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BY LH- BAILEY

LANDSCAPE
ARCH.
UBRAR?

IRural Science Series

EDITED BY L. H. BAILEY

PLANT-BREEDING

Elje Eural Science Series

THE SOIL. King.

THE SPRAYING OF PLANTS. Lodeman.

MILK AND ITS PRODUCTS. Wing. Enlarged and Revised.

THE FERTILITY OF THE LAND. Roberts.

THE PRINCIPLES OF FRUIT-GROWING. Bailey. 20th

Edition, Revised.
BUSH-FRUITS. Card.
FERTILIZERS. Voorhees.
THE PRINCIPLES OF AGRICULTURE. Bailey. 15th Edition,

Revised.

IRRIGATION AND DRAINAGE. King.
THE FARMSTEAD. Roberts.
RURAL WEALTH AND WELFARE. Fairchild.
THE PRINCIPLES OF VEGETABLE-GARDENING. Bailey.
FARM POULTRY. Watson. Enlarged and Revised.
THE FEEDING OF ANIMALS. Jordan.
THE FARMER'S BUSINESS HANDBOOK. Roberts.
THE DISEASES OF ANIMALS. Mayo.
THE HORSE. Roberts.
How TO CHOOSE A FARM. Hunt.
FORAGE CROPS. Voorhees.

BACTERIA IN RELATION TO COUNTRY LIFE. Lipman.
THE NURSERY-BOOK. Bailey.
PLANT-BREEDING. Bailey and Gilbert. Revised.
THE FORCING-BOOK. Bailey.
THE PRUNING-BOOK. Bailey.

FRUIT-GROWING IN ARID REGIONS. Paddock and Whipple.
RURAL HYGIENE. Ogden.
DRY-FARMING. Widtsoe.
LAW FOR THE AMERICAN FARMER. Green.
FARM BOYS AND GIRLS. McKeever.
THE TRAINING AND BREAKING OF HORSES. Harper.
SHEEP-FARMING IN NORTH AMERICA. Craig.
COOPERATION IN AGRICULTURE. Powell.
THE FARM WOODLOT. Cheyney and Wentling.
HOUSEHOLD INSECTS. Herrick.

PLANT-BREEDING

BY

L. H. BAILEY

NEW EDITION REVISED BY

ARTHUR W. GILBERT, PH.D.

PROFESSOR OF PLANT-BREEDING IN THE NEW YORK

STATE COLLEGE OF AGRICULTURE AT

CORNELL UNIVERSITY

gorfe

THE MACMILLAN COMPANY
1915

All rights reserved

COPYRIGHT, 1395, 1906,
BY L. H. BAILEY.

Set up and electrotyped. Published December, 1895. Reprinted
April, 1896; August, October, 1897; March, 1902; March, 1904.

Fourth edition, with additions, April, 1906; April, 1907; July,
1908; August, 1910; February, 1912; October, 1913.

NEW REVISED EDITION, ENTIRELY RESET.

COPYRIGHT, 1915,
BY THE MACMILLAN COMPANY.

Set up and electrotyped. Published February, 1915.

J. 8. Cushing Co. — Berwick & Smith Co.
Norwood, Mass., U.S.A.

,
I9»b

LANDSCAPE

ARCH.
LIBRARY

HISTORY

THIS book had its -beginning in a lecture that I gave
twenty-three years ago (December 1, 1891) before the Mas-
sachusetts State Board of Agriculture, in Boston, on " Cross-
Breeding and Hybridizing " ; and this lecture, in turn, was
the outgrowth of one given in 1885 and soon afterwards
published. Under the same title, but with a bibliography
added, the Boston lecture was published as a pamphlet in
1892, and placed on sale, by the Rural Publishing Company
of New York, as one of the Rural Library Series. It com-
prised forty-four pages, and sold for 40 cents. In the sum-
mer of 1895, I gave two addresses on variation and the
origination of domestic varieties of plants under the auspices
of the American Society for the Extension of University
Teaching at the University of Pennsylvania. In the mean-
time, I had been teaching the subject to my classes in
horticulture in Cornell University. In the latter part of
1895, I put together these materials in book form, and hav-
ing no short descriptive title I used the word or compound
" Plant-Breeding." Of this work, the Massachusetts lec-
ture comprised Chapter II, and the Philadelphia lectures
Chapters I and III. The bibliography was not included.
Chapter IV comprised "Borrowed opinions" from the
writings of Verlot, Carriere, and Focke. Carriere's work
on "Production et Fixation des Varietes dans les Vege-
taux" had been translated, with a view to publication, as
early as 1886. The book, " Plant-Breeding," was translated

3Q9£69

vi History

into the French by J. M. and E. Harraca, and published in
Paris in 1901 as " La Production des Plantes."

Having been thrice reprinted, the second edition was
issued in 1902, although, through an inadvertence, it was
not so marked on the title-page. Few text-changes were
made, but the bibliography was included.

Early in 1904 the third edition was issued. The bibli-
ography was extended, and some changes were made in the
text; but the principal departure was a new Chapter IV,
from which the old "Borrowed opinions" were omitted,
and " Recent opinions " were substituted, comprising a dis-
cussion of the work of de Vries, Mendel, and others, and
a statement of the current tendencies of American plant-
breeding practice. " In the eight years since this book was
sent to the printer," it was stated in the preface to the third
edition, "there have been great changes in our attitude
toward most of the fundamental questions that are dis-
cussed in its pages. In fact, these years may be said to
have marked a transition between two habits of thought in
respect to the means of the evolution of plants, — from the
points of view held by Darwin and the older writers to
those arising from definite experimental studies in species
and varieties. We have not given up the old nor wholly
accepted the new, but it is certain that our outlook is shift-
ing. So far as practical plant-breeding is involved, the
changing attitude is concerned chiefly with discussions of
tjie nature of varieties and the nature of hybridization."
It was declared that " the time cannot be far distant when
the subject of plant-breeding will be rewritten from a new
point of view."

In 1906, the fourth edition appeared, with a new chapter
on " Current plant-breeding practice " ; and the book had

History vii

grown from the 293 pages of the original edition to 483
pages. This edition was translated into the Japanese by
D. Karashima, and published in 1907.

We now come to the present edition. The book has been
made over by Dr. Gilbert, who has rewritten some of it
and who has added all the new material, and in whose
hands I have been glad to place it. My work in this
edition has been only editorial. A considerable part of the
old work has been preserved, whether wisely or not will
be the occasion for different opinions. It has seemed to be
desirable to retain something of a former point of view
while at the same time expressing the applications of the
work in the method and the language of the day. Con-
siderable use has been made of the work of others, as is
apparent in the pages. The Open Court Publishing Com-
pany has loaned illustrations from the important work of
de Vries, and pictures have been taken from the Yearbooks
of the United States Department of Agriculture. All these
aids we are glad to acknowledge.

These new investigations have taken us far from the
point of view of Darwin, in which the original editions of
the book were founded. I doubt whether the students
.receiving their instruction to-day, with all their abounding
facilities and opportunities, have any such feeling for a
master-spirit as we had in those days when the studies of
Darwin had given a new meaning to nature, when there
were still a few naturalists left, and when the glow of his
writings was warm in every person's work. To one coming
out of a plant-growing relationship, the masterful works of
Darwin had introduced order, and the forms of cultivated
plants had been made worthy of serious study. This inter-
est was further stimulated by the writings of Wallace and

viii History

others. All these writings were fascinating to read. How
to produce new forms of vegetation seized some of us with
irresistible power. The literature has now become complex
and difficult, with considerable gain, no doubt, in a closer
acquaintance with the subject, and a nearer approach to the
ultimate truth; but the charm of the simple literature is
largely buried, and I fear that much of our interest is now
expressed in the discussion of methods and in disputing
about the reasons. Yet we are accumulating knowledge,
and after a time we shall come back to clarity and to a
simplicity that the layman can use.

L. H. BAILEY.

/ ITHACA, N. Y.,

December 1, 1914.

TABLE OF CONTENTS

CHAPTER T

PAGES

THE FACT AND PHILOSOPHY OF VARIATION . . . 1-13

The fact of individuality, 2 — variation and adapta-
tion, 7 — species-formation, 8 — conception of unit char-
acters, 9 — differences between plants and animals with
regard to general association of parts and their methods
of reproduction, 10 — bud-variation and bud-varieties, 11.

CHAPTER II

THE CAUSES OF INDIVIDUAL DIFFERENCES .... 13-33

Fortuitous variation, 14 — action of natural selection
on variation, 14 — sex as a factor in the variation of
plants, 15 — physical environment and variation, 16 —
do external influences produce permanent effects in
plants, 17 — natal and post-natal variations, 18 — con-
ception of biotypes, 19 — variation in food supply, 20
— variation in climate, 22 — food supply in different
branches, 23 — what cultivation is, 24 — variation in cli-
mate, 25 — man's control over climate as a means of •
making plants vary, 27 — change of seed, 28 — bud-
variation, 29 — struggle for life a cause of variation, 30.

CHAPTER III

THE CHOICE AND FIXATION OF VARIATIONS . . . 34-40

What is a variety, 35 — adaptation in nature, 37 —
artificial selection, 37 — bud selection, 39 — variation
and selection not entirely within man's control, 39.
ix

x Table of Contents

CHAPTER IV

PAGES

THE MEASUREMENT OF VARIATION 41-51

The science of biometry , 41 — type, 43 — biometrical
expression of variability, 43 — mode, 44 — modal coeffi-
cient, 45 — mean, 45 — use of mean, 46 — mathematical
expression of variability, 47 — average deviation, 47 —
standard deviation, 48 — coefficient of variability, 49 —
probable error, 50 — use of statistical methods, 51.

i
CHAPTER V

MUTATIONS 52-91

Evolutionary theories of Darwin and de Vries, 52 —
differences between fluctuating variations and mutations,
54 — history of mutation, 55 — history of the appear-
ance of double flowers, 56 — de Vries' experiment with
cenotheras, 59 — analytical table of seedlings (after de
Vries), 68 — how the mutants were produced in the gar-
den, 71 — mutating strains of O. Lamarkiana, 72 — de
Vries' laws of mutability of the evening-primroses, 72 —
frequency of occurrence of mutations, 79 — spontaneous
occurrence of new elementary species in the wild state,
80 — spontaneous occurrence of new elementary species
and varieties under cultivation, 80 — experimental study
of the origin of mutations, 84 — experiments in the pro-
duction of double flowers, 86 — what do new characters
come from, 90 — can mutations be produced artificially,
90 — economic significance of mutations, 90.

CHAPTER VI

THE PHILOSOPHY OF THE CROSSING OF PLANTS, CONSIDERED
IN REFERENCE TO THEIR IMPROVEMENT UNDER

CULTIVATION 92-148

The struggle fgr life, 92 — survival of the most fit, 93
— flexibility as an aid to survival, 93 — causes of varia-
bility, 94 — origin and function of sex, 95 — effects of

Table of Contents

crossing on the species, 97 — the limits of crossing, 97

— swamping effects of inter-crossing, 98 — what deter-
mines the limits of crossing, 98 — the limits of crossing
tend to preserve the identity of species, 99 — the refusal
to cross, the result of natural selection, 100 — for the
production of useful hybrids, do not have the parents
too diverse, 101 — function of the cross, 101 — rarity of
natural hybrids, 102 — change of seed and crossing, 103

— results from change of stock, 105 — crossing from
standpoint of plant improvement, 108 — understanding
of terms, 108 — history of plant hybrids, 110 — what
plants can be hybridized, 111 — vigor as a result of
crossing, 112 — Darwin's experiments with morning-
glories, 114 — Darwin's results with other plants, 115 —
increased vigor in other crosses, 115 — three factors, 117

— the outright production of new varieties, 118 — how
to overcome antipathy to crossing, 121 — variability of
hybrids, 122 — characteristics of crosses, 123 — difficul-
ties in making successful crosses, 125 — hybridization

and asexual propagation, 125 — in-breeding, 127 — expe-
rience with egg-plants and squashes, 128 — influence of
sex on hybrids, 138 — uncertainties of pollination, 140

— graft hybrids, 142 — the case of Cytisus Adami, 142

— Winkler's Solatium graft-hybrids, 146 — are these
real graft-hybrids, 147.

CHAPTER VII
HEREDITY ..........

Heredity studied collectively, 149 — the coefficient of
heredity, 152 — notation, 153 — conception of unit char-
acters, 154 — knowledge of heredity has come through
experimental breeding, 154 — rediscovery of Mendel's
work by de Vries and others, 155 — Mendel's experi-
ments, 157 — explanation of mendelian results, 166 —
explanation of diagram, 171 — Mendel's results with the
offspring of hybrids in which several differentiating char-

149-208

Xll

Table of Contents

acters are associated, 171 — Mendel's law of inheritance
of unit characters (table), 175 — results in jp2 with com-
plete dominance in every character-pair (table 1), 176 —
results involving three pairs of characters (trihybrid),
177 — incomplete dominance, 179 — presence and ab-
sence hypothesis, 181 — examples of mendelian inherit-
ance due to the presence and absence of a single unit,
181 — mendelian inheritance of color, 185— white flowers
in F2 from red x cream, 187 — the ratio 9:3:4, 188 —
colored forms from white x white and the 9 : 7 ratio,
188 — Emerson's experiments with beans, 189 — absence
factors, 192 — mutations resulting from mendelian segre-
gation and recombination, 193 — mutations which men-
delize are constant, 193 — mendelism in wheats 194 —
mendelism summarized, 200 — application to plant-
breeding, 202 — the probable limits of mendelism in the
production of new varieties, 204 — conclusion, 208.

CHAPTER VIII

How DOMESTIC VARIETIES ORIGINATE . . . .
Indeterminate varieties, 209 — plant-breeding, 212 —
plant-breeding by selection, 218 — rules for breeding
plants, 222 — specific examples, 253 — the dewberry and
blackberry, 253 — the apple, 255 — beans, 260 — cannas,
265 — the cabbage family, 267 — the chrysanthemum, 267.

CHAPTER IX

POLLINATION : OR How TO CROSS PLANTS ....
The structure of the flower, 270 — manipulating the
flowers, 281.

CHAPTER X
THE FORWARD MOVEMENT IN PLANT-BREEDING .

Systematic improvement of plants, 295 — the plant-
breeder should aim toward definite ideals, 297 — plant

209-269

270-293

294-323

Table of Contents xiii

improvement a serious business, 298 — the results of
plant-breeding effort, 299 — state plant-breeding associ-
ations, 300 — other plant-breeding associations, 304 —
commercial breeding agencies, 308 — work of the council
of grain exchanges, 310 — United States Department of
Agriculture and state experiment stations, 310 — work
of the state agricultural experiment stations, 314 — in-
struction in plant-breeding in the United States, 321 —
Luther Burbank, 321.

APPENDIX A
GLOSSARY OF TECHNICAL PLANT-BREEDING TERMS , . 325-327

APPENDIX B
PLANT-BREEDING BOOKS 328-331

APPENDIX C
LIST OF PERIODICALS CONTAINING BREEDING LITERATURE 332-334

APPENDIX D
BIBLIOGRAPHY 335-393

APPENDIX E
LABORATORY EXERCISES ....... 394-467

Exercise 1 — Field study of variations by making an
herbarium of variations 394-399

Exercise 2 — The statistical study of type and
variability 399-412

Exercise 3 — Correlation 412-420

Exercise 4 — Statistical study of apples from different
trees 420

Exercise 5 — Statistical study of branches of different
trees . 420-423

XIV

Table of Contents

PAGES

Exercise 6 — Statistical study of the quantity of grapes
from different grape vines . . . . . . 423

Exercise 7 — Study of variation in pressed specimens
of ragweed or some plant showing many different types 423

Exercise 8 — Study of bud variation and reversions in

ferns 423-424

Exercise 9 — Study of the morphology of different

kinds of flowers 424-426

Exercise 10 — Technique of the cross-pollination of
plants . . . . . .• . . . . 426-428

Exercise 11 — Embryological studies from slides show-
ing cell division at different stages, chromosomes, pollen
mother cells, development of the embryo sac, etc. . 428

Exercise 12 — Study of pollen germination and
fecundation . . ... . . . . . 428

Exercise 13 — Practice in the cross-pollination of ap-
ples, pears, peaches, plums, etc. . . , . . 429
Exercise 14 — Studies of mendelian inheritance . 429-435
Exercise 15 — A study of mendelian characters in
timothy and oats ... .... . . . 435-438

Exercise 16 — Mendelian problems . . .. . 438-445

Exercise 17 — Ear-to-row test with corn . . . 445-447
Exercise 18 — Corn judging .'.... . . 447-448

Exercise 19 — Statistical study of ears of corn . . 448-449
Exercise 20 — Study of correlations of characters in
corn . . . ...... . . 449-450

Exercise 21 — Corn selection — laboratory study . 450-452
Exercise 22 — A study in potato selection . . . 452-457
Exercise 23 — Study of citrus hybrids . . . 457-458
Exercise 24 — Study of the results of the plant-to-row
tests of wheat, oats, cabbage, onions, or any crop where
data are available . . . .• , ": -. , ".'-., 458

Exercise 25— Studies of origin of varieties — corn,
wheat, apples, plums, grapes, etc. .... 458

Exercise 26 — Field trip to experimental grounds . 458-459
Exercise 27 — Working plans for practical breeding
experiments . , . ••'. . 459

LIST OF ILLUSTRATIONS

1. Variation in heads of timothy 3

2. Two seedling timothy plants, growing side by side, showing

a common kind and degree of difference ... 4

3. A productive timothy plant ....... 5

4. A timothy plant that runs much to seed . . . . 6

5. A timothy plant that runs almost wholly to leaf ... 7

6. Couch or quack grass, showing means of asexual propaga-

tion by underground root stalks 13

7. Orange hawkweed ........ 32

8. A frequency curve illustrating the distribution, of the height

of the pea plants ........ 42

9. Variations in statures of CEnothera nanella, a mutant, and

(Enothera Lamarkiana, its parent 53

10. Variations in the amount of sugar in 40,000 beets . . 64

11. Chelidonium majus ........ 55

12. Chelidonium laciniatum . . . . .56

13. Anemone coronaria, single-flowered form .... 57

14. Anemone coronaria, semi-double-flowered form ... 57

15. Anemone coronaria var. florepleno ..... 58

16. Hugo de Vries . .59

17. CEnothera Lamarkiana and (Enothera nanella in bloom . 60

18. CEnothera Lamarkiana. Curve exhibiting variations in the

length of fruits of 568 plants 61

1 9. CEnothera lata — CEnothera Lamarkiana — CEnothera nanella 63

20. A, spike with almost ripe fruits of CEnothera gigas, a mutant

species; B, the same of CEnothera Lamarkiana, its

parent form 66

21. The cage in Professor de Vries' experiment garden, showing

corn and various species of CEnothera . . . .70
xv

xvi List of Illustrations

FIGURE PAGE

22. Cupid sweet pea (photo by Beal) . . . . . .78

23. Linaria vulgaris — peloric flowers * . . . . .81

24. Linaria vulgaris peloria ....... 82

25. Antirrhinum majus ' -. .83

26. Chrysanthemum segetum plenum . . . . . . 86

27. Chrysanthemum inodorum plenissimum .... 87

28. Ancestral generations of Chrysanthemum segetum plenum . 88

29. A, Chrysanthemum segetum; B, Chrysanthemum segetum

grandiflorium (after purification) . . . . .89

30. Extreme variability in the shape of the leaves of hybrid pop-

pies. Second generation from a cross between the Bride
variety of the Opium poppy and the Oriental poppy . 96

31. Inbred corn plants, showing lessened vigor of growth

(adapted from Yearbook) .113

32 Hybrid walnut and parents . . . * » . . 117

33. A hybrid walnut (Juglans calif ornica nigra), reaching

double the height of ordinary trees . . . . 119

34. Variation in hybrid pineapples . . . v . . 123

35. Variation in hybrid squashes . . . ... .129

36. Hybrid citrange and its parents, Poncirus (citrus) trifoliata

and common sweet orange . . . . . .132

37 . Hybrid tangelo and its parents, pomelo and tangerine . . 133

38. Samson tangelo (adapted from Yearbook) . . . . 134

39. Citranges (hybrid of orange and Poncirus (citrus} trifoliata) 135

40. Teosinte and its hybrids with Indian corn . .... 137

41. Cytisus Adami '. . 143

42. Cytisus Adami . 144

43. Mendelism in maize . . . . . . . . 162

44. Diagrammatic representation of Mendel's law . . . 170

45. Hybrid carnation between a single and a burster, showing

intermediacy . . 180

46. Fowls' combs 184

47. Three generations of hybrid wheat 195

48. Mendelism in tomatoes 203

49. Pride of Georgia, a good short-staple cotton .... 213

50. Select Jones improved cotton with uniform long staple . 214
61. Improving the tomato 215

List of Illustrations xvii

52. Crop averages in corn breeding for high and for low protein.

Results of twelve generations. (111. Exp. Sta.) . . 216

53. Fruit of wild elderberry 217

54. Fruit of a cultivated variety of the elderberry which ap-

peared as a variation from the wild form . . .218

55. Field of wilt-resistant watermelons, growing free from disease

on infected land (from Yearbook) . . . .219

56. Disease resistance in cowpeas ...... 220

57. Improved types of lettuce and the varieties from which they

were developed ........ 221

58. Wild cabbage 240

59. Curled kale . . 241

60. Collard 242

61. Brussels sprouts ......... 243

62. Savoy cabbage 244

63. Cabbage shapes 245

64. Swede turnip, kohl-rabi, and cauliflower .... 248

65. Wild form of Chrysanthemum morifolium .... 249

66. Wild form of Chrysanthemum indicum .... 250

67. Pompon anemone type ........ 251

68. Single type 252

69. Type of pompon chrysanthemum 253

70. Japanese anemone type .... ... 256

71. The small and regular anemone type ..... 257

72. A pompon chrysanthemum ....... 258

73. Type of Japanese incurved chrysanthemum . . . 259

74. Japanese anemone chrysanthemum when fully expanded . 262

75. New type with short stem 263

76. Incurved type ......... 264

77. Hairy type . . . . 267

78. Japanese type 268

79. Reflexed type . 269

80. Bellflower . ......... 270

81. Flower of white lily 271

82. Flower of greenhouse cypripedium ..... 272

83. Flower of niglit-blooming cereus ...... 273

84. Flower. of the shrubby hibiscus (Hibiscus syriacus) . . 274

xviii List of Illustrations

FIGURE PAGE

85. Bugbane (Cimicifuga racemosa} . . . -.. . 275

86. Blossom of flowering raspberry (Rubus odoratus) . . 276

87. Squash flowers of each sex . . . . . . 277

88. Flowers of clematis ( Clematis virginiana) . . . . 278

89. Tobacco flowers, showing the parts of the flower, a bud

ready to be emasculated, and an emasculated subject . 282

90. Zinnia flowers • . . . ... . .283

91. Instruments used in pollinating flowers . . . . 284

92. Ladle for pollinating house tomatoes . • . . . 285

93. Bag for covering the flowers . . . . . .286

94. Fuchsias, showing the stamens and pistils, and a bud ready

to be emasculated . . . ... . . 287

95. Fuchsia flower emasculated . . •'..'. - . . . 288

96. Fuchsia flower tied up after emasculation i 289

97. Tomato and quince . . . . . . 290

98. Pollinating kit . . . ..;.'"..•'.; . . 291

99. Pollinating kit ". . . .292

100. Main building of Seed Association, offices of Swedish Com-
pany (photo by Newman) . . , 'v . . • 307

10L Gardens at Luther Burbank's . . . • • • 319

102. Some of Burbank's frames and garden beds . . . . 320

103. Spineless and spine-bearing cacti at Burbank's . . . 322

104. A specimen herbarium sheet, showing variations in the

leaves of the mulberry . . . . . . . . 395

105. A specimen herbarium sheet, showing differences between

two leaves of the horse radish . .:,....... . 396

106. A specimen herbarium sheet, showing variations in leaves

of the Persian lilac , . 398

107. A specimen herbarium sheet, showing variations in leaves

of the blackberry 400

108. A common form of ragweed . . . . . .421

109. Another form of ragweed . 422

110. Demonstration of allelomorphism and of complete dominance 431

111. Demonstration of presence and absence hypothesis and of

intermediacy . . . . . . ... 432

112. Demonstration of the presence of an inhibitor factor . . 434

113. Explanation of so-called " dominance and absence " . . 436

Ube IRural Science Series

EDITED BY L. H. BAILEY

PLANT-BREEDING

PLANT-BREEDING

CHAPTER I
THE FACT AND PHILOSOPHY OF VARIATION

THERE is no one fact connected with agriculture that
more greatly interests all persons than the existence of
numerous varieties of plants that seem to satisfy every need
of the gardener. Whence came all this multitude of
forms? What are the methods employed in securing
them? Are they merely isolated facts or phenomena
of gardening, or have they some relation to the broader
phases of the evolution of the forms of life ? These .are
some of the questions that occur to every reflective
mind when it contemplates an attractive garden, but
they are questions that seem never to be answered.
Whatever attempt the gardener may make at answer-
ing them is either obscured by an effort to define what
a variety is, or else it consists in simply reciting how a
few given varieties came to be known. But there must
be some method of arriving at a conception of the ways
whereby the varieties of fruits and flowers and other culti-
vated plants have originated. If there is no such method,
then the origination of these varieties must follow no
law, and the discussion of the whole subject is fruitless.
But we have every confidence in the consecutive uniform-
B 1

2 /:».- *: lpJn,nl.-Bieeding

ity of the operations of nature, and it were strange if
some underlying principle of the unfolding or progression
of plant-life does not dominate the origin of the varied
and innumerable varieties which, from time unknown,
have responded to the touch of the cultivator. Let us
first, therefore, make a broad survey of the subject in
a philosophical spirit, and later, discuss the more specific
instances of the origination of varieties.

The fact of individuality. — There is universal difference
in nature. No two living things are counterparts, for no
two are born alike or into exactly the same conditions and
experiences. Every living object has individuality; that
is, there is something about it that enables the acute
observer to distinguish it from all other objects, even of
the same class or species. Every plant in a row of lettuce
is different from every other plant, and the gardener,
when transplanting them, selects out, almost uncon-
sciously, some plants that please him and others that do
not. Every apple tree in an orchard of a thousand
Baldwins is unlike every other one, perhaps in size or
shape, or possibly in the vigor of growth or the kind of
fruit it bears. Persons who buy apples for export know
that fruit from certain regions stands the shipments better
than the same variety from other regions ; and if one were
to go into the orchards where these apples are grown, he
would find the owner still further refining the problem by
talking about the merits of individual trees in his orchard.
If one were to make the effort, he would find that it is
possible to distinguish differences between every two
spears of grass in a meadow, or every two heads of wheat
in a grain-field.

The Fact and Philosophy of Variation 3

In timothy, one of the commonest of our grasses, a
casual observer may find differences in the length, shape,
and color of heads; tendency of some plants to produce
asexual leaves in the head: form. of base of the head;

FIG. 1. — Variation in heads of timothy.

length, width, and color of leaves; erect or drooping
character of the leaves ; susceptibility of the leaves and
stems to rust ; period of blooming ; habit of growth of
plant, — • erect or decumbent ; few or many culms to the
plant ; ability to recover after cutting ; quantity of seed

Plant-Breeding

The Fact and Philosophy of Variation

FIG. 3. — A productive timothy plant.

produced, and others (Figs. 1-5). Similar differences
may be found in any group of plants if the group is suffi-
ciently studied.

Plant-Breeding

FIG. 4. — A timothy plant that runs much to seed.

Variation and adaptation. — All this is equivalent to
saying that plants are infinitely variable. The ultimate

The Fact and Philosophy of Variation 7

causes of all this variation are beyond the purposes of the
present discussion, but it must be evident, to the reflective
mind, that these differences are a means of adapting
the innumerable individuals to every little difference or

FIG. 5. — A timothy plant that runs almost wholly to leaf.

advantage in the environment in which they live. And
if the result of variation is better adaption to the physical
conditions of life, then the same forces must have been
present in the circumstances which determined the birth
of the individual. This change in environment may be

8 Plant-Breeding

the cause of much of the variation in plants, since differ-
ences in plants were positively injurious if it were possible
for the conditions of environment to be the same.

Species-formation. — If no two plants are anywhere
alike, then it is not strange if now and then some de-
parture, more marked than common, is named and becomes
a garden variety. We have been taught to feel that
plants are essentially stable and inelastic, and that any
departure from the type is an exception and calls for im-
mediate explanation. The fact is, however, that plants
are essentially unstable and plastic, and that variation
between the individuals must everywhere be expected.
This erroneous notion of the stability of organisms comes
of our habit of studying what we call species. We set
for ourselves a type of plant or animal, and group about it
all those individuals that are more like this type than
they are like any other, and this group we name a species.

Nowadays, the species is regarded as nothing more than a
convenient and arbitrary expression for classifying our
knowledge of the forms of life, but the older naturalists
conceived that the species is the real entity or unit in
nature, and we have not yet wholly outgrown the habit of
mind which was born of that fallacy. Nature knows
little about species ; she is concerned with the individual,
the ultimate complete and working unit. This individual
she molds and fits into the opportunities of environment,
and each individual tends to become the more unlike its
birthmates the more the environments of the various in-
dividuals are unlike.

We must consider, therefore, as a fundamental concep-
tion to the discussion of the general subject before us, the

The Fact and. Philosophy of Variation 9

importance of the individual plant, rather than the im-
portance of the species ; for thereby we put ourselves as
nearly as possible in sympathetic attitude with nature, and,
resting upon the ultimate object of her concern, we are
able to understand what may be conceived to be her motive
in working out the problem of life. Recall the fact that
the whole tendency of contemporary civilization, in soci-
ology and religion, is to deal with the individual person
and not with the mass. The present-day method of study-
ing the evolution of plants and animals is essentially an-
alytical. As the chemist attempts to discover the smallest
units from which the substances of nature have been built
up, so the student of biology and evolution is seeking for
the smallest heritable units of which plants and animals
are composed. This is only an unconscious feeling after
natural methods of solving the most complex of problems,
for it is exactly the means to which every organic thing
has been subjected from the beginning.

Conception of unit-characters. — The student of evolution
now conceives animals and plants to be composed of what
he terms " unit-characters," analogous, roughly, to the
atoms of the chemist. These are the smallest heritable
units that a plant or animal may possess. Any distinct
entity that can be traced from one generation to another,
such as the presence or absence of pubescence on the leaves
or stems, the height of the plant, whether dwarf or tall,
the color of the flower or fruits, and very many others are
now known as unit-characters. The more any group of
plants is studied, the more definite and distinct these
unit-characters become. The time may come when the
gardener, from long experience, shall become acquainted

10 Plant-Breeding

with these qualities, so that he may synthetically put
many units together by crossing and produce new varieties
almost at will.

Differences between plants and animals with regard to
general association of parts and their methods of reproduction.
- Unit-characters are nature's blocks, which she uses to
build up plants and animals into various shapes for dif-
ferent purposes. These combinations of units when
added together in proper extent and proportion consti-
tute the plant and animal as we know it, the ultimate
living and working organism, with power of growth and
reproduction.

In looking for the ultimate working unit, individuality or
personality in nature, we must make a broad distinction
between the animal and the plant. Every higher animal
is itself a working unit ; it is one. It has a more or less
definite span of life, and every part and organ contributes
a certain indispensable part to the life and personality
of the organism. No part is capable of propagating itself
independently of the sex-organs of the animal, nor is it
capable of developing sex-organs of its own. If any part
is removed, the animal is maimed and perhaps it dies.
The plant, on the contrary, has no definite or distinct
autonomy. Most plants live an indefinite existence,
dependent very closely upon the immediate conditions in
which they grow. Every part or branch of the plant lives
largely for itself, it is capable of propagating and multi-
plying itself when removed from the parent or the colony
of branches of which it is a member, and it develops sex-
organs and other individual features of its own. If any
branch is removed, the tree or plant does not necessarily

The Fact and Philosophy of Variation 11

suffer; in fact, the remaining branches usually profit
by the removal, a fact which shows that there is a competi-
tion, or struggle for existence, between the different
branches or elements of the plant. The whole theory and
practice of pruning rests upon the fact of the individual
unlikenesses of the branches ; and the unlikenesses are of
the same kind and often of the same degree as those that
exist between different plants grown from seeds.

Bud-variation and bud-varieties. — The branches of a
Crawford peach tree, for example, differ amongst them-
selves in size, shape, vigor, productiveness, and season
of maturity, much the same as any two or more separate
Crawford trees, or any number of trees of other varieties,
differ the one from the others. If any one of these
branches or buds is removed and is grown into an inde-
pendent tree, a person could not tell — if he were ignorant
of its history — whether this tree were derived from a
branch or a seed. This proves that there is no essential
unlikeness between branches and independent plants, ex-
cept the mere accident that one grows upon another branch
or plant whilst the other grows in the ground. But the
branch may be severed and grown in the ground, and the
seedling may be pulled up and grafted on the tree, and no
one can distinguish the different origins of the two. And
then, as a matter of fact, a very large proportion of our culti-
vated plants are not distinct plants at all, in the sense of
being different creations from seeds, but are simply the
result of the division of branches of one original plant or
branch. All the fruit trees of any one variety are obtained
from the dividing up and multiplication of the branches of
the first or original tree.

12 Plant-Breeding

The reader is curious to know how this original tree came
to be, and this we may find out before we are done ; but
for the present, let it be said that it is equally possible for
it to have come from a seed, or to have sprung from a
branch which some person had noticed to be very dif-
ferent from the associated branches in the tree-top. In
other words, the ultimate unit or individual of variation
is the bud and the bit of wood or tissue to which it is
attached; for every bud, like every seed, produces an
offspring that can be distinguished from every other
offspring whatsoever.

CHAPTER II
THE CAUSES OF INDIVIDUAL DIFFERENCES

WE have now gone back to the starting-point, to that
unit with which nature begins to make her initial differ-
ences or individualities ; that is, to the point where varia-
tions arise. This point is the bud and the seed, — one
sexless, or the offspring of one parent ; the other sexual,
or the offspring of two parents. Now, inasmuch as the
horticultural variety is only a well-marked variation which
the gardener has chanced to notice and to propagate, it
follows that the only logical method of determining how
garden varieties originate is to discover the means by
which plants in general vary or differ one from another.

There is probably no one fact of organic nature concern-
ing the origin of which modern philosophers are so much
divided as the causes or reasons for the beginnings of
variations or differences. It seems to be an inscrutable
problem, and it would be useless, therefore, for us to
attempt to discover these ultimate forces in the present
book. Still, we must give them sufficient thought to
enable us to satisfy our minds as to how far these variations
may be produced by man; and, in doing this, we must
discover at least the underlying philosophy of plant
variation. It is the nature of organisms to be unlike
their parents and their birthmates. Why?

13

14 Plant-Breeding

Fortuitous variation. — It will probably never be pos-
sible to refer every variation to a distinct cause, for it is
probable that some of them have no antecedent. If we
conceive of the forms of life as having been created with
characters exactly uniform from generation to generation,
then we should be led to look for a distinct occasion or
cause for every departure from the type ; but we know, as
has already been pointed out, that heredity by its very
nature is not so exact as to carry over every attribute, and
no other, of the parent to the offspring. Plasticity is a
part of the essential constitution of all organic beings.
There is perhaps no inherent tendency in organisms
towards any ultimate or predetermined completion of
forms, as the older naturalists supposed, but simply a
laxity or indefiniteness of constitution which is expressed in
numberless minor differences in individuals.

That is, some variation may be simply fortuitous, an
inevitable result of the inherent plasticity of organisms,
and it may have no immediate inciting cause.

Action of natural selection on variation. — If we were to
assume that every minor difference is the result of some
immediate cause, then we should expect every individual
plant or animal to fill some niche, to satisfy some need, to
produce the definite effect for which the cause stands.
But it is apparent to one who contemplates the operations
of nature that very many — certainly more than half — of
the organisms which are born are not useful to the per-
petuity of the species and very soon perish. From these
fortuitous variations nature selects, to be sure, many
individuals to be the parents of other generations because
they chance to be fitted to live, but this does not affect

The Causes of Individual Differences 15

the methods or reasons of their origin. It is possible that,
whilst many of these mere individual differences have no
direct and immediate cause, they may still be the result of
a devious line of antecedent causes long since so much
diffused and modified that they will remain forever un-
recognizable; but even so, the fact still remains that
these present differences or variations may be purposeless,
and it is quite as well to say that they exist because it is a
part of the organic constitution of living things that un-
like produces unlike.

Sex as a factor in the variation of plants. — All plants
have the faculty, either potential or expressed, of propagat-
ing themselves by means of buds, or asexual parts. This is
obviously the cheapest and most direct possible method
of propagation for many-membered plants, since it re-
quires no special reproductive organization and energy,
and, as only one parent is concerned in it, there is none of
the risk of failure that obtains in any mode of propaga-
tion in which two parents must find each other and form
a union. There must be some reason, therefore, for the
existence of such a costly mechanism as sex aside from
its use as a mere means of propagation.

It may be said that sex exists because it is a means of
more rapid multiplication than bud-propagation, but such
is not necessarily the fact. Many plants produce buds as
freely as they produce seeds ; and then, if mere multipli-
cation were the only destiny of the plant, bud-production
would no doubt have greatly increased to have met the
demand for new generations. The chief reason for
the existence of sex in the vegetable world seems to be the
need for a constant rejuvenation and modification of the

16 Plant-Breeding

offspring by uniting the features of two individuals into
one. There thus arises from every sexual union a number
of new or different forms from which nature may select
the best, — that is, those best fitted to live in the condi-
tions in which they chance to be placed. But whilst
sex is undoubtedly one of the most potent sources of pres-
ent unlikenesses, it is not necessarily an original cause of
individual differences, since the two parties to any sexual con-
tract must be unlike before they can produce unlike. When
once the initial unlikenesses were established, every new
sexual union must produce new combinations, so that
now, when every new form, from whatever source it
appears, comes into existence, there are other intimately
related forms with which it may cross. This state of
things has existed to a greater or less degree from the
moment sex first appeared, so that the organic world is
now endlessly varied as the result of a most complex
ancestry.

Physical environment and variation. — Every phase and
condition of physical circumstances, which are not ab-
solutely prohibitive of plant life, have plants which thrive in
them. Every soil and climate, every degree of humidity,
hills, swamps, and ponds, — every place is filled with
plants. Even the trunks and branches of trees support
other plants, as epiphytes and parasites. That is, plants
have adapted themselves to every physical environment ;
or, to turn the proposition around, every physical en-
vironment produces adaptive changes in plants. There
are those, like Weismann and his adherents, who contend,
from purely speculative reasons, that these changes do
not become hereditary or permanent until they have in-

The Causes of Individual Differences 17

fluenced a certain physiological substance which is assumed
to reside in the reproductive regions of the organisms,
and that all those changes which have not yet reached
this germ-plasm are, therefore, lost, or die with the or-
ganisms.

Do external influences produce permanent effects in
plants ? — It is not necessary to discuss here the intri-
cate arguments in the time-honored controversy of the
permanent inheritance of external modifications. Such
violent modifications as traumatic injury do not affect its
germ cells and are not inherited. But it is the common
experience of gardeners that the modifications of the envi-
ronment of plants, such as changing food supply or changing
seed from one environment to another, produce changes
which eventually become hereditary. Whether these
changes of environment act directly upon the germ-plasm
to produce the change or whether they stimulate a ger-
minal change which was otherwise latent, is a question
which long and patient experimentation must decide.
Certain it is, that plants have gone through a profound
modification and it is easy to believe that environment has
played no little part in these changes.

Weismann teaches that " acquired characters," or those
variations which first appear in the life-time of the indi-
vidual because of the influences of environment, are lost,
because they have not yet affected the reproductive sub-
stances ; but if these characters are induced by the effect
of impinging environment during two or more generations,
they may come to be so persistent that the plant cannot
throw them off, and they become, thereby, a part of the
hereditary and non-negotiable property of the species.

18 Plant-Breeding

Now, it is apparent that in one or another of the genera-
tions which are thus acted upon by the environment, there
must be a beginning towards the fixing or hereditable
permanency of the new forms, and we might as well
assume that this beginning takes place in the first genera-
tion as in the last, since there can be no proof that it does
not take place in either one. The tendency towards
fixity, if it exists at all, undoubtedly originates at the very
time that the variation itself originates, and it is only
sophistry to assume that the form appears at one time
and the tendency towards permanency at another time.
Since plants fit themselves into their circumstances by
means of adaptive variations, we must conclude that all
adaptive variations have the power of persisting, upon
occasion.

All these remarks, whilst somewhat abstruse, have a
most important bearing on the philosophy of the origin
of garden varieties, because they show, first that changes
in the conditions in which plants grow introduce modifi-
cations in the plants themselves, and second, that wher-
ever any modification occurs it is probable that it may
be fixed and perpetuated.

Natal and post-natal variations. — It is necessary at this
point that we distinguish between natal and post-natal
variations, — that is, between those variations which are
born with plants, and those which appear, as a result of
environment, after the plant has begun to grow. It is
commonly assumed that the form and general characters
of the plant are already determined in the seed, but a
moment's reflection will show that this is far from the
truth. One may sow a hundred selected peas, for example,

The Causes of Individual Differences 19

all of which may be alike in every discernible character.
If these are planted in a space of a foot apart, it will be
found, after two or three weeks, that some individuals
are outstripping the others, although all of them came up
equally well and were at first practically indistinguishable.
This means that, because of a little advantage in food or
moisture, or other circumstances, some plants have ob-
tained the mastery and are crowding out the less fortunate
ones. The theory and practice of agriculture rests on
the fact that plants can be modified greatly by the condi-
tions in which they grow, after they have become thor-
oughly established in the soil. Plants may start equal,
but differ widely at the harvest ; and this difference may
be controlled to a nicety by the cultivator. Every farmer
is confident, also, that the best results for the succeeding
year are to be got only when he selects seeds from the best
that he has been able to produce this year. So, given
uniformity or equality at the start, the operator molds
the individual plants largely at his will.

Conception of biotypes. — Most varieties are not as
uniform as would at first appear. A careful study of
plants, when growing, indicates that they are not only
modified in different degrees by environment but the plants
themselves are not the same. They have different po-
tentialities to begin with. Environment causes direct
modifications to appear ; it also allows expression in differ-
1 ent degrees of the inherent variability present. Most
varieties of plants are polytypic, being composed of many
distinct types, or " biotypes" as they have been called by
Johannsen. All this is a matter of the commonest ob-
servation with the gardener, who is so accustomed to

20 Plant-Breeding

seeing great differences arise in batches of plants, all of
which start apparently equal and with an equal chance,
that he never thinks to comment upon the occurrence.

Having noticed that physical environments may modify
plants, we are now ready to consider just what changes
in these circumstances of plant life are most fruitful in
the production of new forms.

Variation in food supply. — The greater part of the
changes in the physical conditions of life hinge upon the
relative supply of food. Climbing plants assume their
form because, by virtue of the divergence of character,
they are enabled to fit themselves into places that other
plants cannot occupy. They rear their foliage into the
air, where food and sunlight are unappropriated. The
lower branches of tree-tops die, and the others thereby
appropriate the more food and grow the faster. The
entire practice of agriculture is built upon the augmenta-
tion of the food supply. For this purpose, we set the
plants in isolated positions, we till the ground, keep down
other plants or weeds, add plant-food to the soil, and prune
the tree and thin the fruit.

Thomas Andrew Knight, the chief of horticultural
philosophers, appears to have been the first clearly to
enunciate the law that excess of food supply is the most
prolific cause of the variations of plants. Darwin sub-
scribes to it without reserve: "Of all the causes which
induce variability, excess of food, whether or not changed
in nature, is probably the most powerful." Alexander
Braun, an earlier philosophical writer on natural history,
said that "it appears rather, on the whole, as if the unusual
conditions favorable to a luxuriant state of development,

The Causes of Individual Differences 21

afforded by cultivation, awakened in the plant the inward
impulse to the display of all those variations possible
within the more or less narrowly circumscribed limits of
the species." It is generally agreed by those who have
given the matter much thought, that an excess of food
above the amount normally or habitually received is one
of the very chief, if not the most dominant, causes of in-
dividual differences in plants. Certainly every farmer
or gardener knows that the richer the soil in available
plant-food, the stronger and the more abnormal and
unusual his product will be.

If, then, excess of food supply is a strong factor in the
modification of plants, and the one fundamental aim of
agriculture is to supply food in excess of natural conditions,
it must naturally follow that cultivated plants should be,
of all others, the most variable. This is notably true.
Now, the first variation that usually comes of this liberal
food supply is increase in mere bulk. Probably every
plant which has ever been cultivated has increased its
stature or the size of some or all of its parts. Moreover,
this is generally the direct object of cultivation, — to
secure larger herbage, fruits, seeds, or flowers. Inci-
dentally, we find here an indubitable proof of the truth
of the hypothesis of evolution, for if it were impossible for
plants to vary or to assume new characters, there would be
no cultivation and no agriculture; for there would be
little object in cultivating a product if it grew equally well
in the wild.

This variation into mere bigness is more important than
it may seem at first. All thoughtful horticulturists agree
in thinking that the first thing to be done in ameliorating

22 Plant-Breeding

any plant is to " break the type," that is, to cause it to vary.
The particular direction of variation is not so important,
at first ; for all experience . has shown that if once the
seedlings of a plant begin to depart from the parental
type, other and various modifications will soon follow. If
a plant is once strongly modified in size, variations in
shape, color, flavor, or other attributes are forthcoming.
This apparent accumulation of variation seems at first to
be incapable of scientific explanation, but the reasons for
it are not difficult to understand when once they are
presented.

We now ask ourselves why these many variations appear
when once the type begins to modify itself. Consider
the fact that the world is now full of plants. In untamed
nature, but one more plant can grow unless another plant
dies. All plants, therefore, are held down to narrow limits
of numbers, and since there are so few individuals, — in
comparison with the seeds and buds which each plant
produces for the chance of multiplying itself, — there
must be, also, few kinds and degrees of individual dif-
ferences. The farther and more freely a plant distributes
itself, the greater must be the differences between various
individuals, because they must adapt themselves to a
wider range of conditions. All plants are held in equilib-
rium, so to speak ; but the plant organism is plastic by
nature and quickly responds to every touch of environ-
ment ; so, as soon as the pressure is removed in any direc-
tion, the plant at once springs into the breach. Recall
the monotonous vegetation of the deep forest, where the
battle of centuries has subdued all but the strongest.
Clear away the forest, and then observe the fierce scramble

The Causes of Individual Differences 23

for place and life amongst a multitude of forms which
spring in for an opportunity to better their conditions.
In a few years more, the tender low herbs have gone.
The briers and underbrush have usurped the land. As
time goes on, one species after another perishes, and when
the place is again reforested, two or three species hold un-
disputed sway over the land. The poplars that followed
the pines have long since perished and pines again dominate
the forest. Or, if the area were turned to pasture a few
years after the woods were removed, the herbs and bushes
die with the browsing, and in time the June-grass covers
the whole landscape with the mantle of conquest. So
plants may be said to be always ready to fill new places
in the polity of nature by adapting themselves to the new
circumstances as they grow into them. The appearance
of any one marked variation, therefore, is indication that
the plant may have found a new condition, that pressure is
somewhat lifted, and that the whole plastic organization
may soon respond to. the new environment. It is ap-
parent, then, how the simplest and rudest cultivation has
been able, through the centuries, so profoundly to modify
our domestic plants that we are often unable to recognize
the forms from which they have sprung.

Food supply of different branches. — We must not forget
to notice, at this point, that the food supply differs amongst
the various branches of the same plant. Some branches,
by reason of position with reference to the main trunk or
with reference to air and sunlight, or, because of a better
start in the beginning as a result of some incidental
advantage, gain the mastery over others and crowd
them out. We have already seen that no two branches

24 Plant-Breeding

on a plant are alike ; and we are now able to understand
that sports or bud-varieties are no more inexplicable
than seed-varieties.

What cultivation is. — Cultivation is really but an ex-
tension or intensification of nature's methods of dealing
with the plant world. The ultimate result of both nature
and man is to supply more food. The variations which
arise from the effects of mere cultivation, therefore, are in
kind very like those which nature produces, the chief
differences being that of degree. The accustomed opera-
tions of the farmer, therefore, have been powerful agents
in the evolution of vegetable forms. The ways in which
cultivation affords a more liberal food supply are as
follows : —

1. By isolating the individual plant. The husbandman
sets each plant by itself, and then protects it by destroying
the weeds or plants which endeavor to crowd it out.
There is a partial exception to this in the " sowed crops,"
like the grains, and it is noticeable that variation in these
plants is usually less marked than in the "hoed crops."

2. By giving the plant the advantage of position,
whereby it is allowed the most congenial exposure to sun
and contour of land.

3. By increasing the fertility of the land, either by tillage
or the direct application of plant-food, or both. Rich
and moist soils tend to "break" the type, — or to cause
initial variations, — to produce verdant colors and loss
of saccharine and pungent qualities, to induce redundant
growth, and to delay maturity and thereby to render
plants tender to cold winter climates.

4. By thinning the tops of plants and the fruits, whereby

The Causes of Individual Differences 25

the remaining parts receive an amount of food in excess
of the habitual allowance.

5. By divergence of character in associated plants.
It is well known that a field planted so thickly to corn
that it cannot grow more with profit, may still grow
pumpkins between. The pumpkins and the corn are so
unlike in form that they complement each other, the one
filling the place which the other is not fitted to occupy.
We have already seen that a copse ever so full of bushes
may still grow vines. A meadow full of timothy may still
grow clover in the bottom, and land covered with apple
trees still grows weeds beneath. " The more di versed the
descendants from one species become in structure, con-
stitution, and habits," writes Darwin, "by so much will
they be better enabled to seize on many and widely diver-
sified places in the polity of nature, and so be enabled to
increase in numbers."

Variation in climate. — The fact that any distinct
climatic region usually has plants that are very closely
related to those of other climatic regions in the same
zone, points strongly to the probable profound modifica-
tion of plants by climate. And, furthermore, we should
expect that if the food environment modifies plants, the
climatic environment must have the same power. More-
over, there is abundant historical and experimental proof
that climate is capable of greatly modifying the vegetable
kingdom. There are those who contradict any great effect
of climate in the variation of plants, and acclimatization
has been even stoutly denied. These persons make the
mistake of asking that a visible modification take place
at once upon the transfer of a plant from one climate to

26 Plant-Breeding

another, and they also err in supposing that a plant can
adapt itself to a cold climate only by developing a capa-
bility to withstand more cold. Indian corn is sometimes
cited as proof that plants do not become acclimatized,
for it is as tender to frost now as ever, for all that we know.
Yet this very plant affords a most unequivocal example of
complete acclimatization, because it has shortened its
period of growth fully one-half whereby it escapes the
cold of the North.

The influence on plants of a change of climate, or,
what may amount to the same thing, the result of a trans-
fer of plants to new climates, is so complex and so general
that no discussion of the subject can be made at this
time. It will answer present purposes briefly to designate
the ways in which climate modifies plants : —

1. Climate generally modifies the stature of plants.
They become dwarfer in high latitudes and altitudes.

2. It modifies form. Plants tend to be broader-headed,
and also more prostrate, in high latitudes and altitudes.

3. Proportionate leafmess generally increases, at the
same time.

4. There is also often a gain in comparative fruitful-
ness following transfer towards the poles.

5. The colors of leaves, flowers, fruits, and seeds are
greatly influenced by climate, there being a general
tendency, in plants of temperate regions, to augmentation
in intensity of colors as they are carried towards the poles.

6. There is modification in the flavor and essential
ingredients of various parts, following a change of climate.

7. There is a variation in variability itself. The more
difficult the climate in which a plant finds itself, the more

The Causes of Individual Differences 27

it tends to vary to meet the uncongenial environments.
In the high North, many plants are so variable that the
marks used to identify the species in other latitudes are
often lost.

8. There may be a profound variation or modification
in constitution and habit by which plants become ac-
climatized, or enabled to endure a climate at first injurious
to them. This may occur by a variation in the constitu- l
tion of the descendants, which enables them directly to
endure more untoward conditions. It generally comes
about, however, through a change in habit, by which
plants, when transferred towards the poles, shorten their
season of growth or even become annuals. Plants become
more sensitive to spring temperatures in cold climates,
so that they start relatively much earlier in the season —
that is, at a lower sum-temperature — than in warm
climates. Any one who has passed the springtime in both
the North and South must have noticed how much more
suddenly the vegetation comes forward in the North;
and it is surprising how the spring-sown crops accelerate
their growth in the North over those in the South.

Man's control over climate as a means of making plants
to vary. — The characters that result from a change of
climatic environment are peculiarly within the control
of the agriculturist, for a leading factor in his business
is the transfer of plants far and wide over the earth. So
it has come that the staple varieties of the important
grains and fruits are unlike in Europe and America and
in all great geographical areas, although all the various
forms may have sprung from one ancestor within historic
times. A new country is stocked with varieties from

28 Plant-Breeding

the mother country; but in the course of a few genera-
tions it is found that the varieties in cultivation are unlike
the ones originally introduced, and from which they came.
As wild plants have become separated from each other as
species in the different geographical regions, so the cul-
tivated plants soon begin to follow similar lines of diver-
gence. In the beginning of the colonization of this
country, for example, all the varieties of apples were of
European origin. But in 1817, over sixty per cent of the
apples recommended for cultivation here were of American
origin, that is American-grown seedlings from the original
stock. At present, probably fully ninety per cent of the
popular apples of the Atlantic States are American pro-
ductions. The northern states of the Mississippi Valley
to which most of our eastern apples are not adapted, are
now witnessing a similar transformation in the adaptation
and modification of the varieties introduced from the East
and from Russia. The recently introduced Japanese
plums are conceded to be great acquisitions to our fruit-
growing, but no doubt the best results are yet to come
with the origination of domestic varieties of them. So
there is an irresistible tendency towards a divergence of
forms in different continental or geographical regions,
and much of the inevitable result is no doubt chargeable
to climatic environment.

Change of seed. — We may now pause for a moment to
consider two agencies or phenomena often associated with
the genesis of varieties. One of these is the fact that
the simple change of seed from one locality to another
usually gives a larger or better product or even more
marked variation. Mere transfer of seed is not of itself,

The Causes of Individual Differences 29

however, a cause of variation. The change is beneficial
because it fits together characters and environments that
are not in equilibrium with each other. A plant grown
for several years in one set of conditions becomes fitted
to them, so to speak, and it is in a state of comparative
rest. When the plant or its progeny is taken to other
conditions, all the adjustments are broken up, and in
the refitting to the new circumstances new or strange
characters are likely to appear. We shall leave this sub-
ject for the present, expecting to give it a fuller treatment
in a later chapter.

Bud-variation. — Bud-variation, or sport, is a name
given to those branches which are so much unlike the
normal plant in any particular that they attract atten-
tion. Many garden varieties are simply multiplications
of such abnormal branches. This bud-variation is com-
monly held to be such an unusual and inexplicable phenom-
enon that it is considered apart from all the general
discussions of variation. It is not, of course, a cause of
variability, but only an effect of some antecedent, the
same as seed-variation is. We have already seen that all
the different branches, or even nodes of any plant are,
in a very important sense, distinct individuals, since
every one develops its own organs, each is capable of
reproducing itself independently, and each is unlike every
other because it is acted upon differently by environment
and food supply. It is not strange, therefore, that some
of these individuals should now and then depart very
widely from the ordinary type, and thereby attract the
attention of the gardener, who would forthwith make
cuttings or set grafts from the part. Every branch is a

30 Plant-Breeding

bud-variety, just as truly as every seedling is a seed-
variety, — since no seedling is ever like its parent, — and
there should be no greater mystery connected with the
sports of buds than there is with the varieties from seeds,
for the causes that produce the one may be and probably
are equally competent to produce the other (Figs. 6, 7).

Struggle for life a cause of variation. — We have seen
that the world is full of plants. There is room for more
only as the present individuals die. Yet nearly every
species produces a great number of seeds, and makes a
most strenuous effort to multiply its kind. Any one
plant, if left to itself, is capable of covering the earth in
a comparatively short time. A fierce struggle for a chance
to live is therefore inevitable. This conflict is most
apparent to the general observer in the springtime, when
every "herb yielding seed after his kind, and the tree
yielding fruit, whose seed was in itself, after his kind," are
sending forth a host of sturdy offspring. The very land
seems to be pregnant with weeds and aspiring young
growths. But by midsummer the numbers may be
less. The weaker and less fortunate ones have perished,
and the victors have waxed stronger thereby. The
annual and half of the biennial species complete their
course upon the approach of winter, and the older peren-
nial herbs are becoming weak; so in the succeeding
springtime there is again a fierce combat for the vacant
places.

One of the results of this conflict is the adjustment of
plants to each other. We have seen how the climbing
plant insinuates itself amongst the shrubberies and ties
them together in an impenetrable tangle in order that

The Causes of Individual Differences 31

FIG. 6. — Couch-grass or quack-grass. Showing means of sexual propa-
gation by seed and a sexual propagation by underground rootstocks.
(After Clark and Fletcher.)

it, itself, may have a chance to live. So the low plants
of the deep forest are such as have been plastic enough to

32

Plant-Breeding

FIG. 7. — Orange hawkweed. This plant can withstand the struggle for
existence. It produces immense quantities of seed and also repro-
duces itself by underground rootstocks. (After Clark and Fletcher.)

adapt themselves to the damp shades. Thus plants have
developed companionships or divergences in character,

The Causes of Individual Differences 33

by means of which, under the stress of circumstances,
they are able to live together. Plants have adapted
themselves to other plants as truly as to soil or climate ;
and if these latter environments are ever the sources or
causes of variation, then the first must be also. We must
look upon the struggle for existence, therefore, as itself
a cause of individual differences, since we know that any
continued pressure from without awakens an adaptive
response in the form of the vegetable organisms.

CHAPTER III
THE CHOICE AND FIXATION OF VARIATIONS

WE have now seen that every living object is unlike
every other. In plants, even every branch is unlike any
other branch. We have endeavored to discover some of
these universal differences. We have found that they
are intimately associated with the welfare of the type or
species, inasmuch as they appear, for the most part,
to be the means of fitting the plant to live in the conditions
in which it is placed. But we have also seen that there
are more individuals than can find a place to live. How,
then, does nature choose the best from the poorest (or,
rather, the fit from the unfit), and, having chosen them,
how does she endeavor to fix them or to make them more
or less stable ?

"This preservation of favorable individual differences
and variations, and the destruction of those which are
injurious, I have called Natural Selection or the Survival
of the Fittest." This is the philosophy which was pro-
pounded by Darwin, and which will carry his name to the
last generation of men. It looks simple enough. Those
forms which are best fitted to live, do live, because they
crowd out the others. Yet, this simple principle of
natural selection was the first explanation of the process
of evolution that seemed to be capable of interpreting

34

The Choice and Fixation of Variations 35

the complex phenomena of the forms of organic life. For
a time, this philosophy was thought to be the one funda-
mental motive of the evolution or progression of life, but
we are n6w convinced that there are other motives or forces
at work; but it seems to be indisputable that natural
selection is a major force underlying the evolution of
plants, and it is the only one with which the person who
desires to breed plants need intimately concern himself.

We must now determine what a variety is. This is a
vexed question, and one which seems never to be capable
of an answer that is satisfactory to the gardener. Time
and again, some person has introduced what he considered
to be a distinct new variety, only to find that other horticul-
turists dispute him and declare that it is only some old
variety renamed. And yet the introducer knows that
he has not renamed an old variety, but that he has propa-
gated a form which appeared or originated on his own
grounds.

What is a variety? — Now, let us see. Nature starts
out with the individual to make a new form. Every in-
dividual is unlike every other one. When the individual
differences are so well marked that we can readily de-
scribe and distinguish them, and so permanent that they
pass down nearly intact to a few generations, we say that
we have a variety. If the differences are still more
marked, we say that we have a species. Where the
variety ends and the species begins it may be utterly
impossible to determine ; and so we mark off at a certain
point and say, arbitrarily, that this much is variety and
that much is species. Asa Gray once said that " species
are judgments." Now, if there is no hard and fast line

36 Plant-Breeding

between the variety and the species, so there is none
between the individual and the variety ; for a variety is
only the family of descendants from some one individual.
That is, the idea of variety or species rests on difference,
but just how much difference shall constitute one grade
or another is a matter of individual opinion. There is
no standardized practice. So, when two gardeners cannot
agree as to whether a given introduction is a new variety
or not, they are having the same kind of difficulty that two
botanists have when they cannot decide whether two plants
are two species or one.

It is apparent, then, that every individual plant is
a distinct variety, only that the differences between it and
other individuals may be so slight that they have no
practical utility and cannot be described and recorded.
Just as soon as an individual plant has characters so un-
like its kin that it has some commercial value, then the
plant will be increased by cuttings or grafts or seeds,
the brood of offspring will be given a name, and a new
variety is born.

Individuals with the same general features may appear
simultaneously in two or more places, and two or more
men may propagate, name, and introduce them. When
they are all brought together and compared, it will be said
that they are all the same variety, that, according to the
rules of nomenclature, the brood which chanced to be
named first must " stand" or be held to be the type of the
variety and the other names must become synonyms.
Yet some persons may discover minor differences in them
and demand that the variety be kept distinct. So the
see-saw goes on — a variety is a variety so long as it an-

The Choice and Fixation of Variations 37

swers some purpose in use or trade, and it is not a variety
when it is so much like some other variety that it has no
merit that the other does not possess.

As soon as a plant appears with some features which
are more desirable than anything that has preceded it,
therefore, it may be the beginning of a new variety. Man
chooses it, and then propagates it. This is human selec-
tion. If nature did the same thing, it would be natural
selection.

It must not be understood that there are no definite
species hi nature. Some plants are so distinct, and so
constant in their characters, as to leave no doubt. But
wide variability is very common, and it may obscure the
relationship.

Adaptation in nature. — Now, how does nature preserve
or fix this type ? She does not preserve it. She simply
chooses it as a beginning and gradually modifies it and
shapes it into the form which she needs. She has no
permanent forms. There is a general onward progression
of one type either towards other types or towards ex-
tinction. We have seen that nature is constantly choosing
and selecting. If she selects an individual for the be-
ginning of a race, then she selects just as keenly from every
offspring of that individual, and so on to the end of time.
The process never stops. So nature fixes her forms by
keeping them moving, growing, constantly developing
farther away from their beginnings.

The vexed question as to whether there is an accumula-
tive effect in variation, need not be considered here, as it
is foreign to the particular point of view at this place.

Artificial selection. — Now, man does the same thing.

38 Plant-Breeding

A plant in a cabbage row pleases him. It has a solid
small head and stout stem. He stores it away for seed.
Amongst the offspring, perhaps fifty per cent are as good
as the parent. These are saved. So the process goes
on, from season to season. In four or five generations
of plants, he finds that ninety per cent of the seeds "come
true." Then he names it and introduces it. It is well
advertised in the seed catalogues. Many persons buy the
seeds. Some of these persons will grow their own seeds,
and every one of them has a different ideal in mind when
selecting the seed parents. So, in the course of a few
years it is found that there are really several more or less
different forms under the same name. Some persons may
observe this difference and legitimately introduce one or
more of the forms as distinct varieties. Some other
person, however, who has known the history of the stock
and who is not aware that varieties pass into other forms,
objects to the new names and declares that the introducer
is imposing on the public.

This is the history of ninety out of every hundred
varieties which are habitually propagated by seeds, like
the kitchen-garden vegetables and the annual flowers.
Some peculiar individual, appearing we know not why, is
discovered, and seeds are saved and selection — perhaps
unconscious selection — begins. After a time the variety
is broken up into several, or else, if it varies only slightly,
into divergent forms, the whole body or generations of
the variety move onward, gradually departing from the
initial type until it is no longer the same, although it
may bear the same name. The life of seed varieties, in
their pure and original forms, is very short. Even the

The Choice and Fixation of Variations 39

best of them are usually measured by a score of years or
less. They run out or pass out by variation, into other
forms. The Trophy tomato is not the Trophy tomato
which was introduced over forty years ago, although it bears
the old name and is a direct descendant of the first stock.

Bud selection. — In plants multiplied by buds — that is,
by budding, grafting, cuttings, tubers, and the like —
there is less variation in the offspring than in those prop-
agated by seeds. Yet we have seen that no two Baldwin
apple trees — all of which are but divisions, more or less
remote, of the same original tree — are alike, and now
and then one branch of a fruit tree may " sport " or develop
a strange bud-variety. We know, also, that the same
variety of fruit tree takes on different characters in
different geographical regions, so that the Greening apple
is no longer the Greening of Rhode Island in the West
and South. So, it is apparent that even when we divide
a plant into many parts and distribute the members far
and wide, and when there is no occasion for concerning
ourselves with fixing the type, — even here there is
variation. In some cases, particularly in those in which
we multiply the plant by dividing abnormally developed
parts, there is a tendency to scatter or to vary in many
directions, and also a tendency to run out by degeneration.
This is admirably true of the potato, varieties of which,
in ten years or less, become so mixed in their characters,
through rapid variation and deterioration, that we must
return to seedling productions for a new start.

Variation and selection not entirely within man's con-
trol. — Man is only rarely the direct means of originating
variations. He finds them among the normal plants of

40 Plant-Breeding

the fields and gardens. His skill and science are exercised
in the selection and so-called breeding of the offspring,
more than in the original genesis of the new form. It is
usually only in those plants which he multiplies by simple
division that he gains much immediate profit by crossing
or hybridizing. It is the slow and patient care and selec-
tion, day by day, which permanently ameliorates and
improves the vegetable world. Nature starts the work;
man may complete it.

It is now generally held that species in nature some-
times originate suddenly, by means of " leaps." In fact,
the de Vriesian view is that real species so originate,
and the steps whereby a few species come into existence
are called mutations. (See Chapter V.) However this
may be, it is nevertheless true that these mutations are
yet beyond the power of man directly to produce. Selec-
tion is t still a powerful agent with which to ameliorate
domestic plants.

CHAPTER IV
THE MEASUREMENT OF VARIATION

IT is often desirable to describe a plant or a group of
plants in exact mathematical terms. Most of the plant
characters with which a breeder deals are measurable,
and an individual plant may be described as having so
many leaves, so many grains, and so on throughout a
long list of measurements ; or a group of plants may be
expressed in the form of averages ; likewise, the degree
of resemblance or difference between plants and their
offspring, or among plants of a certain group or " popula-
tion. " The degree or extent of correlation or association
of plant characters may also be expressed mathematically.

The science of biometry. — The expression of variation
and heredity by means of statistical methods is known as
the science of Biometry. This method of description is
now being widely employed by experimental plant-breeders.
It is another tool which the breeder uses to record his
progress and describe his plants. The biometrician
should be cautioned to keep his use of mathematical
treatment subservient to the biological facts, not forgetting
that biometry is simply a means toward an end and not
an end in itself. It is better first of all to become ac-
quainted with the real plants before any mathematical
treatment of their variability is attempted. It is often

41

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42

The Measurement of Variation 43

desirable, however, to treat plants in groups by means of
statistical generalizations.

Type. — In the study of any group of plants, called a
" population, " whether it be corn, wheat, the ray-florets
of daisies, or what not, the breeder has in mind a certain
type around which the individuals tend to center.

The corn breeder has in mind a certain length of an ear
of corn which is his ideal type. He chooses ears of this
length and plants them in his plat, and at harvest time
what does he get ? Not all ears of this length, but ears
ranging above and below this length. The offspring will
be distributed, in all probability, above and below this
parental type and may possibly reach the upper and lower
limits of the race. There will be a group near the average
which will contain a larger number of individuals than
any other and thus we have another conception of type.
There is the ideal parental type which the breeder has in
mind, and another type, probably different, shown by the
offspring. To find the latter, the ears of corn are' care-
fully measured and their average length determined.
This average constitutes a concrete mathematical expres-
sion for the type of the offspring.

Biometrical expression of variability. — The amount and
range of variability may also be well expressed statistically.

As an illustration, a number of pea plants were measured
and their height was found to range from 5 to 30J inches.
A few were short and a few were tall, but most of the plants
were of average height. For the sake of convenience, the
plants having similar measurements were placed together
in one class. When all the results had been brought
together they appeared as in the following table : —

44 Plant-Breeding

TTwTnwT TXT Tie™™ NUMBER OF INDIVID-

UALS IN EACH CLASS (/)

5.1- 6.5 1

6.6- 8 4

8.1- 9.5 6

9.6-11 29

11.1-12.5 30

12.6-14 37

14.1-15.5 39

15.6-17 43

17.1-18.5 34

18.6-20 26

20.1-21.5 18

21.6-23 8

23.1-24.5 5

24.6-26 2

26.1-27.5 2

27.6-29 1

29.1-30.5 _1

286

Here we have what is called a "frequency distribution,"
representing the crop as it falls into the different groups.

The curve in Fig. 8, known as the "Quetelet curve,"
represents the results graphically.

The frequencies, that is, the number of times each
measurement appears (see column / in the table), are
plotted on the axis of ordinates, line A-C, and the classes
on the axis of abscissas, line C-B. For the purpose of
plotting and working the data the mid-class is used, that
is, 5.8 inches instead of 5.1-6.6 inches, and so forth.

Mode. — We see by inspection of the foregoing data
that there is one group of the most common height, that is, (
there are more plants having a height of 15.6 to 17 inches
(16.3) than any other class.

The group containing the greatest number of plants,

The Measurement of Variation 45

that is, of the greatest frequency, is called the mode.
It is an excellent expression of type. When the group of
plants or population which is being studied is measured
and arranged with some suitable grouping, as illustrated
here, we see what the variety tends to do on the whole.

Modal coefficient. — It is desirable to know what per-
centage of the individuals falls into this group of highest
frequency, called the mode. This can be readily found by
dividing the number of individuals in this class (43) by
the total number (286) and multiplying by 100. This is
called the modal coefficient, and denotes the percentage of
individuals conforming to type. This modal coefficient is
.15 or 15%; that is, fifteen per cent of all of the plants
in this variety are found in one class.

