THE FEEDING OF
CROPS AND STOCK

A.D. HALL

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THE FEEDING OF CROPS AND
STOCK

THE FEEDING OF
CROPS AND STOCK

AN INTRODUCTION TO THE

SCIENCE OF THE NUTRITION OF

PLANTS AND ANIMALS

BY A. D. HALL, M.A., F.R.S.

DIRKCTOB OF THE ROTHAMSTKD EXPERIMENTAL STATION

FOBEION MEMBER OF THE ROYAL ACADEMY OF AGRI-

CITLTURE OF SWEDEN

WITH ILLUSTRATIONS AND DIAGRAMS

NEW YORK
E. P. DUTTON AND COMPANY

1911

n

n/

immM^Z FilKO

INTRODUCTION

In this book I have endeavoured to provide a general
introduction to the science of growing crops and feeding
animals : an outline, in fact, of the theory of the nutri-
tion, first of the plant and then of the animal. The book
is intended on one side to give the student of agriculture
a general framework of ideas, before he enters upon the
more detailed study of agricultural chemistry that will
be presented to him by his professor. I have found that
such students often experience a difficulty in following and
making the best use of their lectures because the whole
trend of the subject is strange to them ; they would
be better able to appreciate the value of the illustrations
they receive if they could at once see their bearing upon
the scheme of nutrition of plant or animal. There are
many students also in our schools and colleges who do
not as a rule pursue the subject any further than it is
carried in these pages ; both on their account and for
the student who is only laying a foundation, I have
insisted as far as possible on the main principles govern-
ing this branch of science, hoping thereby to induce a
sound way of thinking that will not prove misleading on

vi INTRODUCTION

further study and practical experience. The writer of
an elementary book must always adopt short views and
make dogmatic statements which he knows to be no
more than approximations to the truth. I can only hope
that the constant reference to experiment, and the whole
style in which the book has been written, will keep
before the reader an appreciation of how much still
remains unsaid.

Even more than for the student, this book is intended
for the workaday farmer who wants to get an intelli-
gent conception of how his crops and stock make their
growth. Complex and unknown as many of these
processes are, the main outlines are sufficiently estab-
lished to have a bearing upon practice ; but the practical
application can be more surely and readily made if the
farmer, with his inside knowledge of the way things can
be done, will learn the theory, than by any attempt of the
scientific man striving from the outside to get up the
working conditions.

Moreover, the subject is interesting ; it should neither
be difficult nor tedious for the man with an ordinary
education to learn how a plant draws its nutriment
from the soil, and how the animal depends in its turn
upon the plant ; so if this book is not readable, mine is
the fault, and I have failed in the object with which I
set out. To this end I have avoided technical language
as much as possible, and I have assumed that the reader
possesses little or no knowledge of chemistry. Of
course, a book of this kind cannot be finally intelligible
unless the reader possesses some ideas about the con-
stitution of air and water and the nature of chemical

INTRODUCTION vii

change, but these ideas are becoming more generally
diffused every day, and the unfamiliar reader may to
some extent gather them as he goes along. I must
express my indebtedness to Dr E. J. Russell for his
advice on certain sections of the book, and to Miss
W. E. Brenchley for the botanical drawings therein con-
tained. Miss L. M. Underwood also has greatly helped
me by compiling the index. As on other occasions
also, I have to thank Mr G. T. Dunkley for the care he
has taken in looking through the proofs, and verifying
the results quoted.

A. D. HALL.

The Rothamsted Experimental Station,
June 1910.

TABLE OF CONTENTS

CHAPTER I

WHAT THE PLANT IS MADE OF

PAQB

Elements present in the Plant. The Chief Compounds form-
ing Plant Tissues — Carbohydrates, Fats, Proteins, a-Fro-
teins, and Ash. The Growth of a Plant from a Seed ;
the Embryo and the Food Store. Conditions necessary
for Germination — Water, Warmth, Air. How Materials
are moved to the Growing Parts of a Plant. Seed
Testing ....... I

CHAPTER II

THE WORK OF THE LEAF

The Increase of Weight in a Growing Plant is derived from
the Air. Plants split up Carbon Dioxide and give off
Oxygen. Purification of the Air by Plants. Formation
of Starch in the Green Leaf. Motive Power supplied
by Light All parts of the Living Plant are also
breathing. Necessity of Leaves to the Growth and
Ripening of the Plant. The Leaves of the Plant give
off Water. How much Rainfall is required by Crops . 19

X CONTENTS

CHAPTER III

THE WORK OF THE ROOTS

PAGB

The Roots as anchoring the Plant. The Roots supply the
Plant with Water. Roots require Air. Roots can only
take in dissolved Material. Etching Action of Roots
due to their Excretion of Carbon Dioxide. Elements
necessary to the Nutrition of Plants. Plants require
Combined Nitrogen ..... 42

CHAPTER IV

CHANGES OF COMPOSITION WITHIN THE
PLANT

The Manufacturing, Resting, and Spending Stages in a
Plant's Development. The Course of Nutrition and
Migration in the Growth of Wheat. The Ripening of
the Grain. Storage and Migration in Root Crops.
Removal of Food Materials from the Leaves of Trees
as they Ripen. The Ripening of Fruit. Effect of Soil
and Climate upon the Composition and Quality of the
Crop ....... 59

