated readily by layers, either of the summer or older wood; and
even from cuttings, without artificial heat; for such strike root freely. "^^

Advantages and Disadvantages. — Propagation by cuttings may or
may not be advantageous; there is nothing in the process itself that makes
it one or the other. When it is readily accomplished it is obviously the
cheapest process, but the plant may do better on some other roots than its

590 FUNDAMENTALS OF FRUIT PRODUCTION

own. The lemon, for example, is reported in Australia'*" as inferior on
its own roots, being more susceptible to unfavorable soil moisture con-
ditions. The Vinifera grapes root readily from cuttings but the roots so
formed are subject to phylloxera infestation; recourse is therefore made to
grafting these grapes on resistant stocks which in turn are grown from
cuttings. The Oldenburg apple on its own roots appears decidedly
inferior, ^^•^ though Mcintosh and Stayman make notably fine growth on
their own roots. Sometimes when it would be desirable to have trees on
their roots their failure to root readily from cuttings makes the process im-
practicable. Many of the apples and plums that are extremely resistant
to cold winter weather form, if set deeply, roots from the cion that are
much hardier than those of the stocks commonly supplied. A method of
ready propagation by cuttings in such cases would be of great advantage.
To meet this difficulty special methods have been devised; these are dis-
cussed presently. To take advantage of the relative immunity of North-
ern Spy roots to the woolly aphis, Australian growers take considerable
pains to develop these roots, either by layering, stooling or grafting with a
"starter," and upon the Spy stock work the variety they wish to grow.
In some cases, then, fruit plants which grow readily from cuttings are
grafted on other stocks at greater expense; in other cases, plants which do
not form their own roots readily are induced to do so, though such plants
are more expensive.

Objection is sometimes made to plants propagated by cuttings as
compared with those developed on seedlings, because of certain supposed
shortcomings. They are occasionally said to be shallow rooted ; Hatton,^°
however, states, regarding dwarf apple stocks: "We have found it just
as possible to raise stocks of deep anchorage by layers and other vegeta-
tive methods as it is easy to find shallow-rooted ones in any collection of
free stocks raised from pips." This supposed shallowness of the root
system was turned to account by the early Spanish settlers of Louisiana,
who propagated the peach by layering to suit it to alluvial lands where the
water table is high.^^^ Cock,^** writing on citrus fruits in Victoria, states
that layers and cuttings are always weak and more liable to disease than
seedlings. Macdonald,^"^ also in Victoria, writing of the olive, states:
"It is possible that, in poor soils or trying situations, the seedling may be
the more thrifty and long-lived tree, but experience in this country has not
gone to prove that this is the case. Many of the oldest trees in Australia
were raised from truncheons and are still doing well. However, their age
is comparative youth in the life of the olive tree, and perhaps it is as well
to accept the opinion of continental writers on the greater longevity of
seedling trees until there is greater evidence at hand to the contrary."

In New South Wales seedling plums are considered to make better
root systems than cuttings.^ Grapes, gooseberries and currants have
passed through many generations of cuttings, without perceptible

THE ROOT SYSTEMS OF FRUIT PLANTS 591

diminution in vigor. The process, therefore, apparently is not per se
devitalizing. It has, moreover, certain marked advantages, one of
which is uniformity of the roots.

This uniformity in the roots frequently is of considerable importance.
The constant tendency to variation in seedlings is not confined to quality,
color and size of the fruit but extends to every character of the plant.
They may vary in vigor of growth as much as in the color of the fruit;
the (juality of fruit varies no more than the stature; the depth of rooting,
resistance to cold, to drought, to moisture, to alkali, all are variable
characteristics. Hatton^'' states: "Free stock is a comprehensive term,
meaning no more than seedlings which include dwarf stocks both fibrous
and stump-rooted, as well as vigorous ones resulting from a well-balanced
root system." The seedling root, then, is in a measure an unknown
quantity. The tree planted in the orchard is standardized above ground,
uncertain below ground. The stock for any individual tree may be more
vigorous or more hardy or more resistant than the average; it is just as
likely to be less so. In France the prospective grape grower whose soil is
strong in lime knows that certain stocks do not thrive on those soils ; he is
able to pick a lime-enduring stock, for grape root stocks have been stand-
ardized through growth from cuttings. If, however, he has a rocky,
thin soil in a hot, dry exposure, he can select another stock, known to be
the best for such locations. Were he to rely on seedlings he would be
indulging in a lottery whose results could be told only after a year or more.
To replace those which failed he would use more unknown quantities.

Grapes in Particular. — Varietal differences in the character of root
systems produced from cuttings are recognized in grapes. Bioletti and
dal Piaz" explain the susceptibility of Riparia and the immunity of
Rupestris stocks to drought by the shallow roots of the former and
the deeply penetrating roots of the latter. In poorly drained soils and
in soils with the water table high for any length of time, these same
peculiarities tend to reverse the order of suitability. Hedrick sug-
gests that the small amount of winter killing of grapes on Rupestris
St. George stock as compared with that on other stocks in an experimental
vineyard in New York may have been due to its deep rooting habit.''*
The advantage of having stocks of known performance is obvious.

Apples and Pears in Particular. — Fortunately apple and pear stocks
are fairly adaptable. They seem so, certainly— perhaps because there
is no standard with which to compare them. However, every careful
grower recognizes that some of his trees consistently bear more or less
than others. This raggedness may be attributed to minor variations
in soil and doubtless correctly so in many cases; it is sometimes attributed
to bud variation, though the work of Crandall^^ and of Gardner*^^ suggests
the doubtful importance of this source of variation. The unevenness
in a seedling orchard strongly suggests that were the tops all removed

592 FUNDAMENTALS OF FRUIT PRODUCTION

and grafts of one variety inserted on the roots the resulting trees would
show considerable differences in vigor and productiveness. Mention
is made elsewhere of results in Missouri showing considerable variation
in seedling apples.

Hatton'"' states, in the course of a comparison of Paradise, free and crab
stocks: "We are faced, then, with two converging series quite arbitrarily divided,
the one ranging from dwarfness to vigour and the other from vigour to dwarf-
ness; the only real distinction being that the Paradise series has been raised
vegetatively, and any particular meml^er of the series can be reproduced by that
method again and again, whilst the free series has been raised from seed, and as
long as this method is employed infinite variety and inequahty will continue,
except in rare cases.

"It is often argued that 'true crabs' are less variable than 'ordinary free
stocks' but I cannot learn what the trade distinction stands for. If free stocks
are the chance children of cider fruits, crabs (commercial not botanical) are the
chance progeny of wildings; but every district has many, many so-called crabs
varying in vigour and character. I have seen them strong and clean; dwarfing
and root knotted, whilst the types of fruit are various. I do not pretend to
assert that free stocks from particular sources may not be more even than from
other sources. That simply depends on the chance crosses, on the varieties
mixed or cross pollinated, which in some cases may be more advantageous than
in others; but I do say that stocks raised from pips will always be variable, and
therefore incompletelj^ satisfactory, except for the purpose of raising new types
of stock for subsequent vegetative propagation, if we find degeneration or im-
perfection in the existing types."

Examination of an orchard, injured here and there by root killing,
forces belief in the variation shown by the seedling roots and an apprecia-
tion of the desirability of a stock that is uniformly hardy. If a vigorous,
hardy, resistant stock could be isolated and propagated, much of the
unevenness in yield and uncertainty in hardiness would be eliminated.

Furthermore, the importance to the experimenter of having each tree
on its own roots should be emphasized. The lack of uniformity in
yields of trees in the same plot in fertilizer, cultural or pruning experi-
ments has done much to invalidate results and more definite conclusions
might well be expected if the root systems as well as the tops of the trees
were identical.

Vegetative propagation of apple stocks seems not only of probable
value but worthy of study as a real possibility. Hatton^*^ in a paper
of great importance reports that in the investigations of Paradise apple
stock at East Mailing one type was isolated which is free growing, not
in the least dwarfing in its effects; this stock is propagated readily by
vegetative methods. Further study of this type and search for others
like it seem of great importance. The great amount of variation found
by Hatton gives promise of isolating stocks which will show particular

THE ROOT SYSTEMS OF FRUIT PLANTS 593

adaptabilities to different conditions in a manner comparable to those
now catalogued for grapes and of making possible much finer fitting
of trees to environment.

Propagating Apples and Pears by Layerage and Hardwood Cuttings. —
Investigation of propagation of apples and pears by hardwood cuttings
seems of possible value as well. These cuttings root readily in the
tropics and in some of the southern states, such as Florida, Mississippi
and Texas, and could perhaps be rooted elsewhere if proper soil tempera-
tures were provided. Kieffer and LeConte among pears and Northern
Spy among apples seem to root especially well, though this ability
is possessed by other varieties. Similar cases have been reported in
England.

Warcollier in France is reported to have had mediocre results with
cuttings of 30 to 50 centimeters of the previous season, well ripened;
success was possible only with soft wooded varieties. Others in France
reported very satisfactory results using branches of 3 or 4 years' growth,
with side growths removed, plunged into the soil to a depth of 10 to 25
centimeters. Varieties of moderate or feeble vigor, particularly one
known as "Petit doux, " gave the best results. "■*

The propagation of the Northern Spy stocks used for all apples in Victoria
is chiefly from layers and stools. The parent Spy stocks are planted 2 feet apart
in rows 4 or 5 feet distant in June (autumn in Australia). The processes followed
are described by Cole:*° "In August cut back to within an inch of the ground
level, so as to get a supply of buds to or below the soil to push out. The
following August cut back to two buds any weak or light growth, pegging down
the stronger parallel with the row or other planted stocks. The buds upon the
pegged-down growths, being now brought into a vertical position, will send up a
sufficient supply of shoots for working upon sound lines. About November,
mould them up lightly by removing some of the higher soil from the middle of
the rows. During the following winter remove soil about the layers and cut
away any light shoots that may have rooted hardening back others close to
the main layer.

"The propagator should not be too eager in removing rooted shoots from the
main laj^ers until after the fourth season, but will be repaid by cutting hard back,
forming good, well-rooted crowns for future use. From now out the operator
mil require to use his own judgment regarding the growths he cuts hard back and
those he leaves for pegging down after removing any that may be rooted. In
the winter mould up after cutting away any rooted stocks and the pegging down
is finished, and again in November or December. Deep or over moulding should
be avoided.

" Stooling. — This method is somewhat similar to that of layering, but instead
of pegging down the unrooted shoots they are cut hard back each year, so as to
encourage as many as possible to show out. The second season from planting,
and after the shoots have been cut back to within an inch or so of the stool, mould
lightly, and again in November or December. If the shoots do not root, this

594 FUNDAMENTALS OF FRUIT PRODUCTION

moulding will cause them to become bleached close to the crown of the stool.
Upon being hardened back, shoots that give the best results will be formed.
When removing rooted shoots in the winter, leave any that are very small for
the following year; also any that are weak and spindly. . . .

"The cooler and moister districts are the best adapted for the raising of Spy
stocks by these two methods (layering and stooling), as the rooting of the shoots
is controlled by even moisture during late summer and early autumn. From
healthy, old, and well estabhshed stools, and those putting up medium and not
over-strong shoots, the best results are obtained. The writer advises that layer-
ing and stooling should be worked conjointly."

The use of Northern Spy stock is mentioned by Wickson^^^ in CaUfornia.
Paul C. Stark, however, states that Northern Spy has not proved satisfactory
in the central states, as a stock, forming knots on the roots and rooting with
some difficulty.

In the northern central states where seedling roots have proved
tender in the colder winters recourse has long been made to an indirect
method of securing trees on their own roots. Long cions are wliip grafted
on small pieces of seedling roots and planted deep. Roots are formed
more or less freely from the underground portion of the cion; since the
varieties grown are necessarily hardy the roots seem to share in this
hardiness and have proved actually hardier than the average seedling
roots. In a short time these cion roots generally outgrow the seedling
starter which becomes much reduced in proportion and plays an insig-
nificant part in the mature tree.

Varietal Differe7ices and Contributing Factors. — Varieties differ in the
readiness with which they emit roots in this way. Shaw^^" found that
some varieties root readily, others only in very niggardly fashion;
Baldwin, for example, showing 32 per cent., Ben Davis 51, Sweet Bough
98, Delicious 22, Mcintosh 74, Jonathan 11, Grimes 41, Gravenstein 55,
Northern Spy 58, Oldenburg 25, Tolman 3, Winesap 34, Wolf River 71,
Yellow Bellflower 3, Yellow Transparent 26. He found also that the
same variety performs differently from year to year, possibly from
internal conditions, possibly from external. Stark reports that Delicious
forms cion roots very readily and the roots are aphis resistant. Moore^^^
reports on similar work in Wisconsin. Of the varieties tested Livland
Raspberry, Hyslop, McMahon, Pewaukee and Transcendent showed cion
roots on 50 per cent, of the trees studied, in the third year. Cion roots
are formed more readily in moist soil and, because of this, Moore con-
cludes that grafts planted deep form roots more readily. Table 8,
reproduced from Moore's report, shows the difference in cion root forma-
tion in moist and in dry soil.

Recent investigations in Iowa show that the formation of cion roots
is much accelerated by winding the point of grafting tightly with a
copper wire.^^

THE ROOT SYSTEMS OF FRUIT PLANTS

595

Table 8. — Cion Roots Produced in Apple under Different Soil Moisture
Conditions (After Moore^^^)

Trees observed

Cion-rooted

Strong cion-rooted

Variety

Moist

Dry

Moist,
per cent.

Dry,
per cent.

Moist,
per cent.

Dry,
per cent.

Peerless

Northwestern

Mcintosh

Hyslop

McMahon

263

142

94

40

31

311

328
110
98
103

42.6

63.4

56.4

100.0

87.1

31.4
24.1
29.1
50.0
32.0

6.1

18.3

21.3

100.0

58.0

5.8

2.7

1.8

23.5

10.7

Maynard^"^ mentions the use of short pieces of apple roots as nurse
grafts for refractory quince cuttings. "The apple root," he states,
"supplies moisture and a little food material until roots are formed on
the cion, when it fnils to grow more, and we have the quince on its own
root."

Another method of propagating trees on their own roots is the plant-
ing of own rooted trees secured as just described and taking cuttings
from the roots they form. This depends on the formation of adven-
titious buds on the roots which some species and some varieties accom-
plish readily while others apparently do not.

Finally should be mentioned propagation of fruit trees, especially
some of the plums and some varieties of apple, from sprouts arising on
the roots. This method is perhaps more common in some sections of
Europe than in the United States, partly because the varieties grown lend
themselves to this treatment and partly because of the very positive, if
somewhat exaggerated, prejudice in the United States against root
stocks which sprout freely.

SOURCES OF NURSERY STOCK

With certain reservations it may be said that the proximity of the
source of nursery stock is unimportant. If the stock is healthy, well
developed and well matured, it will grow. Some of the ornamentals,
grown from seed, tend to mature earlier if from northern seed than if from
southern and there may be temporarily a somewhat readier response to
climatic changes in vegetatively propagated plants from one section than
from another but, if there is, it quickly disappears and there is little or no
evidence that it is of any practical importance.

It should, however, be reaUzed that different stocks are used in grow-
ing certain fruits by nurseries in different parts of the country and that
this may be of extreme importance. The northern plum grower, for

596 FUNDAMENTALS OF FRUIT PRODUCTION

example, is more likely to get hardy plum roots from a nursery near home
than he is from a nursery whose chief clientage is in a section with milder
winters.

For fall planting, northern growers will be more likely to get well
ripened trees from northern sources where the trees naturally mature
earlier. That this may assume importance is shown in the section on
Temperature Relations.

Withal the mere mailing of an order to a local nursery is not always a
guarantee that the stock sent to fill the order is of local origin. Many
nurseries buy much of their stock from distant points. However, if the
stock is good and, in cases where a difference in roots is important, if the
roots are of the right kind, the grower need not concern himself greatly
about its origin.

GRADES OF NURSERY STOCK

Fruit trees are offered for sale by nurseries in several grades, which
are based on size as measured by either height or diameter or both. Since
the largest trees cost the most, the question whether there is any ultimate
advantage in them is of practical importance.

The very fact of the grading shows the difference between individuals.
If this is a temporary matter, due to better immediate environment of
one tree in the nursery row there will be no final difference in the growth
and performance of these trees. If, however, the variation be an expres-
sion of inherent differences, the planting of lower grade stock may have
serious consequences.

It is shown elsewhere in this section that bud mutations in the decidu-
ous fruits are uncommon; hence, uniformity in the tops may be presumed.
If there be a fundamental difference between the large tree and the small
tree in the nursery the cause must lie in the stock. Most of the stocks
used are seedlings and therefore more variable than the vegetatively
propagated stocks, some kinds more than others. Some of this variation
is undoubtedly temporary, but there are good reasons for thinking some
of it is more deeply seated.

Webber^^i reports investigations with citrus fruits that bring out these
inherent differences in seedling stocks very strikingly.

He summarizes his investigations in part as follows:

"Nursery trees even when grown from selected buds taken from selected
trees differ greatly in size when they reach transplanting age. Commonly the
large trees are sold first and the small trees later when they reach the required
size.

"Large, medium and small nursery trees of Washington navel and Valencia
oranges and Marsh grapefruit grown in comparative tests show that after 2H
years in the orchard the large trees remain large, the intermediate trees remain

THE ROOT SYSTEMS OF FRUIT PLANTS 597

intermediate and the small remain small. The evidence indicates that this
condition is inherent in the trees and that in planting orchards only the large
nursery trees should be used.

"An examination of sweet and sour orange seedling stock, such as is used for
budding, showed the presence of many widely different types. Some of these
types were propagated and the trees at the end of the 4H years still show the same
marked difference. Some are fully five times as large as others. Yet all such
types are used as stocks.

"Budding on seedhng stocks of different types and unknown character of
growth is believed to be largely responsible for the different sizes of budded
trees developed in the nurseVy and also for many of the irregularities in size and
fruitfulness of orchard trees."

These differences probably hold for the apple. A seedling apple
orchard seven years planted, at the Missouri Station, contains trees rang-
ing in circumference from one inch to sixteen. It is not likely that if
these seedling roots had been topworked to the same variety they would
all have made equally good trees. From all appearances, they have
maintained or increased — but not changed — their relative differences
in size; the trees that are largest have made good growth each year,
while those that are now inferior appear to have been inferior continuously.

It should, however, be recalled that there are cases of a delayed effect
in dwarfing. Plums worked on sand cherry frequently make vigorous
growth in the first year, greater in fact than on other stocks which ulti-
matel}^ grow the larger trees.

Gravenstein, on the Paradise apple in Germany is said to grow very
vigorously at first, but to grow very little after bearing."^ Chester
Pearmain and other varieties behave similarly. ^^ Like effects have been
recorded with Castanea vulgaris grafted on Quercus sessiliflora in an attempt
to grow chestnut in soils strong in lime; growth was very vigorous the
first year, but few grafts lived till the third year. Even shorter was the
success of Vinifera grapes on Cissus orientalis Lamarck. ^-^ Hatton'"'
may be quoted on this point: "It is often denied that this inequality in
the stocks shows itself in the worked trees. Although it is true that a
strong-growing variety, such as Bramley's Seedling, may largely obliterate
this inequality in the maiden, differences again become apparent in the
second and third years." To this extent, then, the grower buying 2-year
old graded stocks of some trees may perhaps be a little surer of having
runts weeded out. At present, however, the extent to which this delayed
effect is operative in common fruits cannot be stated.

Briefly, in buying nursery stock, the grower who gets trees of good
size for their age, other things equal, is more nearly sure of getting trees
that will do well in his orchard. Buying the smaller grades he is buying
uncertain plants. They may be stunted only and may ultimately
make good trees. They may, however, be composed of runts which are

598 FUNDAMENTAL."^ OF FRUIT PRODUCTION

inherently incapable of being anything else. In practice the inferior
grades probably contain some stunted and some "runt " trees. The only
sure way of differentiating between them is the test of time which is
likely to prove more costly to the grower than the difference in price.
The inferior grades, therefore, should be regarded with suspicion.

On the other hand, the extremely large tree is open to objections, seri-
ous in some cases. If the tree is large only because it is older, only be-
cause it has — as often happens — stood in the nursery an extra year or two,
it carries no guarantee of inherent good growth; on the contrary, the
presumption is against it. It may be only an elder runt.

Gardeners know well that the smaller the plant the less disturbance
it suffers in transplanting and the more readily it reestablishes itself. A
large proportion of the root system of the larger trees is cut off in
digging. Data gathered in California show that the largest trees made
the smallest percentage diameter increase during the first year in the
orchard, indicating a slowness in adjusting themselves to the new loca-
tion." Furthermore, trees of unduly large size, produced sometimes by
over irrigation or heavy fertilization, are more liable to winter injury when
planted in the autumn.

Other objections to the larger trees are voiced by Hendrickson :^^
"Branches are often produced the first year in the nursery row. If
these branches could be utilized they would be a distinct advantage but
they are often broken or injured in the process of packing and must be
cut off when the tree is planted. In other cases the branching does not
begin near the bottom of the tree or the bottom branches have been
shaded out, and hence it is difficult to secure a low-headed tree by using
the branches produced in the nursery. Furthermore, the buds on the
lower portion are far apart and the tree has a tendency to grow from the
top buds. . . .

"The small 1-year old tree as a rule, depending on the kind, produces
few or no side branches. Consequently the buds, instead of growing into
branches in the nursery, remain dormant until the following year. They
are also less liable to injury in packing. Consequently the small tree
within a few weeks after the beginning of the growing season is covered
from top to bottom with leaves and small branches. The growth is
generally more evenly distributed among the several growing points,
than in the case of the overgrown tree."

Withal, "large" and "small" sizes, or even grades based on definite
measurements, are relative only. Different nursery fields, or the same
fields in different years, produce trees varying considerably in size.
Varieties differ more or less in their characteristic growths. Conse-
quentl}'' even among trees of the same age any grading must be on a rela-
tive basis; a certain caliper measurement may denote small trees in one
case and medium sized trees in another.

THE ROOT SYSTEMS OF FRUIT PLANTS 599

Definite, though not invariable, objections have been shown to both
extreme grades in nursery stock, on the one hand practical and on the
other hand primarily theoretical but none the less real. The logical
consequence is the approval of the medium grades. Experience usually
justifies this course.

Selection of Seedling Stocks. — For good or evil, seedling stocks will
continue in use, for some fruits, indefinitely. It is likely, however, that
at no distant time the sources of seedling stock will receive closer scrutiny
than has been given. Indeed a rough selection has been exercised for
many years in some cases. The so-called Vermont crab stock for apples,
in reality grown from cider mill pomace and tracing ultimately in many
cases to seedling apples, sometimes has been preferred to crab stock.
Feral peach stock from Tennessee has been used to a considerable extent.

Gradually, however, imported French seedlings have been used
increasingly for apple stocks, because they were cheaper than native
grown stock. With the rise of canneries, peach stones and cherry pits
have been available at little cost to growers of nursery stocks and have
been widely used.

The variation in seedlings has been mentioned. It is probable,
however, that investigation will show certain varieties to produce
larger proportions of good seedlings than others. Commercial varieties
of fruit are not grown for the value of the seedling stocks they produce.
Doubtless some of them will prove of value for this purpose; others will
not.

Roeding'25 g^yg; "For several j^ears I have been carrying on experiments
with different varieties [of peaches] todetermine their value from a standpoint
of growth and general freedom from crown gall, and taking it all in all, the Salway
comes first, and the trees produced from Lovell and Muir seed next. Within the
last few years I have been carrying on experiments with Tennessee natural
pits and am already convinced of their value as to the vigor of growth. If the
root system is found to be healthy and of a fibrous character, this stock will be
given the preference."

Apple seedlings from different parentage will probably, in some cases,
show differences worthy of consideration. Data from an orchard of
seedhngs of known parentage at the Missouri Experiment Station"
show a marked tendency to inferior growth in all seedlings of Ralls
(Geniton) parentage. Careful study doubtless would show certain
varieties to be admirable parents for nursery stock, while others would
turn out to be parents of an unduly large number of runts, sources of loss
both to nurseryman and to grower.

The desirability of care in the selection of the source of seedling stocks
has received attention in Europe.

600 FUNDAMENTALS OF FRUIT PRODUCTION

Duplessix,^^ writing on apple growing in Brittany, states: "The choice of
apple trees furnishing seeds for sowing is very important, for the tree coming
from the seed will generally have the principal characters of that tree which
supphed the seed. But there are numerous varieties whose wood has a slow,
twisting growth, without vigor, and these varieties are not suitable for generating
good stocks, which ought to be straight and of a vigorous and rapid growth.
Other varieties, as most of the Reinettes and Calvilles, are very subject to canker;

" It is necessary then to extract the seeds from fruits from trees whose wood is
healthy and of a very vigorous growth. Right here is a difficulty for cultivators,
for the wood varieties generally used by nurserymen, such as the Frequin de
Chartres, Noire de Vitry, Genereuse de Vitry, Maman Lily, yield few fruits or
fruits of second quality and, for this reason, are almost unknown in our orchards."

The same writer carries the matter of selection still further and
advocates growing stock from seed of trees corresponding in season of
growth inception with those whose grafts they are destined to bear.

Grafted or Budded Trees. — Certain fruits such as cherries and peaches
are propagated customarily by budding and no question is raised as to the
value of trees produced in this manner. Some others, as the apple, are
readily propagated either by budding or by grafting and the question of
preference between trees grown by these methods has been raised fre-
quently. There may be a difference in the adaptability to a given locality
of budded or grafted trees, but it rests on a basis other than that usually
discussed.

Much of the alleged superiority of budded trees rests on the use of a
whole root in budding while in bench grafting one root may be cut to
serve three or four cions. It is argued that this Cutting down of the root
system produces a tree that is permanently inferior to the budded tree.
Budding frequently produces a larger tree in a given time in the nursery
than grafting, but there is no positive evidence of any permanent differ-
ence in trees raised by the two methods and there is much negative evi-
dence that points to the absence of any difference due to the process used
per se or the amount of root used per se.

The real difference between budded trees and grafted trees has been
appreciated only in certain sections where the difference was brought
out occasionally by the death of one class and the survival of the other.
Trees grafted with long cions and short pieces of root and set deep in the
nursery tend to throw out roots from the cion, while the seedling root
becomes unimportant or dies, as explained elsewhere. Experience has
indicated that cion roots arising from wood of varieties that are hardy are
themselves more uniformly hardy than the roots on which they are
grafted. Such trees are therefore better adapted to localities where root
killing is likely. It is regrettable that in recent years so many budded
trees have been set in northern fruit growing sections where root grafted
cion rooted trees provide an insurance well worth consideration.

THE ROOT SYSTEMS OF FRUIT PLANTS 601

Cion rooted trees may prove superior in other localities because
of their persistence or spread or depth or other qualities. If experience
with grapes is a valid analogy, considerable difference between varieties
is these qualities would appear upon investigation, some cion roots
proving superior and other inferior. In the one case, then, root grafted
trees would be superior, in the other, budded trees, since the seedling
roots would average better than the cion roots. In sections with cold
winters, particularly sections with scanty snowfall, root grafted trees
should be used.

Double Worked Trees. — There are several possible reasons for double
working: (1) a lack of congeniality between stock and cion, (2) need of a
trunk and scaffold limbs that are mechanically stronger, (3) the top may
be subject to disease or winter injury that is more or less characteristic
of the trunk.