However, as this is dependent on the system of measure-
ment, one modal coefficient is not directly comparable
with another unless the same practice of measurement has
been used. Moreover, one could not compare the modal
coefficient of height directly with that of weight or any
other character of a different nature.

It may readily be seen that a knowledge of the distribu-
tion of plants as represented by the mode or modal coeffi-
cient is of scientific and practical importance. It enables
the breeder at any time to spread out before himself a
fair representation of his variety. He can see at a glance
what is the prevailing type and in what direction and to
what degree his breeding is extending.

Mean. — There is another conception of type known
as the mean or average. One can understand that the
average height will differ in most cases from the
commonest height. The mean is most easily obtained by

46

Plant-Breeding

multiplying the mid-value of each class, say 5.8, by the
number in that class, adding their products, and dividing
by the total number of individuals. This is expressed

by the formula M (mean) = * where V represents the

n

variables, / the frequency of each variable, n the total
number of individuals, and 2 the summation of fV.

MEAN. —

F

/

fV

5.8

1

5.8

7.3

4

29.2

8.8

6

52.8

10.3

29

298.7

11.8

30

354.0

13.3

37

492.1

14.8

39

577.2

16.3

43

700.9

17.8

34

605.2

19.3

26

501.8

20.8

18

374.4

22.3

8

178.4

23.8

5

119.0

25.3

2

50.6

26.8

2

53.6

28.3

1

28.3

29.8

1

29.8

n = 286

2 = 4451.8

Mean,

445L8
286

Use of mean. — The mean gives a good average value
of the character and is often more useful than the mode
in expressing type. The breeder must use his judgment

The Measurement of Variation 47

as to which should be used in each case, the mean or the
mode.

Mathematical expression of variability. — After the
average or mean of any group of plants has been deter-
mined, it is desirable to know the amount of deviation of
the different individuals from the mean. This determina-
tion gives a concrete expression which is an index of the
amount of variability exhibited. This variability is ex-
pressed as the average deviation or the standard deviation.
The latter is ordinarily employed by mathematicians.

Average deviation. — The average deviation is deter-
mined by obtaining, first of all, the amount which each
class varies from the mean and multiplying each deviation
by the number of individuals concerned. For example,
the column D is obtained by finding the difference between
the mean, 15.5, and the variations in column V : thus
in the first case the difference between 5.8 and 15.5 is — 9.7
while farther down column V we find 16.3, which is greater
than the mean, giving us a value of 0.8 in column D.

Now, if there were the same number of individuals in
each class, the average deviation could be found by adding
up the deviations in column D, and dividing by the total
number of individuals in column /, but there is one indi-
vidual deviating - 9.7 while there are 43 deviating 0.8
and 18 deviating 5.3, and so forth. In order to overcome
this the deviations are multiplied by the number of in-
dividuals giving the column /D. The sum of this column
divided by the total number of individuals gives the
average deviation. This is an index of variability.
The average deviation is expressed by the following
formula : —

48

Plant-Breeding

Average deviation =

Standard deviation. — The operations for finding the
standard deviation are the same as for the average devia-
tion except that the deviations in column D are squared
before multiplying by the frequency numbers (/), thus
giving the columns D2 and D2f respectively. The sum
of the latter divided by the total number of individuals
and the square root of the result extracted gives the
standard deviation. This can be expressed by the follow-
ing formula : — ^ r\if

The details of determining the average and standard
deviation are as follows : —

V

/

D

/£>

Z>2

D*f

5.8

1

- 9.7

9.70

94.09

94.09

7.3

4

- 8.2

32.80

67.24

268.96

8.8

6

- 6.7

40.20

44.89

269.34

10.3

29

- 5.2

150.80

27.04

784.16

11.8

30

- 3.7

111.00

13.69

410.70

13.3

37

- 2.2

81.40

4.84

179.08

14.8

39

- 0.7

27.30

0.49

19.11

16.3

43

0.8

34.40

0.64

28.12

17.8

34

2.3

78.20

5.29

179.86

19.3

26

3.8

98.80

14.44

375.44

20.8

18

5.3

95.40

28.09

505.62

22.3

8

6.8

54.40

46.24

369.92

23.8

5

8.3

41.50

68.89

551.12

25.3

2

9.8

19.60

96.04

192.08

26.8

2

11.3

22.60

127.69

255.38

28.3

1

12.8

12.80

163.84

163.84

29.8

1

14.3

14.30

204.49

204.49

n=286

925.20

5 = 4851.31

The Measurement of Variation 49

nor on

Average deviation = = 3.24 inches.

Standard deviation, (<r) = /485L31 = 4.1+ in.

Coefficient of variability. — The average deviation or
standard deviation as outlined above is always determined
in the denomination of the unit in which the plant is
measured ; if it is height of plant in inches, the deviation
will be in inches and so forth. This prohibits the careful
comparison of the deviations of different plants or parts
of a plant because some deviations may be in pounds
or others in inches, and hence they will not be directly
comparable.

It is desirable, therefore, to have an abstract expression
so that the relative amount of variability of one class of
organs may be directly compared with the variability of
another. This is called the coefficient of variability. It is
found by dividing the standard deviation by the mean.
Thus an abstract number is found which expresses the
variability. In our case the standard deviation = 4.1
inches and the mean =15.5 inches, so that

.264 = 26.4 % = the coefficient of variability.

15.5

If the coefficient of variability of the weight of the plants
had to be determined and was found to be, say, .384, it
would follow at once that the height of the plant was
considerably more variable than the weight.

The coefficient of variability may be expressed as
follows : —

50 Plant-Breeding

• / = F*IOO.

Probable error.1 — It is obvious that these mathematical
expressions of type and variability will be modified some-
what by the number of individuals measured. The
greater the number of individuals employed, the less the
error. These differences which arise from the fewness
of individuals employed is known as the probable error.
It is expressed by a pair of divergences (=t E), the one
above and the other below the actual value found, and
indicates that the chances are even that the true value
lies somewhere between the value found plus the error
and the value minus the error. .For example, the probable
error of the mean in the problem here cited is =•= .016 and
is found by the formula given below. This means that

1 Formulae for probable errors : —

E mean = ± .6745 standard deviation

number of individuals

E standard deviation = * .6745 standard deviation - _

V2 X number of individuals

E coefficient of variability = ± .6745 coefficient of variability

v 2 X number of individuals

C

= ± .6745 7=
V2n

But when C is greater than 10% use the formula

The Measurement of Variation 51

the true mean is probably somewhere between 15.5 -f .016
and 15.5 - .016 or 'between 15.516 and 15.484. The size
of the error is generally indicative of the number of the
individuals employed and the general dependability of the
work.

Use of statistical methods. — The use of statistical
methods enables the breeder to express quite accurately
the amount of variability which would otherwise be
expressed with considerable difficulty. It enables him
also to keep an accurate record of his work from year to
year and affords him a convenient method of comparing
one year's crop with another.

It will be seen later that statistical methods may also be
employed to express correlation and extent of inherit-
ance.

CHAPTER V
MUTATIONS

THERE is endless dissimilarity in nature. No two
plants and no two animals are exactly alike. There are
more plants and animals than can find a place in which
to live and thrive. There results a struggle for existence.
Those animals or plants which, by virtue of the individual
differences or peculiarities, are best fitted to the condi-
tions in which they are placed, survive in this struggle
for existence. They are " selected to live." Those that
survive, propagate their peculiarities. By virtue of
continued variation, and of continued selection along a
certain line, the peculiarities may become augmented;
finally the gulf of separation from the parental stem
becomes great, and what we call a new species has origi-
nated.

Evolutionary theories of Darwin and de Vries. — This,
in epitome, is the philosophy of Darwin in respect to evolu-
tion of organic forms. It contains the well-known postu-
late of natural selection, the principle that we know as
Darwinism. This principle has had more adherents
than any other hypothesis of the process of evolution.
All recent hypotheses in some way relate to it. A number
of them modify it, and some dispute it. The most pro-
nounced counter-hypothesis is also the newest. It is that

52

Mutations

53

of Professor de Vries, botanist, of Amsterdam, Holland,
who denies that natural selection is competent to produce
species, or that organic ascent is the product of small
differences gradually enlarging into great ones. According
to de Vries' view, species-characters arise suddenly, or
all at once, and they are ordinarily stable from the moment
they arise.

-15 16-20 20-25 26-80

70-75 75-SO 80-Si 8i-90 00-95 05- !l

FIG. 9. — Variations in statures of (Enothera nanella (left), a mutant,
and (Enothera Lamarkiana (right), its parent. (Enothera nanella :
Range, 7-35 cm. ; M., 22.81 =±= 1.02 cm. ; <r, 7.26 ± 0.72 cm. ; C. V.,
31.84 ±3. 16 per cent. (Enothera Lamarkiana: Range, 77-96 cm. ;
M., 88.68 =«= 0.55 cm. ; v, 4.76 ± 0.39 cm. ; C. V. 5.37 =•= 0.44 per
cent.

De Vries conceives that variations, or differences, are of
two general categories : (1) Variations proper, or small,
fluctuating, unstable differences peculiar to the individual
(only partially transmitted to offspring) ; and (2) muta-
tions, or differences that are usually of marked character,
appear suddenly and without transition to other forms
and are at once the starting-points of new species or races.
Variations proper may be due to the immediate environ-

54

Plant-Breeding

ment in which the plant lives. The mutations arise from
causes yet unknown, although these causes are considered
to be physiological. Probably many so-called mutations
are hybrids and hence not mutations in the strictest
sense.

Differences between fluctuating variations and mutations : —

1. Fluctuating variations are very common and are
to be found in all plants and animals. Mutations occur
intermediately and are rare.

2. Fluctuating variations are thought not to be trans-

mitted. Muta-
tions are trans-
mitted.

3. Fluctuating
variations pre-
sent a series of
differences which
may be plotted
on a frequency
curve and obey
the laws of
chance. Muta-
tions or saltatory
variations do not
obey the laws of
chance, and can-
not be plotted in
the form of a
frequency curve.

4. Fluctuating variations do not lead to a new perma-
nent mean of the race. Mutations cause a new mean to be

its « Its 13 OS

16 16.5 17 125

FIG. 10. — Variations in the amount
in 40,000 beets.

of sugar

Mutations

55

formed, around which is grouped a new series of fluctuating
variations, forming a frequency curve. (See Fig. 9.)

5. In a fluctuating variation no new unit characters are
added. The same char-
acters are merely found

in greater or less quan-
tity or number (Fig. 10) .
Where a mutation oc-
curs, new unit charac-
ters are added or old
ones lost.

6. Fluctuating vari-
ations represent indi-
viduals or parts of them.
Mutations represent
groups of individuals.

In fluctuating vari-
ations, the small differ-
ences are grouped
around what may be
called a " center of fluc-
tuation," which is the

„ . „ FIG. 11. — Chelidonium majus.

mean of the frequency

curve. When a mutation is formed, a new center of

fluctuation is established around a new mean.

History of mutation. — The first mutation was recorded
in 1590. In the garden of Sprenger, an apothecary of
Heidelberg, was found a peculiar form of Chelidonium
majus. The new form appeared suddenly and without
intermediates from a lot of plants which had been culti-
vated for many years. This mutant had " leaves cut into

56

Plant-Breeding

narrow lobes with almost linear tips, and the petals were
also cut up." The new species has been constant since
the first, and follows Mendel's law when crossed with

C. majus, its par-
ent. (See Figs.
11 and 12.)

The word
"mutation" was
first used in 1650
by Dr. Thomas
Browne, in his
book "Pseudo-
doxia Epidem-
ic a. ' ' Lock
quotes from
Book VI, Chap-
ter X, "Of the
Blackness of Ne-
groes," as fol-
lows : —

"We may say
that men become
black in the same
manner that
some foxes, squir-
rels, lions, first turned of this complexion, whereof there
are a constant sort in diverse countries; that crows
became pyed, all which mutations, however, they began,
depend upon durable foundations and such as may con-
tinue forever."

History of the appearance of double flowers. — Double

FIG. 12. — Chelidonium laciniatum. A flower of
it to the left. Below a flower of C. majus.

Mutations

57

flowers which have persisted for a long time are thought to
be mutations from single types. Some of the first re-
corded appearances of double flowers were described in
1671 by Abraham Hunting in a
book called, "Waare Oeffeninge
der Planten" or "True Exercises
wjth Plants." This large book
on garden plants contained a
long list of double flowers which

FIG. 13. — Anemone coro-
naria, single-flowered
form.

FIG. 14. — Anemone coronaria, semi-
double-flowered form.

were found growing in gardens at that time. Double
flowers of such plants as poppies, liver-leaf (hepatica),
wallflowers (cheiranthus) , violets, caltha, althea, colchium,
and periwinkle (vinca), were described.

58

Plant-Breeding

Other double forms have since been added. The double
marigold (Chrysanthemum indicum) came from Japan;
double zinnias from Mexico ; and double dahlias which
were first produced in Belgium in 1814, are examples.

The garden anemone (Anemone coronaria) is said to
have been first found double in an English nursery in
the first half of the last century. . One flower with a single

broadened stamen was
observed by William-
son, owner of the nurs-
ery. The seed from this
was saved separately
and planted the next
year. After a few gen-
erations of selection of
this kind, the double
flowers appeared as mu-
tations and bred true to
type (Figs. 13-15).

The origin of the
double petunia dates
back to the year 1855,
when it suddenly arose from ordinary seed in a garden
at Lyons. Carriere reported that from this one plant
all double races and varieties of petunias have been
derived by natural and partly by artificial crosses, and
he added that likewise other species were known at that
time to produce new double varieties rapidly.

Geoffroy St. Hilaire, about 1825, expressed his belief
in saltatory variations as a means of evolution. He
thought that evolution does not take place entirely by

FIG. 15. — Anemone coronaria, var. flore-
pleno. (Full double.)

Mutations

59

the slow changes advocated by Lamark. His ideas were
theoretical, however, and at that time were not borne out
by experimental evidence.

Darwin recognized the appearance of sudden variations
of a marked character, such as is seen in the origin of
large-crested Polish fowls and short-legged Ancon sheep.
He thought that these new and strange forms would be
lost soon by intercrossing and, being rare, that they pos-
sessed no value. He held that the slow accumulation
of minute fluctuating variations was the important factor
in evolution.

De Vries' experiment with cenotheras. — De Vries became
convinced long ago that Darwin's theory of the origin
of species through ac-
cumulation of minute
changes was not the only
means of creating new
types. He determined
to produce mutations ex-
perimentally, if possible.
His results in the forma-
tion of a new variety of
the corn marigold will be
described later. After
making preliminary ex-
periments with some
hundred species, de Vries

finally decided upon (Enothera Lamarkiana as the most
suitable form to use (Figs. 17 and 18). "Only one of my
tests met with expectations. This species proved to be
in a state of mutation, producing new elementary forms

FIG. 16. — Hugo de Vries.

60 Plant-Breeding

continually, and it soon became the chief member of my
experimental garden. It was one of the evening prim-
roses." This (E. Lamarkiana was found to produce a
large number of mutants, both when growing wild and
under cultivation.

The (E. Lamarkiana plants which became the basis of

FIG. 17. — (Enothera Lamarkiana and (Enothera nanella in bloom.

future experiments were found growing wild in a field at
Hilversum, near Amsterdam, Holland. Little is known
of its history except that it is a native of America. It has
not been found growing wild in America in recent years,
although there seems to be evidence that it was seen and
collected in the Southern States in the last century. The
near relatives of (E. muricata, which were very common in
the sandy regions of Holland, are very stable ; de Vries

Mutations

61

found no appreciable change in them, although he watched
them for more than forty years.

Lamark's evening-primrose is grown in Europe as a cul-
tivated plant, used principally for ornamental planting.
It seeds abundantly and some of the plants have escaped
cultivation. Groups of plants are found growing wild
in many places. These wild plants remain in groups
rather than being widely scattered, suggesting a definite

\

\

FIG. 18. — (Enothera Lamarkiana. Curve exhibiting variations in the
length of fruits of 568 plants. The dotted line is that given by
Quetelet-Galton Law.

origin for each group. CE. Lamarkiana is described as a
"stately plant with a stout stem, attaining often a height
of 1.6 meters and more. When not crowded, the main
stem is surrounded by a large circle of smaller branches,
growing upwards from its base so as often to form a dense
bush. These branches in their turn have numerous
lateral branches. Most of them are crowded with flowers
in summer, which regularly succeed each other, leaving
behind them long spikes of young fruits. The flowers are

62 Plant-Breeding

large and of a bright yellow color, attracting immediate
attention, even at a distance. They open towards
evening, as the name indicates, and are pollinated by
bumble-bees and moths. On bright days their duration
is confined to one evening, but during cloudy weather they
may still be found open on the following morning. Con-
'trary to their congeners, they are dependent on visiting
insects for pollination.

" In CE. Lamarkiana no self-fertilization takes place.
The stigmas are above the anthers in the bud, and as the
style increases in length at the time of the opening of
the corolla, they are elevated above the anthers and do
not receive the pollen. Ordinarily the flowers remained
sterile if not visited by insects or pollinated by myself,
although rare instances of self-fertilization were seen."

(E. Lamarkiana is a biennial, producing rosettes in
the first year and stems in the second year. This species
was found to be variable in all periods of its life cycle, —
in the seedlings, the rosettes, and the stems.

De Vries pursued three methods in obtaining his muta-
tions :—

1. Observations and studies of the plants while growing
in the wild state in the fields.

2. Some of the plants were removed from the wild state
and placed under cultivation. Many of the plants were
self -fertilized and their seed sown under controlled con-
ditions. By this method several mutants were found
which were too weak to withstand the competition of field
conditions.

3. Repetition of the sowing process for several genera-
tions, leading to the production of new forms.

Mutations

63

De Vries divided the new types of plants into five groups,
classified as follows : —

1. Retrograde varieties with 'negative attributes,
(E. Icevifolia, (E. brevistylis, and (E. nanella (Figs. 17
and 19).

FIG. 19. — (Enothera lata (left), (Enothera Lamarkiana (middle),
(Enothera nanella (right).

2. Progressive elementary species possessing new
characters, and appearing as vigorous as the parent plant,
(E. gigas and (E. rubrinervis.

64 Plant-Breeding

3. Progressive elementary species, which are weaker
than the parent species, (E. albida and (E. oblonga.

4. Organically incomplete forms, (E. lota (Fig. 19).

5. Fertile but inconstant species forms, (E. scintillans
and (E. elliptica.

The new species and varieties may be described as
follows : —

Group I, retrograde varieties, which have lost some
of the characters possessed by the parent, (E. Lamarkiana : —

(E. Icevifolia is easily distinguished from its parent,
(E. Lamarkiana, by having smooth, bright leaves, without
undulations. These leaves are narrower and more slender
than in Lamarkiana and the flowers of the brighter yellow.
This variety was constant from seed, showing no reversion.
It is a strong-growing plant and perfectly fertile.

(E. brevistylis is a short-styled form. The ovary of
this plant is abnormally situated and is not conducive to
proper fertilization. The ovary is reached by only a few
pollen tubes and fertilization must be incomplete. The
few seeds that are obtained reproduce this type without
reversion to Lamarkiana. (E. brevistylis may be dis-
tinguished from the other forms before blossoming as
the buds are much shorter and thicker than in the other
species. The presence of leaves more rounded at the
tip also distinguishes this form from others before
flowering.

(E. nanella is a dwarf form, attaining often only one-
fourth the height of the other types. The flowers on this
dwarf form are as large as upon Lamarkiana, which is a
striking feature. The size of the leaves is proportionate
to the height of the plant, but retain the same form as the

Mutations 65

parent species. The stems are unbranched and very
brittle. CE. nanella is frequently produced as a mutation
and is absolutely constant (Figs. 17 and 19).

Group II, progressive elementary species, possessing new
characters : —

CE. gigas is a giant form which is much larger in every
respect than its parent, except in height. The stems are
much larger ; internodes are shorter and the leaves more
numerous than the parent species (CE. Lamarkiana).
The flower-buds are large and closely crowded on the
spike, and when the flowers open, they make a beautiful
appearance (Fig. 20) .

CE. rubrinervis is characterized by the red veins and red
streaks on the fruits. This plant is as tall as CE. gigas,
but a little more slender. A feature of this type is the
brittleness of the leaves and stems, especially in the annual
individuals, of which many are found.

Many of these mutants may be recognized before the
adult stage has been reached, for example, at about the
age of two months. The leaves of CE. gigas are broad, of a
deep green, the blade sharply cut off from the stalk, all
of the rosettes becoming stout and crowded with leaves.
In CE. rubrinervis, on the contrary, the leaves are thin,
of a paler green, and with a silvery white surface; the
blades are in the form of an ellipse, acute at the apex,
and gradually narrowing into the petiole.

Both of these species are quite constant and do not
revert to CE. Lamarkiana. However, other mutants have
sprung from these two species, especially from rubrinervis,
which is produced in greater numbers from Lamarkiana
than is gigas.
F

FIG. 20. — A, spike with almost ripe fruits of (Enothera gigas, a mutant
species ; B, the same of (Enothera Lamarkiana, its parent form.

ae

Mutations 67

Group III, progressive elementary species which make a
very weak growth : —

(E. albida has whitish, narrow leaves, apparently in-
capable of producing sufficient quantities of organic food,
and hence are very 'weak. These plants are not suffi-
ciently robust to withstand competition in the field and
require transplanting into rich soil in pots in order to
allow them to live through the first year so that they
can produce seed the second year. When these seeds
are planted they produce individuals true to type.

(E. oblonga is a small plant about half the size of Lamark-
iana and may be grown either as an" annual or as a bien-
nial. It is characterized by its narrow leaves, which are
fleshy and of a bright green color. Another striking
feature of this type is the presence of numerous little
capsules covering the axis of the spike after the fading
away of the petals. (E. oblonga is very constant if grown
from pure seed.

The forms already described are relatively very con-
stant and never revert to the parent form. Contrasted
with these constant forms, de Vries found several incon-
stant types as follows : — •

Group IV, organically incomplete types : —

(E. lata is characterized by the fact that only pistillate
flowers are formed. The anthers seem to be robust,
but they are dry, wrinkled, and nearly devoid of contents.
It is a low plant with very dense and luxuriant, but brittle,
foliage. It has bright yellow flowers which open only
partially and remain wrinkled throughout the flowering
time. (E. lata may be recognized by its seedlings, which
have leaves of a nearly orbicular shape and are very

68 Plant-Breeding

sharply set off against the stalk. The mature ' plant
has broad sinuate leaves with rounded tips, which are
often crowded together on the summits of the stems and
branches to form rosettes. (E. lata may be considered
a true mutation, and when crossed with (E. Lamarkiana,
the progeny of the second generation segregates into
mendelian proportions, lata being recessive (Fig. 19).
Group V, perfectly fertile but inconstant species : —
(E. scintillans is characterized by the production of
deep green leaves with smooth, shiny surfaces, "glisten-
ing in the sunshine." The plants are smaller and less
branched than the parental type. (E. scintillans is a
very inconstant form ; from the seeds which are produced
in great numbers, there results not only scintillans, but
Lamarkiana, oblonga, lata, and nanella, with a predomi-
nance of the parental Lamarkiana. In regard to its in-
stability, de Vries says, "The instability seems to be a
constant quality, although the words themselves are at
first sight contradictory. I mean to convey the con-
ception that the degree of instability remains unchanged
during the successive generations."

(E. elliptica is a very rare form both in the wild state
and in cultivation. It is characterized by having narrow
elliptical leaves and elliptical petals.

ANALYTICAL TABLE OF SEEDLINGS (After de Vries)

I. Leaves stalked.

A. Leaves of the same breadth or

broader.1

1. Of the same breadth and shape,
not to be distinguished as

1 " (than in Lamarkiana) " as also in the other analytical tables.

Mutations

69

1. (E. Lamarkiana.

2. (E. brevistylis.

3. (E. leptocarpa.

2. Broader, pointed, with many

crumples. 4. (E. gigas.

3. Broader, rounded at the tip

with very deep crumples,
edge incurved.

b.

5. (E. lata.

6. (E. semilata.

B. Leaves narrower.

1. Broadest in the middle.

a. Very long with long stalks,

with narrow veins, almost
smooth.

b. Small with broad leaf- stalk

and broad, principal veins,
very smooth, shiny dark
green.

2. Of equal breadth over the

7. (E. elliptica.

8. (E. scintillans.

greater part of their length.

a. Green.

a. 1. Only slightly nar-
rower, smooth with-
out, or almost with-
out crumples. 9. (E. Icevijolia.

a. 2. Very narrow with

broad leaf-stalks
and broad veins
which often are red-
dish; wrinkled. 10. (E. oblonga.

b. Whitish.

b. 1. Crumples many,

pointed, narrowing
off into the stalk. 11. (E. albida.
b. 2. Crumples few, nar-
rowing off into the
stalk, wavy, brittle,
veins reddish. 12. (E. rubrinervis.

70

Plant-Breeding

Mutations 71

b. 3. Crumples few,
scarcely narrowing
into the stalk,
almost grasslike. 13. CE. sublinearis.

II. Leaves sessile, short and broad,

almost heart-shaped, crumpled. 14. CE. nandla.

How the mutants were produced in the garden. — Most
of the types previously described were found growing
wild near their parent species, CE. Lamarkiana.

De Vries wished to determine whether these mutations
could be produced from seed of (E. Lamarkiana planted in
the garden (Fig. 21). Four series of experiments were
performed, lasting through five to nine generations in
which thousands of individuals were grown and studied.
A description is here given of one of these experiments.1
The others were very similar. The pedigree culture foegan
in 1886, when seed was planted in the garden from
nine plants found growing wild. These nine plants
constituted the first generation. The second generation
flowered in 1889. This generation consisted of fifteen
thousand seedlings of which ten were distinct mutations
— five la ta and five nandla. There were no intermediates.

The third generation of ten thousand plants produced for
the first time in pedigree cultures a plant of CE. rubrinervis,
along with three plants of CE. lata and three of CE. nandla.

The fourth generation of fourteen thousand plants
yielded a higher percentage of mutants. These were
as follows : oblonga 176 ; lata 73 ; nandla 60 ; albida 15 ;
rubrinervis 8 ; scintillans 1 ; and gigas 1 .

1 De Vries, "Species and Variation, their Origin by Mutation," pp.
549-575.

72

Plant-Breeding

At this stage of the experiment, de Vries became expert
in detecting variations at an early period. This accounts
in part for the large number of mutants found in the
fourth generation. By being able to pick out the mutat-
ing forms at an early age, a much larger number of the
diverging types could be obtained in proportion to the
total number of individuals.

De Vries gives the following table which represents
graphically the results from eight generations of a mutating
strain of (E. Lamarkiana : —

MUTATING STRAINS OF (E. LAMARKIANA

GENERA-
TIONS

GlQAS

ALBIDA

OB-

LONGA

RUBRI-

NERVI8

LAMARK-
IANA

NA-

NELLA

LATA

SCINTIL-
LANS

I

II

15000

5

5

III

1

10000

3

3

IV

1

15

176

8

14000

60

73

1

V

25

136

20

8000

49

112

6

VI

11

29

3

1800

9

5

1

VII

9

3000

11

VIII

5

1

1700

21

1

De Vries' laws of mutability of the evening-primroses. —
de Vries deduced certain laws from the mutations in these
(Enotheras. " Obviously," he says, "they apply not only
to our evening-primroses, but may be expected to be of
general validity."

These laws are as follows : —

1. New elementary species appear suddenly, without
intermediate steps.

Mutations 73

The ordinary conception had been that new types of
plants had been produced by the slow and gradual piling
up of small fluctuating variations. The experience with
the primroses shows that new types are formed in much
less time than it would take by the accumulation of small
variations. It is remarkable that so many different new
types of forms should have been produced from the same
parent and with no intermediates appearing. When
(E. lata, which is a pistillate form, was crossed with
(E. Lamarkiana, the progeny of the second generation
segregated in mendelian proportion to the pure types of
the parents, with no intermediates. This same absence
of intermediacy is found when the progeny of the in-
constant forms return each year to the parent species,
Lamarkiana.

2. New forms spring laterally from the main stem.

This conception of the origin of new forms differs
markedly from the Darwinian idea which assumes that
species are slowly converted into others in the same
direction and in the same degree.

In such plants as draba or helianthemum, from which
mutations have been known to arise, no center or "main
stem" of mutation would have been known if it had not
been seen to occur in pedigree-cultures. For instance,
if gigas, rubrinervis, and Lamarkiana had been found
growing side by side in equal numbers in the wild state,
it would have been impossible to tell which type had
been the center of fluctuation. Many years of crossing,
together with some vicinism which would probably have
followed, would have- been necessary to determine this.
De Vries says, "According to the current belief the con-

74 Plant-Breeding

version of a group of plants growing in any locality and
flowering simultaneously would be restricted to one type.
In my own experiments several new species arose from
the parental form at once, giving a wide range of new forms
at the same time and under same conditions."

3. New elementary species attain their full constancy
at once.

" Constancy is not the result of selection or of improve-
ment. It is a quality of its own. It can neither be
constrained by selection, if it is absent from the beginning,
nor does it need any natural or artificial aid if it is present."

No atavism was exhibited by the primrose mutations
with the exceptions of (E. sdntillans and (E. elliptica.
These latter types reproduce themselves only in part in
the offspring. De Vries says that the instability in these
types seems to be as permanent a quality as the stability
of the other forms.

4. Some of the new strains are evidently elementary
species, while others are to be considered as retrograde
varieties.

Such new forms as (E. gigas, rubrinervis, oblonga, and
albida may be called new elementary species. They are
not differentiated from Lamarkiana by one or two main
features, but they differ from it in nearly all organs, and
hence may be considered new elementary species. The
differences exist, not only in the foliage where they are
most manifest, but in the stems, flowers, seeds, and in-
deed, in many instances, to the minutest cell structure.

(E. Icevifolia, (E. brevistylis, and (E. nanella, on the
other hand, may be considered as retrograde varieties.
They seem to differ from the parental form in but one

Mutations 75

character; Icevifolia is characterized by the loss of the
crinkling of the leaves ; brevistylis, by the partial loss of
the pistil ; and nanella, by the loss of stature.

5. The new species are produced in a large number of
individuals.

It will be remembered that there were produced a
large number of similar mutants in the same year, and
also that the same mutations were produced in successive
generations.

There is obviously some cause for the production of
these mutations. Whatever the exciting cause may be,
the different mutants are not affected in the same way.
Oblonga, nanella, and lata are frequently produced, while
gigas, rubrinervis, and scintillans are more rare. It has
been found through later studies by Gates, Davis, Shull,
and others that some of the types formerly thought by
de Vries and others to be mutations are hybrids.

It was found also that when the mutants were crossed
together, types were found in the progeny which were
the same as produced by (E. Lamarkiana itself. For
example, (E. rubrinervis was observed by de Vries
to arise in the hybrid progeny of (E. lata x nanella;
(E. lata x brevistylis; (E. nanella X brevistylis; and (E.
scintillans x nanella.

In nature, repeated mutations are probably of far more
importance than isolated ones. The competition of
plants is so great that the chances of the survival of one
divergent individual are much less than as if these mutants
were repeatedly produced in considerable quantity.

6. Mutability is distinct from fluctuating variability.
The foregoing evidence points to the fact that new

76 Plant-Breeding

forms are produced from quick sudden leaps. The new
type is formed regardless of fluctuating variability, but
the new form becomes a center of fluctuating variability
similar to that around the parental form.

7. The mutations take place in nearly all directions.

De Vries says, "Some of my new types are stouter and
others weaker than their parents, as shown by gigas and
albida. Some have broader leaves and some narrower
(lata and oblonga). Some have larger flowers (gigas) or
deeper yellow ones (rubrinervis) or smaller blossoms
(scintillans) or of a paler hue (albida). In some the
capsules are longer (rubrinervis) or thicker (gigas) or
more rounded (lata) or small (oblonga) or nearly destitute
of seeds (brevistylis) . The unevenness of the surface of
the leaves may increase as in lata or decrease as in Icevi-
folia. The tendency to become annual prevails in ru-
brinervis, but gigas tends to become biennial. Some are
rich in pollen, while scintillans is poor. Some have large
seeds, others small. Lata has become pistillate, while
brevistylis has nearly lost the faculty to produce seeds.
Some undescribed forms were quite sterile, and some I
observed which produced no flowers at all."

Examples of mutations. Shirley poppy. — Lock cites 1
the Shirley poppy as a mutation from the wild field poppy
(Papaver Rhoeas) so common in England. It was first
noticed in 1880 by the Rev. W. Wilks, Vicar of Shirley,
near Croydon, England, in a patch of the wild forms
growing in a waste corner of his garden. There suddenly
appeared a solitary flower showing a very narrow border

1 " Recent Progress in the Study of Variation, Heredity, and Evolu-
tion," p. 133.

Mutations 77

of white. The seeds from this plant were saved and
sown the next year. From this progeny of two hundred
plants, four or five individuals appeared which showed
the same diverging characteristics.

"From these, by further horticultural processes, the
strain of Shirley poppies originated." Lock remarks,
in passing, that if the original plant had been self-pol-
linated, a much larger proportion of the new type might
have been expected to appear hi the next generation.

Cupid sweet pea. — Another example of a mutation is
found in the case of the Cupid sweet pea (Fig. 22) . Until
about fifteen years ago the only sweet peas known were
the tall, climbing sorts, which grew to a height of
three to six feet, depending on the richness of the soil.
At this time, there was found in the seed trial grounds of
Morse & Company of California, a small dwarf sweet
pea plant only about six or eight inches high. This was
growing in a row of the Emily Henderson variety, one of
the ordinary tall sorts from which it evidently sprang.
Seed of this dwarf plant was saved and grown and it was
found to reproduce plants of the same dwarf character.
The variety was designated "The Cupid," under which
name it was introduced to the seed trade and distributed
over the world. The Cupid differed from other sweet
peas not only in height, but in its closely set leaves and
general habit of growth. Indeed, it is as distinct from
other sweet peas as are distinct species of plants in
nature.

It has been found that this dwarf Cupid sweet pea
mendelized with the tall ordinary sorts and appears as
recessive.

78

Plant-Breeding

FIG. 22. — Cupid sweet peas. (Photo by Beal.)

Mutations 79

Frequency of occurrence of mutations. — In general, it
may be said that the occurrence of mutations is rare.1

In order to obtain a clear understanding of this subject,
it may be divided into four sections : —

1. Spontaneous occurrence of new varieties in the wild
state.

2. Spontaneous occurrence of new species in the wild
state.

3. Spontaneous occurrence of new varieties under
cultivation.

4. Spontaneous occurrence of new species under
cultivation.

The term "variety" as here used carries the meaning
given by de Vries, — that of a group of plants differing
from others in one systematic character.

Spontaneous occurrence of new varieties in the wild
state.2 — New varieties of plants are seen to occur rather
rarely in the wild state. This may be due to two causes :
(1) A lack of critical examination of wild plants for such
spontaneous mutation; and (2) if these mutations do
occur, they are likely to meet premature death because
of the severe competition to which all wild forms are
subjected.

As our wild plants are being studied more critically,
it is being found that they do produce a much larger
number of new varieties than was formerly supposed.

In the case of the peloric toad-flax, which has been
studied carefully by de Vries, the mutations are so numer-

1 De Vries, p. 191.

2 De Vries, " Species and Varieties, their Origin by Mutation,"
chapter on the Origin of Wild Species and Varieties, p. 576.

80 Plant-Breeding

ous that they seem to be quite regular. The peloric
type is known to have originated from the ordinary type
at different times and in different countries, under more
or less divergent conditions.

White varieties of many species of bluebells, gentians,
and nearly all of the berry-bearing species in the large
heather family are quite common. The same is true of
the white flowers of Brunella vulgaris, Ononis repens, and
Thymus vulgaris.

Spontaneous occurrence of new elementary species in the
wild state. — It will be. remembered that new elementary
species of the CEnothera were found to occur in the wild
state before any attempt was made to study them under
cultivation. It is difficult to say how frequently these
mutations occurred in the wild because unquestionably
most of them were destroyed prematurely, from the com-
petition of other plants.

The occurrence of new elementary species in the wild
state seems to be much more rare than the occurrence of
new varieties. This is natural, for, of course, elementary
species present greater differences from the parental
forms than do varieties.

The spontaneous origin of the new elementary species,
Capsella Heegeri, in 1897, has never been observed to have
been repeated since that time.1 This new form of shep-
herd's purse originated in the market-place near Landau,
in Germany.

Spontaneous occurrence of new elementary species and
varieties under cultivation. — Whenever new forms occur
spontaneously under cultivation, it should first be deter-

1 De Vries, " Species and Varieties, their Origin by Mutation," p. 582.

Mutations

81

mined whether they are the product of pure lines or not.
If they come from pure lines, in all probability they are
mutations ; if not, the new forms may be a result of hybridi-
zation, which may have taken place immediately preced-
ing the appearance of the anomaly or at a considerable
time previous to its appearance.

New varieties and elementary species are seen to occur
more often under cultivation for three reasons : —

1. When new forms do occur, they are more likely to be
seen.

2. Because of the relative lack of competition and hence
a better opportunity for preservation.

3. The transfer of plants from the wild to the cultivated
state has a tendency to break the type and cause spon-
taneous new forms to ap-
pear. For this reason,

we may expect a more
frequent occurrence of
mutations under culti-
vation.

It is commonly ob-
served among gardeners
that so-called " sports"
are of very common oc-
currence. Some of these
are monstrosities which
are not inherited, but
many of them are mu-
tations and are inherited
true to type. The occurrence of double-flowered types
as mutations is common.

B

FIG. 23. — A, B, Linaria vulgaris; C,
D, peloric flowers.

82

Plant-Breeding

FIG. 24. — Linaria vulgaris peloria. A richly branched stem of a plant
of the second generation. Raised in 1898 from seed of the first
generation of 1897, and photographed in August, 1900. All flowers
are peloric.

Mutations

83

Many mutations among cultivated plants are the result
of continued selection for a period of years. This selection
assists in breaking the type and thus permits the mutation
to occur, and after the mutation has appeared, constant
selection is not necessary to keep the new variety pure.

It has been stated that the peloric type of toad-flax
is of frequent occurrence in the wild state (Figs. 23 and
24). De Vries found its appearance even more common
under cultivation than when growing wild. He planted
the' seed of two toad-flax plants, one of which contained
a single peloric flower. Eighteen hundred plants were
obtained, of which seventeen, or nearly one per cent,
were wholly peloric.

The snapdragon (Antirrhinum majus) is also known to
produce peloric flowers from time to time as mutations
(Fig. 25). Pelorics occur sometimes in Linaria dalmatica
and other species of Linaria; in fox-glove (Digitalis pur-

FIG. 25. — Antirrhinum majus: A, peloric flower from the middle of an
otherwise normal raceme ; B, normal flower of the same spike.

84 Plant-Breeding

purea), and in gloxinia. Many other instances of peloric
flowers are on record, which indicates that pelorism as a
mutation is frequent.

Experimental study of the origin of mutations. — De Vries
has conducted a series of experiments for the purpose of
observing the origin of mutations, if any should occur.
One of the plants chosen for these studies was the peloric
toad-flax (Linaria vulgaris peloria). The most accurate
laboratory methods were applied. The plants were
carefully isolated }n his garden.

The reason for this choice of the peloric toad-flax lay
in the fact that this form is known to have originated
from the ordinary type at different times and in different
countries under more or less divergent conditions. The
ordinary toad-flax bears exceedingly unsymmetrical
flowers. (See Fig. 23, A.) But symmetrical flowers are
not uncommon in such plants as the toad-flax and snap-
dragon, which have similar types of flowers. In these
experiments, de Vries sought to observe the birth of this
anomaly in his pedigree cultures.

The experiments were begun in 1886 with normal
plants ; a few peloric flowers were produced, however,
which is not an uncommon occurrence among plants of
this genus. Throughout the next few generations,
nothing more than the normal number of peloric flowers
were produced.

In the third generation, among the many thousands of
flowers there occurred one having five spurs. This was
inbred by hand and produced a considerable quantity of
seed. All other seed was discarded and this plant now
became the parent of all future plants.

Mutations 85

The next (fourth) generation contained about twenty
plants having only one peloric flower among them. The
plant bearing this flower, and one other plant, were saved
and all others discarded. These two were bred together
and produced a considerable quantity of seed.

In the next year (1894) fifty plants were in flower.
Eleven of these were found to bear the normal number
of peloric flowers. In addition to these eleven, there was
found one plant which bore peloric flowers only. This
was a mutation. Its appearance had been observed. It
was found to breed true in future generations.

In regard to the production of this mutation, de Vries
says, "Here we have the first experimental mutation of
a normal into a peloric race. The facts were clear and
simple : First, the ancestry was known for over a period
of four generations. This ancestry was quite constant
as to the peloric peculiarity remaining true to the wild
type as it occurs everywhere in any country and showing
in no respect any tendency to the production of a new
variety.

" Second, the mutation took place at once. It was a
sudden leap from the normal plants with very rare peloric
flowers to a type exclusively peloric. The parents them-
selves had borne thousands of flowers during two sum-
mers, and these were inspected nearly every day in the
hope of finding some peloric and of saving their seed
separately. Only one such flower was seen. There was
no visible preparation for this sudden leap.

"This leap, on the other hand, was full and complete.
No reminiscence of the former condition remained. Not
a single flower on the mutated plant reverted to the

86

Plant-Breeding

previous type. The whole plant departed absolutely
from the old type of its progenitors."

What is true of the toad-flax is also true of the snap-
dragon and other unsymmetrical flowers — the production
of peloric flowers by mutation.

FIG. 26. — Chrysanthemum segetum plenum. One of the six inflorescences
which in 1899 first exhibited true " doubling." The figure represents
the parent plant of the " double " variety.

Experiments in the production of double flowers (Figs. 26-
29) . — De Vries performed a series of experiments with the
corn marigold (Chrysanthemum segetum) with the object
of the production of double flowers. This plant has never
been known to produce double flowers. The cultivated
variety (grandiflorum) was found to be more stable and
was used as a basis of the experiments. This cultivated

Mutations

87

form has on the average twenty-one petals on each flower.
In the population of the next generation there appeared
one plant having twenty-one petals, but on one of its
secondary heads twenty-two petals were found. This
had never been observed before. This plant was the

FIG. 27. — Chrysanthemum inodorum plenissimum : A, inflorescence with
central disk of tube florets (fertile) ; B, with scattered tongue florets
in the disk (half fertile) ; C, highest degree of " doubling " (sterile).

beginning of what developed later into the desired muta-
tion.

This plant produced the next year (1897) plants having
thirty-four rays to the head. Next year (1898) this was
increased to forty-eight ; next year (1899) to sixty-six.

88

Plant-Breeding

During this time the means of the different generations
were gradually increasing. So far there was observed a

12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 99102

1897.

1898.

AJL

4?-

1900.

AAAAA

12 15 18 21 24 27 30 33 36 39 42 4S 48 SI 54 5? 60 63 66 69 72 75 78 81 84 87 90 93 96 99 102

FIG. 28. — Ancestral generations of Chrysanthemum segetum plenum.
Curves of the number of rays in the terminal inflorescence in the
several individuals of the generations of 1897—1900.

rapid increase in number of petals, but no indication of
doubling.

But this character soon appeared; three secondary
heads on one plant in the fall of 1899 showed a few ray-

Mutations

89

florets scattered over the disk. An indication of the
mutation was now seen.

The next year, 1900, the highest number of rays arose
to one hundred, and reached two hundred in 1901. These

21 22 23 24 25 26 27 28

B

FIG. 29. — A, Chrysanthemum segetum; B, Chrysanthemum segetum
grandiflorum (after purification). Curves of the races after isolation :
A, curve of the 13-rayed race in 1894 ; B, curve of the 21 -rayed race
in 1897. The ordinates give the number of individuals with like num-
ber of ray-florets in the primary inflorescences of the individual plants.
The number of ray-florets themselves is given below the abscissa.

heads were completely double and the mutation had ap-
peared, not quite as suddenly, perhaps, as with toad-
flax, but nevertheless as surely. The new race was per-
manent and constant.

Complete doubleness caused sterility, so that the race
had to be perpetuated from slightly inferior stock.

Here, again, was the origin of a new mutation produced
in control cultures by careful laboratory methods.

90 Plant-Breeding

What do new characters come from ? — If mutations are
the result of the appearance of new characters or the loss
of old ones, where do these new characters come from
and what causes the loss of existing ones? The answer
to this question would give us the keynote to the whole
situation. If breeders possessed definite knowledge of
the cause of mutations, they would then have within
their control a kind of variation which could be made
of tremendous economic importance. The causes are
evidently from an internal origin. In all probability,
many so-called mutations are due to hybrid origin and
in the strictest sense are not mutations at all, even though
they may be bred true. Much experimental evidence
is necessary to determine with certainty their cause and
control.

Can mutations be produced artificially ? — Must breeders
passively wait for mutations to arise, or may they be
produced artificially? Many experiments are now being
conducted to test this. So far, experiments do not seem
to have led to any definite conclusion.

Economic significance of mutations. — Agricultural and
horticultural literature is full of accounts of the sudden
origin, or at least the sudden finding, of exceptionally good
plants which, when propagated, became the progenitors
of new and valued races. So great is their number that
not even an attempt to catalogue them can be made here.

The pages of " Evolution of our Native Fruits" (Bailey)
are filled with examples of mutation. The experience of
plant-breeders and nurserymen show the origin of many
varieties in this way.

Many observing growers of cereals and other plants

Mutations 91

have originated varieties by finding occasionally unusually
good plants and propagating from them. These excep-
tional plants seem to bear no relationship to the others
among which they are growing. Hybrid origin may
account for certain of them and mutations for the others.
Many of our well-known races of wheat have originated
in this way. The Fultz wheat, which is a very popular
and excellent race grown extensively in the Eastern States,
was found in 1862 in a field of Lancaster Red by Mr.
Abraham Fultz of Pennsylvania. Some beautiful heads
of smoother wheat attracted his attention and they were
saved and the seeds planted by themselves. These pro-
duced the wheat later named the Fultz. The Tappa-
hannock wheat, which, in 1872, was considered to be a
valuable race, was found in 1854 by a Mr. Boughton, of
Essex County, Virginia. The account of its discovery
as given in the Report of the Department of Agriculture
for 1872 is as follows : "He noticed in his field a bunch
of wheat of such growth as to attract his attention. . . .
At harvest he found it to be a white wheat, at least two
weeks earlier than the surrounding red wheat." Gold
Coin Wheat, a seedling sport, differing from the hybrid
Mediterranean in being bald and white, was found by
Ira W. Green, of New York, in a field of that race and
improved by selection. In the next five years the type
was fixed and increased in yield about ten per cent. The
American races, Wheatland Red, Pride Butte, and the
well-known English races, Hopetown and Cavalier, were
other accidental seedling races.

CHAPTER VI

THE PHILOSOPHY OF THE CROSSING OF
PLANTS, CONSIDERED IN REFERENCE TO
THEIR IMPROVEMENT UNDER CULTIVA-
TION

IT is now understood that the specific forms or groups
of plants have been determined largely by the survival
of the fittest in a long and severe struggle for existence.
The proof that this struggle everywhere exists becomes
evident on a moment's reflection. We know that all
organisms are eminently variable. In fact, no two plants
or animals in the world are exactly alike. We also know
that a very few of the whole number of seeds which are
produced in any area ever grow into plants. If all the
seeds produced by the elms upon Boston Common in
any" fruitful year were to grow into trees, the city would
become a forest as a result. If all the seeds of the rarest
orchids in our woods were to grow, in a few generations
of plants even our farms would be. overrun. If all the
rabbits which are born were to reach old age, and all
their offspring were to do the same, in less than ten years
every vestige of herbage would be swept from the country,
and our farms would become barren.
"The struggle for life. — There is, then, a wonderful

92

Hybridization 93

latent potency in these species ; but the same may be said
of every species of plant and animal, even of man himself.
If one species of plant would overrun and usurp the land,
if it increased to the fullest extent of its possibilities,
what would be the result if each of the two thousand and
sixty-one plants known to inhabit Middlesex County
were to do the same ? And then fancy the result if each
of the animals from rabbits and mice to frogs and leeches
were to increase without check! The plagues of Egypt
would be insignificant in the comparison!

Survival of the most fit. — The fact is, the world is not
big enough to hold the possible first offspring of the
plants and animals at this moment living upon it.
Struggle for existence, then, is inevitable, and it must
be severe. It follows as a necessity that those seeds
grow or those plants live which are the best fitted to
grow and live, or which are fortunate enough to find a
congenial foothold. It would never appear, at first
thought, that much depends on the accident of falling
into a congenial place, or one unoccupied by other plants
or animals; but, inasmuch as scores of plants are con-
tending for every unoccupied place, it follows that every-
where only the fittest can germinate or grow. In the
greater number of cases, plants grow in a certain place
because they are better fitted to grow there, to hold
their own, than any other plants are; and the instances
are rare in which a plant is so fortunate as to find an un-
occupied place. We are likely to think that plants chance
to grow where we find them, but the chance is determined
by law, and, therefore, is not chance.

Flexibility as an aid to survival. — Much of the capa-

94 Plant-Breeding

bility of a plant to persist under all this struggle depends,
therefore, upon how much it varies ; for the more it varies,
the more likely it is to find places of least struggle. It
grows under various conditions, in the sun and shade,
in sand and clay, by the sea-shore or upon the hills, in
the humidity of the forest, or the aridity of the plain.
In some directions it very likely finds less struggle than
in others, and in these directions it may expand itself,
multiply, and gradually die out in other directions ; so it
happens that it tends to take on new forms or to undergo
an evolution. In the meantime, all the intermediate
forms, which are at best only indifferently adapted to
their conditions, tend to disappear. In other words,
gaps appear that we call "missing links." The weak
links break and fall away, and what was once a chain
becomes a series of rings. So the " missing links" are
amongst the best proofs of evolution.

Causes of variability. — The question now arises as to
the cause of these numerous variations in animals and
plants. Why are no two individuals in nature exactly
alike? The question is exceedingly difficult to answer.
It was once said that plants vary because it is their nature
to vary ; that variation is a necessary function, as much
as growth or fructification. This really removes the ques-
tion beyond the reach of philosophy ; and direct observa-
tion leads us to think that some variation, at least, is
due to external circumstances. We are now looking for
the cause of variation as a part of the scheme of evolu-
tion ; and we are wondering whether the varied surround-
ings, or, as Darwin puts it, " changed conditions of life," may
not actually induce variability. This conclusion would

Hybridization 95

seem to follow from the fact of the severe and universal
struggle in nature whereby plants are constantly forced
into new and strange conditions. But there is un-
doubtedly much variation which has sprung from more
remote causes, one of which it is our purpose to discuss
here.

In the lowest plants and animals — which are merely
single cells — the species multiplies by means of simple
division or budding. One individual, of itself, becomes
two, and the two are therefore recasts of the one. But,
as organisms multiplied and conditions became more
complex, that is, as struggle increased, there came a
differentiation in the parts of the individual, so that one
cell or one cluster of cells performed one labor and other
cells performed other labor; and this tendency resulted
in the development of organs. Simple division, there-
fore, might no longer reproduce the whole complex in-
dividual ; and, as all organs are necessary to the existence
of life, the organism may die if it is divided.

Origin and function of sex. — Along with this specializa-
tion came the differentiation into sex; and sex clearly
has two offices : to hand over the complex organization
of the parent to the offspring and also to unite the essen-
tial characters or tendencies of two beings into one. The
second office is manifestly the greater, for, as it unites
two organisms into one, it insures that the offspring is
somewhat unlike either parent, and is therefore better
fitted to seize upon any place or condition new to its
kind. And as the generations increase, the tendency to
variation in the offspring may be constantly greater be-
cause of the impressions of the greater number of ancestors

96

Plant-Breeding

transmitted to it. We have said that this office of sex to
induce variation is more important than the mere fact of
reproduction of a complex organization ; for it must be
borne in mind that the complexity of organization is
itself a variation and adaptation made necessary by the
increasing struggle for existence.

FIG. 30. — Extreme variability in the shape of the leaves of hybrid
poppies. Second generation from a cross between the Bride variety

r^rvlTlm Tvrf-ir-vr-vtr o-r»rl -fVio O-nion-fol r-i/-kr\-r\tr

puppies. oecuiiu gtmerauou irum a cross ut;
of the Opium poppy and the Oriental poppy,

If, therefore, the philosophy of sex is to promote variation
by the union of different individuals, it must follow that
the greatest variation must come from parents consider-
ably unlike each other in their minor characters (Fig. 30) .
Thus it comes that in-breeding tends to weaken a type
and cross-breeding tends to strengthen it. At this point
we meet that particular subject that we wish to discuss.

Hybridization 97

This preliminary discussion has been introduced because
we can understand crossing only as we make it a part of
the general philosophy of nature. There are the vaguest
notions concerning the possibilities of crossing, some of
which may be corrected by presenting the subject in its
relations to the general aspects of the vegetable world.

Effects of crossing on the species. — We are now pre-
pared to understand that crossing is good for the species,
because it constantly revitalizes offspring with the strong-
est traits of the parents, and ever presents new com-
binations that enable the individuals to stand a better
chance of securing a place in the polity of nature. The
further discussions of the subject are such as have to do
with the extent to which crossing is possible and advisable,
and the general results of the operation.

The limits of crossing. — If crossing is good for the
species, which philosophy and direct experiment abun-
dantly show, it is necessary at once to find out to what
extent it can be carried. Does the good increase in pro-
portion as the cross becomes more violent or as the parents
are more and more unlike ? Or do we soon find a limit
beyond which it is not profitable or even possible to go ?
If great variability is good for the species in the struggle
for existence, and if crossing induces variability because
of the union of unlike individuals, it would seem to follow
that the more unlike the parents, the greater will be
the variation in offspring and the more the type will
prosper; and, carrying this thought to its logical con-
clusion, we shall expect to find that the most closely
related plants would constantly tend to refuse to cross,
because the offspring of them would be little variable

98 Plant- Breeding

and, therefore, little adapted to struggle for existence;
while the most widely separated plants would constantly
tend to cross more and more, because their offspring
would present the greatest possible degree of differences.

Swamping effects of inter-crossing. — Now, essentially
this reason has been advanced to combat the evolution
of plants and animals by means of natural selection ; and
this proposition that inter-mixing must constantly tend
to obliterate all differences between plants and to prevent
the establishment of well-marked types, has been called
the " swamping effects of inter-crossing." It is exceed-
ingly important that we consider this question, for it
really lies at the foundation of the improvement of cul-
tivated plants by means of crossing, as well as the persist-
ence and evolution of varieties and species under wholly
natural conditions.

What determines the limits of crossing f — We find,
however, that distinct species, as a rule, refuse to cross ;
and the first question which naturally arises is, what is
the immediate cause of the refusal of plants to cross?
How does this refusal express itself? It comes about
in many ways. The commonest cause is the positive
refusal of a plant to allow its ovule to be impregnated
by the pollen of another plant. The pollen will not
"take." For instance, if we apply the pollen of a Hub-
bard squash to the flower of a common field pumpkin,
there will be no result, — the fruit will not form. The
same is true of the pear and the apple, the oat and the
wheat, and most very unlike species. Or the refusal may
come in the sterility of the cross or hybrid : the pollen
may "take" and seeds may be formed and the seeds

Hybridization 99

may grow, but the plants they produce may be wholly
barren, sometimes even refusing to produce flowers
as well as seeds, as in the instance of some hybrids be-
tween the Wild Goose plum and the peach. Sometimes
the refusal to cross is due to some difference in the time
of blooming or some incompatibility in the structure of
the flowers. But it is enough for our purpose to know
that there are certain characters in widely dissimilar
plants which prevent inter-crossing, and that these
characters are just as closely and just as much influenced
by change of environment and natural selection as are
size, color, reproductiveness, and other characters.

The limits of crossing tend to preserve the identity of
species. — Here, then, is the sufficient answer to the prop-
osition that inter-crossing must swamp all natural
selection, and also the explanation of the varying and
often restricted limits within which crossing is possible.
That is, the checks to crossing have been developed
through the principle of universal variability and natural
selection, as has been shown by Darwin and Wallace.
Plants vary in their reproductive organs and powers,
as they do in other directions; and when such a varia-
tion is useful it is perpetuated, and when hurtful it is
lost. Suppose that a certain well-marked individual of
a species should find an unusually good place in nature,
and it should multiply rapidly. Crosses would be made
between its own offspring and perhaps between those
offspring and itself in succeeding years; and it is fair
to suppose that some of the crosses would be particularly
well adapted to the conditions in which the parents
grew, and these would constantly tend to perpetuate

100 Plant-Breeding

themselves, while less adaptive forms would tend similarly
to disappear. Now the same thing would take place
if this individual or its adaptive offspring were to cross
with the main stock of the parent species ; for all the
offspring of such a cross which is intermediate in character
and therefore less adapted to the new conditions would
tend to disappear, and the two types would, as a result,
become more and more fixed and the tendency to cross
would constantly decrease.

The refusal to cross, the result of natural selection. —
The refusal to cross, therefore, becomes a positive character
of separation, and the " missing links" that result from
crossing are no more or no less inexplicable than the
''missing links" due to simple selection; or, to state the
case more accurately, natural selection weeds out the tend-
ency to promiscuous crossing, when it is hurtful, in the
same way that it weeds out any other injurious tendency.
It makes no difference in what way this tendency ex-
presses itself, whether in some constitutional refusal to
cross, — if such exists, — or infertility of offspring, or
in different times of blooming: all equally come under
the power of natural selection. We are likely to look upon
infertility as the absence of a character, a sort of negative
feature which is somehow not the legitimate field of
natural selection; but such is not the case. We are
perhaps led the more to this feeling because the word
infertility is itself negative, and because we associate
full productiveness with the positive attributes of plants.
But loss of productiveness is surely no more a subject
of wonder than loss of color or size, if there is some corre-
sponding gain to be accomplished. In fact, we see, in

Hybridization 101

numerous plants which propagate usually by means of
runners and suckers, a very low degree of productiveness,
that is, infertility.

For the production of useful hybrids, do not have the
parents too diverse. — Now, if this reasoning is sound,
it leads us to conclusions quite the reverse of those held
by the advocates of the swamping effects of inter-crossing,
and these conclusions are of the most vital importance
to every man who tills the soil. The logical result is
simply this : the best results of crossing are obtained,
as a rule, when the cross is made between different in-
dividuals of the same variety, or at farthest, between
different individuals of the same species. In other words,
crosses between species are very rarely useful in nature,
and it follows that the more unlike the species, the less
useful will be the hybrids. This is counter to the notions
of most horticulturists, and, if true, must entirely over-
throw our common thinking upon this subject. But we
shall be able to show that observation and experiment
lead to the same conclusion to which our philosophy
has brought us.

Function of the cross. — At this point, we must ask
ourselves what we mean by "best results." This phrase
may be taken to refer to those plants that are best fitted to
survive in the struggle for existence, those that are most
vigorous or most productive or most hardy, or that
possess any well-marked character or characters which
distinguish them in virility from their fellows. We
commonly associate the term more particularly with
marked vigor and productiveness ; these are the char-
acters most useful in nature and also in cultivation, the

102 Plant-Breeding

ones which we oftenest desire to obtain. Another type
of variation that we constantly covet is something
that we call a new character, which will lead to the
production of a new cultural variety, and we are always
looking to this as the legitimate result of crossing. We
have forgotten — if, indeed, we ever knew — that the
commoner, all-pervading, more important function of the
cross is to introduce some new feature or power into the
offspring, to improve or to perpetuate an existing variety,
rather than to create a new one. Or, if a new one is
created, it comes from the gradual passing of one into
another, an inferior variety into a good one, a good one
into a superlative one. So nature usually employs crossing
in a process of slow or gradual improvement, one step
leading to another, and not in any bold or sudden creation
of new forms. And there is evidence to show that some-
thing akin to this must be done to secure the best and
most permanent results under cultivation.

Rarity of natural hybrids. — Think of the great rarity
of hybrids or pronounced crosses in nature. No doubt
all the authentic cases on record could be entered into
one or two volumes, but a list of all the individual plants
of the world could not be compressed into ten thousand
volumes. There are a few genera, in which the species
are not well defined, or in which some character of in-
florescence favors promiscuous crossing, in which hybrids
are conspicuous ; but even here the number of individual
hybrids is very small in comparison to the whole number
of individuals. That is, the hybrids are rare, while the
parents may be common. This is well illustrated even
in the willows and the oaks, in which, perhaps, hybrids

Hybridization 103

are better known than in any other American plants.
The great genus Carex, or sedge, which occurs in great
numbers and many species in almost every locality in
the United States, and in which the species are particularly
adapted to inter-crossing by the character of their in-
florescence, furnishes but few undoubted hybrids. Among
one hundred and eighty-five species and .prominent
varieties inhabiting the Northeastern States, there are
only about a score of hybrids recorded, and all of them are
rare or local, some of them having been collected but
once. Species of Carex of remarkable similarity may
grow side by side for years, even inter-tangled in the
same clump, and yet produce no hybrid. These examples
show that nature avoids hybridization, a conclusion at
which we have already arrived from philosophical con-
siderations. And we have reason to infer the same
conclusion from the fact that flowers of different species
are so constructed as not to invite inter-crossing. But,
on the other hand, the fact that all higher plants habitually
propagate by means of seeds, which is far the most ex-
pensive to the plant of all methods -of propagation, while
at the same time most flowers are so constructed as to
prevent self-fertilization, shows that some corresponding
good must come from crossing within the limits of the
species or variety ; and there are also philosophical reasons,
as we have seen, that warrant this conclusion.

Change of seed and crossing. — Bearing in mind these
good influences of crossing, let us recall another series
of facts following the simple change of seed. Almost
every farmer and gardener at the present day feels that
an occasional change of seed results in better crops, and

104 Plant-Breeding

there are definite records to show that such is often the
case. In fact, much of the rapid improvement in fruits
and vegetables in recent years is probably due to the
practice of buying plants and seeds so largely of dealers,
by means of which the stock is often changed. Even
a slight change, as between farms or neighboring villages,
sometimes produces marked results, such as more vigorous
plants and often more fruitful ones. We must not sup-
pose, however, that because a small change gives a good
result, a violent or very pronounced change gives a better
one. There are many facts on record to show that
great changes often profoundly influence plants, and when
such influence results in lessened vigor or lessened pro-
ductiveness, we call it an injurious one. Now, this in-
jurious influence may result even when all the condi-
tions in the new place are favorable to the health and
development of the plant; it is an influence wholly in-
dependent, as far as we can see, of any condition which
interferes injuriously with the simple processes of growth.
Seeds of a native physalis, or husk-tomato, were sent from
Paraguay in 1889 by Dr. Thomas Morong, then traveling
in that country. It was grown from cuttings in the house
and out of doors, and for two generations it failed to set
fruit, even though the flowers were hand pollinated ; yet the
plants were healthy and grew vigorously. The third cut-
ting-generation grown out of doors set freely. This is an
instance of the fact that very great changes of conditions
may injuriously affect the plant, and an equally good
illustration of the power to overcome these conditions.
Now there is great similarity between the effects of slight
and violent changes of conditions and small and violent

Hybridization 105

degrees of crossing, as both Darwin and Wallace have
pointed out, and it is pertinent to this discussion to
endeavor to discover why this similarity exists. It is
well proved that crossing is good for the resulting off-
spring, because the difference between the parents carries
over new combinations of characters, or at least new
powers into the crosses. It is a process of revitaliza-
tion, and the more different the stocks in desirable
characters within the limits of the variety, the greater
may be the revitalization ; and frequently the good is of a
more positive kind, resulting in pronounced characters
which may serve as the basis for new varieties. In the
cross, therefore, a new combination of characters or a
new power fit it to live better than its parents in the
conditions under which they lived.

Results from change of stock. — In the case of change of
stock we find the reverse, which, however, amounts to the
same thing, that the same characters or powers fit the plant
to live better in conditions new to it than plants which
have long lived in those conditions. In either case, the
good comes from the fitting together of new characters or
powers and new environments. Plants which live during
many generations in one place become accustomed to the
place, thoroughly fitted into its conditions, and are in
what Spencer calls a state of equilibrium. When either
plant or conditions change, new adjustments must take
place; and the plant may find an opportunity to take
advantage, to expand in some direction in which it has
before been held back ; for plants always possess greater
power than they are able to express. " These rhythmical
actions or functions (of the organism)," writes Spencer,

106 Plant-Breeding

"and the various compound rhythms resulting from their
combinations, are in such adjustment as to balance the
actions to which the organism is subject. There is a
constant or periodic genesis of forces which, in their kind,
amounts, and directions, suffice to antagonize the forces
which the organism has constantly or periodically to bear.
If, then, there exists this state of moving equilibrium
among a definite set of internal actions, exposed to a
definite set of external actions, what must result if any of
the external actions are changed ? Of course there is no
longer an equilibrium. Some force which the organism
habitually generates is too great or too small to balance
some incident force; and there arises a residuary force
exerted by the environment on the organism, or by the
organism on the environment. This residuary force, this
unbalanced force, of necessity expends itself in producing
some change of state in the organism."

The good results, therefore, are processes of adaptation,
and when adaptation is perfect or complete, the plant may
have gained no permanent advantage over its former
conditions, and new crossing or another change may be
necessary ; yet there is often a permanent gain, as when a
plant becomes visibly modified by change to another cli-
mate. Now this adaptive change may express itself in
two ways : either by some direct influence on the stature,
vigor, or other general characters ; or directly on the
reproductive powers, by which some new influence is
carried to the offspring. If the direct influences become
hereditary, as observations seem to show may sometimes
occur, the two directions of modification may amount,
ultimately, to the same thing.

Hybridization 107

For the purpose of this discussion it is enough to know
that crossing within the variety and change of stock within
ordinary bounds are beneficial, that the results in the two
cases seem to flow from essentially the same causes, and
that crossing and change of stock combined may give
better results than either one alone ; and this benefit is
expressed more in increased vigor and yield than in novel
and striking variations. These processes are much more
important than any mere groping after new variations,
as we have already said, not only because they are surer,
but because they are -universal and necessary means of
maintaining and improving both wild and cultivated
plants. Even after one succeeds in securing and fixing
the new variety, one must employ these means to a greater
or less extent to maintain fertility and vigor, and to keep
the variety true to its type. In the case of some garden
crops, in which many seeds are produced in each fruit and
in which the operation of pollination is easy, actual hand-
crossing from new stock now and then may be found to be
profitable. But in most cases the operation can be left
to nature, if the new stock is planted among the old.
Upon this point Darwin expressed himself as follows:
"It is a common practice with horticulturists to obtain
seeds from another place having a very different soil, so as
to avoid raising plants for a long succession of generations
under the same conditions ; but with all the species which
freely inter-crossed by the aid of the insects or the wind, it
would be an incomparably better plan to obtain seeds of
the required variety, which had been raised for some
generations under as different conditions as possible, and
sow them in alternate rows with seeds matured in the old

108 Plant-Breeding

garden. The two stocks would then intercross, with a
thorough blending of their whole organizations, and with
no loss of purity to the variety, and this would yield far
more favorable results than a mere change of seed."

CROSSING FROM STANDPOINT OF PLANT IMPROVEMENT

The making of crosses for man's use may have a very dif-
ferent meaning from the effect of crossing upon the plant
itself. Man removes from a plant by cultivation most of
the factors which make for struggle and determines whether
the plant shall survive or not. In making crosses or
hybrids with a practical object in view, the welfare of the
species is taken into account only sufficiently to insure
vigorous plants particularly adapted to man's purposes.

Understanding of terms. — At this point it is worth
while to consider a few definitions.

The Latin word hybrida, or ibrida, has been assumed to be
derived from the Greek v/fyus, an insult or outrage, and a
hybrid has been supposed to be an outrage on nature, an un-
natural product. The term hybrid is by many applied only
to the offspring obtained by crossing two plants or animals
sufficiently different to be considered by naturalists as
distinct species, while the term cross is used to designate
the offspring of two races or varieties of one species. A
closer scrutiny of the facts, however, makes the term
hybridism less isolated and more vague. The words
species and genera, and still more sub-species and varieties,
do not correspond with clearly marked botanical categories,
and no exact line can be drawn between the various kinds
of crossings from those between individuals apparently
identical to those belonging to genera universally recog-

Hybridization 109

nized as distinct. It was formerly supposed that all
hybrids were more or less sterile, in contradistinction to
crosses, which were thought to be very fertile. It has
been found, however, that many hybrids, in the narrow
sense, are very fertile, and that some crosses are nearly
sterile. Since it is impossible to indicate by any two words,
such as hybrid or cross, the various degrees of difference
of the forms crossed, the word hybrid is now generally
used as a generic term to include all organisms arising
from a cross of two forms noticeably different, whether the
difference be great or slight. Adjectives are sometimes
used to indicate the grade of the forms crossed, such as
racial hybrids, bigeneric hybrids, and so forth.

The offspring produced by the union of two plants
identical in kind, but separated in descent by at least
several seed generations, is often called a cross, cross-
fertilized, or cross-bred plant, but it is not a hybrid, as
the essential character of a hybrid is that it results from
the union of plants differing more or less in kind, or, in
other words, is the result of a union between different races,
varieties, species, or genera. On the other hand, flowers
impregnated with their own pollen, with the pollen of
another flower on the same plant, or even pollen from
another plant derived from the same original stock by
cuttings or grafts, are said to be self-fertilized, and the
offspring resulting from such unions are often termed self-
fertilized plants. Strictly speaking, however, self- or close-
fertilization is impregnation with pollen of the same flower.
With such plants as tobacco and wheat, self-fertilization
is the rule. In many cases, however, the flowers are so
constructed that cross-fertilization is favored, as in corn

110 Plant-Breeding

and rye, and in some cases cross-fertilization is necessary,
all possibility of self-pollinization being precluded, as in
the case of hemp and other plants having the male and
female flowers on separate individuals.