CHAPTER V

THE ORIGIN AND NATURE OF SOILS

The Weathering of Rocks to Soil. Solution of Rock
Materials in Water containing Carbon Dioxide.
Action of Frost. Transport of Soil by Rain and Run-
ning Water. Action of Worms. Approximate Analysis
of Soils. Properties of Clay and Sand. Chemical
Constituents of Soils. Soils and Subsoils , » 78

CONTENTS

CHAPTER VI

CULTIVATION AND THE MOVEMENTS OF SOIL
WATER

PAQB

Nature of the Film of Liquid surrounding Wet Particles of
Soil. Retention and Movements of Water due to
Surface Tension. Percolation. Rise of Subsoil Water
by Capillarity. Value of Autumn Ploughing. Effect
of Spring Cultivations. Cooling of the Land by
Evaporation. Effect of Hoeing and Rolling upon the
Temperature and Water-content of the Soil. Dry
Farming in Semi-arid Regions. Drainage and the
Temperature of Soils. Spring Frosts. Early and
Late Soils lOO

CHAPTER Vn

THE LIVING ORGANISMS OF THE SOIL

Formation of Nitrates in the Soil. Bacteria in the Soil
which decompose Organic Matter. Bacterial Loss of
Nitrogen from the Soil. Formation of Humus. Fixation
of Nitrogen by Bacteria associated with Leguminous
Plants. Value of Clover Crops in the Rotation. In-
oculation of Soil. Other Bacteria-fixing Nitrogen in
the Soil. Accumulation of Nitrogen in Virgin Soils.
Dependence of Soil Fertility upon Bacteria . .120

CHAPTER Vni

THE CHEMICAL COMPOSITION OF THE SOIL

Plant Food found in Normal Soils. Dormant and Available
Plant Food. Rotations and Plant Food in the Soil.
Systems of Farming— Wasteful and Conservative.
Requirements of Different Crops for Fertilisers. Types
of Soil— Characteristic Weeds and Crops . . I49

xii CONTENTS

CHAPTER IX

FOODS

PAOI

Composition of Cattle Foods. Nature of Carbohydrates,
Fat, Proteins, Fibre, Ash. Processes of Digestion in
the Animal Body. Digestibility. Character of various
Concentrated Foods, Cereals, Roots, Straw, and Hay.
Valuation of Feeding Stuffs . . . .169

CHAPTER X

THE UTILISATION OF FOOD BY THE ANIMAL

Food as a Source of Energy. Heat Value of various
Foods. Energy consumed in Digestion and In-
ternal Work. Maintenance Rations. Feeding for
Rapid Work or Increase of Weight. Amount of Food
required for a given Amount of Work. Nitrogenous
Materials required to repair Tissue Waste. Minimum
of Protein necessary . . . . .185

CHAPTER XI

FOOD REQUIRED BY THE GROWING AND
FATTENING ANIMAL

Composition of Lean and Fat Animals. Food required to
produce a given Increase of Live Weight. Starch
Values of Foods. Albuminoid Ratio. Food Rations
for various Purposes, based upon Starch Values . 207

CHAPTER XII

FARMYARD MANURE

Composition of Animal Excretions. Litter. Changes
taking place during the Making and Storage of

CONTENTS xiii

Manure. Losses of Nitrogen in Manure-making —
Unavoidable or due to wasteful Methods. Composi-
tion of Farmyard Manure from various Sources. Care
of Farmyard Manure. Farmyard Manure as a
Fertiliser. Value of Farmyard Manure. Valuation of
Manure Residues derived from the Consumption of
Purchased Feeding Stuffs. Cost of Farmyard Manure 224

CHAPTER XIII
ARTIFICIAL MANURES AND FERTILISERS

Nature of a Fertiliser. Fertilisers containing Nitrogen —
Nitrate of Soda, Sulphate of Ammonia, Soot — their
Use and Value. Fertilisers containing Phosphoric
Acid. Bones, Superphosphate or Acid Phosphate,
Basic Slag or Phosphate Powder, Ground Rock
Phosphate. Potash Fertilisers. Guanos. Industrial
Residues. Tankage. Action of Fertilising Ingredients
upon Crops. Expenditure on Fertilisers. Character of
Fertiliser required for particular Crops. Valuation of
Fertilisers ....... 248

CHAPTER XIV

Composition of Milk. Variations to which the Composition
of Milk is subject. Effect of Individuality, Breed, Food,
Time of Milking, Period of Lactation. Feeding for
Milk. Composition of Butter. Nature of the Churn-
ing Process. Effect of various Foods upon the Quality
of the Butter. Composition of Cheese. Changes
taking place during the Cheese-making Process. The
Ripening of Cheese. Importance of Cleanliness in all
dealings with Milk . . . . . 269