Certain varieties of the pear unite poorly with quince stock though
they unite well with pear. Therefore, on the quince is worked a variety
that does unite well and into this as a stock is budded the desired variety.
Beurre Hardy is used by many nurserymen as the linking variety.
Bailey^ recommends Angouleme for the same purpose; Rivers, ^^i jj^
England, found a number of varieties useful, including Beurr^ d'Amanlis.
Clairgeau and Seckel are among the varieties said to thrive better when
double worked. In California double working is favored for Bartlett
on quince roots. ^^^

Burbidge^^ mentions another combination in double working: "In soils
which do not suit the Quince, but in which the Pear luxuriates, this order may
often be reversed by using some good-constituted Pear as the root stock on which
to graft the Quince, which again in its turn is worked the following year with
the kind of Pear desired to form a fruiting specimen." He also quotes Parkin-
son (1629) for another interesting example: "Speaking of the red Nectarine,
then the rarest and dearest of all fruit trees, he remarks: 'The other two sorts
of red Nectarines must not be immediately grafted on the Plum stock, but upon
a branch of an Apricock that hath been formerly grafted on a Plum stock.' "

The apricot as described by Baltet^- is adjusted to dry sites along
the Mediterranean by almond roots. Since the grafts do not take well
in direct contact, double working is invoked, using a vigorous peach as
the connecting link. The same author states that the Damask plum is
sometimes used in France as intermediary between the peach top and
Myrobolan roots. ^^

Certain varieties of apples are notoriously subject to collar rot.
To escape this difficulty they may be worked on another variety that
is noted for its resistance. Grimes double worked on Delicious in the
nursery is now available. Delicious is said to induce \igorous growth,
transforming Bechtel Crab, for example, into a much more satisfactory

602 FUNDAMENTALS OF FRUIT PRODUCTION

tree than the ordinary seedhng stocks develop. It is probable that more
of this kind of double working will be employed in the future.

Blight resistant kinds of pear are coming into use as stock on
which the more susceptible but better flavored pears are worked. The
"Japanese" pear has been used for this purpose, with results varying
because several species have been imported under this name. Some
are comparatively tender, others are uninjured by a temperature of
-40°F. or even lower; some are comparatively susceptible to blight, others
practically immune. Among the more promising of these stocks are Pyrus
ussuriensis, P. ovoidea and P. calleryana.^^'^ The first of these is extremely
hardy; the last is comparatively hardy and is able to thrive in very wet
soils. There is no doubt that working of dessert varieties in limbs of these
trees will greatly decrease the labor and cost of fighting pear blight.

Top working to insure hardiness in the trunk is discussed elsewhere.
It may be mentioned here, however, that the use of Rome Beauty trunks
for Gravenstein, the leading apple variety in the Sebastopol apple section
of California, has prevented the "sour-sap," which has been exceedingly
troublesome there. ^''^

An interesting possibility in the future of fruit growing in America
is top working for the development of a .better framework. Increasing
competition will ultimately tend toward the use of fruit of high quality.
Heretofore, varieties with good quality in fruit but weak growing habits
have been discarded; enhanced appreciation of quality is likely to force
the fruit grower to use such varieties whether he likes the tree or not.
With weak growing varieties he will likely resort to top working on frames
formed by more sturdy varieties. For this reason it is interesting to
note that in growing certain choice dessert varieties many European grow-
ers have followed this practice for a long time. Certain plums, as Petit
Mirabelle, which are weak growers, are worked into a sturdy interme-
diary such as Quetsche, Reine Claude de Bavay, St. Catherine, Krasensky
or Andre Leroy.^^ In Algeria the Japanese plums grow better when
top worked into peach limbs. The same process is followed with several
pears. Growers of choice apples appear to resort to similar devices for
Baltet lists numerous varieties as suitable intermediaries and states that
nurserymen grow certain varieties especially for this purpose.

According to Lindemuth double worked apple trees have been in
great favor in Holland. A variety called "Sweet Pippin" is grafted
into seedhng stocks close to the ground and on this intermediary the
fruiting variety is worked at the height of the head. The sole reason
for this preference, it is said, is the thick trunk formed by the Sweet
Pippin, obviating the necessity of supporting the young tree during
its first few years by a stake. Since apple trees in northern Europe
are grown commonly with much higher heads than in the United States
this precise quality would be more important there.

THE ROOT SYSTEMS OF FRUIT PLANTS 603

Maynard^"^ rccommonds working Bosc, a notoriously poor growing
pear, into tops of strong growing varieties such as Ansault, Clapp or
Flemish Beauty. In sections particularly subject to pear blight, how-
ever, these particular frame stocks would not be advisable. Maynard
stated in 1909 that Kieffer had been recommended for this purpose but
had "not been successfully tried in the eastern states."

It should be recorded, perhaps, that double working was advocated
many years ago, for increasing the quantity and quality of fruit. Graft-
ing in itself was supposed to have this effect and it was thought as voiced
by Noisette, i''2 i\^^i ^}^g more the operation was repated the greater
would be the improvement. In more recent times, however, the tendency
has been to use double working for more specific purposes, or not at all.
Here again, as in so many cases, distinction must be made between the
effects of the process itself and the effects of the material used in the
process.

PEDIGREED TREES

Observation commonly shows much individual variation between
the trees in an orchard that has been planted and tended with the purpose
of providing conditions as uniform as possible. Furthermore, these
differences extend to practically every feature of the tree growth and
they are often extreme. Naturally this has suggested the possibility
of perpetuating by vegetative propagation the favorable variations.
There has been much discussion on this question and on the value of
the so-called " pedigreed " trees that are grown from cions cut from indivi-
duals of unusual excellence. In many cases very little actual evidence
has been available and opinions have been based on an assumed analogy
between a vegetatively propagated tree and a sexually reproduced animal
or on theoretical considerations.

Some Results with Citrus Fruits. — Shamel and some of his associates
have clearly demonstrated that in a number of the varieties of citrus
fruits there is a large amount of bud variation that is of real significance.
A number of intra-variety strains have been isolated, propagated and
have "bred true," if such an expression can be used for the vegetative
propagation employed in the citrus fruits.

The following quotations from the reports of Shamel and his associates will
make clear the results of their investigation: "Thirteen important strains [of
Washington Navel orange] have been found in the investigational performance
record plots. "^^^

"Twelve important strains of the Valencia variety have been found and
described :"^^^ "The lowest percentage of off type tree, i.e. marked variations
from the best or Washington strain, found in commercial orchards have been
about 10 per cent., and the highest about 75 per cent., of the total number of

604 FUNDAMENTALS OF FRUIT PRODUCTION

trees in the orchard. "^^^ "Tree-census observations in Navel orange orchards
in California show a general average of about 25 per cent, of trees of diverse
strains, most of which are inferior to the Washington as regards both the amount
and the commercial quahty of the fruit."

"Occasional limbs have been found in such trees [Washington strain] pro-
ducing typical Golden Nugget fruits consistently from year to year during the
entire period of observation. . . . The variation in the amount of annual
crops produced by a given series of individual Washington Navel orange trees
is relatively uniform throughout the series each year. That is, the highest
producing trees in any one year are in general the highest producing ones each
year, and the lowest ones remain at the bottom of the list continually. Indi-
vidual trees are relatively very stable over a series of years in the character and
the amount of their production. . . . Suckers, or unusually vigorous non-
bearing branches have been used almost universally for this purpose. This
practice has led to the propagation of a continually increasing proportion of
trees of those strains producing the largest amount of sucker growth. Inasmuch
as such trees are usually light bearers and produce inferior fruits this practice
has been unfortunate and is the direct cause of the presence of the large propor-
tion of unproductive trees found in many orchards. Fruit bearing bud wood has
been selected from limb variations occurring in trees of the Washington or other
strains and in several hundred cases where the growth from these buds has
fruited every selection has come true."^^^

With such fruits pedigreed is to be preferred to common stock for it
represents definite types of strains that run true, when there is consider-
able uncertainty as to what to expect from the general run of unselected
stock. Perhaps "pedigreed" is an unfortunate term to apply to such
selected stock; it is rather "improved" stock.

Some Results with Apples. — Hedrick^^ represents fairly well one school
of opinion when he says, concerning "pedigreed" apples:

"At the very outset it must be pointed out that the seeming analogy between
plants propagated from buds and cions and those grown from seeds has given a
false simplicity to the fact and has led many astray. Analogy is the most
treacherous kind of reasoning. We have here a case in which the similarity of
properties is suggested but the two things are wholly different upon close analysis.
In the case of seeds there is a combination of definite characters, in the offspring
from two parents. Since the combinations of characters handed down from
parents to children are never the same, individual seedhngs from the same
two plants may vary greatly. On the other hand, a graft is literally a ' chip of the
old block' and while plants grown from buds may vary because of environment
they do not often vary through heredity. . . The Geneva Station has an
experiment which gives precise evidences upon this question of pedigreed stock.
Sixteen years ago a fertilizer experiment was started with 60 Rome trees propa-
gated from buds taken from one branch of a Rome tree. Quite as much varia-
tion can be found in these trees from selected buds as could be found in an orchard
of Romes propagated indiscriminately and growing under similar condition.
Data showing the variations in diameter of tree and in productiveness . . .

THE ROOT SYSTEMS OF FRUIT PLANTS

605

will go far to convince anyone that uniformity of behavior as regards vigor and
productiveness of tree and size and color of fruit cannot be perpetuated."

In 1895 the Missouri Station propagated from the highest and from the
lowest yielding trees in an orchard of over 200 Ben Davis then in full
bearing. The resulting trees were planted alternately in orchard rows
and individual yield records were kept from 1912 to 1918 inclusive. These
are summarized in Table 9, which shows no difference in favor of trees
propagated from the best tree. Though there was a difference in size and
•finish of the fruit in the original trees there was none in the fruit borne by
their offspring. Investigations in Vermont, reported by Cummings,^^
show no consistent superiority in cions from superior trees of several
varieties of apple.

Table 9. — Avekage Yields of Apple Trees Propagated from High-yielding

AND from Low-yielding Parents

(After Gardner^^)

From "good" parent

From "poor" parent

(bushels)

(bushels)

1912

6.1

5.4

1913

7.0

11.3

1914

10 2

6.3

1915

7.1

10.3

1916

4.7

8.1

1917

11.4

6.6

1918

4.2

11.8

Averaiie

7,2 .

8.5

The statement has often been made that cion wood taken from
certain parts of the tree gives rise to trees that are better than those pro-
pagated from less carefully selected wood. CrandalP^ has given this
matter thorough investigation in the apple and reports the following
conclusions:

"Summarized data giving comparisons between trees propagated from large
buds and those propagated from small buds, together with the aggregate of
impressions derived from careful inspections of trees of all groups, admit but one
conclusion, namely, that there are no differences, for purposes of propagation,
between buds of large size and those of small size.

"Growth curves of trees propagated from buds of different situations on the
trees so closely approximate as to leave no basis for assuming that it makes
any difference from what situation on the tree the buds are taken.

"All buds from healthy shoots are of equal value for purposes of propagation,
at least so far as growth of tree is concerned.

606 FUNDAMENTALS OF FRUIT PRODUCTION

"Fluctuations in growth of individuals within particular groups are decided,
often extreme. In general, differences become less with increase in age, provided
the trees remain healthy.

"There is no tangible basis upon which to establish the assumption that
robust scions are superior to scions of small diameter for purposes of pro-
pagation."

These conclusions apparently differ from those of Shamel, Scott and
Pomeroy working with citrus fruits. However, it should be noted that
sucker growth was found in great abundance only in citrus trees that were
"off type" individuals and it was to trees from such parentage that these
workers particularly referred. In other words it was only because excess-
ive sucker growth was correlated with a certain type of degeneration that
propagation from wood of that kind yielded unsatisfactory results in
practice. The evidence seems to warrant the conclusion that normal
buds, whether borne on slow or rapid growing shoots or on suckers, are
satisfactory for propagation, provided they are healthy and do not come
from limbs that are bud mutations. Furthermore, it justifies the nursery-
man in propagating from the nursery row, i.e., from young trees, provided
there is no question of identity.

In General. — At present comparatively little is known as to the extent
of bud mutation within the various fruit groups. It is possible that
opinions regarding pedigreed trees may need revision. Considering the
present state of knowledge the prospective purchaser should ascertain
accurately just what is meant by the term "pedigreed" stock in each
case, the extent to which such nursery stock differs from the ordinary in its
source and in its later performance record. Not until then can he tell how
to reckon its comparative value.

There is no doubt that occasional variations occur and can be per-
petuated, but there is also no doubt that much of the variation between
trees in the same orchard is due to soil variations or to differences in
stocks and that these variations are not perpetuated. The fact that stock
is propagated from a superior individual indicates a bare possibility that
it is superior but it does not establish a probability that it is, much less
a certainty.

Suggested Collateral Reading

Webber, H. J. Selection of Stocks in Citrus Propagation. Calif. Agr. Exp. Sta.

Bui. 317. 1920.
Burbidge, A. F. W. The Propagation and Improvement of Cultivated Plants.

Pp. 57-86. London, 1877.
Bonns, W. W., and Mertz, W. M. Experiments with Stocks for Citrus Calif.

Agr. Exp. Sta. Bui. 267. 1916.
Bioletti, F. T. Grape Culture in California. Calif. Agr. Exp. Sta. Bui. 197. 1908.
Bioletti, F. T. Resistant Vineyards. Calif. Agr. Exp. Sta. Bui. 180. 1906.

PROPAGATION 607

Hedrick, U. P. Grape Stocks for American Grapes. N. Y. Agr. Exp. Sta. Bui. 355.

1912.

Hatton, R. G. Suggestions for the Right Selection of Apple Stocks. Jour. Roy.

Hort. Soc. 45: 257-268. 1920.

Literature Cited

1. Allen, W. J. New South Wales Dept. Agr. Farmers' Bui. 86. 1914.

2. Baco, F. Trav. sci. Univ. Rennes. 10 (2): 88-90. 1911.

3. Ibid. 10 (2) : 97.

4. Ibid. 10 (2) : 152.

5. Ibid. 10 (2) : 158.

6. Ibid. 10 (2): 175.

7. Bailey, L. H. Cornell Univ. Agr. Exp. Sta. Bui. 71. 1894.

8. Bailey, L. H. Stand. Cycl. Hort. 3: 1363. New York, 1917.

9. Bailey, L. H. Nursery Manual. P. 167. New York, 1920.

10. Baltet, C. L'Art de Greffer. P. 7. Paris, 1902.

11. Ibid. P. 119.

12. Ibid. P. 211.

13. Ibid. P. 369.

14. Ibid. P. 415.

15. Ibid. P. 453.

16. Barry, P. Horticulturist. 3:136. 1848.

17. Barry, P. The Fruit Garden. P. 303. Detroit, 1853

18. Ibid. P. 310.

19. Barss, H. P. Ore. Agr. Exp. Sta. Bienn. Crop Pest and Hort. Rept. 1:213.

1913

20. Berckmanns, P. J. Proc. Am. Pom. Soc. P. 70. 1881.

21. Biffen, R. H. Ann. Bot. 16: 174. 1902.

22. Bioletti, F. T. Cal. Agr. Exp. Sta. Bui. 197. 1908

23. Bioletti, F. T. Cal. Agr. Exp. Sta. Bui. 180. 1906.

24. Bioletti, F. T., and dal Piaz, A. M. Cal. Agr. Exp. Sta. Bui. 127. 1900.

25. Blunno, M. New South Wales Dept. Agr. Farmers' Bui. 80. 1914.

26. Bonus, W. W., and Mertz, W. M. Cal. Agr. Exp. Sta. Bui. 267. 1916.

27. Bradford, F. C. Nat. Nurseryman. 29:1.52. 1921.

28. Brown, B. S. Modern Propagation of Tree Fruits. P. 157. New York, 1916.

29. Ibid. P. 160.

30. Brown, W. R. Agr. Res. Inst. Pusa Bui. 93. 1920.

31. Budd, J. L. la. Hort. Soc. Proc. 14: 464. 1879.

32. Budd, J. L. la. Agr. Exp. Sta. Bui. 10. 1890.

33. Burbidge, F. W. Propagation and Improvement of Cultivated Plants. P. 59.

London, 1877.

34. Ibid. P. 60.

35. Ibid. P. 69.

36. Ibid. P. 264.

37. Ibid. P. 267.

38. Cock, S. A. Jour. Dept. Agr. Victoria. 11: 372. 1913.

39. Ibid. 11: 714.

40. Cole, C. F. Jour. Dept. Agr. Victoria. 9. 1911.

41. Condit, I. J. Cal. Agr. Exp. Sta. Bui. 250. 1915.

42. Corsa, W. P. Nut Culture in the United States. P. 80. Washington, 1896.

43. Coulter, J. L., Barnes, C. R., and Cowles, H. C. Text Book of Botany. 2:777.

New York, 1911.

608 FUNDAMENTALS OF FRUIT PRODUCTION

44. Ibid. 2: 779.

45. Crandall, C. S. 111. Agr. Exp. Sta. Bui. 211. 1918.

46. Cummings, M. B. Vt. Agr. Exp. Sta. Bui. 221. 1921.

47. Cartel, G. Compt. rend. 139: 491. 1904.

48. Daniel, L. Compt. rend. 114: 1294. 1892.

49. Ibid. 136: 1157. 1903.

50. Daniel, L. Trav. sci. Univ. Rennes. 2: 73. 1903.

51. Ibid. 2: 173.

52. Ibid. 2: 210.

53. Daniel, L. Rev. hort. 10 (N.S.): 469. 1910.

54. Ibid. 13 (N.S.): 348. 1913.

55. Ibid. 14 (N.S.): 135. 1914.

56. Darwin, C. Animals and Plants under Domestication. 2: 266. New York.

1894.

57. Dawson, J. Mass. Hort. Soc. Trans. P. 123. 1895.

58. Ibid. P. 134.

59. Dental, J. B. Rev. hort. 16 (N.S.): 47. 1916.

60. Downing, A. J. Fruits and Fruit Trees of America. P. 25. New York, 1856.

61. Diiplessix. Trav. sci. Univ. Rennes. 10 (2): 5. 1911.

62. Ibid. 10 (2): 18.

63. Ibid. 10 (2): 38.

64. Ibid. 10 (2): 192.

65. Gardner, V. R. Mo. Agr. Exp. Sta. Res. Bui. 39. 1920.

66. Gould, H. P. U. S. D. A. Farmers' Bui. 776. 1916.

67. Hansen, N. E. S. D. Agr. Exp. Sta. Bui. 87. 1904.

68. Hansen, N. E. S. D. Agr. Exp. Sta. Bui. 93. 1905.

69. Harwell, R. Horticulturist. 5: 257. 1850.

70. Hatton, R. G. Jour. Roy. Hort. Soc. 45 (2): 257. 1919-1920.

71. Ibid. 45 (2). 269.

72. Hedrick, U. P. Plums of New York. P. 115. Albany, 1911.

73. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 355. 1912.

74. Hedrick, U. P. N. Y. Agr. Exp. Sta. Cir. 18. 1912.

75. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 406. 1915.

76. Hedrick, U. P. Cherries of New York. P. 72. Albany, 1919.

77. Hendrickson, A. H. Cal. Sta. Dept. Agr. Mo. Bui. 4: 171-174. 1918.

78. Horticulturist. 6:337. 1851.

79. Ibid. 6:374.

80. Howard, A., and Howard, G. L. C. Sci. Rept. Agr. Inst. Pusa. P. 48. 1916-

1917.

81. Howard, W. L. Cal. Board Hort. Mo. Bui. 9: 3. 1920.

82. Hume, H. H. Fla. Agr. Exp. Sta. Bui. 71. 1904.

83. Husmann, G. C. U .S. D. A., Bur. PI. Ind. Bui. 172. 1910.

84. Husmann, G. C. U. S. D. A., Bui. 856. 1920.

85. la. Agr. Exp. Sta. Ann. Rept. P. 33. 1919.

86. Jost, L. Pflanzenphysiologie. 3te. Auflage. P. 448. Jena, 1913.

87. Kelly, W. P., and Thomas, E. E. Cal. Agr. Exp. Sta. Bui. 318. 1920.

88. Knight, T. A. Phys. and Hort. Papers. P. 155. London, 1841.

89. Ibid. P. 223.

90. Ibid. P. 273.

91. Ibid. P. 274.

92. Laurent, C. Trav. sci. Univ. Rennes. 8: 37. 1909.

93. Lawrence, J. Clergyman's Recreation. P. 64. London, 1717.

94. Leclerc du Sablon. Compt. rend. 136: 623. 1903.

PROPAGATION 609

95. Lindemuth, H. Landw. Jahrb. 7: 909. 1878.

96. Ibid. 7: 912.

97. Lindemuth, H. Ber. Bot. Gesel. 19: 515. 1901.

98. Ibid. 19: 527.

99. Lindley, J. Theory and Practice of Horticulture. P. 355. London, 1855.

100. Livingstone, J. Trans. Hort. Soc. London. 4: 231. 1822.

101. Loudon, J. C. The Horticulturist. P. 283. London, 1860.

102. Lucas, E. Die Lehre vom Baumschnitt. P. 37. Ravensburg, 1874. Cited in

Lindemuth, H., Landw. Jahrb. 7: 911. 1878.

103. Macdonald, L. Jour. Dept. Agr. Victoria. 10: 69. 1912.

104. Macoun, W. T. Cent. (Can.) Exp. Farms. Bui. 38. 1907.

105. Manning, R. Mass. Hort. Soc. Trans. P. 37. 1S79.

106. Mass. Hort. Soc. Trans. Pp. 6-43. 1879.

107. Maynard, S. T. Hatch (Mass.) Agr. Exp. Sta. Bui. 17. 1892.

108. Maynard, S. T. Successful Fruit Culture. P. 74. New York, 1909.

109. Ibid. P. 197.

110. Mills, J. W. Cal. Agr. Exp. Sta. Eul. 138. 1902.

111. Moore, J. G. Proc. Am. Soc. Hort. Sci. 16: 84. 1919.

112. Murneek, A. L. Better Fruit. 15: No. 7. 1921.

113. Neer, F. E. Correspondence. 1921.

114. Noisette, L. Vollstand. Handb. der Gartenkunst. Uebersetzt von Sigwart.

Stuttgart. 1826.

115. Oberdieck. Illus. Monatshefte fiir Obst- und Weinbau. P. 44. 1873.

Cited by Lindemuth, H., Landw. Jahrb. 7: 909. 1878.

116. Onderdonik, G. Proc. Am. Pom. Soc. P. 92. 1901.

117. Pepin. Rev. hort. Ser. 3. 2: 183. 1848.

118. Proc. Am. Pom. Soc. 1881.

119. Proc. Am. Pom. Soc. P. 128. 1889.

120. Reimer, F. C. Ann. Rept. Pac. Coast Assoc. Nurserymen. 1916.

121. Rivers, T. The Miniature Fruit Garden. P. 103. New York, 1866.

122. Riviere, G. et Bailhache, G. Compt. rend. 124: 477. 1897.

123. Roeding, G. C. Fruit Growers' Guide. P. 18. Fresno, 1919.

124. Ibid. P. 20.

125. Ibid. P. 26.

126. Rolfs, P. H. Fla. Agr. Exp. Sta. Bui. 127. 1915.

127. Sahut, F. Rev. hort. 57: 149. 1885.

128. Ibid. 57: 201.

129. Ibid. -57: 258.

130. Ibid. 57: 305.

131. Ibid. 57: 398.

132. Shamel, A. D. et al. U. S. D. A., Bui. 623. 1918.

133. Shamel, A. D. et al. U. S. D. A., Bui. 624. 1918.

134. Shaw, J. K. Proc. Am. Soc. Hort. Sci. 14: 64. 1917.

135. vShaw, J. K. Science. 45 (N.S.); 461. 1917.

136. Shaw, J. K. Mass. Agr. Exp. Sta. Bui. 190. 1919.

137. vShaw, J. K. Correspondence. 1921.

138. Sorauer, P. Manual of Plant Diseases. 3d ed. (transl.) 1: 841. Wilkes-

barre, 1920.

139. Stuart, W. Vt. Agr. Exp. Sta. Ann. Rept. 18: 300. 1905.

140. Swingle, W. T. U. S. D. A., Bur. PI. Ind. Cir. 46. 1909.

141. Talbot, J. Mass. Hort. Soc. Trans. P. 6. 1879.

142. Taylor, R. H. Cal. Agr. Exp. Sta. Bui. 297. 1918.

143. Tufts, W. P. Correspondence. 1921.

610 FUNDAMENTALS OF FRUIT PRODUCTION

144. Yard, E. Rev. hort. 63: 514. 1891.

145. Victoria Jour. Dept. Agr. 14: 6. 1916.

146. Voechting, H. Cited by Lindemuth, H. Ber. Bot. Gesel. 19: 515. 1901.

147. Vosbury, E. D. U. S. D. A. Farmers' Bui. 1122. 1920.

148. Waugh, F. A. Vt. Agr. Exp. Sta. Ann. Rept. 13: 333. 1900.

149. Waugh, F. A. Vt. Agr. Exp. Sta. Ann. Rept. 14: 259. 1901.

150. Waugh, F. A. Plums and Plum Culture. P. 238. New York. 1910.

151. Webber, H. J. Cal. Agr. Exp. Sta. Bui. 317. 1920.

152. Webber, H. J. et al. Cal. Agr. Exp. Sta. Bui. 304. 1919.

153. Wickson, E. J. California Fruits. P. 246. San Francisco. 1910.

154. Ibid. P. 345.

155. Ibid. P. 439.

156. Wisker, A. L. Cal. Board Hort. Mo. Bui. 5: 112. 1916.

SECTION VII
GEOGRAPHIC INFLUENCES IN FRUIT PRODUCTION

Perseverance has not only developed fruits with qualities superior
to those of the wild; it has extended their growth into regions to which
they are not native. The two most important orchard fruits of the
United States are not indigenous. Social and economic conditions have
played no unimportant parts in developing fruit growing or in preventing
its development. Transportation facilities or neighboring markets are
of utmost importance. Necessary as these all are, however, they can
not estabhsh a fruit growing industry unless its development is possible
under the complex of natural influences which are grouped conveniently
under the term geographic. Though complete analysis of this complex
is impossible, since one factor's influence may be modified by that of
another factor, some general statements can be made with safety.

A knowledge of the conditions which favor, interfere with or prevent
fruit growing at various points may be of considerable value for local
application, since it may suggest the capitalization of certain features of
the local climate through the growing of fruits best suited to those condi-
tions or it may indicate certain departures of the local climate from the
best conditions for a given fruit, necessitating particular care in some
phase of management. Furthermore, it may suggest to the plant breeder
definite aims in improvement to secure adaptation or possibly it may
indicate sources of material with which he can work most profitably.
Plant improvement for one section may be quite different from the
amelioration necessary in the same fruit for another.

611

CHAPTER XXXIII
THE GEOGRAPHY OF FRUIT GROWING

Certain fruits like the apple are grown throughout most of the tem-
perate regions of both hemispheres, the industry in the case of the apple
reaching its height in the northern half of the United States and Europe
and in the southern part of Australia, Tasmania and New Zealand. The
pear is cultivated throughout practically the same range; its quantity
production is much more localized. Sweet cherry production is developed
mainly in the western nations of Europe and the western states of North
America. None of these fruits is of great importance in South America,
though the grape, which is grown along with the apple and pear in North
America, Europe, Asia and Australia is an extremely important fruit
on that continent. On the other hand, certain fruits have very restricted
geographic ranges. The date is grown mainly in countries bordering the
Mediterranean, the jaboticaba in parts of Brazil, the jujube in central
China, the pecan in the southeastern United States, the loganberry in
Washington, Oregon and California. The accompanying maps (Figs.
59 to 64) present graphically a few interesting facts regarding the geo-
graphic distribution of certain of the more common fruits. Incidentally
Figs. 59 and 60, representing total apple production and total number of
apple trees of bearing age in the United States in 1909, show that actual
production is often not proportional to ti'ee number.

The distribution of individual varieties is equally interesting. For
instance the Fameuse apple is of great importance in the St. Lawrence
river region, the Yellow Bellflower in parts of California, the Huntsman
in Missouri; Yellow Newtown is important in New York, Virginia,
Washington, Oregon, California, Tasmania and New South Wales.

It is one thing to construct a map which shows the geographic dis-
tribution of various fruits; it is quite another to find the exact reasons for
this distribution. Without doubt many factors are operative. Some
are of relatively great, others of much less, importance. A single factor
may' be decisive with one fruit, an entirely different factor with another
and a group of several factors may be of almost equal importance in a
third case.