History of plant hybrids. — Inasmuch as the sexuality of
plants was unknown, or at least very imperfectly under-
stood, prior to the last two centuries, while a knowledge
of the sex distinction of animals dates from the dawn of
human history, it is not surprising that while the hybridiz-
ing of animals was well understood by the ancients, they
did not know that crossing was possible with plants.
Experimental proof of the sexuality of plants was pub-
lished for the first time by Camerarius, December 28,
1691, and only after this discovery was the function
of pollen and its necessity for seed formation under-
stood.

The earliest recorded observation of a plant hybrid is by
J. G. Gmelin toward the end of the seventeenth century;
the next is that of Thomas Fairchild, who in the second
decade of the eighteenth century produced the cross
which is still grown in literature under the name of
"Fairchild's Sweet William." It was a cross between the
carnation and sweet William.

Linnaeus made many experiments in the cross-fertiliza-
tion of plants and produced several hybrids, but Joseph
Gottlieb Kolreuter (1733-1806) laid the real foundation
of our scientific knowledge of the subject. Later on,
Thomas Andrew Knight, a celebrated English horticul-
turist, devoted much successful labor to the improvement
of fruit trees and vegetables by crossing. In the second
quarter of the nineteenth century, C. F. Gartner made

Hybridization 111

and published the results of a number of experiments that
have not been equaled by any other worker.

What plants can be hybridized f — It is a fact of prime
importance that plants so different as to be classed by
botanists in widely different families never yield offspring
when crossed ; for example, it is impossible successfully
to cross Indian corn and lilies or the apple and the wal-
nut. Usually plants diverse enough to be considered as
belonging to clearly distinct genera, even though of the
same natural family, are perfectly sterile when crossed ;
for example, Indian corn yields no offspring when cross-
pollinated with wheat, nor does wheat when crossed with
oats, although all belong to the great family of grasses.
Plants belonging to the different cultivated races or to
natural varieties of the same species are almost invariably
fertile when crossed. Indeed, as will be shown later, they
are sometimes more fertile when crossed with a related
species than when fertilized with their own pollen. Dif-
ferent species of plants closely enough related to be placed
in the same genus by naturalists are very often, though by
no means always, capable of being hybridized.

Gartner found that "one of the tobaccoes, Nicotiana
acuminata, which is not a particularly distinct species,
obstinately failed to fertilize or to be fertilized by no less
than eight species of Nicotiana." Darwin states that "in
the same family there may be a genus, as Dianthus, in
which very many species can most readily be crossed;
and another genus, as Silene, in which the most persever-
ing efforts have failed to produce, between extremely close
species, a single hybrid." Again, there is considerable
diversity in results in certain reciprocal crosses between

112 Plant-Breeding

the same two species. "Mirabilis jalapa can easily be
fertilized by the pollen of M . longiflora, and the hybrids
thus produced are sufficiently fertile ; but Kolreuter tried
more than two hundred times during eight following years
to fertilize reciprocally M. longiflora with the pollen of
M. jalapa and utterly failed," as have also many other
hybridizers. Frequently very closely related species
absolutely refuse to cross. This is true of the pumpkin
(Cucurbita Pepo) and squash (C. maxima). It is, never-
theless, true that hosts of very distinct species hybridize
readily, and a number of cases are known of species be-
longing to different and quite distinct genera having
hybridized, producing the so-called bigeneric hybrids.
For example, wheat and rye, and wheat and barley, be-
longing to closely related genera, cross with difficulty, and
Luther Burbank is said to have succeeded in obtaining a
hybrid of strawberry and raspberry. Bigeneric hybrids
are many among the orchids, even though they are highly
specialized plants ; and some trigeneric hybrids are known.

Hybrids between plants belonging to different families
are very rare. The results obtained by hosts of experi-
menters and practical gardeners show conclusively that
the greater part of closely related species can be readily
crossed, while very distinct species, and species belonging
to distinct genera, can be crossed in only comparatively
few cases. It is impossible to predict what plants may or
may not be hybridized.

Vigor as a result of crossing. — Darwin was the first to
show that crossing within the limits of the species or
variety results in a constant revitalizing of the offspring,
and that this is the particular ultimate function of crossing

Hybridization 113

or cross-fertilization. Kolreuter, Sprengel, Knight, and
others had observed many, if, indeed, not all, the facts
obtained by Darwin ; but they had not generalized upon
them broadly, and did not conceive the relation to the
complex life of the vegetable world. Darwin's results
are, concisely, these : self-fertilization tends to weaken the
offspring (Fig. 31) ; crossing between different plants of the

FIG. 31. — Inbred corn plants, showing lessened vigor of growth.
(Adapted from Yearbook.)

same variety gives a stronger and more productive offspring
than arises from self-fertilization ; crossing between stocks
of the same variety grown in different places or under
different conditions gives better offspring than crossing
between different plants grown in the same place or under
similar conditions ; and his researches have also shown that,
as a rule, flowers are so constructed as to favor cross-
i

114 Plant-Breeding

fertilization. In short, he found, as he expressed it, that
" nature abhors perpetual self-fertilization." Some of his
particular results, although often quoted, will be useful in
fixing these facts in our minds.

Darwin's experiments with morning-glories. — Plants
from crossed seeds of morning-glory exceeded in height
those from self-fertilized seeds as 100 exceeds 76, in the
first generation. Some flowers from these plants were
self-pollinated and some were crossed, and in this second
generation the crossed plants were to the uncrossed as
100 is to 79 ; the operation was again repeated, and in the
third generation, the plant having been grown in mid-
winter, when none of them did well, 100 to 86 ; fifth
generation, 100 to 75 ; sixth generation, 100 to 72 ; seventh
generation, 100 to 81 ; eighth generation, 100 to 85 ; ninth
generation, 100 to 79 ; tenth generation, 100 to 54. The
average total gain in height of the crossed over the un-
crossed was as 100 to 77, or about 30 per cent. There
was a corresponding gain in fertility, or the number of
seeds and seed-pods produced. Yet, striking as the results
are, they were produced by simple crossing between plants
grown near together, and under what would ordinarily
be called uniform conditions. In order to determine the
influence of crossing with fresh stock, plants of the same
variety were obtained from another garden and these
were crossed with the ninth generation mentioned above.
The offspring of this cross exceeded those of the other
crossed plants as 100 exceeds 78, in height ; as 100 exceeds
57, in the number of seed-pods; and as 100 exceeds 51,
in the weight of the seed-pods. In other words, crosses
between fresh stock of the same variety were nearly 30

Hybridization 115

per cent more vigorous than crosses between plants grown
side by side for some time and over 44 per cent more
vigorous than plants from self-fertilized seeds. On the
other hand, experiments showed that crosses between
different flowers on the same plant gave actually poorer
results than offspring of self -fertilized flowers. It is
evident, from all of these figures, that nature desires
crosses between plants, and, if possible, between plants
grown under somewhat different conditions. All these
results are exceedingly interesting and important ; and
there is every reason to believe that, as a rule, similar
results can be obtained with all plants.

Darwin's results with other plants. — Darwin extended
his investigation to many plants, only a few of which need
be discussed here. Cabbage gave pronounced results.
Crossed plants were to self-fertilized plants in weight as
100 is to 37. A cross was now made between these crossed
plants and a plant of the same variety from another
garden, and the difference in weight of the resulting off-
spring was the difference between 100 and 22, showing a
gain of over 350 per cent, due to a cross with fresh stock.
Crossed lettuce plants exceeded uncrossed in height as
100 exceeds 82. Buckwheat gave an increase in weight
of seeds as 100 to 82, and in height of plants as 100 to 69.
Beets gave an increase in height represented by 100 to 87.
Maize, when full grown, from crossed and uncrossed seeds,
gave the difference in height between 100 and 91. Canary
grass gave similar results.

Increased vigor in other crosses. — Results as well
marked as these have been secured on a large and what
might be called a commercial scale. The first gen-

116 Plant-Breeding

eration was raised from seeds of known parentage,
the flowers from which they came having been carefully
pollinated by hand. In some instances the second genera-
tions were grown from hand-crossed seeds, but in other
cases the second generations were grown from seeds simply
selected from the first-year patches. As the experiments
have been made in the field and upon a somewhat exten-
sive scale, it was not possible accurately to measure the
plants and the fruits from individuals in all cases ; but the
results have been so marked as to admit of no doubt as
to their character. In 1889, several hand-crosses were
made among egg-plants. The fruits matured, and the
seeds from them were grown in 1890. Some two hundred
plants were grown, and they were characterized through-
out the season by great sturdiness and vigor of growth.
They grew more erect and taller than other plants near by
grown from commercial seeds. It was impossible to deter-
mine productiveness, from the fact that the seasons were
too short for egg-plants, and only the earliest flowers, in
the large varieties, perfect their fruit, and the plant blooms
continuously through the season. In order to determine
how much a plant will bear, it must be grown until it
ceases to bloom. When frost came, little difference could
be seen in productiveness between these crossed plants
and commercial plants. A dozen fruits were selected from
various parts of the patch, and in 1891 about twenty-five
hundred plants were grown from them. Again the plants
were remarkably robust and healthy, with fine foliage,
and they grew erect and tall, — an indication of vigor.
They were also very productive; but, as the cross had
been made between unlike varieties, and the offspring

Hybridization

117

was therefore unlike either parent, an accurate comparison
could not be made. But they compared well with com-
mercial egg-plants, and un-
doubtedly they would have
shown themselves to be
more productive than com-
mon stock could they have
grown a month or six weeks
longer. Professor Munson,
of the Maine Experiment
Station, grew some of this
crossed stock in 1891, and
found that it was better
than any commercial stock
in his gardens.

In extended experiments
in the crossing of pumpkins,
squashes, and gourds, con-
ducted several years, in-
crease in productiveness
due to crossing has been
marked in many instances.
Marked increase in produc-
tiveness has been obtained
from tomato crosses even
when no other results of
crossing could be seen.

Three factors . — Attention
has been called by Willis to

three factors in the gain resulting from cross-fertilization,
viz. (a) fertility of mother plant ; (6) vigor of offspring ;

FIG. 32. — Hybrid walnut and
parents : ra, California black
walnut (Juglans calif ornica),
male parent; /, Eastern black
walnut (J. nigra), female par-
ent; h, hybrid. Natural size.
(After Burbank.)

118 Plant-Breeding

and (c) fertility of offspring. The relative values of these
factors varies with different plants. In the carnation, for
instance, factor (a) of cross-fertilized plants was 9 per cent
greater than in self -fertilized plants, (b) was 16 per cent
greater, and (c) was 54 per cent greater; in tobacco,
factor (a) was 33 per cent less than in self -fertilized plants,
but factor (b) was 28 per cent greater and factor (c) 3 per
cent greater. Even when the fertility of the mother
plant is greatly reduced by hybridizing with a distinct
species and the hybrids themselves are sterile or very
infertile, they nevertheless often show extraordinary vigor,
that is, (b) is often greater in hybrids than in pure-bred
plants, but factors (a) and (c) are usually less. In plant-
breeding the importance of this increased vigor is very
great (Figs. 32 and 33).

The outright production of new varieties. — The reader is
waiting for a discussion of the second of the great features
of crossing, — the summary production of new varieties.
This is the subject that is almost universally associated
with crossing in the popular mind, and even among hor-
ticulturists themselves. It is the commonest notion that
the desirable characters of given parents can be definitely
combined in a pronounced cross of hybrids. There are
two or three philosophical reasons which somewhat oppose
this doctrine, and which we will do well to consider at the
outset. In the first place, nature is opposed to hybrids,
for species have been bred away from each other in the
ability to cross. If, therefore, there is no advantage for
nature to hybridize, we may suppose that there would be
little advantage for man to do so ; and there would be no
advantage for man did he not place the plant under condi-

FIG. 33. — A hybrid walnut (Juglans calif ornica nigra), reaching double
the height of ordinary trees.

120 Plant-Breeding

tions different from nature, or desires a different set of
characters. We have seen that nature's chief barriers to
hybridization are total refusal of many species to unite,
and entire or comparative seedlessness of offspring.

The notion is somewhat firmly rooted in the popular
mind that new varieties can be produced with the greatest
ease by crossing parents of given attributes. There is
something captivating about the notion. It smacks of a
somewhat magic power that man evokes as he passes his
wand over the untamed forces of nature. But the wand
is often a gilded stick, and is likely to serve no better
purpose than the drum major's pretentious baton !

Let it be said further that crossing alone can accomplish
comparatively little. The chief power in the evolution or
progression of plants appears to be selection, or, as Darwin
puts it, the law of " preservation of favorable individual
differences and variations, and the destruction of those
which are injurious." Selection is the force which aug-
ments, develops, and fixes types. Man must not only
practice a judicious selection of parents from which the
cross is to come, which is in reality but the exercise of a
choice, but he must constantly select the best from among
the crosses, in order to maintain a high degree of usefulness
and to make any advancement ; and it sometimes happens
that the selection is much more important to the cultivator
than the crossing.

Further discussion of this subject naturally falls under
two heads : the improvement of existing types or varieties
by means of crossing, and the summary production of new
varieties. As already stated, the former office is the more
important, and the proposition is easy of proof. It is

Hybridization 121

the chief use which nature makes of crossing, to strengthen
the type.

How to overcome antipathy to crossing. — We can over-
come the refusal to cross in many cases by bringing the
plant under cultivation; for the character of the species
becomes so changed by the wholly new conditions that its
former antipathies may be overpowered. Yet, it is doubt-
ful whether such a plant will ever acquire a complete willing- '
ness to cross. In like manner we can overcome in a meas-
ure the comparative seedlessness of hybrids, but it is very
doubtful whether we can ever make such hybrids com-
pletely fruitful.

It is evident that species which have been differentiated
or bred away from each other in a given locality will have
more opposed qualities or powers than similar species
which have arisen quite independently in places remote
from each other. In the one case the species have likely
struggled with each other until each one has attained to a
degree of divergence which allows it to persist ; while in
the other case, there has been no struggle between species,
but similar conditions have brought about similar results.
These similar species which appear independently of each
other in different places are called representative species.
Islands remote from each other but similarly situated with
reference to climate very often contain representative
species ; and the same may be said of other regions much
like each other, as eastern North America and Japan.
Now, it follows that, if representative species are less
opposed than others, they are more likely to hybridize with
good results ; and this fact is remarkably well illustrated in
the Kieffer and allied pears, which are hybrids between

122 Plant-Breeding

representative species of Europe and Japan; and the
same may be found to be true of the common European
apple and the wild crab of .the Mississippi Valley.
Various crabs of the Soulard type, which were once
thought to constitute a distinct species, appear upon
further study to be hybrids. We will also recall that
the hybrid grapes which have so far proved most
valuable are those obtained by Rogers between the
American Vitis Labrusca and the European wine grape,
Vitis vinifera; and that the attempts of Haskell and
others to hybridize associated species of native grapes have
given, at best, only indifferent results. To these good
results from hybrids and fruit trees and vines, we shall
revert presently.

Variability of hybrids. — Another theoretical point
which is borne out by practice is the conclusion that,
because of the great differences and lack of affinity between
parents, pronounced hybrid offsprings are unstable. This
is one of the greatest difficulties in the way of the summary
production of new varieties by means of hybridization.
It would appear, also, that, because of the unlikeness of
parents, hybrid offspring must be exceedingly variable;
but, as a matter of fact, in many instances the parents are
so pronouncedly different that the hybrids represent a
distinct type by themselves, or else they approach very
nearly to the characters of one of the parents. There are,
to be sure, many examples of exceedingly variable hybrid
offspring, but they are usually the offspring of variable
parents (Fig. 34) . In other words, variability in offspring'
appears to follow rather as a result of variability in parents
than as a result of mere unlikeness of characters. But

Hybridization

123

the instability of hybrid offspring when propagated by
seed is notorious. We shall see the reasons for this later
when discussing mendelism. Wallace writes that "the
effect of occasional crosses often results in a great amount
of variability, but it also leads to instability of character,
and is therefore very little employed in the production of
fixed and well-marked races." We may remark again that,
because of the unequal and unknown powers of the parents,
we can never predict what characters will appear in the

FIG. 34. — Variation in hybrid pineapples.

hybrids, although we are now beginning to understand
the reasons and to have rather definite expectations as
to probabilities. This fact is well expressed by Lindley a
half century ago, in the phrase, "Hybridizing is a game
of chance played between man and plants."

Characteristics of crosses. — Bearing these fundamental
propositions in mind, let us pursue the subject somewhat
in detail. We shall find that the characters of hybrids,
as compared with the characters of simple crosses between
stocks of the same variety, are ambiguous, negative, and

124 Plant- Breeding

often prejudicial. Focke lays down the five following
propositions concerning the character of hybrid offspring :

1. "All individuals which have come from the crossing
of two pure species or races, when produced and grown
under like conditions, are usually exactly like each other,
or at least scarcely more different from each other than
plants of the same species are." This proposition, al-
though perhaps true in the main, appears to be too broadly
and positively stated.

2. "The characters of hybrids may be different from
the characters of the parents. The hybrids differ most in
size and vigor and in their sexual powers.

3. "Hybrids are distinguished from their parents by
their powers of vegetation or growth. Hybrids between
very different species are often weak, especially when
young, so that it is difficult to raise them. On the other
hand, crossbreds are, as a rule, . uncommonly vigorous ;
they are distinguished mostly in size, rapidity of growth,
early flowering, productiveness, longer life, stronger repro-
ductive power, unusual size of some special organs, and
similar characteristics.

4. "Hybrids produce a less amount of pollen and fewer
seeds than their parents, and they often produce none.
In cross-breeds this weakening of the reproductive powers
does not occur. The flowers of sterile or nearly sterile
hybrids usually remain fresh a long time.

5. "Malformations and odd forms are likely to appear
in hybrids, especially in the flowers."

Some of the relations between hybridization and cross-
ing within narrow limits are stated as follows by Darwin :
" It is an extraordinary fact that with many species flowers

Hybridization 125

fertilized with their own pollen are either absolutely or in
some degree sterile ; if fertilized with pollen from another
flower on the same plant, they are sometimes, though
rarely, a little more fertile ; if fertilized with pollen from
another individual or variety of the same species, they
are fully fertile ; but if with pollen from a distinct species,
they are sterile in all possible degrees, until utter sterility
is reached. We thus have a long series with absolute
sterility at the two ends; at one end due to the sexual
elements not having been sufficiently differentiated, and
at the other end to their having been differentiated in too
great a degree, or in some peculiar manner."

Difficulties in making successful crosses. — The diffi-
culties in the way of successful results through hybridiza-
tion are, therefore, these : the difficulty of effecting the
cross, infertility, instability, variability, and often weak-
ness and monstrosity of the hybrids; and the general
impossibility in most cases of predicting results. The
advantage to be derived from a successful hybridization
is the securing of a new variety which shall combine in
some measure the most desirable features of both parents ;
and this advantage is often of so great moment that it is
worth while to make repeated efforts and to overlook
numerous failures.

Hybridization and asexual propagation. — Among the
various characters of hybrid offspring, probably the most
prejudicial one is their instability, their tendency to vary
into new forms or to return to one or the other parent
in succeeding generations. At the outset, we notice that
this discouraging feature is manifested chiefly through
the fact of seed-reproduction, and we thereby come

126 Plant-Breeding

upon what is perhaps the most important practical con-
sideration in hybridization, — the fact that the greater
number of the best hybrids in cultivation are increased
by bud-propagation, as cuttings, layers, suckers, buds, or
grafts. In fact, there are very few examples in this country
of good undoubted hybrids which are propagated with
practical certainty by means of seeds. The genera in
which the hybrids are most common are those in which
bud-propagation is the rule ; as begonia, pelargonium,
orchids, gladiolus, rhododendron, roses, cannas, and the
fruits. This simply means that it is difficult to fix hybrids
so that they will come "true to seed," and makes apparent
the fact that if we desire named hybrids, we must expect
to propagate them by means of buds.

This point appears to have been overlooked by those
who contend that hybridization must necessarily swamp
all results of natural selection; for, as comparatively
few plants propagate habitually by means of buds,
whatever hybrids might have appeared would have been
speedily lost, and all the more because, by the terms of
their reasoning, the hybrids would cross with other and
dissimilar forms, and therefore lose their identity as
intermediates. Or, starting with the assumption that
hybrids are intermediates, and would therefore obliterate
specific types, we must conclude that they should have
some marked degree of stability if they are to swamp or
obliterate the characters of species; but, as all hybrids
tend to break up when propagated by seeds, it must follow
that bud-propagation would become more and more
common, and this is associated in nature with decreased
seed-production. Now, seed-production is the legitimate

Hybridization 127

function of flowers; and we must concede that, as seed-
production decreased, floriferousness must have decreased ;
and that, therefore, pronounced inter-crossing would have
obliterated the very organs upon which it depends, or have
destroyed itself!

In-breeding. — But we may be met with objection that
there is no inherent reason why hybrids should not become
stable through seed-production by in-breeding, and we
might be cited to the opinion of Darwin and others that
in-breeding tends to fix any variety, whether it originates
by crossing or other means. And it is a fact that in-
breeding tends to fix varieties within certain limits, but
those limits are often overpassed in the case of very pro-
nounced crosses, whether cross-breeds or true hybrids.
And if it is true, as all observation and experiments show,
that sexual or reproductive powers of crosses are weakened
as the cross becomes more violent, we shall expect less and
less possibility of successful in-breeding; for in-breeding
without disastrous results is possible only with compara-
tively strong reproductive powers. As a matter of fact,
it is found in practice that it is exceedingly difficult to fix
pronounced hybrids by means of in-breeding. It some-
times happens, also, that the hybrid individual that we
wish to perpetuate may be infertile with itself, as has been
often found in the case of squashes. It is often advised
that we cross the hybrid individual which we wish to fix
with another like individual, or with one of its parents.
These results are often successful, but oftener they are not.
In the first place, it often happens that the hybrid individ-
uals may be so diverse that no two of them are alike;
this has been the experience in many cases. And, again

128 Plant-Breeding

crossing with a parent may draw the hybrid back again to
the parent form. So long ago as last century Kolreuter
proved this fact with Nicotiana and Dianthus. A hybrid
between Nicotiana rustica and N. panicutata was crossed
with N. paniculata until it was indistinguishable from it ;
and it was then crossed with N. rustica until it became
indistinguishable from that parent. Yet there is no other
way of fixing a hybrid to be propagated by seeds than
by in-breeding, and by constant attention to selection.
Fortunately, it occasionally happens that a hybrid is
stable, and therefore needs no fixing.

Experience with egg-plants and squashes. — Offspring of
egg-plant crosses were grown in 1890, and upon some of
the most promising plants some flowers were self -pollinated.
But these self-pollinated seeds gave just as variable offspring
in 1891 as those selected almost at random from the patch ;
and what was worse, none of them reproduced the parents,
or "came true to seed," and all further motive for in-
breeding was gone. " My labor, therefore, amounted to
nothing more than my own edification. My experience
in crossing pumpkins and squashes has now extended
through many years ; and, although I have obtained about
one thousand types not named or described, I have not
yet succeeded in fixing one. The difficulty here is an
aggravated one, however. The species are so exceedingly
variable that all the hybrid individuals may be unlike, so
that there can be no crossing between identical stocks;
and, if in-breeding is attempted, it may be found that the
flowers will not in-breed. And the refusal to in-breed is
all the more strange because the sexes are separated in
different flowers on the plant. In other words, in my

Hybridization 129

experience, it is very difficult to get good seeds from
squashes fertilized by a flower upon the same vine.
The squashes may grow normally to full maturity but be
entirely hollow, or contain only empty seeds. In some
instances the seeds may appear to be good, but may
refuse to grow under the best conditions. Finally, a

FIG. 35. — Variation in hybrid squashes.

small number of flowers may give good seeds. I have
many times observed this refusal of squashes (Cucurbita
Pepo) to in-breed. It was first brought to my attention
through efforts to fix certain types into varieties. The
figures of the season's tests will sufficiently indicate the
character of the problem. In 1890, one hundred and

1 30 Plant-Breeding

eighty-five squash flowers were carefully pollinated with
staminate flowers taken from the same vine that bore the
pistillate flowers. Only twenty-two of these produced
fruit, and of those only seven, or less than one-third, bore
good seeds, and in some of these the seeds were few. Now,
these twenty-two fruits represented as many different
varieties, so that the inability to set fruit with pollen
from the same vine is not a peculiarity of a particular
variety. The records of the seeds of the seven fruits in
1891 are as follows : —

" Fruit No. 1. Four vines were obtained, with four
different types, two of them being white, one yellow, and
one black.

" Fruit No. 2. Twenty-three vines. Fifteen types very
unlike, twelve being white and three yellow.

" Fruit No. 3. Two vines. One type of fruit, which is
almost like one of the original parents.

" Fruit No. 4. Thirty-two vines. Six types, differing
chiefly in size and shape.

" Fruit No. 5. Twenty vines. Nineteen types, of which
ten were white, eight orange, one striped, and all very unlike.

"Fruit No. 6. Thirteen vines. Eleven types, — eight
yellow, two black, one white.

"Fruit No. 7. One vine.

"These offspring were just as variable as those from
flowers not in-bred and no more likely, apparently, to
reproduce the parent. These tests leave me without any
method of fixing a pronounced cross of squashes, and lead
me to think that the legitimate process of origination of
new kinds here, as, indeed, if not in general, is a more
gradual process of selection, coupled, perhaps, with minor
crossing.

Hybridization 131

" I will relate a definite attempt towards the fixation of
a squash that I had obtained from crossing. The his-
tory of it runs back to 1887, when a cross was effected
between a summer yellow crook-neck and a white bush
scallop squash. In 1889 there appeared a squash of
great excellence, combining the merits of summer and
winter squashes with very attractive form, size, and color,
and a good habit of plant. I showed the fruit to one of
the most expert seedsmen of the country, and he pro-
nounced it one of the most promising types he had
ever seen; and, as he informed me that he had fixed
squashes by breeding in and in, I was all the more anxious
to carry out my own convictions in the same direction.
It is needless to say that I was very happy over what I
regarded as a great triumph. Of course, I must have a
large number of plants of my new variety, that I might
select the best, both for in-breeding and for crossing similar
types. So I selected the very finest squash, having placed
it where I could admire it for some days, and saved every
seed of it. These seeds were planted on the most con-
spicuous knoll in my garden in 1890. It was soon
evident that something was wrong. I seemed to have
everything except my squash. One plant, however, bore
fruits almost like the parent, and upon this I began my
attempts towards in-breeding. But flower after flower
failed, and I soon saw that the plant was infertile with itself.
Careful search revealed two or three other plants very
like this one, and I then proceeded to make crosses with
them. I was equally confident that this method would suc-
ceed. When I harvested my squashes in the fall and took
account of stock, I found that the seeds of my one squash

132

Plant-Breeding

had given just as many different types as there were
plants, and I actually counted one hundred and ten kinds
distinct enough to be named and recognized. Still con-
fident, in 1891 I planted the seeds of my few crosses, and
as the summer days grew long and the crickets chirped
in the meadows, I watched the expanding squash blossoms
and wondered what they would bring forth. But they

FIG. 36. — Hybrid citrange and its parents, Citrus (or Poncirus) trifoliata
and common sweet orange.

brought only disappointment. Not one seed produced a
squash like the parent. My squash had taken an unscien-
tific leave of absence, and I do not know its whereabouts.
And when the frost came and killed every ambitious blos-
som, my hope went out and has not yet returned ! " *•

Important hybrids of fruits and vegetables. — Let us
now recall how many undoubted hybrids there are, named

1 Bailey, "Plant-Breeding," earlier editions. See also, "A Medley of
Pumpkins," Proc. Intern. PI. Breeding Conf., New York City.

Hybridization

133

and known, among our fruits and vegetables. In grapes
there are the most. There are Rogers' hybrids, as the
Agawam, Lindley, Wilder, Salem, and Barry; and there
is some reason for supposing that the Delaware, Catawba,
and other varieties are of hybrid origin. And many
hybrids have come to notice lately through the work of

FIG. 37. — Hybrid tangelo and its parents/pomelo and tangerine.

Munson and others. But it must be remembered that
grapes are naturally exceedingly variable, and the specific
limits are not well known, and that hybridization among
them lacks much of that defmiteness which ordinarily
attaches to the subject. In oranges, hybrid citranges and
tangelos made by Webber and Swingle are now reaching
considerable commercial importance (Figs. 36-39). In

134

Plant-Breeding

FIG. 38. — Samson tangelo. {j natural size. (Adapted from Yearbook.)

Hybridization

135

Fig. 39. — Citranges (hybrids of orange and Citrus trifoliata). Top
fruit Citrus (or Poncirus) trifoliata. Top pair, rusk citrange.
Bottom pair, Willits citrange. f natural size. (Reduced from
colored figures in Yearbook of the Department of Agriculture.)

136 Plant-Breeding

pears there is the Kieffer class. In apples, peaches, plums,
cherries, and currants, there are no important recognized
commercial hybrids. In blackberries there is the black-
berry-dewberry class, represented by the Wilson Early and
others. Some of the raspberries, as the Philadelphia and
Shaffer, are hybrids between the red and black species.
Hybrids have been produced between the raspberry and
blackberry by two or three persons, but they possess
no promise of economic results. It is probable that
some of the gooseberries are hybrids. Among all the
list of garden vegetables (plants which are propagated
by seeds) there is apparently not a single important
recorded hybrid ; and the same is true of wheat, — unless
the Carman wheat-rye varieties become prominent,—
oats, the grasses, and other farm crops (Fig. 40). But
among ornamental plants there are many ; and it is signifi-
cant that the most numerous, most marked, and most
successful hybrids occur in the plants most carefully
cultivated and protected, those, in other words, that are
farthest removed from all untoward circumstances and an
independent position. This is nowhere so well illustrated
as in the case of cultivated orchids, in which hybridization
has played no end of freaks, and in which, also, every
individual plant is nursed and coddled.1 With such
plants the struggle for existence is reduced to its lowest
terms ; for it must be borne in mind that, even in the
garden, plants must fight severely for a chance to live,
and even then only the very best can persist, or are even
allowed to try.

Consult E. Bohnhof, " Dictionnaire des Orchidees Hybrides," Paris,
1905 ; also the recent Sanders lists.

Hybridization

137

This list of hybrids is much more meager than most
catalogues and trade-lists would have us believe. It is,
of course, equivalent to saying that most of the so-called
hybrid fruits and vegetables are doubtful. There is every-

FIG. 40. — Teosinte and its hybrids with Indian corn : a and &, ears of
teosinte, showing an entire absence of cob, kernels being attached to
each other ; c and d, ears of first-generation cross of teosinte and
Indian corn ; e and /, Zea canina, a fourth-generation hybrid of
teosinte and corn. All are natural size and were grown by the
Department of Agriculture in 1900 on the Potomac Flats, near
Washington, B.C.

where a misconception of what a hybrid is, and how it
comes to exist ; and yet, perhaps because of this indefinite
knowledge, there is a wide-spread feeling that a hybrid
is necessarily good, while the presumption is directly
the opposite. The identity of a hybrid in the popular

138 Plant-Breeding

mind rests entirely on some superficial character, and
proceeds upon the assumption that it is necessarily inter-
mediate between the parents. Hence, we find one of our
popular authors asserting that, because the kohl-rabi bears
its thickened part midway of its stem, it is evidently
a hybrid between the cabbage and turnip, which bear
respectively the thickened parts at the opposite extrem-
ities of the stem! And then there are those who con-
found the word hybrid with high-bred, and who build
attractive castles upon the unconscious error. And thus
is confusion confounded!

Influence of sex on hybrids. — But, before leaving this
subject of hybridization, we must speak of the old yet
common notion that there is some peculiar influence
exerted by each sex in the parentage of hybrids. It
was held by certain early observers, of whom the great
Linnaeus was one, that the female parent determines the
constitution of the hybrid, while the male parent gives
the external attributes, as form, size, and color. The
accumulated experience of nearly a century and a half
appears to contradict this proposition, and Focke, who has
gone over the whole ground, positively declares that it is un-
true. There are instances, to be sure, in which this old idea
is affirmed, but there are others in which it is contradicted.
It is usually impossible to determine beforehand which
parent is the stronger. It is certain that strength does not
lie in size, neither in the high development of any character.
It appears to be more particularly associated with what
we call fixity or stability of character, or the tendency
towards invariability.

" This has been well illustrated in my own experiments

Hybridiza tion 139

with squashes, gourds, and pumpkins. The common
little pear-shaped gourd will impress itself more strongly
upon crosses than any of the edible squashes and pumpkins
with which it will effect a cross, whether it is used as male
or female parent. It contains many dominant unit-
characters. Even the imposing and ubiquitous great
field pumpkin which every New Englander associates
with pies, is overpowered by the little gourd. Seeds from
a large and sleek pumpkin which had been fertilized by
gourd pollen produced gourds and small hard-shelled
globular fruits which were entirely inedible. A more inter-
esting experiment was made between the handsome
green-striped Bergen fall squash and the little pear gourd.
Several flowers of the gourd were pollinated by the Ber-
gen in 1889. The fruits raised from these seeds in 1890
were remarkably gourd-like. Some of these crosses were
pollinated again in 1890 by the Bergen, and the seeds were
grown in 1891. Here, then, were crosses into which the
gourd had gone once and the Bergen twice, and both
parents are to all appearances equally fixed, the difference
in strength, if any, attaching rather to the Bergen. Now,
the crop of 1891 still carried pronounced characters of the
gourd. Even in the fruits that most resembled the Ber-
gen, the shells were almost flinty hard, and the flesh, even
when thick and tender, was bitter. Some of the fruits
looked so much like the Bergen that I was led to think
that the gourd had largely disappeared. The very hard
but thin paper-like shell which the gourd had laid over
the thick yellow flesh of the Bergen, I thought might
serve a useful purpose, and make the squash a better
keeper. And I found that it was a great protection, for

140 Plant-Breeding

the squash could stand any amount of rough-handling,
and was not even injured by ten degrees of frost. All
this was an acquisition, and, as the squash was handsome
and exceedingly productive, nothing more seemed to be
desired. But it still remained to have a squash for dinner.
The cook complained of the hard shell, but, once inside,
the flesh was thick and attractive, and it cooked nicely.
But the flavor ! Dregs of quinine, gall, and boneset !
The gourd was still there ! " l

Uncertainties of pollination. — We have now seen that
uncertainty follows hybridization, as well as the mere act
of pollination. Between some species which are closely
allied and which have large and strong flowers, four-
fifths of the attempts towards cross-pollination may be
successful; but such a large proportion of successes is
not common, and it may be infrequent even in pollination
between plants of the same species or variety. Some of
the failure is due in many cases to unskillful operation, but
even the most expert operators fail as often as they suc-
ceed in promiscuous pollinating. There is good reason to
believe, as Darwin has shown, that the failure may be due
to some selective power of individual plants, by which
they refuse pollen which is, in many instances, acceptable
to other plants even of the same variety or stock. The
lesson to be drawn from these facts is that operations
should be as many as possible, and that discouragement
should not come from failure.

"Two hundred and thirty-four pollinations of gourds,
pumpkins, and squashes, mostly between varieties of one
species (Cucurbita Pepo), and including some individual

1 Bailey, earlier editions of "Plant-Breeding."

Hybridization 141

pollinations, gave one hundred and seventeen failures and
one hundred and seventeen successes. These crosses
were made in varying weather, from July 28 to August 30.
In some periods nearly all the operations would succeed
and at other times most of them would fall. I have
always regarded these experiments as among my most
successful ones, and yet but half of the pollinations 'took.'
But one must not understand that I actually secured seeds
from even all these one hundred and seventeen fruits,
for some of them turned out to be seedless, and some were
destroyed by insects before they were ripe, or they were
lost by accidental means. A few more than half of the
successful pollinations — if by success we mean the for-
mation and growth of fruit — really secured us seeds,
or about one-fourth of the whole number of efforts.

" Twenty pollinations were made between potato flowers,
and they all failed ; also, seven pollinations of red peppers,
four of husk tomato, two of Nicotiana affinis upon petunia
and two of the reciprocal cross, twelve of radish, one of
Mirabilis jalapa upon M. longiflora and two of the recip-
rocal cross, three Convolvulus major upon C. minor and
one of the reciprocal, one muskmelon by squash, two
muskmelons by watermelon, and one muskmelon by cu-
cumber.

" This is but one record. Let me give another : —
" Cucumber, ninety-five efforts: fifty-two successes;
forty-three failures. Tomato, forty-three efforts : nine-
teen successes; twenty-four failures. Egg-plant, seven
efforts : one success ; six failures. Pepper, fifteen efforts :
one success; fourteen failures. Husk-tomato, forty-five
efforts : forty-five failures. Pepino, twelve efforts : twelve

142 Plant-Breeding

failures. Petunia by Nicotiana affinis, eleven efforts :
eleven failures. Nicotiana affinis by petunia, six efforts :
six failures. General Grant tobacco by Nicotiana affinis,
eleven efforts : eight successes ; three failures. Nicotiana
affinis by General Grant tobacco, fifteen efforts : fifteen
failures. General Grant tobacco by General Grant
tobacco, one effort : one success. Nicotiana affinis by
Nicotiana affinis, three efforts : two successes ; one failure.
Tuberous begonia, five efforts : five successes.

"Total, three hundred and twelve efforts: eighty-nine
successes, two hundred and twenty-three failures." l

Graft-hybrids. — It is well known that, when two varie-
ties or allied species are grafted together, each retains its
distinctive characters. But to this general, if not uni-
versal, rule there are on record several alleged exceptions,
in which either the cion is said to have partaken of the
qualities of the stock, the stock of the cion, or each to
have affected the other. Supposing any of these in-
fluences to have been exerted, the resulting product would
deserve to be called a graft-hybrid.

It is clearly a matter of great interest to ascertain
whether such formation of hybrids by grafting is really
possible ; for, even if one example of such formation could
be unequivocably proved, it would show that sexual
and asexual reproduction are essentially identical.

The case of Cytisus Adami (Figs. 41, 42). — The cases of
alleged graft-hybridization are exceedingly few, considering
the enormous number of grafts that are made every year
by horticulturists and have been made for centuries.

Of these cases, one of the most celebrated is that of

1 Bailey, earlier editions.

Hybridization

143

FIG. 41. — Cytisus Adami, A, A', A"', B, a branch of C, laburum, L,
Lf, L" , with numerous racemes bearing ripe pods.

Adam's laburnum (Cytisus Adami). This plant is now
flourishing in many places throughout Europe, all of the
trees having been raised as cuttings from the original
graft, which was made by inserting a bud of the purple

144

Plant-Breeding

FIG. 42. — Cytisus Adami, A, A', bearing at I a bunch of twigs of
C. purpureus, P, H, and /.

Hybridization 145

laburnum (Cytisus purpureus) into a stock of the yellow
(Cytisus laburnum). M. Adami, who made the graft at
Vitry, near Paris, about 1826, has left on record that from
it there sprang the existing hybrid. There can be no
question as to the truly hybrid nature of the latter. It
is, however, absolutely sterile, and is multiplied by grafts.
It bears three kinds of flowers — some pink, others large
and yellow, others small and purple. That is to say, it
bore its own hybrid flowers, also those of its two parents,
and the leaves and ramifications of the parts of the tree
which bore these three kinds of flowers were likewise of
the same three kinds and could be distinguished even in
winter.

Strasburger made a careful cytological study of Cytisus
Adami, which has been retained in cultivation ever since
its origin some eighty years ago. He came to the con-
clusion that Cytisus Adami was a real sexual hybrid and
not a graft-hybrid. He thinks that if the latter were
true, the nuclei of the hybrid would show a double number
of chromosomes. This, of course, implies that in hybrids
arising otherwise than sexually, assuming that a nuclear
fusion would precede the formation of such a hybrid,
there would be no reduction division of the nuclei com-
parable to that which normally occurs before the fusion
of the sexual cells in normal fertilization.

Nemec, however, thinks that a reduction division
does occur and there is, therefore, no reason to expect
an increase in the number of chromosomes in the cells
of the hybrid. If such a reduction does occur, Cytisus
Adami would show the same number of chromosomes as
C. laburnum, which has the same number as C. purpureus.
L

146 Plant-Breeding

Winkler's Solatium graft-hybrids. — Professor H. Winkler
of Tubingen has carefully performed experiments in
making graft-hybrids with the black nightshade, Solanum
nigrum, and two varieties of the tomato, Solanum lyco-
persicum. These two species are very distinct, and indeed
many botanists regard the tomato as belonging to a dis-
tinct genus lycopersicum, so that Winkler's graft-hybrids
may be regarded as bigeneric hybrids. Seedlings of each
were grown and reciprocal grafts made. The graft and
stock united readily whether the nightshade or the tomato
was used as the stock.

Naturally the majority of the shoots arising from the
cut surface of the stem were either pure nightshade or
pure tomato. But finally shoots were observed which
were evidently of mixed origin. The first of these graft-
hybrids were obviously composed of pure elements
derived from the two parents. Some of these shoots were
almost equally divided by a median line, on one side of
which the organs — stem, leaf — were those of the night-
shade, while on the other the organs were evidently derived
from the tomato. It is obvious that such unusual forms,
which Winkler called "Chimaera," are not hybrids in any
true sense of the word, but have arisen from buds which
contain the tissue of the two parent formed at the junction
of the stock and graft.

Later on there developed, however, shoots which were
evidently of hybrid origin. Cell fusion had unquestion-
ably taken place. Several hybrids with different attributes
were produced. These have been given different names
by Professor Winkler, and may be described as follows : —

1. Solanum tubingense is intermediate in the size and

Hybridization 147

shape of the leaves and the color and type of the flowers
between the nightshade and the tomato. The fruit is
very much like that of the nightshade, but is rather larger,
and although it is black there are some traces of the red
or yellow color of the tomato.

2. Solanum proteus has very variable leaves, which,
on the whole, are more divided than those of S. tubingense,
while in the characters of the flowers and the fruit it is
more like the tomato than like the nightshade.

3. Solanum Kolreuterianum, and

4. Solanum Gartnerianum. These forms have been
produced several times. The first is more like the tomato,
the second more like the nightshade, but each differs in
important particulars from either of the parents.

5. Solanum Darwinianum. The point of especial inter-
est in connection with this form is that of all the so-called
" graft-hybrids " secured by Winkler this seems to be the
only one which is likely to prove a hybrid in the strict
sense of the word. The fruit of this plant, unlike the
others, was sterile, no perfect seeds being formed. The
fruit itself is a round small berry like the fruit of the night-
shade in form, but having the color and structure of the
tomato.

Are these real graft-hybrids ? — In all of these forms when
seed was produced at all, it produced seedlings of one parent
or the other, never producing the apparent hybrid.

It has been suggested by Bauer that these apparent
true hybrids might be chimaeras of a type which he has
called "periclinal," i.e. the outer tissues are derived
from one parent, and the inner tissues from the other,
but none of the tissues themselves are of hybrid origin.

148 Plant-Breeding

This explanation has also been applied to Cytisus hybrids
in which it has been shown that the epidermal tissues were
strikingly like those of C. purpureus, while the inner tissues
were like those of C. laburnum.

In a later paper, Winkler arrives at the following
conclusions : —

Hybrids may be arranged in two groups, sexual and
graft-hybrids. The latter may be divided into three
classes according to the theoretical possibility of their
method of origin, viz. : (1) Fusion graft-hybrids arising
from a fusion of two somatic cells derived from distinct
species. (2) " Influenced " graft-hybrids which arise from
specific influences of one graft component upon the other
without cell fusion (as through chemical substances, trans-
location of cytoplasm, etc.). (3) Chimseras, in which
specifically pure cells from both graft components are
combined to form a new individual. These chimseras may
be : (a) Sectorial chimseras in which the two sorts of cells
in the growing point are divided by a longitudinal plane.
(6) Periclinal chimseras in which the periclinal cell layers
of the growing point are furnished respectively from one or
the other parent form, (c) Hyper-chimseras in which the
growing point is made up of a mosaic of cells derived from
the two parent forms.

CHAPTER VII
HEREDITY

ALL plants arise from parents more or less like them-
selves. This reproduction has a visible material basis in
the egg-cells and pollen-grains liberated from the parental
bodies. By inheritance is meant all the qualities which
have their physical basis in the fertilized egg-cell, the ex-
pression of which results in the organism. "Thus," says
Thomson, "heredity is no force, no principle, but a con-
venient term for the genetic relation between successive
organisms."

The inheritance of plants may be studied by considering
parents and their offspring collectively or by studying
the separate characters and their modes of transmission.
The former is statistical, the latter, analytical. Studies
of heredity from both points of view are being extensively
conducted by the biometricians on the one hand and the
mendelians on the other.

Heredity studied collectively. — "To define heredity,"
says Davenport, "as the direct and personal relation
between the individual parent and the individual offspring
is not only to restrict its meaning within too narrow limits,
but to destroy its significance to the breeder and deceive
him as to the actual facts of transmission during descent.
' Heredity ' properly refers to the group that constitutes

149

150

Plant-Breeding
NUMBER OF TUBERS — 1909

V

1.5

3.5

5.5

7.5

9.5

11.5

13.5

15.5

17.5

19.5

21.5

23.5

1.5

1

2

1

3.5

1

6

6

3

2

2

5.5

4

6

8

8

5

6

1

o

7.5

4

7

11

8

8

3

2

9.5

2

7

17

13

15

4

1

3

1

1

11.5

2

2

14

11

14

6

3

4

2

13.5

1

5

4

10

7

3

5

1

1

15.5

1

1

1

1

5

9

6

5

2

3

3

1

17.5

2

4

2

3

2

2

3

1

19.5

1

1

2

2

2

2

21.5

2

1

1

1

1

2

23.5

2

1

1

1

1

25.5

1

1

27.5

29.5

1

31.5

33.5

1

0

*%

2

20

33

62

60

70

38

19

22

13

6

6

0

o

o

iO

0

o

o

o

iO

o

iO

o

0

s^

CO

o

pH

iO

o

iO

CO

-"•

iO

co

O5

^4

^S

1>

00
1— 1

CO

i>

00

r— I

3

co

*

T— 1

3

0

N

^

^

N

^

o

o

0

o

§

o

0

Q'

05

1

>&
\

co
1

i-H
1

+

<N

'

CO

oo

o

1— 1

SH

0

B

O5

§

g

S

8

S

05

i

S

g

8

s

a

05

»o

8

co

T— 1

<N

iO

oo

T—t

s

00

CO

8

rH

o

00

7— (

o

>-H

R

O

o

§

CO

00
1— 1

g

S

S

2

%

1-H

i-H

1

1

CO
1— 1

CO

r— 1

i

co
So

1

1

I

Heredity

151

25.5

27.5

41.5

43.5

/10 1/09 '09

D09

»m

-^09/09

2P

4

6

-9.83

96.62

386.48

165.14

20

70

-7.83

61.30

1226.00

814.32

40

220

-5.83

33.98

1359.20

443.08

1

44

330

-3.83

14.66

645.04

347.76

1

65

617.5

-1.83

3.34

217.10

92.41

58

667

0.17

.02

1.16

- 4.18

37

499.5

2.17

4.70

173.90

119.56

2

1

41

635.5

4.17

17.38

712.58

535.01

19

332.5

6.17

38.06

723.14

318.98

10

195

8.17

66.74

667.40

285.95

8

172

10.17

103.42

827.36

410.86

1

7

164.5

12.17

148.10

1036.70

390.65

2

51.0

14.17

200.78

401.56

93.52

0

16.17

261.46

1

29.5

18.17

330.14

330.14

-67.22

0

20.17

406.82

1

0

67

22.17

491.50

983.0

456.70

3

3

1

358

4057

9690.76

4402.54

10 O \o

o

CO £ CO

co

l> 00 TfH

o M09 = 11.33 ± .182

M10 = 11.20 ± .182

33 '3

0-09 = 5.20 ± .130

"^ CO ^J

<r10 = 5.23 ± .131

i— i i— i CO

r = 4402'54 =.452

Oi Oi Oi

358(5.2) (5.23)

T^H CO <N

Er .6745(1 -r2)

11 1

.6745(.80) , ft.

l> t>- Oi

pn ! * — ••• ^- .\Jtj

oq 18.9

co t> co

i— 1 Oi TfH

S

CO l> C

|

152 Plant-Breeding

the parentage and the related group that constitutes
the offspring."

The coefficient of heredity. — The degree of inheritance
between a parental group of plants and their corresponding
group of offspring is determined by the use of a correlation
table. The degree of correlation or the resemblance is
determined between the parents and offspring. This may
be expressed mathematically and the result is known as
the "coefficient of heredity." The latter is, therefore,
nothing more nor less than the correlation coefficient (r)
obtained from a table in which two sets of individuals
related by descent are tabulated with respect to the same
character. The coefficient of heredity is expressed as a
decimal, somewhere between 0 and 1. The nearer 1,
the greater the closeness of resemblance between parents
and offspring, and conversely the nearer 0, the smaller
the degree of resemblance.

In the table (pp. 150-151) will be found the number of
tubers in hills of potatoes in 1909 as compared with the off-
spring from these hills in 1910. For example, there were 3
hills of seedling potatoes having either 7 or 8 tubers in 1909
represented in the table by the midpoint 7.5 which gave
offspring in 1910 having either 3 or 4 tubers (3.5) ; 8
parental hills numbering either 7 or 8 tubers in 1909 which
produced offspring in 1910 having either 5 or 6 tubers ;
11 parental hills having the same number of tubers as
above which produced offspring having either 7 or 8 hills,
and so forth for each number in the table : —
Notation. —

n = Total number of individuals in the population,
equals summation of all frequencies.

Heredity 153

/og = Class frequencies of total population in 1909.

Fog = Value or measurement corresponding to a given
frequency in 1909.

MW = Mean number of potatoes per hill in 1909.

Dog = Deviation of number of tubers per hill from mean,
1909.

cr09 = Standard deviations of number of tubers per hill,
1909.

/io = Class frequencies of total population in 1910.

y10 = Value or measurement corresponding to a given
frequency in 1910.

MIQ = Mean number of potatoes per hill in 1910.

DIO = Deviation of numbers of tubers per hill from
mean, 1910.

o-10 = Standard deviation of number of tubers per hill,
1910.

r — Coefficient of correlation.

The process of finding the mean and standard devia-
tion is the same as is given in Chapter IV, so that the
only column that needs explanation is the one headed
SP.

As an example, we will take the column on the 1910
tubers, beginning with 15.5. The figures 1, 1, 1, 1, 5,
9, 6, 5, 2, 3, 3, 1, 2, 1 are known as a horizontal array;
similarly the vertical columns are known as a vertical
array. We will now show how 535.01 in 3P column is
obtained.

The first number after 15.5 is 1. Going down the verti-
cal column to column Di0, we find — 9.7, which is multi-
plied by 1 ; the same process is gone through for each
number following 15.5 and the algebraic sum is taken,

154 Plant-Breeding

which is multiplied by 4.17, found in column D09 opposite
15.5. So the result is as follows : —

4.17+ l(-9.7) +l(-7.7)+ 1 (-5.7)+ l(-

9(0.30) +6(2.3) +5(4.3) +2(6.3) +3(8.3) +3(10.3)+1(12.3)

+ 2(14.3)+ 1(16.3) = 535.01.

Having obtained all the numbers in the 2P column, the
sum is taken and the coefficient of correlation is found ac-
cording to the following formula : —

SP

4402.54

358(5.20) (5.23)

Conception of unit-characters. — Most recent studies are
analytical in their nature. We now conceive of plants
and animals to be composed of separately heritable units
known as unit-characters. It is not possible at present to
say exactly what a unit-character is, but we may call it
the smallest heritable part or attribute a plant may
possess. For example, the color of the flower, size and
shape of leaf, height of the plant, susceptibility or im-
munity to disease, and so forth, may be unit-characters.

Knowledge of heredity has come through experimental
breeding. — Much has been written and many conjectures
made by earlier horticulturists in their attempt to classify
hybrids so that inheritance could be found to proceed in
an orderly and regular manner. All of these attempts
had been more or less failures until Gregor Mendel, an
Austrian monk, began a series of classic experiments in

Heredity 155

crossing garden peas. Mendel's work, however, was little
known at the time and did not receive public recognition
until many years afterwards.

Rediscovery of Mendel's work by de Vries and others. —
de Vries made a thorough search of the literature of plant
evolution. In an American publication x he saw a ref-
erence to an article on plant hybrids by G. Mendel,
published in 1865 in the proceedings of a natural history
of Briinn in Austria.

On looking up this paper he was astonished to find that
it discussed fundamental questions of hybridization and
heredity, and that it had remained practically unknown
for a generation. In 1900 he published an account of it,
and this was soon followed by independent discussions
by Correns, Tschermak, and Bateson. In May, 1900,
Bateson gave an abstract of Mendel's work before the
Royal Horticultural Society of England; and later the
society published a translation of Mendel's original paper.
It is only within the last 10 or 12 years that a knowledge
of Mendel's work has become widespread in this country.
Perhaps the agencies that are most responsible for dis-

1 The following extract from a letter from Professor de Vries (printed
here by permission) will explain the reference in the text : " Many years
ago you had the kindness to send me your article on ' Cross-breeding and
Hybridizing ' of 1892 ; and I hope it will interest you to know that it was
by means of your bibliography therein that I learnt some years after-
wards of the existence of Mendel's papers, which now are coming to so
high credit. Without your aid I fear I should not have found them at
all." My reference to Mendel in the bibliography referred to was taken
from Focke's writing. I had not seen Mendel's paper. The essay,
"Cross-breeding and Hybridizing," formed Chapter II of the old
"Plant-Breeding"; but the bibliography that accompanied it was not
reprinted until the second edition of the book. — L. H. B.

156 Plant-Breeding

semination of the mendelian ideas in America are the in-
struction given by Webber and others in the Graduate
School of Agriculture at Columbus, Ohio, in the summer
of 1904 and the prolonged discussion before the Interna-
tional Conference on Plant Breeding at New York in the
fall of 1902. Since that time many articles on the subject
have appeared from our scientific press.

Mendel's work is important because it cuts across many
of the current notions respecting hybridization. As
de Vries' discussions call a halt in the current belief re-
garding the gradualness and slowness of evolution, so
Mendel's call a halt in respect to the common opinion
that the results of hybridizing are largely chance, and that
hybridization is necessarily only an empirical subject.
Mendel found uniformity and constancy of action in
hybridization, and to explain this uniformity he proposed
a theory of heredity.

One of the most significant points connected with
Mendel's work is the great care he took to select plants
for his experiments. He thought that hybridism is a
complex and intricate subject, and that, if we are ever to
discover laws, we must begin with the simplest and least
complicated problems. He was aware of the general
opinion that the most diverse and contradictory results are
likely to follow any hybridization. He conceived that
some of this diversity may be due to instability of parents
rather than to the proper results of hybridizing. He also
saw that he must exclude all inter-crossing in the progeny.
Furthermore, the progeny must be numerous, for, since
incidental and aberrant variation may arise in the plants,
it is only by a study of averages of large numbers that the

Heredity 157

true results of the hybridization are to be discovered.
Moreover, the study must be more exact than a mere con-
trasting and comparing of plants : character must be com-
pared with character.

Mendel's experiments. — The garden pea seemed to fulfill
all of the requirements. Mendel chose well-marked hor-
ticultural races or varieties. He grew these two years
before the experiment proper was begun in order to de-
termine their stability or trueness to type. When the
experiments were finally begun, he used only normal
plants as parents, throwing out such as were weak or
aberrant. Peas are self-fertile. It was to be expected
that under such conditions the hybrid offspring would
show uniformity of action ; and it did.

In order to study the behavior of the hybrids, it was
necessary to choose certain prominent marks or characters
for comparison. Seven of these characters were chosen
for observation. These marks pertain to seed, fruit,
position of flowers, and length of stem, and they may be
assumed to be representative of all other characters in
the plant. These characters were paired (practically
opposites) as long-stem vs. short-stem, round-seed vs.
angular-seed, inflated pods vs. constricted pods. They
were " constant" and "differentiating." Of course every
parent plant possessed one or the other of every pair of
contrasting characters ; but in order to facilitate his
studies, Mendel chose a special set of parents to illustrate
each character.

The seed-shape characters were roundness and angu-
larity— the former being the " smooth" pea of gardeners
and the latter the " wrinkled" pea. Let us suppose that

158 Plant-Breeding

twenty-five flowers on round-seeded plants were cross-
pollinated in the summer of 1900 with pollen from angular -
seeded plants, or vice versa, and that an average of four
seeds formed in each pod. With the death of the parent
plants the old generation ended, and the 100 seeds that
matured in 1900 — the year in which the cross was made —
began the next generation; and these 100 seeds were
hybrids. Now, all of these 100 seeds were round. Round-
ness in this case was "dominant." (Dominance per-
taining to the vegetative stage of the plant of course would
not appear until 1901, when the seeds "grow."") These
seeds are sown in the spring of 1901. If each seed be
supposed to give rise to four seeds, — or 400 in all, — this
next generation of seeds (produced in 1901) will show
300 round and 100 angular seeds. That is, the other seed-
shape now appears in one-fourth of all the progeny; this
character is said to have been "recessive" in the first
hybrid generation. If the 100 angular seeds, or reces-
sives, are sown in 1902, it will be found that all the progeny
will be angular-seeded or will "come true"; and this
occurs in all succeeding generations, providing no crossing
takes place. If the 300 round seeds, or dominants, are
sown in the spring of 1902, it will be found that 100 of them
produce dominants only, and that 200 of them behave as
before — one-fourth giving rise to recessives and three-
fourths to dominants; and this occurs in all succeeding
generations, providing no crossing takes place. In other
words, the three-fourths of dominants in any generation
are of two kinds, — one-third that produce only dominants,
and two-thirds that are hybrids. That is, there is con-
stantly appearing from the hybrids one-fourth that are

Heredity

159

recessives, one-fourth that are constant dominants, and
one-half that are dominants to all appearances, but which
in the next generation break up again into dominants
and recessives. This one-half part that breaks up into
the two characters are the true hybrids; but they are
hybrids only in the sense that they hold each of the two
parental characteristics — roundness and angularity — in
their purity and not as blends or intermediates ; and these
two characteristics reappear in all succeeding generations
in a definite mathematical ratio. Proportionally, these
facts may be expressed as follows : —

1900.

Iseed

1901.

8R

16 R

It will be seen that two-thirds of the dominants break
up the following year into one-fourth constant dominants,
one-fourth recessives, and one-half that again break up,
the half that break up being the hybrids. This formula
for the hybrids is Mendel's law. In words, it may be
expressed as follows : Differentiating characters in plants
reappear in their purity and in mathematical regularity

160 Plant-Breeding

in the second and succeeding hybrid offspring of these
plants; the mathematical law is that each character
separates in each of these generations in one-fourth of the
progeny and thereafter remains true. In concise figures,
it is expressed as follows : —

1 D : 2 DR : 1 R.

1 D and 1 R come true, but 2 DR breaks up again into
dominant and recessives in the ratio of 3 to 1.

Mendel found that this law holds more or less for the
other characters that he studied in the pea, as well as for
the seed-shape. He did not conclude, however, that it
holds good for all plants, but left the subject for further
investigation. It will be seen at once that it will be a
very difficult matter to follow this law when many char-
acters are to be constrasted, particularly when the char-
acters are quantitative, or qualitative which grade into
each other.

The dominant characters pertain to either parent. Some
of them may come from the seed parent and some from
the pollen parent. When this roundness is dominant from
the male parent, there can be seen the immediate effect of
pollen, the same as if the dominant roundness came from
the female parent. In the case of the pea, the seed-content
is embryo and we are not surprised to find this immediate
effect of pollen. In those plants in which the embryo
is embedded in endosperm, however, the effect of the cross-
fertilization is not seen until the seed has been planted
and produced a new generation. The endosperm is a part
of the female parent and is not ordinarily changed by the
process of cross-fertilization. In the case of a few plants,

Heredity 161

of which the Indian corn is the most conspicuous example
(Fig. 43), there is double fecundation, both the embryo and
endosperm being fertilized, and hence if the male parent
contains dominant characters, they will be seen immediately
because of the cross-fertilized endosperm. This is called
Xenia and has been carefully worked out by de Vries,
Webber,1 and others.
Mendel's numerical results.2 —

In the experiments conducted by Mendel with peas the
relative numbers obtained for each pair of differentiating
characters are as follows : —

Experiment 1. — Form of seed. From 253 hybrids,
7324 seeds were obtained in the second trial year. Among
them were 5474 round and roundish and 1850 angular,
wrinkled ones. Therefore, the ratio 2.96 is to 1 is de-
duced.

Experiment 2. — Color of albumen. 258 plants yielded
8023 seeds, 6022 yellow and 2001 green ; their ratio, there-
fore, is 3.01 to 1.

Experiment 3. — Color of seed-coats. Among 929
plants, 705 bore violet-red flowers and gray-brown seed-
coats ; 224 had white flowers and white seed-coats, giving
the proportion of 3.15 to 1.

Experiment 4. — Form of pods. Of 1181 plants, 882
had them simply inflated and in 299 they were constricted.
Resulting ratio 2.95 to 1.

Experiment 5. — Color of unripe pods. The number

1 Bull. 22, Div. of Veg. Phys. and Path., U. S. Dept. of Agric., 1900.

2 The following is taken from a translation of Mendel's article as given
by Bateson, and slightly revised. See Bateson-Mendel's "Principles of
Heredity," Appendix.

M

FIG. 43. — Mendelism in maize. — Stowell Evergreen (sweet corn) was pol-
linated with Indian flour corn, giving a hybrid similar to the latter the
first year. This was self-pollinated, giving the ear on the right, and
pollinated with the evergreen, giving the ear on the left (Webber).

162

Heredity 163

of trial plants was 500, of which 428 had green pods and
152 yellow pods. Consequently these stand in the ratio
2.82 to 1.

Experiment 6. — Position of flowers. Among 858 cases,
651 had inflorescence axial and 207 terminal. Ratio 3.14
to 1.

Experiment 7. — Length of stem. Out of 1064 plants
in 787 cases the stem was long and in 277 short. Hence
a mutual ratio of 2.84 to 1.

If the results of the whole experiment be brought to-
gether, there is found, as between the numbers of forms
with the dominant and recessive characters, an average
ratio of 2.98 to 1 or 3 to 1.

The following is an account of Mendel's results with
peas in their third hybrid generation (F3) : —

These forms which in the F2 generation exhibit the
recessive character do not further vary in the F$ generation
as regards this character : they remain constant in their
offspring.

It is otherwise with those that possess the dominant
character in the second generation. Of these, two-thirds
yield offspring that display the dominant and recessive
characters in the proportion of 3 to 1, and thereby show
exactly the same ratio as the hybrid forms, while only
one-third remain with the dominant character constant.

The separate experiments yield the following results : —

Experiment 1. — Among 665 plants which were raised
from round seeds of the second generation, 193 yielded
round seeds only, and remained, therefore, constant in
this character; 372, however, gave both round and
wrinkled seeds, in the proportion of 3 to 1. The number

164 Plant-Breeding

of the hybrids, therefore, as compared with the constants,
is 1.93 to 1.

Experiment 2. — Of 509 plants which were raised from
seeds whose albumen was of yellow color in the second
generation, 166 yielded exclusively yellow,while 353 yielded
yellow and green seeds, in the proportion of 3 to 1. There
resulted, therefore, a division into hybrid and constant
forms in the proportion of 2.13 to 1.

For each separate trial in the following experiments,
100 plants were selected which displayed the dominant
character in the second generation, and in order to as-
certain the significance of this, ten seeds of each were
cultivated.

Experiment 3. -- The offspring of 36 plants yielded
exclusively gray-brown- seed-coats, while of the off-
spring of 64 plants some had gray-brown and some
had white.

Experiment 4. — The offspring of 29 plants had only
inflated pods ; of the offspring of 71, on the other hand,
some had inflated and some had constricted.

Experiment 5. — The offspring of 40 plants had only
green pods ; of the offspring of 60 plants, some had green
and some yellow ones.

Experiment 6. — The offspring of 33 plants had only
axial flowers; of the offspring of 67, on the other hand,
some had axial and some terminal flowers.

Experiment 7. — The offspring of 28 plants inherited
the long axis, and those of the 72 plants some of the long
and some of the short axis.

In each of these experiments a certain number of plants
came constant with the dominant character. For the

Heredity 165

determination of the proportion in which the separation
of the forms with the constantly persistent character
results, the first two experiments are of especial importance
since in these a greater number of plants can be compared.
The ratios 1.93 to 1 and 2.3 to 1 gave together almost
exactly the average ratio of 2 to 1. The sixth experiment
gave a quite concordant result; in the others the ratio
varies more or less, as was only to be expected in view of
the small number of 100 trial plants. Experiment 5,
which shows the greatest departure, was repeated, and
then in place of the ratio of 60 and 40 that of 65 and 35
resulted. The average ratio of 2 to 1 appears, therefore,
as fixed with certainty. It is, therefore, demonstrated
that, of those forms which possess the dominant character
in the second generation, two-thirds have the hybrid-
characters, while one-third remain constant with the
dominant characters.

The ratio of 3 to 1, in accordance with which the dis-
tribution of the dominant and recessive characters re-
sults in the second generation, resolves itself, therefore, in
all experiments into the ratio of 2 : 1 : 1 if the dominant
character be differentiated according to its significance
as a hybrid-character or as a parental one. Since the
second generation (^2) springs directly from the seed of
the first generation (Fi), it is now clear that the hybrids
from seeds have one or the other of the two differen-
tiating characters, and of those one-half develop again
the hybrid form, while the other yields plants which re-
main constant and receive the dominant or the recessive
characters, respectively, in equal numbers.

Dominance and recessiveness. — Which characters will

166 Plant-Breeding

be dominant in any species we cannot determine until we
perform the experiment; that is, there is no mark or
attribute which distinguishes to us a priori a dominant or
a recessive character. However, the mere fact as to
whether the one or the other character is dominant is
relatively unimportant, for constant dominance is no
more a regular behavior than recessiveness is. In various
subsequent experiments it has been found that even
when marked dominance is not shown in the first product,
the hybridization may follow the law in essential numeri-
cal results. The really important points are : (1) That
the characters typically remain pure or do not blend,
and (2) that their reappearance follows a numerical
order.

Explanation of mendelian results. — After finding such
surprising results as these, Mendel naturally endeavored
to discover the reasons why. The product of his specu-
lations is the theory of gametic purity (to use our present-
day terminology), which is a partial theory of heredity.
Every plant is the product of the egg, or female, cell
fertilized by the sperm, or male, cell. When constant
progeny is produced, it must be because the two cells, or
gametes, are of like character. When inconstant progeny
is produced, it must be because the sperm-cell is of one
character and the egg-cell of another. When these un-
like gametes come together, they will unite according to
the law of mathematical probabilities, one-fourth of those
of each kind coming together and one-half of those of
both kinds coming together. If A and B represent the
contrasting parental characteristics, they would combine
as: —

Heredity 167

A + A = A\
A + B = AB.
B +A = BA.
B + B = B\

A2 and B2 are equivalent only to A and B. Since both
of the opposed or contrasted characters cannot be visible
at the same time, we have the following : —

B

in which small 6 represents the character that for the
time being is not able to express itself, or is recessive, and
large B represents the same character fully expressed.

In these gametes, the unit-characters of the plants that
bear them are pure. Even in hybrid plants the pollen-
grains and the egg-cells are not hybrids. According to
the hypothesis of gametic purity, therefore, hybrids
follow natural and numerical laws; but these laws are
always obscured by new crossing. True intermediate
characters do not occur. If new characters appear, it is
because they have been recessive or latent for a genera-
tion, or because the plant has varied from other causes ;
they are not the proper results of hybridization, unless
they are due to a reconstruction of characters. We may
suppose that a new character that appears because of
some internal change may be impressed on the gametes
and thereby be perpetuated. The results of hybridiza-
tion, according to the mendelian view, are not funda-

168 Plant-Breeding

mentally a mere game of chance, but follow a law of
regularity of averages ; but the results are so often masked
that it is sometimes impossible to recognize the law.

It is a question, of course, whether the proportional
results secured by Mendel and others express a biological
principle, or whether they are only the numerical propor-
tions that may be adduced from the averages of large
numbers of combinations — whether these combinations
are of gametes or letters, or words, or figures. It is a
fundamental necessity that certain proportions follow
from " chance " combinations often repeated. But whether
the " theorem of probabilities" can express a real bio-
logical fact may well be doubted. Perhaps the basis of
heredity is something more than the mechanico-physical
conceptions that we habitually apply to it.

Mendel's law of heredity is stated as follows by Bateson
and Saunders : "The essential part of the discovery is the
evidence that the germ-cells or gametes produced by
cross-bred organisms may in respect of given characters
be of the pure parental types and consequently incapable
of transmitting the opposite character; that when such
pure similar gametes of opposite sexes are united together
in fertilization, the individuals so formed and their pos-
terity are free from all taint of the cross, that there may
be, in short, perfect or almost perfect discontinuity
between these germs in respect of one of each pair of op-
posite characters."

The genetic constitutions of plants, if they are known,
may be conveniently represented by formulae containing
the gametic make-up of the parents entering into their
union. At least such unit-characters as are known may

Heredity

169

be represented in this manner. For example, RR may
represent a plant which has been formed by the union
of a red pollen-grain (pollen-grain from a pure red parent)
R and a red egg-cell R. This plant if self -fertilized will
always remain red. Similarly rr represents a plant
which has the absence (or the opposite) of red, say, yellow.
If a red plant R were crossed with a yellow plant r, the
result would be a hybrid Rr. Red being dominant, the
first generation hybrid, F\, would appear as red.