Index •...,... 291

LIST OF ILLUSTRATIONS

1. Germinating Seedlings of Beans . . Face page 6

2. Seeds of Barley at Various Stages of Growth . „ 8

3. Mint Plant in Water splitting up Carbon Dioxide

and evolving Oxygen . . . . „ 24

4. Apparatus to show the Absorption of Carbon

Dioxide by Green Leaves . . • »> 24

5. Starch Formation in the parts of an Artichoke

Leaf exposed to Light . . . • v 26

6. Barley Seedlings enclosed within Bottle . „ 30

7. Fern that has been growing inside a closed Bottle

for Thirty-six Years ••••»} 32

8. Transpiration of Water from Leaf . . „ 35

9. Apparatus for Measuring Transpiration from Leaf „ 36
10. Stomata on Lower Surface of Sweet Pea Leaf . „ 38
I \. Root Hairs of Barley • • • • „ 50

12. Contractile Taproot of Dandelion . . „ 44

13. Slab of Polished Marble etched by Roots of Bean

Plant ....... 50

14. Series of Plants grown in Water Cultures . „ 52

15. Diagram showing Migration of Foodstuffs with

the Grain of Wheat • . . . „ 64

xvi LIST OF ILLUSTRATIONS

i6. Formation of a Sedentary Soil . . .Face page 78

17. Formation of a Drift Soil . . • » 84

18. Experiment to show Percolation and Absorption

of Water by Different Soils . . • » 92

19. Photograph illustrating Liquid Film round Soil

Particles ...... 100

20. Diagram illustrating Capillary Rise of Liquids „ 104

21. Distribution of Sun's Rays upon Southerly and

Northerly Slope .... Page 1 1 7

22. Apparatus used for Experiments with Bacteria Face page 122

23. Diagram showing the Energy required from the

Food by Oxen of Different Weights . . „ 198

24. Diagram showing the Composition of the Carcass

of Lean, Half- Fat, and Fat Oxen . . „ 208

THE FEEDING OF CROPS
AND STOCK

CHAPTER I

WHAT THE PLANT IS MADE OF

Elements present in the Plant. The Chief Compounds forming
Plant Tissues — Carbohydrates, Fats, Proteins, ^-Proteins, and
Ash. The Growth of a Plant from a Seed ; the Embryo and
the Food Store. Conditions necessary for Germination —
Water, Warmth, Air. How Materials are moved to the
Growing Parts of a Plant. Seed Testing.

Before we can obtain any idea of how a plant feeds
and grows, it is necessary to find out to some extent of
what it is composed, and for this purpose a few simple
experiments must be made. Let us begin by taking
some green leaves of any plant, a carrot or a potato to
represent a root, and some wheat or maize as examples of
seeds ; weigh out portions of each in basins of porcelain,
nickel, or (best) of platinum, and then put them on a
sand bath or over a low flame with glass plates covering
the tops of the basins. In a very few moments the
glass plates will be dimmed over and water will begin
to collect in drops, water that has been driven out of
the plant material by the heat. As soon as you have
satisfied yourself that the plant stuff is losing water^
remove the glass coverings and put the basins in the
oven to dry completely, a process which will require a
day or so. On reweighing the dishes it will be found
1 A

2 WHAT THE PLANT IS MADE OF [chap.

that the contents have lost a good deal of water,
amounting to 80 to 90 per cent, of the original weight
of the green leaves ; the roots lose nearly as much,
but the seeds only 10 to 15 per cent.

Water is an invariable, and indeed the chief
constituent of the living plant.

Take now the dry plant tissues still in their basins,
and heat them more strongly over the Bunsen or
Argand flame, covering the greater part of the basins
with a sheet of metal. Thick gases possessing a
pungent smell will be given off, and these after a time
will take fire if allowed to come in contact with the
lamp ; after a time extinguish the flame by completely
covering the basin, and cease heating until the contents
are cool enough for examination. It will now be seen
that the whole interior of the basin is covered with
black soot, and that the plant material is charred or
carbonised ; there is abundant evidence that the black
element, Carbon^ has been set free from the original
plant tissues. Now resume the heating, but without
any covering, push it as rapidly as possible, and let the
contents of the basins burn away until little or nothing
of the black carbon is left, though to get rid of the last
traces it may be necessary to put the basins in a
muffle furnace and raise the contents to a bright red
heat. At the end, when everything possible has been
burnt away, there will still be found a little grey or
white ash, which on weighing will amount to from 2 to 5
per cent, of the dry matter that was left after the water
had been driven off. In the plant ash only a few
elements are to be found, but these are the same what-
ever the plant or wherever it has been grown, with a few
exceptions that are small and unimportant. By tests
which need not here be detailed, we can always demon-
strate in the plant's ash the presence of the elements

I.] ELEMENTS PRESENT IN PLANTS 3

phosphorus, sulphur, and to a smaller degree, chlorine.
Similarly we shall always find five metallic compounds,
— potash, soda, lime (oxide of calcium), magnesia, and a
smaller quantity of iron ; when we are dealing with
cereals or grasses, there will also be a large proportion
of silica in the ash, though it is absent or only found in
very small quantities in the ash of other plants. Thus
we distinguish in the plant, (i) water; (2) a combustible
part, of which carbon is the base ; and (3) a small pro-
portion of incombustible mineral ash. There remains
another element which disappeared with the combustible
portion, but which belongs neither to the carbon nor to
the hydrogen and oxygen with which the carbon are
mainly combined. To detect it we must mix some of
the dry plant material in a test-tube with lime, or
better with the mixture called soda-lime, and then
heat the whole ; gases will soon be given off in which
we can detect the familiar smell of ammonia or hartshorn.
Now ammonia is a compound of the element nitrogen,
and ammonia is as a rule liberated from any compound
of nitrogen with carbon and its associated elements,
hydrogen and oxygen, when the compound is heated
with lime or other alkali. A proper analysis will
show that only i to 2 per cent, of the dry matter of
the plant consists of nitrogen, but it is an indispensable
element and always found in the plant.