LIFE ZONES, CROP ZONES AND FRUIT ZONES

In a broad way the fruit zones of the world coincide more or less closely
with the general life zones and crop zones, though the pomologist may use

612

THE GEOGRAPHY OF FRUIT GROWING

613

614

FUNDAMENTALS OF FRUIT PRODUCTION

0^'Vr^-—~^

_^

V-,,

&

m*i~S\

r

/ .'•' ' ' (• 1 * -• ■

^

P

fe/V^

\

\ 'xZ-Htlir

" 3

NiYT~T^

'■. ^

f>

UNITED STATES \

)L

J

APPLES Vr^

JV^^-^SAiS

\

TREES OF BEARING AGE

\ r

? \

APPROXIMATE ACREAGE

\ {

\ J

EACH DOT REPRESENTS 500 ACRES

^

V

Fig.

60. — Apple trees of bearing age, approximate acreage, 1910.
Baker^)

(After Finch and

>■# \'--'/77"""^~"~---_

. i>

4^

\ -^ 1 ^■~~-^>^ /

\^A

?^^-^

W\ pl — ^lZ

W

^M

y\

1 V^

\j : /^~~~" U

ZXj

r^^r

UNITED STATEsV

PEARS Vr-x

TREES OF BEARING AND \
NOT OF BEARING AGE \
APPROXIMATE ACREAGE \

iL

^

EACH DOT REPRESENTS 100 ACRES

y^

Fig. 61.

-Approximate acreage of pear trees in the United States. (After Finch i
Baker^)

THE GEOGRAPHY OF FRUIT GROWING

615

616

FUNDAMENTALS OF FRUIT PRODUCTION

THE GEOGRAPHY OF FRUIT GROWING

617

other names to designate them than the biological cartographer does.

These general life zones as determined for the United States, southern

Canada and northern Mexico

by the Bureau of Biological

Survey of the United States

Department of Agriculture, are

shown in Fig. 65.

The Boreal Zone. — As here
outlined, the Boreal zone or
region includes all of Canada
except a portion of Nova
Scotia, a strip along the St.
Lawrence River and running
west through Ontario to Lake
Huron and Georgian Bay,
southern Saskatchewan and
limited areas in southern
Manitoba, Alberta and British
Columbia. Its southern boun-
dary dips down into the United
States so as to include parts of
northern New England, north-
ern Michigan, a small strip of
northeastern Wisconsin and a
considerable part of Minnesota
and North Dakota. Irregular-
ly shaped areas characterized
by the life of the Boreal region
are found here and there in
New York and Pennsylvania
and at some of the higher eleva-
tions of the Allegheny Moun-
tains as far south as southern
Tennessee. In the western
parts of the United States
there are finger-like projections
of this region and isolated areas
with its characteristic fauna
and flora extending as far south
as the state of Zacatecas in
Mexico. For the most part these extreme southern extensions are Hmited
to the higher elevations of the Rocky, Sierra Nevada, Cascade and Coast
mountain ranges. Its southern limit is marked by the isotherm of 18°C.
(64.4°F.) for the six hottest consecutive weeks of midsummer. ^^ On the

618

FUNDAMENTALS OF FRUIT PRODUCTION

whole this region is not suited to fruit growing; nevertheless a number of
fruits are thoroughly at home and indeed reach their best development

along its southern borders. Among these arc the cranberry, blueberry,
currant and gooseberry.

THE GEOGRAPHY OF FRUIT GROWING 619

The Tropical Zone. — Only a very small part of the continental United
States is included within the Tropical region or zone. To be exact, there
are three widely separated areas where tropical conditions prevail and
tropical vegetation abounds — one in southern Florida, one in extreme
southeastern Texas, and one along the California-Arizona line, extending
as far north as southern Nevada. Within these areas are such fruits as
the banana, pineapple, mango, date palm, cocoanut, papaya and cheri-
moya. This region is never visited by frosts or freezing temperatures and
many of the fruits grown in it are said to be seriously injured by tempera-
tures even closely approaching the freezing point. To the pomologist,
as to the biologist, this region is known as the Tropical zone. It is char-
acterized by having more than 14,400°C. (26,000°F.) of heat during the
year — degrees of normal mean daily heat in excess of a minimum of 6°C.
(43°F.),*^ which is rather arbitrarily assumed as marking the inception
of physiological activity in plants.

Austral or Temperate Zone. — Between the Boreal region on the north
and the Tropical region on the south and embracing most of the area of the
United States, is a region designated as Austral on the maps of biological
surveys and designated as the Temperate zone by the pomologist. Frosts
and freezes are likely to occur throughout most of this region, but mini-
mum winter temperatures seldom go below — 30°F. at the north and the
mean temperature of midwinter months even of the more northern
sections is well above zero.

Transition Zone. — Biologists recognize three transcontinental life
zones within this region, a so-called Transition zone to the north and an
Upper Austral and Lower Austral zone to the south. Some of the more
hardy fruits, as the apple, pear, red raspberry and the Nigra and European
groups of plums find their most congenial home in the Transition zone.
In the east this zone includes most of those portions of New England,
New York, Pennsylvania and Michigan and in the middle west most of
those portions of Wisconsin, Minnesota and the Dakotas not included
in the Boreal region; in the west it includes many irregularly shaped
areas from the Canadian border to Mexico, and even in Mexico, where
elevation causes comparatively low temperatures. "Transition zone
species", Merriam states, ''require a total quantity of heat of at least
5500°C. (10,000°F.) but can not endure a summer temperature the mean
of which for the six hottest weeks exceeds 22°C. (71.6°F.) The northern
boundary of the Transition zone, therefore, is marked by the isotherm
showing a sum of normal positive temperatures of 5,500°C. (10,000°F.),
while its southern boundary is coincident with the isotherm of 22°C.
(71.6°F.) for the six hottest consecutive weeks. "''^

This Transition zone is in turn divided into three areas by lines having
a general north and south direction, areas that differ from one another
primarily in rainfall and atmospheric humidity. The eastern area,

620 FUNDAMENTALS OF FRUIT PRODUCTION

known as the Alleghanian, extends from the Atlantic seaboard approxi-
mately to the 100° meridian, which runs through central North and South
Dakota, Nebraska and Texas. To the west of this is a central arid area
extending to the Sierra Nevada-Cascade mountain range. West of this
is the Pacific coast humid area, very humid at the north but toward the
south gradually merging into the conditions presented by the central
arid area. Generally speaking, the same fruit species thrive in all of these
areas, though they cannot be grown without irrigation in the central
arid section. However, though the same fruit species are grown in all
three areas the same varieties are not equally successful; consequently
each area has a more or less distinctive variety flora.

Upper Austral Zone. — The Upper Austral region includes a compara-
tively narrow belt of territory in the central Atlantic States but widens
out to include a comparatively large part of the corn belt area in the
middle west and like the Boreal and Transition regions it includes many
irregularly shaped areas from the Canadian line to far below the Mexican
border. According to Merriam: "Upper Austral species require a total
quantity of heat of at least 6,400°C. (11,500°F.), but apparently cannot
endure a summer temperature the mean of which for the six hottest
consecutive weeks exceeds 26°C. (78.8°F.). The northern boundary of
the Upper Austral zone, therefore, is marked by the isotherm showing a
sum of normal positive temperatures of 6400°C. (11,511°F.) while its
southern boundary agrees very closely with the isotherm of 26°C.
(78.8°F.) for the six hottest weeks. "*^ The eastern half of this zone,
known as the Carolinian area, has a humid climate; the western half,
known as the Upper Sonoran area, is comparatively arid. The walnut,
hickory, sassafras, sycamore, red bud and papaw are typical native
trees of the Carohnian area; the sage brush, grease wood and juniper
characterize the Upper Sonoran. Within this zone the peach, the
Japanese plum, the persimmon and many varieties of the apple, pear,
cherry and grape attain their highest development.

Lower Austral or Subtropic Zone. — The Lower Austral zone lies
between the Upper Austral and Tropical regions. On the east it includes
most of the south Atlantic seaboard and in the Mississippi valley it
extends north into southern Missouri, Ilhnois and Indiana; in the west
it includes most of southern California and much of the Sacramento and
San Joaquin valleys. Merriam states: "Lower Austral species require a
total quantity of heat. of at least 10,000°C. (18,000°F.).'"»5 Like the
Upper Austral zone, its eastern half has a humid and its western half an
arid climate. The eastern half is known as the Austroriparian area, the
western half as the Lower Sonoran. The former is characterized by such
native vegetation as the long-leaf and loblolly pines, the magnolia, the
Hve oak and the pecan. It is a rich agricultural area producing cotton,
rice, sugar cane and many other warm season crops. The distinctive

THE GEOGRAPHY OF FRUIT GROWING 621

fruits of its more northern reaches are the pecan, the muscadine grapes
and pears of the oriental hybrid class. The Lower Sonoran area is
characterized by many cacti, yuccas, agaves, mesquites and other desert
plants. It produces plums, prunes, peaches, cherries, apricots, almonds,
grapes and many other fruits in great quantities where irrigation water is
available. The southern part of the Lower Austral zone is known to the
pomologist as the Subtropic zone. Horticulturally it is one of the most
important in the United States. Within it are produced citrus fruits,
figs, avocados, loquats, Japanese persimmons and many other less
known fruits.

Attention may be directed to the fact that the boundaries of the
pomological districts of the United States, as they have been mapped by
the American Pomological Society do not coincide exactly with those of
the life zones that have been discussed, though the two maps have many
features in common.

GEOGRAPHY OF FRUIT PRODUCTION AS INFLUENCED BY TEMPERATURE

It will be noted that these life zones or crop zones include areas charac-
terized by a certain uniformity of climate and that, of all the features
that constitute climate, temperature is given first consideration. Indeed
the boundaries of the different regions and zones are for the most part
isothermals, and the main reason for such irregular outlines, especially
in the mountainous districts, is the influence of altitude upon temperature.
High altitude through its accompaniment low-temperatur, accounts for
the island-like areas of the Boreal or Transition zones in latitudes gen-
erally dominated by the life of the Austral. Generally there is a lower-
ing of about 4°F. in mean temperature for each increase in elevation
of 1,000 feet. Even at the equator frost will occur at an elevation of
about 18,000 feet; on the island of Hawaii, at a latitude of 20° North,
frost occurs at an altitude of 4,500 feet or above. ''^

Temperature here is meant to include • not only the mean annual
temperature but also the minimum and maximum temperatures of
winter, spring, summer and autumn, respectively, the mean temperature
month by month, particularly through the growing season, the occurrence
of frost during the critical period just before, during and just after,
blossoming, the length of the growing season (see Fig. 66), the evenness
of temperature from day to day, and many other characteristics of the
weather that are more or less directly attributable to temperature
changes. Sometimes it is one of these features of temperature, e.g.,
minimum winter temperature, or mean temperature during the growing
season, that sets the limits for a certain fruit; sometimes it is another.
Broadly speaking it is the minimum winter temperatures that set northern

622

FUNDAMENTALS OF FRUIT PRODUCTION

limits to the production of fruits of particular kinds and mean rather than
maximum temperatures during four to six weeks of the warmest weather,
that set their southern limits. ^^ There are, however, numerous
exceptions.

Fig. 66. — Computed length of available growing season 4 years in 5. (After R^

Peach Growing as Influenced by Temperature. — The varying in-
fluences of temperature on the geographic range of fruits are shown
clearly by the peach, if comparison be made between Europe and the
United States. Table 1 shows mean monthly temperatures at selected
points. Bordeaux, Perpignan, Montpelher and Lyons in France may be
considered to have temperatures favorable to peach growing. Roscoff,
in Brittany, Plymouth, England, and Bergen, Norway, are in regions
where few or no peaches are grown, though they are warmer in winter than
Rochester, New York, which is typical of much of the peach-growing area
in the northeastern states. The difference between the points named
where peach growing is successful and those where it is not Hes in the sum-
mer temperatures. So far as winter temperature is concerned peaches
apparently could be grown in Berufjord, Iceland; deficiency in summer
temperatures seems the limiting factor in a considerable part of
Europe.

Between Nashua and Concord, in New Hampshire, about 35 miles
apart, runs the northern limit of commercial peach growing in that section.
Examination of the table shows only small differences in mean monthly

THE GEOGRAPHY OF FRUIT GROWING 623

temperatures; the absolute minima for the two stations are, respectively,
— 25°F. and — 35°F. Near the one point commercial peach growing is
profitable; a few miles away it becomes unprofitable. The July tempera-
ture for Concord is identical with that for Fitchburg, Mass. (c/. Table
3), well within the zone of peach growing, and greater than that of
Roseburg, Ore. Apparently, then, for conditions obtaining in southern
New Hampshire, the northern limit of commercial peach production is
set by winter temperatures averaging between those for the two stations
given.

Pierre, S. D., has as high or higher summer temperatures than many
sections where the peach grows readily, but its winter temperatures are
too low. Near Portland, Maine, the peach reaches its limit in ordinary
cultivation and is subject to winter injury. Portland, Ore., with a summer
temperature slightly lower, provides, through milder winters, conditions
such that the peach grows fairly well. Near Lincoln, Neb., the peach
grows about as at Portland, Maine; though the winter temperature
averages a shade lower, the summer is warmer, suggesting a greater
maturity in the fall with consequent ability better to withstand the winter.
This, however, is the only waj'- in which summer temperature may be
considered to influence peach growing in any large area of the United
States. The chief limiting temperature factor here comes in the winter.
Nevertheless the factor of summer temperature or the length of the grow-
ing season may become important in isolated areas along the northern
border of peach growing.

Grape Growing as Influenced by Temperature. — The northern limit
of grape culture, as with the peach, is set by summer temperatures at
some points and by winter temperatures at others. Its course in Europe
has been defined as extending "from somewhat north of the mouth of the
Loire, where the Marne empties into the Seine, to the junction of the Aar
and the Rhine, north of the Erzgebirge, to about the 52° of latitude,
descends along the Carpathians to the 49°, extends on this parallel east-
ward, and near the Volga turns southward to its mouth, in the Caspian
Sea."ii

Wine in considerable quantities was made north of this line, in Eng-
land, and even in Zeeland, in former times. This fact, sometimes cited
as proving a change in climate probably proves no more than a change in
taste. " It must be taken for granted that in those times when there was
no communication over long distances they were not very exacting in
regard to wine, particularly as the best wines were unknown, as must
have been the case in northern Germany, the Netherlands and England.
If the wine was harsh and sour, it was still wine. . . . With the
present facilities for communication and the competition in the wine
business resulting therefrom; vine culture is no longer profitable in many
places where 30 years ago it was so; . . ."

624

FUNDAMENTALS OF FRUIT PRODUCTION

The boundary thus set, therefore, is not necessarily the Hmit of the
abihty of the grape to grow; it does, however, mark the Hmit of its abihty
to ripen sufficiently for wine making. This line in western Europe is set
by summer temperatures. In eastern Europe it is set by winter tem-
peratures and does represent approximately the real limit of culture of
the vine.

Table 2 shows the mean monthly temperatures for a number of selected
European stations. Some of these, for example, Bordeaux in France,
Florence in Italy, Patras in Greece and Odessa in Russia, are either centers
of important viticultural industries or they fairly represent such districts.
Others, like Bergen in Norway, Plymouth in England and Roscoff in Brit-
tany are places where outdoor grape culture for wine is impracticable.

Table 1.-

-Mean Monthly Temperatures in Relation to Peach Growing
(Degrees Fahrenheit)

Bordeaux, France (1) .
Perpignan, France (1) .
Montpellier, France (1)
Roscoff, France (1). . . .
Plymouth, England (1)
Bergen, Norway (1) . .
Lyons, France (1) . . . .
Berufjord, Iceland (1) .

Concord, N. H. (2)

Nashua, N. H. (2)

Rochester, N. Y. (3) ..
Portland, Maine (3) . .
Portland, Ore. (3) . . . .

Pierre, S. D. (3)

Lincoln, Neb. (3)

1. Hann. J., Handb. der Klimatologie, Stuttgart (1911).

2. United States Department Agriculture, Weather Bureau, Bui. Q. (1906).

3. United States Department Agriculture, Weather Bureau, Bui. R. (1908).

Yet these latter points have mean winter temperatures above those of
some of the grape growing districts and their absolute minimum tempera-
tures are likewise higher. However, their mean summer temperatures are
comparatively low — too low for the grape to mature its fruit and wood
properly; consequently the industry does not flourish there.

Temperature and the Geographic Range of Apple Varieties. — The
same general principles operate to establish limits for the profitable
culture of different varieties of the same fruit. Thus, winter tempera-
tures at Eastport, Maine, are higher than those at Lewiston, in the same
state. The Baldwin apple grows very well around Lewiston but not at
Eastport. The difference in suitability of the two places hes evidently

THE GEOaRAPHY OF FRUIT GROWING 625

in the summer temperatures. Madison, Wis., has evidently sufficient
summer heat to satisfy the Baldwin's requirements; the difficulty in
growing Baldwin at this last point is known to be winter temperature.
So far as apple growing in the United States is concerned, then, there
are along the northern limit, two different factors operating, summer
temperature and winter temperature; the effects of the one sometimes
mask those of the other. However, there appear to be very few places
listed in the table where the Baldwin apple would suffer from lack of
summer heat. Data are presented in Tables 3 and 4 showing the mean
monthly temperatures throughout the year and the minimum tempera-
tures for the six winter months at a number of stations in the United
States. Except for the California and Alaska points, each station
included in the tables may be taken as representing fairly well a commer-
cial apple producing section. The figures afford an idea of the range in
mean and minimum temperatures within which apple growing is profi-
table and by inference, an idea of the temperature limits for the commer-
cial varieties. A comparison of these data with the records of the
leading varieties in the several districts represented, likewise affords a
fairly accurate measure of their particular temperature requirements
and this, in turn, may be used as a basis for judging their probable
suitability for sections where they have not been tried but where tem-
perature records are available.

Averages are treacherous at times and caution should be observed
in their interpretation. Lewiston, Maine, shows the lowest mean winter
temperatures of any of the apple sections represented in Table 3. Never-
theless this region grows successfully several apple varieties which cannot
be grown in the Bitter Root valley, as represented by Missoula. Refer-
ence to Table 4 shows that the mean temperatures for Missoula conceal
a November minimum of — 20°F. as compared with plus 2°F. for Lewiston
and a January minimum of — 42°F. for Missoula as compared with
— 24°F. for Lewiston. Over a long period the amount of winter killing
around Lewiston is probably no greater than that around Spokane, Wash.,
though Lewiston averages 8° colder in January and 10° colder in February.
The October and November means, however, are only 1° apart. Abso-
lute minima for Lewiston in October, November and January are actually
higher than those for Spokane (6°, 15° and 6°F. respectively). The
November temperatures, mean and minimum, seem particularly impor-
tant in relation to winter injury along the northern border of apple
growing.

The total effective growing temperatures at Portland, Oregon, and
Portland, Maine, are practically the same and the same varieties of
apples attain an almost equal development in the two places. Appar-
ently in this case neither maximum nor mean summer temperatures in
Oregon nor minimum winter temperatures in Maine are limiting factors

40

626 FUNDAMENTALS OF FRUIT PRODUCTION

in the growth of the varieties in question. Mean temperature during
the growing season, therefore, in this case becomes an accurate index of
adaptation to chmate.

On the other hand the loganberry and sweet cherry which thrive so
well in the vicinity of Portland, Ore., cannot be grown profitably near
Portland, Maine, because minimum winter temperature is a hmiting
factor. The blueberry, which grows so luxuriantly near Portland, Maine,
fails to grow near Portland, Ore., not because temperature is a limiting
factor but presumably because it does not find a congenial soil.

Investigations in fruit growing at Sitka, Alaska, show interesting effects of
a rather unusual chmate. From November to March inclusive the mean tem-
peratures are higher than those of Lewiston, Maine; they exceed those of Roches-
ter, N. Y., for nearly the same period and for December to February they are
somewhat higher than those of Martinsburg, W. Va. Zero temperatures are
very rare; nevertheless winter killing is common. Records of the Alaska Agri-
cultural Experiment Stations show that such hardy plums as De Soto and RoU-
ingstone, numerous apple varieties selected for hardiness, the sand cherry and
blackberries have suffered considerable injury.

The causes of this condition are indicated in the following quotations from
reports of the station:

"Only early maturing sorts will succeed. Varieties which are summer
apples in the States will be fall apples in Alaska, and those which are fall apples
in the States will not mature at all in Alaska. The summer heat is not great
enough. In the coast region the season between frosts is long — longer, indeed,
by at least two months than in the northern tier of states.

"In the larger portion of the coast region there is little, if any, damaging frost
between May 1 and October 1, and some seasons damaging frosts do not occur
until the end of October. The drawback to the climate in this region hes not
in too great cold, but, anomalous as the statement seems, in the lack of summer
heat. . . . The maximum temperature is more generally between 60° and 70°,
and some summers it will not go much above 60°. In the interior, on the other
hand, the summers are warm enough, at least in places but the season is too
short to hope to mature any but the earliest sorts and there is considerable doubt
if they will succeed.""

"The excessive rainfall and continuous mild weather prolongs the growing
season until long into October. The young wood is soft and succulent, and
moderately cold weather the following winter kills it."^*

"The winter of 1908-1909 was quite severe for this part of the coast region.
The temperature fell to 2° above zero and 3° above zero in January and Febru-
ary, respectively, and the cold period was protracted over many weeks. As a
consequence, the young growth produced in the season of 1908 was partly killed
in most cases, and in some cases entirely. "^"^

"Blackberries and dewberries cannot be grown successfully in any part of
Alaska. They have been tried repeatedly at the Sitka Experiment Station and
the attempt has always resulted in failure. The summer is not warm enough to
develop the fruit and the plants usually winterkill even in mild winters, probably
due to the late succulent growth resulting from the abundance of moisture."^®

THE GEOGRAPHY OF FRUIT GROWING

627

Phenological data taken at Sitka are interesting. Apples are recorded as
leafing out June 1; Early Richmond cherry in blossom June 15, the Whitney

Table 2. — Mean Monthly Temperature at Selected European Stations
(Cornp iled fro m Ha nn^^)
(In degrees Fahrenheit)

Bordeaux, France . .
Budapest, Hungary
Patras, Greece . . . .
Bremen, Germany.
Plymouth, England
Lemburg, Austria. .
Roscoff , France ....
Bergen, Norway . . .

Florence, Italy

Nantes, France

Odessa, Russia

40.6
2
51.1
33.6
42. 1
24.3
45.0
34.2
40.7
40. 1
25.3

42.9
31.4
53.0
34.7
42.8
25.7
44.8
33.6
42.1
41.9
27.7'

46.9
39.9
56.1
38.1
43.8
31.1
46.2
42.1
48.9
45.2
34.9

53.0
51. 1
61. 1
46.0
48.0
46.2
50.0
48.9
56.1

;i.3

68.2
70.5
80.8
63.1
61.0
66.4
61.3
55.7
76.1
65.7
47. 5 59. 2168.0 72. 5

.3
. 1

67.8
54. 1
52.9
57.0
53.4
55.1
63.1
56.3

64.2
66.7
74.5
60.3
58.4
64.3
57.7
55.2
70.7
62.2

63.7
61.1
76.6
56.5
57.6
57.0
59.4
50.7
68.6
60.4
62.1

.446.941.2
. 1 40.2|30.6

.861.1
.4139.4
1 46.8

;34.7

49.3
138.5
;49.3

53.6
35.1
43.2
27.2
45.8
34.7
42.6

45.3 40.6

41.0'30.2

Table 3. — Mean Temperatures of Selected Stations
{Compiled from United States Weather Bureau Bui. Q)
(Degrees Fahrenheit)

Lewiston, Maine. . . .
Fitchburg, Mass. . . .

Rochester, N. Y

Albany, N. Y

Vineland, N. J

Charlottesville, Va. . .
Martinsburg, W. Va.
Waynesville, N. C. . .

Clayton, Ga

Marietta, Ohio

Griggsville, 111

Springfield, Mo

Montrose, Colo

Provo, Utah

Missoula, Mont

Payette, Idaho

The Dalles. Ore

Albany, Ore

Roseburg, Ore

Spokane, Wash

Moxee Wells, Wash..
Walla Walla, Wash. .

Sacramento, Cal

Fresno, Cal

Los Angeles, Cal....

RosweU, N. M

Sitka, Alaska

628

FUNDAMENTALS OF FRUIT PRODUCTION

apnle on June 20. Early Richmond cherries and Champion gooseberries were
ripe August 15; the Cuthbert raspberry usually ripens during the last of August.
These dates explain the ability of only a few apple varieties to mature fruit there,
the most satisfactory being Yellow Transparent and Livland Raspberry. Pat-
ten Greening has set good crops but failed to ripen its fruit.

On the other hand, gooseberries, currants and red raspberries thrive at this
point and bear heavily. At the Kenai Station, where repeated efforts failed to
produce grain crops because of the cool summers, these fruits were satisfactory."
Evidently then, though these fruits endure less heat and drought than grain
they endure more rain and low growing season temperatures. Their growing
season requirements appear to resemble those of cabbage and potatoes.

Table 4. — Absolute Minimum Temperatures op Selected Stations

{Compiled from United States Weather Bureau Bui. Q)

(To 1906, Degrees Fahrenheit)

October

November

18

2

22

5

19

1

23

-10

22

14

26

15

23

15

16

9

24

14

19

15

20

2

21

6

19

-18

12

3

7

-20

16

- 6

20

- 2

29

23

22

14

12

-13

13

-22

24

- 9

36

27

36
40

27
34

19

10

January

February

-24

-24

-14

-16

-12

-12

-24

-18

-11

-13

- 1

- 9

- 2

-13

-12

-10

- 1

- 5

- 8

-22

-20

-22

-17

-29

-20

-13

- 7

-18

-42

-36

-13

-15

-13

-19

10

11

- 6

3

-30

-23

-15

-22

-17

-15

19

21

20

24

30

28

- 4

-14

Lewiston, Maine. . . .

Fitchburg, Mass

Rochester, N. Y

Albany, N. Y

Vineland, N. J

Charlottesville, Va. .
Martinsburg, W. Va
WajTiesville, N. C. .

Clayton, Ga

Marietta, Ohio

Griggsville, 111

Springfield, Mo ....
Montrose, Colo ....

Provo, Utah

Missoula, Mont. . . .

Fayette, Idaho

The Dalles, Ore....

Albany, Ore

Roseburg, Ore

Spokane, Wash

Moxee Wells, Wash.
Walla Walla, Wash.
Sacramento, Cal. . . .

Fresno, Cal

Los Angeles, Cal. . . .
Roswell, N. M

-21
-14
-11
-17

- 5
4

- 2

- 4
2

- 4
-16
-11
-17

- 6
-23

- 6
-18

18

7

-18

- 8

- 2
24
23
30

- 3

The Effect of Bodies of Water on Temperature.— Large bodies of
water have been said to retard temperature changes, making conditions
.in their vicinity rather more favorable for fruit growing. Table 5
assembles data showing mean monthly temperatures for stations selected

THE GEOGRAPHY OF FRUIT GROWING

629

Table 5. — Monthly Mean Temperatures at Coastal and at Inland Points

{Compiled from Bigelow^)
(Degrees Fahrenheit)

1. Grand Haven, Mich

2. Grand Rapids, Mich

3. Buffalo, N. Y

4. Syracuse, N. Y

5. Milwaukee, Wis

6. Madison, Wis

7. Eastport, Maine

8. Northfield, Vt

9. Erie, Pa

10. Scranton, Pa 25.

11. Charles City, Iowa 11.

12. Dubuque, Iowa 18,

'o/i o in a

■.\

^1
533.

031

831

8|44.
046.
2'42.
4|44.
941.
1J44.
938.
2 40.

44.

47.

46.

48.

8 64.

0 68.

5[65.

66.

7 69.7 67.
1 72. 6l70.

1,70.2
9 70.8

5 69.7

3 72.4

4 59.8

7 66.6
0J71.8
2J71.8

8 73.5

6 74.7

61.1

61.8
8|62.9
661.6
761.5

61.1
55.2
54.6
63.9
62.2

38. o;

38.1

39.3;

38.7

36.1

34.2;

36.8;

32. o;

41.
39.1
33.0 19.0
36.0 24.5

30.1
28.8
1

28.3
26.0
22.7
25.3
20.5
31.7

to illustrate this influence. With the exception of the Iowa points, the
stations are arranged in contrasting pairs, the odd-numbered stations
being located close to considerable bodies of water. In practically every
case these stations show higher January means and lower July means
than the respective stations with which they are contrasted. In every
case the April temperature for the inland station is higher and November
temperature lower than at the points near water. The Iowa stations of
approximately the same latitude as the majority of the more eastern
points show intensification in all these differences. Milwaukee and
Grand Haven, at almost opposite points on Lake Michigan, show the
influence of the lake on the prevailing winds blowing over it. That the
retardation for these stations is generally somewhat greater in the spring
than in the fall is shown by Table 6.