The following method of squares will be found very
convenient to illustrate the action of chance which governs
the union of gametes to form the F2 hybrid plants : —

POLLEN-GEAINS

R r

(1)

(2)

RR

Rr

(3)
Rr

(4)
rr

Square (1) represents a plant (RR) formed from the
union of a red pollen-grain R with a red egg-cell R,
and is pure red. Square (2) represents a hybrid plant
(Rr) formed by r pollen-grain and R egg-cell. Square (3)

170

Plant-Breeding

Heredity 171

is the same as (2) except formed by pollen-grain R and
egg-cell r, and square (4) is a pure recessive rr in which
pollen-grain r united with egg-cell r.

This may be illustrated diagrammatically in another
manner, as in the colored plate (Fig. 44) .

Explanation of diagram. — It is assumed that a variety
having red flowers (R) is crossed with another variety
having yellow flowers (r). The arrow indicates the
direction of the cross and also the transfer of pollen from
the anthers of the yellow variety to the stigma of the red.
The plants produced from these fertilized ovules will
have red flowers because redness is dominant. This F\
hybrid, however, contains both red and yellow qualities
and at the time of the formation of its gametes will give
rise to red and yellow pollen-grains and egg-cells. During
the process of self-fertilization the law of chance will
govern the union of the red and yellow egg-cells. These
FI ovules will give rise to the plants indicated by Fz.
The subsequent operations are assumed to follow regular
mendelian ratios.

Mendel's results with the offspring of hybrids in which
several differentiating characters are associated. — Two ex-
periments were made with a considerable number of plants.
In the first experiment the parental plants differed in the
form of the seed and in the color of the albumen. Experi-
ments with seed characters give the results in the simplest
and most certain way.

Experiment 1 . — Seed parent = round seeds (R) and
yellow cotyledons (Y). Both dominant and hence their
symbols are expressed as capital letters. Pollen parent
= angular seeds (r) and green cotyledons (y). Round

1 72 Plant-Breeding

yellow (RY) X angular green (ry) = RrYy appearing as
round and yellow in FI.

Gametes of F\ = RR, Ry, rY, and ry.

Visible types of F2 = 9 (apparently) RY, 3 Ry, 3 rY,
and 1 ry.

The following were actually found by Mendel in F2 : — •

RY, round and yellow, 315.

rY, angular and yellow, 101.

Ry, round and green, 108.

ry, angular and green, 32.

These figures stand approximately in the ratio of 9 RY :
3 rY : 3 Ry : 1 ry, but these forms, which appeared to be
only four classes, were found in the next generation to be
made up of nine really different classes.

From the round yellow seeds (apparently RY) there
were obtained in the next year : —

1. RY, round and yellow seeds, 38

2. RYy, round, yellow and green seeds, 65

3. RrYj round, yellow and angular seeds, 60

4. RrYy, round, yellow and green angular, yellow
and green, 138

From the round and green seeds (apparently Ry) were
obtained : —

5. Ry, round and green seeds, 35

6. Rry, round angular and green seeds, 67
From the angular and yellow seeds (apparently rY)

were obtained : —

7. rY, angular and yellow seeds, 28

8. rYy, angular and yellow-green seeds, 67
From the angular and green ry seeds were obtained : —

9. ry, angular and green seeds, 30

Heredity 173

Compare this carefully with problem 4 with special
reference to the actual counts as compared with theo-
retical ones.

The offspring of the hybrids appeared, therefore, under
nine different forms, some of them in very unequal num-
bers. When these are collected and coordinated, we
find:-

38 plants with the sign RY.

35 plants with the sign Ry.

28 plants with the sign rY.

30 plants with the sign ry.

65 plants with the sign RYy.

68 plants with the sign rYY.

60 plants with the sign RrY.

76 plants with the sign Rry.
138 plants with the sign RrYy.

The whole of the forms may be classed into three essen-
tially different groups. The first includes those with
the signs RY (or RRYY, as previously designated — it is
not necessary, however, to repeat the letters), Ry, rY, and
ry ; they possess only constant characters and do not vary
again in the next generation. Each of these forms is
represented, on the average, thirty-three times.

The second group includes the signs RYy, RrY, Rry;
these are constant in one character and hybrid in another,
and vary in the next generation only as regards the
hybrid character. Each of these appears, on the average,
sixty-five times. The form RrYy occurs 138 times; it
is hybrid in both characters and behaves as do the hybrids
from which it is derived.

174 Plant-Breeding

If the numbers in which the forms belonging to these
classes appear, be compared, the ratios of 1, 2, and 4 are
evidently unmistakable. The numbers 32, 65, 138 present
very fair approximations to the ratio numbers of 33, 66, 132.

The developmental series consists, therefore, of nine
classes of which four appear therein always once and are
constant in both characters; the forms RY, ry resemble
the parental forms, the two others present combinations
between the conjoined characters R, r, F, y, which com-
binations are likewise possibly constant. Four classes
appear always twice, and are constant in one character
and hybrid in the other. One class appears four times,
and is hybrid in both characters. Consequently the off-
spring of the hybrids, if two kinds of differentiating char-
acters are combined therein, are represented by the ex-
pression RY — Ry — rY—ry — 2 RYy — 2rYy — 2 RrY

This expression is indisputably a combination series
in which the two expressions for the characters R and r,
y and Y are combined. We arrive at the full number of
the classes of the series by the combinations of the ex-
pressions.

The following, quoted from East, has reduced the
above to a mathematical expression : "The numerical rela-
tions found are approximately the following series : AB,
Ab, aB, ab, 2 ABb, 2 aBb, 2 Aab, 2 AaB, and 4 AaBb. This
is really a combination by multiplication of the two series
(A — 2Aa — a) x (B — 2 Bb — b) = AB — Ab — aB
- ab — 2 ABb — 2 aBb — 2 Aab — 2 AaB — 4 AaBb.
The two pairs of characters behave independently of each
other and as if chance only governed their combinations.

Heredity

175

Moreover, three pairs of contrasted characters were found
to behave in exactly the same manner, the number of
forms found being what would theoretically be expected
if the above product were multiplied by another series
represented by C — 2 Cc — c.

" These results can be reduced to still simpler terms, as
is shown in the following table. Let N represent the
number of pairs of contrasted characters in the parents.
When they are crossed the second generation, when self-
fertilized, shows visible differences of 2 to the nth power.
These visibly different classes actually contain 3 to the
nth power different classes, the phenomena of dominance
obscuring part of them. Finally, when crossing to secure
combinations of n characters, we must have 4 to the nth
power number of individuals, to be theoretically certain
of at least one individual in each class.

MENDEL'S LAW OF INHERITANCE OF UNIT-CHARACTERS

No. OF PAIRS

OF DlF. BE-
TWEENPARENTS

NO. OF VISIBLY

DIF. CLASSES
EACH CONT. ONE
PURE INDIVIDUAL

No. OF ACTUAL
CLASSES BOTH
PURE AND HYBRID

SMALLEST No. OFFSPRING,
ALLOWING AT LEAST ONE TO
A CLASS

n

2n

3n

4n

1

2

3

41

Experimentally

2

4

9

16

tested by Men-

3

8

27

65 j

del for peas

4

16

81

256

5

32

243

1024

Calculated

6

64

729

4096 J

A is substituted for R, a for r, B for T7, and 6 for t, and
instead of writing AA and aa in the series, one of the
letters is dropped."

176

Plant-Breeding

Heredity 177

Results involving three pairs of characters (trihybrid). —
When three allelomorphic pairs are concerned, the num-
ber of forms in the second and subsequent generations is
greatly increased. For illustration, let us take a hypo-
thetical case. Suppose we cross together a tomato having
red fruit, dwarf vine, and hairy stems and leaves (the
latter is hypothetical) with a variety having yellow fruit,
tall vine, and smooth stems. Their formulae would be as
follows, using capitals again to represent dominant units
and small letters to represent recessive units : red,
dwarf, hairy (RtH) X yellow, tall, smooth (rTh) = red,
tall and hairy (in appearance) RrTtHh. F2 generation
will be as shown in table on page 178.

In order to get a better understanding of the probable
union of gametes of various kinds of crosses, the student
should carefully master the method of squares, always
having in mind that the use of formulae is only a con-
venient method of representing plants. Each square
represents a plant. (See methods as already outlined on
page 169.) Capital letters will be used for dominant
units and small letters for recessives as formerly. Plants
having as their formulae large and small of any letter, i.e.
Rr, are hybrids (heterozygous) for that character, and those
in which the letters are the same, i.e. RR, are pure (homo-
zygous) for that character.

It will be seen that when three pairs of characters are
involved, at least 64 squares are necessary to allow for
the theoretically possible number of combinations to be
formed. A very careful study of the table will show that
there are produced 8 visible types (2n) with proportions
as follows : 27 Red Tall Hairy, RTH ; 9 Red Tall smooth,

178

Plant-Breeding
POLLEN-GRAINS

RTH

RTh

RtH

Rth

rTH

rTh

rtH

rth

RR

RR

RR

RR

Rr

Rr

Rr

Rr

RT

TT

TT

Tt

Tt

TT

TT

Tt

Tt

HH

Hh

HH

Hh

HH

Hh

HH

Hh

RR

RR

RR

RR

Rr

Rr

Rr

Rr

RTh

TT

TT

Tt

Tt

TT

TT

Tt

Tt

Hh

hh

Hh

hh

Hh

hh

Hh

hh

RR

RR

RR

RR

Rr

Rr

Rr

Rr

RtH

Tt

Tt

tt

tt

Tt

Tt

tt

tt

HH

Hh

HH

Hh

HH

Hh

HH

Hh

RR

RR

RR

RR

Rr

Rr

Rr

Rr

Rth

Tt

Tt

tt

tt

Tt

Tt

tt

tt

Hh

hh

Hh

hh

Hh

hh

Hh

hh

Rr

Rr

Rr

Rr

rr

rr

rr

rr

rTH

TT

TT

Tt

Tt

TT

TT

Tt

Tt

HH

Hh

HH

Hh

HH

Hh

HH

Hh

Rr

Rr

Rr

Rr

rr

rr

rr

rr

rTh

TT

TT

Tt

Tt

TT

TT

Tt

Tt

Hh

hh

Hh

hh

Hh

hh

Hh

hh

Rr

Rr

Rr

Rr

rr

rr

rr

rr

rtH

Tt

Tt

tt

tt

Tt

Tt

tt

tt

HH

Hh

HH

Hh

HH

Hh

HH

Hh

Rr

Rr

Rr

Rr

rr

rr

rr

rr

rth

Tt

Tt

tt

tt

Tt

Tt

tt

t!

Hh

hh

Hh

hh

Hh

hh

Hh

hh

NOTE. It must be remembered that these are different visible types
and not actual types. For example, the 27 which appear as RTh are
not all alike, their identity is obscured of dominance.

Heredity 179

RTh ; 9 Red dwarf Hairy, RtH ; 9 yellow Tall Hairy, rTH ;
3 Red dwarf smooth, Rth ; 3 yellow Tall smooth, rTh ;
3 yellow dwarf Hairy, rtH ;' and 1 yellow dwarf smooth,
rth. Of course most of the visible types are multiple,
containing both pure and hybrid forms. The number of
actually different types is 27 (3n) .

Incomplete dominance. — It was stated previously that
dominance is due to an unequal potency between the
unit-characters associated in a cross, the dominant unit
being " stronger" and covering up the weaker unit in the
FI generation.

This is not always the rule, by any means. There are
various degrees of equilibrium between the opposed
units : if one is much stronger than the other, complete
dominance occurs ; if they are of equal potency, we
have a form in the first generation which is intermediate
between the . two parents. This intermediacy may
lean to one parent or the other in proportion to their
strength.

When intermediacy exists, the mendelian ratios are
somewhat modified. Instead of having 3 : 1 ratio, we
have a 1 : 2 : 1, in which the 2 represents the heterozygous
or intermediate forms and the 1's represent the homo-
zygous forms.

If we are concerned with more than one allelomorphic
pair, complete dominance may occur in certain units and
intermediacy or incomplete dominance in others.

The commercial carnation is a heterozygous form which
is an intermediate between a single type and a type
which in commerce is called a " bull-head" or a " buster."
This latter is exceedingly double. When the hybrid

180 Plant-Breeding

commercial types are self-fertilized, they produce progeny
in the approximate ratio of 1 single : 2 commercial doubles :
1 dpuble-double or bull-head (Fig. 45).

FIG. 45. — Hybrid carnation (center) between a single and a burster,
showing intermediacy.

The hybrids between a large, apple-shaped tomato
and a small, pear-shaped one are intermediate between
the parents in the first generation, as has already been
noted. In all probability there are represented in the
above characters more than one unit. Emerson has
made similar observations in beans, gourds, and maize,
Locke in maize, and Castle in rabbits.

"While it is not uncommon," says Spillman, "for a
character to be dominant or recessive in a cross, it is
seldom that dominance is absolute. The presence of the
recessive characters can easily be detected, and in some
cases very easily. Thus in the cross between bearded

Heredity 181

and smooth wheat the hybrids usually show a slight tend-
ency to be bearded. Likewise, the cross between horned
and polled cattle may have scars (hornlessness is dominant) .
It frequently happens that instead of either of two opposite
characters being dominant, we get a form intermediate
between the two parent forms. Thus, in the cross be-
tween long-headed wheat and the short-headed club
wheats of the Pacific Coast, the hybrids have heads of
intermediate length, though they are much more like
club wheat than they are like the ordinary kinds, so that
the club character is at least partially dominant. In cer-
tain crosses between red-flowered and white-flowered
ornamental plants the hybrids are pink."

Presence-and-absence hypothesis. — The phenomena of
mendelian inheritance may be explained in one of two
ways : first, the presence of a definite substance in the
germ cells of both parents representing each unit-character
in the allelomorphic pair, and, second, the " presence-and-
absence" hypothesis. The latter assumes that what
appears to be a pair of characters is really the presence
and absence of a single character.

Examples of mendelian inheritance due to the presence-
and-absence of a single unit. — Red flowers may be
due to the presence of red, and white flowers to its
absence.

The wrinkled pea owes its character to the absence of
something which the round pea possesses. Darbishire
has found in the round pea that all of the sugar has been
converted into starch, while only a part of it has been
thus converted in the wrinkled pea and the wrinkling is
primarily due to the escape of the water from the solu-

182 Plant-Breeding

tion of sugar left over after ripening, and, consequently,
in the last resort due to the absence of that which completes
the conversion of the sugar into starch or, at any rate,
to an insufficiency in the quantity of that substance,
whatever it is. The round pea has the full share of this
substance, the wrinkled pea an insufficient one. Some-
thing is absent from the wrinkled which is fully present
in the round.

The same author applies the presence-and-absence
hypothesis to another pair of characters in peas, the
color of the cotyledons. The two characters which meet
the eye are yellow and green. But the matter is ' not
so simple as this. Bunyard has shown that there is a
yellow and a green pigment both in the yellow and in
the green cotyledon. When both are present at'
the same time, as in the ripe but still moist pea,
the green masks the yellow. All peas, both yellow
and green varieties, are green when they are eaten.
Just as cooks think that all peas -are round, so they
think that all peas are green. It is only gardeners who
sow and harvest them who know the distinction between
yellow and green.

The ripe but still moist cotyledons of both yellow- and
green-seeded varieties are, therefore, green. The yellow
kinds become yellow as they ripen ; the green do not
change color during this process. The yellowing of the
former is brought about by the gradual fading and dis-
appearance of the green pigment, which thus leaves the
yellow pigment (which is present in both kinds) exposed.
The successive stages in the fading of the green can be
easily observed. The simultaneous presence of both

Heredity 183

green and yellow pigment in yellow and in green peas
has also been demonstrated.

Green-seeded varieties therefore contain two pigments
in their cotyledons, a yellow and a green ; neither of them
fades during the process of ripening, and inasmuch as
the green masks the yellow, the ripe seed is green. Yellow-
seeded varieties also contain the same two pigments, but
the green fades in the process of ripening, so that the
ripe seed is yellow. This fading of the green pigment in
the yellow pea is supposed to be brought about by the
presence of some substance which is absent from the green
pea. Similarly, when the apparent absence of a character
is dominant, as in the case of dominance of hornlessness in
cattle and of white color in swine, there is believed to be
present an inhibiting factor or " inhibitor" which pre-
vents the formation of the black pigment. In other
words, it is the presence of the inhibitor (causing white)
over its absence (black) which explains the phenomena of
the dominance of white over black.

It is not the dominance of an absent factor, but the
presence of an unseen inhibitor, which reacts upon the
otherwise visible character, causing it to disappear.

Let us now consider another type of cause which may
be explained on the basis of the presence-and-absence
hypothesis. The heredity of the combs of fowls has been
carefully studied by Bateson, Davenport, Punnett, and
others. The latter gives an excellent description l of this
on the presence-and-absence hypothesis.

Four types of combs are recognized ; namely, rose, pea,
walnut, and single. (See Fig. 46.)

1 Punnett, " Mendelism," pp. 35, 36.

184

Plant-Breeding

B

Rose and pea combs behave as simple dominants to
single comb, segregating in the F% generation in the nor-
mal 3 : 1 ratio. What happens when the two dominants
are bred together? It was found that a third type ap-
peared as an FI hybrid, the so-called walnut comb.
When these FI hybrids were bred inter se, four types of

combs were found
among the F2 prog-
eny ; namely, walnut,
pea, rose, and single
in the approximate
ratios of 9:3:3:1
respectively. What
is the explanation
of this unusual phe-
nomenon ?

We are evidently
concerned with two
allelomorphic pairs
of characters, which
are the presence-and-
absence of rose comb
(R) and the presence-and-absence of pea comb (P).
As suggested by Punnett, let us denote the rose comb
by RRpp (containing the presence of rose and the
absence of pea) and the pea comb by rrPP. When these
are crossed together, the zygote RrPp results. This
differs from either and has a walnut comb. When these
FI hybrids are crossed together (RrPp X RrPp), the fol-
lowing results may be graphically expressed in the series
of squares : — •

FIG. 46. — Fowls' combs: A, pea; B, rose
C, single ; D, walnut.

Heredity

185

RP

SPERMATOZOA
Rp rP

rp

RP

Rp

rP

rp

RP
RP
Walnut

RP
Rp
Walnut

RP
rP
Walnut

RP

rp
Walnut

RP
Rp
Walnut

Rp

Rp
Walnut

Rp
rP
Walnut

Rp
rp
Rose

RP
rP
Walnut

Rp
rP

Walnut

rP
rP
Pea

rP
rp
Pea

RP

rp
Walnut

Rp

rp
Rose

rp
rP
Pea

rp
rp
Single

Diagram to illustrate the nature of the F2 generation from the cross of
rose comb X pea comb. (After Punnett.)

All the resulting zygotes containing both rose and pea
(RP) will be walnut ; those containing rose only (R) and
not pea (p) will be rose and those containing pea only (P)
and not rose (r) will be pea-combed. But all individuals
containing neither rose nor pea will have single combs.
This was found to be a pure recessive and to breed true.
The character of singleness seems to underlie all the types
of comb and appears whenever allowed to do so by the
absence of something representing the other kinds.

Mendelian inheritance of color. — Colors of plants or
animals are generally very complex and often consist of
many units of different kinds. Very rarely a certain color
may be said to be due to a single unit acting alone. A
knowledge of the kinds of color and the constitution of
each is necessary to understand their inheritance.

186 Plant-Breeding

1. White is due to the absence of pigment, and to the
reflection of light from the cells.

2. Green color is caused by the presence of a green
pigment in the chlorophyll.

3. Yellow, cream, and related colors are due to a
yellow pigment either associated with green in the chloro-
plasts or found alone in the chromoplasts, generally the
latter. Yellow may sometimes come from the cell-sap.

4. Red color may, under certain circumstances, be due
to the presence of that pigment in the chromoplasts, but
it is ordinarily a cell-sap color.

5. Most of the remaining colors, purple, blue, generally
red, pink, etc., are due to pigments in the cell-sap.

6. Many of the colors and shades found in flowers
are the result of both plastid colors and cell-sap colors
acting together in various amounts.

7. Certain of the denser plastids or cell-sap colors may
cover up the more delicate colors so that they cannot be
seen.

8. Finally, the color in the cell-sap may be due to
the relative presence of a non-nitrogenous and chemical
substance anthocyanin. This is blue in an alkaline and red
in acid reacting cell-sap, and, under certain conditions,
also dark red, violet, dark blue, and even blackish blue.
Anthocyanin can be obtained from the supersaturated
cell-sap of a number of deeply colored parts of plants in
a crystalline or amorphous form. Blood-colored leaves,
such as those of the Copper Beach, owe their characteris-
tic appearance to the united presence of green chlorophyll
and anthocyanin. The different colors of flowers are due
to the varying color of the cell-sap, to the different dis-

Heredity 187

tribution of the cells containing the colored cell-sap,
and also to the combinations of dissolved coloring
matter with the yellow, orange, and red chromoplasts
and the green chloroplasts. There is occasionally found
in the cell-sap a yellow coloring matter known as xan-
thein ; it is nearly related to xanthophyll, but soluble in
water.

Thus we see the plant colors are not always unit-charac-
ters, such as hairiness, glabrousness, and the like. Certain
colors found in plants, purple flowers, for example, are
the result of the union of certain other pigments. These
pigments are produced by definite units in the gametes.
Color inheritance thus becomes very complicated as the
results of certain crossings indicate.

White flowers in F2 from red X cream. — Bateson points
out a typical case of the paradoxical appearance of white-
flowered individuals in the F2 from the cross of a sap-
colored variety with a variety having cream-colored
flowers. For example, in sweet peas or stocks, when a
red-flowered type is crossed with a cream, FI is red with-
out any cream color. F2 consists of 9 without cream, 3
reds with cream, 3 whites, 1 cream.

The red-flowered variety consists of red sap color only
and the cream variety of yellow plastids only. These
are inherited separately in the hybrids. The 9 reds of
the Ft hybrids have a much brighter red color than the
red-creams. In the latter the red is diluted by the yellow
plastids.

When the allelomorphs are correctly distinguished, the
significance of this series is obvious. The operations may
be shown in tabular form, thus : —

188 Plant-Breeding

Parents .... Red variety X Cream variety
Red Sap (D) Colorless sap (r)

Colorless corpuscles (D) Yellow corpuscles (r)

p ( Red sap

\ Colorless corpuscles

2 T 1 1

F~ ~V~ HT ~ I

Red sap Red sap Colorless sap Colorless sap
Colorless Yellow Colorless Yellow

corpuscles corpuscles corpuscles corpuscles

Appearance 9 red 3 red-cream 3 white 1 cream

The ratio 9:3:4. — The F* ratio, 9 : 3 : 4, is one which
very frequently occurs in mendelian analysis. For ex-
ample, as Tschermak found, when a pink-and-white
flowered eating pea (Pisum sativum) is crossed with a
white-flowered type, FI is often the original purple-flowered.
Then F2 will be

9 purple : 3 pink and white : 4 white.

In this case the factor for purple is evidently brought in
by the albino. The latter contains the presence of
purple, which needs a factor from the other parent to
bring it out, and the absence of pink and white. The
other parent contains the presence of pink and white
and the absence of a factor for purple. All that is essen-
tial for the production of the ratio in F2 is that F\ should
be heterozygous for two factors, of which one is percep-
tible whenever present, while the other needs the presence
of the first in order that its own effects may be mani-
fested.

Emerson's experiments with beans. — By crossing self-
colored varieties of beans with white varieties, Emerson

Heredity 189

obtained in the FI generation, 65 mottled. In F2 genera-
tion there were 113 mottled, 52 self-colored, and 70
white, that is, in the ratio of 6.45 : 2.97 : 4 instead of
9:3:4.

In the Fz generation he secured the following results : —

1. All white seeds produced white seeds.

2. 7 mottled gave 22 mottled, 19 self-colored, 11 white.

3. 2 mottled yielded 13 mottled, 13 self-colored.

4. 4 mottled bore 5 mottled, 5 white.

5. 2 mottled produced 6 mottled.

6. 5 self-colored gave 63 self-colored.

7. 9 self-colored yielded 80 self-colored, 29 whites.
For the purpose of explaining the above, Emerson adopted
the formula of Shull.

1. P and p for the factor presence and absence of pig-
ment.

2. M and ra for the factor presence and absence of
mottling.

3. Pm = self-colored.

4. pM = white.

5. PM = mottled.

Thus he considers a self-colored variety containing the
factor for pigment and having no factor for mottling.
The white variety lacks the factor for pigment, but has
the factor for mottling. The mottled form is originated
by the presence of two factors, for the pigment and
mottling.

If we follow these formulae, we must confer to the F\
generation the following gametic composition, PpMm,
since FI hybrids will produce 9 mottled, 3 self-colored,
and 4 white for the F2 generation as seen on page 190 : —

190

Plant-Breeding

PM

POLLEN-GRAINS
Pm pM

pm

PM

Pm

pm

PM
PM
Mottled

Pm
PM
Mottled

pM
PM
Mottled

pm
PM
Mottled

PM
Pm
Mottled

Pm
Pm
Self

pM
Pm
Mottled

pm
Pm
Self

PM

pM
Mottled

Pm

pm
Mottled

pM
pM
White

pm
pM
White

PM

pm
Mottled

Pm
pm
Self

pM

pm
White

pm
pm
White

The ratio of 6.45 : 2.97, instead of 9 : 3 : 4, seems to be
chiefly due to the paucity of number treated for hybridi-
zation. Doubtless it is no small importance to study
the ratio of offspring in Fs in the light of the theoretical
deduction. But here again the insufficient number of
seeds informs us of its inadvisibility.

In conclusion Emerson says: "The result of most of
my own experiments might be explained as due to the
mendelian behavior of an allelomorphic pair, Mm presence
and absence of mottling, M being visible only in the pres-
ence of P."

Colored forms from white X white and the 9 : 7 ratio. — •
In the case of the sweet peas, Bateson has shown that the
formation of color in the flowers can be proved to depend
on the coexistence of two complementary factors in the
individual.

He says that the first indication of this phenomenon

Heredity 191

was found in the fact that two plants, each totally devoid
of color in the flowers and stems and each breeding true
to albinism may, when crossed together, give purple
flowers in FI. The two white parents each contain a
factor which, alone, is incapable of forming color. Each
of these factors is independently transmitted in gameto-
genesis, and thus in F2 the ratio of colored individuals to
whites is 9:7. This proportion depends on the fact that
a series of 16 individuals is necessary to exhibit all the
possible combinations of germ cells, for, as in any example
of hybridization involving two pairs of allelomorphs,
there will be four types of female cells and four types of
male cells produced by FI. Of these sixteen individuals,
9 will contain both the dominant or present factors, while
of the remaining seven individuals, 3 will contain one
dominant, 3 will contain the other, and 1 will contain
neither. There will, therefore, be 9 which are colored
and 7 which are albino. In the diagram (p. 192) C
and R are the symbols representing the two comple-
mentary factors, c and r being their respective allelomor-
phic absences.

Absence factors. — It may be well for us in this connection
to touch upon the different conceptions of several investiga-
tors on such characters as cannot be seen without resorting
to breeding tests. Tschermak considers the appearance of
mottling in FI between a white and self-colored varieties
due to the presence of mottling in a latent condition in
the self-colored variety. Latency in his view is inactivity.
Shull often speaks of latent characters, but latency,
according to him, means invisibility and not dormancy or
inactivity.

192

Plant-Breeding

CR

POLLEN-GRAINS
Cr cR

cr

CR

3 Cr

H

1

O

cr

CR
CR
Colored

Cr
CR
Colored

cR
CR

Colored

cr
CR
Colored

CR
Cr
Colored

Cr
Cr
White

cR
Cr
Colored

cr
Cr
White

CR
cR
Colored

Cr
cR
Colored

cR
cR
White

cr
cR
White

CR

cr
Colored

Cr
cr
White

cR
cr
White

cr
cr
White

Composition of the 9 colored and 7 albino offspring in FZ from the
cross between the albino Cr with albino cR, showing the ratio 9 colored :
7 albino.

On the other hand, Bateson advocates the undesir-
ability of using such a terminology. He scorns the idea
that there is latency of mottling or red in the white forms.
Certain factors may be present which are absolutely
necessary for the production of such pigments, but this
fact does not lead us to contend that there are those colors
latent. He emphasizes stating that " sulphate of copper
is blue and chloride of copper is green, but it would be
incorrect to speak of blue as latent in sulphuric acid, or
of green as latent in hydrochloric acid."

Hurst seems to have difficulty to perceive a factor for
absence. He brings forth three distinct views : —

1. The absence factor may be a concrete one, literally
representing absence.

Heredity 193

2. It may be nothing but presence in a latent state.

3. There may not be such a factor as the absence
factor.

Of the three proposed, the first seems to be, Hurst
remarks, the simplest, but it is difficult to realize and
understand how such an absence factor is originated.
Furthermore, he says: " There are many cases where
the factor .for presence is in a latent condition." The
third explanation meets an objection in the fact that there
is no pairing of factors in cross-breeding. Consequently,
it follows that, according to this view, it is impossible to
explain the phenomenon of segregation.

Mutations resulting from mendelian segregation and re-
combination. — It is very probable that many mutations
which appear suddenly and remain constant are the result
of mendelian segregation and recombination. If many
unit-characters are involved, it is easily perceived how
certain combinations of these would produce plants
of unusual appearance which will be homozygous and
breed true. Reference to Table I, p. 176, will show the
great possibilities of obtaining apparently new characters
by new combinations of old ones. It will be noted that
when as many as 10 allelomorphs are involved, and this
does not seem to be an impossible number, there is the
possibility of producing 1024 different visible types.

Mutations which mendelize are constant. — The effect
of swamping of mutations by crossing is prevented be-
cause of their continued identity due to the purity of the
germ-cells which represent them.

Mutations may be due to three things : (a) the ac-
quisition of one or more new characters, (6) the loss of
o

194 Plant-Breeding

one or more characters, and (c) recombination of existing
characters.

If the mutation is due to the addition of a new char-
acter and it remains constant, there must be present in
its germ-cells some unit to represent that new character as
there was in the gametes of the parent which produced it.
Likewise, if a character is lost, its germinal potentiality
must have become lost or entered into a latent condition.

If mutations of these types are crossed, the new gametic
representatives or absences in the case of a lost character
become pure in the germ-cells and reappear in the next
generation. Hence they are not lost.

If the mutation has a hybrid beginning and is due to
an unusual combination of characters, this condition can-
not be lost, as this certain combination which has once
occurred will reproduce true if it is homozygous, or if not,
it having occurred once may appear again through a like
combination of unit-characters even though crossing and
amphimixis may have taken place.

Mendelism in wheat. — As a specific example of evident
mendelian results, W. J. Spillman, agriculturist of the
Department of Agriculture, here explains some of his ex-
periments with wheat.1 Mr. Spillman independently dis-
covered numerical results, before the knowledge of the
mendelian experiments had become generally known.

"The photograph (Fig. 47) shows three generations of
one of my hybrid wheats. Of the three heads in the
upper row, the left-hand one is the male parent (variety
Valley) ; the right-hand one is the female parent (variety

1 Published in fourth edition of this work, 1906 ; and here reproduced
nearly entire for its historical as well as for its plant-breeding value.

Heredity

195

FIG. 47. — Three generations of hybrid wheat: A 1 = male parent,
A 2 = the hybrid, A 3 = female parent ; B 1-6 = the progeny of A 2 ;
C 1 = progeny of B 1, C 2-4 = progeny of B 2, C 5 = progeny of B 3,
C 6 and 7 = progeny of B 4, C 8-13 = progeny of B 5, C 14 and 15
= progeny of B 6. The results in the fourth generation, available
too late to include in the photograph, indicate that B 2 and B 3,
while not always separable on external appearances, are absolutely
different, the one being hybrid, the other pure.

Little Club) ; and the middle one is the hybrid. The
second row shows the second generation, and .the third
row the third generation. Of the six types in the second
generation, the following points are important : Each

196

Plant-Breeding

type was present in a certain proportion, which was ap-
proximately the same as in thirteen other similar cases,
and the average of these fourteen cases approximated the
theoretical numbers called for by Mendel's hypothesis
of the disjunction of parental characters. The three
at the left, being bearded, possess a character which
was latent in the first generation. The fact that the
beards show in these three indicates that the opposite
character is absent, and they should therefore remain
bearded in succeeding generations. That is, they are no
longer hybrid with reference to this character. It will
be observed that this was actually the case, for no beard-
less heads appeared in the progeny of either of these three
(see lower row, first five heads). The following diagram
will show the character of each of the six types in row 2.
In this diagram the letters have the following meanings : —

B = bearded (written b when latent) .
S = smooth (not bearded).
L = long heads.
C = Club heads (short).

I = Intermediate in length of head. (The hybrid was
intermediate in this respect.)

PARENTS FIRST GENERATION

SECOND GENERATION

BL

SC,

Sbl

BL
BI
BC

SbL

Sbl

2 SbC

1 SL

2 SI

16

Heredity 197

"This diagram shows the nine types called for by
Mendel's theory. Of these, EL, BC, SL, and SC are
no longer hybrids — at least they have no latent char-
acters, and will therefore reproduce true to seed. Of the
remaining five types, BI and SI are hybrid only with
reference to length of head, and SbL and SbC only with
reference to beards; while Sbl is hybrid with reference
to both characters, as in the preceding generation.

"It will readily be seen that the types BL and BC can
be separated from the others even by external appearances,
and obtained in a pure state. BL is the type shown at
the left in the second row in the picture, and all its prog-
eny was like it, showing that it conformed to theory. BC
is the type shown at No. 3 in the second row of heads ;
being pure, it should reproduce itself true to type, which
it did, with an easily explained exception to be noted be-
low. The type BI (shown at No. 2, row 2), being hybrid
with reference to length of head, should produce again
all types based on this character, and it did this, as is seen
in heads Z-4, row 3. Referring again to the above
diagram, it will be seen that the types SL and SbL cannot
be distinguished by external characters. SL will of course
reproduce true to type, while SbL will reproduce SL}
SbL, and BL. Now SL and SbL being mixed together in
the selection made in the second generation, we shall find
a large percentage of SL mixed with some SbL from which
it cannot be distinguished, and a small percentage of BL
in the third generation. Heads 6 and 7, row 3, show that
the types called for actually occurred. Types SI and Sbl
of the diagram appear alike externally, and were there-
fore selected together in the second generation (see head

198 Plant-Breeding

5, row 2). Now SI should produce the types SL, SI,
SC, while. Sbl should produce all nine types again
(these nine types can be separated only into six by exter-
nal appearance). It is therefore seen that the group
represented by head 5, row 2, should produce all six types
again. Heads 8-13, row 3, show these types. Types
SbC and SC of the diagram are alike externally, and were
hence selected together last year. Of these SC should
produce only SC, while SbC should produce SC, SbC, and
EC. But since SC and SbC look alike, the progeny of
these two types should show only SC and BC. The last
two heads in row 3 show that this actually occurred.
"In the single set of heads shown, there were two easily
explained exceptions to theory. It will be seen that
heads 2 and 3, row 2, differ only in length ; now the group
represented by head 2 varied in length from that of 1 to
that of 3. In separating 2 and 3, it might easily happen
that some of 3 should be placed with 2. In this case
the progeny of 3 would show a few heads like 1, and this
was the case. I have shown in the photograph only the
heads called for by theory, for it would only lead to con-
fusion to include the exceptions which would probably
not have occurred if 2 and 3 of row 2 had been accurately
separated last year. Again, in the progeny of the group
represented by head 5, row 2, only five of the six types
shown (row 3, heads 8-13) were found in this particular
case, though all six were found in most of the others.
As the missing type should constitute only 4£ per cent
of the group, and as it differed from one of the others
only slightly, it is possible that it was included with the
related type when the selections were made.

Heredity 199

"I have not yet seen the data for the third generation
of all these wheats, but those which are at hand are
decidedly interesting. The following are the data for
the third generation of the cross between Jones Winter
Fife (male) and Little Club (female). The fife is long-
headed and has velvet chaff (V) ; the Club short-headed,
and has glabrous chaff (G). Velvet proved to be domi-
nant over glabrous and the hybrids were intermediate in
length. Type I of the second generation included the
two types VL and VgL, since these could not be distin-
guished by external appearances. Seed of Type I pro-
duced in the third generation : —

PERCENTAGE OP TYPES
PLOT I = VL ll = GL

1 87 13

2 81 19

Theory 83 1 16f

The figures for the remaining five second-generation types
are as follows : -

TYPE II = GL

PERCENTAGE OP TYPES
PLOT II

1 100

2 100

Theory 100

TYPE III = VI AND Vgl

PLOT I II III IV V VI

1 21 7 38 9 20 5

2 W_ 4| 38_ 12 15 4|

Theory 20 f 4| 41 f 8£ 20 f 4*

200 Plant-Breeding

TYPE IV = GI

PLOT II IV VI

1 28 52 20

2 31 47 22

Theory 25 50 25

TYPE V = VC AND VgC

PLOT % I II V VI

1 2.4 80.0 17.6

2 4.72.6 79.8 12.9

Theory 83£ 16f

TYPE VI = GC
PLOT II VI

1 7.7 92.3

2 100.0

Theory 100.0

"The only departures from theory of any consequence
in these data are the occurrence of small amounts of
Types I and II in the progeny of V, and of II in the prog-
eny of VI. Now, Type V of the second generation
(VC and VgC) differed from Type III (77) only in being
slightly shorter. If a few individuals of III had been
included in V in separating the types of the second gen-
eration, we should have the actual result obtained in the
third generation. Likewise, Type VI of the second gen-
eration (GC) differed from II (GI) in the same manner.
Evidently a few plants of II got into the Type VI last
year, and thus gave the results shown."

Mendelism summarized. — This, in barest epitome, is the
teaching of Mendel. This teaching strikes at the root
of two or three difficult and vital problems. It represents

Heredity 201

a new conception of the proximate mechanism of heredity,
although it does not represent a complete hypothesis of
heredity, since it begins with the gametes after they are
formed and does not account for the constitution of the
gametes, nor the way in which the parental characters
are impressed upon them. This hypothesis focuses our
attention along new lines, and will arouse more discussion
than Weismann's hypothesis did ; and it will have a much
wider influence. Whether it expresses the actual means
of heredity or not it is yet much too early to say ; but
this hypothesis is a greater contribution to science than
the so-called "Mendel Law" as to the numerical results
of hybridization : the hypothesis attempts to explain the
"law."

One great merit of the hypothesis is the fact that its
basis is a morphological unit, or at least an appreciable
unit, not a mere imaginary concept. This unit should be
capable of direct study, at least in some of its phases.
It would seem that the mendelian hypothesis would give
a new direction to cytological research.1

It is yet too early to say how far Mendel's law applies.
We shall need to restudy the work that has been done
and to do new work along more definite lines. There
are relatively few former results or experiments that can
be conformed to Mendel's law, because the data are not
complete enough or not made from the proper point of
view. We should expect the fundamental results to
be masked when the plants with which we work are

1 See, for example, "A Cytological Basis for the Mendelian Laws,"
Bull. Torr. Bot. Club, 29, 657 (1902), by W. A. Cannon; and other
papers of this kind.

202 Plant-Breeding

themselves unstable, when cross-fertilization is allowed
to take place, or when the pairs of contrasting characters
are very numerous and very complex.

Application to plant-breeding. — The wildest prophecies
have been made in respect to the application of Mendel's
law to the practice of plant-breeding, for the mathe-
matical formulae express only definiteness and precision.
Unfortunately, the formulae cannot express the indefinite-
ness and the unprecision which even Mendel found in his
work. The greatest benefit of Mendel's work to the
plant-breeder will be in improving the methods of ex-
perimenting. We can no longer be satisfied with mere
" trials'' in hybridizing: we must plan the work with
great care, have definite ideals, "work to a line," and
make accurate and statistical studies of the separate
marks or characters of plants. His work suggests what
we are to look for.

The time may come when the hybridizer will be able
with many plants to make out beforehand plans and speci-
fications for their breeding and for carrying these through
with a large degree of exactness.

The best breeders now breed to unit-characters, for this
is the significance of such expressions as "avoid breeding
for antagonistic characters," "breed for one thing at a
time," "know what you want," "have a definite ideal,"
" keep the variety up to a standard." In certain classes
of plants the mendelian laws will be found to apply with
great regularity, and in these we shall be able to know be-
forehand about what to expect (Fig. 48) . The number of
cases in which the law or some modification of it applies
is being extended daily, both for animals and plants ; but

FEMALE PARENT
VARIETY— Yellow Plum

HYBRID

MALE PARENT
VARIETY— Quarter Century

Height— tall
Color— yellow
Size— small plum

Height-/a«
Color— red
Size— intermediate

FJ HYBRIDS

Helght-4u>ar/
Color-red
Slto-larae round

Height— tall
Color— red
Size— small plum

Height— tall

Color— red

Size — intermediate

Height— tall
Color-yellow
Size— small plum

Height— dwarf
Color — red
Size— small plum

Height— dwarf

Color— ^red

S Iz e — in ter mediate

Height— tall

Color— red

Size — large round

Height— tall
Color— yellow
Size— intermediate

Height— dwqrf
Color— -yellow
Size— small plum

O

Height-tall
Color— yellow
Size— large round

Height— dwarf

Color—red

Size — large round

Height— dwarf
Color — yellow
Size — intermediate

Height— dwarf
Color— yellow
Size — large round

FIG. 48. — Mendelism in tomatoes. There were, found in a field of Fz
hybrids, the 12 distinct types, illustrated above. This redistribution
of characters illustrates an important economic bearing of Mendel's
law.

203

204 Plant-Breeding

in practice we shall probably find as many exceptions to
the formula? as confirmations of them, even though the
exceptions can be explained, after we find them, by Men-
del's principles of heredity.

The probable limits of mendelism in the production of
new varieties. — It has been said that we shall soon be
able, as a result of Mendel's discoveries, to predict varie-
ties in plant-breeding. Before considering this question,
we must recall the fact that a cultural variety is a succes-
sion of plants with characters sufficiently marked and
uniform to make it worth while cultivating in place of
some older variety. Now and then it may be worth
while to introduce some new energy or new trend into a
general lot of offspring by making wholesale crosses, not
expecting ever ta segregate any particular variety or
strain from the progeny ; but these cases are rare, and the
gain is indefinite *and temporary. So far as our knowledge
at present goes, we see no warrant for the hope that we can
predict varieties with any degree of exactness, at least
not beyond a very narrow effort. Following are some of
the reasons that seem to argue against the probability
of useful prophecy of varieties so far as the mende-
lian results are concerned : (1) We do not know what
plants will mendelize until we try. (2) Even in plants
that do not mendelize, one-half of the offspring have
stable characters. But we cannot predict for even this
half, for it is impossible to determine beforehand which
seeds showing dominant characters (and these are three-
fourths of the offspring) will "come true." Dominance,
as we have seen, is of two kinds in respect to its behavior
in the next generation, — constant and hybrid ; and the

Heredity 205

hybrid dominance, which is twice as frequent as the
other, breaks up into constant dominance, hybrid domi-
nance, and recessiveness. (3) Mendel's law deals pri-
•marily with mere characters, not with a variety or with
a plant as a whole. Every plant is a composite of a mul-
titude of characters, and from the plant-breeder's point
of view there may be as many undesirable characters as
desirable ones. No plant is perfect; if it were, there
would be no need of plant-breeding. The breeders want
to preserve the desirable characters or traits and elimi-
nate the undesirable ones ; but under the strict interpre-
tation of mendelism this may be difficult and perhaps
impossible. The one egg gamete and the one sperm
gamete that unite to make the new plant, each contains
all the alternative parental characters; these various
characters appear in the offspring, and all that the breeder
gains is a new combination or arrangement of characters,
and the undesirable attributes may be as troublesome
as before. (4) The breeder usually wants wholly new
characters as well as recombinations of old ones, or he
wants augmented characters, and these lie outside the
true mendelian categories. For example, a carnation
grower wants a four-inch flower, but he has only three-
inch flowers to work with, and the augmentation of char-
acters is no part of the original mendelian law. Perhaps
these augmented and new characters are to be got by
means of ordinary variation and selection, or other extra-
crossing means; but we know, as a matter of fact, that
augmented characters do sometimes appear in hybrids.
(5) New and unpredictable characters are likely to arise
from the influence of environment or other causes, and

206 Plant-Breeding

very likely may be recorded in the gametes and vitiate
the final results. (6) Variability itself may be a unit-
character and therefore pass over. There is probably
such a thing as a " tendency to vary/' wholly aside from
the fact of variation. (7) Many of the plants with which
we need most to work in plant-breeding are themselves
eminently variable, and the results, even if there is true
mendelism, may be so uncertain as to be wholly unpre-
dictable. (8) Many plants with which we must work
will not close-fertilize. Some of them are monoecious or
dioecious. Even if there is gametic purity in such plants,
the probability is that the fact can be discovered only by
a long line of scientific experimenting for that particular
purpose and not by the work of the man who desires only
to breed new plants. (9) A cultural variety, in any true
acceptation of the term, is a series of closely related
plants having a pedigree. It runs back to one individ-
ual plant, from which propagation has been made
by seeds or asexual parts. Now, one can never predict
just what combination of characters any plant will have,
even though it be strictly mendelian. A person might
have a thousand hybrids of which no one plant shows any
two characters in the proportion of 3 to 1 (both seed-char-
acters may appear in the same pod or in different pods) on
the same plant, let alone all the characters as 3 to 1 or in
other definite relation ; and yet the total average numeri-
cal results might conform exactly to the mendelian law.
Mendel's law is a law of averages. For example, in ten
plants of peas, Mendel found the following ratios in respect
to seed-shape and seed-color. (Similar ratios were found
for other characters.)

Heredity 207

SHAPE

COLOR

SHAPE

COLOB

3.75 : 1

2.27 : 1

4.33 : 1

3.33 : 1

3.37 : 1

4.57 : 1

3.66 : 1

2.43 : 1

3.43 : 1

2.80 : 1

2.20 : 1

4.88 : 1

1.90:1

2.59 : 1

4.66 : 1

3.57 : 1

2.91 : 1

1.85:1

3.57 : 1

2.44 r 1

Mendel reports one instance in which the ratio in seed-
shape was 21 to 1, and another of 1 to 1. He also reports
instances of seed-color of 32 to 1, and 1 to 1. It has been
said that, because of Mendel's work, we shall be able to
produce hybrid varieties with the same certainty that we
produce chemical compounds. Now, a plant is made
up of many combinations of many units, and these com-
binations are the results of mathematical chance or prob-
ability. Of course, when the offspring are numerous,
all possible combinations are likely to occur; but these
occurrences are essentially fortuitous. Chemical com-
pounds are specific entities in which the parts combine by
necessity with definiteness. The comparison is fallacious
and the conclusion unsound.

We must remember that there are whole classes of cases
of plant-breeding that do not fall under hybridization at
all. Granting the de Vriesan view that selection is incom-
petent to produce species from individual fluctuations, it
is nevertheless well established (and admitted by de Vries)
that very many of our best cultural varieties have been
brought to their present state of perfection by means of
selection; and by selection they are maintained in their
usefulness. Selection will always be a most important
agency in the hands of the gardener and the plant-breeder

208 Plant-Breeding

— none the less so now that we have challenged its role
in the evolution of the plant kingdom. For the time
being, the new discussions of hybridizations are likely
to overshadow all other agencies in plant-breeding; but
selection under cultivation is as important now as it was
in the days of van Mons and Darwin.

Conclusion. — Now, in conclusion, what are ihe great
things that we have learned from these newer studies?
(1) In the first place, we have been brought to a full stop
in respect to our ways of thinking on these evolution
subjects. (2) We are compelled to give up forever the
taxonomic idea of rigid species as a basis for studying the
process of evolution. (3) The experimental method has
finally been completely launched and set under way.
Laboratory methods, comparative morphology, embry-
ological recapitulation, life-history studies, ecological in-
vestigations — all these means are likely to be overshad-
owed for a time by experiments in actually growing the
things under conditions of control. (4) We must study
great numbers of individuals and employ statistical
methods of comparison. (5) The doctrine of discontin-
uous evolution is now clearly before us. (6) We are
beginning to find a pathway through the bewildering maze
of hybridization.

CHAPTER VIII
HOW DOMESTIC VARIETIES ORIGINATE

"THE key is man's power of accumulative selection:
nature gives successive variations; man adds them up
in certain directions useful to him." This, in Darwin's
phrase, is the essence of the cultivator's skill in ameliorat-
ing the vegetable kingdom. So far as man is concerned,
the origin of the initial variation is largely chance, but
this start or variation once given, he has the power, in
most cases, to perpetuate it and to modify its characters.
There, then, are two very different factors or problems
in the origination of garden varieties, — the production
of the first departure or variation, and the subsequent
breeding of it. Persons who give little thought to the
subject look upon variation as the end of their endeavors,
thinking that a form comes into being with all its char-
acters well marked and fixed. In reality, however,
variation may be but the beginning in the process ; selec-
tion is the end so far as the plant-breeder is concerned.

Indeterminate varieties. — There are two general classes
of garden varieties in respect to the method of their
origin, — those that come into existence somewhat
suddenly and which require little else of the husband-
man than the multiplication of them, and those that
p 209

210 Plant-Breeding

are the result of a slow evolution or direct breeding. The
former are indeterminate or uncertain, and the latter are
determinate or definite. The greater part of those in the
first class are plants that are multiplied or divided by
bud-propagation. They comprise nearly all our fruits,
the woody ornamental plants, and such herbaceous gen-
era as begonia, canna, gladiolus, lily, dahlia, carnation,
chrysanthemum, and the like, — in fact, all those multi-
plied by grafting, cuttings, bulbs, or other asexual parts.
The original plant may be either a seedling or a bud-sport.
The gardener, who is always on the look-out for novelties,
discovers its good qualities and propagates it.

Varieties which are habitually multiplied by buds, as
in those plants that have been mentioned in the last para-
graph, vary widely when grown from seeds, so that every
seedling may be markedly distinct. As soon, however, as
varieties are widely and exclusively propagated by seeds,
they develop a capability of carrying the greater part of
the individual differences down to the offspring. That
is, seedlings from bud-multiplied plants do not ''come
true," as a rule, whilst those from seed-propagated plants
do "come true." The reason of this difference will be-
come apparent on a moment's reflection. In the seed-
propagated plants, like the kitchen-garden vegetables
and the annual flowers, we select the seeds and thereby
eliminate all those variations which would have arisen had
the discarded seeds been sown. In other words, we are
constantly fixing the tendency to "come true," for this
feature of plants is as much a variation as is form or
color or any other attribute. Suppose, for example, that a
certain variation were to receive two opposite treatments,

How Domestic Varieties Originate 211

the seeds from one-half of the progeny being carefully
selected year by year, and all those from untypical plants
discarded, whilst in the other half all the seeds from all
the plants, whether good or bad, are saved and sown. In
the one case, it will be seen, we are fixing the tendency
to "come true," for this is all that constitutes a horticul-
tural variety, — a brood very much like all its parents.
In the other case, we are constantly eliminating the
tendency to "come true" by allowing every modifying
agency full chance. So the very act of taking seeds only
from plants that have "come true," tends still more
strongly to fix the hereditary force within narrow limits.
Working against this restrictive force, however, are all
the agencies of environment and atavism, so that, fortu-
nately, now and then a seed gives a "rogue," or a plant
widely unlike its parents, and this may be the start for a
new variety.

With bud-multiplied varieties, however, the case is
very different. Here every seed may be sown, as in the
illustrative case above, because the seedlings are not
wanted for themselves, but only as stocks on which
to bud or graft the desired varieties. So there is no seed
selection in the ordinary propagation of apples, pears,
peaches, and the usual orchard fruits. The seeds are
taken indiscriminately from pomace or the refuse of can-
ning or evaporating factories. Moreover, many such
varieties are hybrid, and when propagated by seed, split
up into many forms. But every annual garden vegetable
is always grown from seeds more or less carefully saved
from plants that possess some desired attribute. There is
no reason why the tree fruits should not reproduce them-

212 Plant-Breeding

selves from seeds just as closely as do the annual herbs,
if they were to be as carefully propagated by selected seeds
through a long course of generations. There is excellent
proof of this in the well-marked races or families of Rus-
sian apples. In that country, grafting had been little
employed, and consequently it has been necessary to select
seeds only from acceptable trees in order that the off-
spring might be more acceptable. So the Russian apples
have come to run in groups or families, each family bear-
ing the mark of some strong ancestor. Most of the
seedlings of the Oldenburg are recognizable because of
their likeness to the parent. We may thus trace an
incipient tendency in our own fruits towards racial
characters. The Fameuse type of apples, for example,
tends to perpetuate itself ; and a similar tendency is very
well marked in the Damson and Green Gage plums, the
Orange quince, Concord grapes, and Hill's Chili and
Crawford peaches. But inasmuch as bud-multiplication
is so essential in nursery practice, we can hardly hope
for the time when our trees and shrubs, or even our per-
ennial herbs, will "come true" with much certainty. In
them, therefore, we get new varieties by simply sowing
seeds; but in seed-propagated varieties we must depend
either on chance variations or else we must resort to
definite plant-breeding.

Plant-breeding. — The breeding of domestic animals is
attended, for the most part, with such definite and often
precise results that there has come to be a general desire
to extend the same principles to plants. It is not unusual
to hear well-informed people say that it is possible to breed
plants with as much certainty and exactness as it is to

How Domestic Varieties Originate

213

214

Plant-Breeding

How Domestic Varieties Originate 215

breed animals. The fact is, however, that such exactness
will never be possible, because plants are very unlike
animals in organization, and because, also, the objects
sought in the two
cases are character-
istically unlike.
Plants, as we have
seen, are made up
of a colony of poten-
tial individuals, and
to breed between
two plants by cross-
ing means that we
must choose the
sex-parents from
amongst as many
individuals as there
are f 1 o wers or
branches on the two
plants, whilst in
animals we choose
two definite personal
parents. And these
personal parents are
either male or fe-

FIG. 51. — Improving the tomato : A, fruit of
approximately ideal form secured by cross-
ing and selection; B, fruit showing im-
perfections and undesirable characters.
(Yearbook, U. S. Dept. Agric.)

male, and the union
is essential to the
production of offspring, whilst in plants each parent —
that is, each flower — is usually both male and female^
and the union of two is not essential to the produc-
tion of offspring, for the plant is capable of multiplying

216

Plant- Breeding

itself by buds. The element of chance, therefore, is one
hundred, or more, to one in crossing plants as compared
with crossing animals. Then, again, the plant-parents
may be modified profoundly by every environmental condi-
tion of soil and temperature and sunshine, or other ex-
ternal conditions, since they possess no bodily tempera-

/<7

VJ

\

N

/*7//3fc/

\/

FIG. 52. — Crop averages in corn breeding for high and for low protein.
Results of twelve generations. (Illinois Experiment Station.)

ture, no choice of conditions, and no volition to enable
them to overcome the circumstances in which they are
placed. Animals, on the contrary, have all these ele-
ments of personality, and the breeder is also "able to con-
trol the conditions of their lives to a nicety. In view of
all these facts, it is not strange that animals can be bred
by crossing with more confidence than can plants. But
there is another and even more important difference

How Domestic Varieties Originate 217

between the breeding of animals and the breeding of
plants. In animals, our sole object is to secure simply
one animal or one brood of offspring. In plants, our
object is, in general, to secure a race or generation of

FIG. 53. — Fruit of wild elderberry.

offspring, which may be disseminated freely over the
earth. In the bovine race, for example, our object in
breeding is to produce one cow with given characters;
in turnips, our object is to produce a new variety, the
seed of which will reproduce the variety, whether sown in
Pennsylvania or Ceylon. It is apparent, therefore, that

218

Plant-Breeding

any comparisons drawn between the breeding of animals
and plants are likely to be fallacious.

Is there, then, any such thing as plant-breeding, any
possibility that the operator can proceed with some con-

FIG. 54. — Fruit of a cultivated variety of the elderberry which appeared
as a variation from the wild form.

fidence that he may obtain the ideal he has in mind?
Yes, to a certain extent.

Plant-breeding by selection. — It is apparent that the
very first effort on the part of the plant-breeder must be
to secure individual differences ; for so long as the plants

How Domestic Varieties Originate 219

that he handles are very closely alike, so long there will
be little hope of obtaining new varieties. He must,
therefore, cause his plants to vary. In plants that
are comparatively unvariable, it is frequently impossible
to produce variations in the desired direction at once, but
it is more important to "break" the type, — that is, to

FIG. 55. — Field of wilt-resistant watermelons, growing free from disease
on infected land. (From Yeai'book.)

make it depart markedly from its normal behavior in
any or many directions. If the type once begins to vary,
to break up into different forms, the operator may expect
that it will soon become plastic enough to allow of modi-
fication in the ways he desires. But whilst it is impor-
tant or even necessary to break a well-marked type into
many forms, it would no doubt be unwise to encourage this

220 Plant-Breeding

tendency after it once appears, lest the plant acquire a too
strong habit of scattering. This initial variation is induced
by changing the conditions in which the plant has habit-
ually grown, as a change of seed, change of soil, tillage,
varying the food supply, crossing, and the like.

As a matter of fact, however, nearly all plants that

FIG. 56. — Disease resistance in cowpeas. Showing a variety which
is immune (on the left) and a susceptible variety (on the right)
to cowpea wilt.

have been long cultivated are already sufficiently variable
to afford a starting-point for breeding. The operator
should have a vivid mental picture of the variety which
he designs to obtain ; then he should select that plant in
his plantation which is nearest his ideal, and sow the
seeds of it. From the seedlings he should again select
his type, and so on, generation after generation, until

How Domestic Varieties Originate

221

the desired object is attained. It is important, if he is
to make rapid progress, that he keep the same ideal in

(1) Grand Rapids, one parent
used in developing improved
types.

(2) Golden Queen, the other
parent used in developing
improved types.

(3) New loose type for the
western market, secured by
crossing the varieties shown
in (1) and (2).

(4) New head type for eastern
conditions, secured by cross-
ing the varieties shown in
(1) and (2).

FIG. 57. — Improved types of lettuce and the varieties from which
they were developed.

mind year after year, otherwise there will be vacillation,
and the progress of one year may be undone by a counter-
direction the following year. In this way it will be

222 Plant-Breeding

found that almost any character of a plant may be either
intensified or lessened within certain limits. This is man's
nearest approach to the Creator in his control over the
physical forms of life, and it is great and potent in pro-
portion as it sets for itself correct ideals in the beginning
and adheres to them until the end.

For examples of improvement by selection see Figs. 49-
56, that represent familiar results.

RULES FOB BREEDING PLANTS

When beginning this selection or breeding for an ideal,
it is important that impossible or contradictory results be
avoided. Some of the cautions and suggestions that
need to be considered are these : —

1. Avoid striving after features that are antagonistic
or foreign to the species or genus with which you are
working. Every group of plants has become endowed
with certain characters or lines of development, and the
cultivator will secure quicker and surer results if he works
along the same lines, rather than attempt to thwart them.
Nature gives the hint : let man follow it out, rather than
to endeavor to create new types of characters. Consider
some of the solanaceous plants for examples. There
are certain types of the genus Solanum which have a
natural habit of tuber-bearing, as the potato. Such
species should be bred for tubers and not for fruits. There
are other Solanums, however, as the egg-plants and the
pepinoes, which naturally vary or develop in the direc-
tion of fruit-bearing, and these should be bred for fruits
and not for tubers ; and the same should be true in the
related genera of tomatoes, red peppers, and physalis.

How Domestic Varieties Originate 223

Those ambitious persons who are always looking for a
tuber-bearing tomato, therefore, might better concen-
trate their energies on the potato, for the tomato is not
developing in that direction; and even if the tomato
could be made to produce tubers, it would thereby lessen
its fruit production, for plants cannot maintain two diverse
and profitable crops at the same time. It is more rea-
sonable, and certainly more practicable, to grow potatoes
on potato plants and tomatoes on tomato plants.

2. The quickest and most marked results are to be ex-
pected in those groups or species which are normally the
most variable. There are a greater number of variations
or starting-points in such species ; but it also follows that
the forms are less stable, the more the species is variable.
Yet the variations, being very plastic, yield themselves
readily to the wishes of the operator. Carri&re puts the
thought in this form: "The stability of forms, in any
group of plants, is, in general, in inverse ratio to the num-
ber of the species which it contains, and also to the degree
of its domestication."

The most variable types are the most dominant ones
over the earth; that is, they occur in greater numbers
and under more diverse conditions than the compara-
tively invariable types do. The Compositse, or sunflower-
like plants, comprise a ninth or tenth of the total species
of flowering plants, and the larger part of the subordinate
types or genera contain many forms or species. Aster,
goldenrod, the hawkweeds, thistles, and other groups, are
representative of .the cosmopolitan or variable types of
composites. Whenever, for any reason, any type begins to
decline in variability, it usually begins to perish ; it is then

224 Plant-Breeding

tending towards extinction. Monotypic genera — those
which contain but a single species — are usually of local
or disconnected distribution, and are probably, for the
most part, vanishing remnants of a once important type.
As a rule, most of our widely variable and staple culti-
vated species are members of large, or at least polytypic,
genera. Such, for example, are the apples and pears,
peaches and plums, oranges and lemons, roses, bananas,
chrysanthemums, pinks, cucurbits, beans, potatoes,
grapes, barley, rice, cotton. A marked exception to this
statement is maize, which is immensely variable and is
generally held to have come from a single species ; but
the genesis of maize is unknown, and it is possible that
more than one species is concerned in it. Wheat is also
a partial exception, although the original specific type is
not understood ; and the latest monographers admit three
or four other species to the genus, aside from wheat.
There are other exceptions, but they are mostly unim-
portant, and, in the main, it may be said that the domi-
nant domestic types of plants represent markedly poly-
typic genera.

3. Breed for one thing at a time. The person who
strives at the same time for increase or modification in
prolificacy and flavor will be likely to fail in both. He
should work for one object alone, simply giving sufficient
attention to subsidiary objects to keep them up to normal
standard. This is really equivalent to saying that there
can be no such thing as the perfect all-around variety that
so many people covet. Varieties must be adapted to
specific uses, — one for shipping, one for canning, one for
dessert, one for keeping qualities, and the like. The

How Domestic Varieties Originate 225

more good varieties there are of any species, the more
widely and successfully that species can be cultivated.
A knowledge of Mendel's laws of heredity assists the
breeder to secure more rapidly the proper combination
of qualities and to fix them.

4. Do not desire contradictory attributes in any variety.
A variety, for example, that bears the maximum number
of fruits or flowers cannot be expected greatly to increase
the size of those organs without loss in numbers. This is
well shown in the tomato. The original tomato produced
from six to ten fruits in a cluster, but as the fruits in-
creased in size the numbers in each cluster fell to two or
three. That is, increase in size proceeded somewhat at
the expense of numerical productivity; yet the total
weight of fruit to the plant has greatly increased. The
same is true of apples and pears ; for whilst these trees bear
flowers in clusters, they generally bear their fruits singly.
Originally, every flower normally set fruit. The reason
why blackberries, currants, and grapes do not increase
more markedly in size, is probably because the size of
cluster has been given greater attention than the size of
berry. Plants which now bear a full crop of tubers can-
not be expected to increase greatly in fruit bearing, as
already explained under Rule 1. This fact is illustrated
in the potato, in which, as tuber-production has increased,
seed-production has decreased, so that growers now com-
plain that potatoes do not produce bolls as freely as they
did years ago.

5. When selecting seeds, remember that the character
of the whole plant is more important than the character
of any one branch or part of the plant ; and the more

Q

226 Plant-Breeding

uniform the plant in all its parts, the greater is the likeli-
hood that it will transmit its characters. If one is striv-
ing for larger flowers, for example, he will secure better
results if he choose seeds from plants that bear large
flowers throughout, than he will if he choose them from
some one of the large flowering branches on a plant that
bears indifferent flowers on the remaining branches, even
though this given branch produces much larger flowers
than those borne on the large-flowered plant. Small
potatoes from productive hills give a better product than
large potatoes from unproductive hills. The habit of
selecting large ears from a bin of corn, or large melons
from the grocer's wagon, is much less efficient in producing
large products the following season than the practice of
going into the fields and selecting the most uniformly
large-fruited parents. A very poor plant may occasion-
ally produce one or two very superior fruits, but the seeds
are more likely to perpetuate the characters of the plant
than of the fruits.

The following experiences detailed by Henri L. de
Vilmorin illustrate the proposition admirably: "I tried
an experiment with seeds of Chrysanthemum carinatum
gathered on double, single, and semi-double heads, all
growing on one plant, and found no difference whatever
in the proportion of single and double-flowered plants.
In striped verbenas, an unequal distribution of the color
is often noticed; some heads are pure white, some of a
self-color, and most are marked with colored stripes on
white ground. I had seeds taken severally from all and
tested alongside one another. The result was the same.
All the seeds from one plant, whatever the color of the

How Domestic Varieties Originate 227

flower that bore them, gave the same proportion of plain
and variegated flowers."

The second part of the proposition is equally as impor-
tant as the first, — the fact that a plant which is uniform
in all its branches or parts is more likely to transmit its
general features than one which varies within itself.
It is well known that bean plants often produce beans
with various styles of markings on the same plant or even
in the same pod, yet these variations rarely, if ever, perpet-
uate themselves. The same remark may be applied to
variations in peas. These illustrations only add emphasis
to the fact that intending plant-breeders should give
greater heed than they usually do to the entire plant,
rather than confine their attention to the particular
part or organ which they desire to improve.

At first thought, it may look as if these facts are
directly opposed to the prop6sition emphasized in the first
chapter that every branch of a plant is a potential auton-
omy, but it is really a confirmation of it. The variation
itself shows that the branch is measurably independent,
but it is not until the conditions or causes of the variation
are powerful enough to affect the entire plant that they
are sufficiently impressed upon the organization of the
plant to make their effects hereditary through seeds.

There is an apparent exception to the law that the
character of the entire plant is more important than any
one organ or part of it, in the case of the seeds themselves.
That is, better results usually follow the sowing of large
and heavy seeds than of small or unselected seeds from the
same plant. This, however, does not affect the main
proposition, for the seed is in a measure independent of

228 Plant-Breeding

the plant body, and is not so directly influenced by envi-
ronment as are the other organs. And, again, the seed
receives a part of its elements from a second or male
parent. The good results which follow the use of large
seeds are, chiefly, greater uniformity of crop, increased
vigor, often a gain in earliness and sometimes in bulk,
and usually a greater capacity for the production of
seeds. These results are probably associated less with
any innate hereditable tendencies than with the mere
vegetative strength and uniformness of the large seeds.
The large seeds usually germinate more quickly than the
small ones, provided both are equally mature, and they
push the plantlet on more vigorously. This initial
gain, coming at the most critical time in the life of the new
individual, is no doubt responsible for very much of the
result that follows. The uniformity of crop is the most
important advantage which comes of the use of large
seeds, and this is obviously the result of the elimination of
all seeds of varying degrees of maturity, of incomplete
growth and formation, and of low vitality.

Another important consideration touching the selection
of seeds, is the fact that very immature seeds give a feeble
but precocious progeny. This has long been observed
by gardeners, but Sturtevant, Arthur, and Goff have made
a critical examination of the subject. "It is not the
slightly, unripe seeds that give a noticeable increase in
earliness," according to Arthur, "but very unripe seeds,
gathered from fruit (tomatoes) scarcely of full size and
still very green. Such seeds do not weigh more than
two-thirds as much as those fully ripe. They germinate
readily and are more easily affected by retarding or harm-

How Domestic Varieties Originate 229

ful influences. If they can be brought through the early
period of growth and become well established, and the
foliage or fruit is not attacked by rots or blights, the
grower will usually be rewarded by an earlier and more
abundant crop of slightly smaller and less firm fruit.
These characters will be more slightly emphasized in sub-
sequent years by continuous seed propagation." Goff
remarks that the increase in earliness in tomatoes, fol-
lowing the use of markedly immature seeds, "is accom-
panied by a marked decrease in the vigor of the plant, and
in the size, firmness, and keeping quality of the fruit."
These results are probably closely associated with the
chemical constitution and content of the immature seeds.
The organic compounds have probably not yet reached
a state of stability, and therefore they respond quickly
to external stimuli when placed in conditions suitable to
germination ; and there is little food for nourishment of
the plant let. The consequent weakness of the plant let
results in a loss of vegetative vigor, which is earliness.
(See Rule 2.)

Still another feature connected with the choice of seeds
is the fact that in some plants, as in various Ipomceas, for
example, the color of the seed is more or less intimately
associated 'with the color of the flower which produced
them and also with the color of the flower which they
will produce.

6. Plants that have any desired characteristics in
common may differ widely in their ability to transmit
these characters. It is usually impossible for the cul-
tivator to determine, from the appearance of any given
progeny, which is the most unvariable and the most like

230 Plant-Breeding

its parent ; but it may be said that those individuals that
grow in the most usual or normal environments are most
likely to perpetuate themselves. A very unusual condi-
tion, as of soil, moisture, or exposure, is not easily im-
itated when providing for the succeeding generation, and
a return to normal conditions of environment may be ex-
pected to be followed by a more or less complete return
to normal attributes on the part of the plant. If the same
variation, therefore, were to occur in plants growing under
widely different conditions, the operator who wishes to
preserve the new form should take particular care to
select his seeds from those individuals that seem to have
been least influenced by the immediate conditions in
which they have grown.

Again, if the same variation appears both in uncrossed
and crossed plants, the best results should be expected
in selecting seeds from the former. We have already
seen, in the seventh chapter, how it is that crosses are
unstable, and how the unstability is likely to be the
greater the more violent the cross. " Cross-breeding
greatly increases the chance of wide variation," writes
Henri L. de Vilmorin, "but it makes the task of fixation
more difficult."

It is very important, therefore, when selecting seeds
from plants which seem to give promise of a new variety,
to sow seeds of each plant separately, and then make the
subsequent selections from the most stable generation ;
and it is equally important that the operator should not
trust to a single plant as a starting-point, whenever he
has several promising plants from which to choose.