To illustrate more definitely what may be expected
in the plant and in what proportions, in Table I. is set
out a list of the quantities of the various elements found
in the grass cut from an average acre of land at the
time it was ready for mowing, this example being
chosen because it gives a composite analysis represent-
ing a large variety of plants. The analys"s is set out
both in pounds per acre, and as percentages of the
whole plant and of the dry matter respectively.

4 WHAT THE PLANT IS MADE OF [chap.

Table I.— Composition of Meadow Grass from One Acre.

Lb. per Acre.

Percentages

Of whole plant.

Of dry matter.

<l>

Is
is

o

Water .
'Carbon .
Hydrogen
Nitrogen .
Oxygen .
Sulphur .

'Phosphoric Acid

Sulphuric Acid .

Chlorine .

Silica . .

Potash .

Soda . . .

Magnesia .

Lime

Oxide of Iron .
^Sand, etc.

8,378

1,315

144

49
1,090

15

13
II
16
57
56
12
10
28
I
5

74-8

117

1-3

0.4

9-7
o«i

O-I
O-I
O-I

0-5
0-5

O-I
O-I

0-31

46-6
5-1
17

38-6

0-5

0-5
0-4
0.6

2'0

2-0

0-4
0-4

I-O

0-04

0-2

11,200

99.8

100-04

So far we have only been dealing with the elements
common to all plants, which, as will be seen later, are
also common to animals as well ; but the elements are
only the raw material — bricks, stones, beams, mortar,
etc. — out of which all sorts of different edifices can be
constructed. There exist in fact in the plant material
certain characteristic groups of compounds, the members
of each group being built up in much the same way but
quite differently from the members of any other group,
although only the same elements may have been used
in the building of both groups. For example, the fats
form a definite class of bodies common in the seeds of
plants ; they are easily recognisable and are distinct in
every outward property from the sugars, another natural
group of substances found in plants. Yet both fats and
sugars contain the same elements — carbon, hydrogen.

I.] PROXIMATE CONSTITUENTS OF PLANTS 5

oxygen — and no other; the difference between them
arises from certain differences in the proportions, and
particularly in the manner of building up the structure.
Moreover there are particular natural agencies by which
one class of bodies can be transformed into the other,
just as a house might be taken down and rebuilt from
the same materials in a totally different style.

Among the more important of these universal
constituents of plants we may place first of all the
carbohydrates, a great group of substances so called
because in them the elements carbon, hydrogen, and
oxygen are combined together in the proportions that
suggest a combination of carbon with water. The
carbohydrate group includes the sugars, so easily
recognisable in the sugar-cane and the beetroot, but
also detectable in fruits (a raisin is most easily tested),
and by special tests in the leaves and other parts of the
living plant. Then come the starches, which are readily
washed out of flour, potatoes, and many other storage
organs of plants ; also certain gums and mucilages,
which are closely related to the starches. Finally, we
can include the celluloses and fibres, which we obtain in
a very pure state in the simple vegetable cells con-
stituting cotton and linen, and less pure in other fibres
such as hemp and jute, and in wood itself

Rather more concentrated than the carbohydrates,
/>., containing still only carbon, hydrogen, and oxygen,
but with a higher proportion of carbon, are the fats,
oils, and waxes which are present in many vegetable
tissues ; but only in the seeds, nuts, and fruits of certain
plants is there enough to be squeezed out for commercial
purposes. The seed is always a very concentrated
storehouse of food for the future plant, and it is in the
seed that such concentrated materials as oils and fats
are mainly found.

6 WHAT THE PLANT IS MADE OF [chap.

So far the compounds have only contained carbon,
hydrogen, and oxygen, but in all plants there is another
group of compounds built up as before with carbon
as the centre, but with nitrogen also as part of
the fabric. Of these compounds containing nitrogen
the most important are the proteins (in older phraseology
proteids or albuminoids) — complex bodies containing
carbon, nitrogen, hydrogen, oxygen, and smaller propor-
tions of sulphur and phosphorus. Perhaps the easiest
of these bodies to separate is gluten from wheat flour,
but by suitable tests they may be recognised in all
plants and in all parts of the tissues. The proteins are
very elaborately constructed bodies, and are either
insoluble or not properly soluble in water ; but as a sort
of intermediate stage in their building up or breaking
down, come certain simpler soluble compounds of carbon,
hydrogen, oxygen, and nitrogen, often called amides,
though the name is not very correct, and it will be
simpler to call them ^-proteins.