Table 6. — Dates When Normal Temperature Crosses 40°F.
{Compiled from Bigelow'^)

1. Grand Haven, Mich Apr. 7 Nov. 8

2. Grand Rapids, Mich Apr. 3 Nov. 9

3. Buffalo, N. Y Apr. 11 Nov. 12

4. Syracuse, N. Y Apr. 7 Nov. 11

5. Milwaukee, Wis Apr. 12 Nov. 5

6. Madison, Wis Apr. 7 Nov. 2

7. Eastport, Maine Apr. 23 Nov. 5

8. Northfield, Vt Apr. 16 Oct. 25

9. Erie, Pa Apr. 5 Nov. 17

10. Scranton, Pa Mar. 30 Nov. 12

11. Charles City, Iowa Apr. 4 Nov. 2

12. Dubuque, Iowa Mar. 31 Nov. 7

630 FUNDAMENTALS OF FRUIT PRODUCTION

Attention may be called to some of the northern finger-like extensions
of the Lower Austral zone into latitudes that for the most part belong in
the Transition zone. Those along the eastern shore of Lakes Michigan
and Huron, the southern shores of Lakes Erie and Ontario and the eastern
shore of Lake Champlain are cases in point and illustrate the extent to
which chmate is tempered and consequently life zones are modified
through the influence of large bodies of water. Lippincott gives one
concrete illustration of this influence :*i On Jan. 1, 1864, a cold wave
swept over the north central part of the United States. Many Minnesota
points registered temperatures as low as — 38°F. ; at Milwaukee the
thermometer went to — 30°F.; yet at Holland, Mich., across Lake Michi-
gan from Milwaukee —8°F. was the lowest temperature recorded.
Further inland, at Lansing, Mich., however, — 22°F. was experienced.
Peach buds were uninjured in a narrow belt along the eastern shore of the
lake but were killed at distant points. The data for Milwaukee and
Grand Haven in Table 5 show that this influence is constant.

Influence of Altitude on Air and Soil Temperatures. — It is well known
that an increase in altitude is accompanied by many of the same changes
as an increase in latitude, the most important being one in temperature.
It is true also that an increase in altitude is accompanied by certain
changes in physical environment that are not found at correspondingly
higher latitudes. Thus Kerner and Oliver report that in the Tyrolese
Alps at an altitude of 2600 meters the chemical activity of the sun's rays
is 11 per cent, greater than at sea level. This alone may account for
some of the peculiarities of plant associations noted at different altitudes
and possibly may go far toward explaining the more brilliant and intense
coloring of certain fruits and their better finish at high altitudes. The
same authors report a different ratio between mean soil and air tempera-
tures at high as compared with low elevations (see Table 7) and this too
may either intensify or suppress, as the case may be, the differences
associated with variations in air temperature only.

Table 7. — Increase of Mean Soil Temperature Over Mean Air Temperature
WITH Increased Altitude in Tyrolese Alps^^

Excess of mean soil temperature over

Elevation, meters

mean air temperature, degrees Centigrade

1000

1.5

1300

1.7

1600

2.4

1900

3.0

2200

3.6

THE GEOGRAPHY OF FRUIT GROWING 631

GEOGRAPHY OF FRUIT PRODUCTION AS INFLUENCED BY RAINFALL AND

HUMIDITY

Of hardly less significance than temperature is the influence of humid-
ity in determining the limits of life and crop zones and in the geography
of fruit growing. By humidity is meant here total rainfall, distribution
throughout the season, availability for plant growth and atmospheric
humidity. Only in countries or districts where the topography leads to
marked differences in rainfall between points close together and enjoying
practically the same temperatures are the full effectsof humidity strikingly
brought out. Thus " . . .at one of the substations of the United States
Experiment Station on the Island of Hawaii, a rainfall of 360 inches was
recorded for 1 year, while at a point 28 miles away the annual rainfall for
the same year was 6 inches. It is possible ... in the space of an hour's
ride to pass from a desert covered with cacti and other drought-resistant
plants into a dense tropical jungle reeking with moisture." ^^

For the most part fruit trees thrive better in a fairly humid climate,
a fact shown by the natural distribution of their undomesticated relatives.
Many species, however, like the date palm and olive, succeed in a very
arid climate. Some of the great variations in the actual water require-
ments of different kinds of fruit are shown by data presented in the sec-
tion on Water Relations. Often different varieties of the same kind
of fruit vary considerably in water requirements. The Yellow Trans-
parent apple will thrive and produce good fruit on less water than the
Winesap or York. Certain varieties or types of dates are grown at
Alexandria, Egypt, where the mean atmospheric humidity is from 64 to
72 per cent, while certain other varieties are grown in some of the desert
oases having an atmospheric humidity of only 34 per cent. Those varie-
ties that thrive under the one set of conditions, however, cannot be grown
successfully in the other environment.^^ As these humidity requirements
of different fruits become known it is possible to draw, more or less accur-
ately, iso-hyetal lines setting approximate boundaries for districts in
which they may be expected to reach a high degree of development.

Data presented in Table 8, however, show the danger in placing too
much reliance upon rainfall figures as an index to fruit crop or varietal
adaptation. Thus Fitchburg, Mass. has a mean annual rainfall of 45.4
inches, 28.6 coming during the growing months, while Missoula, Mont.,
has a total precipitation of only 15.5 inches, of which 10.4 comes during
the growing months; yet both are apple growing centers and Mcintosh
is one of the most satisfactorj^ varieties in both places. Irrigation, how-
ever, is employed in Montana. Vineland, N. J., has an annual rainfall
of 47.3 inches, three-fourths of which falls during the growing season;
yet The Dalles, Ore., with less than one-third of that total rainfall and
with only one-sixth as much falling during the growing season as comes
during the corresponding period in New Jersey, produces peaches and

632

FUNDAMENTALS OF FRUIT PRODUCTION

other stone fruits with success and without the aid of irrigation. A
season with a summer rainfall as low as that of The Dalles, would involve
considerable loss in New Jersey. The summer temperatures of the two
locations are very much alike, as shown in Table 3. Irrigation is con-
sidered an absolute necessity in many localities with higher yearly and
growing season rainfalls than those of The Dalles. The explanation of the
ability of the Oregon section to produce fruit successfully and with such
a limited water supply lies in the depth and character of its soil and in the
methods of soil management employed. The data in this table, however,
taken in consideration with the methods of culture that are practiced and
the varieties that are grown in the different sections point out certain
general limitations that are placed on fruit culture by rainfall and the
methods that may be employed by fitting practice and variety to varying
conditions of humidity.

Table 8. — Mean Rainfall of Selected Stations

(Compiled Chiefly from United States Weather Bureau Bui. Q)

(inches)

Rumford Falls, Mail

Fitchbiirg, Mass

Rochester, N. Y

Albany, N. Y

Vineland, N. J

Martinsburg, W. Va
Charlottesville, Va. .
Waynesville, N. C. .

Clayton, Ga

Marietta, O

Griggsville, 111

Springfield, Mo

Montrose, Colo

Provo, Utah

Missoula, Mont

Payette, Idaho

The Dalles, Ore

Albany, Ore

Roseburg, Ore

Spokane, Wash

Moxee Wells, Wash.
Walla Walla, Wash.
Sacramento, Cal. . ..

Fresno, Cal

Los Angeles, Cal. . . .

Roswell, N. M

Sitka, Alaska

Lincoln, Neb

3.0
3.3
2.4
2.4

1.0
1. 1
1.0
1.0
0.7
3.6
2.5
1.3
0.6
1.8
2.0
0.6
1. 1
0.4
6.3
2.8

3.7
3.6
3.0
3.0
3.7
4.2
5. 1
3.7
3.2
4.0
5.3
5.9
0.7
1.5
2.2
1.4
0.6
2.6
2.0
1.4
0.9
1.7
1.0
0.5
0.5
1.2
3.5
4.3

3.8
3.0
3.1
3.7
3.6
3.6
5.5
4.4
5.3
4.5
4.5
4.8
0.2
0.5
2.1
0.6
0.6

4.5
2.9
3.1
3.9
4.6
3.7
5.7
4.6
7.0
4.4
3.7
4.2
0.8
0.2
1.0
0.4
0. 1
0.3
0.4
0.7
0. 1
0.4
T
T
T
3.4
4.2
3.8

3.2
4.4
2.9
4.0
4.8
3.2
5.0
4.5
7.2
3.9
2.7
3.9
1. 2
0.2
0.7
0.3
0.2
0.4
0.4
0.5
0.2
0.4
T
T
T
2.2
6.7
3.7

3.0
3.4
2.3
3.2
3.8
2.5
5.2
2.4
4.9
3.0
4.0
3.8

0.4
1.2
0.5
0.6
2.0
1. 1
1.0
0.4
1.0
0.3
0.3
0.8
2.0
10.7
2.6

3.0
4.0
2.8
3. 1
3.6
1.6
3.5
2.1
4.0
2.9
1.9
2.9
0.8
0.8
1.2
1.0
1.3
3.4
2.6
1.4
0.5
1.5
1.1
0.6
1.5
1.6
12.1
1.8

28.3

28.6

22.7

26. 1

31.7

25.1

37.0

32.2

45.7

29.2

28.6

33.2

6.5

6.0

10.4

6. 1

5.4

7.4
3.6
6.7
13.0
52.1
24.6

42.1
45.4
34.5
36.9
47.3
35.2
49.8
47.7
68.5
42.1
37.0
43.6

9.3
10.9
15.5
12.1
15.4
44.2
34.9
18.3

8.9
17.7
19.9

9.2
15.6
15.6
82.3
27.5

THE GEOGRAPHY OF FRUIT GROWING

633

OTHER FACTORS INFLUENCING THE GEOGRAPHIC DISTRIBUTION OF

FRUITS

Sunshine. — The amount of sunshine to which the trees are exposed
during their growing season is perhaps of secondary importance in deter-
mining the character of the fruit industry that may develop in different
sections, since it nowhere becomes so reduced as to be permanently a Hmit-
ing factor. However it is often decisive in determining the varieties that
can be grown to advantage. This is true at least in the apple in which
coloration depends directly on the relative amount of sunshine that reaches
the fruit during the ripening season. Thus the data in Table 9 suggest
why it is practicable to grow varieties like Winesap at Grand Junction,
Col. and in eastern Washington, but not in the vicinity of Portland,
Ore.

Table 9.— Hours of Sunshine for Selected Stations
(Compiled from United States Weather Bureau Bui. Q)

March

April

May

June

July

August

September

October

19.5
186
171
152
198
197
178
199
192
128
196
193
252
194
166
241
255

213
240
225
221
250
255
236
240
204
181
222
236
279
235
200
324
275

258
279
266
263
284
312
244
267
232
224
294
288
337
286
230
370
259

274
300
290
287
293
303
275
295
261
240
354
355
369
330
329
404
289

276
279
296
318
299
274
312
341
291
279
405
370
370
372
268
429
341

258
248
258
269
271
253
256
290
279
240
354
329
317
310
183
400
328

232
240
223
213
271
250
235
250
252
199
298
296
312
226
148
336
282

185

Albany, N. Y

Rochester, N. Y

Erie, Pa

Raleigh, N. C

Atlanta Ga

186
158
157
220
235

St Paul Minn

176

202

Kansas City, Mo

Parkersburg, W. Va.. . .
Boise, Idaho

236
159
216

Salt Lake City, Utah...
Grand Junction, Col....
Spokane Wash

236
265
160

Portland, Ore

Fresno, Cal

Los Angeles, Cal

64
290

263

Parasites. — The prevalence of certain parasites is another factor of no
mean importance in determining the geographic distribution of fruit
growing — at least in determining what kinds of fruit shall be grown
in different districts. For instance, European grapes are not grown in
the southeastern United States on account of the prevalence there of the
grapevine phylloxera and the downy mildew. European plums are
commercially unimportant in the Middle West on account of the brown
rot and the black knot. Perhaps in the last analysis certain insects and
diseases are particularly troublesome in certain districts because they
find there temperature and humidity conditions that are especially favor-
able for their development and spread ; hence fundamentally it is temper-
ature or humidity that really sets limits for these fruits. Nevertheless

634 FUNDAMENTALS OF FRUIT PRODUCTION

the immediate factor responsible for limitation of the industry is a
parasite.

Wind.— Wind is often considered important in determining whether
fruits can or cannot be grown successfully in certain sections. It is to
be doubted if wind alone is of great significance over any wide areas. On
the other hand, extreme heat or dryness accompanied by winds may
cause much damage and practically prevent the culture of certain fruits
in large areas where they frequently occur. Actually in such cases it is
the combination of high temperature or low humidity — or both — with the
wind that is the real factor.

Native Range of Parent Species. — The native range of the parent
species without doubt furnishes some indication of the probable geo-
graphic range of the forms that are brought under cultivation; neverthe-
less it is doubtful if it is an index with most fruits of the extent to which
they may be grown for commercial production. For instance, the com-
mon European plum {Prunus domestica) is native to central and south-
eastern Europe. Its cultivation extends to practically all of Europe
and to much of temperate North America and it is grown to a limited
extent in many other parts of the world. Though the native home
of the peach is supposed to be China, it reaches its greatest commercial
importance in Europe, North America and southern Africa. The
Evergreen blackberry (Ruhus laciniatus) apparently is not cultivated in
southwestern Europe where it is found wild, but is of considerable impor-
tance in the Pacific Northwest 6,000 miles from its native home. On
the other hand the culture of the North American phim {Prunus ameri-
cana) is restricted to an area considerably less than the native range of
the parent species and the litchi (Nephelhmi litchi) is not grown com-
mercially outside China.

Length of Time in Cultivation. — The length of time a species has been
under cultivation naturally has some influence on the amount of territory
over which it extents. Fruits of recent introduction, such as the pecan,
the blueberry and the loganberry have not had time to become dissemin-
ated widely and tried thoroughly in many sections. On the other hand,
though the Chinese jujube probably has been in cultivation as long as
the peach, its present geographic range is very small as compared with
that of its sister fruit coming from the same general region. Some
species, such as the fox grape ( Vitis labrusca) , are cultivated over a very
wide range of territory though they have been in cultivation only a few
decades.

Uses and Quality of Product. — The variety of uses that the fruit and
the plant producing it serves has been doubtless an important factor in
making the cocoanut palm one of the most widely distributed fruits in
cultivation. For many tropical peoples it is the one most important
plant and there has thus been every encouragement to disseminate it

THE GEOGRAPHY OF FRUIT GROWING 635

widely. The same may be said of the banana. On the other hand,
though the date pahii and the fig are hardly less important, their actual
cultural range is much more restricted.

Quality of product is certainly relatively unimportant in determining
geographic distribution. Best evidence on this point is obtained by a
comparison of varieties within a group, for it is hardly fair to compare the
quality of one group, for example the orange, with that of another, for
example the raspberry. Though Elberta is admittedly a second rate
peach in quality, it dominates the peach industry of America. The
Kieffer pear and the Ben Davis apple occupy similar, though perhaps not
quite so prominent, positions in their respective groups.

Relation to Consuming Centers and Transportation Facilities. — The
location of large consuming centers and their relation to efficient systems
of transportation is very important in determining where many fruits,
particularly those of a more perishable character, are grown in quantity.
For instance a map showing the distribution of the strawberry industry
of North America indicates production centers close to nearly all the
larger markets; those production centers distantly located from large
markets are connected with them by good transportation systems.
The same statements hold for raspberry, blackberry and dewberry pro-
duction and to a certain extent for fruits like the peach, cherry and plum.
However, many centers of heavy production of these fruits are not par-
ticularly well located from the standpoint of nearby markets or quick
and cheap transportation. Almost invariably the presence of fruit
product plants of one kind or another makes possible the location of the
industry. Were it not that a comparatively large percentage of the
world's grape crop has been utilized for wine making for thousands of
years, it might be said that fruit product facilities are becoming of
increasing importance in determining the location of fruit production
centers.

Sometimes factors that are more or less artificial operate, at least for a
time, in determining the development of large fruit industries. For in-
stance a large fruit product establishment may be located at some point —
its exact location being determined largely by considerations quite dis-
tinct from those concerned with fruit production. Within a short time
a large fruit industry develops in the vicinity of this plant to supply it
with fresh fruit. Had this plant been located a hundred miles away, the
first place would have raised no fruit commercially but the industry would
have developed around the other. It often happens that a pioneer
in some branch of horticulture makes a marked success of growing some
particular kind of fruit. His neighbors promptly follow him in the busi-
ness and soon a whole community or a whole section becomes famous for
its Cuthbert raspberries, or Mcintosh apples, or Evergreen blackberries
or Neunan strawberries. In the long run, however, a specialized indus-

636 FUNDAMENTALS OF FRUIT PRODUCTION

try develops and remains chiefly in those sections or districts where fac-
tors governing production, harvesting, distribution and marketing are
most favorable. In other words, the present geographic distribution of
the different fruit industries represents the result of a struggle for
existence, a real natural selection.

Summary.^ — The most important environmental factor determining
the geographic range of cultivated fruits is temperature, though rainfall
and humidity act as important limiting factors within the wider limits set
by temperature. The boundary lines of fruit zones follow rather closely
those of the life zones established by the biologist. Apparently, mini-
mum winter temperatures are most important in setting the northern
limits (in the Northern Hemisphere) to the geographic range of species
and varieties and mean summer temperature during the hottest 6 weeks
in setting their southern bounds. The limiting effects of natural rainfall
are often alleviated by the use of irrigation water or by other cultural
practices and also by the selection of drought resistant varieties. Sun-
shine, wind and the presence of certain parasites are often important
factors in determining the range of particular varieties. There is no
very close relation between the length of time a species or variety has been
in cultivation or between the natural range of related forms and its
range in cultivation. Artificial factors, such as nearness to large centers
of population, transportation and storage facilities, and temporary
market demands, often are of considerable importance in determining the
approximate range of a variety or of a fruit and in determining its
elative importance within different portions of its range.

CHAPTER XXXIV
ORCHARD LOCATIONS AND SITES

The production of fruit on a scale sufficient to meet the needs of the
home at least partly has a general appeal. Indeed it is exceptional to find
the farm or even the suburban lot that is without trace of fruit tree,
shrub or vine. Such planting of a few fruit-producing plants is often done
as much for the pleasure derived from their culture as for the monetary
returns. On the other hand, commercial fruit production is a business
and appeals to only a comparatively small percentage of the popula-
tion— even of the farming population. Perhaps this is because it is
generally considered an exacting business, requiring special training or
special aptitude, or perhaps it is due to other reasons. Whatever the
reason, the commercial fruit growers are few in comparison with other
classes of farmers. Nevertheless there are frequent recurring waves of
interest in commercial fruit production, bringing to those already engaged
in some line of farming the question whether or not it would be desirable
for them to set a part of their acreage to fruit, or raising in the minds
of those who are not engaged in agriculture the question whether they
might not raise fruit with profit. In either case a number of matters
concerning the establishment of an orchard should be considered before
any definite decision is made. These questions are much the same
fundamentally for the one group of prospective growers as for the other,
though the points of view may be somewhat different. In the one case
the problem is to determine what fruits can be grown to best advantage
in some particular field, farm or locality; in the other it may take the
form of first deciding on what kinds to grow and then in finding the proper
place to grow them.

Orcharding In or Outside of an Established Fruit Growing Section. —
Incidental to the discussion of the geography of fruit growing some of the
factors influencing the choice of a location for certain fruits or of fruits
for certain locations are mentioned. An intelligent selection in either
case depends on a detailed knowledge of the geographic distribution of the
industries concerned. Obviously there would be considerable risk in the
commercial culture of some fruit in a section where it is not being grown —
where it has never been tried or where its cultivation has been discon-
tinued. Thus it would not seem wise to attempt commercial filbert
culture in New York or Pennsylvania, or to make other than experimental
plantings of the jaboticaba in southern Florida. It would be safer

637

638 FUNDAMENTALS OF FRUIT PRODUCTION

to undertake the commercial production of any fruit where an industry in
that particular fruit is already established.

One great advantage in producing fruit of a kind that is well and
favorably known and in a section where it is extensively grown is that
the marketing problem usually presents fewer difficulties. The reputa-
tion attracts buyers and the fact that growers have been established there
often means that efficient selling organizations have been formed. How-
ever, such marketing advantages are often over-emphasized. In years
of heavy production, the apple grower in western New York may wish
his orchard were in Indiana or Nebraska. Moreover, land prices are
likely to be high in sections with established reputations; this means a
permanently large overhead charge in the cost of production. If fruit
is to be grown under these conditions, the choice of kinds and varieties
and the methods of culture must be such as will yield large returns.
The usual advantages of production where little fruit is raised are cheap
land and good local markets. However, isolation may mean difficulty
in getting in contact with buyers, trouble in securing supplies and no
possibility of cooperative effort. Probably much would depend on
the scale of operations contemplated. The small grower can often
produce to better advantage in the less developed sections, though
conditions favorable to developing a large enterprise are more likely
to be found where an industry of some size is already established.

Land Values. — Among the important factors determining the desir-
ability of a piece of land for fruit growing are : land values, the availability
of transportation and storage facilities, of fruit products establishments,
of labor supply, the social conditions and the educational advantages.
Locations only a few miles apart may vary greatly in respect to one or all
of these factors.

Perhaps the price paid for land or its valuation has nothing to do
with the grade or quantity of fruit that can be produced on a given area
and the question of conditions favorable for production can possibly be
considered entirely aside from it. Nevertheless it should be realized
that successful orcharding is a question not only of production, but
even more of economical production. This means that there must be a
reasonably large margin between production costs and selling prices.
Both production costs and selling prices for fruit fluctuate from year to
year and the difference between them will likewise vary, but interest on
investment constitutes a fixed and important part of the overhead charges
figured into the cost of production. This charge must be discounted
every year, crop or no crop. For instance, if the orchard at bearing age
represents an investment of $300 per acre and it yields an average crop
of 300 bushels per acre the interest charge against each bushel is about
6 cents; if, however, the orchard represents an investment of $1,000 per
acre, a crop of the same size would represent an interest charge of 20

ORCHARD LOCATIONS AND SITES 639

cents per bushel. Of course, if a bumper crop were harvested in the
latter case — a crop say of 600 bushels per acre — the interest charge per
bushel would be only 10 cents; but on the other hand if a light crop, say
100 bushels, is harvested, the interest charge per bushel would be 60
cents. It is not the intent here to recommend cheap land for growing
fruit; such land may prove the most expensive in the end. On the other
hand the purchaser or owner of high priced land should figure out before
planting the probable charges per bushel, pound, barrel or other unit of
fruit produced, that the cost of land contributes toward cost of
production.

Transportation Facilities. — The importance of the distance between
the orchard and the shipping point or the market depends on the character
of the roads and the value and nature of the crop. Of course the ideal
location is adjacent to a railroad or other transportation system so that
there may be facilities for loading at the orchard. Since this is seldom
possible, access to a loading point must be considered. Six or eight
miles of ordinary country road has been considered about the longest
haul practicable with most fruits. If the distance to the shipping point
is much greater, the item of hauling becomes too large a part of the total
cost of production and unduly reduces the margin of profit, or possibly
turns profit into loss. The cost per mile of hauling barreled apples over
average country roads should not exceed 2 to 3 per cent of the average
price received for them. Let the distance be such that 10 to 15 per cent
of the selling price is required to cover this item and it becomes very
important. The character of the fruit also must be considered. Obvi-
ously it is impracticable to haul strawberries or other soft fruits as far
or over as difficult roads as winter apples may be. The better the
road, however, the greater the distance the crop may be hauled with-
out injury. A trip of 12 to 15 miles over well graded and smooth sur-
faced roads may cause much less injury than one or two miles over
a poor country road. Finally the value of the crop per load is important.
Thus it may be entirelj^ practicable to plant an English walnut, prune
or chestnut orchard 10 to 15 miles from a shipping point, for one load
would carry the crop from 2 acres, while a corresponding area of apple
orchard would require 10 to 20 two-horse load trips. Furthermore a
nut crop is not subject to the mechanical injury which would result
from hauling apples long distances.

SLOPE OR ASPECT

Many advantages have been claimed for certain slopes — advantages
so great that prospective fruit growers are sometimes led to believe that
success is practically guaranteed if the land but slopes in a certain direc-
tion and that failure is almost equally certain if it slopes the opposite

640 FUNDAMENTALS OF FRUIT PRODUCTION

way. Southern are generally warmer and earlier than northern slopes
because they receive the more direct rays of the sun. Shreve,^^ who
has studied the effect of varying physical environment on vegetation
in mountain regions, summarizes some of the more important influences
as follows: "Two slopes of the same inclination, which lie in opposed
positions so that one faces north and the other south, will present to
plants two environments differing in almost every essential physical
feature. The temperature of the air on two such slopes might be identical
as determined by the thermometer of a carefully established meteoro-
logical station, but they are distinctly different as they affect vegetation,
for the plants receive very different amounts of heat through diurnal
terrestrial radiation. This circumstance is of small importance to full-
grown trees and large plants, but is of great importance to young plants
and seedlings. The soil temperatures of opposed slopes are also widely
unlike, even in the presence of the undisturbed cover of natural vegeta-
tion. The two opposed slopes would in all likelihood receive the same
rainfall, although this is not necessarily the case. An equal amount of
rain might effect an equal elevation of the soil moisture on the two slopes,
and to the same depth, but the soil evaporation of the south slope would
greatly exceed that of the north slope, and a lower moisture would soon
prevail in the soil of the former. Greater or less differences may thus
be shown to obtain between the opposed slopes with respect to the most
vital features of plant environment. "

Influence on Soil Temperatures and on the Plant. — Table 10 affords a
quantitative expression of the influence of slope on mean soil tempera-
ture. Even more significant are the differences in the temperatures of
the plants themselves on different slopes. Table 11 shows the mean
temperatures one inch beneath the surface of the bark on the north and
south sides of tree trunks at the summit of a hill and on its north and
south slopes during the winter months in Wisconsin. As would be

Table 10. — Mean Soil Temperatures (Centigrade) at a Depth op 80 Centi-
meters FOR 3 Years on Different Slopes of an Isolated Conical
Sandhill at Innsbruck, Tyrol
{After Kerner and Oliver^'')
N. N.E. E. S. E. S. S.W. W. N.W.

15.3° 17.0° 18.7° 20.0° 19.3° 18.3° 18.5° 15.0°

expected, the trees on the south slope show higher midday and afternoon
temperatures than those on the northern slope. They also show rather
surprisingly lower early morning temperatures. This means that they
are exposed to greater extremes and more rapid temperature changes.
The relation of such conditions to certain forms of winter injury is pointed
out in . the section on Temperature Relations. The tendency of the
north side of the trunk on the north slope to be colder than the south side
in the early morning while on the south slope the reverse condition holds

ORCHARD LOCATIONS AND SITES

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642 FUNDAMENTALS OF FRUIT PRODUCTION

is due probably to the stronger radiation of heat from the ground on the
uphill side against the trunk.

Specific Influence on Fruit Growing. — These data indicate that south-
ern and eastern slopes are preferable for the production of fruits for the
early markets or for any fruit or variety with which hastened maturity
is an important consideration. Thus in New England there are many
locations where certain varieties of grapes can be ripened properly only
when grown in sheltered spots with a southern exposure. Often there
is a difference of a week or more in the maturing seasons of the same
variety on the northern and southern sides of the same hill, equivalent
to a location many miles southward or northward. On the other hand
northern and western slopes are preferable when delayed maturity is the
object. Fruits of certain species like the apple and peach are likely to
be somewhat higher colored on southern than on northern slopes. It
should be noted that late spring and early fall frosts are no more likely
to occur on one slope than on another and that consequently more
trouble from spring frosts at least will be encountered on southern than
on northern slopes because vegetation starts earlier on the former. It is
probably on this account mainly that, for general fruit growing, a northern
exposure is preferred by most growers. Areas with eastern and western
exposures are intermediate in the qualities mentioned between those with
northern and southern exposures. Western and southwestern slopes
are perhaps least desirable under average conditions and with most fruits
because of the action of the sun and of temperature in causing sunscald
on the west and southwest sides of the trunk.