7. The less marked the departure from the genus of

How Domestic Varieties Originate 231

the normal type, the greater, in general, is the likeli-
hood that it will be perpetuated, although this may
not be true of sports. This is admirably illustrated in
crosses. The seed-progeny of crosses between closely
related varieties, or between different plants of the same
variety, is more uniform and usually more easy of improve-
ment by selection than the progeny of hybrids. In un-
crossed plants, the general tendency is to resemble their
parents, and the greater the number of like ancestors,
the greater is the tendency to "come true." There is
thought to be a tendency, though necessarily a weak
one, to return to some particular ancestor, or to "date
back." This is known as atavism. The so-called ata-
vistic forms are likely to be unstable, to break up into
numerous forms, or to return more or less completely to
the type of the main line of the ancestry. The following
statements touching some of the relations of atavism to
the amelioration of plants are the results of an excellent
study of heredity in lupines by Louis Leveque de Vil-
morin : —

"1. The tendency to resemble its parents is generally
the strongest tendency in any plant;

"2. But it is notably impaired as it comes into conflict
with the tendency to resemble the general line of its
ancestry.

"3. This latter tendency, or atavism, is constant,
though not strong, and scarcely becomes impaired by the
intervention of a series of generations in which no rever-
sion has taken place.

"4. The tendency to resemble a near progenitor (only
two or three generations removed), on the other hand, is

232 Plant-Breeding

very soon obliterated if the given progenitor is different
from the bulk of its ancestors."

8. The crossing of plants should be looked upon as a
means or starting-point, not as an end. We cross two
flowers and sow the seeds. The resulting seedlings may
be unlike either parent (see Fig. 57) . Here, then, is varia-
tion. The operator should choose that plant which most
nearly satisfies his ideal, and then, by selection from its
progeny and the progeny of succeeding generations, gradu-
ally obtain the plant which he desires. It is only in plants
which are propagated by asexual parts — as grafts, cut-
tings, layers, bulbs, and the like — that hybrids or crosses
are commonly immediately valuable ; for in these plants
we really cut up and multiply the one individual plant
which pleases us in the first1 batch of seedlings, rather than
to take the offspring or seedlings of it. Thus, if any par-
ticular plant in a lot of seedlings of crosses of cannas, or
plums, or hops, or strawberries, or potatoes, is valuable,
we multiply that one individual. There is no reason for
fixing the variety. But any satisfactory plant in a lot of
seedlings of crosses of pumpkins, or wheat, or beans, must
be made the parent of a new variety by sowing the seeds
of it and then by selecting for seed-parents, year by year,
those plants which are the best. "The unsettled forms
arising from crosses," Focke writes, "are the plastic
material out of which gardeners form their varieties."

But even in the fruits, and other bud-propagated
plants, crossing may often be used to as good advantage
for the purpose of originating variation as it may in peas
or buckwheat. It only requires a longer time to fix and
select variations because the plants mature so slowly.

How Domestic Varieties Originate 233

Ordinarily, if the operator does not find satisfactory plants
among the seedlings of any cross of fruit trees, he roots
up the whole batch as profitless. But if he were to allow
the best plants to stand and were to sow seeds from them,
the second generation might produce something more to
his liking. But it is generally quicker to make another
cross and to try the experiment over again, than to wait
for unpromising seedlings to bear. This repeated repeti-
tion of the experiment, however, — continual crossing
and sowing and uprooting, — is gambling. Throwing dice
to see what will turn up is a comparable proceeding.
The sowing of uncrossed seed is little better. Peter M.
Gideon sowed over a bushel of apple seed, and one seed
produced the Wealthy apple.1 D. B. Wier raised a mil-
lion seedlings of soft maple, and one plant of the lot had
finely divided leaves, and is now Wier's Cut-leaved maple.
Teas' Weeping mulberry, which is now so deservedly
popular, was, as Mr. Teas tells me, "merely an accidental
seedling." So this explains why the production of new
varieties of fruits is always chance, while a skilled man
can sit in his study in the winter time and . picture to
himself a new bean or muskmelon, and then go out in the
next three or four summers and produce it.

9. If it is desired to employ crossing as a direct means

1 The facts in the origination of the Wealthy apple, as related to me
by Mr. Gideon, are these : he first planted a bushel of apple seeds .and
then each year, for nine years, he planted enough to give a thousand trees.
At the end of ten years, all the seedlings had perished (this was in Min-
nesota) except one hard seedling crab. Then a small lot of seeds of
apples and crab apples was obtained in Maine, and from these the
Wealthy came. There were only about fifty seeds in the batch of crab
seed which gave the Wealthy ; but before this variety was obtained,
much over a bushel of seed had been sown.

234 Plant-Breeding

of producing new varieties, each parent to the proposed
cross should be chosen in agreement with the rules already
specified, and also because it possesses in an emphatic
degree one or more of the qualities which it is desired to
combine; and the more uniformly and persistently the
parent presents a given character, the greater is the chance
that it will transmit that character. It has already been
said that crossing for the instant production of new va-
rieties is most certain to give valuable results in those
species which are propagated by buds, because the initial
individual differences are not dissipated by seed reproduc-
tion. This is especially true of crossing between distinct
species ; for in such violent crossing as this the offspring
is particularly likely to be unstable when propagated by
seeds. The results of hybridization appear to be most
certain in those plants grown under glass, and in which,
therefore, the selection of the seed-parents is most care-
fully made, and where the conditions of existence are
most uniform. The most remarkable results in hybridiza-
tion yet attained are with the choicer glass-house plants,
such as orchids, begonias, anthuriums, and the like.

The more violent the cross, the less is the likelihood
that desirable offspring will follow. Species which refuse
to give satisfactory results when hybridized directly or
between the pure stocks, may give good varieties when
the " blood" has become somewhat attenuated through
previous crossings. The best results in hybridizing our
native grape with the European grape, for example, have
come from the use of one parent which is already a hy-
brid. Two notable examples are the Brighton and Diamond
Grapes, raised by Jacob Moore. The Brighton is a cross

How Domestic Varieties Originate 235

of Concord (pure native) by Diana-Hamburg (hybrid of
impure native and European). Diamond is a cross of
Concord by lona, the latter parent undoubtedly of impure
origin, containing a trace of the European vine. T. V.
Munson's Brilliant is a secondary hybrid, its parents,
Lindley and Delaware, both containing hybrid blood.
Others of his varieties have similar histories. Even when
the cross is much attenuated — or three or four or even
more times removed from a pure hybrid origin by means
of subsequent crossings — it may still produce marked
effects in a cross without introducing such contradictory
characters as to jeopardize the value of the offspring.

Among American fruit plants there are comparatively
few valuable species-hybrids. The most conspicuous are
grapes, particularly the various Rogers varieties, such
as Agawam, Lindley, Wilder, Barry, and others, which
are hybrids of the European and native species. Other
hybrids are the Keiffer and allied pears (between the
common pear and the Oriental pear), probably the
Transcendent and a few other crabs (between the com-
mon apple and the Siberian crab), the Soulard and kin-
dred crabs (between the common apple and the native
Western crab), a few blackberries of the Wilson Early
type (between the blackberry and the dewberry), the
purple-cane raspberries (between the native red and
black raspberries, and possibly sometimes combined with
the European raspberry), the Utah Hybrid cherry (be-
tween the Western sand cherry and the sand plum), prob-
ably some plums, and a few others. There is undoubtedly
a fertile field for further work in hybridizing our fruits,
particularly those of native origin, and also many of the

236 Plant-Breeding

ornamental plants ; the danger is that persons are likely
to expect too much from hybridization, and too little
from the betterment of all the other conditions which so
profoundly modify plants. Violent hybridizations gen-
erally give unsatisfactory and unreliable results; but
subsequent crossings, when the " blood" of the original
species to the contract is considerably attenuated, may be
expected to correct or overcome the first incompatibility,
as explained above.

10. Establish the ideal of the desired variety firmly in
mind before any attempt is made at plant-breeding. If
one is to make any progress in securing new varieties, he
must first be an expert judge of the capabilities and merits
of the plants with which he is dealing, otherwise he may
attempt the impossible or he may obtain a variety that
has no merit. Make frequent use of a score-card to famil-
iarize yourself with all details. It is important, also,
that the person bear in mind the fact that a variety which
is simply as good as any other in cultivation is not worth
introducing. It should be better in some particular than
any other in existence. The operator must know the
points of his plant, as an expert stock-breeder knows the
points of an animal, and he must possess the rare judgment
to de'termine which characters are most likely to reappear
in the offspring. Inasmuch as a person can be an expert
in only a few plants, it follows that he cannot expect satis-
factory results in breeding any species that may chance
to come before him. Persistent and uniform effort, con-
tinued over a series of years, is usually demanded for
the production of really valuable varieties. Thus it often
happens that one man excels all competitors in breeding a

How Domestic Varieties Originate 237

particular class of plants. The horticulturists will recall,
for example, Lemoine in the breeding of gladiolus, Eckford
in peas, Crozy in cannas, Bruant in pelargoniums, and
others. There are now and then varieties which arise
from no effort, but because of that very fact they reflect
no credit upon the so-called originator, who is really only
the lucky finder. So far as the originator is concerned,
such varieties are merely chance. If, however, the
operator — himself an expert judge of the plant with
which he deals — chooses his seeds with care and dis-
crimination, and then proposes, if need be, to follow up
his work generation after generation of plants by means
of selection, the work becomes plant-breeding of the
highest type.

First of all, therefore, the operator must know what
he can likely get, and what will likely be, worth getting.
Many persons, however, begin at the other end of the
problem, — they get what they can, and then let
the public judge whether the effort has been worth
the while.

11. Having derived a specific and correct ideal, the
operator must next seek to make his plant vary in the
desired direction. This may be done by crossing, or by
modifying the conditions under which the plant grows.
If there are any two plants that possess indications of
the desired attributes, cross them; among the seedlings
there may be some that may serve as starting-points for
further effort.

A change in the circumstances or environment of the
plant may start the desired attribute. If the plant must
be dwarfer, plant it on poorer or drier soil, transfer it

238 Plant-Breeding

towards the poles, plant it late in the season, or transplant
it repeatedly. Dwarf peas become climbing peas on rich,
moist lands. If the plant must have large fruits, allow it
more food and room, and give attention to pruning and
thinning. Certain geographical regions develop certain
characters in plants, as we have seen ; if, therefore, the
desired feature does not appear spontaneously or as a
result of any other treatment, transfer the plant for a
time to that region which is characterized by such attri-
butes, if there is any such. It is not intended to convey
the impression that the placing of plants on poor soil will
directly cause a dwarfing which will be inherited, or large
size on good soils, but if the plant already holds the
characteristic of dwarfness or some other quality in a
latent form, it will probably appear if the conditions are
made right.

The importance of growing the plant under conditions
or environments in which the desired type of characters
is most frequently found, is admirably emphasized in the
evolution of varieties which are adapted to forcing under
glass. Within a century — and in many instances within
a score of years — species that are practically unknown
to glass-houses have produced varieties perfectly adapted
to them. This has been accomplished by growing the
most tractable existing varieties, selecting those which
most completely adapt themselves to their environment
and to the ideals of the operator. One of the most re-
markable examples of this kind is afforded by the carna-
tion. In Europe it was chiefly a border or outdoor plant,
but within a generation it had produced hosts of excellent
forcing varieties in America, where it is grown almost ex-

How Domestic Varieties Originate 239

clusivqly as a glass-house flower. So the carnation types
of Europe and America have been widely unlike.

Sowing the seeds of hardy annual plants in autumn
often stimulates a tendency to produce thickened roots.
The plant, rinding itself unable to perfect seeds, stores its
reserve in the root, and it therefore tends to become
biennial. In this manner, with the aid of selection and
the variation of the soil, Carriere was able to produce
good radishes from the wild slender-rooted charlock
(Raphanus Raphanistrum) .

Lessened vigor, so long as the plant continues to be
healthy, nearly always results in a comparative increase of
fruits or reproductive organs. It is an old horticultural
maxim that checking growth induces fruitfulness. It is
largely in consequence of this fact that plants bear heaviest
when they attain approximate maturity. Trees are
often thrown into bearing by girdling, heavy pruning,
the attacks of borers, and various accidental injuries.
The gardener knows that if he keeps his plants in vigorous
growth by constantly putting them into larger pots, he
will get little, or at least very late, bloom. The plant-
breeder, therefore, may be able to induce the desired
initial variation by attention to this principle. (See dis-
cussion of variation in relation to food supply.) Arthur
has recently put the principle into this formula: "A
decrease in nutrition during the period of growth of an
organism favors the development of the reproductive
parts at the expense of the vegetative parts."

A most important means of inducing variation is the
simple change of seed, the philosophical reasons for
which are explained on earlier pages. A plant becomes

240

Plant-Breeding

closely fitted or accustomed to one set of conditions, and
when it is placed in new conditions, it at once makes an
effort to adapt itself to them. This adaptation is varia-
tion. No doubt the free interchange of seeds between
seed-merchants and customers is one of the causes of
the enormous increase in varieties in recent times.

When once a novel variety appears, others of a similar
kind are likely soon to follow in other places, and some

persons have supposed
that there is a synchro-
nistic variation in
plants, or a tendency
for like variations to
appear simultaneously
in widely separated lo-
calities. There is per-
haps some remote reason
for this opinion, because
there is, as Darwin ex-
presses it, an accumula-
tive effect of domestica-
tion or cultivation, by virtue of which plants that long
remain comparatively invariable may, within a short
time, when cultivation has been continued long enough,
vary widely and in many directions ; and it is to be ex-
pected that even when plants have long since responded
to the wishes of the cultivator, an equal amount or accumu-
lation of the force of domestication would tend to produce
like effects in different places. But it is probable that by
far the greater part of this synchronistic variation is
simply apparent, for whenever any marked novelty appears

FIG. 58. — Wild cabbage.

How Domestic Varieties Originate

241

the attention of all interested persons is directed to looking
for similar variations amongst their own plants.

12. The person who is wishing for new varieties should
look critically to all perennial plants, and particularly to
trees and shrubs, for bud-varieties or sports. It has
already been said that the branches of a tree may vary
among themselves in the same way in which seedlings

FIG. 59. — Curled kale. Brassica oleracea var. acephala.

vary, and for the same reason. As a rule, any marked
sport is capable of being perpetuated by bud-propagation.
The number of bud-varieties now in cultivation is really
very large. Many of the cut-leaved and colored or
variegated varieties of ornamental plants were originally
found on other trees as sports. The "mixing in the
hill" of potatoes is bud-variation. Nectarines are de-
rived from the peach, some of them as sports and some as
seedlings. The moss-rose was probably originally a sport

242

Plant-Breeding

from the Provence rose. Greening apple trees often bear
Russet apples, and Russets sometimes bear Greenings.

Bud-varieties may not only come from buds, — as
grafts, cuttings, and layers, — but they sometimes
perpetuate themselves by seeds. Now, these seedlings

are amenable to selec-
tion, just the same as
any other seedlings are ;
the bud-variety, there-
fore, may give the in-
itial starting-point for
plant-breeding. But,
more than this, it is
sometimes possible to
improve and fix the
type by bud-selection
as well as by seed-se-
lection. Darwin cites
this interesting testi-
mony: "Mr. Salter
brings the principle of
selection to bear on
variegated plants prop-
agated by buds, and has thus greatly improved and
fixed several varieties. He informs me that at first a
branch often produces variegated leaves on one side alone,
and that the leaves are marked only with an irregular
edging, or with a few lines of white and yellow. To im-
prove and fix such varieties, he finds it necessary to en-
courage the buds at the bases of the most distinctly marked
leaves and to propagate from them alone. By following,

FIG. 60. — Collard.

How Domestic Varieties Originate 243

with perseverance, this plan during three or four successive
seasons a distinct and fixed variety can generally be
secured." Ernest Walker, then a gardener at New Al-
bany, Indiana, is of the opinion that the abnormal charac-
ter of sports often intensifies itself if the sport is allowed
to remain on the parent plant for a considerable time.
He has observed this particularly in coleus, where color
sports are frequent. "In these," he says, "the sport
begins with a branch which may
be taken off and propagated as
a new variety. If left on the
parent, other parts of the plant
are 'apt to show similar varia-
tions. Indeed, I think it is not
best to be in too great hurry to
remove a sporting branch, for its
character seems to tend to be-
come more fixed if it remains on
the plant."

13. The starting-point once
given, all permanent progress lies
in continued selection. This, as
we have already pointed out, is really the key to the whole
matter. In the great number of cases, the operator cannot
produce the initial variation which he desires, but, by look-
ing carefully among many plants, he may find one which
shows an indication of his ideal. This plant must be
carefully saved, and all of the seeds sown in a place where
crossing with other types cannot take place. Of a hundred
seedlings from this plant, perhaps one or two will still
further emphasize the character which is sought. These,

FIG. 61. — Brussels sprouts.

244

Plant-Breeding

again, are saved, and all the seeds are sown. So the
operation goes on, patiently and persistently, and there is
a reward at the end. This is the one fundamental practice
that underlies the amelioration of plants under the touch
of man ; and because we know, from experience, that it
is so important, we are sure, as Darwin was, that selec-
tion in nature must be a factor in the progress of the
vegetable world.

But suppose this suggestion of the new variety does

not appear among the
batch of plants that
we raise? Then sow
again ; vary the con-
ditions; choose the
most widely variable
types ; cross ; at length

— if the ideal is true

— the suggestion will
come. " Cultivation,
diversification of the
conditions of existence,

and repeated sowings" are the means which Verlot
would employ to induce variations. But the skill and
the character of the final result lie not so much in the
securing of the initial start, as in the subsequent se-
lection. Nature affords starting-points in endless num-
bers, but there are few men alert and skillful enough
to take the hint and improve it. If we want a new
tomato, we first endeavor to discover what we want. We
decide that we must have one like the Acme in color, but
.more spherical, with a firmer flesh, and a little earlier.

FIG. 62. — Savoy cabbage.

How Domestic Varieties Originate 245

Then we shall raise an acre of Acme tomatoes, and closely
allied varieties ; if we cannot do that, we make arrange-
ments to inspect the neighbor's fields. We scrutinize
every plant as the first fruits are ripening. Finally, one
plant is found — not one fruit — which is something like
the variety desired. Very well. Wait two to five years
and you shall see the new variety.

FIG. 63. — Cabbage shapes: flat; round or ball; egg-shaped; oval;

conical.

Some of these initial variations possess no tendency to
, reproduce themselves. The seedlings of them may break
up into a great diversity of forms, no form representing
the parent closely. In such cases, it is generally useless
to proceed further with this brood. Another start
should be made with another plant. So it is always im-
portant, as we have already seen (Rule 6), to have as

246 Plant-Breeding

many starting-points as possible, to lessen the risk of
failure. Whilst it requires nice judgment to choose
those plants which possess the most important and the
most transmissible combination of characters, the great-
est skill is nevertheless required to carry forward a correct
system of selection.

14. Even when the desired variety is obtained, it must
be kept up to the standard by constant attention to
selection. That is, there is no real stability in the forms
of life. So long as the conditions of existence vary,
so long will the plants make the effort to adapt themselves
to the changes. No two seasons are alike ; and no two
fields, or even parts of fields, are alike ; and there are no
two cultivators who give exactly the same and equal at-
tention to tillage, fertilizing, and the other treatment of
plants. All forms or varieties, therefore, tend to "run
out" by variation or gradual evolution into other forms;
but because we keep the same name for all the succeeding
generations, we fancy that we still have the same variety.

" In 1887 I found a single tomato plant in my garden
in Michigan, that had several points of superiority over
any other of the one hundred and seventy varieties I
was then growing. It came from a packet of German
seed of an inferior variety. The tomato was very solid,
an unusually long keeper, productive, and attractive in
size and appearance. The variation was so promising
that I named it in a sketch of tomatoes that I published
that year, calling it the Ignotum (that is, unknown),
to indicate that the origin of it was no merit of my own. I
sent seeds to a few friends for testing. I sowed the seeds
for about five hundred plants in 1888 in an isolated patch

How Domestic Varieties Originate 247

on uniform soil. The larger part of the plants were more
or less like the parent. A few reverted. A few of the
best plants were selected and the seed saved. I then
moved to New York and took the seed with me. This
was sown in uniform soil in an isolated position in 1889.
This crop, probably as a result of the careful selection of
the year before and of the change of locality, was re-
markably uniform and handsome. Of the 442 plants
I grew that year, none reverted to the little Eiformige
Dauer, the German variety from which it had come, but
there was some variation in them due to different methods
of treatment. I again saved the seeds, and I was now
ready to introduce the variety. I therefore sold my seeds,
six pounds, to V. H. Hallock & Son, Queens, New York,
who introduced it in 1890. The very next year, 1891, I
obtained the Ignotum from fifteen dealers and grew the
plants side by side. Of the fifteen lots, eight bore small
'and poor fruits which were not worth growing and which
could not be recognized as Ignotum ! Grown from our
own seeds, it still held its character well. Here, then,
only a year after its introduction, half the seedsmen were
selling a spurious stock. It is possible that some of this
variation arose from substitution of other varieties by
seedsmen, although I have yet secured no evidence of any
unfair dealing. It is possible, also, that the product of
some of the samples which I early sent out for testing had
found their way into seedsmen's hands. But I am
convinced that very much of this variation was a legiti-
mate result of the various conditions in which the crops of
1890 had been grown, and the varying ideals of those who
saved seeds. I am the more positive of this from the

248

Plant-Breeding

fact that the Ignotum tomato, as I first knew it and bred
it, appears now to be lost to cultivation, although the name

is still used for the legitimate
family of descendants from my
original stock. All this experi-
ence illustrates how quickly varie-
ties pass out by variation and by
the unconscious and unlike selec-
tion practiced by different per-
sons."— Bailey, earlier editions.

The longevity of any variety
is inversely proportional to the
frequency of its generations. An-
nual plants, other conditions
being the same, run out sooner
than perennials, because seed-re-
production — or the generations
- intervenes more frequently.
Trees, on the other hand, carry
their variations longer, because
the seed generations — in which
departures chiefly take place —
are farther apart. Of all the so-
called fruit plants, the strawberry
runs out soonest and the varie-
ties change the oftenest, because
a new generation can be brought
into fruit-bearing in two years,
whilst it may require ten years or
more to bring a new generation of apples or chestnuts into
bearing. " Yet, my reader will remind me that the Wilson

FIG. 64. — Swede turnip
(top) ; kohl-rabi (middle) ;
cauliflower (bottom).

How Domestic Varieties Originate 249

strawberry has been and is the leading variety in many
places for nearly forty years, to which I reply that the Wilson
of to-day is not necessarily the same as that introduced

FIG. 65. — Wild form of Chrysanthemum morifolium, as grown in

England.

by James Wilson, simply because the name is the same.
Every different soil or treatment tends to produce a different
strain or variation in the Wilson strawberry, as it does in
any other plant; and every grower, when setting a new

250 Plant-Breeding

plantation, chooses his plants from that part of his field
which pleases him best, rather than from those plants
that most nearly correspond to the original type of the
Wilson. That is, the unconscious selection on the part
of the grower takes no account of what the variety was,
but only of what it ought to be, and this ideal differs with

FIG. 66. — Wild form of Chrysanthemum indicum, as grown in England.

every person. It is not surprising, therefore, to find strains
of Wilson strawberry as unlike as are many named vari-
eties ; and it is to be expected that all the strains now in
existence have departed considerably from the original
type." — Bailey, earlier editions.

This example borrowed from the strawberry is a most
important one, because it illustrates how a variety may

How Domestic Varieties Originate 251

vary and pass out of existence even though it is propa-
gated wholly asexually or by buds. There are to-day
several different types of Rhode Island Greening apple in
cultivation which have probably originated from varia-
tions induced by environment and by the different ideals
of propagators ; and the same is true in other fruits.

All the foregoing remarks illustrate the importance
of constant attention to selection if
one desires to maintain the exact
type of any variety which he has
produced. They explain the value
of the "roguing" —or systematic
destruction of all "rogues" or non-
typical plants — which is invariably
practiced by all good seed growers.
But they still more emphatically
show that every variety is essen-
tially unstable, and that the only
abiding result is constant evolution,
the old forms being left behind as
the type expands into new and
better forms. Varieties to be valu-
able, therefore, ought not to be rigidly fixed, and, for-
tunately, nature has prescribed that they cannot be.
Probably every ten years sees a marked change in every
variety of any annual species which is propagated ex-
clusively from seeds, and every century must see a like
change in the tree fruits. These changes are so gradual
and the original basis of comparison fades away so com-
pletely that we generally fail to recognize the evolution.

15. Itr is evident, therefore, that the most abiding

FIG. 67. — Pompon anem-
one chrysanthemum.

252

Plant-Breeding

progress in the amelioration of plants must come as a re-
sult of the very best cultivation and the most intelligent
selection and change of seed. Every reflective person
must admit that the cultivation of plants — which is the
fundamental conception of agriculture — has been and is

crude and imperfect, and that
there has been no conscious effort
on the part of the human race to
produce any given final result
upon the cultivated flora. Yet,
this imperfect cultivation has al-
ready modified plants so pro-
foundly that we cannot deter-
mine the originals of many of
them, and we can trace the evo-
lution of but few. The science of
rural industry is now fairly well
understood in its essential funda-
mental principles, and the in-
telligence of those classes of per-
sons who deal with plants is
rapidly enlarging. The first part
of the twentieth century will vir-
tually mark a new era for agri-
culture, and from that time on the onward evolution
of plants should proceed confidently and unchecked.
Our eyes are too often dazzled by the novelties which
suddenly thrust themselves upon us, and we look for
some mystic power which shall enable us to produce
varieties forthwith at our will. We need not so much
varieties with new names as we do a general increase

FIG. 68. — Single type.

How Domestic Varieties Originate 253

in productiveness and efficiency of the types we
already possess; and this augmentation must come
chiefly in the form of a gradual evolution under the
stimulus of good care. The man who will accomplish
most for the amelioration and unfolding of the forms of
plants is he who fixes his eyes steadily upon the future,
and, with the inspiration of a long forecast, urges the
betterment of all conditions in which plants grow.

SPECIFIC EXAMPLES

The foregoing principles and discussions will become
more concrete if a few actual examples of the origination
of varieties are given. To
begin with a very simple
case, we relate the intro-
duction of the varieties of
the dewberries, for this
fruit is yet little cultivated,
the varieties are few, and
the domestication of it is
not yet fifty years old.

The dewberry and black-
berry. - The dewberries
are native fruits, and it is
only within twenty-five
years that they have
become prominent among
fruit-growers. The most
important is the Lucretia.

r™ . <• i . FIG. 69. — Type of pompon chrys-

ThlS was found growing anthemum. Grown outdoors,

wild on a plantation in ™th no special care.

254 Plant-Breeding

West Virginia in war time. In 1876, a few of the plants
were sent to Ohio, and from this start the present stock
has come. It is probable that similar wild varieties are
growing to-day in many parts of the country, but they
have not chanced to have -been seen by persons who are
interested in cultivating them. It is a form of the com-
mon wild dewberry that grows all over the Northeastern
states. Just why this particular patch in West Virginia
should have been so much better than the general run of
the species nobody knows, but it was undoubtedly the
product of some local environment or special ancestry.

Early in the seventies, T. C. Bartel, of Huey, Clinton
County, Illinois, observed very excellent dewberries grow-
ing in rows between the lines of stubble in an old cornfield,
where the plant had evidently been quick to avail itself
of unoccupied land. This was introduced as the Bartel
dewberry, and is now the second in point of prominence
amongst the cultivated varieties. Other varieties have
appeared in much the same way. A fruit-grower in
Michigan found an extra good dewberry in a neighboring
wood-lot, and introduced it under the name of Geer, in
compliment to the owner of the place. In Florida an
unusually good plant of the common wild dewberry of
that region was discovered, and introduced by Reasoner
Brothers under the name of Manatee. There are now
about twenty named varieties of dewberries in cultivation
as described in our horticultural writings, all of which,
apparently, are chance plants from the wild.

As the dewberries become more widely grown, good seed-
lings will now and then appear in cultivated ground, and
these will be named and sold. After a time persons will

How Domestic Varieties Originate 255

begin to sow seed for the purpose of producing new
varieties ; and those seedlings which chance to possess
unusual merit will be propagated, and in due time intro-
duced. This is the history of the cultivated blackberries
and raspberries which have come from the wild plants in
little more than half a century. These fruits are now so
far developed that we no longer think of looking to the
woods and copses for new varieties of promise, yet the
novelties are mostly chance seedlings from cultivated
varieties. A few years ago a friend purchased plants of
the Snyder blackberry. When they came into bearing,
he noticed that one plant was better than the others. It
bore larger fruits, and the bearing season was longer. He
took suckers from this plant, and from these others were
taken, until he had a large plantation of the novelty,
mostly selected from plants which pleased him best.
The variety had such distinct merit that it was named
the Mersereau, in honor of the man who recognized and
propagated it.

The apple. — The original apple is not definitely known,
but it was certainly a very small and inferior crabbed
fruit, borne mostly in clusters. When we first find it
described by historians, it was still of small value. Pliny
said that some kinds were so sour as to take the edge off
a knife. But better and better seedlings continued to
come up about habitations, until, when printed descrip-
tions of fruits began to be made, three or four hundred
years ago, there were many named kinds in existence.
The size had vastly improved, and with this increase
came the reduction of the number of fruits in the cluster ;
so that, at the present time, whilst apple flowers are borne

256

Plant-Breeding

in clusters, the fruits are usually borne singly. That
is, most of the flowers fail to set fruit, and they complete
their mission when they have shed their pollen for the
benefit of the one which persists.

The American colonists brought with them the staple
varieties of the mother countries. But the needs of the

new country were unlike those
of the old, and the tastes and
fashions of the people were chang-
ing. So, as seedlings came up
about the buildings and along
the fences, where the seeds had
been scattered, the ones that
promised to satisfy the new needs
were saved, and many of the old
varieties were allowed to pass
away. In 1817, the date of the
first American fruit-book, over
sixty per cent of the varieties
particularly recommended for
cultivation in this country were

Fm. 70. -Japanese anemone Qf American origin In 1845)

nearly two hundred varieties of

apples were described as having been fruited in this
country, of which over half were of American origin.
Between these two dates introduction of foreign varie-
ties had been freely made, so that the percentage of
domestic varieties had fallen. But the next thirty years
saw a great change. Of 1823 varieties described in
1872, nearly or quite seventy per cent were American,
and a still greater proportion of the most prized

How Domestic Varieties Originate

257

kinds were of domestic origin. In the older states, the
apple had now become so completely accustomed to its
environment, and the tastes of the people were so well
supplied, that there was no longer much need for the in-

FIG. 71. — The small and regular anemone type.

troduction of foreign kinds. It was not so in the North-
west. There the apples of the Eastern states did not
thrive. The climate was too cold and too dry. Atten-
tion was turned to other countries with similar or rigorous

s

258

Plant-Breeding

climate. In 1870, the Department of Agriculture at
Washington imported cions ' of many varieties of apples
from Russia, but these did not satisfy all fruit-growers

of the Northern states.
It was then conceived
that the great interior
plain of Russia should
yield apples adapted to
the upper Mississippi
Valley, whilst those al-
ready imported had come
from the seaboard terri-
tory. Accordingly, early
in the eighties, Charles
Gibb, of the province of
Quebec, and Professor
Budd, of Iowa, went to
Russia to introduce the
promising fruits of the
central plain. The re-
sults have been most in-
teresting to the pacific
looker-on. There are ar-
dent advocates of the
Russian varieties, and
there are others who see
nothing good in them.
There are those who

think that all progress must come by securing seedlings
from the hardiest varieties of the Eastern states ; there
are others who would derive everything from the Siberian

FIG. 72. — A pompon chrysanthemum.

How Domestic Varieties Originate 259

crabs; and still others who hold that the final result lies
in improving the native crabs. There has been no end
of discussion and cross-purposes. In the meantime, nature
is quietly doing the work. Here is a good seedling of some
old variety, there a good one from some Russian, and
now and then one from the crab stocks. The new varie-

FIG. 73. — Type of Japanese incurved chrysanthemum.

ties are gradually supplanting the old, so quietly that few
people are aware of it ; and by the time the contestants are
done disputing, it will be found that there are no Russians
and no Eastern apples, but a brood of Northwestern apples
that have grown out of the old confusion.

All these new apples are simply seedlings, almost all
of them chance trees which come up here and there

260 Plant-Breeding

wherever man has allowed nature a bit of ground upon
which to make garden as she likes. In 1892, there were
878 varieties of apples offered for sale by American nursery-
men, and it is doubtful if one of the whole lot was the
result of any attempt on the part of the originator to pro-
duce a variety with definite qualities. And what is true
of the apple is about equally true of the other fruit trees.
In the small fruits and the grapes, where the generations
are shorter and the results quicker, more has been done
in the way of direct selection of seeds and the crossing
of chosen parents ; but even here, the methods are mostly
haphazard. Latterly, however, the professional experi-
menters have begun the breeding of the apple and new
varieties on a new basis have been secured; and there is
now considerable literature on the subject.

Beans. — Perhaps there are no plants more tractable
in the hands of the plant-breeder than the garden beans.
A few years ago, a leading Eastern seedsman conceived
of a new form of bean pod that would at once com-
mend itself to his customers. He was so well con-
vinced of the merits of this prospective variety, that he
made a descriptive and "taking" name for it. He
then wrote to a noted bean-raiser, describing the proposed
variety and giving the name. "Can you make it for
me?" he asked. "Yes, I will make you the bean," re-
plied the grower. The seedsman then announced in his
catalogue that he would soon introduce a new bean, and,
in order to hold the name, he published it, along with the
announcement. Two years later, I visited the bean-
grower. "Did you get the bean?" I asked. "Yes, here
it is." Sure enough, he had it, and it answered the re-

How Domestic Varieties Originate 261

quirements very well. Another seedsman would like a
round-podded, stringless, green-podded bean. This same
man produced it, and I went into a field of fifteen acres
of it, where it was growing for seed, and the most fas-
tidious person could not have asked for a closer approach
to the ideal which the dealer had set before him some
four or five years before.

How is all this done ? It looks simple enough. The
ideal is established first of all. The breeder revolves it
in his mind, and eliminates all the impracticable and con-
tradictory elements of it. Then he goes carefully and
critically through his bean fields, particularly through
those varieties most like the desired kind, and marks
those plants which most nearly approach his ideal. The
seeds of these are carefully saved, and they are planted
in an isolated position. If he finds no promising variations
among his plantations, then he must start off the varia-
tion in some other way. This is usually done by crossing
those varieties which are most like the proposed kind.
He has got a start ; but now the care and skill begin.
Year by year he selects just those plants which please
him best and which he judges, from experience, will most
surely carry their features over to the offspring. He
starts with one plant; the next year he may have only
two. If he has ten or twenty good ones, then the task
is easy, for the variety has elements of permanence
— that is, of hereditability — in it. But he may have
no plants the second year. In that case, he begins again ;
for if the ideal is true, it can be attained. This par-
ticular bean-breeder upon whom many of our best seeds-
men rely for new varieties, says that he has discarded

262

Plant-Breeding

fully three thousand varieties and forms as profitless.
This only means that he is a most astute judge of beans,
and that he knows when any type is likely to prove to be
a poor breeder.

The bean also affords an excellent example of the care

which it is generally
necessary to exercise to
keep any variety true to
the type. The person of
whom we have spoken,
in common with all care-
ful seed-growers, searches
his field with great pains
to discover the " rogues,"
or those plants which
vary perceptibly from
the type of the given
variety. The rogue may
be a variation in size or
habit of plant, season of
maturity, color or form
of pods, productiveness,
susceptibility to rust, or
other aberrance. In the
dwarf or bush beans,
which are now most exclusively grown, the most fre-
quent rogue is a climbing or half-climbing plant. This
is a reversion to the ancestral type of the bean, which
was no doubt a twining plant. This rogue is always
destroyed even though it may be, itself, a good bean.
In some cases, the men who perform the roguing are

FIG. 74. — Japanese anemone chrys-
anthemum when fully expanded.

How Domestic Varieties Originate 263

sent along every row of a whole field on their hands
and knees, critically examining every plant. The effect
of "this continual selection is always to push the variety
to greater excellence. The various " improved" strains
of plants are obtained in essen-
tially this way. If the grower
has been painstaking with his
roguing, he soon finds that
his seed gives better and
more uniform crops than the
common stock of the variety.
If the improvement is marked,
he may dignify his strain
with a distinct name, and
it thereby becomes a new
variety The improvement
may be a very important one
to a careful bean-grower and
at the same time be so slight
as to escape the attention of
the general farmer, or even
of experimenters who are not
particularly skilled in judging
the merits of beans.

All these examples drawn from the bean are excellent
illustrations of the best and most scientific plant-breeding,
and the same methods — varied to suit the different needs
— apply to the amelioration of all other plants. The
recent dwarf lima beans may be cited as examples of
accidental or fortuitous varieties, in which the precon-
ceived ideal of the plant-breeder had no place. Four

FIG. 75. — New type with short
stem, which is becoming very
popular with commercial
growers.

264

Plant-Breeding

or five of these beans have attained some prominence.
Henderson and Kumerle Dwarf limas were introduced in
1889, Burpee in 1890, and Barteldes in 1892 or 1893.
The variety now called the Henderson was picked up
thirty or more years before by a negro, who found it

growing along a roadside in Vir-
ginia. It was afterwards grown
in various gardens, and about
1885 it fell into the hands of a
seedsman in Richmond. Hen-
derson purchased the stock of it
in 1887, grew it in 1888, and offered
it to the general public in 1889.
The introduction of Henderson's
bean attracted the attention of
Asa Palmer, of Kennett Square,
Pennsylvania, who had also been
growing a dwarf lima. He called
on Burpee, the well-known seeds-
man of Philadelphia, described
his variety, and left four beans
for trial. These were planted in
the test grounds and were found

FIG. 76. -Incurved type. ^ be yaluable Mr Palmer's

entire stock was then purchased, — comprising over an
acre, which had been carefully inspected during the
season, — and Burpee Bush lima was presented to the
public in the spring of 1890. Mr. Palmer's dwarf lima
originated in 1883, when his entire crop of Large White
(Pole) limas was destroyed by cut-worms. He went
over his field to remove the poles before fitting the land

How Domestic Varieties Originate 265

for other uses, but he found one little plant, about ten
inches high, which had been cut off about an inch above
the ground, but which had re-rooted. It bore three pods,
each containing one seed. These three seeds were planted
in 1884, and two of the plants were dwarf, like the parent.
By discarding all plants which had a tendency to climb,
in succeeding crops, the Burpee Bush lima, as we now
have it, was developed.

The Kumerle, Thorburn, or Dreer, Dwarf lima origi-
nated from occasional dwarf forms of the Challenger Pole
lima, which J. W. Kumerle, of Newark, New Jersey,
found growing in his field. The stock which came from
these selected dwarf plants was introduced by Thorburn
and Dreer, under their respective names. The singular
Barteldes Bush lima came from Colorado, and is a
similar dwarf sport of the old White Spanish or Dutch
Runner bean. Barteldes received about a peck of the
seed and introduced it sparingly. It attracted very little
attention, and as the following season was dry, Barteldes
himself failed to get a crop, and the variety was lost to
the trade.

C annas. — Few plants have shown more remarkable
evolution in very recent years than the cannas. At the
present time, the Crozy cannas — so named from Crozy,
of Lyons, France, who has introduced the greater number
of them — are most popular. This type is often called
the French Dwarf, or the Flowering Canna, and it is
marked by comparatively low stature, and very large
and showy spreading flowers in many colors, whereas
the cannas of former years were very tall plants, with
small and late dull red narrow flowers, and they were

266 Plant-Breeding

grown for their foliage effects. How has this transforma-
tion come about?

In the first place, it should be said that there are many
species of canna, and about a half-dozen of these were
well known to gardeners at the opening of last century.
About 1830, the cannas began to attract much attention
from cultivators, and the original species were soon
variously hybridized. Crossed seeds, and seeds from
the successive generations of hybrids, introduced a host
of new and variable forms. The first distinct fashion in
cannas seems to have been tall late-flowering forms.
In 1848, Annee, a cultivator in France, sowed seeds of
Canna nepalensis, a tall oriental species, and there sprung
up a race of plants which has since been known as Canna
Anncei. It is probable that this Canna nepalensis had
become fertilized with other species growing in AnneVs
collection, very likely with Canna glauca. At all events,
this race of cannas became popular, and was to its time
what the French dwarfs are to the present day. The
plants were freely introduced into parks, beginning about
1856, but their use began to decline by 1870 or before.
Descendants of this type, variously crossed and modified,
are now frequently seen in parks and gardens.

The beginning of the modern race of dwarf large-
flowered cannas was in 1863, when one of the smaller-
flowered Costa Rican species (Canna Warscewiczii) was
crossed upon a larger-flowered Peruvian species (Canna
iridi flora). The offspring of this union came to be called
Canna Ehemannii. This hybrid has been again variously
crossed with other species, and modified by cultivation
and selection, until the present composite type is the re-

How Domestic Varieties Originate 267

suit. Seeds give new varieties; and any seedling which
is worth saving is thereafter multiplied by divisions of the
root, and the resulting plants are introduced to commerce.

The cabbage family (see Figs. 58-64). — A good illustra-
tion of unconscious improvement is to be found in cabbage,
kale, collard, borecale, Brussels sprouts, kohl-rabi, and cau-
liflower. These probably came
from a single, somewhat woody,
branching perennial (Brassica
oleracea) which is to be found
growing wild on limestone bluffs
in southwestern Europe. Some
are a modification of the leaf, as
in the cabbage and kale, others
of the stem, as kohl-rabi, while
in the cauliflower it is the selec-
tion of the inflorescence that
has caused the peculiar modifi-
cation. Some of these types
have twenty and more varieties,
so that there are probably over
one hundred distinct forms from
this one wild type. All of these forms are the result of long
and patient selection of variations that were considered
desirable by the gardener without any conscious attempt
to produce these specific forms.

The chrysanthemum. — An excellent illustration of the
appearing of a wide range of forms within the epoch of
the systematic botanists is afforded by the florist's chrys-
anthemum (Figs. 65-79). These chrysanthemums are now
so widely variable and so little referable to wild species

FIG. 77. — Hairy type.

268

Plant-Breeding

that they have recently been named as a garden group-
species, Chrysanthemum hortorum (Stand. Cyc. Hort. ii.
755) . These plants now comprise forms single and double ;
pompon and giant ; discoid, flat-rayed, and quilled ; ball-
head and reflexed ; hairy-rayed ; a wide range of colors ;
bizarre forms ; and marked differences in stature and habit
of plant. If one were to bring together the little pompons,

the hardy border types, the
anemone-flowered, the Japanese
incurved, and the slender singles,
he would have difficulty in refer-
ring them to any single origin.

And yet the records show that
these multitudes .of forms have
come from one oriental feral
group, or what some botanists re-
gard as two very similar species.
The original was introduced to
England about 150 years ago.
In 1796 the Botanical Magazine figured an important large-
flowered departure, marking the beginning, or practically
the beginning, of the modern record and development.
The plants may have been long cultivated and consider-
ably modified in China and Japan. What are considered
to be the feral forms have been introduced within very
recent years. They are most unpromising looking herbs,
one (C. morifolium) with white rays, and the other (C.
indicum) with yellow rays. They look no more promising
than many weedy composites of the fields ; and yet some
process has evolved a multitude of astonishing forms
without our knowing how or why even though the evolu-

FIG. 78. — Japanese type.

How Domestic Varieties Originate

269

tion has proceeded under our eyes and within the period
when plants have been under close scrutiny.

These various examples are but types of what has
been and can be accomplished in a given group of plants.
There is nothing mysterious
about the subject, so far as
the cultivator is concerned.
He simply sets his ideal, makes
sure that it does not contra-
dict any of the fundamental
laws of development of the
plant with which he is to work,
then patiently and persistently
keeps at his task. He must
have good judgment, skill, and
inspiration, but he does not
need genius.

"In the improvement of
plants," writes Henri L. de
Vilmorin, "the action of man,
much like influences which act in the wild state, only
brings about slow and gradual changes, often scarcely
noticeable at first. But if the efforts towards the de-
sired end be kept on steadily, the changes will soon be-
come greater and greater, and the last stages of the
improvement will become much more rapid than the
first ones."

FIG. 79. — Reflexed type.

CHAPTER IX

POLLINATION: OR HOW TO CROSS PLANTS

POLLINATION is the act of conveying pollen from the
anther to the stigma. It is the manual part of the cross-
ing of plants. The word fertilization is often used in a
like sense, although erroneously; for it is the office of
the pollen, not of the operator, to fertilize or fecundate

-that part of the flower
which is to develop
into a seed.

The structure of the
flower. — The chief re-
quirement in pollinat-
ing flowers is to know
the parts of the flower
itself. The conspicu-
ous or showy part of
the flower is the envelope, which is endlessly modified in size,
form, and color. This envelope covers the inner or essential
organs, and it also attracts insects, which often perform
the labor of pollination. This floral envelope is usually
of two series or parts, — an outer and commonly green
series known as the calyx, and an inner and usually more
showy series known as the corolla. These two series are
well shown in the bellflower, Fig. 80. The calyx, with

270

FIG. 80. — Bellflower.

Pollination: or How to Cross Plants 271

its reflexed lobes, is at C, and the large bell-form part
is the corolla. When the calyx is composed of separate
parts or leaves, each part is called a sepal ; in like manner
each separate part of the corolla is a petal. In the lily,
Fig. 81, there is no distinction between calyx and corolla ;
or, it may be said, the calyx
is wanting. These envelopes
of the flower are often much
disguised. This is particu-
larly true in the orchids, one
of which, a lady-slipper, is
illustrated in Fig. 82. The
sepals are seen at DD. They
are apparently only two, but
there is reason to believe that
the lower sepal is really made
up of a union of two. The
three inner leaves are the
petals, the lower one, H,
being enlarged into the sac
or slipper.

The most important organs
of the flower, however, to
one who wishes to make crosses, are the so-called sexual
organs, the stamens and pistils. They can be readily
distinguished in the lily, Fig. 81. The six bodies shown
at S are the ends of the stamens, or so-called male organs.
These stamens generally have a stalk or stem, known as
a filament, and the enlarged tip as the anther. It is in
this anther that the pollen is borne. The pollen is usu-
ally made up of very minute yellow or brownish grains,

FIG. 81. — Flower of white lily.

272

Plant-Breeding

although it is sometimes in the form of a more or less
glutinous or adhesive mass, as in the milk-weeds and
orchids. The irritating dust which falls from the corn
tassels at the later cultivatings is the pollen.

The pistil, or so-called female organ, is shown at OP,

Fig. 81. The enlarged
portion at 0 is the ovary,
which develops into the
seed-pod. The stigma, or
the enlarged and rough-
ened part which receives
the pollen, is at P. Be-
tween these two parts is
the slender style, a part
that is absent in many
flowers.

The stamens and pistils
are known as the essen-
tial organs of the flower,
for, whilst the calyx and
corolla may be entirely
absent, either one or both
of these organs is present ;
and these are the parts
that are directly concerned in the reproduction of the species.
Like the floral envelopes, these essential organs are often
modified, so much so that botanists are sometimes perplexed
to distinguish them from each other or from modified forms
of the petals or sepals. The particular features of these
organs which the plant-breeder must be able to distin-
guish are the anther and the stigma ; for the anther bears

FIG. 82. — Flower of greenhouse
cypripedium.

Pollination: or How to Cross Plants 273

the pollen and the stigma must receive it. In Fig. 80, the
stamens are shown at E. In the flower A, which has just

FIG. 83. — Flower of night-blooming cereus.

expanded, these stamens are rigid and in condition to
shed the pollen, but in the flower B, they have shed the
pollen and have collapsed. The stigma in this case is

274 Plant-Breeding

divided into three parts, but when the flower first opens,
these parts are closed together, H in flower A, so that it
is impossible that they receive any pollen from the same
flower; when the stamens have withered, however, as in
B, the stigma, H, spreads open and is ready to receive
any pollen which may be brought to it by insects or

FIG. 84. — Flower of the shrubby hibiscus (Hibiscus syriacus).

other agencies. In this case, the ovary or young seed-pod,
which is hi the bottom of the flower, is not shown in the
engraving.

Some of the particular forms of essential organs are
well illustrated in the accompanying photographs. In
the night-blooming cereus, Fig. 83, the many-rayed stigma
is shown just below the center of the mouth of the flower,

Pollination: or How to Cross Plants 275

and the numerous stamens are
arranged in a circular form out-
side of it. The many petals and
numerous spreading sepals are
also well shown. The hibiscus,
Fig. 84, has a central column
with the anthers hanging upon
it, and a large stigma raised
beyond them. The wild bug-
bane, or cimicifuga, is seen in
Fig. 85, natural size. Here is a
long spike or cluster of flowers.
At the top are the unopened
buds, in the center the expanded
flowers with the floral envelopes
fallen away, — the fringe-like
stamens very prominent, — and
below are seen the pistils, the
stamens having fallen. These
pistils will now ripen into pods,
but the tip-like stigma may still
be seen on them. The stamens
and the long protruding style
are also shown in the fuchsia,
Fig. 94. The essential organs
of orchids are curiously dis-
guised. They are combined into
a single body. In the lady-slip-
per, Fig. 82, the lip-like stigma
is shown at P. On either side,
at its base, is an anther, S. Pro-

FIG. 85. — Bugbane (Cimici-
fuga racemosa).

276

Plant-Breeding

jecting over the stigma is a greenish ladle-like body, T,
which is a transformed and ^sterile anther. In all lady-
slippers, these organs are essentially the same as in the
drawing, although they vary much in size and shape ;
but in most other orchids, the two side anthers, S, are

wholly wanting,
and the terminal
organ, T, is a
pollen-bearing
anther. In nu-
merous plants,
there are many
distinct pistils
in each flower.
Such is the case
in the straw-
berry, where
each little yellow
"seed" on the
ripened berry
represents a pis-
til ; and the
blackberry and
the raspberry,
where each little grain or drupelet of the fruit stands
for the same organ. A flowering raspberry is illustrated
natural size in Fig. 86, for the purpose of showing the
ring of many anthers near the center of the flower, inside
of which, in the very center, is a little head of pistils.

It frequently occurs that the stamens and pistils are
borne in different flowers, rather than together in the

FIG. 86. — Blossom of flowering raspberry
(Rubus odoratus).

Pollination: or How to Cross Plants 277

same flower, as they are in the examples we have studied.
In these cases the flower is said to be staminate, or
male or sterile, in one case, and pistillate, female or fer-

FIG. 87. — Squash flowers of each sex.

tile, in the other case. If these two kinds of flowers are
borne together on the - same plant, , as in pumpkins,
melons, cucumbers, chestnuts, oaks, and begonias, the
plant is said to be monoecious; but if the staminate and

278

Plant-Breeding

pistillate flowers are on entirely different plants, as in
willows and poplars, the plant is dioecious. The two kinds
of squash flowers are shown in Fig. 87. The pistillate
flower is on the left, and it is at once distinguished by the
ovary or little squash below the colored part, or corolla
of the flower. The lobed stigma is seen in the center.
The staminate flower is on the right. It has a longer

FIG. 88. — Flowers of clematis (Clematis virginiana).

stem, no ovary, and the anthers are united into a con-
spicuous cone in the center. The flowers expand early
in the morning. Insects carry pollen to the pistillate
flower, which then begins to set its fruit, whilst the
staminate flower dies. The flower of the common wild
clematis is shown in Fig. 88. On the right are the
sterile flowers, which are wholly staminate. On the left,
the flowers with larger sepals — the petals are absent —
have a cone of pistils in the center, and a few short and

Pollination: or How to Cross Plants 279

sterile stamens spreading from the base of the cone.
These different flowers are borne on different plants in
this species of clematis, and the plants are therefore
practically dioecious, because the stamens of the pistillate
flowers generally bear no pollen. A similar mixed ar-
rangement occurs in some strawberries, except that there
are no purely staminate flowers. There are purely pistil-
late varieties, others, as the Crescent, with a few nearly
or quite abortive stamens at the base of the cone of pistils,
and others in which the flowers are perfect or hermaph-
rodites, that is, containing the two sexes.

The compositous flowers — as the asters, daisies, golden-
rods, sunflowers, dahlias, zinnias, chrysanthemums, and
their kin — need to be considered in still a different
category. In these plants, the head, or so-called flower,
is an aggregation of several or many small flowers or
florets. Each seed in a sunflower head, for example,
represents a distinct flower. Sometimes all of these flowers
are perfect, — contain the two sexes, — and sometimes
they are pistillate or staminate in different parts of the
head; and in some cases the plants are dioecious. In
many plants of the composite family, the flowers near the
border of the head are unlike those of the center or disk,
in having a long ray-like corolla; and these ray-flowers
are frequently of different form from the others in the
character of the essential organs. Very frequently the
ray-flowers are pistillate, whilst the disk flowers are
generally hermaphrodite. The anthers in these plants
are united in a ring closely about the style and below the
stigma.

The ovary, as we have seen, ripens into the pod, berry,

280 Plant-Breeding

or other fruit ; but it is not able to bear seeds until it is
assisted by the pollen. The pollen falls upon the roughish
or sticky surface of the stigma, and there germinates or
sends a minute tube downwards through the style and
finally reaches the ovule, which, when fertilized, rapidly
ripens into the seed. The nature of this fecundation is
not germane to the present subject ; but it may be said
that only one pollen-grain is necessary to the fertilization
of a single ovule, but the addition of a superabundance
of pollen greatly stimulates the growth of the fleshy or
enveloping parts of the fruit. It is important that the
person who desires to cross plants should become familiar
with the stigma when it is "ripe," receptive, or ready to
receive the pollen. This condition is usually indicated
by the glutinous or sticky or moist condition of the stigma,
or in those stigmas which are not glutinous it is told by
the appearing of a distinctly roughened or papillose
condition. This receptive condition generally occurs
about as soon as the flower opens. If pollen is withheld,
the stigma will remain receptive much longer than when
fertilization has taken place, — in some flowers for two
or three days.

The pollen is discharged from the anther in various
ways, but it most commonly escapes through a chink or
crack in the side of the anther. Sometimes it escapes
through pores at one end of the anther; and in other
cases there are more elaborate mechanisms to admit of
its discharge. In most plants, the anthers and stigma
in the same flower mature at different times, so that
close-fertilization or in-breeding is avoided. This is
well illustrated in the bellflower, Fig. 80. Here the anthers

Pollination: or How to Cross Plants 281

wither and die before the stigmatic lobes open. In other
cases, the stigma matures first, although this is not the
usual condition.

Manipulating the flowers. — We are now familiar with
the essential principles in the pollination of flowers.
Before a person proceeds to operate on a flower with which
he is unfamiliar, he should carefully study its structure,
so as to be able to locate the different organs, and to dis-
cover when the pollen and the stigma are ready for work.

The first and last rule in the pollinating of plants is this :
Exercise every precaution to prevent any other pollina-
tion than that which you design to give. The anthers,
therefore, must be removed from the flower before it
opens. This removal of the anthers is known as emascula-
tion. Just as soon as this is done, tie up the flower securely
in a bag to protect it from foreign pollen, which may be
brought by winds or insects. As soon as «the stigma is
ripe, remove the bag and apply the desired pollen, placing
the bag on the flower again, where it must remain until
the seeds begin to form. The stigma may be receptive
the day following emasculation, or, perhaps, not until a
week afterwards. Much depends on the age of the bud
when emasculation takes place. It is commonly best
to delay emasculation as long as possible and not have
the flower open; but the operator must be sure that
the anthers do not discharge or that insects do not get
into the flower before he has emasculated it. The bud at
B, in Fig. 82, is nearly ready to emasculate. The older
buds on the top of the spike of bugbane, Fig. 85, are
ready to operate ; and so is the bud seen at the left in
Fig. 86.

282 Plant-Breeding

The manner of emasculating the flower varies with the
operator. It is a common practice to clip off the anthers
with a pair of small scissors, or to hook them out with a
bent pin or a crochet hook. There are disadvantages
in any of these methods, because the anthers are likely

FIG. 89. — Tobacco flowers, showing the parts of the flower, a bud ready
to be emasculated, and an emasculated subject.

to drop into the bottom of the corolla, where it is some-
times difficult to rescue them ; and if one uses tweezers,
there is always danger that the anthers may be crushed
and that some of the pollen may adhere to the instrument
and contaminate future crosses. We may therefore cut
the corolla completely off just above the ovary, with a

Pollination: or How to Cross Plants 283

pair of small, long-handled surgeon's scissors (see Fig.
91), removing everything but the pistil. The operation
is explained in Fig. 89, which shows the tobacco flower.

FIG. 90. — Zinnia flowers ; the upper head ready for emasculation, the
lower one showing the operation performed.

The flower at the left shows the pin-head stigma in the
center of the throat, and the five anthers surrounding
it. The second flower is spread open for the purpose
of showing these organs. The third figure is a bud in

284

Plant-Breeding

FIG. 91. — Instruments used in pollinating flowers, natural size,
scalpel, scissors, lens.

Pin

the right condition for operation. The right-hand figure
shows this bud cut around with the points of the scissors,

Pollination: or Hov) to Cross Plants 285

leaving only the pistil. The line at W, in Fig. 81, shows
where the flower of the lily might be cut off.

The method for a compositous flower is shown in the
picture of the zinnia, Fig. 90. In this plant the outer
flowers of the head are pistillate, whilst those of the
disk are perfect. It is only necessary, therefore, to remove
the central stamen-bearing flowers before any of them
open, and to cover the flower up before any of the pistils
near the border have protruded themselves. The upper
head in Fig. 90 shows the untreated sample, while the
lower one shows the same with the cone of central flowers
pulled out. This treated head should now be covered,

FIG. 92. — Ladle for pollinating house tomatoes.

to await the maturing of the stigmas. In many composi-
tous plants, however, the case is not so simple as this,
because all the flowers are perfect. In such cases, nearly
all the florets should be removed from the head, and a
few remaining ones emasculated in essentially the same
method as described for the tobacco, Fig. 89.

Whenever flowers are borne in clusters, nearly all of
them should be removed and the attention confined to
only two or three of them. One is then more certain of
getting seeds to set. In some cases, like the apple cluster,
only one or two flowers of any cluster ever set fruit,
and the operator should then choose the two or three
strongest and most promising buds, and cut all the others
off.

286

Plant-Breeding

Flowers that bear no stamens, as the pistillate flowers
of squashes, strawberries, and many other plants, of
course do not require emasculating. They should be
tied up while in bud, however, to prevent the access of any
foreign pollen. Indian corn is a case in point. The
pistillate flowers are on the ear, each
kernel of corn representing a single
flower. The silks are the stigmas.
If it is desired to cross corn, there-
fore, the ear should be covered before
any silks are protruded, and the
pollen should be applied some days
later, when the silks are fully grown.
The staminate or male flowers are
in the tassel.

The pollen should be derived from
a flower which has also been pro-
tected from wind and insects, be-
cause foreign pollen may have been
dropped upon an anther by an insect
visitor, and it may be unknowingly
transferred by the operator. The
pollen-bearing parent needs no oper-
ation, of course, but the flower should have been tied up in
a bag when it was in bud. The pollen is best obtained by
picking off a ripe anther and crushing it upon the thumb-
nail. Then it is transferred to the stigma by a tiny scalpel
made by hammering out the small end of a pin, as shown,
full size, at the left in Fig. 91. The stigma should be
entirely covered with the pollen, if possible. It is often
advised to use a camel's-hair brush to transfer pollen.

FIG. 93. — Bag for cov-
ering the flowers.

Pollination* or How to Cross Plants 287

but much of the pollen sticks amongst the hairs of the
brush and is ready to contaminate a future cross; and
when the pollen is scarce it cannot be conserved to ad-

FIG. 94. — Fuchsias, showing the stamens and pistils, and a bud ready
to be emasculated.

vantage by a brush. In some cases the pollen is discharged
so freely that the anther may be rubbed upon the stigma,
or even shaken over it, but in most instances it will be

288 Plant-Breeding

necessary actually to place the pollen upon the stigma
with some hand instrument. When pollinating house-
grown melons and cucumbers, the staminate flower is
broken off, the corolla stripped back, and the anther-
cone inserted into the pistillate flower, where it is allowed
to remain until it driesxand falls away. In pollinating
house tomatoes, an implement shown in Fig. 92, one-third
size, is used. This is simply a watch-glass, T, secured to a

FIG. 95. — Fuchsia flower emasculated.

handle. When the house is dry, at midday, the watch-
glass is held under the flowers, which are tapped, and the
pollen falls into the glass. The glass is then held up
under another flower until the stigma rests in the pollen.
It should be said, however, that this pollination of toma-
toes is for the purpose of making the fruit set in the ab-
sence of insects, not to effect a cross. If the latter pur-
pose were the object sought, the flowers which are to
bear the seeds would need to be emasculated.

Pollination: or How to Cross Plants 289

Sometimes it is im-
possible to secure the
pollen at the time the
stigma is ready. In
some cases of this kind,
the intended parents can
be grown under glass so
as to bring them into
bloom at the same time.
In other cases, it is nec-
essary to keep the pollen
for some time. The
length of time that pol-
len will keep varies with
the species and probably
also with the strength
and vigor of the plants
that bear it. As a rule,
it will not keep more
than a week or two,
and, in general, it may
be said that the fresher
it is, the better it may
be expected to act. It
is best kept in dry and
tight paper bags, such
as are used for covering
the flowers.

Something more should be said about the bags which are
used for covering the flowers. It has been found that
light transparent oiled paper bags are the best. For

FIG. 96. — Fuchsia flower tied up after
emasculation.

290 Plant-Breeding

small flowers use the two-ounce bags and for larger flowers
use the four-ounce size. If oiled bags are not available,
the ordinary manilla bags may be used. When they are
still flat, as they come from the packages, a hole is made
near the opening, and a string is passed through it and
then tied at one of the folds, as shown in Fig. 93. The
bag is then ready for use. Before it is put on the flower,
the lower end of it is dipped in water to soften it so that

FIG. 97. — Tomato and quince, showing how the sepals were cut off
in emasculating.

it can be puckered tightly about the stem and thereby
prevent the entrance of any insect. A bag is put upon
the seed-bearing flower when emasculation is performed,
and upon the intended pollen parent when the flower is
still in bud. The bag may be removed from the emas-
culated flower from time to time to examine the stigma,
and again when the pollen is applied; but it should
not be taken off permanently until the pod or fruit
begins to grow.

By way of recapitulation, let us consider the crossing

Pollination: or How to Cross Plants 291

of a fuchsia flower. In Fig. 94 two flowers are shown in
full bloom, with the long style and the eight shorter sta-
mens. The single bud is just the right age to emasculate.
We therefore cut off the two flowers and emasculate the
bud, as in Fig. 95. The pollen of another flower is applied
and the bag is tied on, as seen in Fig. 96. The best label
is a small merchandise tag, and this records the staminate
parent and the date.

It will be seen that in
the operation of emas-
culating the fuchsia
flower we cut off the
sepals as well as the
petals. In some plants
the calyx adheres to
the full-grown fruit,
as on the apple, pear,
quince, gooseberry, or
persists at the base
of the fruit, as in the
tomato, pea, raspberry.
In these fruits, there-
fore, the cutting away
of the calyx leaves an
indelible mark which
at once distinguishes the fruits which have been crossed,
even if the labels are lost. In Fig. 97 a tomato and quince
are shown thus marked.

All the foregoing remarks do not apply to the crossing
of ferns, lycopodes, and the like, because these plants
have no flowers; yet cross-fertilization may take place

FIG. 98. — Pollinating kit.

292

Plant-Breeding

in them. When the spores of these flowerless plants are
sown, a thin green tissue, or prothallus, appears and
spreads over the ground. In this tissue the , separate
sex-organs appear, and after fecundation takes place,
the fern, as we commonly understand it, springs forth.
Thereafter, this fern lives an asexual life and produces
spores year after year; but it is only in this primitive
prothallic stage that fertilization takes place, once in the

life time of the plant.
If these plants are to
be crossed, the only
procedure open to the
gardener is to sow the
spores of the intended
parents together in
FIG. 99. — Pollinating kit. the hope that a nat-

ural mixing may take

place. There are various well-authenticated fern hy-
brids.

The pollination of flowers is such a simple work that
few implements are required for its easy performance.
Great care is more important than any number of tools.
Every one who expects to cross plants should provide him-
self with the three instruments shown in Fig. 91, — a pin
scalpel, sharp-pointed scissors, and a large hand-lens. If
one contemplates much experimenting in this direction,
however, it is economy of time to have some sort of box
in which there are compartments for the various necessi-
ties. These various compartments suggest at once whatever
accessories are wanting, and they hold a sufficient supply
for several hundred operations. There should be a com-

Pollination: or How to Cross Plants 293

partment for bags, string, lens, scissors, and pencils, tags,
note-book, and the like. Figs. 98 and 99 show a con-
venient case for an experimenter, and one that has been
used with satisfaction for several years. This kit is
twelve inches long, nine inches wide, and three inches
deep.

CHAPTER X

THE FORWARD MOVEMENT IN PLANT-
' BREEDING

THE first specific interest in cultivated plants was in
the gross kinds or species. As the contact with plants be-
came more intimate, various indefinite form-groups were
recognized within the limits of the species. Gradually,
with the intensifying of domestication and cultivation,
very particular groups appeared and were recognized.
These smaller groups came finally to be designated by
names, and the idea of the definite and homogeneous
cultural variety came into existence. The variety-con-
ception is really a late one in the development of the human
race. It is practically only within the past two centuries
that cultivated varieties of plants have been recognized
as being worthy of receiving designative names. It is
within this period, also, that most of the great breeds of
animals have been defined and separately named.

All this measures the increasing intimacy of our contact
with domesticated plants and animals. It is a record
of our progress. The peoples that are most advanced in
the cultivation of any plant are the ones that have the
most named varieties of that plant. In Japan, to this
day, the plums are said to pass under ill-defined class

294

The Forward Movement in Plant- Breeding 295

names. We have introduced these classes, have sorted
out the particular forms that promise to be of value to us,
and have given them specific American names* Some time
ago a native professor in Japan wrote me asking for cions
of these plums, in order that he might introduce Japanese
plums into Japan. The Russian apples are designated to
some extent by class names ; in fact, it was not until the
appearance of Regel's work, about a. generation ago, that
Russian pomology may be said to have begun. What
constitutes a variety is increasingly more difficult to define,
because we are constantly differentiating on smaller
points. The growth of the variety-conception is really
the growth of the power of analysis.

The earlier recognized varieties seem to have come into
existence unchallenged. There is very little record of
inquiry as to how or why or even where they originated.
That is, the quest of the origin arose long after the
recognition of the variety as a variety. Even after
inquisitive search into origins had begun, there was little
effort to produce these varieties. The describing of varie-
ties and the search into their histories was a special work
of the nineteenth century. One has only to consult such
American works as Downing's " Fruits and Fruit Trees
of America," and Burr's " Field and Garden Vegetables of
America," to see how carefully and methodically the
descriptions and synonymy of the varieties were worked
out. These are types of excellent pieces of editorial and
formal systematic work.

Systematic improvement of plants. — There have been
isolated efforts at producing varieties for many years.
These efforts began before the time of the general discus-

296 Plant-Breeding

sion of organic evolution. In fact, it was on such experi-
ments that Darwin drew heavily in some of his most
important writing. Roughly speaking, however, the
conception that the kinds of plants can be definitely modi-
fied and varied by man is a product of the last half century.
We now think that there is such a possibility as plant-
breeding. It is really a more modern conception, so far
as its general acceptance is concerned, than animal-
breeding. But both animal-breeding and plant-breeding
are the results of a new attitude toward the forms of
life — a conviction that the very structure, habits, and
attributes are amenable to change and control by man.
This is really one of the great new attitudes of the modern
world.

The term plant-breeding itself is new. It occurs only
in the most recent supplements of dictionaries. Before this
term came into use, such words as " improvement " and
" amelioration " of plants were employed, although cross-
breeding had long been current. The early writings of
Verlot and Carriere were under the title of " production
and fixation of varieties of plants." The term plant-
breeding carries the conception of a definite purpose in the
producing of new forms and attributes of plants, by cross-
ing, selection, and whatever other means may be useful.

One of the " signs of the times" in North America is the
attention that is being given to the practical breeding of
plants. A host of persons is actually at work. There
are professorships devoted to the subject. Many societies
are giving special attention to the practical improvement
of plants. Results are accumulating rapidly with very
many kinds of plants, and the literature is growing rapidly.

The Forward Movement in Plant-Breeding 297

Eventually, of course, we shall be able to formulate
somewhat definite statements as to how to proceed to
secure desired results, and then the literature of plant-
breeding can be intelligently rewritten. However, there
is no hope that plant-breeding can ever proceed with such
exactness as to enable us to produce forthwith the things
that we desire, in the way in which the mechanician devises
new machines, notwithstanding all the suggestions of
persons who write with much self-assurance. For all
that we can now see, plant-breeding will always be an
experimental process. It is this very experimental
uncertainty of the work that gives it much of its charm to
inquisitive and sensitive minds.

The plant-breeder should aim toward definite ideals. —
Now, plant-breeding is worthy of the name only as it sets
definite ideals and is able to attain them. Merely to
produce new things is of no merit ; that was done long
before man was evolved. A child can " produce" a new
variety, but it may learn nothing and contribute nothing
in producing it. In many "new" things that are pro-
duced there may be dispute as to whether they are new,
and as to whether they are distinct enough to be named
and therefore to be ranked as varieties at all. This is not
science, nor even breeding : it is playing and guessing.
What does the world care whether John Jones produces
" Jones' Giant Beardless Wheat" ? But it does care if he
produces wheat having a half of one per cent more protein.
We must give up the production of mere "varieties" ; we
must breed for certain definite attributes that will make
the new generation of plants more efficient for certain
purposes : this is the new out-look in plant-breeding.