Of course the carbohydrates, the fats, the proteins
are not the only groups of compounds occurring in plant
materials : there are also bodies like the essential oils,
which give scent to plants, the resins, the vegetable
acids, the bitter and poisonous principles, etc., etc.; but
the three groups enumerated constitute by far the
greater part of every plant, and on them only depends,
at least in its broad outlines, the life of the plant and in
its turn of the animal.

Since the crop starts with the seed, we must begin
by finding out how a seed is constructed and what
conditions are necessary to make it germinate and grow
into a plant capable of yielding seed in its turn. Take
some conveniently large seeds — beans and maize form
the best examples, though they may be supplemented
or replaced by sunflowers and wheat — soak them in

III.

Torn Testa...
Cotyledon . . .

Plumule )]

Radicle

II.

Testa

.. cotyledons

Fig. I.— Germinating Seedlings of Beans,

I. Seed split open after germinating.
II. Root a few days old.
III. Still older seedling showing leaves and secondary root?.

[Face page 6.

I.] STRUCTURE OF THE SEED 7

water for a few hours, surround them with damp sawdust,
and then keep them in a warm place for a day or two in
order to start their germination. As soon, however, as
they have been well soaked they may be pulled to pieces,
and the function of each part can be followed up day
by day as the growth advances. Taking first the bean,
v/e begin by finding a tough outer skin, which after
soaking can be peeled off entirely ; when the plant
germinates under natural conditions, this skin is burst
and thrown off. Under the skin we find^the mass of the
seed, which splits at once into two flat discs, united at
one point by a small structure, that for the moment we
may liken to a hinge. Notice the position of this hinge
with regard to the markings in the seed coat which
indicate where the bean was attached to the pod, and
therefore to the parent plant. The meaning of the
structure of the bean will only become plain by following
up the successive stages in its growth. It will then be
seen that what we have called the hinge develops into
the future plant ; it puts out a root, and in the opposite
direction it elongates into a shoot, from the tip of
which leaves begin to unfold — it is indeed the " embryo,"
the seat of life in the plant. The two flat discs which
are united by the embryo open apart and set them-
selves at right angles to the new stem, if the plant is
being grown in the ordinary way ; in the open air they
become green, but at the same time they slowly shrink
and become emptied of their contents, finally they
shrivel and drop off. They are known as " cotyledons,"
or seed leaves. In the case of the maize the structure
is somewhat different ; at one end of the grain will be
found, as before, the embryo from which proceed the
rootlets, no longer a single one but several, and a shoot
which shows a single leaf. The greater part of the grain,
however, is occupied not by a pair of seed leaves, but

8 WHAT THE PLANT IS MADE OF [chap.

by a mass of material which remains attached to the
side of the stem of the young plant. As the plant
grows the seed material gradually disappears, until after
a time only an empty husk remains, and then falls off.
In the case of maize and similar seeds like wheat and
barley, which begin by throwing up only a single leaf,
this attached food store does the work of the seed
leaves in the bean and similar plants, and is known as
the endosperm. Now take some of the soaked seeds
and mutilate them in various ways before setting them
to germinate : cut out the embryo, cut bits off the
embryo, poison it by touching it with a trace of carbolic
acid or a drop of boiling water, cut off one cotyledon or
half of both cotyledons, cut off a large and a small part
of the endosperm.

The seeds will not grow at all if the embryo is cut
out and killed or much mutilated, but the embryo itself
will make a start to grow without cotyledons or endo-
sperm, though the length of time it will subsist will
depend on how much of the latter has been left to it.
The embryo is in fact the seat of life in the seed,
the rest (cotyledons or endosperm) is dead food material
stored up by the parent plant to give sustenance to the
new plant (embryo) until it can establish itself in the
world. It has been found possible to grow an embryo
removed from its endosperm on blotting paper or
similar porous material, if it is kept moistened with an
appropriate food solution containing sugars, <3'-proteins,
and similar plant constituents.

We may now sum up the facts we have ascertained
about the seed : it possesses a coat of one or more
membranes, an embryo (which is the seat of the life of
the seed), and a food store for the nutrition of the embryo
until it has sufficiently developed to feed itself on the
soil and the air, and this food store may take the form

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I.] GERMINATION 9

of a pair of cotyledons or a single endosperm. There
are other minor differences in arrangement that need
not concern us ; there are also very interesting variations
in the way the root develops, in the origin of secondary
roots, side buds, etc., etc., and again in the character of
the cotyledons and the way they develop above ground,
but these points do not bear directly on nutrition, and
the student must follow them up for himself.