Without doubt too much importance is attached by many to the
advantages or disadvantages offered by particular exposures — at least as
these exposures have a direct bearing on tree and fruit through a
modification of temperature and light conditions. In the great majority
of cases the grower can raise fruit successfully on any and all slopes, pro-
vided they are not unreasonably steep and have suitable soils. It may be,
and often is, desirable to plant certain slopes with fruits of one kind or one
variety and other slopes with other kinds or other varieties, so that the ad-
vantages offered by the different exposures may be fully utilized. Thus
early strawberries might be grown on the south and east sides of a hill
and midseason and late varieties on its west and north sides and the har-
vesting season thereby lengthened a week at each end. The idea that
one slope is always best for a certain fruit or a certain variety is erroneous.
Much depends on where and for what special purpose that variety is
grown.

Indirect Effects. — There are certain indirect influences of slope or
exposure on the growth of trees and their maturing of a crop that are of
importance equal to, or greater than, that of the more direct influences.
Southern and western slopes dry out more rapidly and are more subject

ORCHARD LOCATIONS AND SITES 643

to drought than others. Fruit grown on northern or eastern slopes
therefore tends to average somewhat larger in size than that produced
on a southern or western exposure. In some sections the soil on many
southern slopes is much thinner than that on northern, eastern or western
exposures and in such instances a particular slope is to be avoided, not
because of the slope itself but because of the factors with which it is asso-
ciated. In much the same way certain slopes are to be avoided in certain
sections because of their exposure to prevailing winds. When land slopes
away from the direction of the prevailing wind considerable protection
is afforded the trees by the contour of the ground, but when it slopes in
the direction of the prevailing wind much more trouble is likely.

Abruptness of Slope. — Gentle slopes are almost always preferable to
abrupt slopes. Many orchards on very steep hillsides have proved
profitable, but the cost of production under such conditions is likely to
be considerably higher than on more nearly level land of the same char-
acter. This of course assumes equally good soil and other conditions on
the steep and the gentle slopes. Different environmental conditions in
the two locations may reverse the situation. Thus, in the Piedmont
section of Virginia where the orchards are planted on steep hillsides and
where it is necessary to spray five to seven times, apples are produced at
a lower cost than in the Shenandoah valley where less spraying is required.
As a rule it is best to limit orchard planting to slopes so gradual that cul-
tivation may be practiced without great danger from erosion and over
which spraying machinery and other equipment may be hauled without
serious difficulty. The necessity of gentle slopes is still greater in sections
where irrigation is practiced.

AIR DRAINAGE

Fruit growing, more than almost any other branch of agriculture,
requires comparative freedom from untimely late spring and early fall
frosts; in turn the occurrence of frosts within certain limits is determined
largel}^ by what is commonly known as "air drainage," the settling of
cold air to lower levels. This is discussed in some detail in the section on
Temperature Relations.

Influence of Elevation. — Many factors influence air drainage, some
to a very marked extent and others only to a comparatively small degree.
Probably the most important single factor in air drainage is elevation.
Height above adjoining land or fields usually is of greater significance
than absolute elevation above sea level. Frost is as likely to occur during
the danger period at the high elevations found in some of the intermoun-
tain fruit growing districts as at the low elevations of the seaboard.
Portions of the Ozarks with an elevation of over 1,000 feet are as frosty
as the Hudson River valley, which lies only a little above sea level.

644

FUNDAMENTALS OF FRUIT PRODUCTION

However, as a rule, low lying land is more subject to frost than that
somewhat elevated above surrounding or adjoining fields, though there
are certain exceptions which are discussed later.

The dilTerence in temperature between two points, one of which is
50 or 100 feet above the other, of course depends on many factors, such
as general lay of land, relative areas of the land having the respective
elevations and proximity to bodies of water. However, the inequality
in temperature, particularly on quiet nights, in spring and fall when

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Fig. 67. — Continuous records of the temperature from 4 p. m. to 9 a. m. at the base and
at different heights above the base of a steep hillside, showing the great differences in
temperature that sometimes develop on a clear, still night. Although the temperature at
the base was low enough to cause considerable damage to fruit, the lowest temperature
225 feet above on the slope was only 51°F. Note that the duration of the lowest tempera-
ture was much shorter on the hillside than at the base. (After Batchelor and West"^)

there is greatest danger from frost, between points only a few dozen feet
apart in elevation is often considerable — often enough to make the
difference between no frost or a very light frost and a killing frost. Fig-
ure 67 shows graphically the diversity in minimum temperature that
sometimes occurs with variations in elevation of 25, 50 and 225 feet.
In this case a disparity of only 25 feet in elevation was accompanied
by a difference of approximately 5°F. between 8:00 p.m. and 8:00 a.m.
and an inequality of 50 feet was accompanied by a variation of 15°
to 20°F. At greater elevations the temperature was still higher, though
its rise was not proportional to the increase in height.

This suggests that extreme divergencies in altitude, therefore, are
likely to afford much greater security from frost than moderate differences,
very slight inequalities, even of only a few feet, often are associated with
a sufficient variance in temperature to result in crop safety or crop loss.
Perhaps more nearly average differences in minimum temperature due

ORCHARD LOCATIONS AND SITES

645

to elevation are shown in Fig. 68. These graphs represent temperature
variations on comparatively still, clear nights at stations in a mountain
valley during the blossoming period of fruits. Though the minimum
temperature was not invariably recorded at the lowest elevations, on
each of the four nights when there was danger from frost the higher

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Fig. 68. — The daily minimum temperatures for stations of different elevations extend-
ing from the high agricultural land to the lowest agricultural land of the valley. {After
Batchelor and West^}

elevations registered temperatures above the probable danger point
and a fruit crop on the lower levels probably would have been destroyed.
"The minimum temperatures experienced by the bench lands and upper
slopes of the tillable area in a mountain valley average from 6 to 10°F.
warmer than the valley bottoms due to the drainage of cold air to the
low areas during the typical clear, calm, frosty nights. "^ On calm but
cloudy nights the variation in minimum temperatures between high
and low points in this valley is reduced to about 40 per cent, of that
on calm, clear nights and during windy weather there is very little differ-
ence in their minimum temperatures.

646 FUNDAMENTALS OF FRUIT PRODUCTION

The point should be emphasized that the amount of air drainage
secured by selecting a site somewhat above the adjoining fields depends
not alone on the amount of elevation, but also on the area from which
the cold air drains in comparison with the extent of that to which it
may settle. If the low ground upon which the cold air may sink is
limited in extent and has little outlet while the area to be drained is
large, this depression will soon be filled with cold air and the slope above
will be afforded no further protection. The case is comparable with a
large watershed supplied with an inadequate drainage system. An
elevation of 20 or 25 feet above a wide valley may thus afford better
air drainage for one orchard than an elevation of 50 feet above a narrow
valley affords another. In many cases a ravine or narrow draw along one
side of an orchard will afford a given site better air drainage than an
adjoining low-lying field covering many acres, provided the draw or
ravine is deep, has a good outlet and is not clogged with brush and timber
that interferes with free movement of the air. In other words, of
two areas having the same elevation one may enjoy much better air
drainage and greater freedom from frost because of differences in the
contour and topography of the land that borders them.

The graphs in Fig. 68 show the maximum variations in temperatures
during the night between stations at different elevations on a hillside.
Though day temperatures are not given there is the suggestion that
they approximate rather closely. Available data show that such in-
equalities in elevation as are normally found within single fruit growing
districts are responsible for but small differences in maximum day
temperatures. 2 In other words, elevation materially influences minimum
and average, but not maximum, temperatures.

Thermal Belts. — The influence of elevation on air drainage and
consequently on the selection of sites for fruit growing should not be
passed over without a reference to the so-called "thermal belts," "ther-
mal zones," "frostless belts" or "verdant zones," as they are variously
called. They are comparatively frost-free belts along hillsides or mountain
ranges, below and above which frost occurrence is not uncommon. The
limits of comparatively few such zones have been accurately mapped;
consequently the fruit industry has developed more or less independently
of them. However, their occurrence presents an interesting phenomenon
and it is desirable to recognize and if possible, make use of the obvious
advantages they provide, for without doubt the fruit growing districts
of the country include many such zones that are not being utihzed for
fruit production.

The following quotations from an article by Abbe^ will point out
more exactly the conditions characteristic of thermal belts :

"Prof. J. W. Chickering, Jr., in the Bulletin of the Philosophical Society of
Washington, March, 1883, and in the American Meteorological Journal, Vol. I,

ORCHARD LOCATIONS AND SITES 647

describes the following thermal belt: 'In Polk County, North Carolina, along
the eastern slope of the Tryon Mountain range, in latitude north 35°, the thermal
belt begins at the base of the mountain, at an elevation of 1200 feet. It is
about 8 miles long, and is distinguished by magnificent flora, such as would be
characteristic of a point 3° south of the actual latitude.'

"Prof. John Leconte, of Berkeley, Cahfornia, in Science, Vol. I, p. 278, states
that at Flat Rock, near Hendersonville, Henderson County, North Carolina, on
the flank of the mountain spur adjacent to the valleys of the Blue Ridge, he also
observed a frostless zone. The valley is about 2200 feet above sea level, and
the thermal belt is 200 to 300 feet above the valley.

"J. W. Pike, of Vineland, N. J., states that among the mountains of
California he has discovered that during the night the cold is much greater in
the valleys than on the terraces several hundred feet above, due to the settling
of the cold air, so that a thermal belt is formed at that height separating the
frosty valleys from the colder highlands.

"In the Tennessee Journal of Meteorology for January, 1894, published by the
State Weather Service, the author describes a thermal belt between Los Angeles
and the Pacific Coast. It traverses the foothills of the Cahuenga range, and
has an elevation of between 200 and 400 feet and a breadth of about 3 miles.
It occupies the midway region of the range.

"In the American Meteorological Journal, Vol. I, S. Alexander describes
a thermal belt in which the peach tree flourishes in the southeastern portion of
Michigan. He shows that the cold island discovered by Winchell in that region
is really the bottom of a topographical depression into which the cold air settles.
It is a long valley surrounded by a belt of elevated country from 50 to 600 feet
above Lakes Michigan and Huron. The valley and the isotherms trend north-
east and southwest from Huron County through Sanilac, Lapeer, Oakland, Liv-
ingston, and Washtenaw to Hillsdale Counties. The highlands of this region
are all much freer from frost than the lowlands, and all much more favorable for
early vegetation. He does not state that any point is high enough to be above
the thermal belt, but that, in general, two equal parallel thermal belts inclose the
cold island between them.

"It is generally conceded that these thermal belts depend both upon the
drainage of cold air downward into the lower valleys and the freedom of radiation
from the surface of the ground to the clear sky overhead. During a still night,
when frosts occur, the surface of the hillside cools by radiation, and hence cools
the air in contact with it; the latter flows downward as long as its cooling by
radiation and conduction exceeds its warming by compression. Inasmuch as its
cooUng depends on contact with a still colder soil or plant, it soon accumulates
in the lowlands as a layer of cold air, which grows thicker during the night by
the steady addition of the thin layer of descending air in contact with the ground
on the hillsides. The warmer air, which has not yet had an opportunity to cool
by contact with the ground, floats on top of the cold mass; it spreads out toward
the hills, and is continuously furnishing its heat to the adjacent hillsides as fast
as it comes in contact with them before it also cools and descends. The formation
of the thermal belt seems to depend largely upon this gentle circulation during
the night time. 1 he lower limit of the belt is defined by the depth of the accumu-
lation of cold air in the confined valley and rises higher in proportion as the night

648 FUNDAMENTALS OF FRUIT PRODUCTION

is clearer and longer, and also in proportion as the valley is more or less perfectly-
inclosed. The upper limit of the thermal belt may depend upon the strength of
the wind, and the general temperature of the air. But if there be no wind, then
it depends equally on the freedom of radiation to the clear sky and on the above-
described circulation of air."

Influence of Bodies of Water. — After elevation, probably the next
most important factor influencing air temperature and drainage is
proximity to bodies of water. The specific heat of water is high; it
absorbs heat slowly and gives it up slowly. Consequently in the spring
a large body of water warms more slowly and in the fall it cools more
slowly than the surface of the adjacent land or than near by vegetation.
It is slower even than the atmosphere in responding to changes in tem-
perature. Relatively the air shows a great variation in temperature
between night and day, while a body of water of considerable size shows
no appreciable change. The air warmed during the day, coming in
contact with the surface of a body of water, is cooled; consequently the
air in close proximity to such a body is cooler than it would be otherwise.
On the other hand, at night air cooled to a temperature below that of
the water, is warmed by contact with its surface and in turn gives up
that heat to vegetation and other bodies with which it comes in contact.
Consequently points close to bodies of water are frequently somewhat
cooler during the day and warmer at night than corresponding inland
points and are freer from frosts, while blossoming is at the same time
retarded in their proximity.

Influence of Distance from Water. — Some measure of this influence
may be obtained from data presented in Table 12 showing the air tem-
peratures, atmospheric humidity and dewpoints for three stations in
New Jersey and one on Kelley's Island in Lake Erie for the months of
July and August, 1866. Vineland is about 30, Haddonfield, 50 and
Greenwich 5 miles from the ocean, or from wide ocean tributaries, while
Kelley's Island, as the name indicates, is surrounded by water. The
daily range of temperature is higher the farther the station is removed
from the influence of water and also the more remote the station the
lower is its mean atmospheric humidity and the lower its mean dewpoint.
In other words, those stations close to large bodies of water enjoy a
climate more equable in temperature and consequently less subject to
frost injury.

The interchange of heat and equalization of temperature in the
vicinity of bodies of water is favored by a gentle breeze but it will occur
to a certain extent when there is practically no air stirring at inland
points. The water is itself responsible for a certain amount of air move-
ment and the attendant air drainage. It is almost needless to state that
the larger the body of water the greater is its influence on air movement
and air temperature. Much, too, depends on the topography in the

ORCHARD LOCATIONS AND SITES 649

immediate vicinity of the body of water. For instance, the so-called
*' fruit belt" on the eastern shore of Lake Michigan varies in width from
less than 2 to over 20 miles. The lake is as wide where the belt is narrow
as where the belt is wide, but the lay of the land is quite different. As a
rule but little influence of the water is felt back of the crest of the slope
toward the lake, bay or river and frequently its influence does not extend
to the crest of the slope. Naturally, if the slope is gradual the influence
is likely to be felt further back than if it is abrupt.

Influence of Size and Shape of Body of Water. — Something of the
relation between the size of the body of water and that of the area
influenced by it may be understood by comparing the width of the fruit
belts bordering Lake Michigan or Lake Ontario with those bordering
Lakes Seneca or Canandaigua in New York. As already stated, the
Michigan fruit belt is from 2 to 20 miles wide. The fruit belt along
Lake Ontario is of equal width. Lakes Seneca and Canandaigua, them-
selves only about 4 miles wide at the most, have distinct fruit belts only a
quarter of a mile to 2 miles in width. A deep body of water has a much
greater influence on the climate of the adjoining land than one which is
shallow. The water is in effect a heat sponge, absorbing heat whenever
air temperatures rise above the mean and liberating heat whenever they
fall below it. Naturally, then, the larger this sponge the greater is its
absorbing and liberating capacity. This is particularly important in
the case of bodies of water so deep that they seldom freeze over or
remain frozen for only a short time, as it relates to their modifying
influence on midwinter minimum temperatures. On the other hand
many lakes as wide as the finger lakes of central New York, because they
are very shallow, furnish little protection to the neighboring slopes.
Protection is likely in the vicinity of large rivers, especially if they are
deep. Their currents, which delay or prevent their freezing over, may
partly compensate for their lack of depth; a river 10 to 20 feet deep and a
quarter of a mile wide may afford as much protection to orchards along
its course as a lake twice that depth and of the same width. Indeed it is
likely to afford greater protection because of its channel down which the
cold air may continue to drain indefinitely.

Indirect Ternperature Effects. — Bodies of water influence temperatures
in their vicinities in other ways than through promoting air drainage.
There are certain favored spots where the increased atmospheric humidity
due to proximity of water leads to the frequent formation of fog during
periods when dangerously low temperatures occur at nearby points and
a very effective check is thus placed on loss of heat by radiation.
Kelley's Island in Lake Erie has been noted as a place thus rendered
especially suited to the culture of comparatively tender long-season
fruits and without doubt this is one of the chief factors in making possible
the successful culture of European plums in the vicinity of Ste. Anne de

650

FUNDAMENTALS OF FRUIT PRODUCTION

Beaupr^ in Quebec, 200 miles north of the general northern limit for the
same varieties.

Probably it would be difficult to separate entirely the different
influences of bodies of water upon climate, assigning to air drainage or to
increased atmospheric humidity exact figures representing their pro-
tective effects. The fact, however, that these other protective influences
are at work does not lessen in importance the air drainage that is asso-
ciated with water surfaces.

Minor Temperature Effects. — Even small bodies of water have meas-
urable, though slight, influences on temperature. Observations of mini-
mum temperatures near a stream 40 feet wide in England, summarized
in Table 13, show that the extent of the influence varies.

Table 13.-

-AvERAGE Minimum Temperatures (Centigrade) At and Near River
Bank^o

(Six inches above ground)

Station 6, 196

Station 8, on river

Station 7, on river

bank (confluence

of river and

ditch), degrees

feet from river,
degrees

bank (straight
part), degrees

Minimum all nights

2.2

3,0

3.3

Excess on river banks

0,8

1.1

Minimum still nights

0.0

0,9

1.4

Excess on river banks

0.9

1.4

Minimum nights with south

or southeast wind

3.5

4.4

5.4

Excess on river banks

0.9

1.9

Minimum nights with north

or northeast wind

1.6

2,0

2.5

Excess on river bank

0.4

0 9

Importance during the Winter.^ — Attention has been called particularly
to the effects of air drainage on temperature during the soring and fall
months and its bearing on the occurrence of frosts. It should not be in-
ferred, however, that air drainage does not take place during other sea-
sons where elevation and topography make it possible. Figures 69 and
70 show differences in minimum temperatures during some of the winter
months between stations at unequal elevations in a mountain valley in
Utah. These range between 2° and 8°F. on the coldest nights for stations
having 64 feet disparity in elevation and are about 10° for stations having
350 feet variance in altitude. Such differences in minimum temper-
atures during midwinter may often influence the amount of certain kinds
of winter injury or winter killing experienced. Air drainage, therefore, is
sometimes of as great importance in preventing winter injury as it is in

ORCHARD LOCATIONS AND SITES

651

warding off injury from late spring or early fall frosts. Indeed, there are
certain sections in which and certain fruits with which elevation to secure
air drainage is of greater importance in dealing with midwinter freezing
than with spring frost. The bark and trunk splitting occasionally

30

Fig.

0
I9I4 20

/

/

/

/

/

/

/

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/

/

\

/

/

^^^

/

/

N /

N

v/

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■^

\

•V

/

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w

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1

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25 24 26
November

27

?8

). — The minimum daily temperature for a bench land and a valley bottom
station during 9 clear, autumn nights. {After Batchelor and West'^)

accompanying sudden midwinter drops in temperature in the compara-
tively mild climate of the Willamette valley is a case in point.

Obstructions. — Air drainage is often impeded more or less seriously
by obstructions of one kind or another, such as a stone wall, a hedge or a
high board fence, a mass or belt of shrubbery. Thus it happens that a

652

FUNDAMENTALS OF FRUIT PRODUCTION

natural or artificial planting sometimes serving admirably as a wind break
and protecting the orchard at certain seasons, hinders air movement on
calm nights to such an extent that little of the frost protection naturally
expected from the orchard's elevation is actually obtained. No rules can
be given for dealing effectively with these hindrances to air drainage, but
the whole question should be considered on the ground when selecting an
orchard site.

\

N~~l

1

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1

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11 II

24 25 26 Z1 28 23 30 31 . I 2

December, 1913 Januaa),l914

Fig. 70. — Minimum temperatures for stations of different elevations during 12 clear,
calm, winter nights. (After Batchelor and West'^)

LOCAL VARIATIONS AND THEIR SIGNIFICANCE
Data have been presented showing that points only a few miles apart
sometimes, because of topographic pecuharities, present climatic
differences great enough to be of considerable importance in fruit growing.

ORCHARD LOCATIONS AND SITES

653

The magnitude of such disparities often found between points on the
same farm and occupying positions differing Uttle in elevation or exposure,
is not appreciated. Their influence is often subtle, but nevertheless real.
They may make the difference between the necessity of one or of three
applications of a fungicide, an interval of a week in the time of partic-
ular spray applications, or of a week in the blossoming or maturing seasons
of a fruit.

Temperature. — It is not the intention in this discussion to present
further data on the influence of a certain number of "heat-units" in
bringing to particular stages of maturity plants of different kinds.
However, mention may be made of the variation in the mean temperature
between stations only a short distance apart. MacDougaH^ presents
data showing that, of two stations in the New York Botanic Garden only
a few hundred yards apart and presenting no great difference in elevation,
one received 78,836 hour-degrees of heat in 1 year and the other only
68,596. One of these points registered a temperature below freezing
during 1478 hours in the course of the year and the other during 1736
hours. Here is a difference of 13 per cent in heat units; in other words,
one station enjoyed a temperature that was equivalent to an active grow-
ing season of about 11 days longer than the other. Such a disparity is
large enough to account for the difference between success and failure
with many fruit crops, as for instance grapes, along the northern limits
of their cultural range and it shows the importance to the grower of study-
ing carefully the local variations often found within the limits of a single
farm.

Equally or even more striking are the figures recording the temper-
atures of two stations on the campus of the University of California at

Table 14. — Showing Variations in Temperature Between Two Stations on
THE Campus of the University of California^

Month

Mean
monthly maximum

Mean
monthly minimum

Maximum

Minimum

-

B

A

B

A

B

A B

September, 1902

79.3
62.3
70.8
74.5
75.6
77.4
76.6
66.7
76.2
80.5

71.4
62.0
66.9
73.4
70.0
69.6
70.2
64.5
70.0
71.7

54.5
36.8
43.1
49.7
50.0
48.2
48.3
42.5
45.8
47.9

55. 8
44.7
48.3
52.3
52.0
51.9
52.2
46.5
49.4
51.3

94
74
84
108
100
86
102
88
92
98

83.2
70.0
79.1
101.1
94.0
78.9
91.7
82.9
85.3
92.8

48
32
34
36

44
44
44
34
38
42

49.0
36.6

May, 1903

42.6

June, 1903

42.4

July, 1903

46.8
49.0

September 1903

April, 1904

46.0
37.2

May, 1904

40.6

June, 1904

48.2

73.4

09.0

46.7

50.4

92.6

85.9

39.0

43.8

654 FUNDAMENTALS OF FRUIT PRODUCTION

Berkeley, presented in Table 14. Though these stations were 120 feet
apart in elevation, elevation alone cannot be held responsible for the
differences recorded, for, as mentioned elsewhere, the influence of ele-
vation on mean temperature amounts to only 4°F. for each 1000 feet.
Without doubt many factors contribute to these local variations in tem-
perature, some being more important in one case and others in another.
It is not so important that all these factors be known and exactly evaluated
in every instance as it is that their combined effect be recognized and
properly utilized.

Evaporation, Rainfall and Other Factors. — It is generally recognized
that some spots or some locations are more subject than others to the
drying action of the wind; however, the extent and importance of differ-
ences in this respect are not generally recognized. Gager^^ records results
of evaporimeter experiments in the New York Botanic Garden in 1907 that
are particularly interesting. Three specially constructed evaporimeters
were placed at several points in the garden ; one was on a dry rocky knoll
partly shaded by trees; a second was on low, poorly drained, marshy
ground, also partly shaded and the third was in the open on well drained
ground with sod on the one side and cultivated ground on the other. The
evaporation losses from these different instruments between June 3 and
October 14 were equivalent to 8.47, 4.84 and 12.10 inches, respectively.
The precipitation during the same period was 9.32 inches. At the first
station precipitation exceeded evaporation loss by only 0.85 inch, at the
second station by 4.48 inches, while at the third station the evaporation
loss exceeded precipitation by 2.78 inches. In commenting on these
data, Gager says: "It should be kept in mind that the loss of water
from the evaporimeters is not a measure of the amount of water lost by
the soil through evaporation, but it is only an index of the evapor-
ating power of the air for the given station. For the same locality the
rate of evaporation from soil and from evaporimeter will materially
differ, being less from soil and varying with its nature and condition, as
well as with the surroundings above the soil surface." Nevertheless at
one station the evaporation losses were between two and three times those
at one of the others and such a difference may often be enough to have a
great influence on plant growth and crop yield.

Local variations in rainfall are likely to be especially large in sections
showing considerable difference in elevation, but they are often important
where the elevations are substantially the same. Thus at Davis, Cali-
fornia, when the annual rainfall was 16 inches, it was about 25 inches at
a point ten miles to the west and having the same elevation. Thirty
miles still further west, but in the foothills of the Coast Range, it was
over 50 inches.

With the local variations in temperature and humidity there are often
important differences in the prevalence of insects and diseases that.,

ORCHARD LOCATIONS AND SITES 655

independent of direct influence of the environment on the plant, may
set definite Hmits to the profitable culture of certain fruit varieties.

There may be also minor local variations in their life histories which
modify the effectiveness of spraying treatments. The best time for a
certain spray in one neighborhood may differ several days from that for
another neighborhood not far away.

Summary. — The selection of a location for fruit production, or of
kinds and varieties of fruit to be grown in a particular location, involves
a consideration and application of the same general principles. The
more important economic considerations are the cost of land and the
nearness and character of transportation facilities. The overhead charge
due to cost of land should never exceed 10 per cent, of the value of the
product at the orchard and should not amount to more than half that
figure. The cost of hauling to the local market or to a shipping station
should levy no greater tax against the total income. Other factors,
such as fruit product establishments and cooperative shipping organiza-
tions affecting the ability to dispose of products quickly and advantage-
ously are important in commercial production.

Different slopes offer quite distinct environmental conditions for
the growth of the plant and certain slopes may be much preferred to
others for certain fruits when grown in some sections, though the reverse
condition may hold for the same varieties in another section. These
environmental differences can be profitably capitalized in many cases
if kinds and varieties are selected so as to obtain the closest adaptation
to the particular farm or parts of the farm. The same may be said of
minor inequalities in temperature, rainfall and evaporation between
near by points that possess nearly the same elevation and exposure.

Factors of great importance in determining danger from late spring
and early fall frosts are the air drainage incident to unequal eleva-
tion and the proximity to bodies of water. Often comparatively small
disparities in elevation (25 to 50 feet) make a considerable difference in
danger from frost injury. This influence is important also in determining
the amount of damage from midwinter freezing. Proximity to large
bodies of water, particularly on their windward side, affords considerable
protection from extremes of climate. The range of influence of such
bodies of water varies with their size and depth and with the topography
of the adjoining slopes.

CHAPTER XXXV
ORCHARD SOILS

All field crops are influenced more or less by the kind of soil in which
they are grown. The same may be said of all fruit crops. Just as some
land is classed as good for general crops so some may be classed as good
for orchard fruits and just as some is considered good for wheat but poor
for alfalfa, so some may be good for pears but poor for strawberries. In
a way the factors that are important in determining the value of a particu-
lar soil for field crops are also important in determining its value for fruit
production. However, were the judging of soils for general farming
purposes and for orcharding to be placed on a score-card basis the cards
would differ considerably in a number of respects.

For field crops, both surface soil and subsoil are important in deter-
mining relative value of the land but the surface soil is generally regarded
as of far greater importance. For fruit crops in general they are of more
nearly equal significance. Indeed there are many conditions presented
in which there is little doubt but that the nature of the subsoil is more
significant than that of the surface soil. For field crops physical and
chemical conditions are generally considered of substantially equal
importance in determining productivity and suitability to individual
crops. Though chemical composition is likewise important in the produc-
tion of trees and other fruit plants, physical condition is a first considera-
tion. The fact that certain fruits, such as the apple, are grown with equal
success in some of the heavy clay loams of western New York, the light
sandy loams of New Jersey, the loess bordering the Missouri River, the
adobes of the Rogue River valley, Oregon and the volcanic ash of the
Hood River section of Oregon appears to contradict this; nevertheless
closer analysis reveals certain common characteristics of their physical
condition — a similarity much greater than is shown in a comparison of their
chemical composition.