298 Plant-Breeding

Plant improvement a serious business. — In considering
the American achievement in plant-breeding, we must
divest ourselves at the outset of all idea of " wonder," and
"miracle," and other nonsense, which has been so much
written into the subject in very recent time. Plant-
breeding is a plain and serious business, to be conducted
by carefully trained persons in a painstaking and method-
ical way. It is not magic. There are persons who have
unusual native judgment as to the merits and capabilities
of plants and who develop great manual skill; but they
are plain and modest citizens, nevertheless, and their
methods are perfectly normal and scrutable. The wonder-
mongers are the reporters, not the plant-breeders.

It is a curious psychological phenomenon that the popu-
lace, or a certain part of it, seems to lose its head now and
then. This phenomenon is not peculiar to politics. It
enters those domains that are compassed by fact and that
in ordinary times are dominated by common sense.
Plant-breeding has been seized of this sensationalism.
Newspapers, magazines, and books have spread the most
wonderful tales. The lay writers have at last awakened
to the fact that great progress is making in agricultural
subjects, and, with a fragmentary and superficial view
here and there, have written of the subjects with all the
enthusiasm and partiality of new discovery. We have
now in mind not only the inflated writing about plant-
breeding, which constitutes a regrettable contribution to
current horticultural literature, but also that general
tendency to exploit everything that is capable of high
coloring. The agricultural historian, when he takes ac-
count of the exploitations of the present day, will recall other

The Forward Movement in Plant-Breeding 299

stages in which we seem temporarily to have lost our better
judgment, of which the Morus multicaulis craze and the
lightning-rod boom are examples in two past generations.

Having now warned our readers that we have nothing
marvelous in store, we shall proceed to indicate some of
the ways in which American plant-breeders are working,
fully conscious that the space at our disposal is much
too little to allow of any adequate presentation of the
subject. It may not be out of place to call the reader's
attention to the three foundations on which rests the in-
creased productiveness of crops and animals : —

The enrichment of the land;

The tillage and care ;

The producing of better varieties and strains.

We have long given careful attention to the first two ;
now we are studying the third with new enthusiasm an,d
purpose.

The results of plant-breeding effort. — Happily, we are
not without abundant accomplishment in this new field.
The last ten years has seen a remarkable specialization
in the producing of plants that are adapted to particular
needs. The days of merely crossing and sowing the
seeds to see what will turn up are already past with
those who are engaged seriously in the work. The old
method was hit-and-miss, and the result was to take
what good luck put in our way : the new method proceeds
definitely and directly, and the result is the necessary
outcome of the line of effort. The crux of the new ideal is
efficiency in one particular attribute in the product of
the breeding. These attributes are measurable; the
kinds of results are foreseen in the plan.

300 Plant-Breeding

State plant-breeding associations. — One of the most
significant advances in popular interest in plant improve-
ment is the banding together of persons in many of the
states and provinces in an organized effort to improve
plants, especially field crops. This line of effort has been
largely brought about at the suggestion of some officer
of the state agricultural college, who is often an expert
plant-breeder himself, and usually acts as secretary of the
association. These associations have done great good
in arousing interest in plant-breeding.

The Wisconsin Association, known as the Wisconsin
Agricultural Improvement Association, was established
Feb. 22, 1901, and now has a paid-up membership of
over 2000 persons, consisting of "all former, present, and
future students and instructors of the Wisconsin College
of Agriculture," also " any person residing within the state
having completed a course in agriculture in any college
equivalent to that given by the Wisconsin University."
More recently the county agricultural schools have been
admitted to membership and honorary members may be
elected by a majority vote at any annual or special meet-
ing of the association.

The association has organized some 44 county sub-
orders, which are smaller units conducting an active
work in more restricted areas. These county orders con-
tain approximately 4000 members. Any one interested in
agriculture may unite with the county order. They have
become live centers which stand behind all agricultural
activities and lend a helping hand in making agricultural
and other resources of the county known far and near.
As a result of the association there has been established

The Forward Movement in Plant-Breeding 301

in the neighborhood of 2000 seed-grain centers where
pure-bred seed barley may be obtained. It is estimated
that over seventy-five per cent of the seed barley of Wis-
consin is of one distinct variety.

Another series of organizations, to be known as "town-
ship organizations," has been planned. These are smaller
groups within the county orders. Three are already in
existence. This scheme of organization brings the activi-
ties of the association to practically every farmer of the
state.

Starting out primarily as breeding associations, their
activities have extended in many directions. An alfalfa
order has been established which is closely affiliated with
the main association : its object is "to promote the alfalfa
interests of the state in general,"

1st. By cooperating with the Department of Agronomy
and the Wisconsin Agricultural Experiment Association
in growing, experimenting, and in the wide dissemination
of alfalfa;

2d. By having alfalfa exhibits at agricultural fairs ;

3d. By having annual meetings in order to report and
discuss topics beneficial to the members of the order ;

4th. By distributing literature and information bearing
upon the production of alfalfa for seed and forage.

The alfalfa order was organized three years ago and now
has a membership of 1200. In 1914, 50 tons of alfalfa
seed were sent out for experimental purposes.

The association receives state aid, $5000 a year, and
some of the county orders receive financial aid from the
county. The annual dues of members is fifty cents.

One of the principal aims of the Wisconsin association

302 Plant-Breeding

is to place pure-bred seed on the market. This seed is
to bear the seal of the association.

It is estimated that members of the association sell
over three hundred thousand dollars' worth of pure-bred
seed a year. The members are in close touch with the
breeding work of the experiment station and test, propa-
gate, and disseminate the improved grains which are pro-
duced on the station farm.

The association prints an annual report of over one
hundred pages containing the progress of the members in
improving seed grain and much valuable information
concerning plant-breeding in general. Such titles as the
following appear in recent annual reports : —

Dissemination of Pure Bred Seed Grains, Through the Coopera-
tion of Students in the Country Schools, J. C. Brockert.

Necessity of Thorough Preparation of Pure Bred Seed Grain for
the General Trade, Wm. R. Leonard.

County Order of Experiment Association as Factor to Promote
Dissemination of Pure Bred Grain, R. A. Moore.

Importance of Testing Our Pure Seed Grains Previous to Sowing
Season's Crop, H. L. Post. •

Importance of the Farm Inspection Work, and How Shall It Be
Carried Out? E. B. Skewes.

Growing and Preparing Seed Grains and Forage Plants for
Exhibition, O. R. Frauenheim.

Wheat Breeding — The Value of the Individual, F. H. Demaree.

In this connection, mention should be made of the
Wisconsin Potato Growers' Association, an active and
growing organization whose object is to improve the seed
and table potatoes of Wisconsin by breeding and to

The Forward Movement in Plant-Breeding 303

guarantee variety shipments true to name and free from
disease. This association, like its sister organization, does
business on a large scale and has at present nearly 300
members. " Potato Special" trains have been run through-
out the state under its auspices and that of the State
College of Agriculture, and several very successful potato
exhibits have been held.

This association has done much to standardize certain
commercial varieties of potatoes and to put seed on the
market which is true to name. Its members found our
varieties badly mixed up and containing many distinct
types. This purifying of varieties is the first step toward
careful and systematic breeding.

A Minnesota association, known as the " Minnesota
Field Crop Breeders' Association," has been organized
with a similar plan and objects as the Wisconsin associa-
tions. It publishes an elaborate annual report giving
information concerning the work of the association as a
whole and the activities of the county sections, of which
there are many. One of the functions of the association,
besides encouraging the production and sale of pure-bred
seeds, is to stage elaborate exhibits of farm products at
the state and other fairs. •

In some states, notably Illinois, Ohio, and New York,
associations of breeders have been established on a dif-
ferent membership basis. They have chosen to have
smaller associations consisting of persons who bind them-
selves to follow certain rules and regulations laid down
by the association. The Illinois Seed-corn Breeders'
Association is such an organization. Its members grow
.certain varieties of corn recognized by the association

304 Plant- Breeding

and offer these for sale with the approval and backing of
the association.

The Ohio and New York associations laid out elabo-
rate plans of breeding for their members to follow, but it
was found that farmers were not ready for such work and
as a result the Ohio association has never been very large
and the New York association has abandoned this plan
and is turning its attention to bringing the farmers and
seedsmen into closer relations, encouraging the farmer to
demand a better product and the seedsmen to produce one.

Other plant-breeding associations. — • The most notable
breeders' associations are the Canadian Seed Growers'
Association and the Swedish Seed Association.

The former has an elaborate system of inspection of all
seeds sold by members of the association under the su-
pervision of a permanent, salaried secretary. The results
are noteworthy. The standard of seed grain has been
tremendously raised in Canada and much better crops
are the result. Canadian seed grain is now in demand
all over the world. The Canadian experiment stations
are leading in this work by carefully and systematically
producing improved varieties on their experimental farms
and distributing them to members of the association who
grow them, keeping up a careful selection from year to
year and offering them for sale.

The Swedish association has an interesting history and
an enviable record. It has done more, probably, than
any other organization to reshape our conception and
methods of selection. Dr. Nilsson and his associates
have started on a large scale the principle of individual
selection in contrast to the older method of mass selection

The Forward Movement in Plant-Breeding 305

which is now largely given up. The group of scientists
at Svalof have not only shown their ability to produce
practical results, but they have also elaborated scientific
principles.

The founding of the station at Svalof is wholly due to
the private initiative of a group of Swedish farmers. The
purpose of the association has always been to produce
practical results, to breed better grains for local use.

But the station has been fortunate from the first in
having in its employ expert botanists whose skill has not
only produced many noteworthy new varieties, but who
have elaborated scientific principles of far-reaching im-
portance. These men have been given a free hand to
pursue their work without such distracting activities as
teaching, comparative field trials, commercial analyses,
and the like. This fact together with an unrestricted
organization, a well-selected program, and an expert corps
of assistants accounts for the wonderful success of this
station.

This Swedish seed association has two groups of mem-
bers: those who are permanent after having paid $28
once for all ; and those who pay annually $1.40.

The association has an annual budget of about $40,000
derived from dues of members, contributions from agri-
cultural associations, government aid, and sale of pedigreed
seed. Funds from the last two sources have increased
very rapidly in recent years. Gifts of various kinds
amounting to $77,000 have been set aside for buildings.

Accordingly, the society now has at its disposal a large
and well-equipped establishment, comprising two con-
nected buildings serving as laboratories (Fig. 100), a house

306

Plant-Breeding

The Forward Movement in Plant-Breeding 307

for preparatory work, with a little farm and a dwelling
house ; it also owns 40 acres of land, of which special
cultures and seed multiplication plots occupy 25 acres.
Despite this, it has been found necessary to make most
of the cultural experiments on the wide fields of the huge
property adjoining, in order to give the different cereals,
occupying in all about 30 acres a year, their proper place
in the rotation of crops, which is found absolutely neces-
sary for a normal development.

The program of work in Sweden was, at first, vague
and uncertain. Theorizing scientists were attempting to
solve problems for practical farmers and nobody had
blazed the trail. The starting-point of the work was
naturally the method of selection in vogue at the time,
that is, the Darwinian method of " methodical selection"
or of "mass selection" as it is now called. By this system,
a selection of seed was made from a large number of plants
and the whole thrown together and sown "en masse"
in a single plot. But it soon became evident that this
method of selection was not yielding the results which the
Swedish farmers demanded — better varieties which would
be constant. The method of selection was therefore
changed and in two years the difficulties were being over-
come by the new method.

This new method consisted of testing individual plants
and their progeny instead of making, at once, a com-
posite test of many plants. 'This plan of individual
selection has proved itself. The results were convincing.
It left no doubt as to the fact that the only true starting-
point for the fixation of different types must be plants
taken one by one.

308 Plant-Breeding

This Swedish discovery has changed the outlook on
the problem of plant-breeding, especially the methods of
selection. It could be easily demonstrated that there
existed in any cultural variety of plants a large number
of independent forms having widely divergent qualities
and a practical value that was quite useful. It was
found, moreover, that most of the descendants or " pedigree
culture " of single individuals were constant.

In employing the old method of "mass selection,"
they were working blindly without knowing how or when
or even whether they were going to reach a stability of
type ; on the other hand the method of pedigreed culture
or "individual selection" eliminated the fear of failure
because of the appearance of the hitherto unsurmountable
variations. The varieties are already there, and fixed
from the beginning of the work ; the only difficulty is to
learn to recognize them and to place the proper valuations
upon them.

The success of this method of breeding at Svalof has
profoundly modified the method of selection in this
country. The principle almost universally applied now
is the method of individual selection. Thus we hear
about plant-to-row, head-to-row, ear-to-row, or tuber-unit
testing, depending upon the plant used.

This method of selection is by no means the only one
used for plant improvement at the Swedish station, hy-
bridization also plays an important part in the work.

The work has grown very rapidly and has now been
split up into different departments with an expert in
charge of each.

Commercial breeding agencies. — The chief among com-

The Forward Movement in Plant-Breeding 309

mercial breeding agencies are, of course, the professional
seedsmen. The demand for " novelties " is ever present
and the seedsman must meet it. Therefore every seeds-
man's catalogue each spring features them, giving them
a prominent place and often painted in radiant colors.
Everybody knows that novelties are often no better
than the old standard sorts. But this demand for some-
thing new seems to be inherent.

It does not seem to be the common practice among
American seedsmen to produce their own novelties by
precise and recognized plant-breeding methods. Many
of them are purchased abroad and others are accidental
discoveries picked up here and there.

Our standard sorts of seeds of all kinds are being
gradually improved, but usually not by any particular up-
to-date methods, except in certain unusual or exceptional
instances. The seedsmen, however, carefully rogue their
fields to eliminate divergent plants in an attempt to pro-
duce seed of more importance.

Recently, however, the American Seed Trade Associa-
tion, consisting of the better class of seedsmen of the
United States, has begun a general movement for im-
proving crops by methods such as are used by careful
breeders at the agricultural experiment stations. A
committee on crop improvement has . been organized
whose duties are to ascertain, so far as possible, how the
seed trade can be most helpful in these movements for
better bred seed, and to bring about a close harmony
between the seedsmen and the plant-breeding experts of
the agricultural experiment stations.

Many seedsmen feel, at present, that the extra cost

310 Plant-Breeding

entailed in producing pedigreed seed will not be ade-
quately paid for by the average American buyer. There
is probably much justification for this feeling. Two
things should be done — to educate the buying public to the
importance of better seed and the justification for its
greater cost, and also to devise methods whereby this
seed may be more cheaply and economically produced.
The agricultural colleges through various channels are
doing much to solve these two difficulties.

Work of the council of grain exchanges. — The National
Council of Grain Exchanges is the associated body of the
various grain exchanges or boards of trade of this coun-
try. This organization is interested in a larger yield of
better grain. It has a crop improvement committee
which is very active in grain-improvement work, including
grain-breeding. This committee is conducting a very
extensive publicity campaign in an attempt to induce
farmers to use select seed and improve their crops. The
executive work is done by a secretary, who acts as general
manager, and an agronomist, who is an expert plant-
breeder and advises concerning the technical features of
the work, most of which is done through the county
agents. To aid in this work, the committee publishes a
monthly publication called The County Agent, a paper
filled with terse information concerning all phases of farm
improvement work. The secretary and agronomist have
large funds at their disposal, which are being used to bring
about concerted action by farming communities for the
improvement of seed grain.

United States Department of Agriculture and state experi-
ment stations, — The most methodical plant-breeding is

The Forward Movement in Plant-Breeding 311

now being done by officers of the experiment stations in
the United States and Canada, and by the United States
Department of Agriculture. In most of the experiment
stations there is at least one person interested in improv-
ing horticultural plants and others interested in field
crops; as there is an experiment station in every state
and territory and in the provinces of Canada, it will be
seen that there are several hundred persons who, by
their profession, are directly concerned in plant-breeding,
aside from a number of persons in the federal Department
of Agriculture who devote themselves exclusively to this
subject. 'The work is extended, also, into the hands of
various assistants in the different institutions ; so that it
is probably no exaggeration to say that three to four
hundred professional investigators are now giving atten-
tion, for a greater or less part of their time, to measures
for improving American crop production by means of
breeding.

The breeding enterprises of the federal Department of
Agriculture were formerly confined to investigators in the
Plant-Breeding Laboratory. But the work has grown to
such an extent and breeding now touches so many phases
of plant work that the former organization, as such, has
been discontinued, and breeding is taken up in connec-
tion with many other departments. There is now more
of a tendency for the administrative divisions to group
themselves around the crops such as corn, cotton, wheat,
vegetables, and so forth, rather than processes such as
plant-breeding, or culture.

The work of the federal investigators has been tre-
mendously important both from the standpoint of original

312 Plant-Breeding

research and the production of improved varieties and
strains for dissemination.

The success of the cotton-breeding experiments is
noteworthy. These have been conducted with the object
of increasing the length and strength of lint ; and an early
variety to avoid the ravages of the boll-weevil is desired.
The famous long-stapled Sea Island Cotton has been
much used for hybridizing with the upland cottons to
increase the length of lint of the latter. The length has
been increased very considerably by this method and the
varieties have been made more uniform, an important
factor in ginning.

The work of Webber and Swingle in producing new
types of oranges which are resistant to cold is exceedingly
important. Various varieties of the common sweet
orange were crossed with Pondrus (or Citrus) trifoliata, a
hardy hedge orange, and hybrids have been produced which
are called " citranges." These will grow some four hundred
miles farther north than the present orange belt, which is
no small factor in orange-growing. These hybrids are too
bitter to be eaten out-of-hand, but they make an excellent
ade ; many of them have more juice than lemons.

A cross has also been made between the pomelo or
grapefruit and the tangerine. A hybrid was produced
which combines the easily removable rind of the tan-
gerine and has the flavor, not of the pomelo, but of the
sweet orange. A fruit of this kind, combining these char-
acteristics so well, bids fair to play an important part in
orange-growing of the future.

The division of Plant Introduction has contributed no
small part to breeding work. Through its activities, a great

The Forward Movement in Plant-Breeding 313

many plants have been imported from all over the world
which have formed rich material for the plant-breeder to
take and improve, and many other varieties have been
introduced which have immediately become valuable
without further improvement. Such plants as durum
wheat, Japanese kinshu rice, Swedish select oats, Wash-
ington navel orange, cold-resistant varieties of alfalfa,
Russian apples, varieties of dates for Southern Cali-
fornia and Arizona, drought-resistant olives, Egyptian
cotton, and very many others have added millions to our
agricultural wealth.

The work of Orton and his associates in breeding plants
resistant to disease forms an important chapter in this
work. They have been successful in waging war on wilt
of cotton, cowpeas, watermelons (see Figs. 55 and 56), and
other crops by means of breeding to obtain wilt-resistant
strains. The only successful method of combating certain
maladies seems to be in this way. Strains of disease-resist-
ant asparagus and of rust-resistant cereals have reached
economic importance.

Many great sections of the United States which are
now nearly barren could be made productive if varieties
of plants could be developed which are resistant to drought
and alkali. This work has occupied the attention of a
large corps of plant-breeders and not without results.
The experts from eighteen state experiment stations be-
sides the men from Washington are engaged in this work.
As a result, varieties of wheat and other cereals, alfalfa,
nuts, olives, and various fruits have been developed which
will grow in parts of this great region and are of considerable
economic importance.

314 Plant-Breeding

Work of the state agricultural experiment stations. —
Investigators in the state experiment stations have always
taken an active part in plant-breeding work. Five years
ago, in an admirable editorial in the Experiment Station
Record, Dr. Allen says as follows: "The list of proj-
ects conducted by the experiment stations under the
Adams fund includes sixty-three which fall under the head
of investigations in breeding (eleven of these relate to the
breeding of animals). This relatively large number indi-
cates the popularity of the subject, and an evident feeling
that it not only presents large research possibility, but is
a line in which investigation is greatly needed. The
attention which is being given to breeding is encouraging
and the number of enterprises suggests the possibility of
material additions to the general understanding of its
various phases."

The experiments subsequent to that time have, to a
considerable extent, justified the hope of "material
additions to the general understanding of its various
phases." Numerous bulletins have been published which
have added to that knowledge, and the experiment station
men have written many articles which have appeared in
various serial publications.

The lines of work which have received the greatest
attention and in which the most constructive work has
been done are the application of Mendel's laws to economic
plants and the elucidation of individual selection and pure-
line breeding. Not only have important practical results
been obtained in improving our economic plants, but a
considerable amount of material of scientific value has
been accumulated.

The Forward Movement in Plant-Breeding 315

The experiments with corn at the Illinois and other
experiment stations and those with timothy at the Cornell
station stand out prominently as examples of pieces of
scientific research which, at the same time, have tre-
mendous economic importance.

There is scarcely an economic crop but is receiving
some attention by the plant-breeders of our experiment
stations, and bulletins are appearing frequently dealing
with this phase of the work.

Many experiment stations, such as Wisconsin, Minne-
sota. Ohio, New York, and Kansas, are also busily engaged
in producing superior varieties upon their own grounds
for distribution to their constituents.

The old-time very prevalent variety tests are still
made, but these are now supplemented by variety im-
provement and careful studies of variety adaptation.

Beside the large amount of practical work which most
of the stations are doing, there are a large number of
breeding projects prosecuted by them, and which are
destined to become of scientific importance.

The following projects have been reported by Dr.
Allen of the federal Office of Experiment Stations as
now conducted at the different stations : —

Breeding Corn — Alabama Station.
Breeding Experiments with Cotton — Alabama Station.
Breeding Oats — Alabama Station.
Wheat Breeding Investigations — Kansas Station.
Alfalfa Breeding Investigations — Kansas Station.
Analysis of Cellular Structure of Hybrids — Maine Station.
Experimental Modification of the Hereditary Process — Maine
Station.

316 Plant-Breeding

Breeding Alfalfa with Reference to the Extreme and Sub-tropical

Conditions of Arizona — Arizona Station.
Cotton Breeding — Arkansas Station.
Nicotiana Hybrids — California Station.
Improvement of Dent, Flint, and Sweet Corn in Yield and

Feeding Value, by Breeding Work in Six Different Localities

— Connecticut Station (State).
Breeding Investigations with Tobacco — Connecticut State

Station.

Zenia in Maize and Hereditary Transmission of Various Char-
acters — Connecticut State Station.
The Effect of Variations in Physical Characters and Chemical

Composition of the Corn Kernel upon the Vigor of the

Plant — Delaware Station.
Plant Breeding — Florida Station.
Investigation of Mendelian Laws in Application to the Cotton

Plant — Georgia Station.

Inheritance of Contrasted Characters — Mississippi Station.
Study of the Correlation of Characters and of Inheritance in

Pure Lines and Varieties — Montana Station.
Degree of Close Breeding in Maize — Nebraska Station.
Plant Breeding Work with Pure Lines of Cereals — New Mexico

Station.

Place Variation with Cotton — North Carolina Station.
The Increase and Fixation of Desirable Properties in Plants —

Ohio Station.
Breeding Drought-resistant Corn ; Study of Qualities of Drought

Resistance — Oklahoma Station.
Breeding Sorghums, especially Kafir Corn, Milo Maize, and

Broom Corn, to secure more Drought-resistant Types —

Oklahoma Station.

Fundamental Study of Inheritance in Cotton — Texas Station.
Comparative Study of Durum, Poulard, and Bread Wheats —

Arizona Station.

The Forward Movement in Plant- Breeding 317

Study of Principles Underlying the Development of Disease

Resistance or Immunity in Farm Crops — North Dakota

Station.
Effects of Pollen from Barren Stalks of Corn — South Carolina

Station.
Breeding a Strain of Peaches resistant to Brown Rot — Alabama

Station.
Biological Analysis of Papago Sweet Corn for the Synthesis of

Desirable Characters — Arizona Station.
Principles relating to Transmission of Characters in the

Apple as affected by Selection and by Crossing — Illinois

Station.

Apple Breeding — Iowa Station.

Investigations upon Asparagus — Massachusetts Station.
Study of the Principles of Heredity underlying Disease and

Climatic Resistance in the Apple, Plum, and Strawberry —

Minnesota Station.

Heredity in Plants — Nebraska Station.
Studies of Heredity in Vegetables, especially Squashes and

Tomatoes — New Hampshire Station.
Carnation Breeding — New Hampshire Station.
Nature of the Inheritance and Correlation of Structural Char-
acters in Crosses — New Jersey Station.
Improvement of Mexican Chili by Breeding and Selection —

New Mexico Station.
Investigation of the Laws of Inheritance in Hybridization —

New York (Cornell) Station.
An Investigation of Mutation and Other Types of Variation

in Wild and Cultivated Plants, to determine their Value

in Plant Breeding — New York (Cornell) Station.
Influence of Environment in producing Variation of Value to

the Breeder — New York (Cornell) Station.
Study of Transmission of Characters in Hybrids of Rotundifolia

Grapes — North Carolina Station.

318 Plant-Breeding

A Study of the Fecundation of the Rotundifolia Grapes — South
Carolina Station.

Improvement of Hardy Wild Fruits of the Northwest by Breed-
ing and Crossing — South Dakota Station.

The Breeding of Apple and Pear Varieties for Resistance to
Blight — Tennessee Station.

Breeding Work with Blackberry — Texas Station.

Breeding Experiments with Apples — Virginia Station.

Mendelism of the Hybrids of Blackberries and Raspberries,
particularly with Reference to Leaf Structure and Habits
of Growth — Washington Station.

Pollination of the Apple — West Virginia Station.

Investigation of Mendel's Law as applied to Hybridizing the
White with the Black Varieties of Muscadine Grape —
Georgia Station.

Apple Breeding Investigations — Idaho Station.

Effects of Fertilizers on Cell Structure of Crops and their Rela-
tions to Mutations in Fruits, Vegetables, and Flowers —
Maryland Station.

Investigations on "Double Flower" and Sterility in Blackberries
and Dewberries — North Carolina Station.

Pollination of the Apple and Conditions affecting It — Oregon
Station.

In addition to the work of the experiment station men,
very much highly valuable work is under way by such
men as East at Harvard, Shull at Cold Spring Harbor,
Harper and Stout at the New York Botanical Garden,
Bradley Moore Davis at the University of Pennsylvania,
B. M. Duggar at the Missouri Botanical Garden, and many
others. This research is undertaken by well-trained
specialists who are producing the very highest type of
fundamental constructive results.

The Forward Movement in Plant- Breeding 319

320

Plant-Breeding

The Forward Movement in Plant-Breeding 321

Instruction in plant-breeding in the United States. — One
of the most, if not the most, significant advances that
plant-breeding has made in recent years is the increase in
the amount of instruction given in the agricultural colleges
and other agricultural schools.

Formerly, the only teaching of this subject was in
connection with a course of horticulture, probably,
and the breeding was likely to receive minor considera-
tion.

All of this has been changed. Strong courses are
given in this subject in all of the agricultural colleges.
Some go so far as to have separate departments. or divi-
sions in which the staff devotes all of its time to plant-
breeding instruction and investigations. It is estimated
that over two thousand students receive regular plant-
breeding instruction each year in this country. This is
bound to have tremendous influence upon practical
plant improvement on the farms of the country. Plant-
breeding holds a very prominent place in the instruction
given to short-term students, as it should, and in the
form of various extension enterprises.

Luther Burbank. — In addition to the large number of
plant-breeders who have some official connection with
the state experiment stations or the federal government,
there has always been a number of men who have
maintained private plant-breeding establishments. Chief
among these is Luther Burbank. He will always be given
a prominent place in American horticulture because of the
many and valuable varieties which he has added to it.

The practical results, however, that Mr. Burbank has
secured have been praised by the writers beyond reason.

322

Plant-Breeding

The Forward Movement in Plant-Breeding 323

His place abounds in interesting and surprising things,
just as would be expected of any man's place if conducted
under similar conditions (Figs. 101-103), and many of the
things will undoubtedly have great value. His work has
been so much written about that it is not necessary to
make any catalogue of the things that are under his hand.
It is not too much to hope that some of his productions,
as the plumcots, may be the starting-points of strong and
noble lines of evolution. Some of those that have been
much heralded are of doubtful economic value.

The value of Mr. Burbank's work lies above all merely
economic considerations. He is a master worker in mak-
ing plants to vary. Plants are plastic material in his
hands. He is demonstrating what can be done. He is
setting new ideals and novel problems. Heretofore,
gardeners and other horticulturists have grown plants
because they are useful or beautiful : Mr. Burbank grows
them because he can make them take on new forms.
This is a new kind of pleasure to be got from gardening,
a new and captivating purpose in plant growing. It is a
new reason for associating with plants.

APPENDIX A

GLOSSARY OF TECHNICAL PLANT-BREEDING
TERMS

Allelomorph. — • One of the pure unit-characters commonly
existing singly or in pairs in the germ-cells of mendelian hybrids,
and exhibited in varying proportion among the organisms them-
selves. Thus an allelomorphic pair of characters comprises the
opposed units, one of which comes from each parent in a hybrid.
For example, the roundness and wrinkledness found in two varie-
ties of peas is an allelomorphic pair.

Biometry. — The application of statistical methods to biological
problems.

Chromosome. — A term applied to certain minute bodies, in
the nuclei of the animal and vegetable cells which appear at
definite periods in the division of the cell ; they are constant in
number for each species of animal or plant, and are characterized
by the fact that they stain very deeply with certain dyes. The
chromosomes are supposed to be the bearers of heredity.

Dominant characters. — It often occurs, when two varieties
or species are crossed, that the characters of one appear in the
first generation hybrid to the exclusion of the other. These
are called dominant characters.

Duplex. — The state of inheriting a character that is present
in both parents.

Epistatic. — Used to describe a color factor which, in hybrid-
ization, covers up or hides other color factors in the first genera-
tion hybrid (opposed to hypostatic).

325

326 Plant-Breeding

Factor hypothesis. — An assumption that organisms may
contain various hereditary units which do not appear in their
body cells. This is especially applied to color units. Very
often these factors do not appear until the plant has been crossed
with another plant containing a complementary factor.

Fi. — A symbol introduced by Bateson, to designate the
first filial or hybrid generation.

F2. — A symbol for the second generation.

F3. — A symbol for the third hybrid generation. And so on.

Galton curve. — A curve, devised by Galton, when the values
for all the individuals are recorded consecutively in an ascending
series. The class values are plotted on the vertical axis.

Gamete. — A mature sex- or germ-cell , which will produce a
new individual upon uniting with another such cell of the op-
posite sex.

Genetics. — A study of the phenomena of variability and
heredity, or of the physiology of descent, as affecting individuals
or races of plants, animals, or human beings.

Genotype. — A type represented by individuals of the same
germinal constitution. The' nature of such a type can be
determined only by a breeding test, not by inspection.

Heterozygote. — An individual formed by the union of two
germ-cells of unlike constitution.

Homozygote. — An individual which is of a pure type in regard
to a certain character because both of its parents were of the
same gametic constitution.

Hybrids. — The offspring of crosses between individuals of
distinctly different natures.

Hypostatic. — Used to describe a color factor which is con-
cealed by higher color factors. (See Epistatic.)

Mutation. — A sudden variation, differing from its parents
in a distinct character or characters, and able to transmit its
new characters in full degree to its offspring.

Nulliplex. — A condition of an individual when it does not

Appendix A 327

possess a character because neither of its parents carried the
possibilities for such a character in their germ-cells.

Phenotype. — The visible type of a group as expressed by
external characteristics. Opposed to genotype. There may be
several genotypes in a phenotype.

Plateation. — (From the Latin platea, meaning place.) A
physiological variation caused by external influences such as
locality, climate, soil, and so forth; sometimes called place-
variation. It is what Darwin called " definite variation." This
word was coined to express in one word the third of the three
kinds of variation — fluctuation, mutation and plateation. (Here
first defined.— A. W. G.)

Quetelet curve. — A curve which shows the relative frequency
with which individuals of a given lot, or population, occur in
certain classes. Class values are plotted on the horizontal
line and frequencies on the vertical. The mode is the highest
point of such a curve and represents the dominating type of
the character studied.

Recessive characters. — (See Dominant characters.) The
characters which are entirely covered up the first generation
but reappear the second and subsequent generations.

Segregation. — The reappearance in definite ratios, in the
second hybrid generation, of the characters of two forms crossed ;
and the first hybrid generation (when this differs from the
dominant character).

Simplex. — The condition of an individual which has inherited
a character from only one parent.

Somatic. — Of, or pertaining to, the body as opposed to the
germ-cells.

Xenia. — The results of a cross-fertilization between different
varieties of plants due to a double fertilization ; found in such
plants as corn, peas, etc.

Zygote. — The result of the union of two gametes. (See
Gamete.)

APPENDIX B
PLANT-BREEDING BOOKS

FOLLOWING is a brief list of books containing material more or
less related to plant-breeding. This list is not intended to be
complete, but is designed to give the reader an idea of the more
important books on the subject. There are many books which
are not listed upon the general subject of botany, others upon
heredity and evolution in their broadest phases, and still others
upon animal breeding which will contain much material which
is related to the subject of plant improvement by breeding.

American Breeder's Association Reports. Washington, D.C.

1905-1912.
Bailey, L. H., Cyclopedia of American Agriculture. Vol. II,

Crops. Macmillan Co. 1907.
BAILEY, L. H., Standard Cyclopedia of Horticulture. 6 vols.

(Continuing) Macmillan Co. 1914.
BAILEY, L. H., Sketch of Evolution of Our Native Fruits. xiii +

472 pp., 125 figs. Macmillan Co: 3d edition. 1898.
BAILEY, L. H.,The Survival of the Unlike. 515 pp., illus. Mac-
millan Co. 1897.
BATESON, W., Mendel's Principles of Heredity, xiv + 396 pp.,

9 pis., and 35 figs. Cambridge. 1909.
BAUR, DR. ERWIN, Einfuhrung in die experimentelle Vererbungs-

lehre. 293 pp., 80 figs. Berlin. Gebriider Borntraeger.

1911.

328

Appendix B 329

CASTLE, W. E., COULTER, J. M., DAVENPORT, C. B., EAST,
E. M., TOWER, W. L., Heredity and Eugenics. 315 pp.,
98 figs. The Univ. of Chicago Press. 1912.

CASTLE, W. E., Heredity, in Relation to Evolution and Animal
Breeding. 184 pp. N. Y. and London. D. Appleton Co.
1911.

CRAMPTON, HENRY EDW., The Doctrine of Evolution; its Basis
and its Scope, ix +311 pp. N. Y. Columbia Univ.
Press. 1911.

DARBISHIRE, A. D., Breeding and the Mendelian Discovery.
xii + 282 pp. Cassell & Co. London. 4 colored pis.,
34 figs. 1911.

DAVENPORT, E., Domesticated Animals and Plants, xiv +
312 pp., 49 figs. Ginn & Co. 1910.

DAVENPORT, E., and RIETZ, H. L., Principles of Breeding (by
E. DAVENPORT). Appendix: Statistical Methods (by
H. L. RIETZ). A treatise on thremmatology, or the prin-
ciples and practices involved in the economic improvement
of domesticated animals and plants, xiii + 727 pp.
Ginn & Co. Boston. 1907.

Fifty Years of Darwinism, v + 274 pp., 5 pis., 1 fig. N. Y.
1909.

FRUWIRTH, C., et al., Die Zuchtung der Landwirtschaftlichen
Kulturpflanzen. Vols. 1-5. 1904-1912.

JOHANNSEN, W., Elements der Exakten Erblichkeitslehre. vi +
515 pp., 30 figs. Gustav Fischer. Jena. 1903.

JOHANNSEN, W., Ueber Erblichkeit in Populationen und in reinen
Linien. 68 pp., 8 figs. Gustav Fischer. Jena. 1903.

KELLOGG, V. L., Darwinism To-Day. 403 pp. Henry Holt
& Co. N. Y. 1907.

KNUTH, P., Handbook of Flower Pollination. Vol. I, xix -f-
382pp. Oxford. Porter. 1906.

LANG, H., Theorie und Praxis der Pflanzenzuchtung. viii +
169 pp., 47 figs. 1910.

330 Plant-Breeding

LOBNER, M., Leitfaden fur Gdrtnerische Pflanzenzuchtung.

vii + 160 pp., 10 figs. Jena. 1909.
LOCK, R. H., Recent Progress in the Study of Variation, Heredity,

and Evolution. 2d ed., xiv + 334 pp. Murray. London.

4 pis., 45 figs., and 5 portraits. 1909.

NEWMAN, L. H., Plant Breeding in Scandinavia. 193 pp.,
63 figs. The Canadian Seed Growers' Association. Ottawa.
1912.

PUNNETT, R. C., Mendelism. 192 pp. N. Y. Macmillan Co.

5 pis., 35 figs. 1911.

REID, G. A., The Laws of Heredity. 548 pp. Methuen & Co.

London. 1910.
RUMKER, VON K., Ueber Organisation der Pflanzenzuchtung.

56 pp. Berlin. 1909.
SEWARD, A. C. (Editor), Darwin and Modern Science, xvii +

595 pp., fig. and pi. 1909.
STEVENS, W. C., Plant Anatomy from the Standpoint of the

Development and Functions of the Tissues and Handbook of

Micro-technic. xii + 349pp. Blakiston's Son & Co. Phila-
delphia. 136 illus. 1907.
THOMSON, J. ARTHUR, Heredity, xvi + 605 pp., 49 figs. 2d

ed. 1912.
VERNON, H. M., Variation in Animals and Plants, pp. ix +

415, 30 figs. Henry Holt & Co. 1902.
VRIES, HUGO DE, Species and Varieties, their Origin by Mutation.

Edited by Daniel Trembly MacDougal. The Open Court

Pub. Co. Chicago. 1904.
VRIES, HUGO DE, Plant Breeding. Comments on the experiments

of Nilsson and Burbank. xiii + 360, figs. 114. 1907.
VRIES, HUGO DE, The Mutation Theory. Vol. I, "The Origin

of Species by Mutation." English translation by Prof.

J. B. Farmer and A. D. Darbishire. xvi + 582 pp. The

Open Court Publishing Co. Chicago. 4 pis. and 119 figs.

1909.

Appendix B 331

VRIES, HUGO DE, The Mutation Theory. Vol. II, " The Origin of
Varieties by Mutation." English translation by Prof.
J. B. Farmer and A. D. Darbishire. viii + 683 pp. Chicago.
The Open Court Publishing Co. 6 pis., 149 figs. 1911.

WALTER, HERBERT EUGENE, Genetics. An Introduction to the
Study of Heredity, xiv + 264 pp. The Macmillan Co.
N. Y. 72 figs, and Diagr. 1913.

WILSON, E. B., The Cell in Development and Inheritance, xxi +
483 pp., 194 figs. Macmillan Co. 1900.

Yearbooks U. S. Department of Agriculture. 1894r-1913.

Hybrid Conference Report (First International Conference).
London. Printed in Journal of the Royal Hort. Soc., April,
1900.

International Conference (Second) on Plant Breeding and Hybrid-
ization. Proceedings published as Memoir, Vol. I. Hort.
Soc. of New York. 1902.

International Conference (Third) on Genetics. London. Report
issued by Royal Hort. Soc. 1906.

International Conference (Fourth) on Genetics. Report pub-
lished in Paris, 1911, under Editorship of Ph. de Vilmorin.

APPENDIX C

LIST OF PERIODICALS CONTAINING BREEDING
LITERATURE

WE have attempted to include in this list such periodicals
as are most likely to contain breeding articles that may be of
interest to the general reader and the teacher and student of
Genetics. This list is not intended to be complete, but to in-
clude the principal publications.

ABBREVIATIONS : semi-a = semi-annual ; q = quarterly ; semi-q = semi-
quarterly ; m = monthly ; bi-m = bi-monthly ; semi-m = semi-monthly ;
w = weekly : semi-w = semi-weekly ; i = irregular.

American Naturalist. New York. m.

American Philosophical Society. Proceedings. Philadelphia.
3 nos.

Annales de la science agronomique. Paris, m.

Annales des science naturelles. Botanique. Paris.

Annals of Applied Biology. London.

Annals of Botany. London, q.

Archiv fur Rassen- und Gesellschafts-Biologie. Leipzig, bi-m.

Archives des sciences biologiques. St. Petersbourg.

Association internationale des botanistes. Progressus rei
botanicse. Jena, semi-a.

Biological Bulletin, m. Wood's Hole, Mass. Marine Bio-
logical Laboratory.

Biologisches Centralblatt. Erlangen, Leipzig, semi-m.

Biometrika. Cambridge, Eng. i.

332

Appendix C 333

Botanical Gazette. Chicago, m.
Botanische Zeitung. Abt. 1 and 2. Leipzig, w.
Botanisches Centralblatt. Jena. w.

Botanisches Centralblatt-Beihefte., Abt. 1 ; 3 nos. Anatomic,
Histologie und Physiologic der Pflanzen. Abt. 2 ; 3 nos.
Systematik, Pflanzengeographie, Augewandte, Botanik, etc.
Dresden.

Deutsche Botanische Gesellschaft. Berichte. Berlin, m.
Deutsche Landwirtschafts-Gesellschaft. Jahrbuch. Berlin, q.
Die Landwirtschaftlichen Versuch-Stationen. Berlin, semi-m.
Florists' Exchange. New York. w.

France — Institut national agronomique. Annales. Paris, i.
Gardeners' Chronicle. London, w.
Jahrbiicher fur Wissenschaftliche Botanik (Pringsheim's) ., 12

nos. Leipzig.

Journal of Agricultural Research, m.
Journal of Agricultural Science. Eng. q.
Journal de botanique. Paris, m.
Journal of Genetics. Cambridge, Eng. q.
Journal of Heredity. Washington, m.
La Cellule. Lierre. i.
La Science agronomique. Paris.
Linnean Society :

Journal, botany. London, m.

Transactions, botany. London, i.
(The) Mendel Journal. London.
New Phytologist. London. 10 nos.
Physiological Researches. Baltimore, i.
Plant World. Tucson, Ariz. m.
Popular Science Monthly. New York. m.
Quarterly Journal of Microscopical Science. London, q.
Revue, generate agronomique. Uccle lez-Bruxelles. m.
Revue gene*rale de botanique. Paris, m.
Royal Microscopical Society. Journal, bi-m.

334 Plant-Breeding

Royal Society of London, Philosophical transactions, i.

Science. New York. w.

Socie*te" de biologic, Comptes rendus. Paris, w.

Socie*te* botanique de France. Bulletin. Paris, m.

Socie*te" des agriculteurs de France. Bulletin. Paris, semi-m.

Socie*te" royale de botanique de Belgique. Bulletin. Bruxelles.

Torrey Botanical Club. Bulletin. New York. m.

United States Dept. of Agriculture, Office of Experiment

Stations. Experiment Station Record. Washington. 16

nos.

Zeitschrift fur Planzenziichtung. Wien.
Zentralblatt f iir Allgemeine und Experimented Biologic. Leipzig.

APPENDIX D

BIBLIOGRAPHY

FOLLOWING is a list of miscellaneous references to writings on
subjects related to plant-breeding. It is not intended to be
either complete or comprehensive. This bibliography begins
with the year 1905. References to earlier writings may be
found in the fourth edition of this work.

For reference to the literature of cross-fertilization, the reader
is directed to d'Arcy Thompson's list in Mueller's " Fertiliza-
tion of Flowers," and an extensive bibliography to the rapidly
growing literature upon the heredity of color can be found in a
technical bulletin by the junior writer of this book. This bulle-
tin will soon be published by the Agricultural Experiment
Station of Cornell University.

1905. BALLS, W. L., The Sexuality of Cotton. Khed. Agr.
Soc. Yearbook, 199-222.

1905. BIFFEN, R. H., Mendel's Laws of Inheritance and Wheat
Breeding. Jour. Agr. Sci., Cambridge, 1 : 4-48, 1 pi.

1905. BIFFEN, R. H., The Inheritance of Sterility in the Bar-
leys (Hordeum sativum, etc.). Jour. Agr. Sci. 1 : 250-257,'
Ifig.

1905. BUTLER, E. J., The Bearing of Mendelism on the Suscep-
tibility of Wheat to Rust. Jour. Agr. Sci. 1 : 361-363.

1905. CONKLIN, EDWIN G., The Mutation Theory from the Stand-
point of Cytology. Science, n.s. 21 : 525-529.

1905. EASTMAN, C. R., On the Spelling of " Clon." Science,
n.s. 22 : 206.

335

336 Plant-Breeding

1905. HURST, C. C., Notes on the " Proceedings of the Inter-
national Conference on Plant Breeding and Hybridisation,

1902." Roy. Hort. Soc. Jour. 29 : 417-433.
1905. JONES, L. R., Disease Resistance of Potatoes. U. S.

Dept. Agr. Bur. Plant Ind. Bull. 87 : (39 pp.).
1905. JONES, L. R., Concerning Disease Resistance of Potatoes.

Vermont Agr. Exp. Sta. 18 : 264-267.
1905. KLINCK, L. S., Corn Breeding in the Corn Belt. Can.

Seed-Grow. Assoc. Rep. 2 : 56-61.
1905. PEARL, RAYMOND, Investigation by Statistical Methods of

Correlation in Variation. Carnegie Inst. (Wash., D.C.),

Yearbook (1905) (No. 4) : 285-286.
1905. PEARL, RAYMOND, Note on Variation in the Ray Flowers

of Rudbeckia. Am. Nat. 39 : 87-88. 1 fig.
1905. PETRUNKEVITCH, ALEXANDER, Natural and Artificial

Parthenogenesis. Am. Nat. 39 : 65-76. Bibliog.
1905. POLLARD, CHARLES Louis, On the Spelling of " Clon."

Science, n.s. 22 : 87-88.
1905. POLLARD, CHARLES Louis, " Clon " versus " Clone."

Science, n.s. 22 : 463.
1905. SHAMEL, A. D., The Effect of Inbreeding in Plants. U. S.

Dept. Agr. Yearbook, 377-392. 3 pis., 1 fig.
1905. SHAMEL, A. D., Tobacco Breeding Experiments in Conn.

Conn. (State) Agr. Exp. Sta. Ann. Rep. 331-343.
1905. STARNES, HUGH N., Japan and Hybrid Plums. Georgia

Agr. Exp. Sta. 68 (see pp. 1-40).
1905. VRIES, H. DE, Dauer der Mutationsperiode bei (Enothera

Lamarckiana. Deutsch. Bot. Gesell. Ber. 23 : 382-387.
1905. VRIES, H. DE, The Mutation Theory. Gard. Chron.

3d ser. 37 : 321-322.
1905. WEBBER, HERBERT J., The Science of Plant Breeding.

Can. Seed-Grow. Assoc. Rep. 2 : 79-92. PI. II., fig. 1 & 2.
1905. WEBBER, HERBERT J., Pedigree or Grade Breeding . Can.

Seed-Grow. Assoc. Rep. 2 : 61-70. PI., Photo., Fig.

Appendix D 337

1905. WIESNER, J., Untersuchungen uber den Lichtgenuss der
Pflanzen im Yellowstone Gebiete und in anderen Gegenden
Nordamerikas. Photometrische Untersuchungen auf pflan-
zenphysiologischem Gebiete (V. Abhandlung). Kais. kon.
Akad. d. Wiss. in Wien, mathem. naturw. Klasse, Sit-
zungsber. 114: (Part 1). Rev. in Am. Nat. 40:600-603.

1905. WILLIAMS, C. G., Pedigreed Seed Corn. Ohio Agr. Exp.
Sta., Circ. 42: 1-11.

1906. ANDREWS, F. M., Some Monstrosities in Trillium. Ind.
Acad. Sci. Proc. 187-188.

1906. BATESON, W., and SAUNDERS, Miss E. R., and PUN-
NETT, R. C., Inheritance in Sweet Peas and Stocks. Roy.
Hort. Soc. (London) Proc. B. 77 : 236-238.

1906. BATESON, W., Coloured Tendrils of Sweet Peas. Gard.
Chron. 39 : 333.

1906. BEAL; W. J., Improving Wild Potatoes by Selection. Soc.
Prom. Agr. Sci. Proc. 27 : 75.

1906. BIFFEN, R. H., Experiments on the Hybridization of
Barley. Phil. Soc. Proc. (Cambridge), 13:304-308.

1906. BLANCHARD, W. H., A New Dwarf Blackberry. Torreya
6 : 235-237.

1906. BUCHANAN, J., Some Effects in Varieties of Cereal Crops
arising from Different Conditions of Growth. Can. Seed-
Grow. Assoc. Rep. 3 : 74-77.

1906. CARD, F. W., BLAKE, M. A., and BARNES, H. L., Rasp-
berry Score Card. Rhode Island Agr. Exp. Sta. 168-169.

1906. CARD, FRED W., Apple Breeding. Rhode Island Agr.
Exp. Sta. 20 : 250-252.

1906. CARD, FRED W., Corn Selection. Rhode Island Agr.
Exp. Sta. Ann. Rept. 20 : 216-220.

1906. CASTLE, W. E., Inbreeding, Crossbreeding and Sterility
in Drosophila. Science, n.s. 23 : 153.

1906. CROCKER, W., Role of Seed Coats in Delayed Germination.
Bot. Gaz. 42:265-291. Fig.

338 Plant-Breeding

1906. DUVEL, J. W. T., The Germination of Seed Corn. U. S.
Dept. Agr. Farmers' Bull. 253 : (16 pp.), 4 figs. (Includ-
ing : Value of a germination test. Average yield of corn
to the acre. Testing individual ears. Selecting seed ears.
Numbering the ears. The germination box. Results of
tests.)

1906. GAGER, C. S., De Vries and His Critics. Science, n.s.
24 : 81-89. Bibliog. in notes.

1906. GRAENICHER, S., Some Notes on the Pollination of Flowers.
Wis. Nat. Hist. Soc. Bull. 4 : 12-21.

1906. GRIFFON, E., Le greffage des Solanees. Acad. Sci. Compt.
Rend. 143: 1249-1251.

1906. HAACKE, WILHELM, Die Gesetze der Rassenmischung
und die Konstitution des Keimplasmes. Arch. f. Entwick'-
mech. d. Org. 21 : 1-93. 104 tab.

1906. HALSTED, B. D., Breeding Sweet Corn — Cooperative
Tests. New Jersey Agr. Exp. Sta. Bull. 192 : 1-30. Fig.

1906. HECKEL, E., Variation in the Potato Tuber. Gard.
Chron. 3d ser. 39 : 88.

1906. HENSLOW, G., Evolution and Adaptation. Roy. Hort.
Soc. Jour. n.s. 31 : 159-163.

1906. HENSLOW, G., The True Meaning of "Natural Selec-
tion " and the "Survival of the Fittest " in Nature. Roy.
Hort. Soc. Jour. n.s. 31 : 90-96.

1906. HENSLOW, G., Species and Varieties; their Origin by
Mutation. Roy. Hort. Soc. Jour. n.s. 31 : 164-168.

1906. HESKETH, R. T., Apple Grafted on Hawthorn. Gard.
Chron. 3d ser. 39 : 347.

1906. HURST, C. C., Mendelian Laws of Inheritance. Gard.
Chron. 3d ser. 39 : 187.

1906. LE CLERC, J. A., The Effect of Climatic Conditions on the
Composition of Durum Wheat. U. S. Dept. Agr. Year-
book: 199-^212, 2 pis. Same. Yearbook Separate, 417:
199-212, 2 pis.

Appendix D 339

1906. LOCK, R. H., Plant Breeding in the Tropics. 777, Ex-
periments with Maize. Roy. Bot. Gard. Ann. 3:2: 95-
184.

1906. MACOUN, W. T., The Improvement of the Potato. Can.
Seed-Grow. Assoc. Rep. 3 : 77-84. Photo., Fig.

1906. MORGAN, T. H., Are the Germ-cells of Mendelian Hybrids
"Pure " f Biol. Centralbl. 26 : 289-296.

1906. MUNSON, W. M., Plant-breeding in its Relation to Ameri-
can Pomology. Maine Agr. Exp. Sta. Bull. 132 : 149-176.

1906. ORTMANN, A. E., The Mutation Theory Again. Science,
n.s. 24 : 314-317. Bibliog. in notes.

1906. OSTERHOUT, W. J. V., Experiments with Plants, x +
493pp. The Macmillan Co., N. Y. 252 figs. Rev. in Am.
Nat. 40 : 146-148.

1906. PEARL, RAYMOND, Variation in the Number of Seeds of
the Lotus. Am. Nat. 40 : 757-768. 4 figs. 5 tab.

1906. RAUNKIAER, C., Transmission par heredite dans les
especes heteromorphes. Vid. Selsk. Overs. 31-39.

1906. RIVIERE, G., and BAILHACHE, G., Influence du porte-
greffe sur le greffon. Acad. Sci. Compt. Rend. 142 : 845-
847.

1906. ROSENBERG, 0., Embryobildung in der Gattung Hieracium.
Deutsch. Bot. Gesell. Ber. 24: 157-161, 1 pi.

190|6. SAAME, 0., Kernverschnelzung bei der karyokinetischen
Kernteilung im protoplasmatischen Wandeelag des Embryo-
sacks von Fritillaria imperialis. Deutsch. Bot. Gesell.
Ber. 24:300-303, 1 pi.

1906. SCHARF, E., Keimkraft-Apparat. Deutsch. landw.
Presse 33 : 507-508, 514r-516.

1906. SCHULTE, J. I., Corn Breeding Work at the Experiment
Stations. U. S. Dept. Agr. Yearbook, 279-294.

1906. SOLMS(-LAUBACH), H. GRAF zu, Cruciferenstudien.
IV. Die Varianten der Embroyolage. Bot. Zeitung, 64:
1 : 1&-43, 1 pi.

340 Plant-Breeding

1906. SPERLING, J., Korrelation zwischen Kornfarbe und Aehren-

formen beim Roggen. Fuhlings landw. Zeitung, 55 : 93-99.
1906. STUART, W., Disease Resistance of Potatoes. Vermont

Agr. Exp. Sta. Bull. 122: (see pp. 107-136). Abstr. in

Exp. Sta. Rec. 17 : 1078.
1906. VAN DEN HEEDE, A., Variation chez les vegetaux. Soc.

Nantaise d'hort. Ann. 79 : 97-103.
1906. VRIES, H. DE, Aelters und neuere Selektionsmethode.

Biol. Centralbl. 26 : 385-395.
1906. VRIES, H. DE, Die Svalofer Methode zur Veredelung land-

wirtschaftlicher Kulturgewachse und ihre Bedeutung fur

die Selektions-Theorie. Arch. Rassenbiol. 3 : 325-358.
1906. VRIES, H. DE, Species and Varieties; their Origin by

Mutation. Second edition, xviii + 847 pp.
1906. WEBBER, H. J., New Citrus and Pineapple Productions

of the Department of Agriculture. U. S. Dept. Agr. Year-
book, 329-346. 8 pis., 1 fig. Same. Yearbook Separate,

427:329-346. 8 pis., 1 fig.
1906. WEISMANN, A., The Evolution Theory. Translated with

the author's cooperation by J. A. & Margaret R. Thomson.

2 vols. xvi +416 pp. and 405 pp. E. Arnold. London.

Rev. in Am. Nat. 40 : 375-377.
1906. WIANCKO, A. T., Corn Improvement. Indiana (Purdue

Univ.) Agr. Exp. Sta. Bull. 110 : 79-120. 14 figs.
1906. WILBRINK, G., Deuxieme rapport sur les experiences de

selection faites avec I'indigotier de Natal. (In Dutch.)

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1906. WILSON, E. B., Mendelian Inheritance and the Purity

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1909. CHAMBLISE, CHARLES E., A Note on Rice Breeding.

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1909. COOK, 0. F., The Superiority of Line Breeding over Narrow

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356 Plant-Breeding

1909. DE LOACH, R. J. H., The Problem of Fixation in Cotton
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1909. EAST, EDWARD M., The Distinction between Development
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1909. EMERSON, R. A., Factors for Mottling in Beans. A. B. A.
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1909. EMERSON, R. A., Inheritance of Color in the Seeds of the
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1909. FORBES, F. E., A New Hybrid Violet. Rhodora, 11:
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1909. GARNER, W. W., Breeding Tobacco for High and Low
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1909. GATES, R. R., The Behavior of the Chromosomes in (Eno-
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1909. GATES, R. R., The Stature and Chromosomes of (Enothera

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358 Plant-Breeding

1909. HECKEL, M., Fixation de la mutation gemmaire culturale
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1909. McALPiNE, D., and DE CASTELLA, F., Bud-variation in
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1909. MCCALLUM, W. B., The Reciprocal Influence of Scion
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1909. NEWMAN, L. H., Certain Biological Principles and their
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360 Plant-Breeding

1909. PATON, J. AIRMAN, Notes on Some Hybrid Tuberous
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1909. RITTER, W. E., The Hypothesis of "Presence and Ab~

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1909. RUSSEL, E. S., The Transmission of Acquired Characters.

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1909. WEBBER, H. J., Methods of Breeding and Improving the
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364 Plant-Breeding

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terre cultivee. Acad. Sci. Paris, Compt. Rend. 150 : 47-

50.

1910. BESSEY, E. A., Air Drainage as Affecting the Acclimatiza-
tion of Plants. N. Y. Hort. Soc. Mem. 2: 25-28.
1910. BLANCHARD, HENRY F., Improvement of the Wheat Crop

in California. U. S. Dept. Agr. Bur. Plant Ind. Bull. 178 :

(37 pp.), 10 figs. '
1910. BORDAGE, E., A propos de I'heredite des caracteres ac-

quis. Bull. Scient. France et Belgique 44: (Heft 1).
1910. BORNET, E., and GARD, M., Recherches sur les hybrides

artificiels de Cistes obtenus par M. Ed. Bornet. I. Notes

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relles (Botanique) 12:71-116.
1910. BRAND, CHARLES J., The Utilization of Crop Plants in

Paper Making. U. S. Dept. Agr. Yearbook, 329-340.

Same. Yearbook Separate, 541 : 329-340.
1910. BRUCE, A. B., The Mendelian Theory of Heredity and the

Augmentation of Vigor. Science, n.s. 32:627-628.
1910. BRUCE, A. B., Self-fertilization and Loss of Vigour. Na-
ture. March 3.
1910. BUDER, J., Pfropfbastarde und Chimaeren. Zeitsch. f.

allg. Physiol. 11: 15-31.
1910. BUDER, J., Studien an Laburnum Adami. Deutsch. Bot.

Gesell. Ber. 28: 188-192.
1910. BURTT-DAVY, J., A Note on the Correlation of Characters

in Maize Breeding. Transvaal Agr. Jour. 8 : 453-455.
1910. BURTT-DAVY, J., An Experiment in Breeding a New Type

of Maize. Transvaal Agr. Jour. 8 : 450-453.
1910. CHEVALIER, J., Influence de la culture sur la teneur en

366 Plant-Breeding

alcaloides de quelques Solanees. Acad. Sci. Paris Compt.
Rend. 150:344^347.

1910. CLARK, CHAS. F., Variation and Correlation in Timothy.
Cornell Univ. Agr. Exp. Sta. Bull. 279 : 421-469, 40 figs.

1910. CLEMENTS, F. E., The Real Factors in Acclimatization.
N. Y. Hort. Soc. Mem. 2 : 37^0.

1910. CLOTHIER, GEO. L., Breeding to Improve Physical Quali-
ties of Timber. Am. Breed. Mag. 1 : 261-263.

1910. COCKERELL, T. D. A., A New Variety of the Sunflower.
Science, n.s. 32 : 384.

1910. COIT, J. E., The Relation of Asexual or Bud Mutation to
the Decadence of California Citrus or Deads. Fruit Growers'
Cons. (Cal.) Proc. 37 : 31-39.

1910. COLLINS, G. N., Increased Fields of Corn from Hybrid
Seed. U. S. Dept. Agr. Yearbook, 319-328. Same.
Yearbook Separate, 540 : 319-328.

1910. COLLINS, G. N., The Value of First-Generation Hybrids
in Corn. U. S. Dept. Agr. Bur. Plant Ind. Bull. 191:
(45 pp.).

1910. COTTE,' J., and COTTE, C., Sur I'indigenat du ble en
Palestine. Soc. Bot. France Bull. 56 : 538-540.

1910. COUPIN, H., Sur la vegetation de quelques moisissures
dans 1'huile. Acad. Sci. Paris Compt. Rend. 150:1192-
1193.

1910. CROSBY, DICK J., and HOWE, F. W., School Lessons on
Corn. U. S. Dept. Agr. Farmers' Bull. 409 : (29 pp.), 12 figs.
(This bulletin contains outlines for class studies and exer-
cises on the growth and structure of the corn plant, selection
and testing of seed corn, and the cultivation and breeding of
corn, with list of publications on the subject.)

1910. CROSBY, DICK J., School Exercises in Plant Production.
U. S. Dept. Agr. Farmers' Bull. 408: (48 pp.), 39 figs.
(This bulletin describes the material needed for laboratory
exercises in plant production, and contains outlines of

Appendix D 367

lessons in the structure and growth of plants, methods of

propagation, seed testing, etc., and a list of publications

on agriculture, of special interest to teachers.)
1910. DACHNOWSKI, A., Physiologically Arid Habitats and

Drought Resistance in Plants. Bot. Gaz. 49 : 325-339.
1910. DERR, H. B., A New Awnless Barley. Science, n.s.

32 : 473-474.
1910. DILLMAN, ARTHUR C., Breeding Drought-Resistant Forage

Plants for the Great Plains Area. U. S. Dept. Agr. Bur.

Plant Ind. Bull. 196: (40 pp. ), 4 pis.
1910. Dow, GEO., The Status of the "False " Wild Oats. Can.

Seed-Grow. Assoc. Rep. 6: 105-107.
1910. DRZEWINA, A., La transmission des caracteres heredi-

taires chez les hybrides. Revue des Idees, 7 : 372-376.
1910. EAST, EDWARD M., A Mendelian Interpretation of Varia-
tion that is apparently Continuous. Am. Nat. 44 : 65-82.

7 tab. Bibliog. in notes.
1910. EAST, EDWARD M., Inheritance in Potatoes. Am. Nat.

44 : 424-430. Bibliog. in notes.
1910. EAST, E. M., Notes on an Experiment concerning the

Nature of Unit Characters. Science; n.s. 32 : 93-95.
1910. EAST, E. M., The Role of Hybridization in Plant Breeding.

Pop. Sci. Mo. 77: 342-355, figs. 1-11.
1910. EAST, E. M., The Transmission of Variations in the

Potato in Asexual Reproduction. Conn. Agr. Exp. Sta.

Rep. 119-160, 5 pis. Rev. in Zeitsch. f. indukt. Abst-

u. Vererb. 4:375-376.
1910. EMERSON, R. A., The Inheritance of Sizes and Shapes in

Plants. Amer. Nat. 44 : 739-746. Rev. in Zeitsch. f.

indukt. Abst.- u. Vererb. 5: 193.
1910. FLETCHER, S. W., Varieties of Fruit Originated in Mich.

Mich. Agr. Exp. Sta. Spec. Bull. 44.
1910. FROST, H. B., Variation as related to the Temperature

Environment. A. B. A. Rep. 6 : 384^396.

368 Plant-Breeding

1910. FRYE, T. C., Height and Dominance of the Douglas Fir.
Forest Quart. 8 : 465-470.

1910. GASSNER, G., Uber Solanum Commersonii und S. "Com-
mersonii violet " in Uruguay. Landw-. Jahrb. 1011-1020.
Ipl.

1910. GATES, R. R., Abnormalities in (Enothera. Missouri
Bot. Gard. Ann. Rep. 21 : 175-184, pis. 29-31.

1910. GATES, R. R., The Earliest Description of (Enothera
Lamarckiana. Science, n.s. 31 : 425-426.

1910. GATES, R. R., The Material Basis of Mendelian Phenom-
ena. Am. Nat. 44 : 203-213. Bibliog., 1 p.

1910. GAUSS, ROBERT, Acclimatization in Breeding Drought-
resistant Cereals. Am. Breed. Mag. 1 : 209-217.

1910. GRIFFON, E., Sur la variation dans le .greffage et I'hybri-
dation asexuelle. Acad. Sci., Paris, Comp. Rend. 150:
629-632.

1910. GRIFFON, E., Variations avec ou sans greffage chez les
Solanees et les Composees. Spc. Bot. de France Bull. 57 :
517-535, 2 pi.

1910. GROFF, H. H., Hybridizing the Gladiolus. Are its Lessons
Possible of General Application? Can. Seed-Grow. Assoc.
Rep. 6 : 52-58.

1910. GUTHRIE, C. C., On Graft Hybrids. A. B. A. Rep. 6 :
356-373.

1910. HAECKER, VALENTIN, Die Radiolarien in der Variations-
und Vererbungslehre. Zeitsch. f. indukt. Abs.- u. Vererb.
2 : 1-17. Rev. in Arch, f . Entwick'mech. d. Org. 29 : 573.

1910. HANSEN, N. E., 7s Acclimatization an Impossibility?
N. Y. Hort. Soc. Mem. 2 : 69-74.

1910. HARPER, J. N., Experiments with Hybrid Cottons. South
Carolina Agr. Exp. Sta. Bull. 148: (17 pp.).

1910. HARTLEY, C. P., Seed Corn. U. S. Dept. Agr. Farmers'
Bull. 415: (12 pp.), 3 figs. (This bulletin contains direc-
tions for the growing^ selection, and care of seed corn,

Appendix D 369

the destruction of weevils or grain moths, the testing,
grading, and shelling of the corn to be planted, with sug-
gestions to the corn grower as to the importance and re-
quirements of good seed, and adaptability of any variety
to his locality.)

1910. HENRY, A., On Elm Seedlings Showing Mendelian Results.
Linn. Soc. Bot. Jour. 39 : 290-300.

1910. HENSLOW, G., The Origin and History of our Garden
Vegetables and their Dietetic Values — II. Royal Hort. Soc.
Jour. 36 : 345-357, figs. 120-125. Roots and tubers.

1910. HENSLOW, G., The Origin and History of our Garden
Vegetables. Roy. Hort. Soc. Jour. 36: 115-127.

1910. HERRE, A. C., Suggestions as to the Origin of California's
Lichen Flora. Plant World, 13 : 215^220.

1910. HEUER, W., Pfropfbastarde. Gartenflora, 59 : 434-438.

1910. HIMMELBAUR, W., Der Gegenwdrtige Stand der Pfropfhy-
bridenfrage. Natw. Ver. Univ. Wien Mitt. 8 : 105-127.

1910. HINDLE, EDWARD, A Cytological Study of Artificial Par-
thenogenesis in Strongylocentrotus Purpuratus. Arch. f.
Entwick'mech. d. Org. 31 : 145-163, 1 pi. Bibliog. 1£ pp.

1910. HOWARD, ALBERT, and HOWARD, GABRIELLE, Wheat
in India. Its Production, Varieties, and Improvement.
Calcutta. 288 pp., 7 maps, 4 figs., 7 pis. Rev. in Zeitsch. f.
indukt. Abst.- u. Vererb. 4 : 153-154.

1910. HUMPHREYS, E. W., Variation among Non-lobed Sassafras
Leaves. Torreya, 10 : 101-108, figs. 1-8.

1910. KURD, WM. D., Corn Selection for Seed and for Show.
Mass. State Board of Agr. Ann. Rep. 58.

1910. HURST, C. C., Mendel's Law of Heredity and its Applica-
tion to Horticulture. Roy. Hort. Soc. Jour. 36 : 22-52.

1910. IKENO, J., Sind Alle Arten der Gattung Taraxacum
Parthenogenetisch? Deutsch. Bot. Gesell. Ber. 28:394-
397.

1910. JAVILLIER, M., Sur la migration des alcaloides dans les
2s

370 Plant-Breeding

greffes de Solanees sur Solonees. Inst. Pasteur Annales,

24 : 569-576.
1910. KEARNEY, THOMAS H., Breeding New Types of Egyptian

Cotton. U. S. Dept. Agr. Bur. Plant Ind. Bull. 200 : (39pp.)

4 pi.
1910. KEEBLE, FREDERICK, and (Miss) PELLEW, C., The Mode

of Inheritance of Stature and of Time of Flowering in Peas.

Pisum sativum. Jour, of Gen. 1 : 47-56.
1910. KEEBLE, FREDERICK, and (Miss) PELLEW, C., White

Flowered Varieties of Primula sinensis. Jour, of Gen.

1 : 1-5.

1910. KEEBLE, F., PELLEW, C., and JONES, W. N., The In-
heritance of Peloria and Flower Colour in Foxgloves (Digi-
talis purpurea). New Phytolog. 9: 68-77, 1 fig.
1910. KROLL, H. G., Uber Polygamie bei Polygonatum officinale.

Bot. Ver. Brandenb. Verh. 52: 98-101.
1910. LECAILLON, A., La parthenogenese naturelle rudimen-

taire. Bull. Scientif . de France et Belgique, 7th ser. 44 :

235-272.
1910. LOVE, HARRY H., Are Fluctuations Inherited? Am. Nat.

44 : 412-423, 9 figs. & 4 tab. Bibliog. in notes.
1910. MACDOUGAL, D. T., VAIL, A. M., and SHULL, G. H.,

Mutations, Variations, and Relationships of the (Enotheras.

Carnegie Inst. Wash. Publ. 81 : (92 pp.) 1907. Rev. in

Zeitsch. f. indukt. Abst.- u. Vererb. 3 : 226-228.
1910. MAIGRE, E. F., L'heredite Mendelienne. Rev. des

IdSes, 234-242.
1910. MOOREHOUSE, L. A., Improvements of Bermuda Grass.

Am. Breed. Mag. 1 : 95-98, fig.
1910. MORGAN, T. H., Chromosomes and Heredity. Am. Nat.

44 : 449-496, 3 tab. Illus.
1910. NAKANO, H., Variation and Correlation in Rays and Disk

of Aster fastigiatus. Bot. Gaz. 49 : 371-378, figs. 1-4.
1910. NASH, G. V., Observations on Hardiness of Plants culti-

Appendix D 371

vated at the New York Botanical, Garden. N. Y. Hort.

Soc. Mem. 2: 130-143.
1910. NEMEC, B., Das Problem der Befruchtungavorgdnge.