We may now proceed to examine the conditions
which favour or are necessary to the germination of the
seed. In the first place, moisture is required ; dry seeds
can be kept a considerable time without apparent change,
it is only when the embryo has absorbed sufficient water
to get some of its soluble constituents into solution that
growth can begin at all. Hence a seed must be sown
in a sufficiently moist soil and the supply of moisture
must be maintained until the plant is established ; more-
over, moisture must reach the embryo inside the seed
coat, yet in some cases the seed coat offers a considerable
resistance to the passage of water through it. Every
seed possesses a fine passage through the seed coat,
called the micropyle, but in many cases soon after the
seed is ripe the micropyle becomes closed by the
shrinkage of the seed coat, which itself also grows
impervious to water. Hence follows a great delay in
germination, which may not take place indeed for a
year or longer until the seed coat has wholly decayed
away. With many garden plants, e.g. the auricula and
the hellebore, germination will take place in a few days
if the seeds are sown directly they are ripe, but if once
they are dried off and stored before sowing they will
probably remain dormant for a year in the seed pans
and then begin to germinate slowly or at irregular
intervals. In any sample of clover seed a certain
number of " hard " seeds will always be found which

lO

WHAT THE PLANT JS MADE OF [chap.

fail to germinate when the usual test is made, although
they are perfectly formed and will eventually start into
growth after a lapse of time. In some of these cases
where the seed coat is obstinate the penetration of
water may be hastened by various mechanical devices ;
the seed coat may be cut or filed through (gardeners do
this with Canna seeds), or the seeds may be dipped for
a moment in boiling water, or even soaked for a short
time in strong sulphuric acid, which is then quickly
washed away. Certain tree seeds only germinate after
a forest fire has swept over the ground ; heat has been
necessary to break up either the nut in which the seeds
were enclosed or the seed coat itself The object is in
all cases the same, to begin the breakdown of the seed
coat and admit moisture to the embryo.

Table II.— Temperatures required by Germinating Seeds,
(Fahrenheit.)

Minimum
limit.

Optimum.

Maximum
limit.

Degrees.

Degrees.

Degrees.

Wheat ....

41

81

99

Barley ....

41

83

100

Mustard

32

83

99

Turnips

46

89

109

Cucumber

56

93

115

Besides requiring a provision of moisture, seeds will
only germinate within certain well-defined limits of
temperature ; for each species there is a minimum
temperature below which no germination will take
place, above that minimum the rapidity of germination
increases with the temperature up to an optimum
point, beyond which it declines until an upper limit is
reached, which again stops germination entirely. The
lower limiting or minimum temperatures for germination

i] AIR REQUIRED FOR GERMINATION ii

have considerable bearings upon practice; gardeners
know well that certain seeds must be sown " in heat " or
they will not start ; amongst farm crops, the seeds of
turnips and mangolds make very little progress if sown
before the land has got warmed up by the spring suns
and cultivation.

The next indispensable factor in the germination of
seeds is the presence of air, and this may be illustrated
by one or two simple experiments. Put some mustard
seeds into a bottle, fill it completely with water and
stopper it, then let it stand in a warm place ; a few of
the seeds may " chit " because there is a little dissolved
air in the water, but they will stop at that and cease
to grow any further. Grease the stopper of a wide-
mouthed bottle holding about a pint, put in half an
ounce of mustard seeds and enough water to wet them
thoroughly, stopper up and set in a warm place as before,
but this time in the dark. In a few days the seeds will
germinate, and as there is some air in the bottle they
will continue to push for a few days before they come
to a pause and stop for lack of more air. Now see what
has happened to the air inside the bottle by taking out
the stopper and inserting a lighted taper. It goes out,
indicating that the oxygen of the original air has been
so far used up that a candle can no longer burn. Now
decant some of the air into a clean bottle and shake it
up with lime water : the lime water becomes milky,
indicating the presence of carbon dioxide or carbonic
acid. The germinating seeds have thus affected the air
with which they were enclosed, just as a burning candle
would do or a breathing animal ; oxygen has been used
up, and carbon dioxide has taken its place ; something,
in fact, in the seed has been burnt, i.e., combined with
the oxygen of the air to form carbon dioxide and water.
The identity of the process going on during germination

12 WHAT THE PLANT IS MADE OF [chap.

with burning and breathing may be further demonstrated
by showing that heat is given off during the process.
To prove this, a pair of sensitive thermometers are
necessary, reading to a tenth of a degree ; put a mark
on each and let them stand in the same jar of water for
a time to note any difference in their readings. Mean-
time, soak about a pint of peas, or mustard, or barley in
water for a few hours, drain off the water, put the peas
in a jar and plunge the thermometer into their midst.
Fill up another jar with water, in which insert the
second thermometer, wrap both jars in flannel to reduce
losses of heat, and then stand the pair in some place
where they are screened from any but slow changes of
temperature, as in an inner cupboard of a room with-
out a fire. In a day or two, when germination has
set in actively, the thermometer among the seeds will be
standing permanently higher than the other one which
indicates the normal surrounding temperature. With
this further proof we may conclude that germination is
a process of breathing or burning, in which some of the
seed material combines with the oxygen of the air to
produce carbon dioxide and water ; only by this sort of
burning does the infant plant get the energy to go on
living and working. Indeed, even while the seed is dry
and apparently dormant it is breathing very slowly, and
so consuming part of its substance; being dry, the
embryo cannot draw upon the materials in the endosperm,
but is confined to burning up any spare material it
possesses within itself. Hence seeds cannot live for
ever ; they vary very greatly in their powers of endurance,
both with the kind of seed and the way they are stored,
but very few of the ordinary farm and garden seeds
remain alive after ten years. The embryo is found to
perish and shrivel up, though the endosperm or coty-
ledons remain perfectly sound ; the slow combustion