CONSIDERED FROM THE STANDPOINT OF PHYSICAL CONDITION

Chief among the physical characteristics desirable in an orchard
soil are porosity and thorough aeration, coupled, if possible, with depth.
The loess soils of the Mississippi, Missouri, Rhine and Hoang-ho val-
leys are among the best in the world for the fruits that will grow in
the climates of these respective regions because they are extremely deep,

656

ORCHARD SOILS 657

drainage is practically perfect (the water table often being 50 or more
feet below the surface) and they are so well aerated that tree roots often
penetrate to a depth of 20 feet and ordinarily to depths of 6, 8 or 10.
In the Rhine valley grape roots have been traced to a depth of 15 meters.
Similar conditions exist in some of the volcanic ash soils of the Pacific
Northwest and the alluvial soils and bench lands of many river valleys
in Washington, Idaho, Oregon and California. One of the main reasons
certain of the arid soils of California have proved so well suited to fruit
growing is that the surface soil grades insensibly into the subsoil and
that the latter is well drained and thoroughly aerated; hence roots
penetrate to great depths and sustain the plant when the surface soil
may become too dry.^^ That good drainage and its corollary good
aeration are associated with this condition is indicated by Hilgard^^
when he states that with the rise of the water table in such soils through
injudicious irrigation trees that had thrived may actually suffer, much
as those planted in shallow soil or soil underlaid with an impervious
hardpan and from practically the same causes.

The extent to which the success of the fruit plantation depends on
these two factors, drainage and aeration, is not generally realized. In
speaking of the soil requirements of the papaya Higgins-^ says: "There
are few, if any, soils in which the papaya will not grow if aeration and
drainage are adequately supplied. Most of the plantings of this Station
are upon soils regarded as unsuitable for other fruit trees, and upon
which the avocado is a failure. . . . They are very porous, permitting
a perfect drainage and aeration." The same writer goes so far as to
say, "There are two essential features of a good banana soil. The
first is abundant moisture, the second, good drainage. "^^ In speaking
of the soil requirements of forest trees one authority maintains that
almost any soil is capable of producing any kind of timber if the moisture
requirements are satisfied. ^^ Even the blueberry, which is often classed
as a semiaquatic or bog plant, requires a well aerated medium for its
roots and does not, contrary to appearances, send them down into the
water or into waterlogged soil.^ Obviously, certain shallow rooted
species such as the strawberry do not require and could not make full
use of a soil of the depth best suited to one of the tree fruits, but even
the strawberry will do much better in a soil that is moderately deep
(say, two and one half to three feet) and well drained than in one that is
shallow or poorly drained and poorlj^ aerated.

Requirements of Different Crops. — However, there are marked
differences between species and even between varieties of the same
species in their preferences for soils of unlike textures. The peach
and almond flourish only in soils of a comparatively light porous texture,
while the pear and quince prefer at least moderately heavy soils and will
often do well in extremely heavy soils. The pomegranate is reported as

658 FUNDAMENTALS OF FRUIT PRODUCTION

doing fairly well in soils ranging from almost pure sand to heavy clay,
but it does its best only in those that are fairly heavy and well drained;
however, it will endure a wet, poorly aerated soil much better than
most fruit plants. ^^ Probably nowhere in the world does the pineapple
do better than along the east coast of Florida, between Fort Pierce and
Lake Worth, where the soil is almost a pure white sand (containing
actually upwards of 98 per cent sand, gravel and silt);^^ nevertheless
they are grown very successfully on some of the heavy soils of the Hawa-
iian Islands. It is generally recognized, however, that the soil that
may be best for a particular fruit or some particular variety in one sec-
tion may not be best in another section with different chmate and distinct
environmental conditions. Thus in New York the Concord grape
grows on a wide variety of soils but seems to prefer a fairly strong loam
with considerable clay; in western Washington the same variety can
be grown successfully only in hght sandy or sandy loam soils that tend
to hasten maturity of fruit and vine. In general, the more favorable
the texture of the soil for both the lateral and vertical development of
the root system, the better.

Requirements as to Depth. — Theoretically, a soil need be only half
as rich as another in order to support equally well a certain amount
of vegetative growth if it is of such a character that roots penetrate
twice as deep. Furthermore, since water is a limiting factor as often
as plant nutrients, a tree with the deeper root system, though in poorer
soil, is really in a better position than one growing in a richer, but shal-
lower, medium. Only under very special conditions should ordinary
deciduous tree fruits be planted in a soil in which the roots cannot pene-
trate freely to a depth of 2}-^ to 3 feet in humid regions and to a depth of 5
to 10 feet in arid and semi-arid regions; soils that will permit greater pene-
tration are preferable. Shallowness of soil, hardpan or plowsole close to
the surface, impervious subsoil and poor drainage are interrelated factors
which check vegetative growth, reduce yields and the size, quality and
grade of the fruit, favor irregular bearing and lead to numerous physio-
logical troubles, the treatment of which is difficult.

Classification of Soils According to Size of Soil Particles. — Since
there is occasion repeatedly to refer to soils of different physical structure,
a classification based on mechanical analysis, as used by the Bureau
of Soils of the Federal Department of Agriculture, is presented here^*
(see Table 15).

It should be noted in connection with this classification that no
account is taken of gravel or stones above 2 millimeters in diameter.
Many soils contain rock particles larger than this maximum and not
infrequently these constitute a large proportion of the soil volume.
Accordingly a soil that in this scheme would be classified as a silt or even
a clay might in fact be gravelly or rocky or stony in character. Though

ORCHARD SOILS

659

these larger components may have a relatively unimportant bearing; on
water holding capacity, aeration, root penetration and related features,
they do influence it materially in its relation to tillage practices and they
often prove a limiting factor in determining the kind of crop that can
be grown in it advantageously, or the kind of orchard culture that must
be practiced. Thus of two soils whose so-called "fine earth" might ana-
lyze the same, one might be suitable to the strawberry and the other
quite unsuited because of the presence or absence of large quantities
of rocks and coarse gravel. It is interesting to compare the mechanical
analyses of several soils used for fruit production.

Table 15.-

-ScHEME OF Soil Classification, Based on the Mechanical
Composition of Soils

(1), (2)
2-0.5
milli-
meters,
per cent.

(1), (2), (3)

(6)

2-0.25

0.05-0.005

milli-

milli-

meters,

meters,

per cent.

per cent.

(7)
Less than
0.005
milli-
meters,
per cent.

(6), (7)
Less than
0.05
milli-
meters,
per cent.

Coarse sand

Medium sand . . .

Fine sand

Sandy loam

Fine sandy loam

Loam

Silt loam

Clay loam

Sandy clay

Silty clay

Clay

>25
<25

>50
>20
<20
>20
<20

0-15

0-15

0-15

10-35

10-35

<55

>55

25-55

<25

>55

0-10
0-10
0-10
5-15
5-15

15-25
<25

25-35
>20

25-35
>35

<20

<20

<20

>20<50

>20<50

>50

>60
<60

>60

(1) "Fine gravel," 2-1 millimeters. (2) "Coarse sand," 1-0.5 millimeters. (3)
"Medium sand," 0.5-0.25 millimeter. (6) "Silt," 0.05-0.005 millimeter. (7)
"Clay," less than 0.005 millimeter. The residue is composed of "fine sand," 0.25-0.1
millimeter and "very fine sand," 0.1-0.05 millimeter.

Mechanical Analyses of Various Fruit Soils. — Soils A and C with their
subsoils B and D (Table 16) are fairly typical of the western New York
fruit district, one of the leading apple producing sections of the world.
Soil A, the Dunkirk sandy loam, contains 64 per cent, of medium and
coarse sand in the surface and slightly more in the subsoil and only
about 5 per cent, of clay in both surface and subsoil, while soil C, the
Dunkirk loam, contains only about 30 per cent, of medium and coarse
sand in the surface soil and a little more than half that amount in the
subsoil, but approximately twice as much of the finer materials — clay

660 FUNDAMENTALS OF FRUIT PRODUCTION

and silt. Here, indeed, are marked differences in the average size of
soil particles, yet there are but slight differences in the way apple trees
grow in these soils. Soil E, a fairly typical loess of Nebraska, contains
no medium or coarse sand and comparatively large amounts of silt and
clay, yet it furnishes excellent drainage and is eminently suited to the
production of fruit, particularly apples. Though probably the Billings
clay loam (Soil M), with its 47 per cent, clay and 91 per cent, of clay and
silt combined is not an ideal soil for apples, it is a characteristic soil of the
Grand Junction section of Colorado and where the topography permits
reasonably good drainage, apple production is profitable. This par-
ticular soil serves to illustrate the point that the mechanical analysis of a
soil is not always an accurate index to its possibilities for fruit growing.
Though this analysis suggests very poor drainage and consequently a
lack of suitability for fruit crops, some of this land is fairly well drained
and does produce good fruit crops. However, it is but proper to state
that the majority of the Grand Junction orchards are on soils of a some-
what lighter character. The Maricopa gravelly sand of California is,
as the name suggests, comparatively light and open in character, con-
taining 57 per cent, fine, medium and coarse sand and 11 per cent, fine
gravel. It is considered very good for grapes; yet the Alamo clay adobe
with 95 per cent, of clay and fine silt is said to be fairly suitable for grapes
where the topography is such that drainage is not particularly poor.^^
Probably the gray-brown clay of Sonoma, California, whose mechanical
analysis is shown in column 0 in the table, represents more nearly average
soil conditions for the grape. Certainly it produces some of the best wine
grapes of the country. ^^ Citrus fruits likewise thrive on soils ranging
from heavy adobes to gravelly loams and gravelly sands. It is interesting
to note the texture of one of the pineapple soils of the Florida coast
(Soil H in the table) — over 98 per cent, fine, medium and coarse sand.
The mechanical analyses of many other fruit soils which might be
included would furnish little information, beyond that already given,
as to the actual soil requirements of the different fruits. It is evident
that the mechanical analysis of a soil carries some suggestion as to its
suitability for fruit crops of different kinds but it is an index only in so far
as it is an index of texture, drainage and aeration; these qualities depend
to a considerable extent on such factors as topography, hardpan, chemi-
cal composition, rainfall and the movement of underground water.
In other words, it is hardly practicable to attempt exact definition, in
terms of soil particle measurements, of the soil requirements for distinct
varieties of the same fruit or even of different fruits.

CONSIDERED FROM THE STANDPOINT OF CHEMICAL COMPOSITION

The statement has been made that, broadly speaking, the physical
condition of the soil is more important in fruit production than is its

ORCHARD SOILS

661

■■»ooj aoBjmg
itSiuJojii'BO 'Biaouog

0

to ^
d -

c

c

tc

CS

c

fe:

11.44
16.1
12.3
28.6
16.7
10.9
4.0

85OpBJOI00

^

0.1
0.3
0.2
1.7
6.2
43.8
47.4

95BIUJOJI1BO 'aqopB

3J3Biq UmbBOf UBg

-^

3:42
1.98
5.86
10.40
50.34
23.12

'aqopB Xbij ouibiv

k

0.3
0.6
0.4
1.1
3.0
41.4
53.5

99-nnoziJV
'niBoi X|[3abj3 udoa!iBj\[

■^J

8.91
8.50
9.51
14.64
34.45
16.22
5.46

•I'osqng
Bpuoi^ 'I108 oiddBauij

-

0.06
3.08
57.50
37.78

0.20
0.52

ES^SBOO

Bpuou 'tios ajddBaaij

a:

0.23
3.03
61.11
33.76
0.54
0.28
0.50

^aaj e o^ saqoui i moi}
[losqng jEajiijsdiuBji

0

6.7
19.0
21.1
27.6

6.9
14.6

4.9

•saqaui i aoBjjng

gj-aaiqsduiBH

Maj«J 'UIBOI XpuBg

li.

3.9
11.4
13.1
16.4
11.9
33.4

9.5

BqBuie^ '[loeqns ssao'j

fel

0. 10
25.83
57.00

9.49

•nosqng

Ci

0.3
15.6
21.5
27.9
29.0

5.5

•saqoui 6 aoBjang
(K-^IJOA
Maj^ 'uiBoi jjaij^una

0

4.4
26.2

9.7
30.0
19.1
10.6

•nosqng
oj'l-JOA -waN

'UIBOJ ApuBS 5IJI5(unQ

03

9.0
60.5
7.1
9.7

8.4
5.1

•saqoui 6 aoB;jng
oj'^-iOA A^aN

'tUBOl ;tpUBS JJJIJJunQ

^

11.7
52.3

3.6
11.1
15.5

5.6

iScj

1

1

i

c

s
s

ta

1

1
1

t

662 FUNDAMENTALS OF FRUIT PRODUCTION

chemical composition. However, it should not be inferred that chemical
composition is of little significance, or that poor soils are preferable to
good soils for orchard purposes. On the contrary, the richer the soil
the better, though productivity as it concerns the orchardist, may be quite
different from productivity as it concerns the man growing cereals or fiber
plants and a soil that is productive in pineapple cultivation may be
unproductive in avocado or prune cultivation. The only satisfactory
measure of soil productivity is in terms of crop production of the specific
plant under consideration. Hardly an orchard of commercial size any-
where fails to show differences in individual tree growth and production
due apparently to variation in soil. However, thorough examination
would show that many such differences are related to variations in texture
or in water-holding capacity rather than in chemical composition. Often
the great inequalities between the size, longevity or productivity of trees
in various fruit producing sections may be regarded as due largely to
chemical composition. The average differences between the apple
orchards of western New York and southern Ohio is a case in point — a
fact emphasized by the response of the orchards of the latter section to
proper fertilizer applications.

Requirements of Different Crops. — It should be recognized, too, that
certain fruits are particularly favored by the presence of some element or
compound in the soil. For instance, a high lime content is said to be
particularly favorable for oil production in the olive. ^'* The cherry like-
wise seems to respond favorably to lime. Vitis berlandieri flourishes in,
even prefers, a limestone soil; but V. labrusca is intolerant of lime.^^ The
chestnut has been shown to be subject to chlorosis on soils containing
upwards of 3 per cent, lime^ and pears are reported as frequently
chlorotic on calcareous soils. ^^ Many crop plants are known to prefer
a nearly neutral soil reaction and it has consequently been assumed that
most fruit plants do; some, however, as the strawberry, thrive only in an
acid medium and the blueberry demands a markedly acid soil.^ Certain
fruits like the grape are very tolerant toward "alkali;" others, like the
mulberry, are very sensitive to it. The pineapple is intolerant of man-
ganese.^^ These and the many other peculiarities of a fruit must be
kept in mind and soils selected accordingly or, conversely, the soil's
peculiarities must be ascertained and the fruit species or varieties selected
accordingly.

Much can be done toward adapting a number of fruits to an uncon-
genial soil by growing them on a stock suited to the soil in question.
This matter is discussed in some detail in the section on Propagation.

Chemical Analyses of Various Fruit Soils. — In the accompanying
tables (17 to 22) are presented chemical analyses of certain typical soils
that are more or less noted for fruit production, together with the analyses
of certain other soils that have unknown value for fruit production or that

ORCHARD SOILS

663

are definitely known to be unsuitable. Comparison may thus be made
between "fruit" soils and soils in general and between good and poor
fruit land.

Table 17. — Chemical Analyses of Average Soils of Humid and Arid Regions
AND of Certain Orchard Soils in Asia Minor and California

A, average of
analyses of 313

soils of arid

regions, 26 per

cent

B, average of
analyses of 4G6
soils of humid
regions,'' per
cent

C, soil from
Erbelli, Asia
Minor (noted
for fig produc-
tion),"'per cent

D, Mesa loam

from near
Riverside, Cali-
fornia,'b per
cent

70. 565
7.266
0.729
0.264
1.362
1.411
0.059
5.752
7.888
0.117
0.041

1-00

Fine earth

Analysis of fine earth:

Insoluble matter

84 031

76 33

63 67

4.213
0.216
0.091
0.108
0.225
0. 133
3. 131
4.296
0.113
0 0.'i2

5.35
1.09
0.19
1.96
1.56
0.01
6.49
3.25
0.29
0.06
1.00

Potash (K'>0) ...

0 73

Soda (NsiiO) .

0 36

Lime (CaO)

1.58

1.85

Manganese oxid (Mn304)

Ferric oxid (FesOs)

Alumina (AI2O3)

Phosphorus pentoxid (. P2O6)

Sulfur trioxid (SO3)

0.03
10.02
5.06
0.07
0.01

Carbonic acid (COs)

1.316 .......

4.945 3.644

Water and organic matter

2.29

2.74

Totals

99.993 100.178
0 750 2 7nn

99.87 M S2

Humus. .

0.27

0.20

Nitrogen, per cent in humus

Nitrogen, per cent in soil

15.870
0.101

5.450
0.122

Table 18. — Chemical Analyses of Typical Fruit Soils of Washington^'

A, upper
bench land,
Wenatchee,

per cent

Insoluble silica

Hydra ted silica

Soluble silica (Si02)

Potash (K2O)

Soda (NazO)

Lime (CaO)

Magnesia (,MgO)

Manganese dioxid (Mn304). .

Iron oxid (.FP2O3)

Alumina (AI2O3)

Phosphorus pentoxide (PaOs)

Sulfur trioxid (SO3)

Carbon dioxid (CO2)

Volatile and organic matter..

Total

Humus

Total nitrogen (N)

81.632
2.498
0.316
0.518
0.233
0.714
0. 186

4.760
6. 145
0.225

B, volcanic

ash, Walla

Walla, per

cent

C, Kenne-

wick sand,

Kennewick,

per cent

77. 772
5.464
0.543
0.328
0.238
0.659
0.104

4.601
3.925
0.037

84.402
3.332
0.265
0.312
0.416
0.944
0.650
trace
4.505
5.889
0. 140
0.018

D, sandy E, sandy

soil, Vashon soil, Vashon

Island, per Island, per

cent cent

76. 652
8.572
0.348
0.126
0. 106
0.615
0.807

3.064

4.852
0.044

r2

297

8

646

0

062

0

157

0

167

0

693

0.548

3

023

7

634

0

073

2.969

5.580

1.219

4.467

6.075

100. 176
1.942
0.061

99.251

.1.400

n.055

100. 040
0.465
0 0.^5

99. 653
1.870
0.077

100. 275
3.100
0. 174

664 FUNDAMENTALS OF FRUIT PRODUCTION

Table 19. — Chemical. Analyses of Certain Oregon Soils*"

"Redhill"

land, Salem,

per cent

White land,
Benton
County,
per cent

Adobe soil,
Benton
County,
per cent

Sandy loam,

Wasco

County,

per cent

"Shot" land,

Multnomah

County,

per cent

Character of soil:

Coarse material

28.88

68.48
4.38
0.47
0.33
0.40
0.96

14.78

0.63
10.19

16.50
83.50

70.26
5.53
0.06
0.07
0.66

0.04
13.51

0.05
0.03
10. 13

2.25
97.75

38.91
16.74
0.11
0.03
1.60
1.78
0.08
23.21

0.01
17.44

25.50
74.50

63.65
12.65
0.12
0.16
1.41
1.10

9.23

0.28
11.81

34.00

Fine earth

66.00

Analysis of fine earths:

67 40

Soluble silica (SiOz)

5.18
0.28

Soda (NajO)

Lime (CaO)

0.05
1.35

Magnesia (MgO)

0.90

Manganese (Mn304)

Iron (.FejOs)

0.40

17.67

Sulfuric acid (SO3)

Phosphoric acid (P2O5)

Water and organic matter . .

0.82
0.34
7.98

Total

99.72
0.52

100. 34
1.22

100. 00
1.80

100.41
4.42

100.07
1.76

Table 20. — Chemical Analyses of Certain Florida Soils

A, surface soil,
West Palm

Beach46 (pine-
apple land),
per cent

B, subsoil.
West Palm
Beaches (pine-
apple land),
per cent

C, surface soil
Volusia

County<8
(orange land),

per cent

D, surface soil,

muck land"

(fruit and

truck),

per cent

Silica (Si02) insoluble

99. 3070
0.0147
0.0037
0.0000
0.0048
0.2210
0.0100
0.0038
0.4860
0. 2000
0.0100

99. 5840
0.0197
0.0000
0.0000
0.0126
0. 2400
0.0087
0.0038
0.1620
0.0675
0.0045

96.0852

0.0526
0.0145
0.0208
1.1726
0.1600
0.0096

0.0890

trace

2.3910

53. 5900

Silica (Si02; soluble

Magnesia (MgO)

trace

Potash (.K2O)

0. 1500

Iron and alumina (Fe203 and AI2O3).
Phosphorus pentoxid (PzOs)

10.0100
trace
0. 0500

Volatile matter

Nitrogen (N)

1.500

Chlorin

0.0200

34.9700

ORCHARD SOILS 665

Table 21. — Chemical Analyses of Manganiferous and Normal Soils of Oahu^^

Constituents

Manganiferous soil

Normal soil

Soil

Subsoil

Soil

Subsoil

33.46
0.83
0.40
1.39
0.5.5
9.74

19.65

15.50
0.21
0.16
0.73

19.93

36.06
0.74
0.42
0.86
0.43
8.76

21.51

15.74
0.16
0.09
1.09

14.45

40.89
0.51
0.21
0.51
0.37
0.22

35.72
3.58
0.07
0.09
3.83

14.22

39.25

Potash (K2O)

0 60

Soda (Na20)

0 32

Lime (CaO)

0 66

0 38

0 06

Ferric oxid (Fe203)

Alumina (AlaOs^

33.28
8.66

Phosphorus pentoxid (PzOb)

Sulfur trioxid (SO3)

0.08
0 07

Titanic oxid (TiOa)

2 74

Loss on ignition

13.99

Total

Nitrogen (N)

100.35
0.39

100.31
0.23

100.22
0.34

100.09
0 25

Table 22. — Chemical Analyses op Miscellaneous Soils

.4, Maricopa

gravelly loam

Arizona,'"

per cent

B, Peach belt
soil, South

Haven,

Mich. ,35 per

cent

C, Olive or-
chard soil,

Ventura,

Cal.,s per

cent

D, Slate col-
ored upland
adobe Ala-
meda. Cal..«
per cent

E, Loess soil,

Kansas City,

Mo. ,30 per

cent

Insoluble silica (SiOi)

Soluble silica (Si02)

72. 35
10.29
2.07
1.36
0.66
0.28
4.41
4.94
0.09
0.03
0.87
0.03

0.51
0.04

87.23

0.51
0.46
0.83
0.34
1.52
2.87
0. 13
0.20

5.64
0.07

82.11
6.88
0.67
0.57
0.47
0.42
5.26
1.30
0.21
0.09

2.23
0.78
0.074

64.790
16.564
0.868
0.978
0.579
0. 100
3.791
7.718
0.143
0.006

4.601
0.697

34.98

Lime (CaO)

1 70

Magnesia (MgO)

1 12

Potash (KzO)

1 84

Soda (Na20)

1 06

Phosphoru^ pentoxid (PaOs). .
Sulfur trioxid (SO3)

0.09
0.02

Chlorine

Water and organic matter ....
Humus

Nitrogen (N)

666 FUNDAMENTALS OF FRUIT PRODUCTION

Probably the most striking fact brought out in a study of the chemical
analyses of fruit soils (Tables 17 to 22) is their extreme variability and
their frequent wide divergence from the averages of the soils of either the
humid or arid sections. It is impossible to associate certain extreme soil
types with special crops. For instance a single fruit crop would hardly
be expected to do equally well on soil like that shown in columns A
and B of Table 20 and those shown in Table 21. The Oahu soils con-
tain seven to 20 times as much phosphorus, 50 to 80 times as much potash
and 30 to 40 times as much nitrogen as those of the Florida coast; the
difference in some of the other constituents is as great or greater. Yet
these soils are almost equally well suited to the pineapple, though their
fertilizer requirements are somewhat different. The two Hawaiian soils
shown in Table 21 resemble each other closely, much more closely than
they resemble the Florida soil, but they show a marked disparity in their
suitability for fruit culture and the soil that is the richer in the nutrient
elements, nitrogen, potash and phosphoric acid, is the poorer when meas-
ured in terms of pineapple production. Though the first three soils from
Washington whose analyses are given in Table 18 show marked differ-
ences in composition, especially in their phosphorus and nitrogen
content, all are noted for their fruit production and proof that even a single
fruit, as the apple, reaches a higher stage of perfection in one than in
the others is difficult. The soil designated in Table 19 as "White land"
does not differ greatly in its analysis from the "Redhill" or the "Shot"
land, except that it contains less potash and phosphoric acid. These ele-
ments are present, however, in larger amounts than in some of the other
fruit soils whose analyses are given. Yet this "White Land" is not
suited to fruit production and the "Redhill" land and the "Shot" land
are among the best fruit soils of the state. The factor determining the
difference betwen them is drainage. The analyses shown in columns D
and E of Table 18 are particularly interesting in that both soils are from
near by fields on Vashon Island, Washington. The differences in compo-
sition as shown by the analyses are comparatively small; both are con-
sidered well suited to strawberry culture and the average variety does
well upon both soils. Yet the Clark variety is reported as thriving only
on the one and as failing to produce satisfactorily on the other.^^

Evidently the relation of the chemical composition of the soil to
suitability for fruit growing is far from well understood, much less
established. Without doubt different fruits and possibly distinct varie-
ties of the same fruit require, or at least grow better in, soils of somewhat
dissimilar chemical composition. However, since present methods of
analysis do not differentiate clearly between those requirements they do
not actually measure soil productivity as it is expressed in terms of fruit
production and they do not afford a very accurate index to fruit crop
adaptation.

ORCHARD SOILS

667

Evidence on Soil Requirements from Fertilizer Ex-periments. — Point
is lent the last statement by data presented in Table 23 assembled
by Stewart, showing the response to fertilizer applications of trees growing
in soils of varying productivity. In commenting on these data Stewart^^
remarks: "These figures show that the correlation between soil composi-
tion, as determined by the methods of soil sampling and analysis above
specified, and the actual response of the associated trees to additional
fertilization is either exceedingly slight or absent entirely. One would
naturally expect that the largest response would appear where the chem-
ical fertility of the soil was lowest, and vice versa. This evidently has not
occurred. In fact, the least response to practically all types of fertiliza-

Table 23. — Relation of Soil Composition to

{After SteivarP^)

Fertii

IZER

Response

Soil type

Nitro-
gen

Phosphorus (P2O5)

Potash (K2O)

Response to fertili-
zation. (Per cent in-
crease in yield)

Per cent,
(total)

Per cent,
(total)

Per cent,
(avail-
able)

Per cent,
(total)

Per cent,
(avail-
able)

N

p

K

CF>

M2

Porters

0.132
0.071
0. 118
0.158
0.163
0.300

0.244,
0.183
0. 123

0.093
0.029
0.087
0.116
0.132
0.233

0.161
0.315
0. 135

0.017
0.009
0.002
0.012
0.007
0.043

0.032
0.122
0.006

2.35
0.66
1.81
2.23
1.69
1.78

1.27
1 . 55
1.97

0.020
0.010
0.029
0.040
0.045
0.051

0.026
0. 145
0.042

24

3
148
15
94
27
CF3
16
24

9

1
5

27

.1

3

M3

21
26
9

33
1

23
3
9

69

43
29

181
24
93

144

75
26
92

20

Montalto

30

DoKalb

294

Chester

46

117

Lackawanna

Frankstown

200

86
24

Hagerstown

83

1 Complete fertilizer. 2 Manure. ^ pgr cent, increase in growth, instead of yield.

tion has occurred in the soil analyzing poorest of all, and some of the largest
responses have appeared in the chemically richest soils. The ordinary
methods of soil analysis are not yet adequate to furnish a reliable indi-
cation of the fertility needs of an orchard. Trees on chemically rich
soils will not of necessity prove unresponsive to additional fertilization,
nor will trees on chemically poor soils always prove responsive. In other
words, some other indicator than the chemical composition of the soil,
as here determined, must be relied upon to determine the real need of
additional fertility in an orchard. At present, therefore, the surest and
most delicate test yet devised for determining the fertility needs of an
orchard soil is the actual response of the living tree in the soil concerned
to appropriate fertility additions."