526 pp. Borntraeger, Berlin. 5 pis. & 119 figs.
1910. NEWMAN, L. H., The Correlation of Characters in Plants

and its Economic Importance to the Plant Breeders. Ottawa

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1910. NIENBURG, W., Die Jungsten Ergebnisse der Pfropf-

bastardforschung. Gartenflora, 59 : 479-495.
1910. NILSSON-EHLE, H., Kreuzungsuntersuchungen an Hafer

und Weizen. Lunds Universitats Areskirft. N. F. Afd.

2. 5 : 1-122. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb.

3:290-291.
1910. NILSSON-EHLE, H., Svalofs Pudelhvete. Sveriges Utsades-

for. Tidskr. 20 : 69-87.
1910. OLIVER, GEORGE W., New Methods of Plant Breeding.

Fig. Am. Breed. Mag. 1 : 21-30.
1910. ORCHARD, HAROLD, Potato Breeding in Manitoba and

Some Results Obtained. Can. Seed-Grow. Assoc. Rep. 6 :

103-104.
1910. OSTENFELD, C. H., Further Studies on Apogamy and

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1910. PATON, ALKMAN, Notes on Some Hybrid Tuberous Solanums.

Roy. Hort. Soc. Jour. 36 : 127-133.
1910. PEARL, RAYMOND, and SURFACE, F. M., Experiments in

Breeding Sweet Corn. Maine Agr. Exp. Sta. Bull. 183 :

(66pp.).
1910. PEARSON, KARL, Darwinism, Biometry and Some Recent

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1910. PEARSON, KARL, On a New Method of Determining Cor-
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Other by Multiple Categories. Biometrika, 7 : 248-257, Tab,

372 Plant-Breeding

1910. PLANCHON, Mutation gemmaire du Solanwn Commersonii.

Soc. Nation. d'Agr. Bull. 70 : 373-375.
1910. REHDER, A., A New Hybrid Cornus (Cornus rugosa X

stolonifera) . Rhodora, 12 : 121-124. C. Slavinii Rehder.
1910. RICHTER, 0., Pfropfungen, Pfropfbastarde und Pflanzen-

chimaeren. Lotos, 58: 1-22.
1910. RIETZ, H. L., Correlation in Corn. 111. Agr. Exp. Sta.

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1910. SALAMAN, R. N ., The Inheritance of Colour and Other Char-
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in Zeitsch. f. indukt. Abst.- u. Vererb. 5 : 192-193.
1910. SAUNDERS, E. R., Studies in the Inheritance of Double-
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1910. SHEPPERD, J. H., Report of Committee on Breeding Fiber

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1910. SHOEMAKER, D. N., Report of Committee on Breeding

Cotton. Am. Breed. Mag. 1 : 293-294.
1910. SHULL, GEORGE HARRISON, Color Inheritance in Lychnis

dioica L. Am. Nat. 44 : 83-91, 3 tab. Bibliog.
1910. SHULL, A. FRANKLIN, The Artificial Production of the

Parthenogenetic and Sexual Phases of the Life Cycle of Hyda-

tina senta. Am. Nat. 44 : 146-150, 5 tab.
1910. SHULL, GEORGE HARRISON, Hybridization Methods in

Corn Breeding. Am. Breed. Mag. 1 : 98-107. Bibliog.
1910. SMITH, LOUIE H., Increasing Protein and Fat in' Corn.

Am. Breed. Mag. 1 : 15-21. Tab.
1910. SMITH, J. RUSSELL, Breeding and Use of Tree Crops.

Am. Breed. Mag. 1 : 86-91.
1910. SPILLMAN, W. J., A Theory of Mendelian Phenomena.

Am. Breed. Mag. 1 : 113-125. Diagr.
1910. SPILLMAN, W. J., Effect of Recent Discoveries on the Art

of Breeding. Am. Breed. Mag. 1 : 69-70.

Appendix D 373

1910. SPILLMAN, W. J., Mendelian Phenomena without de

Vriesian Theory. Am. Nat. 44 : 214-228, 4 tab. Bibliog.

in notes.
1910. SPILLMAN, W. J. (Reviewer), Heredity. (Rev.) Am.

Nat. 44 : 504-512. Bibliog. in notes.
1910. SPILLMAN, W. J., The Nature of "Unit" Characters.

The American Naturalist, 43 : 243-248. Rev. in Zeitsch.

f. indukt. Abst.- u. Vererb. 3 : 110.
1910. STEVENS, R. L., and HALL, J. G., Variation of Fungi

Due to Environment. Bot. Gaz. 48:1-30, fig. 37. Rev.

in Zeitsch. f. indukt. Abst.- u. Vererb. 3 : 343-344.
1910. SUDWORTH, GEORGE S., Report of Committee on Breeding

Nut and Forest Trees. Am. Breed. Mag. 1 : 185-193. Tab.
1910. TAYLOR, GEORGE M., The Cross Fertilization of the

Potato. Gard. Chron. 3d ser. 48 : 279.
1910. TISCHLER, G., Untersuchungen uber die Entwicklung des

Bananen-Pollens. Arch. f. Zellforschung, 5 : 622-670, 2' pis.

& 4 figs.
1910. TRABUT, L., Sur une mutation inerme du Cynana Cardun-

culus. Soc. Bot. de France Bull. 57 : 350-354, 2 pis.
1910. TRACY, W. W., Breeding and Raising Garden Seeds.

Mass. State Board cf Agr. Ann. Rep. 58.
1910. TRACY, W. W., Report of Committee on Breeding Vege-
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1910. TUTTLE, A. H., Mitosis in (Edogonium. Jour. Fxp.

Zool. 9: 143-157, 18 figs.
1910. VILMORIN, PHILIPPE DE, Recherches sur Vheredite men-

delienne. Acad. Sci., Paris, Compt. Rend. 151 : 548-551.
1910. VRIES, H. DE, The Production of Horticultural Varieties.

Roy. Hort. Soc. Jour. 35 : 321-326.
1910. WALDRON, L. R., A Suggestion regarding Heavy and

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1910. WALDRON, L. R., Heredity in Populations and in Pure

Lines. Plant World, 13 : 1-12, figs. 1-5.

374 Plant-Breeding

1910. WESTGATE, J. M., Variegated Alfalfa. U. S. Dept. Agr.

Bur. Plant Ind. Bull. 169 : (63 pp.), 9 pis. & 5 figs.
1910. WHEELER, SEAGER, Plant Breeding of the Farm. Can.

Seed-Grow. Assoc. Rep. 6: 107-109.

1910. WHELDALE, M., Plant Oxydases and the Chemical Inter-
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3 : 457-473. Bibliog. in notes.
1910. WILSON, E. B., Studies on Chromosomes. Jour. Exp.

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1910. WINKLER, H., Uber das Wesender Pfropfbastarde. (Vor-

laufige Mitteilung.) Deutsch. Bot. Gesell. Ber. 28 : 116-118.
1910. WINKLER, H., Uber die Nachkommenschaft der Solanus-

Pfropfbastarde und die Chromosomes zahlen ihre Keimzellen.

Zeitschr. fur Botanik. 2 : 1-33. Rev. in Zeitsch. f. indukt.

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1910. WINKLER, HANS, Weiters Mitteilungen uber Pfropfbastarde.

Zschr. f. Botanik. 1 : 315-345, 1 pi., 4 figs. Rev. in Zeitsch.

f. indukt. Abst.- u. Vererb. 3: 111-113.
1910. WINKLER, HANS, Zur Kritik der Ansichten von der Ent-

stegung der Angiospermenbluten. Schles. Ges. Vaterl.

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1910. WINSLOW, E. J., A New Hybrid Fern. Am. Fern Jour.

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1910. WITTE, H., Vallvdxtforddlingen pa Svalof, dess nodvdndighet

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1910. ZAVITZ, C. A., Heredity in Plants and its Bearing on Agri-
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Meeting Rep. 49-52.

1910. ZEIJLSTRA, H. H., On the Cause of Dimorphism in (Eno-
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1911. AGEE, HAMILTON P., Propagation of Seedlings of Sugar
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Appendix D 375

1911. ATKINSON, ALFRED, Grain Investigations with Different
Varieties of Wheat, Oats, and Barley. (Types and variety
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1911. BABCOCK, ERNEST B., Walnut-Oak Hybrid Experiments.
A. B. A. Rep. 6: 138-141.

1911. BALLS, W. LAWRENCE, The Inheritance of Measurable
Characters in Hybrids between Reputed Species of Cotton.
IV Inter. Conf. Genetique, Paris, 429-440, fig. 9.

1911. ~BALix,W.,CytologischeStudeinanChytridineen. Jahrb.
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1911. BARRUS, M . F . , Variation of Varieties of Beans in their Sus-
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1911. BATESON, W., and PUNNETT, R. C., Reduplication of
Terms in Series of Gametes. IV Inter. Conf. Genet. Paris,
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1911. BEMBOWER, W., Pollination Notes from the Cedar Point
Region. Ohio Nat. 11 : 378-383.

1911. BENEDICT, RALPH C., Do Ferns Hybridize? Science,
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1911. BRINGHAM, E. S., A Year's Work in Potato Breeding.
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1911. BLARINGHEM, L., L'etat present de la theorie de la mu-
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1911. BLARINGHEM, L., Sur I'heredite en Mosaique. IV Inter.
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1911. BRAEM, F., Die Varoation bei den Statoblasten von Pec-
tinatella magnifica. Arch. f. Entwick'mech. d. Org. 32:
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1911. BUFFUM, B. C., Effect of Environment on Plant Breeding.
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1911. CAMPBELL, DOUGLAS HOUGHTON, The Nature of Graft-
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1911. CHUBBUCK, LEVI, A Variety of Corn for Elevated Regions.
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376 Plant-Breeding

1911. CLEMENTS, FREDERICK B., Proposals for a System of

Tree Breeding. A. B. A. Rep. 6 : 275-282.
1911. CLOTHIER, GEO. T., Breeding to Improve Physical Qualities

of Timber. A. B. A. Rep. 6 : 170-172.
1911. CLUTE, W. N., and FERRISS, J. H., A New Species of

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Waxy Endosperm in Hybrids of Chinese Maize. IV Inter.

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1911. COLLINS, G. N., Increased Yields of Corn from Hybrid

Seed. U. S. Dept. Agr. Yearbook, 319-328.
1911. COOK, O. F., Hindi Cotton in Egypt. U. S. Dept. Agr.

Plant Ind. Bull. 210 : 1-58, pis. 1-6.
1911. COOK, 0. F., and MEADE, R. M., Arrangement of Parts

in the Cotton Plant. U. S. Dept. Agr. Plant Ind. Bull.

222 : 26, figs. 1-9.
1911. COUPIN, H., Sur la localisation des pigments dans le

tegument des graines de haricots. Acad. Sci. Compt.

Rend. 153: 1489-1492.
1911. CREED, RICHARD, The Growing of Turnip Seed in the

Maritime Provinces. Can. Seed-Grow. Assoc. Rep. 7 :

49-50.
1911. DALLIMORE, W., Notes on Trees suitable for Experimental

Forestry. Kew Bull. Misc. Inf. 1911 : 211-223.
1911. DANIEL, L., Etude biometrique de la descendance de

Haricots greffes et de Haricots francs de pied. Acad.

Sci. Compt. Rend. 152: 1018-1020.
1911. DANIEL, L., Recherches biometrique sur un hi/bride de

greffe entre poirier et Cognassier. Acad. Sci. Compt.

Rend. 152: 1186-1188.
1911. DAVENPORT, E., " Domesticated Animals and Plants."

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1911. DAVIS, BRADLEY MOORE, Genetical Studies on (Enothera.

II. Some Hybrids of (Enothera biennis and 0. grandi flora

Appendix D 377

that resemble 0. Lamarckiana. Am. Nat. 45 : 193-233, 18

figs. Bibliog. f p.
1911. DECKER, H., Mendel's Law as Related to Heredity and

Breeding. I-V. Horticulture, 13 : 635 ; 13 : 669 ; 13 : 70&-706 ;

13 : 741-742 ; 13 : 780. Illus. Translated from Cosmos by

G. Thommen.
1911. DELACROIX, G., Maladies des plantes cultivees dans les

pays chauds, publie par A. Maublanc, vol. 1., 605 pp.

Challamel. Paris.
1911. EMERSON, R. A., Genetic Correlation and Spurious Allelo-

morphism in Maize. Neb. Agr. Exp. Sta. Ann. Rep. 24:

59-90, 9 figs.
1911. EMERSON, R. A., Latent Colors in Corn. A. B. A. Rep.

6:233-237.
1911. EMERSON, R. A., Production of a White Bean Lacking the

Factor for Total Pigmentation. A Prophecy Fulfilled.

A. B. A. Rep. 6:396-397.
1911. EVANS, G. W., Wheats and Wheat Breeding. Agr. Jour.

of Brit. East Africa, 3 : 348-356.
1911. EWING, E. C., Correlation of Characters in Corn. Cornell

Univ. Agr. Exp. Sta. Bull. 287 : 67-100, 14 tab., 2 figs.
1911. FAIRCHILD, DAVID, Plant Introduction for the Plant

Breeder. U. S. Dept. Agr. Yearbook, 411-422, 6 pis. &

1 fig. Same. Yearbook Separate, 580: 411-422, 6 pis.
1911. FOOTE, E. H., A Study of the Supposed Hybrid of the

Black and Shingle Oaks. Sci. Lab. Denison Univ. Bull.

16:315-338, pis. 11-14.
1911. FREEMAN, E. M., Resistance and Immunity in Plant

Diseases. Phytopathology, 1 : 109-115. (Also published

in Publ. Bot. Soc. Am. 50 : 17-26.)
1911. FREEMAN, G. F., and JONES, D. F., Plant Breeding.

Univ. Arizona Agr. Exp. Sta. Ann. Rep. 541-546.
1911. GATES, R. R., Mutation in (Enothera. Am. Nat. 45:

577-606. Bibliog.

378 Plant-Breeding

1911. GATES, R. R., Studies on the Variability and Heritability

of Pigmentation in (Enothera. Zeitsch. f. indukt. Abst.- u.

Vererb. 4 : 337-372, pi. & 5 figs. Bibliog. J p.
1911. GAUSS, ROBERT, Acclimatization in Breeding Drought-
Resistant Cereals. A. B. A. Rep. 6 : 147-156.
1911. GAUSS, ROBERT, The Plant Breeding Problem. Am. Breed.

Mag. 2:259-263.
1911. GAUTIER, ARMAND, Sur le Principe de la coalescence des

plasmus vivants et I'origine des races et des especes. IV

International Conf. Genetique, Paris, 79-90.
1911. GENTY, C., Note sur deux Carduus hybrides. Monde

des Plantes, 14 : 26.
1911. GILBERT, ARTHUR W., Suggestions for an Undergraduate

Course in Plant Breeding. A. B. A Rep. 6:352-356.
1911. GILBERT, ARTHUR W., Suggestive Laboratory Exercises

for a Course in Plant Breeding. Am. Breed. Mag. 2 : 196-

212, fig. Tab. Bibliog. in notes.
1911. GRANIER, J., and BOULE, L., Sur le phenomene de con-

jugaison des chromosomes a le prophase de la premiere

cinese reductrice (microsporogenese chez Endymion nutans
. Dum). Acad. Sci. Compt. Rend. 152:393-396.
1911. GREGORY, R. P., Experiments with Primula sinensis.

Jour, of Gen. 1 : 73. Illus.
1911. GREGORY, R. P., On Gametic Coupling and Repulsion in

Primula sinensis. Roy. Soc. London Proc. 84 : 12-15.
1911. GRIFFON, E., Greffage et Hybridation Asexuelle. IV

Internat. Conf. Genetique, Paris, 164-196, figs. 24.
1911. GRIFFON, E., Observations et recherches experimentales sur

la variation chez le mais. Soc. Bot. France Bull. 57 : 604-

615.
1911. GROTH, H. A., The FI Heredity of Size, Shape, and Number

in Tomato Leaves. I. Seedlings. N. J. Agr. Exp. Sta.

Bull. 238 : 3-38, 5 figs. & 1 pi.
1911. GROTH, H. A.; The FI Heredity of Size, Shape, Number

Appendix D 379

in Tomato Leaves. Part II. Mature plants. New Jersey

Exp. Sta. Bull. 239: 3-12, pi. 1-9.
1911. HAGEDOORN, A. L., Facteurs Genetiques et Facteurs du

Milieu dans I' amelioration et I'obtentian des races. IV

Internat. Conf. Genetique, Paris, 132-135.
1911. HALSTEAD, B. D., Geometrical Figures in Plant Breeding.

Am. Breed. Mag. 2 : 217-220, fig.
1911. HANSEN, N. E., Some New Fruits. So. Dak. Agr. Exp.

Sta. Bull. 130 : 163-200, 1 fig.
1911. HARRIS, J. ARTHUR, On the Formation of Correlation and

Contingency Tables when the Number of Combinations is

Large. Am. Nat. 45: 566-571, 2 tab. Bibliog. in notes.
1911. HARRIS, J. ARTHUR, The Biometric Proof of the Pure Line

Theory. Am. Nat. 45 : 345-363. Bibliog. in notes.
1911. HARRIS, J. ARTHUR, The Measurement of Natural Selec-
tion. Pop. Sci. Mo. 78 : 521-538, figs. 1-7.
1911. HARTLEY, C. P., The Corn Breeder's Problems. Am.

Breed. Mag. 2 : 212-217. Diagr.
1911. HATAI, . SHINKISHI, The Mendelian Ratio and Blended

Inheritance. Am. Nat. 45 : 99-106. Bibliog.
1911. HAYES, H. K., and EAST, E. M., Improvement in Corn.

Conn. Agr. Exp. Sta. Bull. 168: 21, 4 pis.
1911. HAYES, H. K., Inheritance in Corn. Conn. (State)

Agr. Exp. Sta. Ann. Rep. 407-427.
1911. HECKEL, E., Sur les mutations gemmaires culturales

du Solanum Maglia et sur les premiers resultats culturaux

de ces mutations. Acad. Sci., Paris, Compt. Rend. 153 :

417-420.
1911. HENRY, J. L., Results obtained through the Use of Hand

Selected Seed. Can. Seed-Grow. Assoc. Rep. 7 : 79-80.
1911. HILL, E. J., (Enothera Lamarckiana: its Early Cultiva-
tion and Description. Bot. Gaz. 51 : 136-140.
1911. HILLMAN, F. H., Testing Farm Seeds in the Home and

in the Rural School. U. S. Dept. Agr. Farmers' Bull. 428 :

380 Plant-Breeding

(47 pp.), 32 figs. (This bulletin describes the seed- trade
condition, the seed used as adulterants, methods and ap-
paratus used in making tests, etc.)

1911. HONING, J. A., Die Doppelnatur der (Enothera Lamarck-
iana. Zeitsch. f. indukt. Abst.- u. Vererb. 4:227-278,
10 figs. Bibliog. in notes.

1911. HOPKINS, L. S., A New Variety of the Cinnamon Fern.
Am. Fern Jour. 1 : 100-101. Osmunda cinnamomea auri-
culata var. nov. described and illustrated.

1911. HUMBERT, E. P., A Quantitative Study of Variation.
Natural and Induced, in Pure Lines of Silene noctiflora,
Zeitsch. .f. indukt. Abst.- u. Vererb. 4 : 161-226, 12 figs.
Bibliog. in notes.

1911. HURST, C. C., The Application of the Principles of Genetics
to Some Practical Problems. IV Internat. Conf . Genetique,
Paris, 210-221.

1911. Hus, H., and MURDOCK, A. W., Inheritance of Fascia-
tion in Zea Mays. Plant World, 14 : 88-96, 1 fig.

1911. JANSONIUS, H. H., and MOLL, J. W., Der anatomische
Ban des Holzes der Pfropfhybrids Cytisus Adami und ihrer
Compomenten. Rec. Trav. Bot. Neerland. 8 : 333-368.

1911. JENNINGS, H. S., Computation of the Coefficient of Cor-
relation. Am. Nat. 45 : 413.

1911. JENNINGS, H. S., Pure Lines in the Study of Genetics in
Lower Organism. Am. Nat. 45 : 79-89. Diagr.

1911. JESENKA, F., Sur un hybride fertile entre Triticum
sativum (Ble Mold-Squarehead) and Secale Cereale. (Seigle
de Petkus.) IV Inter. Conf. Genetique, Paris, 501-511.

1911. JOHANNSEN, W., Mutations dans des lignees pures de
haricots et discussion au subject de le mutation en general.
IV Internat. Conf. Genetique, Paris, 160-163.

1911. KASTLE, J. H., and HADEN, R. L., Color Changes in Blue
Flowers of Wild Chicory (Cichorium intybus). Amer.
Chem. Jour. 46: 315-325.

Appendix D 381

1911. KEEBLE, F., and PELLEW, C., The Mode of Inheritance
of Stature and of Time of Flowering in Peas (Pisum sativum) .
Jour, of Gen. 1 : 47-56. Rev. in Zeitsch. f. indukt. Abst.-
u. Vererb. 5:331.

1911. KOCK, G., Eine Mutation der Kartoffelsorte Up to Date.
Monatsh. f. Landw. 4 : 10&-109.

1911. KROEMER, K., Uber das "Mendeln " und seine Bedeutung
fur die gdrtnerische Pflanzenzuchtung. Hollers Deutsche ;
Gartner-Zeitung, 26 : 50-52.

1911. LACKE, M., and PARR, A. E., The Problem of the Im-
provement of Cotton in the United Provinces of Agra and
Oudh. Agr. Jour. India, 6 : 1-13, 5 pi.

1911. LANG, H., Technisches aus dem Gebiete der F utter pflanzen-
zuchtung. Illus. Landw. Zeitung, 704.

1911. LEAKE, H. M., Studies in Indian Cotton. Jour, of Gen.
1 : 205^-272. Illus.

1911. LEIDIGH, A. H., Methods for the Improvement of Sorghum.
Am. Breed. Mag. 2 : 294-296. Port.

1911. LOTSY, J. P., Hybrids entre especes d' antirrhinum. IV
Inter. Conf. Genetique, Paris, 416-428, figs. 9.

1911. LOVE, HARRY H., Studies of Variation in Plants. Cornell
. Univ. Agr. Exp. Sta. Bull. 297 : 593-677, 70 figs., 48 tab.

1911. MACDOUGAL, D. T. , Climatic Selection in a Hybrid Prog-
eny Oak. Plant World, 14: 129-131, 1 fig.

1911. MASON, SILAS C., Drought Resistance of the Olive in the
Southwestern States. U. S. Dept. Agr. Bur. Plant Ind.
Bull. 192: (60 pp.), 6 pis. & 20 figs.

1911. MAYER, A., Bemerkungen zu G. Lewitsky: Uber die
Chondriosomen in pflanzlichen Zellen. Deutsch. Bot.
Gesell. Ber. 29 : 158-160.

1911. MENDEL, G., Versuche uber Pflanzenhybriden. Heraus-
gegeben von E. v. Tachermak. Ostwalds Klassiker der
exakten Wissenschaften, No. 121, 2d ed. Leipzig, Engel-
mann. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb. 6 : 182.

382 Plant-Breeding

1911. MONTGOMERY, E. G., Correlation Studies in Corn. Ne-
braska Agr. Exp. Sta. Ann. Rept. 24 : 109-158.

1911. MONTGOMERY, E. G., Note regarding Maize Flowers.
Science, n.s. 33 : 435.

1911. MONTGOMERY, E. G., Perfect Flowers in Maize. Pop.
Sci. Mo. 79 : 346-349, figs. 1-6.

1911. MOREHOUSE, L. A., Improvement of Bermuda Grass.
Figs. A. B. A. Rep. 6 : 60-63.

1911. MULLER, R., Mutationen ~bei Typhus- und Ruhrbacterian.
Mutation als spezifischee Kulturmerkmal. Centralbl. f.
Bacteriologie, 58 : 1 : 97-106, 2 pis.

1911. MUNDY, H. S., Maize Breeding and Seed Selection. Rho-
desia Agr. Jour. 8 : 385-390.

1911. MUNSON, T. V., Single Character vs. Tout Ensemble Breed-
ing in Grapes. A. B. A. Rep. 6 : 183-189.

1911. NEWMAN, H. H., Reply to E. Godlewski's li Bemerkungen
zu der Arbeit von H. H. Newman: 'Further Studies of the
Process of Heredity in Fundulus Hybrids.' ' Arch. f.
Entwick'mech. d. Org. 32 : 472-476. Bibliog. in notes.

1911. NEWMAN, L. H., Plant Breeding in Sweden. Can. Seed-
Grow. Assoc. Rep. 7 : 89-99, 4 tab.

1911. NILSSON-EHLE, H., Mendelisme et Acclimatation. IV
Internat. Conf. Genetique, Paris, 136-157.

1911. NILSSON-EHLE, H., Svalofs Solhvete, Ny sort for sodra
Sverige. Sveriges Utsadesfor. Tidskr. 21 : 123-126, 1 pi.

1911. NOMBLOT, A., Recherches de varietes fruitier es nou-
velles. IV Inter. Conf. Genetique, Paris, 464-468.

1911. OLIVER, GEORGE W., New Methods of Plant Breeding.
A. B. A. Rep. 6 : 11-20. Figs.

1911. ORTON, W. A., Disease Resistance in Varieties of Potatoes.
Indiana Acad. Sci. Proc. 219-221.

1911. ORTON, W. A., The Development of Disease Resistance
Varieties of Plants. IV Internat. Conf. Genetique, Paris,
247 : 265, figs. 9.

Appendix D 383

1911. OWEN, E. J., Inheritance Studies with Beans. N. J. Agr.

Exp. Sta. Bot. Dept. Rep. 277-281, 1 pi.
1911. PARDE, L., Enquete sur I' acclimation des essences exo-

tiques en France. Soc. Dendr. France Bull. 19 : 5-12. Illus.
1911. PEARL, RAYMOND, Biometrics. Am. Nat. 45:319-320.
1911. PEARL, RAYMOND, Biometric Arguments regarding the

Genotype Concept. Am. Nat. 45 : 561-566. Bibliog. in

notes.
1911. PEARL, RAYMOND (Reviewer), Some Recent Studies on

Variation and Correlation in Agricultural Plants. (Review.)

Am. Nat. 45 : 415-425. Bibliog. 1 p.

1911. PEARL, R., The Personal Equation in Breeding Experi-
ments involving Certain Characters of Maize. Biol. Bull.

21:339-366.

1911. PEARSON, KARL, On a Correction to be made to the Cor-
relation Ration. Biometrika, 8 : 254r-256, pi.
1911. POLE-EVANS, J. B., South African Cereal Rusts with Ob-
servations on the Problem of Breeding Rust-resistant Wheats.

Jour. Agr. Sci. 4 : 95-104.
1911. REDFIELD, R. L., Acquired Characters Defined. Am.

Nat. 45 : 571-573.
1911. ROBERTS, F. B., A Method of Corn Pollination. Am.

Breed. Mag. 2 : 54-60. Fig.
1911. ROBERTS, HERBERT F., Breeding for Type of Kernel in

Wheat. A. B. A. Rep. 6: 142-147. Figs.
1911. RUDOLPH, J., UAster cordifolius et ses varietes. Rev.

Hort. 83 : 326-327.
1911. RuGG-GuNN, A., Sociological and Other Aspects of the

Unit-Character Conception. IV Inter. Conf. Genet., Paris,

204-208.
1911. SALAMAN, R. N., Studies in Potato Breeding. IV Inter.

Conf. Genetique, Paris, 373-376.
1911. SAUNDERS, EDITH R., The Breeding of Double Flowers.

IV Inter. Conf. Genetique, Paris, 397^05.

384 Plant-Breeding

1911. SAUNDERS, CHARLES E., Production de varietes de ble

de haute valeur boulougere. IV Inter. Conf. Genet., Paris,

290-300.
1911. SAUNDERS, E. R., On Inheritance of a Mutation in the

Common Foxglove (Digitalis purpurea). New Phytologist,

10 : 49-63, 1 pi. & 12 figs.
1911. SCUDDER, H., Similarity of Color in Bud and in Leaf.

Rhodora, 13 : 86-87.
1911. SHAMEL, A. D., A Study of the Improvement of Citrus

Fruits through Bud Selection. U. S. Dept. Agr. Plant Ind.

Circ. 77 : 1-19, 5 figs.
1911. SHERFF, E. E., Tragopogon pratensis X porrifolius.

Torreya, 11 : 14-15.
1911. SHULL, G. H., A Pure-Line Method in Corn Breeding.

Amer. Breeders' Assoc. Rep. 5 : 51-59. Rev. in Zeitsch.

f. indukt. Abst.- u. Vererb. 5 : 331-332.
1911. SHULL, G. H., Defective Inheritance-Ratios in Bursa

Hybrids. Naturf. Vereins Briinn Verb. 49: (12 pp.), 6

pis.
1911. SHULL, G. H., Hybridization Methods in Corn Breeding.

A. B. A. Rep. 6 : 63-72, figs.
1911. SHULL, G. H., Reversible Sex-Mutants in Lychnis dioica.

Bot. Gaz. 52 : 329-368, 15 figs.
1911. SMITH, LOUIE H., Increasing Protein and Fat in Corn.

A. B. A. Rep. 6:5-11.
1911. SMITH, RUSSELL J., Breeding and Use of Tree Crops.

A. B. A. Rep. 6 : 51-56.

1911. SPILLMAN, W. J., Heredity. Am. Nat. 45 : 60-64.
1911. STRAMPELLI, N., De V6tude des characteres anormaux

presenter par les plantules pour la recherche des varietes

nouvelles. IV Internat. Conf. Genetique, Paris, 237-246,

figs. 11.
1911. STYAN, K. E., Pollen Grains. Rev. in Am. Bot. 17 : 41-

44. Originally published in Selbourne Magazine.

Appendix D 385

1911. BUTTON, W., Compte Rendu. D'esperiences de Croise-
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de commerce dans le but de decouvris entre eux quelque
trace d'identite specifique, IV Inter. Conf. Genetique,
Paris, 558-567, figs. 4.

1911. TAYLOR, G. M., Disease Resisting Potatoes. Gard.
Chron., 3d ser. 49:181.

1911. TEDIN, H., Ar skalhalten hos arter en sortegenskap?
(With German resume'.) Sveriges Utsadesfor. Tidskr,
21 : 72-77.

1911. The Sugar-Beet Industry is based on Breeding. Am.
Breed. Mag. 2 : 234.

1911. THODAY, M. G., and THODAY, 0., On the Inheritance
of the Yellow Tinge in Sweet Pea Colouring. Cambridge
Phil. Soc. Proc. 16 : 71-84.

1911. THOMAS, ROSE HAIG, Nicotiana Crosses. IV Inter.
Conf. Genetique, Paris, 453-461, figs. 6.

1911. TOWER, W. L., The Determination of Dominance and the
Modification of Behavior in Alternative (Mendelian) In-
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1911. TRACY, W. W., Report of Committee on Breeding Vege-
tables. A. B. A. Rep. 6 : 75-78.

1911. TSCHERMAK, PROF. ERICH VON, Examen de le theorie
des facteurs par le recroisement methodique des hybrids.
IV Internat. Conf. Genetique, Paris : 91-95. Tab. VIIIc.

1911. VILMORIN, P. DE, and BATESON, W., A Case of Gametic
Coupling in Pisum. Roy. Soc. London Proc. B. 84: 9-11.

1911. VILMORIN, PHILIPPE DE, Fixite des races de Froment.
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1911. VILMORIN, PH. DE, Recherches sur I'heredite mendelienne.

Acad. Sci. Compt. Rend., 54&-551.
2c

386 Plant-Breeding

1911. VOGLER, Die Variationen der Blattspreite bei Cybisulabur-

num L. Bot. Zentralbl. Beih. 27 : 337-390.
1911. VRIES, HUGO DE, Intracellular Pangenesis. Translated

into English by C. Stuart Gager, Chicago. Open Court

Publ. Compt. Rev. in Zeitsch. f. indukt. Abst.-u. Vererb.

5:90.
1911. VRIES, H. DE, Uber doppeltreziproke Bastarde von (Eno-

thera biennis L. und 0. muricata L. Biol. Centralbl. 31 :

97-104.
1911. WALDRON, L. R., Variegation of European Alfalfas.

Science, n.s. 33 : 310-312.
1911. WHELDALE, M., On the Formation of Anthocyanin. Jour.

of Gen. 1 : 133.
1911. WHELDALE, M., The Chemical Differentiation of Species.

Biochemical Jour. 5: 445-456.
1911. WITTMACK, L., Botanische Fragen in Beziehung zur

Kartoffehuchtung. Illus. Landw, Zeitung, 51 : 289.
1911. WOODRUFF, CHAS. E., Breeding for Color Adjustment,

under Certain Climates. Am. Breed. Mag. 2 : 313-000.
1911. ZAVITZ, C. A., Report of Committee on Breeding Cereals.

A. B. A. Rep. 6: 141-142.

1911. ZEIJLSTRA, H. H., CEnothera nanella de Vries, eine krank-
hafte Pflanzenart. Biol. Centralbl. 31 : 129-138.

1912. ACLOQUE, A., La genealogie du chrysantheme. Monde
des Plantes, 14 : 27-28.

1912. BALL, CARLETON R., and HASTINGS, STEPHEN H., Grain-
Sorghum Production in the San Antonio Region of Texas.
U. S. Dept. Agr. Bur. Plant Ind. Bull. 237 : (30 pp.), 4 figs.

1912. BATCHELOR, LEON D., Carnation Breeding. A. B. A.
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1912. BAUR, ERWIN, Vererbungs- und Bastardierungeversuche
mil Antirrhinum. II. Faktorenkoppelung. Zeitsch. f. in-
dukt. Abst.- u. Vererb. 6: 201-216, 3 tab. Bibliog. in
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Appendix D 387

1912. BEACH, S, A., and MANEY, T. J., Mendelian Inheritance

in Prunus Hybrids. A. B. A. Rep. 7 : 214^227, fig.
1912. BEACH, S. A., Report of the Committee on Breeding Tree

and Vine Fruits. A. B. A. Rep. 7 : 213.
1912. BELLING, JOHN, Breeding Experiments with Forage Plants

in Florida. A. B. A. Rep. 8 : 43&-440.
1912. BELLING, JOHN, Selection in Pure Lines. Am. Breed.

Mag. 3:311-312.
1912. BLARINGHEM, L., Les problemes de biologie appliquee

examines dans la quatrieme conference Internationale de

genetique. Revue Scientifique, 50 : 50 : 265-269.
1912. BRAINERD, E., Violet Hybrids between Species of the

Palmata Group. Torrey Bot. Club Bull. 39: 85-97, 3

pis.

1912. BURTT-DAVY, J., Observations on the Inheritance of Char-
acters in Zea Mays. Roy. Soc. South Africa Trans. 2 :

261-270.
1912. CASTLE, W. E., The Inconstancy of Unit-Characters.

Am. Nat. 46:352-362.
1912. CHRISTIE, W., Untersuchungen uber alte norwegische

Hafersorten. Fiihlings landw. Zeitung : 297.
1912. COCKERELL, T. D. A., The Red Sunflower. Pop. Sci.

Mo. 80 : 373-382. Illus.
1912. COCKERELL, T. D. A., The Word Genotype. Science,

n.s. 35 : 304.
1912. COLLINS, G. N., and KEMPTON, J. H., An Improved

Method of Artificial Pollination in Corn. U. S. Dept. Agr.

Bur. Plant Ind. Circ. 89: (7 pp.), 2 figs.
1912. COLLINS, G. N., Improvements in Technique of Corn

Breeding. A. B. A. Rep. 8 : 349-353.
1912. COOK, 0. F., Results of Cotton Experiments in 1911.

U. S. Dept. Agr. Bur. Plant Ind. Circ. 96 : (21 pp.).
1912. DAVIS, BRADLEY MOORE, Genetical Studies on (Enothera.

III. Further Hybrids of (Enothera biennis and 0. grandiflora

388 Plant-Breeding

that resemble 0. Lamarckiana. Am. Nat. 46: 377-427,

15 figs. Bibliog. £ p.
1912. DEAN, A., The Potato and Floral Sterility. Gard. Chron.

3d ser. 51 : 13.
1912. DERR, H. B., The Breeding of Winter Barleys. Am.

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1912. DILLMAN, A. C., Breeding Alfalfa as a Dry-land Crop.

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1912. DONCASTER, L., Sex-limited Inheritance in Cats. Science,

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1912. DORSET, M. J., Variation in the Floral Structures of Vitis.

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1912. DORSET, M. J., Variation Studies of the Venation Angles

and Leaf Dimensions in Vitis. A. B. A. Rep. 7 : 227-250,

%.
1912. EAST, E. M., A Study of Hybrids between Nicotiana

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4 figs.
1912. EAST, E. M., and HATS, H. K., Inheritance in Maize.

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1912. EAST, E. M., Inheritance of Color in the Aleurone Cells

of Maize. Am. Nat. 46 : 363-365.
1912. EAST, E. M., The Application of Biological Principles

to Plant Breeding. In Heredity and Eugenics, pp. 113-

138, fig.
1912. EAST, E. M., The Mendelian Notation as a Description

of Physiological Facts. Am. Nat. 46 : 633-655, 1 tab.
1912. FINLOW, R. S., and BURKILL, J. H., The Inheritance of

Red Colour and the Regularity of Self-fertilization in Cor-

chorus capsularis L., the Common Jute-plant. India Dept.

Agr. Bot. Ser. Mem. 4 : 73-92.
1912. FROST, H. B., The Origin of an Early Variety ofMatthiola

by Mutation. A. B. A. Rep. 8 : 536-545.

Appendix D 389

1912. FUNK, EUGENE D., Ten Years of Corn Breeding. Am.

Breed. Mag. 3 : 295-302, 4 figs.
1912. GATES, R. R., Early Historico-botanical Records of the

(Enotheras. Iowa Acad. Sci. Proc. 85-124, 6 pis. Rev.

in Zeitsch. f. indukt. Abst.- u. Vererb. 6 : 285-287.
1912. GERNER, W. W., Some Observations on Tobacco Breeding.

A. B. A. Rep. 8 : 458-468, fig.
1912. GERNERT, WALTER B., A New Subspecies of Zea Mays L.

Am. Nat. 46 : 616-622, 3 figs.

1912. GERNERT, WALTER B., Methods in the Artificial Pollina-
tion of Corn. A. B. A. Rep. 8 : 353-367.
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A. Rep. 7 : 169-188.
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delism and its Application to a Mixed Hybrid Population.

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1912. GILBERT, A. W., Present Status of Plant-breeding In-
struction in the United States. A. B. A. Rep. 7: 7-11.
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Landwirtsch. Gesell. Mitt. 146.
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Number in Tomato Fruits. N. J. Agr. Exp. Sta. Bull.

242 : 3-39, 3 pi.
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L. L., Cross-breeding Corn. U. S. Dept. Agr. Bur. Plant

Ind. Bull. 218: (72 pp.), 1 fig.
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L. L., Cross-breeding Corn. U. S. Dept. Agr. Plant Ind.

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by Factors Other than Heredity. A. B. A. Rep. 8 : 335-338.
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Agr. Bur. Plant Ind. Circ. 95 : (13 pp.), 2 figs.
1912. HAUMAN-MERCK, L., Observations sur la pollination

390 Plant-Breeding

d'une Malpighiacee du genre Stigmaphyllon. Rec. Inst.

Bot. Leo Errera, 9 : 21-28, 1 fig.
1912. HAYES, H. K., Methods of Corn Breeding. Am. Breed.

Mag. 3 : 99-108, pi. Tab. Bibliog.
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Tabacum. Connecticut Agr. Exp. Sta. Bull. 171 : 3-45,

5 pis.
1912. HEDRICK, U. P., and WELLINGTON, R., An Experiment

in Breeding Apples. N. Y. (Geneva) Agr. Exp. Sta. Bull.

350. Rev. in Zeitsch. f. indukt. Abst.- u. Vererb. 8 : 347.
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Hance, under Cultivation, with Some Remarks on the History

of Primula sinensis Sab. Jour, of Gen. 2: 1-20, 2 pis.

Bibliog. in notes.
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107-110.
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Natural Selection. Am. Nat. 46:372-376.
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f. indukt. Abst.- u. Vererb. 6 : 137-139. (Correction :

p. 268), 9 pis., 2 figs., 5 tab.
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An elementary text-book of zoology and human physiology.

495 pp. Henry Holt & Co., N. Y. Rev. in Science, n.s.

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with Special Reference to Breeding. A. B. A. Rep. 7 : 50-61.

Appendix D 391

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392 Plant-Breeding

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Appendix D 393

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the Art of Breeding. Science, n.s. 35 : 597-609.
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APPENDIX E

LABORATORY EXERCISES

THE following laboratory exercises are intended to serve merely
as suggestions. It is impossible and inadvisable to attempt to
outline a rigid set of exercises for instructors to follow. It is
the hope that these may serve as hints or type exercises, capable
of all sorts of modification to suit conditions. An attempt has
been made to avoid elaborate laboratory equipment which is
expensive and unnecessary. The instructor should always aim
to arrange laboratory practicums so that the student's inquisi-
tive curiosity may be aroused and he may be induced to find
out things for himself from the material with which he has to
work. These exercises are not arranged with any particular
order or sequence. The sequence will depend on the time of
the year, material at hand, and so forth. The first group of
exercises is of a general nature, and the exercises on corn,
potatoes, and the cereals are grouped more or less together.

We wish to acknowledge the assistance of Professor E. E.
Barker in the preparation of these exercises, most of which
have been successfully used by him with large classes. A few
new ones have been added.

EXERCISE 1

Field Study of Variations by making an Herbarium of Variations

Have each student collect, press, and mount fifty variations

of plants. This is an excellent exercise, because it calls the

394

Appendix E 395

FIG. 104. — A specimen herbarium sheet, showing variation in the leaves
of the mulberry.

396

Plant-Breeding

FIG. 105. — A specimen herbarium sheet showing differences between two
leaves of the horse-radish.

Appendix E 397

student's attention very effectively to the vast extent of varia-
tion in wild and cultivated plants. Since variation is the basis
of artificial selection as well as evolution in nature, it is highly
important that considerable time and attention should be given
to this study.

Material. — A botanical collecting case, 20 blotters, 12 X 18
inches; 50 mounting sheets, 12 X 18 inches; 50 labels, and glue.

The accompanying photographs represent specimens treated
as above (Figs. 104 to 107). The following directions may be
given to each student : —

Directions for collecting, pressing, and mounting an herbarium of

variations

1. Search for fluctuations, plateations, mutations, and bud-
variations of plant characters which have been discussed in the
lectures.

2. Collect as nearly the whole plant as practicable. The
size of the mounting sheets is 12 X 18 inches. When you collect
your specimens plan upon this size of sheet, and arrange them
accordingly when you are putting them into the blotters.

3. Do not mount large, woody branches showing different
degrees of thorniness, etc., upon the mounting sheets, but pre-
serve them in bundles properly labeled.

4. If you wish to show variations of berries, such as thorn-
apples, etc., dry the fruits and fasten them to the mounting sheets
by threads.

5. Leave specimens in the blotters until they are thoroughly
dry. If you do not have enough blotters, take out the speci-
mens which have been in the blotters for a week or more, and
put them between pieces of newspapers, under pressure, until
they become thoroughly dry. Then dry your blotters near a
radiator and put in the fresh material.

6. After the specimens have become thoroughly dry, stick
them to the mounting sheets, preferably with glue. Put a small

398 Plant-Breeding

.....

FIG. 106. — A specimen herbarium sheet, showing variation in leaves of
the Persian lilac.

Appendix E 399

band of adhesive tissue over the larger stems. Arrange the
specimens, if possible, so that you have at least one variation
on a sheet.

7. Put the label on the lower right-hand corner, leaving a
small margin. Attach the label to the mounting sheet with
glue or paste, putting it only on the left edge of the label, that
is, do not cover the back of the label with paste or glue.

SAMPLE OF LABEL

HERBARIUM OF VARIATIONS

DEPARTMENT OF PLANT-BREEDING. NEW YORK STATE
COLLEGE OF AGRICULTURE

Name

Locality Date

Habitat

Description of variation

Class of variation

Collector . . . . No.

8. Before the specimen is handed in, fill in as many of the
blank spaces on the label as possible. Place your name after
the word " Collector." Fill in both the scientific and common
names.

9. Absolute neatness is essential.

EXERCISE 2

The Statistical Study of Type and Variability

Making measurements. — The value and uses of the statistical
method of studying variation are explained in Chapter IV. In
dealing statistically with a group of organisms, or parts of them,
the first step in the procedure is, of course, to collect data. These

400

Plant-Breeding

FIG. 107. — A specimen herbarium sheet, showing variations in leaves
of the blackberry.

Appendix E 401

will consist of quantitative measurements of characters to be
studied. These data are later analyzed, certain constants are
derived therefrom, and, lastly, the constants are interpreted.
The conclusions of the breeder or the investigator are based on
his interpretations of these constants. The meaning of the
various constants is explained in Chapter IV.

In collecting data, it is important that as large a proportion
as possible of the entire population should be measured. Fail-
ing this, the sample should be fairly representative of the whole.
The time or season during which measurements are taken is
important where populations are to be compared. It would
obviously be unfair to collect data one year on fully matured
plants and another year on immatured plants. It is not always
easy to avoid a selection, conscious or unconscious, but the
collector should try to take his data with absolute impartiality.
He should collect at random until he has obtained a represent-
ative sample. Much time and labor will be saved if he can
conveniently limit the number of individuals measured to a num-
ber whose square root is an integer.

The frequency distribution. — Having measured a representa-
tive sample of the entire population, the next step is to sort the
data. All individuals of the same or nearly the same size are
grouped together in one order of magnitude. In order to give
a clear understanding of what follows, let us take, for example,
the data collected by a class of students on 500 bean plants.
The individual lengths range from 5 cm. to 95 cm. This is
known as the range of variability and the way in which the in-
dividuals are distributed along the successive equal intervals in
this range is spoken of as the frequency distribution of the vary-
ing character. For convenience, these lengths may be grouped
into classes, thus: 5-14; 15-24; 25-34 . . . 85-94.

It is desirable that the number of classes be limited to not
more than about a dozen, and thus the size of the class will
depend upon the nature of the material. For example, bean
2o

402 Plant-Breeding

plants may vary in height from 5 cm. to 95 cm. ; to make the
classes differ by only 1 cm. would give us 90 classes, which
would be very inconvenient to handle mathematically.

The class limits should be given in all cases, not the mid-
point of the class. The magnitude of a class is its value and is
designated by the symbol V. In calculations the mid-point of
a class is "used as the class value. The number of individuals
falling into each class is termed its frequency and is symbolized
by the letter /. The accompanying table shows how the various
bean lengths are distributed throughout the range : —

V f

5-14 4

15-24 72

25-34 169

35-44 125

45-54 64

55-64 38

65-74 11

75-84 11

85-94 6

500

The graph or frequency polygon. — It is often desirable to
present the data in a graphic way so that the eye can take in at
a glance such information as would otherwise require an extended
and careful study of quantities of figures. For this purpose the
frequency polygon is used. Such a simple diagram or chart
presents a picture embodying the chief characteristics of the
given population. Its significance is apparent to the student at
once. The frequency polygon is made, as explained in Chapter
IV, by plotting the class range along the base-line or axis of
abscissas. On the vertical axis, or axis of ordinates, are plotted
the class frequencies.

When all the frequencies have been plotted in their proper
places on the chart they may be connected by a continuous

Appendix E 403

line. This will form the frequency or distribution curve, known
also as the "probability curve." It will take the form of a
Quetelet curve rising from the lowest class value at the left end
of the base-line to an apex at the class of greatest frequency,
then dropping to the right end at the highest class value. Such
a curve shows at once four things about our data : (1) The
extreme values, or the extent of the range, (2) the way in which
the individuals are distributed throughout this range, (3) the
prevailing type, or class of greatest frequency, and (4) whether
the curve is symmetrical, following the normal probability curve
or not. If the classes are arranged along the base-line in the
sequence of their values instead of their frequencies, the curve
will ascend constantly from the lowest value on the left end to-
ward the highest value at the right end. This forms a Gallon
curve. The Galton type of curve shows merely a different
method of exhibiting the frequency distribution of a population
that is under study.

Mode. — The class of greatest frequency, the most "popular "
or "modish" class, so to speak, is known as the mode or modal
class. In our problem, the modal class is 25-34, or the mode is
29.5, the mid-value of this class. This is oneway, and an excel-
lent one, of expressing type. A typical bean plant of this popu-
lation, we can say, is 29.5 cm. long.

Modal coefficient. — It is desirable to know what proportion
of the population conforms to this type, or falls into this modal
class. This proportion, which is expressed as a percentage des-
ignated as the modal coefficient, is found by dividing the number
of individuals in the modal class by the total number of indi-
viduals measured. In our example, it would be *%% = .3836 =
38.36 %, which is the percentage of the population in the class
of greatest frequency, hence, the modal coefficient.

Mean. — If one desires to know what an average individual
in the population is worth, the mean, symbolized by the letter
M, will show it. The mean shows the average value of the

404 Plant-Breeding

population, hence it is only another method of expressing type.
It is found by multiplying the mid-value of each class (V) by
the number of individuals in that class (/), then summing the
products and dividing this sum by the total number of individ-
uals. The formula for this operation is L.1

n

Thus : —

V

/

Vf

9.5 x

4

=

38.0

19.5 x

72

=

1404.0

29.5 x

169

=

4985.5

39.5 x

125

=

4937.5

49.5 x

64

=

3168.0

59.5 x

38

=

2261.0

69.5 x

11

=

764.5

79.5 x

11

=

874.5

89.5 x

6

=

537.0

500

18970.0

18970.0

= 37

.94

cm.

500

We would get exactly the same result if we arranged the bean
plants, in order of size, in. a single line, placing them end to end,
and then divided the total length of this line by 500, the number
of individuals in it.

Average deviation. — One way of expressing variability is to
find out by how much, on the average, any individual in the
population deviates from the mean, the constant thus secured
being termed the average deviation. This is ascertained as
follows : the amount by which each class differs from the mean,
or in other words, the deviation from the mean (designated by
D) is multiplied by the frequency of the corresponding class,
and then the sum of these products is divided by the total

1 The Greek letter capital "sigma" (£) indicates that the sum of
a series of values is to be taken.

The total number of individuals measured is designated by n.

Appendix E 405

number of individuals. The formula for the operation is — *••

n

Thus in our problem it would be found as shown in the table : —

V f D Df

9.5 x 4 28.44 113.76

19.5 x 72 18.44 1327.68

29.5 x 169 8.44 1426.36

39.5 x 125 1.56 195.00

. 49.5 x 64 11.56 739.84

59.5 x 38 21.56 819.28

69.5 x 11 31.56 347.16

79.5 x 11 41.56 457.16

89.5 x 6 51.56 309.36

5735.60

5735'60 = 11.4712cm.
500

Of course, the deviations below the mean (28.44, 18.44, 8.44)
are negative quantities, those above (1.56, 11.56, 21.56, 31.56,
41.56, 51.56) positive, but inasmuch as we are here concerned
only with deviation from type, we are correct in neglecting these
signs, and using the arithmetic sum, and not the algebraic.

We would secure the same result if we went along our line
of bean plants spoken of above with an average or mean indi-
vidual as a measure, added up the lengths by which each one
missed of being an average individual, and then divided this
total by 500, the number of individuals measured. Clearly this
would give the amount by which, on the average, each individual
missed of being the mean or the average individual.

Standard deviation. — Another constant expressing departure
from type, and one which is preferred by biometricians on mathe-
matical grounds, is standard deviation, designated by the Greek
letter small "sigma " (<r). It is found by squaring the deviations
from the mean before multiplying by the frequencies, dividing
the summation of these products by the number of individuals.

406

Plant-Breeding

and then extracting the square root of the quotient. The
formula is : —

or =

V

/

Vf

D

Df

Z)2

D2/

5-14

4

38.0

28.44

113.76

808.8336

3235.3344

15-24

72

1404.0

18.44

1327.68

340.0336

24482.4192

25-34

169

4985.5

8.44

1426.36

71.2336

12038.4784

35-44

125

4937.5

1.56

195.00

2.4336

304.2000

45-54

64

3168.0

11.56

739.84

133.6336

8552.5504

55-64

38

2261.0

21.56

819.28

464.8336

17663.6768

65-74

11

764.5

31.56

347.16

996.0336

10956.3696

75-84

11

874.5

41.56

457.16

1727.2336

18999.5696

85-94

6

537.0

51.56

309.36

2658.4336

15950.6016

500

18970.0

5735.60

112183.2000

M = 37.94 cm.

Av. Dev. = 11.4712 cm.

cr = 14.9789 cm.

Performing the operations indicated by this formula, we find
the standard deviation in our problem to be

112183.2000
500

14.9789 cm.

The squaring of the deviations has the effect of exaggerating
the departures of the extremes, and thus the standard deviation
is always greater than the average deviation, so that the two
are not comparable. For the practical breeder the one is just
as good as the other and whether he employs the average devia-
tion or the standard deviation is of little practical importance
so long as he is consistent in the use of one to the total exclu-
sion of the other in the same piece of work.

Finding the mean and the standard deviation by the " short
method." — Where large numbers are used, the derivation of the
mean and the standard deviation by the method presented

Appendix E

407

above is a long and laborious process, in which the liability to
error is great. A much shorter, simpler, and at the same time
more accurate method has been devised. This consists in mak-
ing a guess at the mean (designated by G), and indicating the
difference between each class value and this guess in a column
marked (F-G). Each of these differences is then multiplied by
the corresponding frequency and the algebraic sum of the total
negative differences and the total positive differences is found.
This is the total amount by which our guess missed the mean
for the whole population, and hence we should divide this
quantity by n to find the average amount by which we missed
our guess. If this amount, which is called the "correction," is
positive, then our guess has been too low by that amount, and it
is to be added to the guess. On the other hand, if it is negative,
then our guess has been too high, and it is to be diminished by
this amount. The formula for this procedure is : —

x ft ~\r /~i\

correction (c) = (Algebraic)—4^ <

n

M = G ± c.

V

5-14
15-24
25-34
35-44
45-54
55-64
65-74
75-84
85-94

LENGTH

4
72
169
125
64
38
11
11
6

OF PLANTS

(F-G)
-30
-20
-10
0
10
20
30
40
50

(SHORT
f(V-G]
- 120
-1440
-1690

METHOD)
-3250

3600
28800
16900
0
6400
15200
9900
17600
15000

0
640
760
330
440
300

2470

500

Sum

= -780

113400

- 780
500

= - 1.56

c2 = 2.4336

408 Plant-Breeding

M= 39.5- 1.56 - 37.94cm.

= - - 2.4336 = V 224.3664 = 14.9789 cm.

500

39.48%.

In our problem, the mean as determined by this method, as
shown in the accompanying table, is exactly the same as was
found by the long method, 37.94 cm.

We would have secured the same result if, after a casual in-
spection of the line of bean plants spoken of above, we guessed
that the mean was 39.5, and taking an individual of this length
as a measure, we found the total amount which the short ones
lack of being equal in length to the assumed mean, or the guess,
and likewise the total amount which the long ones exceed the
guess. The algebraic sum of these two amounts would be the
total amount by which our guess missed of being the true mean,
and since 500 individuals were measured, the average amount
by which we missed on each individual would be found by
dividing this sum by 500. Our assumed length would then
be corrected by this amount, just as above. If we had guessed
that the mean was 37.94, and went through the same process,
then the sum of the negative differences would have exactly
counterbalanced the sum of the positive differences, since our
guess in this case coincides with the true mean.

It would have made no difference whatever had we made our
guess at 9.5. Indeed, this would have the advantage that
minus signs would be eliminated and thus a frequent source of
error removed, since students are prone to forget the algebraic
signs. On the other hand, larger numbers would be involved.

In finding the standard deviation by the short method, the
elements of the (V-G) column are squared before multiplying
by the corresponding class frequencies. The sum of these prod-

Appendix E 409

ducts is then divided by n, just as in the long method. In find-
ing the mean a certain correction was applied to the guess.
Now, since we are here dealing with squares, we must apply as
a correction the square of the correction found previously ; but
unlike the previous procedure, this square of the correction is
always subtracted from the quotient found as stated above.
(All this has been proven mathematically correct, but the proof
is beyond the scope of this study.) The square root is then found
as before. The formula for deriving the standard deviation by
this method is : —

Using this method, we find the standard deviation to be
exactly the same as before, as shown in the table above and the
following calculations : —

<r ^A/1134QO-(- 1.56)2 = 14.9789 cm.

* OUL)

A further considerable shortening of the short method can be
employed when the class values differ by amounts other than
unity or a simple multiple of it, such as 10. In such a case
the class differences are to be treated as unity and a correction
made at the end of the calculation. The modified formulas are : —

M= G ± (c x True Difference between Classes).
a- = -I/*' V-T) _ C2 x True Difference.

* 71

The short method, because of its simplicity and its labor-
saving features, recommends itself for general use. It is also
slightly more accurate than the long method because no deci-
mals are dropped until the very end of the calculation.

Coefficient of variability. — Standard deviation, as a measure

410 Plant-Breeding

of variability, allows of comparison only between similar organ-
isms or parts, between such characters as are measured in the
same denomination, as tubers with tubers, or height measured
in inches with height in inches. This is because it is not an
absolute, or abstract constant, but really represents a certain
number of feet, pounds, centimeters, or what not. And just as
we cannot compare 5 pounds with 5 inches mathematically, so
we cannot compare standard deviation in inches with that in
pounds.

An undenominational abstract constant that will allow of com-
paring diverse variabilities, let us say, height with thickness, or
pounds with inches, is designated as the coefficient of variability.
It is found by dividing the standard deviation by the mean.

The formula is — X 100 and it is symbolized by (7. It is really
M

only the standard deviation measured in terms of the mean. For
our beans the coefficient of variability for length is .3948 or since
it is usually read as percentage, 39.48 %. This constant is now
comparable with any other coefficient of variability for what-
ever character or in whatever denomination it may have been
measured. Thus we can compare the variability in the length
of beans in millimeters with their variability in breadth meas-
ured in millimeters or inches, or with height in men or sugar
content in beets, if we wish.

Probable error. — Probable error does not mean the amount
of error that an investigator is likely to make in his experiments
or measurements. It means that if he would measure another
random sample of a population similar in size and character to
the sample he had measured before, the chances are even that
the mean for the new sample would lie somewhere between the
limits denoted by the probable error. Thus, the mean as to
length of plants for our beans is 37.94 cm. with a probable error
of ± .4518. This means that the mean for the new population
would not be greater than 37.9400 + .4518 = 38.3918 cm., or

Appendix E 411

less than 37.94 - .4518 = 37.4882 cm., but would fall some-
where in between these two limiting values. It is symbolized
by E with the initial of the constant to which it belongs attached
in smaller case type. Thus, the symbol for the probable error
of the standard deviation is Eff; of the mean, EM; of the co-
efficient of variability, EG.

The probable errors are based upon certain relations between
the standard deviation and the number of individuals. The
greater the number of individuals, the smaller will be the prob-
able error. In short, the probable error will indicate how much
confidence we can place in our constant, and should always
accompany the latter. It is really a part of the constant.

In finding the probable errors the constant .6745 is used.
This has been derived mathematically and is used by all biom-
etricians in the same way.

The following formulae will show how the various probable
errors can be found : —

#* = ±.6745-^ •

Vra

Ev=± .6745—?=.

E0 =

C
± .6745 —=, where C is 10 % or

V2n

±.6745— =A/1 +2(— \ where C is greater than 10%.1
» 2i 71 \Hj{j/

Our completed constants for length of bean plants are then
as follows : —

M = 37.9400 ± .4518 cm.

o- = 14.9789 ± .3195 cm.
(7 = 39.48 ±.96%.

1 In these equations the value of C in per cent is to be used. The prob-
able error will come out as a percentage.

412

Plant-Breeding

In the accompanying table the constants for the number of
pods borne on these plants are likewise determined by the short
method. Note that the column (V-G)2 is entirely omitted, a
short cut which is another considerable time saver. Instead,
the elements of column /(F-G) are simply multiplied by the cor-
responding elements of the (F-G) column since f(V-G) times
(V-G) equals /(F-G)2.

NUMBER OF PODS (SHORT METHOD)

F

f

(F-G)

/(F-G)

5-14

16

-20

- 320

15-24

140

-10

-1400 -1720

25-34

169

0

35-44

115

10

1150

45-54

40

20

800

55-64

12

30

360

65-74

5

40

200

75-84

3

50

150 + 2660

500

Sum = 940.

c

y4u -« QQ

= = l.oo

c2 = 3.5344

500

Mode

= 29.5

Modal Coefficient

M

= 29.5 + 1.8

8 = 31.38

± .3631 (pods).

6400

14000

0

11500

16000

10800

8000

7500

74200

= 38.36 %

- 3.5344 = 12.0360 ± .2568 (pods).
, = .3836 = 38.36 ± .93 %.

9 ol.OO

EXERCISE 3

Correlation

Certain characters in organisms tend to appear together
and the inference is that they are causally connected, that is,

(7 =

Appendix E 413

one is the cause of the other or else both are dependent upon
the same cause.

Two phenomena are causally connected if any one of the
following four cases is true : —

(1) If, when the first is present, the second is invariably present
also.

(2) If, when the first increases in amount, the second also in-
variably increases a proportional amount.

(3) If, when the first is absent, the second is invariably absent
also.

(4) If, when the first decreases in amount, the second also
invariably decreases a proportional amount.

Because a fixed or absolute relationship exists in each of the
four cases the correlation between the two phenomena is said
to be perfect, but in the first two cases it is positive in nature,
in the second two negative in nature. If absolutely no relation
existed between the two phenomena, the correlation would be
zero. .

Now, in the bean problem used in the preceding exercise, it
might be asked, "Is there any fixed relation between the length
of plant and its number of pods?" Suppose, for example, that
if on selecting a plant from the whole lot, it was found to be a
long one, could we then say, on this information only, that it will
be found to bear a great number of pods? If so, we are assum-
ing that some relation exists between the two characters.

Let us, for the sake of illustration, suppose that each bean
plant bears one pod for every centimeter in length. Because in
this case there exists a fixed or absolute relationship, the corre-
lation is said to be perfect, and is expressed by 100 %, or more
usually simply by unity (1).

Now, suppose, however, that on selecting 300 plants averag-
ing 80 cm. in length, we find the first 100 plants to bear an
average of 50 pods per plant, the second 25 pods, and the third
10, it is clear that if we select one more plant at random and

414 Plant-Breeding

measure it to be 80 cm. also, we could no more predict the
number of pods it bears than if we had not measured it at all.
Here, then, we say there is no relationship whatever between
length of plant and number of pods, or, in other words, the cor-
relation is 0.

Now suppose a third case, in which we find that invariably
the longest plant bears the fewest pods, and the shortest the
most. Here we could say the relationship is fixed or absolute
too, but in an opposite, or negative manner, and accordingly,
the correlation would be expressed by — 1 .

But now turning back to the first supposition, where it was
assumed that one pod was borne for each centimeter length,
suppose that the relationship were not so definite. Suppose
that one pod occurs not for every centimeter, but sometimes for
a little more than a centimeter, sometimes for a little less ; then
the relationship, though not absolute, is high, and the degree
to which this relationship approaches the perfect 100 % relation-
ship will express the correlation between the two characters.
The correlation coefficient, in other words, would fall between
0 and + 1.

We rarely find characters or organs in an organism to be
absolutely related; usually they are associated in a more or
less intermediate degree, somewhere between 0 and + 1, or
0 and — 1. The degree to which they are associated, or corre-
lated, if it can be determined in an exact manner and expressed
by a mathematical constant, should be an index of the degree
for which one is the cause of the other, or the probability of
finding the other when we know the first is present. This may
be of importance sometimes to the breeder because some easily
seen character may be responsible for, or indicative of, the
presence of a desired, but unseen character. Thus a certain
shaped kernel of corn (one with a large germ) is known to run
high in oil content, one with large endosperm high in starch.
To select kernels with large germs is much easier than to analyze

Appendix E

415

many ears by chemical methods. Or if, after a relation had
been established, we could safely choose the longest or tallest
bean plants right in the field and know that they will bear the
greatest number of pods, it would be of great advantage to the
breeder.

Now, an exact determination of the degree of correlation can
be obtained by the biometrical method. Let us follow the pro-
cess step by step, using our bean data.

First of all, we take our data for the two characters for which
we wish to find the correlation, length of plant, and number of
pods.

Our original observations will be somewhat as follows : —

No. OF OBSERVATION
(OB PLANT)

LENGTH OP PLANT IN CM.

No. OF PODS

1

27

32

2

46

27

3

18

45

etc.

etc.

etc.

In finding the constants — mean, standard deviation, etc., for
each of these characters, the observations for length and those
for number of pods were distributed in separate tables. Now,
however, we distribute both sets of observations on one table,
in what are known as arrays of a correlation table. (See Table
1.) For example, the first observation tabulated above would
fall in the vertical array 25-34, as regards length, and in the
25-34 horizontal array, as regards number of pods. The second
observation would fall in the 5th column (vertical array 45-54)
and in the third row (horizontal array 25-34).

Thus each vertical array would be a frequency distribution
of length of plant with respect to number of pods, and each

416 Plant-Breeding

horizontal array would be a distribution of number of pods
with respect to length of plant. But if we add up all the fre-
quencies along each horizontal array, we will get the frequency
distribution with respect to the number of pods and it will be
exactly the same as that found in the preceding exercise (see
table on p. 404) ; likewise, if we add up the frequencies in the
vertical arrays, we will get the frequency distribution with
respect to length of plants.

The various steps by means of which the constants for length
of plant and those for number of pods were obtained were
given in the preceding exercise and need no repetition. They
are here secured by the " short method" and are given in the
correlation table. We are here concerned with the finding of
the constant which will express the degree of correlation between
these two characters.

The only new feature of this correlation table, aside from the
method in which the observations are distributed, is the column
marked SP. Each element of this column represents the total
deviation (from the assumed mean, or guess) of the individuals
in each array with respect to both length of plant and number of
pods. Thus, taking the first horizontal array, the 5-14 class
as regards number of pods, we wish to find how much the in-
dividuals in this class deviate from the assumed mean for length
of plants. It is found as follows : —

3 individuals each deviated by — 30 = — 90
9 individuals each deviated by — 20 = — 180
3 individuals each deviated by - 10 = - 30 - 300
1 individual deviated by + 20 = 20 + 20

Algebraic Sum = - 280

All the individuals in this array deviate from the assumed
mean for length of plants by the algebraic sum of the total minus
deviations and the total plus deviations, which is - 280, as
indicated. But each individual in this array with respect to

Appendix E 417

length deviated by — 20 from the assumed mean with respect
to number of pods, and hence we must multiply — 280 by — 20
to find the total deviation from both assumed means and this
gives us + 5600.

All the elements in the 2P column are secured in exactly the
same way. The third element is zero, since the deviation from
the assumed mean for number of pods is zero in this case. The
fourth element comes out a minus quantity according to the
following calculation: —

1 x -30 = -30 18 x 10 = 180

11 X - 20 = - 220 5 x 20 = 100

42 x - 10 = - 420 2 x 30 = 60

33 x 0 0 1 x40 = 40

^670 2 x 50 = 100

480

- 670 + 480 = - 190 x 10 = - 1900.

The algebraic signs for each quantity must be carefully ob-
served throughout the calculations.

Finally, the algebraic sum of all the elements in the SP column
is determined.1 This will give us the grand total deviation from
both assumed means for all the individuals, and hence to find
the deviation for each individual we must divide by 500. Per-

33100
forming the operation we get = 66.20.

oUU «

Now all along we have been working from an assumed mean,
or guess, and we must apply a correction, which, mathematicians
tell us, must be the product of the correction for length by that

1 The elements of the SP column can be obtained by finding the total
deviation of each vertical array with respect to number of pods and
multiplying by the deviation of that array with respect to length, instead
of vice versa. The elements will be different, but their sum will be
exactly the same by either method.

418

Plant-Breeding

11

g i
§ s
o

0,

8

CO

co

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00 CO CO O CO , — ,
r-J CO CO 2 CO §

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II II II II II II

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0098

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5

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<N

-ssss-

0691 - 09SS -

OZl -

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II 1 1 1 1 1 1
lO iQ iO *O *O *O *O *O

I

O-A

(O-A) J

M-An

spoj jo jaqran^ 9- 68 = O

Appendix E 419

for number of pods. This product is always subtracted from the

2P.
quotient of — '

66.20 - (1.88 X - 1.56) = 69.1328.

Now this corrected deviation must be secured in terms of the
standard deviations for each character, and hence this quantity
69.1328 is to be divided by the product of both standard devia-
tions : —

69:1328

14.9789 X 12.0360

. 3835.

We have now finally arrived at our correlation coefficient,
designated universally by the letter r, the formula for the deter-
mination of which is as follows : —

Correlation Coefficient (r) =

o-2

Like all other constants the correlation coefficient must be
accompanied by its probable error, the formula for the finding
of which is as follows : —

-6745 (! - r2

Solving this for our correlation coefficient, we find the prob-
able error to be ± .0257.

The amount of confidence which can be placed in the corre-
lation coefficient depends upon the size of its probable error
largely. Biometricians say that in order to be of much value,
the coefficient must be from five to ten times as great as its
probable error. But whether the coefficient shows a high, low,
or intermediate degree of correlation between the two charac-
ters measured depends entirely upon its position with reference
to its two limits, 0 and + 1 or 0 and - 1. According to the

420

Plant-Breeding

size of r found for the data used in our problem, the correlation
existing between the length of plant and its number of pods is
not great.

EXERCISE 4

Statistical Study of Apples from Different Trees

Object. — To study the individuality of fruit trees.

Materials. — Apples representing the total product of different
trees; scales; calipers.

Fill in the following form for each tree. Plot curves repre-
senting the entire population of trees.