I.] VITALITY OF SEEDS 13

process necessary to maintain life exhausts all the
available material in the embryo, which then perishes,
but long before death the vigour of the seed becomes
greatly weakened by age. There seems some evidence
that seeds buried in the ground may retain their vitality
for much longer periods than seeds stored in the open
air, perhaps because the greater supply of moisture
enables the embryo to draw upon the food store to
support the combustion process, instead of dying as soon
as it has used up all its own stock ; but the evidence that
long-buried seeds do retain their vitality is still a little
doubtful. Of course, germination of the so-called
" mummy wheat " is a fairy tale ; whenever wheat grains
are found that were indubitably buried with the mummy,
not only has the embryo perished but the material of
the endosperm is carbonised just as if it had been
charred, so that it is no longer capable of forming food
for an embryo.

Since the food store of the cotyledons or endosperm
exists for the purpose of maintaining the embryo until it
has built up a plant capable of carrying on an independ-
ent existence, it is clear that if this latter process is too
long deferred, the food store may give out and the plant
perish. The larger the seed the more reserve there is,
and the longer the young plant can grow on the seed
store alone ; for this reason the depth at which seeds
can be sown is determined by their size. Provided it
does not get so far down as to be cut off from the daily
warmth of the sun or from the air, the deeper a seed is
sown the better, because it is thereby more sure of
obtaining a continuous supply of moisture. But minute
seeds, like those of a poppy, do not possess enough
material to give rise to more than a very short stem or
leaf with which to reach up to the light : mustard seeds
can hardly struggle up 3 inches, while 6 inches taxes

14 WHAT THE PLANT IS MADE OF [chap.

all the resources of wheat and barley. A few simple
experiments with seeds of various sizes, sown at different
depths in pots, will show how the proper depth for each
seed is conditioned by its weight, i.e. by the amount of
material it has available to lift a leaf up into the light.
Some covering of soil is desirable in order to keep the
seed from drying out ; as far as the light goes it does
not much matter, for all our common seeds germinate
equally well in light or darkness.

One other point in the germination of seeds requires
consideration : the materials in the food store of the
endosperm or cotyledons are mostly insoluble, as we
can convince ourselves by a little experiment ; they
consist as a rule of starch and proteins, with sometimes
fat and oil. Yet when the embryo begins to grow these
materials have to be conveyed to the end of the shoot
where leaves are unfolding, and to the growing tip of
the root ; that they do get transferred is proved by the
eventual emptying of the endosperm or cotyledon.
The transference is only possible if the food store is
first of all rendered soluble in water, for liquids alone
can traverse the cells of the plant. The mechanism of
the process can only be rendered intelligible by another
experiment or two. Soak a handful of barley in water
as before, and put it aside in a warm place to germinate
until the rootlets are an inch or so long ; now smash the
grains up in a mortar, add enough warm water
(at 40° to 50° C.) to make up a sort of thin porridge, and
let the whole stand for an hour or two, then filter.
Meantime make some starch paste by rubbing up a
few grammes of starch with cold water, and pouring
on 300 to 500 c.c. of boiling water; then bring the
whole up to a boil, and put it aside to cool. The starch
paste will form a thick, troubled-looking liquid, and if
to a little of it in a test-tube a drop of a solution of

I.] A CTION OF ENZ YMES 1 5

iodine in alcohol or potassium iodide solution be added,
an intense blue colour will be produced : this is a test
from starch that we shall have to use repeatedly.

When the starch paste has cooled down to 50^ C. or
so, and the germinated barley extract has been filtered
clear, pour about 100 c.c. of starch paste into a beaker
and add to it 10 c.c. of the barley extract, stirring them
well together. Keep the mixture on a warm bath at
50° to 60° C, stir, and watch the result : almost instantly
the starch paste will begin to get thin and limpid, and
if at intervals a little is taken out and tested with iodine
the blue colour will begin to give place to purple, and
will finally cease to appear. When this is the case,
taste the mixture ; it will be faintly sweet, and on testing
it will be found to contain sugar. About one-quarter
fill a test-tube with Fehling's solution, add half as much
of the converted starch paste, and bring to the boil :
the blue colour disappears, and there is a copious
precipitate of bright red oxide of copper. This is a
test from sugars we shall often have occasion to use ;
if it is tried on the unconverted starch paste, no change
takes place. Clearly, then, we have extracted from the
germinated barley some soluble substance which is
capable of transforming the thick starch paste into
freely soluble sugar ; it will do the same to solid starch
grains, as may be seen under the microscope. Dab a
tiny bit of cut potato on a glass slip, the little smear
it leaves consists of starch grains, flood them with a drop
of the barley extract, put on a cover slip, and place
under the microscope. In a few hours the grains will
begin to get etched, and will finally break up and
disappear. Now repeat the first experiment with the
starch paste, but this time boil the barley extract before
adding it — no change to sugar will take place ; the boil-
ing has destroyed the substance in the barley extract