The soil is a very complex substance and the soil solution likewise;
apparently absolute amounts of certain elements or compounds that it
contains are not so important as the state of balance or equilibrium

668 FUNDAMENTALS OF FRUIT PRODUCTION

existing between them. No better evidence to this effect is needed than
some of the facts brought out by the analyses of the Florida and Hawaiian
pineapple soils that have been mentioned. Certainly it would not be
suspected from these analyses that in the Hawaiian soils with their 20 to
35 per cent, of iron (indeed there is one local pineapple district in the
Hawaiian Islands where the soil contains 85 per cent, iron and titanium ^^)
the plants often show symptoms of iron starvation and that iron sulphate
is their most valuable fertilizer, though less than three-tenths of 1 percent,
of iron furnishes an ample supply in the Florida sands. The relationship
between soil and crop is more than that existing between the different
factors in a problem in addition and subtraction. Other aspects of this
general question are discussed in the sections on Water Relations and
Nutrition.

VEGETATION AS AN INDEX TO CROP ADAPTATION

Though at present no single feature of the chemical or mechanical
composition of the soil can be designated the chief cause for the way
some fruit crops grow on it, soil differences, even slight differences, may
be of great significance to the fruit grower. His study of soils should
include more than the features brought into contrast by chemical and
mechanical analyses. The types of the native vegetation may serve as
very useful indices of probable productivity when planted to cultivated
crop plants belonging to the same or a closely related genus or family;
knowledge of plant ecology may make it possible to predict with accuracy
the way some entirely unrelated plant will behave on the soil in question.
For instance, in Ohio, land upon which the sugar maple, beech, oak, or
chestnut thrive naturally is hkely to be well suited to the apple, but land on
which the elm is native is seldom desirable for that fruit. ^^ In western
Oregon and western Washington, hill land supporting a vigorous growth
of the native "brake" or fern (Pteridium aquilinuvi pubescens) is charac-
teristically good for prunes. In the Ozarks "post-oak" land is good for
grape culture. Ney^^ has pointed out that the kinds of forest trees grow-
ing on land often form something of an index of its chemical condition.
He says, "As regards the chemical composition of the soil, even slightly
sour marshy soils are unfavorable to all species of trees except alder,
birch, and spruce ; whilst sour soils, liable to dry up at certain seasons,
are unsuited to all except birch, spruce, Scots and Weymouth pines."
Ash, maple, sycamore, and elm require a moderate quantity of lime and
beech, hornbeam, oak, as also larch and Austrian pine, thrive best on soils
that have at least some lime in their composition. The hardwoods— oak,
ash, maple, sycamore, elm, chestnut, beech and hornbeam — also appear
to demand the presence of a considerable quantity of potash, while on the
other hand, spruce, silver fir and especially Scotch pine and birch thrive

ORCHARD SOILS 669

on soils rich neither in lime nor potash. In Florida a dense growth of
palmettos is Hkely to indicate an undesirable hardpan or subsoil; such
soils should be avoided in citrus fruit plantings.

Not only are the kinds of native trees or plants useful in determining
the value of a soil for fruit growing, but the type of growth that these
species make is of equal significance. Thus Vosbury" states, "Most of
the recent citrus plantings in Florida have been made on high pinelands.
Three grades of high pineland are recognized. The best grade is charac-
terized by large straight-growing pines with occasional oaks, hickories,
or other hardwood trees. The soil is a sandy loam, fairly rich in humus,
and is underlaid with a clay subsoil at a depth of 6 feet or less. In
second-grade pinelands the pine trees are smaller and there are few or no
hardwoods, while the subsoil is further from the surface. In the third
or poorer grade the pines are still smaller and scrubbier and the clay
subsoil far below the surface soil."

The soils picked as especially suited to certain field crops in some
sections are less likely to furnish a reliable guide to their suitability to
certain fruits. In New England apples will generally do well in those
soils considered best suited to corn, for only the lighter earlier soils are
able properly to mature that crop in that section, but in Illinois the best
corn land is quite different in character and the best apple land is outside
the corn belt.

ADAPTATION OF VARIETIES TO PARTICULAR SOILS

In addition to the more or less general soil requirements for different
kinds of fruits that have been mentioned, particular varieties or groups
exhibit certain soil preferences.

For instance, in speaking of soil adaptations of plums, Hedrick^^
states that the Domesticas and Insititias grow most satisfactorily on rich
clay loams, while the Trifloras, Hortulanas and Munsonianas give best
results on light soils. These group names, however, represent distinct
species and consequently differences greater than those usual between
varieties of the same kind of fruit.

Wilder,^^ who has made a special study of the fruit soils of southern New
England, makes the following statements regarding the special soil requirements
of certain well known apple varieties: "Soils grading from medium to semi-light
fulfill the best requirements of the Baldwin. This grouping would include the
medium to light loams, the heavy sandy loams, and also the medium sandy loams,
provided they were underlaid by soil material not lighter than a medium loam
nor heavier than a Ught or medium clay loam of friable structure." From this
broad generalization it will be seen that the surface soil should contain an ap-
preciable amount of sand. The sands, moreover, should not be all of one grade,

670 FUNDAMENTALS OF FRUIT PRODUCTION

that is, a high percentage of coarse sand would give a poor soil, whereas a moderate
admixture of it with the finer grades of sand, together with sufficient clay and
silt, would work no harm.

"A surface soil of heavy, silty loam or light, silty, clay loam underlain by
silty clay loam excells for the 'green' Rhode Island Greening. Such soil will
retain sufficient moisture to be classed as a moist soil, yet it is not so heavy as
ever to be ill drained if surface drainage is inadequate. The soil should be
moderately rich in organic matter, decidedly more so than for the Baldwin.
Such soil conditions maintain a long seasonal growth under uniform conditions
of moisture, and thus produce the firm yet crisp texture, the remarkable juiciness
and the high flavor for which this variety is noted when at its best. If grown on
a soil too sandy, the Rhode Island Greening lacks fineness of grain, flavor and the
juicy quahty in greater or lesser degree, depending on the extent of the departure
from those soil characteristics which contribute to its production.

"This variety [Northern Spy] is one of the most exacting in soil requirements.
To obtain good quality of fruit, i.e., fine texture juiciness and high flavor, the
soil must be moderately heavy, and for the first two qualities alone the Rhode
Island Greening soil would be admirable. The fact that the Northern Spy is a
red apple, however, makes it imperative that the color be well developed and the
skin free from the greasy tendency. This necessitates a fine adjustment of soil
conditions, for the heaviest of the soils adapted to the Rhode Island Greening
produces Northern. Spies with greasy skins and usually of inferior color. Its
tendency to grow upright seems to be accentuated by too clayey soils, if well
enriched and such soils tend to promote growth faster than the tree is able to
mature well. On the other hand, sandy soils, while producing good color and
clear skins, fail to bring fruit satisfactory in quality with respect to texture and
flavor. The keeping quality, too, is inferior to that of the Spy grown on heavier
soils in the same district. Hence the soil requirements of this variety are de-
cidedly exacting, and are best supplied apparently by a medium loam underlain
by a heavy loam or light clay loam. It should not be planted on a soil lighter
than a very heavy, fine, sandy, loam, underlain by a light clay loam, or possibly a
heavy loam. On light soils the Nothern Spy very often yields less per acre
than the Baldwin.

''Both Ben Davis and Gano show less effect from variation in the soils upon
which they are grown than any others observed."

In speaking of tlie special soil requirements of peach varieties the same author
has this to say:

"Judging from the experience of a very large number of growers in Connecti-
cut and in other States, combined with field observations, it seems evident that
the Champion peach is especially sensitive to any condition of subsoil which
hinders the ready movement of moisture within a probable depth of as much as
4 feet from the surface. Carman and Mountain Rose are not quite so dependent
as the Champion on soils that drain out hastilj^, and while they succeed best on
soils of a little greater moisture-holding capacity than the Champion, they never-
theless give the best results on deep and well-drained soils. The Elberta and
the Belle thrive on well-drained soils that are somewhat stronger than the varie-
ties previously mentioned. "^^

ORCHARD SOILS 671

There Is some reason to believe that the importance of these variety
preferences is often overemphasized. For instance to assert that the
Yellow Newtown (Albemarle Pippin) apple will do well only on the so-
called "pippin" soils of Virginia and North Carolina is to misstate the
facts, except perhaps for the soils of those particular states. The variety
does equally well on quite different soils in the Hudson River, Hood
River and Rogue River valleys and in New South Wales, though on these
other soils it may develop a slightly different but in no way inferior,
shape, color or flavor. Some of the variation in the chemical composition
of fruits is without doubt due to diversities in soil and in some parts of
the world these differences are regarded as of considerable importance
in the production of grapes for wine; however, much of the variation in
composition is due to other factors of environment, such as temperature,
sunlight and humidity. Their influence must be subtracted before it
can be said that the difference in the quality of fruit from two different
sections, or even orchards, is due to soil variation. Nevertheless, the
ways in which soil influences the development of individual varieties may
well be studied, for often the information gained can be of much use in
actual fruit production. For instance, if a piece of land that is to be
planted to apple trees includes some light and some heavy soil and two
varieties, one a red and the other a yellow apple, are to be set, it will
generally be wise to plant the red variety on the lighter soil and the
yellow variety on the heavier, so far as possible. Though soil probably
exerts very little, if any, direct influence on pigment production
in the fruit, the type of vegetative growth obtained on the lighter soil
is likely to permit and encourage higher coloration of the fruit than that
obtained on the finer textured land.

It is easier to modify through treatment the chemical condition of the
soil than its physical condition and obviouslj^, it is generally easier to
modify surface soil than subsoil. The subsoil must be taken largely as
it is found. Consequently in selecting a piece of land for fruit growing
the subsoil should be given specially careful consideration, particularly
as regards its physical condition. Both physical and chemical condition
of the surface soil may be modified materially, but to effect any consider-
able change, particularly in physical character, is expensive. The grower
should never forget that the business must yield a fair return on the
investment.

Summary. — In general fruit crops demand the same qualities in a
soil as cereal or forage plants. On account of their growing habits,
however, depth of soil, character of subsoil and general physical condition
are of relatively greater importance to the former. Different fruit crops
show varying adaptation to soils of quite dissimilar textures. Practically
all, however, are alike in requiring considerable depth, thorough aeration
and freedom from hardpan, plowsole or other impervious strata. It is

672 FUNDAMENTALS OF FRUIT PRODUCTION

impracticable at present to attempt a definition of the soil requirements
of different fruit plants in terms of mechanical analysis.

Soils that are unproductive from the standpoint of cereal crops are
often productive from the standpoint of fruit production and the reverse
situation often occurs. It is even more impracticable to attempt a defini-
tion of the soil requirements of different fruits in terms of chemical compo-
sition, than in terms of mechanical analysis. The character of the vegeta-
tion growing naturally on a soil furnishes one of the best indices to the
kinds of fruit that may be expected to thrive on it. Though there are
indications of marked adaptation of particular varieties to certain soil
types, the importance of such special adaptations is often exaggerated.

Suggested Collateral Readings

Batchelor, L. D., and West, F. L. Variation in Minimum Temperatures Due to the

Topography of a Mountain Valley in its Relation to Fruit Growing. Utah Agr.

Exp. Sta. Bui. 141. 1915.
Wickson, E. J. California Fruits: How to Grow Them. Pp. 27-37. San Francisco,

1910.
Russell, E. J. Soil Conditions and Plant Growth. Chapters 3 and 8. Pp. 52-79;

153-169. London, 1915.
Bowman, I. Forest Physiography. Pp. 27-40, 107-126. New York, 1914.

Literature Cited

1. Abbe, C. U. S. D. A., Mo. Weather Rev. 21. 1893. Cited by Garriot, E. B

U. S. D. A. Farmers' Bui. 104. 1899.

2. Batchelor, L. D., and West, F. L. Utah Agr. Exp. Sta. Bui. 141. 1915.

3. Bigelow, F. H. U. S. D. A., Weather Bur. Bui. R. 1908.

4. Cal. Agr. Exp. Sta. Bui. 25. 1884.

5. Cal. Agr. Exp. Sta. Rept. for 1894-95. P. 15. 1896.

6. Cal. Agr. Exp. Sta. Ann. Rept. 1903-1904.

7. Coville, F. V. U. S. D. A., Bur. PL Ind. Bui. 193. 1910.

8. Finch, C, and Baker, D. O. Geography of the World's Agriculture. U. S. D. A.,

Office Farm Management. 1917.

9. Fliche, P., and Grandeau, L. Ann. Chem. et Phys. ser. 5. 2: 354-379. 1874.

10. Forbes, R. H. Ariz. Agr. Exp. Sta. Bui. 28. 1897.

11. Fritz, H. Intern, wissensch. Bibliothek, Band 68. Leipzig^ 1889. Cited by

Abbe, C. U. S. D. A., Weather Bur. Bui. 36. 1905.

12. Gager, C. S. J. N. Y. Bot. Garden 8. 1909. Cited in U. S. D. A., Mo.

Weather Rev. 36: 63. 1908.

13. Georgeson, C. C. Alaska Agr. Exp. Sta. Ann. Rept. P. 9. 1906.

14. Ibid. P. 21. 1907.

15. Ibid. P. 20. 1908.

16. Ibid. Pp. 8, 9. 1909.

17. Green, W. J. Ohio Agr. Exp. Sta. Bui. 137. 1903.

18. Hann, J. Handbuch der Klimatologie. Stuttgart, 1911.

19. Hedrick, U. P. Grapes of New York. Pp. 131, 152. Albany, 1908.

20. Hedrick, U. P. N. Y. Agr. Exp. Sta. Bui. 314. 1909.

21. Hedrick, U. P. Plums of New York. P. 113. Albany, 1911.

22. Heyer, G. Forstl. Bodenk. u. Klimatol. P. 488. 1856. Cited in Nisbet, J.

Studies in Forestry. P. 53. Oxford, 1894.

GEOGRAPHIC INFLUENCES 673

23. Higgins, J. E. Hawaii Agr. Exp. Sta. Bui. 7. 1904.

24. Higgins, J. E., and Holt, V. S. Hawaii Agr. Exp. Sta. Bui. 32. 1914.

25. Hilgard, E. W. Cal. Agr. Exp. Sta. Kept, for 1890. P. 41. 1891.

26. Hilgard, E. W. Cal. Agr. Exp. Sta. Rept. for 1892-3. P. 328. 1894.

27. Hilgard, E. W. Cal. Agr. Exp. Sta. Rept. for 1897-1898. P. 41.

28. Hilgard, E. W. Soils, 6th ed. P. 182. 1914.

29. Hodgson, R. W. Cal. Agr. Exp. Sta. Bui. 276. 1917.

30. Hopkins, C. G. Soil Fertility and Permanent Agriculture. P. 69. 1910.

(Computed from his data.)

31. Husmann, G. C. U. S. D. A., Bur. PL Ind. Bui. 172. 1910.

32. Jaffa, M. E. Cal. Agr. Exp. Sta. Rept. for 1892-3. P. 238. 1894.

33. Johnson, M. O. Hawaii Agr. Exp. Sta. Press Bui. 51. 1916.

34. Kearney, T. H. U. S. D. A. Bur. PI. Ind. Bui. 125. 1908.

35. Kedzie, R. C. Mich. Agr. Exp. Sta. Bui. 99. 1893.

36. Kelley, W. P. Hawaii Agr. Exp. Sta. Bui. 26. 1912.

37. Kerner, A., and Oliver, F. W. Natural History of Plants. 1 (2): 528. New

York, 1895.

38. King, F. A. Wis. Agr. Exp. Sta. Ann. Rept. 12: 268-272. 1895.

39. Kinman, C. F. Porto Rico Agr. Exp. Sta. Bui. 24. 1918.

40. Lippincott, J. S. U. S. Rept. Com. Agr. Pp. 137-190. 1866.

41. Loughridge, R. H. Cal. Agr. Exp. Sta. Bui. 133. 1901.

42. Mac Dougal, D. T. Mem. Hort. Soc. N. Y. 2: 3-22. 1907.

43. Mason, S. C. U. S. D. A. Bui. 271. 1915.

44. Mass. St. Board of Agr., Ann. Rept. 59: 14-15. 1911.

45. Merriam, C. H. U. S. D. A., Div. of Biol. Surv. Bui. 10. 1898.

46. Miller, H. K., and Hume, H. H. Fla. Agr. Exp. Sta. Bui. 68. 1903.

47. Ney. Lehre von Waldbau. P. 64. 1885. Cited in Nisbet, J. Studies in

Forestry. Oxford, 1894.

48. Persons, A. A. Fla. Agr. Exp. Sta. Bui. 43. 1897.

49. Riviere, G., and Bailhache, G. Prog. Agr. et Vit. 53 (15): 453-454. 1910.

50. Shaw, G. W. Ore. Agr. Exp. Sta. Bui. 50. 1898.

51. Shreve, F. Carn. Inst. Wash. Pub. 217. 1915.

52. Stewart, J. P. Pa. Agr. Exp. Sta. Bui. 153. 1918.

53. Thatcher, R. W. Wash. Agr. Exp. Sta. Bui. 85. 1908.

54. U. S. D. A., Bur. Soils, Bui. 5. 1896.

55. U. S. D. A., Operations Div. Soils for 1900. P. 303. 1901.

56. Ibid, for 1901. P. 464. 1902.

57. Ibid, for 1904. P. 1127. 1905.

58. Ibid, for 1905. P. 959. 1907.

59. Ibid, for 1909. P. 1721. 1921.

60. Vinson, R. S., and Russell, E. J. J. Agr. Sci. 2: 225. 1907.

61. Vosbury, E. D. U. S. D. A. Farmers' Bui. 1122. 1920.

62. Wheeler, H. J. U. S. D. A. Farmers' Bui. 77. 1905.

63. 'UTiitney, M. U. S. D. A., Bur. Soils. Bui. 13. 1898.

64. Wilcox, E. V. Tropical Agriculture. Pp. 2, 5. 1916.

65. Ibid. P. 19. 1916.

66. Wilder, H. J., Mass. St. Board Agr. Ann. Rept. 59: 13-23. 1911.

67. Wilder, H. J. U. S. D. A. Bui. 140. 1915.

674 FUNDAMENTALS OF FRUIT PRODUCTION

GLOSSARY

Adiabattc. — A curve exhibiting variations of pressure and volume of a fluid when

it expands without receiving or losing heat.
Adsorption. — The adhesion of molecules of gases or dissolved substance to the sur-
faces of solid particles; distinguished from absorption, which is not a surface
phenomenon.
Aitionomic. — As referred to parthenocarpy, the ability to develop parthenocarpic

fruits only in response to some stimulus external to the ovary.
Akene. — Dry, unilocular, indehiscent fruit, seed-like in appearance, as in the straw-
berry.
Alkali. — (1) In chemistry, a base; (2) as applied to soils, salts present in amounts
harmful to plants, chiefly sodium chloride, sodium sulfate and sodium
carbonate.
Antagonism. — Of salts, a mutual counteraction of their influence on cell permeability.
Arginine. — A basic amino-acid which is a product of protein digestion.
Autocatalysis. — A process of catalysis where the catalytic agent is an end product

of the reaction catalyzed.
Autogamy. — When a flower is fertilized by its own pollen.
Autonomic. — As referred to parthenocarpy, the ability to set fruit without the

stimulus resulting from pollination.
Barren. — Unproductive.

Breba. — One of the crops of the pistillate fig tree, the first to mature in the spring.
Caprifig. — The wild or "male" fig, the uncultivated form.
Chemotropism.— A bending or turning in response to a chemical stimulus.
Chlorosis. — A diseased condition shown by loss of green color.
Choline. — An amine arising as one of the products of lecithin decomposition.
Colloid. — A state of a substance where the units are very large molecules or molecule
complexes. Colloids diffuse slowly or not at all through plant or animal mem-
branes.
Compatibility. — (1) Of sex cells, the ability to unite and form a fertilized egg that
can grow to maturity. (2) Congeniality as determined by the degree of success
of the union between stock and cion.
Coulure. — The failure of blossoms to set, resulting in a premature drop. Cf.

millerandage.
Court-noue. — A physiological disturbance of the grape manifested by short nodes.
Creatine. — A nitrogenous compound readily converted into creatinine.
Creatinine. — A basic nitrogenous compound occuring naturally in muscle tissue and

urine.
Cumarine. — An organic compound with vanilla-like odor known as tonka bean

camphor.
Dichogamy. — Insuring cross fertilization by the sexes being developed at different

times.
Dicliny. — Male and female organs separate and in different flowers.
Dihydroxy-stearic Acid. — A double hj^droxide of a common fatty acid.
Dimorphism. — Presenting two forms, as long and short growths or permanent and

deciduous branches.
Dioecious. — Unisexual, the male and female elements in different individuals.
Disaccharide. — A compound sugar yielding two simple sugars on hydrolysis.
Dormant. — Applied to buds when they are not actively growing and to plants when

they are not in leaf.
Emasculation. — The artificial removal of the stamens from the flower before they
dehisce.

GLOSSARY 675

Embryogenic. — Pertaining to the development of the embryo.

Embryo Sac. — The cell in the ovule in which the embryo is formed.

Endocarp. — The inner layer of the wall of a fructified ovary.

Endosperm. — The nutritive material stored within a seed, originally deposited within

the embryo sac.
Ezocarp. — The outer layer of the wall of a fructified ovary.
Extine. — The outer coat of a pollen grain.

Fasciation. — A diseased condition resembling the growth of several stems into one.
Fecundation. — The fusion of two gametes to form a new cell.
Fecimdity. — The ability of flowers to produce seeds that will germinate.
Fertility. — (1) Of flowers, the capacity of producing seeds that will germinate; (2)

of soils, the crop producing power.
Fertilization. — (1) The fusion of two gametes to form a new cell; (2) the application of

fertilizers.
Frenching. — A disease characterized by loss of color in leaves between the veins.
Fruitfulness. — The capacity of producing fruit.
Fruit Setting. — A development of the ovary and adjacent tissues following the

blossoming period.
Gamete. — A miisexual cell which must fuse with another gamete to produce a new

individual.
Glucosides. — Compounds that yield sugar and some other substance, usually aro-
matic, on hydrolysis.
Guanine. — A basic nitrogenous compound related to uric acid; one of the purines.
Gynaeceum. — The pistil or pistils of a flower.
Hermaphrodite. — A flower with both stamens and pistils.

Heterostyly. — The presence of styles of two or more forms or two or more lengths.
Heterotypic. — Reduction division of a cell.

Histidine. — A basic amino-acid which is a product of protein digestion.
Homotypic. — As applied to cell division, involving the usual process of karyokinesis.
Hydrolysis. — Chemical splitting by taking up the elements of water.
Hygroscopic Coefficient. — The percentage of soil water retained in contact with a

saturated atmosphere and in the absence of any other source of moisture.
Hypoxanthine. — A basic nitrogenous compound related to uric acid; one of the

purines.
Imbibition. — The process of absorption, usuall}^ by a solid.
Imperfect. — In flowers, unisexual.
Impotence. — Inability to produce functional gametes of the one sex or the other;

sometimes used in a more general sense to denote sterility.
Inconjpatibility. — Of sex cells, the inability to unite and form a fertilized egg that can

grow to maturity.
Interfertility. — The ability of one variety to set fruit and produce seeds that will

germinate when poUenized by another variety.
Interfruitfulness. — The ability of one variety to set and mature seed-containing or

seedless fruit when pollenized by another variety.
Intersexualism. — Sex intergrades; a term referring to the varying degrees of develop-
ment of the two sex organs in the same plant; relative maleness or femaleness

of the plant.
Intersterility. — Inability of one variety when pollenzied by another variety to set

fruit and produce seeds that will germinate.
lutine. — The inner coat of a pollen grain.
June Drop. — The abscission of partly developed fruit (often occurring in June).

676 FUNDAMENTALS OF FRUIT PRODUCTION

Latent Bud. — A bud, usually concealed, more than one year old, which may remain

dormant indefinitely or may develop under certain conditions.
Lecithin. — A fat-soluble compound containing nitrogen and phosphorus.
Locule. — The cavity of an anther or ovary.
Mamme. — One of the crops of the caprifig or "male" fig, the first to mature in the

spring. The fruits of this crop winter over as comparatively large specimens.
Mammoni. — One of the crops of the caprifig or "male" fig, which sets in June and

matures in late summer.
Millerandage. — A condition in the grape where the ovary persists but the seeds

remain small or do not attain usual size; produced by conditions similar to tJiose

that lead to coulure.
Monoecious. — The stamens and pistils in separate flowers but borne on the same

individual.
Nucleic Acid. — Phosphorus-containing acids, usually combined with protein in all cell

nuclei.
Nucleins. — Phosphorus-containing compounds of nucleic acid with protein.
Osmosis. — Diffusion through a membrane.

Parthenocarpy. — The production of fruit without true fertilization.
Parthenogenesis. — The development of the unfertilized egg into the usual product of

fertilization without a preceding union of gametes.
Pedicel. — The support of a single flower of an inflorescence.
Peduncle. — The support of an inflorescence or a flower stalk.
Pentosan. — A polysaccharide that yields five-carbon sugars on hydrolysis.
Perennation. — A lasting state, referring particularly to the persistance of fruit long

after its usual season of maturity.
Perfect. — Hermaphrodite flowers.
Picoline. — A basic derivative of pyridine.
Pollination. — The placing of pollen on the stigmatic surface.
Pollinium. — A pollen mass consisting of all the pollen grains of an anther locule.
Polyembryony. — The production of more than one embryo in an ovule.
Polygamo-dioecious. — With hermaphrodite and unisexual flowers on different

individuals of the same species.
Polygamous. — With hermaphrodite and unisexual flowers.
Polysaccharide. — A carbohydrate which yields a large but indefinite number of

simple sugars on hydrolj^sis; usually colloids.
Polyterpenes. — Compounds which yield an indefinite number of simple hemiterpene

units on distillation; ex. caoutchouc, balata.
Profichi. — One of the crops of the caprifig or "mele" fig, the second to mature in the

spring. The fruits of this crop appear as small buttons in the late fall or early

winter.
Proliferation. — A rapid and repeated production of new parts, as the formation of

leafy parts from floral parts.
Protandry. — The pollen being discharged before the pistils are receptive.
Protogyny. — The pistils receptive before the anthers have ripe pollen.
Pseudo-hermaphrodite. — Functional unisexuality in the presence of apparently well

developed stamens and pistils.
Purines. — A group of nitrogenous organic compounds such as uric acid, xanthine and

caffein.
Pyridine. — A nitrogenous base which is the nucleus of many organic compounds, for

example nicotine.
Pyrimidines. — A group of basic nitrogenous compounds related to the purines and

found as products of nucleic acid cleavage.
Quinone. — An oxidation product of benzene.

GLOSSARY 677

Respiration. — Gaseous exchange \)y which the plant absorbs oxygen and gives off

carbon dioxide.
Respiratory CoeflScient. — The amount of carbon dioxide given off divided by the

amount of oxygen used in respiration.
Salicylic Aldehyde. — An oxidation product of sahcin giving the fragrance to

meadow-sweet.
Somaplasm. — The protoplasm other than the germplasm.