NAME OF VARIETY

Tree no

Age of tree

Condition of tree . . .
Total number of apples
Number of marketable apples
Total weight of apples . . .
Weight of marketable apples
Average width of 50 apples
Average length of 50 apples

Color

Any other noticeable differences

EXERCISE 5
Statistical Study of Branches of Different Trees

Object. — To continue the study as outlined in Exercise 4,
to test the individuality of trees.

Materials. — Fruit trees of different kinds, preferably dwarf
trees; tapes.

Measure the new growth of various parts of each tree and of
different trees. Plot curves of each tree and of all of the trees

Appendix E

421

FIG. 108. — A common form of ragweed.

422

Plant-Breeding

FIG. 109. — Another form of ragweed.

Appendix E 423

as a population, to show graphically the extent of bud variation
present.

EXERCISE 6

Statistical Study of the Quantity of Grapes from Different Grape

Vines
Use the same general method as in Exercise 4.

EXERCISE 7

Study of Variation in Pressed Specimens of Ragweed or Some
Plant showing Many Different Types

Object. — Careful study of the large and small variations among
different biotypes of ragweed (Ambrosia artemisiifolid) .

Materials. — Specimens of many different types of the above
plant or any species of plant which is rich in biotypes. These
specimens should be carefully pressed and mounted. (See Figs.
108 and 109.) Have each student make detail drawings to show
minute differences.

EXERCISE 8

Study of Bud Variations and Reversions in Ferns

Object. — To determine the nature and amount of reversion
from the parental type, and if possible to find some cause for
the same.

Material. — Obtain specimens of the sword fern (Nephrolepis
exaltata) and Boston fern (Nephrolepis bostoniensis) and as many
of the other ferns named below as possible.

Study the trueness to type of each variety and any reversions
which they may contain. Draw typical specimens.

The following is the history, according to Cogswell, of some
of the fern varieties. This is not a complete list but gives
an idea of the origin of a few common horticultural varie-
ties.

424

Plant-Breeding

INTRO-
DUCED IN

SPORT OP

Nephrolepis bostoniensis

Nephrolepis Piersonii
Nephrolepis elegantissima ....
Nephrolepis Scottii ....

(about)
1880

1903
1904
1904

nephrolepis
exaltata
(sword fern)
bostoniensis
Piersonii
bostoniensis

Nephrolepis Barrowsii
Nephrolepis Whitmanii
Nephrolepis todeaoides
Nephrolepis superbissima ....
Nephrolepis Scholzelii

1905
1906
1907
1908
1909

Piersonii
Barrowsii
Whitmanii
Scottii
Scottii

Nephrolepis Pruessneri
Nephrolepis magnifica
Nephrolepis elegantissima compacla .

1909
1908
1909

Whitmanii
Whitmanii
elegantissima

EXERCISE 9
Study of the Morphology of Different Kinds of Flowers

Object. — To acquaint the student with floral parts and their
functions. To determine the proper condition of the buds and
flowers for emasculation, crossing, etc.

Material. — Buds and flowers of various kinds and in different
stages of development; microscope or hand lens; set of dis-
secting instruments. The material should represent different
natural families or orders.

Have the students make careful drawings of the floral organs,
of various types of flowers. Take special care to distinguish
the stamens and pistils.

The following outline by Dr. M. J. Dorsey may be found
helpful in this exercise : —

Appendix E 425

STUDY OF FLOWERS (prerequisite to crossing)

Flower —
Non-essential organs —

Calyx — composed of sepals.
Corolla — composed of petals.

Essential organs —

Pistil - f carpels,

a, style ; b, stigma ; c, ovary < placenta.

I ovules.
Stamens — composed of

f loculus or cell.
a, filament ; b, anther < ..

Degree of cross-relationship. —

1. Self- or close-fertilization. (Occurring in perfect or her-
maphrodite flowers.)

2. Cross-fertilization. (Between individuals of same species
or variety.)

3. Hybridization. (Between species and sometimes between
varieties which are very distinct.)

Causes of sterility. —

1. Stamens and pistils maturing at different times. (Di-
chogamy.)

2. Lack of affinity between pollen and stigma.

3. Scanty or insufficient pollen.

4. Lack of viability of pollen.

Relative position between stigma and anthers. —

1. Stigma and anthers the same height.

2. Stigma above anthers.

3. Stigma below anthers.

426 Plant-Breeding

Relative maturity of pistil and anthers. —

1. Both maturing at same time.

2. Stigma matures first — protogyny.

3. Anthers mature first — protandry.

Methods of pollination. —

1 . Insects.

2. Wind.

3. Water.

4. Self-pollination.

Types of plants in regard to sex. —

1. Monoecious (both sexes on same plant).

2. Dioecious (each sex on different individuals within the
species or variety).

3. Polygamous (perfect and imperfect flowers on the same plant) .

Types of flowers in regard to sex. —

1. Imperfect (1) Staminate — bearing only stamens.

(2) Pistillate — bearing only pistils.

2. Perfect or hermaphroditic — bearing both stamens and
pistils. Determine the following : —

(a) Number of parts of flower. —

a, sepals ; b, petals ; c, stamens ; d, pistils.
(6) Type of flower — perfect (hermaphrodite) or imperfect.

(c) Relative position of stigma and anthers.

(d) Relative maturity of pollen and stigma.

(e) Is the flower pollinated by insects, wind, or self ed ?
(/) Draw the essential organs and label each part.

EXERCISE 10

Technique of the Cross-pollination of Plants
This exercise may be carried out in the winter in a green-
house or conducted in the fall and spring out of doors, where

Appendix E 427

additional expense is not involved in growing the plants under

The following suggestive directions may be given to each
student : —

Materials. — 1. Instruments: tweezers; scalpel; small, sharp-
pointed scissors, hand lens, etc.

2. For covering flowers: Manila bags, waxed paper bags,
cheese cloth, etc. Wire labels, stringed tags, fine copper wire
or twine cut into short lengths may be used to fasten the bags.

Preliminary study of plant. —

Before attempting to cross plants, it is necessary to know the
structure of the flower to be used. To do this (A) locate
all parts — sepals, petals, anthers, filaments, stigma, style,
ovary; (B) determine whether the flowers are perfect or
imperfect; ((7) learn to recognize the "ripe" or receptive
condition of the stigma and pollen.

Technique. —

(A) Emasculation. (Unnecessary where stamens and pistils
are borne on different flowers.) For crossing purposes
select flowers in which the anthers have not opened. Re-
move the anthers with tweezers or scalpel, taking care not
to injure the stigma. It may be necessary to remove part
or all of the petals in some flowers in order to get at the
anthers, but it is best to remove only the anthers, if possible.

(B) Bagging. After the anthers have been removed, the
flower should then be covered with some material, as a
manila or oil paper bag, to prevent the entrance of foreign
pollen. When the stigma is receptive, remove the covering,
pollinate with the desired pollen of known purity, and im-
mediately cover again, leaving cover on until fertilization
has taken place — as indicated by withered or brownish
stigma. It is desirable to remove the covering when the
cross has "set."

428 Plant-Breeding

(C) The record. The record should include a description of
each parent, giving particular attention to the contrasted
characters. Colors may be recorded by comparing with a
standard color chart. The female parent should always be
mentioned first. The record on the label should include
variety name or number of each parent, date of emascula-
tion, and pollination. (Name of worker can also be placed
on the label.) As far as possible reciprocal crosses should
be made.

EXERCISE 11

Embryological Studies from Slides showing Cell Division at Dif-
ferent Stages, Chromosomes, Pollen Mother-cells, Development
of the Embryo-sac, etc.

Provide each student with a high-power microscope and mi-
croscopic slides mentioned above. Careful drawings of each slide
should be made.

EXERCISE 12

Study of Pollen Germination and Fecundation

Materials. — Fresh and preserved flowers showing structure
of carpels in cross and long section ; microscopic slides showing
growth and penetration of pollen tubes into ovary, fecundation,
etc. For study of germinating pollen, fresh pollen may be
germinated in sugar solutions of various strengths mounted in
the cells of hanging-drop slides. If this is done at the beginning
of the practicum, the germinated pollen will be ready for ex-
amination before the end of the period.

Careful drawings of all stages observed should be made. The
drawings should show all the differences in the length and size
of the pollen tube in various degrees of concentration of the sugar
solutions. Note also the effect of temperature and other external
influences upon germination.

Appendix E 429

EXERCISE 13

Practice in the Cross-pollination of Apples, Pears, Peaches,

Plums, etc.

To be carried on in the spring, when the trees are in bloom.
For general methods of procedure, see Exercise 10.

EXERCISE 14

Purpose. — To teach the Laws of Probability ; dominance
and recessiveness ; segregation and recombination; presence
and absence hypothesis; inhibitory factors; complementary
factors ; inversed ratios, etc.

Materials. — Coins, wrinkled and smooth peas, both yellow
and green hi equal numbers for two character pairs ; yellow and
white kernels of both dent and flint corn; a pack of playing
cards ; and chemicals.

Program. — The instructor should take special care to make
clear the significance of each step in the exercise and their con-
crete application to problems of plant-breeding and genetics.

1. The Law of Probability is taught by tossing coins. Each
student should toss one coin for 2 or 3 minutes and record the
number of tunes it falls head, and the number of times tail.
Then the total for the whole class is summed up. It will be
found that the latter count, including more tosses, approaches
the theoretical ratio much more nearly. This should be ex-
plained by the instructor.

2. Then in the same way two corns may be tossed by each
student. He now records heads ; heads and tails ; tails.

The application of this law in the formation of gametes should
be made clear by the instructor.

3. Now the material may be changed by way of illustration.
Peas or corn comprising two allelomorphs may be used for this
exercise. They are mixed together in equal numbers in a bag

430 Plant-Breeding

and each student draws blindly from the bag one seed at a time,
recording his draw. This exercise illustrates segregation and
the formation of gametic cells.

4. Now each student may remove simultaneously one pea
from each of two bags, and lay them down side by side to illus-
trate the mating of gametes in an FI hybrid and the subsequent
recombination of characters. He should record only the domi-
nant characters present in each pair taken and his record will
show the phenotypes of his F2 hybrids.

5. The same principles can be illustrated by the use of a pack
of playing cards. Draw at random two cards at a time. Record
each combination observed. Two blacks coming simultaneously
represent a homozygous black individual; a black and a red
represent a heterozygous form appearing as black, two reds
represent a pure recessive. For illustrating the combination of
two character pairs, four cards may be drawn at a time.

6. Some simple chemical reactions 1 afford an excellent series of
demonstrations illustrating the main features of Mendelism.
The following apparatus and chemicals are required : —

4 500 cc. flasks 3 dozen test tubes

1 100 cc. flask 4 small funnels for burettes

1 100 cc. graduate 1 iron stand and clamps

4 50 cc. burettes 3 test tube racks

1 2 cc. pipette 1 pipette dropper

500 cc. 10% cp. NHAOH 500 cc. 5% cp. HCl

500 cc. 25 % cp. NHtOH 100 cc. 2 % litmus powder

500 cc. 10% cp. HCl solution

10 cc. phenolphthalein

While the burettes are not absolutely necessary, they will
greatly facilitate the demonstrations. The solutions are to be
made up beforehand by the instructor, who should try some pre-

1 This portion of the exercise is based on an article by G. H. Shull,
"A Simple Chemical Device for illustrating Mendelian Inheritance,"
Plant World, 12: 145-153, 1909.

Appendix E

BEMaV5Tf7AT/ON
AND OF

431

UOMINANCE

/? Zyga&s

nu

U7=?

77/7

FIG. 110.

432

Plant-Breeding

OF FffESENCE AM7 A05ENEE
A/VH UF

H

/T Zygafes
A A

A a

A a

aa VT'

fl

FACTUffS

A B

ft

FIG. 111.

Appendix E . 433

liminary experiments to see whether or not the strengths of the
solutions are correct. They may have to be varied slightly.
The contents of each test tube representing a gamete (labeled in
the accompanying figures) are given below. In order to secure
the simple 3 : 1 or 1 : 3 ratio in F2, eight test tubes representing
the gametes of FI are necessary in each case. It is of course
impossible to represent the phenomenon 'of segregation in FI
by using the test tube labeled FI. The instructor will have to
explain that after segregation the gametes are exactly the same
in nature as those of the original parents of the cross, and that
the hybrid FI now forms gametes similar to those of both parents,
in equal numbers.

(a) Demonstration of 'Allelomorphism and of Complete
Dominance (Fig. 110).

D contains 10 cc. 10 % HCl + 2 cc. litmus solution.
R contains 10 cc. 10% NH^OH + 2 cc. litmus solution.

The dominance of blue over red can be shown by substituting
5% HCl for the 10 %.

(6) Demonstration of the Presence and Absence Hypothesis
and of Intermediacy (Fig. Ilia).

A contains 10 cc. 10 % NH^OH + 2 drops Phenolphthalein.
a contains 10 cc. 5 % HCl.

(c) Demonstration of Complementary Factors (Fig. lllb).
A contains 10 cc. 10% NH4OH.
B contains 10 cc. H -20 + 2 drops phenolphthalein.

Dominance of a character has usually been taken to be indica-
tive of the presence of a positive factor determining that char-
acter. But in some cases the absence of a factor, e.g. cases of
awnlessness in wheat, or hornlessness in cattle, seems to be
dominant over its presence. To say that the absence of a thing,
in other words a purely negative condition, is dominant over its

434 Plant-Breeding

OEMO/VSTffAT/ON OF THE PflttENCF OF AW MB/TOff FATTUfl
A

A i

Ai

AI

A i

A /

AI

/? Zygofes
A A //

A Alf TF

A AH

ffT "1

^
, 1

A All

v<^

i

^ /7

FIG

12.

Appendix E 435

presence seems an absurdity. However, to make the facts
consistent with the presence and absence hypothesis, two expla-
nations are offered. One consists in assuming the presence of a
positive inhibitory factor, which prevents the production of the
character concerned. The other consists in assuming that one
"dose " of the factor concerned is insufficient to produce the
result, hence in its simplex or heterozygous condition, the char-
acter determined by the factor fails to appear, and it is only
when the factor is in the duplex or positively homozygous con-
dition that it does appear. The first of these explanations is
embodied under demonstration (d). The last is embodied
under the demonstration entitled "Explanation of So-called
' Dominance of Absence.' "

(d) Demonstration of the Presence of an Inhibitory Factor
(Fig. 112).

A contains 10 cc. 2.5 % NH^OH + 2 drops phenolphthalein.
Ai equals A + 5 cc. 10 % HCl.

(e) Explanation of So-called "Dominance of Absence"
(Fig. 113).

A contains 10 cc. 10% NH4OH + 6 drops phenolphthalein.
a contains 10 cc. 10 % HCL

After the zygotes of F2 are obtained, in this last demonstration,
the instructor should add 10 cc. — 10 % NH^OH to each Aa
zygote of F2 to show that another "dose " of factor A will now
produce the result.

EXERCISE 15

A Study of Mendelian Characters in Timothy and Oats

Purpose. — To afford the student concrete illustrations of
Mendel's laws ; to find unit characters in plants and to see their
segregation and recombination.

Materials. — Mature timothy plants of various strains, com-

436

Plant-Breeding

O/= 50-rALLEU

A a. TTr

<•-.!

/?

s

Zygofes

A A

fl

A a.

F

r<

e

A a

D.O.

FIG. 113.

Appendix E 437

prising as great a variety of unit characters as possible. A small
bundle of stems for each student containing samples from different
plants. Photographs and mounted specimens. Varieties of
oats comprising various unit characters that may be readily
distinguished in hybrid plants, such as black and white grains,
side and panicled types of inflorescence; also bearded and
beardless varieties of wheat or barley. Specimen plants of
parent types should be available for inspection, also specimens
of the FI plants. A large number of F2 plants resulting from each
cross studied should be available for examination by the class.

Program. — 1. The instructor should first explain the purpose
of the afternoon's exercise and outline the order of procedure.
Unit characters are to be studied and illustrated with timothy
and oats or barley. Dominance, recessiveness (or presence and
absence), segregation, and recombination can be illustrated here.

2. At this occasion a talk may well be given on artificial
crossing of small cereals for the purpose of creating new varieties.
The instructor may describe the inflorescence of the oat plant,
and the technique of making crosses in these plants. He should
illustrate the talk with charts and with diagrams made on the
blackboard.

3. Mounted specimens of oat types together with the FI and
F2 progeny resulting from their crossing may be handed around
for examination by the class. If enough mounts are available,
the specimens may be drawn and described by each student.

4. Composite samples of timothy should be handed to each
student. He should study them to see what diversity of unit
characters can be found there, in the nature of differentiating
botanical characters. A list should be made of all the unit
characters observed. Drawings of timothy heads may help to
train his observation and fix the idea.

5. A large progeny of Fz oat plants should be distributed
among the class after the parent types have been shown and their
differentiating characters discussed. The class may now examine

438 Plant-Breeding

the plants given to them, and sort out the segregated characters.
When sorting has been completed, the counts for the whole class
may be ascertained. It should serve to illustrate the expected
theoretical mendelian ratio.

Remarks. — Timothy affords very good material for this prac-
ticum, especially when bundled and mounted specimens, together
with photographs, are available.

Oats exhibit excellently contrasted unit characters, but expe-
rience shows them rather poorly adapted for class study, except
when mounted specimens are used. The reasons for this are : —

1. Side and panicled characters — the specimens are often
pressed out of shape, due to drying and storing, and are, therefore,
difficult to distinguish.

2. Color. — Black oats crossed with white give oats of inter-
mediate color which are often difficult to distinguish from black.
White and yellow are impossible of being distinguished by the
inexperienced student. Moreover, color in oat hulls varies
greatly with the seasonal conditions under which it was grown.

3. Plants are likely to become broken up in handling, thus
spoiling the count when mendelian ratios are expected. The
first two of these objections can be obviated by using mounted
specimens. Other characters such as naked, hulled, awned, and
awnless can be illustrated in this way. Probably a better exer-
cise would be given by substituting corn for oats.

EXERCISE 16

Mendelian Problems

Purpose. — To enable students to become familiar with what
might be called the mechanics of mendelism by working out
mendelian problems by the method of squares.

Problem. — Given : Two pairs of contrasted characters —
Tall vine (T), dwarf vine (t) ; Yellow seeds (F), green seeds (y) .
Tallness and yellowness are completely dominant characters.

Appendix E

439

1. What gametes will be formed by an J^i hybrid individual
from the cross between tall, green and dwarf, yellow ?

2. How many offspring will it be necessary to grow in order
to allow every combination to appear in the second generation ?

3. How many genotypes will there be ?

4. How many pheno types will appear ?

5. In what ratio will the pheno types appear?

6. How many pure dominant individuals?

7. How many pure recessive individuals ?

8. If the combination T X t gave plants of medium height
when a tall plant with yellow seeds is crossed with a dwarf plant
with green seeds, how many genotypes will appear in F^ How
many pheno types ? In what ratio ?

Illustrative problems. — The following problems may be studied
by way of illustration. These are taken from actual cases with
the tomato, but will apply in principle to other plants, by sub-
stituting other unit characters : —
Problem 1.—

Tall, homozygous (T) X dwarf, homozygous (t) = Tt ; FI

FI gametes = T ; t

F! self ed =

POLLEN-GRAINS

T

TT

tT

EGG-CELLS

Tt

440

Plant-Breeding

Phenotypes (visible types) (2n) = 3 TT ; 1 tt.
Genotypes (actual types) (3n) = 1 TT ; 2 Tt ; 1 «.

Problem 2. -

Heterozygous Tall (TO X homozygous dwarf (tt).

Whenever a plant which is already heterozygous is used as a
parent, its gametes will become segregated during their formation,
and when the crossing takes place more than one kind of progeny
will be produced. In this case the female parent will produce
two kinds of egg cells, namely, tall and dwarf.

Graphically, this cross may be represented as follows : —

EGG CELLS

POLLEN GRAINS
t t

Tt

Tt

tt

tt

The male parent is pure dwarf, therefore all of the pollen grains
will represent dwarfness only.

Phenotypes = 2 Tt; 2 tt.
Genotypes = 2 Tt ; 2 tt.

If the female parent were crossed with a homozygous tall
instead of a dwarf, the visible types the first year after crossing
would all appear the same (tall) instead of two kinds as above.
There would be

Phenotypes = 4 TT.

Genotypes = 2 TT7; 2 Tt.

Appendix E

441

Problem 3. —

The cases Which have been considered hitherto show perfect
dominance of one unit over another. This is not always the
case. It frequently happens that the first generation hybrid
is intermediate between the two parents, and in the second gen-
eration the heterozygote forms differ from either homozygous
form. Thus when large, round tomatoes are crossed with small,
plum-shaped ones, the FI hybrid is intermediate between the
parents. If L represents largeness and (I) small, plum-shaped,
then F! hybrids (LI) will not be the same as (LL), but will be
distinctly different. The formulae previously given, 2", 3n, etc.,
will not hold in cases of incomplete dominance. This will be
more fully explained later. Large (L) X small, plum-shaped
(/) = LI, an intermediate type of fruit.

gametes
self ed

POLLEN GRAINS

EGG CELLS

LL

LI

LI

Phenotypes = 1 LL; 2 LI; III
Genotypes = 1 LL; 2 LI; III

Problem 4. —
Intermediate (LI) X Large, round (LL)

442

Plant-Breeding

POLLEN GRAINS
L L

EGG CELLS

LL

LI

LL

LI

Phenotypes = 2 LL ; 2 LL
Genotypes = 2 LL', 2 LI

Problem 5. —

Tall, smooth (Th) X dwarf, Hairy (tH) = Tall, Hairy (TtHh)
Fi gametes = TH ; Th; tH ; th.

Fi self ed =

POLLEN GRAINS

TH Th tH th

TH

th

TT

TT

Tt

Tt

HH

Hh

HH

Hh

TT

TT

Tt

Tt

Hh

hh

Hh

hh

Tt

Tt

tt

tt

HH

Hh

HH

Hh

Tt

Tt

tt

tt

Hh

\ hh

Hh

hh

Appendix E

443

Phenotypes (2W) = 9 TH ; 3 Th; 3 tH ; 1 th.
Genotypes (3W) = 1 TTHH, 1 TThh, 1 tf##, 1 ttM, 2
2 tt#A, 2 Tthh, 2 7W#, and 4 TtHh.

Problem 6. -

Tall (Heter) 1 smooth (m) X dwarf, Hairy (tH).
Female gametes = Th, th.
Male gametes = tH.

POLLEN GRAINS
tH

EGG CELLS

Th

th

TtHh

ttHh

It will be seen that two types are produced the first year after
crossing instead of the one where pure parents are used. Segre-
gation takes place immediately in the female parent because of
its hybridity, and two kinds of gametes will be produced.

In order to get a comparison with the Fz when pure parents
are crossed, it is necessary to self both types as follows : —

(a) TtHh produces gametes as follows, Th, Th, tH, th. These
are the same as in problem 5 and hence the resulting plants will
be:-

Phenotypes = 9TH,3 Th, 3 tH, 1 th.

Genotypes = 1 TTHH, I TThh, I ttHH, 1 tthh, 2 TTHh,
2 ttHh, 2 Tthh, 2 TtHH, and 4 TtHh.

(6) ttHh produces the following gametes : tH, th.

1 "Heter" is used for short in place of heterozygote, similarly " homo "
is used for homozygote.

444

Plant-Breeding

tH

EGG CELLS

POLLEN GRAINS

tH th

it
EH

tt
Hh

it
Hh

tt
hh

th

Phenotypes = ttHH, tthh.
Genotypes = ttHH, 2 ttHh, 1 tthh.

Problem 7. —

Tall, large-round (TL) X dwarf, small plum-shaped (tl) = Tall
intermediate (TtLl).

Fl gametes = TL; Tl] tL; tl.

POLLEN GRAINS
TL Tl tL tl

EGG CELLS

TL

Tl
tL

tl

TTLL

TTLl

TILL

TtLl

TTLl

TTll

TtLl

Till

TILL

TtLl

ItLL

ttLl

TtLl

Till

ttLl

till

It must be remembered in this problem that we have incom-
plete dominance in one allelomorphic pair, therefore the number
of visible types is different than in cases where both units exhibit
dominance.

Appendix E

445

Phenotypes = 3 TTLL, 6 TTLl, 3 TTll, 1 ttLL, 2 ttLl, 1 till

Genotypes = 1 TTLL, 1 TTtf, 1 tfLL, 1 till, 2 TTLl, 2 Ttll,
2 Ttll, 2 ttLl, and 4 m/.

What visible types would be produced if incomplete dominance
occurred in both characters?
Problem 8. -

Self-fertilize-Tall, intermediate (TTLl). This is a pure tall,
hence all of its progeny will be tall.

POLLEN GRAINS
TL Tl

EGG CELLS

TL

Tl

TTLL

TTLl

TTLl

TTll

Phenotypes = 1 TTLL, 2 TTLl, 1 TTll.
Genotypes = 1 TTll, 2 TTLl, 1 TTll.

EXERCISE 17
Ear-to-Row Test with Corn

Field Practicum

Purpose. — To demonstrate to the student the method of
testing out the transmitting power of individual plants; to
show him how a breeding plot should be arranged for corn ; to
teach him how to harvest the corn and make notes on which
to base his selections. A practical demonstration of the method
of pure line selection.

Materials. — For each student a sack for holding ears, wired
tags and strings for tying sacks, and sheets for taking data. A
wooden rack with spikes for drying ears of corn. Grocery scales
for weighing the ears from each row.

446

Plant-Breeding

DATA SHEET FOR CORN SELECTION

(Ear-to-Row Method)
Mark Dent (+) ; mark Flint (7).

No. of row

Total no. of hills

Total no. of stalks

No. barren stalks

Total no. of ears

Total wt. of ears

No. mature ears

Wt. mature ears

No. immature ears

Wt. immature ears

Percentage mature ears

Percentage immature ears

Choose 10 of the best-looking ears from one row on which to
take the following data : —

Wt. of ears
Length of ears
Circumference l of ears
No. of rows per ear
Wt. of shelled corn
Wt. of cob

A field plot planted by the ear-to-row method, saving unused
half of each ear for comparison with its progeny. It should
contain two or more rows, as space permits, for each student.
Each row should contain 50 hills. The rows should be planted

1 Circumference should be measured at a point about f of the distance
from the butt toward the tip.

Appendix E 447

and cultivated under regular field conditions. Two buffer rows
should be planted completely around the plot. These should
be cut and discarded before the interior rows of the plot are
studied. Their purpose and use should be explained to the
class.

Program. — After the instructor has explained the purpose of
the practicum, and the manner of procedure for the afternoon,
the class may be taken to .the field. Each student should have
one or two rows for himself. Students may be permitted to
work in pairs, if desirable. Careful and detailed notes should
be made on each row and recorded on data sheets provided for
that purpose. The corn may be taken back to the laboratory
for weighing. Statistics for the whole plot should then be
compiled, so that the individuality of different rows can be
compared. The student should select 10 of the best ears from
each of his rows and put them on the drying rack provided.
These ears are to be used later for a study in the laboratory.

EXERCISE 18

Corn-judging

Students of plant-breeding should be trained to have a critical
judgment of agricultural and horticultural plants. Exercises
in comparative judging are the best way to attain this end.
Utility should be kept constantly in mind.

Details of corn judging will not be given here; they are too
well known to need emphasis. For the East,, both dent and
flint varieties should be used. The ears which are judged in
this exercise may be the ones the student himself has previously
harvested from the ear-to-row plot. The best ten ears should
be used for Exercise 19, which should always accompany exer-
cise 18.

Object. — To encourage critical judgment of corn and, by the
same means, of other crops.

448 Plant-Breeding

Materials. — Ten ears of different races and types of corn to
each student ; tape, scales, charts, etc.

Each student should score a sample of flint corn according to
the following score card : —

New England Flint

POINTS

Maturity and seed condition 20

Uniformity (or regularity of single ears) 15

Kernels 15

Weight of ear 10

Length and proportion 10

Tips 5

Butts 10

Sulci (space between rows) 10

Color 5

Total 100

EXERCISE 19

Statistical Study of Ears of Corn

This should accompany or follow Exercise 18.

Object. — (a) To study critically and statistically the various
parts of ears of corn. (6) To work up these data by biometrical
methods, drawing curves, and ascertaining mean, standard
deviation, coefficient of variability, etc., for the various parts
of the ear. (c) To illustrate testing for germination.

Materials. — Each student should be given the same ears of
corn which he had for Exercise 18 ; tapes, scales, etc.

The following form should be filled in by each student : —

NOTE. — This should not be merely a mechanical process, but
the student should give each step very careful thought. These
tables are given to assist in organizing the student's method and
his thinking, but not to replace them. Do not study the method
but the plants. Consider carefully the significance of each step.

Appendix E

449

STUDY OF CORN
Variety : Dent, flint, sweet, pop. (Underline.)

Where grown
(a) Length of ear in cm.
(6) Circumference of ear in cm. (£ butt to
tip)

(c) Weight of ear

(d) Number of rows

(e) Circumference of cob (£ butt to tip)
(/) Weight of shelled corn

(g) Weight of cob
(h) Percentage of shelled corn
(?') Total number of kernels
(j) Average weight of kernel
(k) Width of kernels in cm. (taken at ran-
dom)

(I) Compute average width
(ra) Length of 50 kernels in cm. (taken at

random)
(n) Compute average length

EXERCISE 20
Study of Correlations of Characters in Corn

Use the same data as employed in Exercises 17 and 19. Make
correlation tables by accepted biometrical methods of such
characters as length and circumference; length and number of
grains ; weight and number of grains ; length and weight ; etc.
Work out correlation coefficients.

Object. — To find out if certain characters are associated so
that a measurement of one will give an indication of the other.

Materials. — Data from Exercises 17 and 19 ; cross-section
paper.

2c

450 Plant-Breeding

EXERCISE 21

Corn Selection — Laboratory Study

Purpose. — To give the student an understanding of the
qualities that constitute a good ear of corn ; to teach the bene-
fits and dangers of cross-pollination.

Material. — For each student : 1 tape measure ; 1 scalpel ;
1 hand lens; 10 ears of corn selected from a row in breeding
plot; samples of various types and colors of corn. These
should have been shelled and soaked in water for 24 hours pre-
vious to this laboratory period in order to render them easy to
dissect. Cobs of corn bearing mixed kernels to illustrate zenia ;
scales ; data sheets ; germinator.

Program. — The instructor should first explain the purpose
of the practicum and outline the afternoon's work. He should
explain the structure of a kernel of corn, calling attention to
the difference between the various types of corn and the ad-
vantage of certain shaped kernels. Fecundation should be
thoroughly discussed, and its effect in causing zenia. Illustrate
with diagrams, charts, and specimens.

Discuss the dangers of mixing varieties by close planting.
The danger of close fertilization and the stimulus resulting from
cross-fertilization should also be discussed.

The advantage and manner of making germination tests
should be explained.

The student should remove 6 kernels from each ear and place
them in the germinator to be examined later, at which time he
should record the percentage of germination.

Questions and problems concerning zenia printed on the
outline sheet should be answered in a written report.

Laboratory Directions for Corn Study

1. Complete taking data on 10 ears of corn. Compare with
remnant half of parent ear. From your data select the best
3 ears for breeding purposes.

Appendix E 451

2. Remove 6 kernels from each ear for germination test,
along a spiral line from 1 inch of butt to near the top, revolving
the ear twice.

3. Draw a typical kernel.
(a) Face aspect.

(6) Side aspect.

4. Make and draw longisections through the middle line
both ways of the kernel, showing the following structures: —

(a) Mass of starch or endosperm.

(6) Crescent-shaped body, the germ or scutellum near the
smaller end of the grain.

(c) Remaining portion of embryo lying in the depression

between scutellum and seed-coat.

(d) In sample kernels where does color lie, in the pericarp,

aleurone layer, or endosperm ?

(e) Note relative amount and position of starchy and
horny endosperm in

1. flint kernel,

2. dent kernel,

3. pop-corn kernel,

4. sweet-corn kernel.

5. How would an FI kernel of corn appear in a cross between

white sugar X yellow flint ?

.yellow flint X white sugar ?

white flint X purple flint ?

purple flint X white flint ?

red sweet X purple flint ?

purple sweet X red flint ?

Dominant Characters. —

Colored over white.
Yellow over non-yellow.

452 Plant-Breeding

Red pericarps may conceal purple aleurone.
Purple in aleurone over red in aleurone.
Starchy over non-starchy.

EXERCISE 22
A Study in Potato Selection

Purpose. — 1. To teach the essential characteristics of a good
tuber and a good tuber-line.

2. To teach the principles of selection by a study of variability
in pure tuber-lines.

3. To demonstrate the tuber-unit method of potato selection.

4. To study variability by means of biometrical data, and
the interpretation of constants and curves derived therefrom.

5. To fix in mind how the hills of different weights look.

6. To calculate the theoretical weights per acre when given
certain weights per hill.

First Exercise

Materials. — Printed directions and sheets for recording data.
Manila paper bags, size 12, for containing product of each hill.
Cloth bags for carrying a number of these small bags when filled.

A breeding plot planted by the 4-hill tuber-unit method,
that is, each four hills having the same progeny-number should
come from the same mother tuber, and they should be planted
and staked so that the progeny of each hill and unit can be
distinguished.

This plot should be planted in good soil and given excellent
care throughout the season as its usefulness to the class will
depend entirely on the condition of the crop at harvest time.
The rows and tuber-units should be labeled carefully and accu-
rately in a convenient way, so that they may be made an object
lesson in record-keeping.

Appendix E

453

i!

_ti i

L

felO

454 Plant-Breeding

Enough hills should be provided so that each student may
have for himself several tuber-units. Five to ten units to each
student will be enough if the student is required to observe and
compare a large number as they lie in the field. The complete
data for the whole field should be compiled by the class as a
whole, and distributed to each student for a comparative study.

Program. — Just prior to the exercise, each hill should be
dug carefully and the tubers replaced where they grew, but
exposed to sight, especial care being taken that no labels be mis-
placed nor lost. The class may then be taken to the field.
The instructor should explain the purpose of the exercise, the
principles of pure-line selection as illustrated here, and the
method of planting a potato-breeding plot by the tuber-unit
method. He should give careful instructions for the after-
noon's work. The class may then examine and compare the
units as they lie exposed in the rows. The instructor should
point out such differences as occur. A certain number of tuber-
units should then be assigned to each student, and he should
be required to take data from these units, as directed on the
printed sheets provided. Such data-taking as involves the use
of apparatus will necessarily have to be postponed until the
following period, when it can be done in the laboratory.

Each student should carefully preserve his tubers properly
labeled for the next laboratory exercise.

Second Exercise

Materials. — Data taken in Exercise 1 ; the tubers collected
in Exercise 1 ; scales ; paper plates (6 for each student) .

Program. — The instructor should first outline the afternoon's
work. He should explain the qualities that constitute a good
tuber ; also how that ideal form, size, and color differ in various
varieties. He should explain a score-card.

The students may now proceed to finish taking the data on
the tubers that they collected at the previous laboratory period.

Appendix E 455

When the data are complete, they can all be summed up for
each tuber-unit and the units compared.

Each student should next make out a score-card embodying
the points of his ideal unit, and score his units by it. The
instructor may now give out a score-card by which the whole
class may score their units alike.

Make up hills weighing £, 1, 1£, .2, 3, and 4 pounds, and
draw them natural size.

Compute the yield per acre from the above weights per hill,
assuming the hills to be planted in rows 3 feet apart and 18
inches apart in the rows. One bushel weighs 60 pounds.

Directions for Report on Potato Selection

1. Distribute the data for the number of tubers per hill into
classes.

2. Determine the mode, modal coefficient, mean, standard
deviation, coefficient of variability, and their probable errors for
the number of tubers per hill.

3. Determine the mode, mean, standard deviation, and co-
efficient of variability for the number of marketable tubers per
hill, weight of tubers per hill, and weight of marketable tubers
per hill.

4. Draw Quetelet curve, showing frequency distributions for
number of tubers per hill, number of marketable tubers per
hill, weight of tubers per hill, and weight of marketable tubers
per hill.

5. Distribute into classes the data for the number of tubers
per four-hill-unit, number of marketable tubers per four-hill-
unit, weight of tubers per four-hill-unit, and weight of market-
able tubers per four-hill-unit.

6. Draw Quetelet curves, showing frequency distributions for
number of tubers per four-hill-unit, number of marketable tubers
per four-hill-unit, weight of tubers per four-hill-unit, and weight
of marketable tubers per four-hill-unit.

456 Plant-Breeding

7. Make a transmission curve from the data on the accom-
panying sheet. Which progeny units would you select for breed-
ing purposes? How do you account for the apparent discrep-
ancies which occur, such as the cases where the offspring give a
very different yield from their parents ?

8. Taking into account the number of tubers per hill, weight
of tubers per hill, number of marketable tubers per hill, and
weight of marketable tubers per hill, select the best 25 four-
hill-units. Tabulate these, giving their progeny number and
data for number of tubers per four-hill-unit, number of market-
able tubers per four-hill-unit, weight of tubers per four-hill-unit,
and weight of marketable tubers per four-hill-unit.

9. Give briefly your reasons for selecting the above four-hill-
units. Draw Galton curves for these 25 four-hill-units, showing
variation in the number of marketable tubers per four-hill-unit
and weight of marketable tubers per four-hill-unit.

10. Determine the possible yield of marketable tubers from
an acre of the highest and lowest yielding of the 150 four-hill-
units, also for the highest and lowest and for the average of the
25 selected units.

11. Give a short summary of results as shown by the con-
stants and curves and their bearing on your final selection.

12. Give direction for starting a potato breeding-plot.1

Potato Data for making a Transmission Curve

The following data have been obtained by the method out-
lined above. They represent the weights in grams of parent
hills and the average weight of their corresponding progeny.
The parent hills have been listed in the order of their weight
from lowest to highest (forming a Galton curve).

1 Reference : H. J. Webber, "Plant Breeding for Farmers." New
York Agr. Exp. Sta., Cornell University, Ithaca, N. Y., Bull. 251 :
162-171, 1908.

Appendix E

457

Nos.

PARENTS

PROGENY

Nos.

PARENTS

PROGENY

1

1077

1463

26

1588

1454

2

1106

1080

27

1588

1615

3

1106

1240

28

1616

1175

4

1361

1881

29

1616

1575

5

1361

837

30

1644

1775

6

1361

1136

31

1644

1807

7

1361

1536

32

1644

1917

8

1361

1605

33

1758

2250

9

1361

1660

34

1814

1660

10

1361

1800

35

1871

1275

11

1361

1895

36

1871

K80

12

1389

1972

37

1871

1665

13

1418

1696

38

1871

1688

14

1418

1904

39

1871

1750

15

1471

1440

40

1874

1555

16

1474

1086

41

1874

1861

17

1474

1215

42

1874

1889

18

1474

1480

43

1928

1440

19

1531

711

44

1928

1481

20

1531

1294

45

1928

1620

21

1531

1574

46

1928

1982

22

1531

1725

47

1984

1575

23

1531

1755

48

2041

1236

24

1588

1320

49

2041

1880

25

1588

1365

50

2098

2365

1 .

EXERCISE 23

Study of Citrus Hybrids

Object. — (a) To study the possibility of obtaining valuable
kinds of citrus fruits by means of hybridization. (6) To study
the structure of citrus hybrids as compared with their parents,
(c) To study the economic value of these hybrids.

Materials. — Obtain from some of the extreme southern ex-

458 Plant-Breeding

periment stations, or from nurserymen or growers, samples of
citrus hybrids, such as citranges, tangelos, and the like, and
samples of Citrus trifoliata. Purchase oranges, lemons, grape-
fruits, and tangerines from the fruit stores. Provide also for
each student, or group of students, a glass, spoon, sugar, and
water.

Compare the hybrids with their parents, with special reference
to the following points : -

(a) Fruit — size, shape, color, amount of juice, quality of
juice, condition of segments, etc.

(6) Trees (if branches or photos are available) — size, shape,
branching, kind of leaves, etc.

(c) General — length of season, resistance to cold, etc.

Squeeze out the juice from several fruits, add sugar and water,
and test the adaptability for beverage and other economic
purposes.

EXERCISE 24

Study of the Results of the Plant-to-Row Tests of Wheat, Oats,
Cabbage, Onions, or any Crop where Data are Available

EXERCISE 25

Studies of Origin of Varieties — Corn, Wheat, Apples, Plums,

Grapes, Etc.

Literature study of the history of varieties. Methods em-
ployed to originate varieties should be carefully noted.

EXERCISE 26

Field Trip to Experimental Grounds

Most experiment stations have plant-breeding experiments
under way, and if a fall inspection of the plats would be in-
structive to students, they should be taken on such a trip early

Appendix E

459

in the fall and required to make careful notes, to be written up
later in the form of a report.

EXERCISE 27

Working Plans for Practical Breeding Experiments
Object. — To familiarize the student with field methods of
breeding plants.

Outline for Timothy Breeding

First Year. — Select 10 heads of timothy and grow 50 plants
from each.

100ft.

10 rows.

40ft.

500 plants in 10 rows 100 ft.
long. Plants 2 ft. apart in
the rows.

Second Year. — Cultivate.

Third Year. — Choose several of the best plants from the best
two rows, and the one best plant from each of the other rows —
14 or 15 in all. With the seed from these, plant a "test plat,"
and plow up the original seedling plat.

60ft.

60ft.

15 rows.

Rows 4 ft. apart — plants 2 ft.
apart in the rows.

Fourth Year. — Cultivate the test plat.

Fifth Year. — Choose 2 or 3 or more of the best rows and save
separately the seed from each. Plow up the remainder of the
rows and plant to vegetables.

460

Plant-Breeding

60ft.

60ft.

4 selected rows.
Plant | acre multiplication
plat from each select row.
Seed them broadcast at the
rate of 16 pounds per acre.
Remainder of the plat utilized
for vegetables.

Sixth Year. — Use seed from multiplication plats to plant a
fairly large-sized field. Continue selection of seedlings, if de-
sired, from select rows according to above scheme.

Outline for Selective Breeding of Timothy

First Year. 1. Manner of procuring seed from starting a selec-
tion. — When timothy is ripening, go over a field and choose a
number of good ripe seed-heads from tall, robust culms which
appear to come from good plants. Also look for exceptionally
good plants from along the roadsides and fences, and whenever
they are found, preserve good heads for seed. Choose good seed-
heads from at least 10 or 12 of these good plants. Thresh the
seed from these heads, keeping the seeds from each plant sepa-
rate, and sow them immediately. No time should be lost.

2. Planting the seed. — The seed should be planted early in
August. Take small boxes about 2 feet long by 1£ feet wide
and 4 inches deep ; fill them with good soil from some locality
where there has been no timothy and thus where there is little
likelihood of timothy seed being in the soil. Pack the soil down
slightly in the box and smooth off the top, removing all lumps.
Plant the seed in the boxes in short rows, placing the rows about
2 to 2f inches apart. In planting the seed open shallow furrows
in the soil and sow the seed by hand, arranging so that the seed
will be only very lightly covered. Sow the seed as thinly as
possible in the rows and thin out later so that the plants will

Appendix E 461

stand about 1 inch apart. Sow enough seed in rows of sufficient
length, so that when properly thinned there will remain about
300 plants. If thinned to 1 inch apart, this will require rows
aggregating 25 feet long. Be careful to keep the seeds from
each head or plant separate from one another and plainly labeled.

After the seed is sown, water the seed boxes carefully, using a
fine spray, in order to prevent washing the seed out. A good
method is to cover the soil with an open mesh cloth, such as
cheese cloth, and sprinkle the water on this until the soil is
thoroughly wet. Then place the seed box in the shade in a moist
place, such as the north side of the house. It is a good practice
to keep the boxes covered with paper or glass, until the young
plants begin to appear. It is important to keep them moist at
all times. When the young plants are well up, thin them to
about one inch apart in the rows, leaving the strongest plants.

The plants should be kept in boxes until about the 20th of
September, when they should be planted in the field. About a
week before transplanting they should be gradually exposed to
the full sunlight in order to harden them up. At this time each
plant should have 2 or 3 leaves, 3 or 4 inches long.

3. Transplanting into the field. — Choose a place in the field
where the plants may remain for at least two years without
being disturbed. Set the plants two feet apart in rows that
are four feet apart. By this method the greater part of the
cultivation can be done with a horse cultivator. In transplant-
ing the seedlings from the boxes, a time must be chosen shortly
after a rain, when the soil is well moistened. The plants should
be set out about the 20th of September, if possible, so that they
may become well rooted before winter comes on. It may be
necessary to hoe them before winter, but this is not likely if the
land is well prepared before planting.

If 10 heads were originally chosen and 50 plants are grown
from each head, there should be 10 rows 100 feet long, which
would occupy a piece of land 40 X 100 feet.

462 Plant-Breeding

4. Second Year. Cultivating the seedlings. — In the spring
the seedlings must be cleaned out very early before they are
hidden by other grasses. The cultivation and hoeing must be
done at sufficient intervals to keep the ground free from weeds
and in good condition. These plants will produce a few culms
each the first summer, which should be cut as soon as they have
bloomed, in order that the strength shall go into the general
growth. Do not attempt to select the best plants the first
season. A safe judgment cannot be rendered until the second
season.

5. Third Year. Selecting the best plants. — When the plants
reach the stage for cutting in the second summer, that is, when
they are in full bloom, the final selection of the best individuals
can be made. Examine each row critically in order to determine
which head or heads have given the best progeny as a whole.
If any one or two rows are markedly superior to the others,
choose several of the best plants in each of these rows. Also,
choose the one best plant in each of the other rows.

6. Testing the selected plants as clonal varieties. — In order to
make a further test of the 14 or 15 best plants, choose another
uniform plat of fairly good soil between the 5th and 20th of Septem-
ber and prepare for planting an area of slightly over 60 feet square.
This plat should be located at some distance from any other
timothy, preferably 200 to 300 feet. Dig up each selected
plant ; divide it into slips or clons and plant this new plat with
them as before, in rows 4 feet apart. Plant one row with slips
from each selected plant, placing the plants 2 feet apart in the
rows. Transplant about 30 slips from each of the selected
plants, so there will be a single row from each about 60 feet long.
This plat may be designated as "the clonal test plat."

As soon as this clonal test plat is planted from the selected
plants, the seedling test plat may be plowed up and used for
other purposes.

7. Fourth Year. Cultivation of "clonal test plat." — The

Appendix E 463

clonal test plat should be cultivated and hoed sufficiently to
keep the weeds down and to allow the full development of the
plants.

8. Fifth Year. Selecting the best clonal rows. — When the
plants are well headed and are , about to begin blooming, the
final examination can be made. Go over each row carefully,
and examine it with reference to yield and desirability of type,
and select the superior row or rows. It will be best to retain
at least 2 or 3 of the best rows ; or more, if there is but little
difference in them. Good early-maturing and late-maturing
rows should be retained if both are present in the test plat.
When this selection has been made, cut the crop on the dis-
carded rows immediately so that the pollen from these dis-
carded rows will not contaminate, by cross-fertilization, the seed
which is being developed in the selected rows. At any con-
venient time these discarded rows may be dug up and the space
filled with new plants grown from cuttings of the chosen plants.
By a little care and cultivation these select rows can be retained
5 or 6 years as a source of supply of seed of a superior kind. As
the rows of selected types begin to run out, or become impure
by ordinary timothy plants around them, or by other grasses
growing in the clumps, other or more extended clonal rows
could be planted from them.

9. The multiplication plat. — The seed from the select rows
of the clonal test plat should be sown in the early fall, sometimes
before the 15th of September in broadcast plats, as large as the
amount of seed obtained will permit. Sow these plats, at the
rate of about 16 pounds to the acre. There should be enough
seed from each row to plant about f acre.

Sixth Year. — The seed from these broadcast multiplication
plats can be utilized the next year to plant a fairly large field
which, if desired, may be harvested for seed to plant still larger
areas. These plats may be utilized for seed for several years
before they run out.

464 Plant-Breeding

10. Continuation of the selection. — If the farmer has in mind
the continuous selection of his seed, with the view of selling his
seed as improved seed, he should plant small samples of seed
from each of the selected rows in the clonal test plat. Their
treatment and subsequent selection should be a repetition of the
original scheme outlined above.1

General Directions and Questions for Report on Corn
Breeding

Suppose you buy a farm of 200 acres on which are growing
the following crops : potatoes, corn, timothy, and one of the
three cereals, wheat, oats, or barley. There are 50 acres of
pasture and woodland. You wish to continue growing these
same crops, and at the same time to improve them by a scheme
of selective breeding. Plan the arrangement of fields and breed-
ing plots for the first 6 years, using the following directions.
Timothy breeding plots should be 200 to 300 feet from any
other timothy. Corn plots, 1200 feet from any other corn.
(Why?) Each year should be planned separately, using
maps and diagrams, but should be included in a definite
six-year scheme. Observe proper rotations for crops where
desirable.

1. In selecting plants for breeding purposes, why do we choose
individual plants?

2. In breeding work, why do we test out the selected individ-
uals by breeding each one separately?

3. Why is it most satisfactory for the breeder to work with
plants that are self-fertilized?

4. Why do we plant border rows around breeding plots?

5. Why do we detassel alternate halves of adjacent rows in
corn breeding plots?

1 For more detailed directions for timothy breeding, see Webber, H. J.,
4 ' Production of New and Improved Varieties of Timothy." Cornell
University Agr. Exp. Sta. Bull. 313, 1912.

Appendix E 465

6. Why should corn breeding plots be isolated? What is a
safe distance?

7. Why should timothy breeding plots be isolated ? What is a
safe distance?

8. Is it necessary to isolate breeding plots of the small cereals?

9. In selection work, what three rules should the breeder
follow who understands the principles of pure-line breeding?

Scheme for Potato Breeding Plots1

First Year. — Choose 500 good tubers. Plant them in a
breeding plot by the tuber-unit method. Rows should be 3
feet apart, hills 1£ feet apart in the rows. At harvest time
choose the best 50 units. Save the best 10 from each of these
units for planting a breeding plot the next year.

Second Year. — Plant the selected tubers in a breeding plot
as in the first year. At harvest time discard all poor units.
Select the best 50 units. Save 10 of the best tubers from each
of these units for planting the third year's breeding plot. Use
the rest for planting a field crop the next year.

Third Year. — Use these 500 tubers to plant a breeding plot.
Plant your field crop with the remaining choice tubers. How

1 For details of the following schemes read Cornell University Exp.
Sta. Bull. 251, "Plant Breeding for Farmers," 1908 ; also Bull. 313, "The
Production and Improvement of New Varieties of Timothy."

For cotton breeding, see Webber, H. J., "Improvement of Cotton by
Seed Selection," U. S. Department of Agr. Yearbook, 1902, pp. 365-
386.

16.5 ft. = 1 rod ; 160.0 sq. rd. = 1 acre.

Plant : Corn, 8-12 qt. per acre ; Oats, 2-3 bu. per acre ; Wheat,
2-3 bu. per acre ; Barley, 2-3 bu. per acre ; Potatoes, 12-15 bu. per acre;
Timothy, 6-8 qt. or 16 Ib. per acre.

Standard weights: Corn, 1 bu. = 70 Ib. shelled, or 56 Ib. on cob;
Oats, 1 bu. = 32 Ib. ; Wheat, 1 bu. = 60 Ib. ; Barley, 1 bu. = 48 Ib. ;
Potatoes, 1 bu. = 60 Ib. ; Timothy, 1 bu. = 45 Ib.

Average yield per acre in United States for 1902: Corn, 20.2 bu. ; Wheat,
15.9 bu. ; Oats, 37.4 bu. ; Barley, 50.4 bu. ; Potatoes, 113.4 bu.
2n

466 Plant-Breeding

large a field can be planted if the yield has been at the rate of
200 bushels per acre ?

Fourth and Subsequent Years. — Continue this same scheme,
constantly discarding the poor units and selecting the best for
breeding.

Estimate how large your breeding plot should be in order to
supply a 5-acre field with seed in the third year, supposing the
yield from your selected units to be the same as the average
yield given by the 25 best selected units in your former report,
i.e. about 370 bu. per acre.

Scheme for Corn Breeding Plots

All corn breeding and increase plots should be at least 1200
feet from any other corn. Why?

First Year. — Select front the field 100 ears. From these
choose the best 50 for planting a breeding plot the next year.

Second Year. — From these 50 ears, plant a breeding plot
by the ear- to-row method. Rows should be 4 feet apart, hills
3 feet apart in the row, each row to contain 100 hills. Surround
the breeding plot with 2 or more border rows planted with seed
from the unused select ears. Why? Detassel alternate halves
of adjacent rows. Why? Select from the best 10 or 12 rows
50 to 100 of the best ears, choosing the best 50 for the next
year's breeding plot. Save the seed from the other best-yielding
rows for an increase plot, or the general field.

Third Year. — Plant your breeding plot as before, with the
best selected 50 ears. With the other selected ears plant an
increase plot or general field. Select as before the best 50 ears
from the breeding plot for the next year's breeding plot, saving
the remainder for a new increase plot. Save ears from this
year's increase plot for planting next year's field.

Fourth and Subsequent Years. — As before, plant your breed-
ing plot, increase plot, and field, using a continuous and pro-
gressive scheme of selection.

Appendix E 467

Scheme for Wheat Breeding Plots

First Year. — Choose 100 fine heads for starting your improve-
ment work.

Second Year. — Plant seed from these select plants in short
rows by the plant- to-row method. Space the rows 1 foot apart.
Select a few rows, say twenty, to furnish seed for a breeding plot
in the third year.

Third Year. — Plant seed from each of these select rows in a
breeding plot. Do not mix the seed from different rows. Plant
as many 17 foot rows in each plot as the amount of seed saved
will permit. This is at the rate of 1^ bushels per acre. The
rows should be 1 foot apart.

Fourth Year. — Find average yield of progeny rows that came
from the selected rows of the third year. Select several of the
best strains which may yield about 24 bu. per acre. With this
seed plant increase plots from each kind of seed. Save seed from
2 or 3 of the best yielding plots for more extensive trials in the
5th year. The rest of the seed can be used for planting a field.
Make new selections of heads in the fields and repeat the whole
program as before. There may be many more valuable types
in the fields that can thus be isolated.

Fifth Year. — Test out your select strains and choose one or
two of the best for increase plots and for planting your field.
Plant the field this year with seed from last year's increase plot
and from the test rows.

Scheme for Oat or Barley Breeding Plots

The principles of selection and methods of breeding these
cereals are the same as for wheat.

INDEX

Absence factors, 192.

Acquired characters, 17.

Adami, M., 145.

Adams fund, 314.

Adam's laburnum, 142.

Adaptation, 7, 37, 106.

Alfalfa, 313.

Alkali resistance, 313.

Allelomorph, 325.

Allen, Dr., 314, 315.

American Seed Trade Association,
309.

Anemone coronaria, 57, 58.

Animals, breeding, 217.

Anthers, 276.

Anthocyanin, 186.

Antirrhinum (see snapdragon) .

Apples, 212, 255, 295 ; hybrid, 235.

Arthur, 228, 239.

Artificial selection, 37.

Asexual propagation and hybridi-
zation, 125.

Asparagus, 313.

Associations, plant-breeding, 300.

Atavism, 211, 231.

Average deviation, 47.

Barker, E. E., 394.

Bartel, T. C., 254.

Barteldes, 264.

Bateson, 155, 183, 187, 192.

Beans, 260 ; Emerson's experiments

with, 189.
Bibliography, 335.
Biometry, 41, 325.
Biotypes, conception of, 19.
Blackberries, hybrid, 136.

Blackberry, 253.

Books, plant-breeding, 328.

Braun, Alexander, 20.

"Breaking the type," 22, 219.

Breeding periodicals, 332.

Breeding plants, rules for, 222.

Broughton, Mr., 91.

Browne, Dr. Thomas, 56.

Bruant, 237.

Brunella vulgaris, 80.

Brussels sprouts, 243.

Budd, Professor, 258.

Buds, methods of emasculation,
291.

Bud-selection, 39, 242.

Bud-sports, 210, 241. .

Bud-variation, 11, 29.

Bud-varieties, 242.

Burbank, 112, 321.

Burpee, 264.

Burr, "Field and Garden Vege-
tables," 295.

Cabbage, evolution of, 267 ; savoy,
244 ; shapes, 245 ; wild, 240.

Gamer arius, 110.

Canadian Seed Growers' Associa-
tion, 304.

Cannas, 237, 265.

Capsella Heegeri, 80.

Carex, little natural crossing in,
103.

Carnation, 179.

Carriere, 58, 223, 239, 296.

Castle, 180.

Cauliflower, 248.

Cavalier, wheat, origin of, 91.

469

470

Index

Cereals, disease-resistant, 313.

Change, of seed, 28 ; of stock, results
from, 105, 107.

Chelidonium, 55, 56.

Cherries, hybrid, 235.

Chimaera, 146, 148.

Chromoplasts, 186.

Chromosome, 325.

Chrysanthemum, 251, 252, 253,
256, 257, 258, 259, 262, 263, 264,
267, 268, 269; carinatum, 226;
indicum, 250 ; inodorum plenis-
simum, 87 ; morifolium, 249 ; sege-
tum, 86, 89 ; segetum plenum, 86,
88.

Citranges, 132, 312.

Citrus trifoliata, 312.

Climate, as factor in variation, 25,
26 ; man's control over, 27.

Coefficient of heredity, 152 ; of va-
riability, 49.

ColJard, 242.

Color, mendelian inheritance of, 185.

Commercial breeding agencies, 308.

Compositae, 223.

Compositous flowers, 279.

Corn breeding, 216.

Correns, 155.

Cotton, 213, 214, 312, 313.

Council of grain exchanges, 310.

County agent, the, 310.

Cowpeas, disease resistance, 220.

Cross, function of, 101, 230.

Crosses, characteristics of, 123.

Crossing, a means not an end, 232 ;
and change of seed, 103 ; effects
on the species, 97 ; from stand-
point of plant improvement, 108 ;
how to overcome antipathy to,
121; limits of , 97, 98, 99 ; process
of, 281 ; refusal result of natural
selection, 100 ; vigor as result of,
112, 115.

Crossing animals, 216.

Crossing plants, philosophy of, 92.

Crozy, 237.

Cucumber pollinations, 141.
Cultivation, philosophy of, 24.
Cupid sweet pea, 77.
Curled kale, 241.
Cytisus Adami, 142, 145.

Darwin, 20, 34, 52, 59, 73, 105, 107,

111, 113, 209, 240, 242, 244, 296,

307.

Dates, 313.

Davenport, C. B.; 183.
Davenport, E., 149.
Davis, Bradley Moore, 318.
Deviation, average, 47 ; standard, 48.
de Vries, Hugo, 52, 53, 59, 62, 63,

72, 73, 74, 76, 79, 155.
Dewberry, 253.
Dihybridism, 171.
Dioecious flowers, 278.
Disease resistance, 219, 220, 313.
Dominance, 165 ; incomplete, 179.
Dominant characters, 325.
Dorsey, M. J., 424.
Double flowers, experiments in

production of, 86 ; history of

appearance of, 56.
Downing's "Fruits and Fruit

Trees," 295.
Draba, 73.

Drought-resistant plants, 313.
Duggar, B. M., 318.
Duplex, 325.
Durum wheat, 313.

Ear-to-row, 308.
East, E. M., 318.
Eckford, 237.
Egg-plant, 128, 141.
Egyptian cotton, 313.
Elderberry, 217, 218.
Elementary species, 63, 80.
Emasculation, 282.
Emerson, 189.

Environment as a cause of varia-
tion, 16, 216.
Epistatic, 325,

Index

471

Error, probable, 50.
Evening-primrose (see (Enothera).
Evening-primroses, laws of muta-
bility of, 72.

Factor hypothesis, 326.

Fairchild, Thomas, 110.

Fertilization, 270.

Flowers, structure of, 270.

Fluctuating variations and muta-
tions, 54.

Focke, 232.

Food supply, as cause of variation,
20, 21 ; of different branches, 23.

Frequency curve, 42.

Fultz wheat, origin of, 91.

Galton curve, 326.
Gametes, 168, 326.
Garden varieties, origin of, 18.
Gartner, C. F., 110, 111.
Genetics, 326.
Genotype, 326.

Germ-plasm, action of environ-
ment upon, 17.
Gibb, 258.

Gideon, Peter M., 233.
Gladiolus, 237.
Glossary, 325.
Gmelin, J. G., 110.
Goff, 228, 229.

Gold Coin wheat, origin of, 91.
Gourds, 140.
Graft-hybrids, 142.
Grain exchanges, council, 310.
Grapes, 212, 235 ; hybrid, 133.
Gray, Asa, 35.
Green, Ira W., 91.

Hallock & Son, 247.
Harper, R. A., 318.
Head-to-row, 308.
Helianthemum, 73.
Henderson, 264.

Heredity, 149; coefficient of, 152. ;
studied collectively, 149.

Heterozygote, 326.

History of mutation, 55.

Homozygote, 326.

Hopetown wheat, origin of, 91.

Hurst, 192.

Husk-tomato pollination, 141.

Hybridization and asexual prop-
agation, 125.

Hybridized, what plants can be,
111.

Hybrids, 326 ; history of , 1 10 ; defini-
tion of, 108 ; influence of sex on,
138 ; production of, 101 ; vari-
ability of, 122.

Hyper-chimaera, 148.

Hypostatic, 326.

Ideal, 220.

Illinois Seed Corn Breeders' Associa-
tion, 303.

Immature seeds, 228.

Implements of pollination, 292.

Improvement of plants, systematic,
295.

In-breeding, 127.

Indeterminate varieties, 209.

Individuality, fact of, 2.

Individual selection, 308.

Inhibitor, 180.

Inter-crossing, swamping effects of,
98.

Ipomceas, 229.

Kiiishu rice, 313.

Knight, Thomas Andrew, 110.

Kohl-rabi, 248.

Kolreuter, J. G., 110.

Kumerle, J. W., 265.

Laboratory exercises, 394.

Lamark, 59.

Lemoine, 237.

Lettuce, improvement in, 221.

Linaria vulgaris (see toad-flax).

Linaria vulgaris peloria, 84.

Linnaeus, 110, 138.

472

Index

Locke, 180.
Lupines, 231.

Maize, 224.

Mass selection, 307.

Mean, 45; use of, 46.

Measurement of, 41.

Mendel, 155.

Mendelian inheritance of color, 185.

Mendelian ratio, 179.

Mendelism, application to plant-
breeding, 202, 225 ; in wheat, 194 ;
limits of, in the production of
new varieties, 204 ; of tomatoes,
203 ; summarized, 200.

Mendel's experiments, 156.

Mendel's law, explanation of, 158.

Methodical selection, 307.

Minnesota Field Crop Growers' As-
sociation, 303.

Mirabilis, 112.

Modal coefficient, 45.

Mode, 44.

Monoecious flowers, 277.

Monotypic genera, 224.

Moore, Jacob, 235.

Morning-glories, Darwin's experi-
ments with, 114.

Morse & Company, 77.

Morus multicaulis, 299.

Munson, Professor, 117, 235.

Munting, Abraham, 57.

Mutability, laws of, with evening-
primroses, 72.

Mutants, how produced in the
garden, 71.

Mutation, history of, 55 ; first use
of word, 56.

Mutations, 40, 52, 326 ; economic
significance of, 90 ; and fluctua-
tions, 54 ; can they be produced
artificially ? 200 ; examples of, 76 ;
experimental study of origin of,
84 ; frequency of occurrence of, 79 ;
mutations resulting from men-
delian segregation and recombi-

nation, 193 ; mutations which
mendelize are constant, 193.

Natal and post-natal variations, 18.

Natural hybrids, rarity of, 102.

Natural selection, 34, 93 ; as cause
of variation, 14.

Navel oranges, 313.

Nectarines, 241.

New York Plant Breeders' Associa-
tion, 304.

Nicotiana pollinations, 142.

Nilsson, Professor, 304.

Nulliplex, 326.

Oats, Swedish select, 313.
(Encthera albida, 63, 67, 71, 74;

analytical table of seedlings,

68-69 ; brevistylis, 63, 64, 71, 74 ;

de Vries' experiments with, 59 ;

elliptica, 64, 68, 71, 74; gigas,

63, 65, 66, 71, 74; Icevifolia, 63,

64, 71, 74; Lamarkiana, 59, 60,
61, 64, 71, 74; lata, 64, 67, 71,
74 ; muricata, 60 ; nanella, 60,
63, 64, 71, 74; oblonga, 63, 67,
71, 74; rubrinervis, 63, 65, 71,
74; scintillans, 64, 68, 71, 74;
variations in stature of, 53.

Ohio Plant Breeders' Association,

304.

Olives, drought-resistant, 313.
Ononis repens, 80.
Organs, essential, 274.
Orton, 313.

Palmer, Asa, 264.

Peaches, 212.

Peas, Mendel's experiments with,

157.

Pedigree culture, 308.
Pelargoniums, 237.
Peloric toad-flax, 79.
Pepino pollination, 141.
Pepper pollinations, 141.
Peppers, 222.

Index

473

Perennial plants, 241.

Periclinal chimsera, 148.

Periodicals, breeding, 332.

Phenotype, 327.

Physalis, 104.

Pineapple hybrids, variation of, 123.

Pistils, 271.

Plant-breeding : associations, state,
300; books, 328; by selection,
218; denned, 212; forward
movement in, 294 ; instruction,
321; laboratory, U. S. Dept.
Agri., 311; projects, 315; use
of term, 296.

Plant improvement a serious busi-
ness, 298.

Plant introductions, division of,
312.

Plants, differences compared with
animals, 10.

Plant-to-row, 308.

Plateation, 397 ; denned, 327.

Plums, 212, 294.

Pollen, 280.

Pollen storage, 289.

Pollination, 270 ; process of cross,
281, 289; uncertainties of, 140.

Poncirus trifoliata, 312.

Population, 41.

Potatoes, 241.

Presence-and-absence hypothesis,
181.

Pride Butte wheat, origin of, 91.

Probabilities, theorem of, 169.

Probable error, 50.

Punnett, 183, 184.

Quetelet curve, 44.

Radishes, division of, 239.
Raspberries, hybrid, 235.
Recessive characters, 327.
Recessiveness, 165.
Regel, cited, 295.

Reproduction, difference between
plants and animals, 10.

Retrograde varieties, 65.
Rogers' grape hybrids, 235.
Roguing, 251.
Russian apples, 212, 258, 295.

Savoy cabbage, 244.

Score card, use of, 236.

Sea Island cotton, 312.

Sectional chimsera, 148.

Seed, change of, 28.

Segregation, 327.

Selection, accumulative, 209 ; ar-
tificial, 37, 243 ; individual, 308 ;
mass, 307; methodical, 307;
plant-breeding by, 218.

Sex, a factor in variation, 15, 215 ;
influence on hybrids, 138 ; origin
and function of, 95.

Shirley poppy, 76.

Shull, 190, 318.

Simplex, 327.

Snapdragon, 83.

Snyder blackberry, 255.

Solanaceous plants, 222.

Solanum darwinianum, 147; Gart-
nerianum, 147 ; graft-hybrids, 146 ;
kolreuterianum, 147 ; proteus, 147 ;
tubingense, 146.

Somatic, 327.

Species, definition, 8.

Species-formation, 8.

Spencer, 105.

Spillman, 180, 194.

Sport, 39.

Sprenger, 55.

Squares, method of, 169.

Squashes, 128, 140.

Stamens, 271.

State experiment stations, 310.

State plant-breeding associations,
302.

Statistical methods (see biometry) .

St. Hilaire, Geoffrey, 58.

Stout, A. B., 318.

Struggle for life, a cause of varia-
tion, 30.

474

Index

Sturtevant, 228.

Sugar beets, variation in amount

of sugar in, 54.
Swede turnip, 248.
Swedish Seed Association, 304.
Swedish select oats, 313.
Swingle, Walter, 312.
Systematic improvements of plants,

295.

Tangelo, 133, 312.
Teas' Weeping mulberry, 233.
Teosinte, 137.
Thomson, 149.
Thymus vulgar is, 80.
Timothy, variability of, 3.
Toad-flax, 79, 81, 82.
Tobacco pollinations, 142.
Tomato, 215, 222, 228, 244, 246;
ignotum, 246; pollinations, 141.
Trihybrid, 177.
Tschermak, 155, 188.
Tuber-unit, 308.
Type, 43.

Unit-characters, 9, 154.
United States Dept. Agri., 310.
Uses, breeding for specific, 224.

Variability, biometrical expression
of, 43, 47; coefficient of, 49.

Variation, action of natural selec-
tion upon, 14 ; and adaptation, 7 ;
causes of, 13, 30, 94 ; caused by
environment ; caused by sex
differences, 15 ; in climate, 25 ;
choice and fixation of, 34 ; de
Vries' classification, 53 ; fluctuat-
ing, 54; in food supply, 20;

measurement of, 41 ; natal and
post-natal, 18.

Varieties, "coming true," 210, 211 ;
how they originate, 209 ; inde-
terminate, 209 ; non-uniformity
of, 19 ; outright production of,
by crossing, 118 ; retrograde, 63 ;
spontaneous appearance in wild
state, 79.

Variety, what is it ? 35.

Verlot, 244, 296.

Vigor as result of crossing, 112, 115.

Vilmorin, 226, 230, 231, 269.

Vitis, 122.

Vries, de, Hugo (see de Vries).

Walker, Ernest, 243.
Wallace, 105, 123.
Watermelons, wilt-resistant, 219.
Wealthy apple, 233.
Webber, 133, 156, 312.
Weismann, 16, 17.
Wheat, Durum, 313.
Wheatland fife wheat, origin of, 91.
Wheat-rye hybrid, 136.
Wier, D. B., 233.
Wild cabbage, 240.
Wilks, Rev. W., 76.
Willis, 117.

Wilson, strawberry, 248.
Wilt-resistant watermelons, 219.
Winkler, Professor, 146, 148.
Wisconsin Agricultural Improve-
ment Association, 300.

Xanthein, 187.
Xenia, 327.

Zygote, 327.

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