Sod Culture. — A method of orchard soil management in which a permanent perennial
crop is grown between the trees, mowed once or twice during the growing season
and then allowed to remain on the ground. A limited area around the trees is
hoed, spaded or otherwise tilled.
Sod Mulch. — A method of orchard soil management in which a permanent perennial
crop is growTi between the trees, mowed once or twice during the growing season
and then allowed to remain on the ground.
Sporogenous. — Producing spores.
Sporophyte. — The plant in the alternating life cycle arising from a fertilized egg and

producing spores.
Sterility. — The inability to produce seeds that will germinate.
Supercooling. — Cooling below the freezing point without solidification.
Temperature Inversion. — A rise in temperature with increasing distance from the

ground, up to a certain height.
Tetrad. — A group of four cells such as the pollen grains derived from one spore mother

cell.
Torus. — (1) The receptacle of a flower, part of the axis on which the flower parts are

inserted; (2) the thickening in the center of the membrane in bordered pits.
Trimorphism. — Heterogomy, or with long-, short-, and mid-styled flowers.
Vacuole.— In cells, the cell sap surrounded by protoplasm.
Vanillin. — An aromatic compound, the fragrant constituent of vanilla.
Wilting Coefficient. — The percentage of moisture in the soil when permanent wilting

of plants takes place.
Xanthine. — A basic nitrogenous compound related to uric acid; one of the purisen.
Xenia. — The direct influence of foreign pollen on the part of the mother plant that
develops into endosperm.

PROPERTY UBRAR7

fl. C. State College

INDEX

(Principal discussions are in bold face type)

Abortion, embryo, 526-S26

embryo sac, 495, 514, 521

ovary, 487

pistil, 484, 495, 504, 507, 511

pollen, 478, 496-498, 507, 511-514
Absorption, 18-22

nitrogen, 130

relation to concentration, 105

relation to transpiration, 127

selective, 126
Acclimatization, 241
Acidity of soil, see Soil Reaction.
Acid tolerance of fruits, 118, 226
Adsorption, 49, 255-260
Aeration of soil, 126
Age and fruit setting, 614
Air drainage, 346-349, 643-652
Alkali, see Concentration, Soil Reaction.
Almond, composition, 101, 138, 144, 149, 152,
156, 160

frost injury, 359

fruit-bud formation, 187

fruiting habits, 402

fruit setting, 500, 542

geography, 621

pruning, 465

soils, 657

stocks, 553, 559, 564, 587, 601

varietal differences, 542

water requirements, 3, 16

winter injury, 291
Alternate bearing, see Fruiting Habits.
Altitude, 621

see Elevation.
Aluminum, in plant tissues, 160

in soils, 663-665
Ammonium, 106
Antagonism, 126
Antipodals, 477

Apple, composition, 4, 5, 102-104, 133-138. 141-
158, 254, 275, 319, 320

cultivation, 66, 71, 77

fertilizers, 206-217

frost injury, 359-362, 364, 381

fruit-bud formation, 186-192

fruit development, 530, .531, 534

fruiting habits, 399, 4.")7-461

fruit setting, .500, 503-505, .509, 511, 518,
521, 531, 640

geography, 612, 614, 619-620, 624-628

irrigation, 71, 73

physiological disturbances, 79, 83, 88-96

propagation, B89-696

679

Apple, pruning, 408-433, 439-447, 450-453, 467-
461

root distribution, S6-6J, 581

soils, 660-662, 666, 668-670

stocks, 312, 316, 653-.554, 568-559, 562,
565-567, 571-578, 581, 588-,592, 599.
601

temperature requirements, 238-248, 624-628

varietal and group differences, 86, 190, 207,
242-244. 254, 271, 319-322, 362, 422-
424, 430, 441-443, 540, 581, 588, 594.
624-626, 669

water requirements, 3, 7, 16

winter injury, 25,5-256, 261, 267-271, 279,
291, 304, 312, 318-322
Apricot, composition, 138, 144, 149, 156

frost injury, 359-360

fruiting habits, 402

fruit setting, 519, 543

geography, 621

physiological disturbances, 95

pruning, 465

stocks, 556, 575

temperature requirements. 245

water requirements, 3, 8. 10, 16

winter injury, 291
Arsenical poisoning, 196
Aspect, see Slope.
Assimilation, 161-166
Atmospheric humidity, see Humidity.
Autogamy, 480
Availability, 107-108

iron, 109, 116-117

nitrogen, 109

phosphorus, 108, 116

sulfur, 109

water, 16, 47-49
Axial row, 477
Azarole. see Hawthorn.

Bark splitting, 300

Barrenness, see Fruitfulness.

Bearing habits, see Fruiting Habits.

Biennial bearing, see Regularity of Bearing.

Bitter-pit, 93, 195, 197

Blackberry (and Dewberry), composition. 4, 150

fertihzers, 207

fruit-bud formation, 188

fruiting habits, 402, 467

fruit setting, 498-500. 544

geography, 626, 634

pruning, 453, 467

soils, 118

680

INDEX

Blackberry, varietal and group differences, 332-
330, 498

winter injury, 315, 332-336
Black-end, 94

Blossoming season, 342-346, 365-369
Blueberry, fruit-bud formation, 403

geography, 618

soils, 118, 657, 662

Calcium, antagonjpm, 126

deficiencies, 199

displacement, 106

in fertilizers, 110, 157. 201-202, 221, 226

and nitrification, 110

in organic compounds, 154

in plant tissues, 101-104, 127, 154-166

relation to chlorosis, 116

in soils, 156-157, 222, 663-605
Carbohydrates, 167-168

in plant tissues, 167, 171-176

relation to fruit-bud formation, 181-186

relation to pigment formation, 180

storage, 170, 182-183

synthesis, 167

translocation, 167-176, 199, 434-435, 451

utilization, 176-180, 184, 199, 451
Carbon assimilation, 162-166
Carotin, 164
Chalaza, 477

Cherry, composition, 4, 102-103, 132-133, 138,
140-141, 144-146, 149-150, 154-156

frost injury, 359-360

fruit-bud formation, 188

fruiting habits, 401, 464

fruit setting, 486, 500-501, 543

geography, 612, 620-621, 620

physiological disturbances, 95

pruning, 410, 464-466

root distribution, 62

stocks, 248, 313, 553-554, 560, 562, 566, 568,
582, 585

temperature requirements, 326, 628

varietal and group differences, 313, 326-328,
401, 486, 543

water requirements, 8, 16

winter injury, 288, 291, 297-298, 313, 326-
328
Chestnut, composition, 4, 101, 102, 138, 144, 149,
152, 153, 156, 158

fruiting habits, 404

stocks, 570

winter injury, 292
Chinquapin, see Chestnut.
Chlorine, 159, 199
Chlorophyll, 164-165
Chlorosis, 85, 116-117, 199, 569, 662
Cion, influence on stock, 579-683

rooting, 594

selection, 603-606
Citrus fruits, composition, 150, 152

geography, 621

physiological disturbances, 106, 116, 120

propagation, 590, 596

soils, 660, 669

Citrus fruits, stocks, 582, 587

water requirements, 3

winter injury, 272

see Orange.
Climate, see Temperature, Winter Injury,

Precipitation.
Clouds and frost, 341
Concentration of sap, see Sap Density.
Concentration of soil solution, injuries from
"alkaU," 119-121, 190

requisites for absorption, 105

and root distribution, 64

tolerance of different plants, 118-119
Congeniality of grafts, 662-557
Copper poisoning, 195
Cork, 89

Coulure, 454, 497, 514
Cover crops, acid tolerance, 118

and nitrogen fixation, 114-115

and soil moisture, 34-35, 41-46, 279-281

and soil temperature, 307

toxic action, 124

and winter injury, 271, 279-281, 310-312
Cranberry, 85, 188, 202, 349-366, 618
Cross sterility, 501
Crotch and crown injury, 271-274
Cultivation, 31, 38-39

and frost danger, 355

and fruit setting, 81

and nitrification, 111-114

and root distribution, 63

an 1 run-off, 32

and soil temperature, 306-307

and vegetative growth, 66

and water requirement, 10

and winter injury, 269, 270, 279, 289
Cup-shake, 300
Currant, composition, 4, 150, 258

fruit-bud formation, 188

fruiting habits, 402

fruit setting, 544

geography, 618

physiological disturbances, 84

pruning, 466

temperature requirements, 628

varietal and group differences, 335, 466

winter injury, 315, 335
Cuttings, propagation by, 689-695

Date palm, 242, 487

DefoUation, 80

see Summer Pruning.

Degeneration, see Abortion.

Dehorning, 427-429

Depth of freezing, see Soil Temperature.

Depth of rooting, see Root Distribution.

Dewberry, see Blackberry.

Dewpoint and frost, 341, 370

Dieback, 88, 91-92, 195

Dioecious plants, 490-492

Disease, extent of injury, 2
fruit setting, 518
susceptibility, 75, 568-569

INDEX

681

Disease, see Parasites, Physiological Disturbances.

Displacement, 106

Distance of planting, see Planting.

Double fertilization, 477, 482

Double working, 601-603

Drought injury, 2, 14-16, 41, 86-96, 257. 274

Dwarfing, 432-434, 557-560, 575, 579-580, 597

Egg apparatus, 477

Elder, 400

Elevation, 339, 346-351, 643-648

Embryo, abortion, 525-526

formation, 482
Embryo sac, 477
Endosperm, 482
Enzymes, 166

Evaporation, 45, 281-282, 654
Exanthema, see Dieback
Exposure, see Slope.

False-blossom, 85
Fasciation, 84, 416
FertiUty, 487, 606, 510

see Fruitfulness, Fruit Setting.
Fertilization, 481
Fertilizers, 151, 222-226

excessive applications, 119

fruit setting, 510

indirect effects, 218-221

lime, 221

methods of action, 200

nitrification, 110

nitrogenous, 204-217, 510

orchard requirements, 200-203, 667

phosphorus, 218-219

protective action, 123

soil temperature, 307

sulfur, 219, 226

time of application, 227-228

water requirement, 10, 12

winter injury, 289
Fig, composition, 138, 144, 149, 156, 158

fruit development, 533-534

fruiting habits, 404

fruit setting, 491, 493, 513, 623-624

geography, 621

physiological disturbances, 83

water requirements, 3, 16
Filbert, 188, 403, 493
Frenching, 106

Freeze and frost distinguished, 338
Frost, crack, 298-300

danger, 342-356, 366

formation, 337-341, 351, 370

injury, 2, 358-365, 380-381

penetration, see Soil Temperature.

prediction, 369-373

protection, 373-380
Fruit-bud formation, 181-193, 413-414, 419-426,

451-452, 570-572
Fruit development, 525, 629-636

Fruitfulness, 487

age and vigor, 614
• compatibility, 600-602, 507

dichogamy, 492-494, 512

evolutionary tendencies, 489-498

external factors, 509-520

genetic factors, 489, 498-502

grafting, 510

heterostyly, 492

hybridity, 499

intersexualism, 490-492

locality, 510-512

moisture supply, 516

nutrient supply, 609

nutritive conditions, 604-607

physiological factors, 489, 502-507

pistil abortion, 494-495, 507

pollen abortion, 496-498, 507, 512

pollen tube growth, 481, 502

season, 612-614

temperature, 514-616

time of pollination, 503
Fruiting habits, 397-406
Fruit-pit, 89, 93
Fruits classified, 475
Fruit setting, 483, 487

disease, 518

humidity, 80-82, 516-.517

individual fruits, 640-646

June drop, 484-487

nitrogenous fertilizers, 209-211

pinching, 454

ringing, 436

spraying, 519

stimulating agents, 521-526

wind, 618
Fruit splitting, 81
Fruit zones, 612-621
Funicle, 477

Girdling, see Ringing.
Gooseberry, composition, 4, 150

fruit-bud formation, 188

fruit development, 529-530

fruiting habits, 402

fruit setting, 544

geography, 618

pruning, 466

stocks, 553, 568

temperature requirements, 243, 248, 628

winter injury, 315, 335
Grafting, 552-557, 600
Grape, composition, 4, 138-139, 143-144, 152-159

coulure, 454, 457, 5l9, 572

fertilizers, 226

frost injury, 350

fruit-bud formation, 188

fruit development, 532

fruiting habits, 402, 468

fruit setting, 436, 484, 49f}-499, 502, 509-
514, 518, 521, 643, 572

geography, 612, 615-616, 620-624, 633

irrigation, 330

millerandage, 572

682

INDEX

Grape, physiological disturbances, 80, 86-87,
117, 569

pinching, 454

propagation, 591

pruning, 438, 453-454, 467-471

ringing, 436

root distribution, 582, 591

soils, 658-662, 668

stocks, 553, 555, 559, 560, 563-582, 586-588

temperature requirements, 241-247, 623-624

training, 470

varietal and group differences, 244, 314, 330,
331, 470, 496, 526, 543

water requirements, 3, 16

winter injury, 314, 329-331
Gummosis, 568

Hail injury, 2

Hardiness, see Frost Injury, Winter Injury,

Winter Killing.
Haw, 400
Hawthorn, 400
Heading back, see Pruning.
Heating, see Orchard Heating.
Heat units and requirements, 336-247
Heeling-in, 19
Heterostyly, 492, 502
Hickory, 405, 620
Humidity, fruit setting, 80-83, 516

geography of fruit production, 631

growth, 78-82

russeting, 79

winter injury, 274
Hybridity and unfruitfulness, 499
Hygroscopic coeflScient, 13

Immaturity, see Winter Injury, Winter Killing.

Impotence, 478, 494-498

Incompatibility, fruitfulness, 600-602, 507, 511

grafts, 562-667
Integuments, 477

Interfertility, see Fertility, Fruitfulness.
Intercrops, 40-41, 81, 124
Interfruitfulness, 601
Intersexualism, 490-492, 499
Inversion of temperature, see Temperature

Inversion.
Iron, availability, 109, 116-117

deficiencies, 116, 199

in fertilizers, 117, 668

in plant tissues, 101, 161-162

in soil, 663-665

solubility, 152
Irregular bearing, see Regularity of Bearing.
Irrigation, 8

"alkali," 121

color and quality of fruit, 74-76

frost danger, 354

fruit size, 71

vegetative growth, 66

winter injury, 278, 335

Jonathan spot, 93

Jujube, 404

Juneberry, 400

June drop, see Fruit Setting.

K

Killing back, 268-271
see Dieback.

Land values, 638
Latitude, 237-239, 342-343

Layering, 593

Leaf pigments, 164

Light, carbohydrate manufacture, 183

frost injury, 262

fruit-bud formation, 183

fruit setting, 516

nitrogen elaboration, 130

phosphorus elaboration, 138

transpiration, 27

water requirement, 11
Lime, see Calcium.
Lithiasis, 95
Location, frost danger, 342-346

fruit setting, 610-612, 515

selection of, 635, 637-639
Loquat, 399, 553, 564. 575, 621

M

Macrosporangium, 473
Macrospore, 477
Magnesium, antagonism, 126

deficiencies, 199

displacement, 106

excesses, 195

in plant tissues, 101-102, 162-163

in soil, 663-665
Manure, see Fertilizers.
Manganese, in plant tissues, 160

in soil, 117, 197, 663-665
Maturity, 272

see Winter Injury, Winter Killing.
Medlar, 400, 555
Micropyle, 477
Microsporangium, 473
Microspore, 478

Moisture, see Humidity, Soil Moisture, Water.
Monoecious plants, 490-492
Mulberry, 404
Mulching, 34, 307, 315, 334, 353, 368

N

Nitrate of soda, see Fertilizers.
Nitrification, 110-112
Nitrogen, absorption, 130

availability, 109-110, 222-224

deficiencies, 198

elaboration, 130

excesses, 195

fixation, 114-116

in fertilizers, 123, 201-202, 222-224

INDEX

683

Nitrogen, in plant tissues, 131-138

relation to fruit-bud formation, 181-186,
207-208

relation to fruit coloration, 212

relation to fruit composition, 215-216

relation to fruit size, 209-212

relation to fruit setting, 209, 510

relation to season of maturity, 216

relation to vegetative growth, 204-207

relation to winter injury, 289

relation to yield, 212-215

in soil, 113, 222, 663-605

storage, 135, 138

translocation, 131-133
Notching, see Ringing.
Nubbins, 495
Nucellus, 477, 483
Nursery stock, 19, 316, 696-606

see Stocks.

(Edema, 84

Olive, composition, 138, 144, 149, 153, 156, 158,

159

fertilizers, 216

geography, 617

planting distance, 8

propagation, 590

root distribution, 63

soils, 662, 665

temperature requirements, 242

water requirements, 8, 16, 77
Orange, composition, 138, 144, 149-153, 156,
158-159

fertilizers, 216

fruit setting, 81, 495, 498

physiological disturbances, 120

root distribution, 62, 64

soils, 118

stocks, 554, 557, 562-563. 572, 575, 580, 587-
588

water requirements, 7

see Citrus Fruits.
Orchard heating, 373-880
Osmosis, 20, 105
Ovary, 473, 475, 487
Ovule, 476-476

Papaya, 491, 515

Parasites and geography of fruit production, 633

see Diseases.
Parenchymatosis, 84
Parthenocarpy, 487, 621-629
Parthenogenesis, 525

Pathological conditions, see Physiological Distur-
bances.
Peach, composition, 4, 138, 144, 148-150, 156, 287

cultivation, 289

fertilizers, 204, 208, 2H-212, 215-216, 289

frost injury, 359-362, 364, 366

fruit-bud formation, 187

fruiting habits, 401, 461

fruit setting, 542

geography, 620-623, 634

Peach, irrigation, 71

propagation, 589

pruning, 288, 325-326. 410-413. 416, 441,
461-464

soils, 657, 665, 670

stocks, 555, 562, 576, 580, 587, 599

temperature requirements, 238-240, 246-
246, 248, 622

thinning, 290

varietal and group differences, 285-291, 326,
362

water requirements, 3, 6, 16

whitewashing, 291

winter injury, 267, 269, 286-292, 298, 312,
323-326
Pear, composition, 4, 103-104, 133, 138, 141, 144,
149, 152-156, 158

frost injury, 359, 364, 380

fruit-bud formation, 187, 192

fruit development, 525, 529, 535

fruiting habits, 399

fruit setting, 500, 518, 641, 572

geography, 248, 612, 614, 619-621

irrigation, 74

physiological disturbances, 84, 94, 95

propagation, 593

pruning, 408-417, 419-433, 439-447, 450-
453, 467-461

soils, 657, 662

stocks, 312, 553, 557, 566, 570, 572-575, 585,
588, 601- 602

varietal and group differences, 323, 430, 541

water requirements, 3

winter injury, 312, 322-323
Pecan, fruiting habits, 405

fruit setting, 493

geography, 612, 620-621

physiological disturbances, 93, 224

winter injury, 269
Pedigreed plants, 603-606
Pentosans, 50. 167. 168-177, 267-260
Percolation, see Seepage.
Perennation, 527
Perisperm, 483
Persimmon, fruit development, 530, 532-634

fruiting habits, 404

fruit setting, 490, 514, 545

stocks, 559
Phosphorus, availability, 108, 116, 225

elaboration, 138

in fertilizers, 123, 202, 218-219

in plant tissues, 101-102, 138-144

in soil, 225, 663-665

solubility, 225
Phyllody, 84
Physiological disturbances , 83-94, 106, 195-197,

224
Pigments, 164, 180
Pinching, 332-333, 453-455, 510
Pineapple, composition, 150, 153, 158, 159

fertilizers, 117

physiological disturbances, 116-117

soils, 116-117, 658, 662-666
Pistil abortion, 484, .504, 509, 511
Placenta, 477
Planting, depth, 315

684

INDEX

Planting, distances, 8, 59

season, 19, 209, 316
Plum, blossoming season, 342

composition, 4, 102, 103, 132, 133, 138-141,
144, 149, 150, 153-159

frost injury, 359, 362

fruit-bud formation, 187, 192

fruiting habits, 401

fruit setting, 484-486, 493, 495, 500, 504,
505, 511, 642

geography, 619, 620, 033, 634

physiological disturbances, 94, 95

propagation, 589, .590

pruning, 410, 429, 440, 465

root distribution, 581

soils, 668, 669

stocks, 248, 314, 553, 555, 561, 564, 571, 580,
581, 584, 586, 588, 602

temperature requirements, 238, 245

varietal and group differences, 285, 328, 329,
362, 495, 542, 669

water requirements, 3, 8, 16

wliitewashing, 291

winter injury, 255, 256, 273, 285, 314, 328-
329
Polar bodies, 477, 482
Pollen, abortion, 478, 496-498, 509, 511-512

carrying agents, 639

formation, 477-479

germination, 480-481, 504

specific effects on fruit, 634-636
Pollen tube growth, 481, 502, 503, 513, 515
Pollination, 478, 503, 515, 638-640
Polyembryony, 504
Pomegranate, 401, 495, 657
Potassium, availability, 109

deficiencies, 106, 198

displacement, 106

in fertihzers, 123, 145, 201, 202, 225

fruit coloration, 145

in plant tissues, 101, 102, 146-160

in soil, 146, 663-665

replacement, 159
Precipitation, fruit setting, 516, 517

geography of fruit production, 631-632, 654

requirements for trees, 6-7

vegetative growth, 67-70

winter injury, 266, 270, 274-278
Propagation, see Grafting, Nursery stock. Stocks.
Proliferation, 527
Protandry, 492-494
Protogyny, 492-494
Prune, see Plum.
Pruning, 388-471

nutritive conditions, 426, 510

winter-injured trees, 316, 326-326, 432

winter injury, 288

Quince, 150, 187. 400, 542. 657

Radiation, 338-340, 351, 373-374

Rainfall, see Precipitation.
Raphe, 477

Raspberry, composition, 4, 150, 258

fertilizers, 207

fruit-bud formation, 188

fruiting habits, 402. 467

fruit setting, 544

geography, 619

irrigation, 335

mulching, 335

pruning, 332, 333, 453, 467

soils, 118

temperature requirements, 628

varietal and group differences, 332-336

winter injury, 315, 332-336
Regularity of bearing, 78, 406
Respiration, 166
Rest period, 284-286, 292
Ringing, 434-437, 506
Root, distribution, 64-64, 679-683

killing, 22, 304, 312-316

pruning, 19. 432-434
Rosette, 91-92
Rough bark disease, 85
Run-off, 7, 32
Russeting of fruit. 79, 381

Sap density and hardiness, 264, 257

Scaly bark disease. 84

Secondary fertilization, 482

Second bloom, 191, 381, 415

Second growth, 70, 270

Seedlessness, 198, 364, 487, 509, 621-627

Seeds and fruit development, 629-634

Seepage, 7, 51. 52

Selective absorption, 126

Self fertility, see Fertility.

Self sterility, see Fertility, Fruitfulness, Fruit

Setting.
Setting fruit trees, see Planting.
Sex distribution, 490-492
Shadbush, 400
Shading, 1, 11. 291

Sihcon in plant tissues, 101, 102, 167-168
Silver leaf, 95
Sites, 346-351, 663-655
Slope, 639-643

Smudging, see Orchard Heating.
Sodium, 106, 158-169, 663-665
Sod-mulch, 32-38, 66, 111, 114, 124, 306. 352

see Soil Management Methods.
Soil, acidity, see Soil Reaction.

alkali, see Concentration.

chemical composition, 662-668

crop adaptation, 668-671

fruit setting, 509

general orchard requirements, 666-688

management methods, 31-46, 62-64. 111-
114. 306-307, 362-367

mechanical analyses, 658-661

reaction, 116-118, 128, 223, 226, 662

solubility, 107

temperature. 247-248, 302-312, 640

toxins, 122-126

type and frost danger, 351

type and frost penetration. 808

INDEX

685

Soil moisture, 47-50

absorption, 21

availability, 16, 47-49

composition, 74

cover crops, 41-45, 279-281

disease susceptibility, 76

evaporation, 282-284

frost danger, 363-366

fruit-bud formation, 185

fruit shape and color, 73

fruit size, 71

fruit setting, 516

intercrops, 39-41

movement, 61-63

physiological disturbances, 83-96

residual effects, 69, 73, 76-78

root distribution, 60-62

root killing, 22

second growth, 70

soil management methods, 32- 38

vegetative growth, 22, 34, 66-71

wilting points, 16

winter injury, 274-284, 309-310

yield, 34, 72-73, 76-78, 228
Solubility of soil, 107
Sour sap, see Sunscald.
Sphtting of fruit, 81
Spraying in bloom, 619
Starch, synthesis, 167

in plant tissues, 169, 173-174

storage and translocation, 169-170,
326

see Carbohydrates.
Sterility, see Fertility, Fruitfulness, Fruit Setting.
Stooling. 593

Stock, influenced by cion, 579-683
Stock, influence on cion, disease resistance, 668-
569

form 660-661

fruit setting, 510, 572

fruit size, 672-574

hardiness, 321, 566-567

longevity, 578

maturity, 562-566

quality, 574-678

stature, 567-560

yield, 569-574
Stocks, congeniality and adaptability, 662-667,

173,

Stocks for, almond, 553, 5.59, 564, 587, 601

apple, 553, 554, 558, 559, 562, 56.5-567, 5/1-

578, 581, 588-592, 599, 601
apricot, 556, 575

cherry, 553, 554, 560, 562, 566, 568. 582, 585
chestnut, 570
gooseberry, 553, 568
grape, 553, 555, 5.59, 560, 663-666, 567-

569, 571-578, 580-582, 686-688
loquat, 553, 564, 575
medlar, 555
orange, 5.54, 557, 562, 563, 567, 572, 575,

580, 587, 588
peach, 555, 562, 576, 580, 587, 599
pear, 553, 557, 566, 570, 572-575, 585, 588,

601, 602
persimmon, 559

Stocks, plum, 553, 555, 561, 562, 564, 571, 574,
580, 581, 584, 586, 588, 602

walnut, 568, 588
Strawberry, composition, 153

fertilizers, 205, 216, 221

frost injury, 361-363

fruit-bud formation, 188, 190

fruit setting, 487, 490, 495, 498, 510, 513, 544

irrigation, 75

mulching, 353

soils. 118, 662, 666

varietal and group differences, 362, 363
Stringfellow root pruning, 19
Stripping, see Ringing.
Submergence and root killing, 22
Sugars, 167-168, 174-179

see Carbohydrates.
Sulfur, availability, 109

deficiencies, 199

in fertilizers, 151, 202, 219, 226

in organic compounds, 150

in plant tissues, 101, 102

in soil, 151, 663-665
Summer pruning, 26, 72, 439-453, 463
Sunscald, 292-296

Sunshine in fruit growing sections, 633
Suspensor, 482
Synergids, 477, 481

Temperature, 234-236, 621-631

and assimilation, 165

and bodies of water, 628-630, 648-650

critical for flowers, 358-363, 366

critical for roots, 304, 312-316

at different elevations, 346-351, 621, 630,
64.3-648

and disease, 248

and fruit-bud formation, 185

and fruit setting, 614-616

heat units and requirements, 236-247, 617-
630

inversion, 339, 349-351, 376-378, 646-648

local variations, 663

and nitrification, 112

of plant tissues, 276-278, 29.3-296, 340, 641

effects of rapid temperature changes, 260-
261, 296-300

sheltered and exposed thermometers, 293,
340

of soil, 247-248, 302-312, 640

influenced by soil and soil management
methods, 349-366

and transpiration, 27, 28
Terminal bud formation, 68-70
Thermal belts, 646-648
Thinning and winter injury, 290
Thinning out, see Pruning.
Tillage, see Cultivation.
Tipburn, 87
Topping, 4.53
Toxins, see Soil Toxins.
Training, 391-396
Transpiration, 23-28, 126, 449
Transplanting, see Planting.

686

INDEX

Transportation facilities, 639
Trunk splitting, 298-300
Tufting of carpels and seeds, 84

U

Unfruitfulncss, see Fruitfulness.

Variegation, 569
Verdant zones, 646-648
Virescence, 85

Walnut, composition, 4, 138, 144, 149, 152-159
fruiting habits, 405
fruit setting, 493
geography, 620
physiological disturbances, 88
stocks, 568, 588
water requirements, 3, 16
winter injury, 268

Water, absorption, see Absorption.

adsorption, see Adsorption.

conduction, 28-29, 276
Watercore, 86

Water content, plant tissues, 4-6, 60, 275, 276,
287, 294, 319, 320

soil, 13-17, 49
Water, requirements, 1-13

retention, 266-260, 274-276
Whitewashing, 291, 296, 368
Wilting coefficient, 13-17
Wind, influence on, evaporation, 45, 281-284, 634

frost, 341, 378, 379

fruit setting, 618

transpiration, 26-27

winter injury, 273
Windbreaks, 46, 81, 281-284, 652
Winter killing, 260-262, 296-300, 566-567
Winter injury, 264-278, 292-336, 651

Xenia, 482