i6 WHAT THE PLANT IS MADE OF [chae

which can convert starch into sugar. This substance in
the extract of the germinated barley belongs to the
class of bodies known as enzymes, or soluble ferments ; it
is called diastase, and it is secreted by the active growing
embryo of the barley, its function being to convert the
stored-up starch of the endosperm into soluble sugar
which can travel to the growing points of the plant.
There are many kinds of enzymes secreted by both
animals and plants ; they are mostly soluble in water ;
they all work most rapidly at a temperature of 50° to
60° C. (122° to 140° F.), and are destroyed at or below the
temperature of boiling water. By very similar experi-
ments we can show that the germinating seed also
contains a protease, i.e. an enzyme attacking the
insoluble proteins and converting them into soluble
amino and amido bodies. Pepsin and papain are
commercial proteases, extracted one from an animal the
other from a plant, and it is easy to show that they will
dissolve insoluble proteins like fragments of boiled
white of Qgg or gluten. Similarly, the embryos of
germinating seeds of mustard or flax secrete a lipase,
or fat-splitting enzyme, capable of reducing fat to soluble
substances which can traverse the plant and be utilised
at the growing points.

The germinated barley from which we have just been
extracting diastase is nothing but incipient malt; the
process of malting consists in steeping good well-ripened
barley for forty-eight hours, and then spreading it in a
layer 4 to 12 inches thick on floors to germinate. After
ten or eleven days, when the rootlets are almost twice as
long as the grain, the barley is slowly and carefully
dried at a temperature not exceeding i8o°F. Finally
it is screened to knock off the rootlets, and put into
store. The germination process develops a quantity of
diastase which accumulates in the embryo and is not

I.] SEED TESTING ij

destroyed at the temperature of drying, so that when the
malt is afterwards ground and extracted with water — the
mashing process — there is sufficient diastase to convert
quickly all the starch of the endosperm into sugar, which
is afterwards fermented by the yeast into alcohol.

Having thus considered the factors that determine
the germination of seeds, we are in a position to consider
the application of them to practice. In the first place,
the seed must be alive ; it must not have begun to
sprout and then been dried off again ; it must not have
been overheated in the stack, or harvested prematurely
before the embryo had come to its full term ; it should
not be so old as to have declined in vitality. It is easy
to make a germination test of the common farm or
garden seeds; select a soft tile, and with a file score
ten parallel grooves across it, then ten more crossing
them at right angles, thus giving rise to lOO points of
intersection. Stand the tile in a dish of water so that
the scored surface is above the water but is kept damp
by the porous nature of the tile, and set out lOO of the
seeds taken at random, one on each intersection. Cover
over with another plate or dish, set it in a warm place
and examine every day, counting the number that have
started, and removing them. A saucer of fine sand or
even three or four thicknesses of blotting paper will do
as well as the tile, though the water supply may require
a little more attention. Most farm seeds will have ger-
minated in ten days, but mangolds require a fortnight,
and the majority of grass seeds three weeks. If the
records are properly kept, a table is finally obtained which
shows both the percentage which eventually germinate
and the rapidity with which they start; with a good
young vigorous sample, most of the seeds start within
a day or two of one another and comparatively early.

Given good seed, it is of no use to sow it until the

B

i8 WHAT THE PLANT IS MADE OF [chap. i.

year is advanced enough to ensure sufficient warmth
in the soil, or without a proper preparation of the land.
Of course some seeds require artificial heat, but all will
grow more quickly on a southern slope, or where the soil
is not kept cold by lack of drainage or insufficient
preparation. The great art of the farmer — the prime
act of husbandry, in fact — lies in the preparation of a
proper seed bed, and its character may in most cases be
summarised in two words : fine and firm. It must be
fine, to ensure that all the seed can be put in at the
proper depth, because there is a proper depth for each
seed depending on its size ; it must be firm, to keep the
seed and the infant plants properly supplied with
moisture. Sometimes the seed is soaked before sowing,
though on the farm this is only occasionally done with
mangold seed, which has a thick, coarse husk. Occasion-
ally the soaking may very much quicken up the
germination, but it is not so easy to sow wet or even
damp seed evenly, and there is some danger in sowing
soaked seed in dry soil, lest a drought should follow and
the seed should perish after its premature start.
Lastly, as air is necessary to the germinating seed, the
soil must be working freely at sowing time ; if the seed
is plastered into wet heavy soil or the surface is smeared
over by incautious cultivation, the seed may die, or
become very weakly for want of air. Certain kinds of
heavy land, again, are apt to develop a tight, glazed skin
on the surface, if seeding on a fine tilth is followed by
heavy rain and later by drying winds and sun ; a roller
should be put over the land to break the crust and let
the air in to the seed.

As soon as the young root has got anchored in the
soil and the young shoot has spread its first leaves into
the air, the function of the seed is over and the plant
begins its independent existence.

CHAPTER II

THE WORK OF THE LEAF

The Increase of Weight in a Growing Plant is derived from the
Air. Plants split up Carbon Dioxide and give off Oxygen.
Purification of the Air by Plants. Formation of Starch in the
Green Leaf. Motive Power supplied by Light. All parts of
the Living Plant are also breathing. Necessity of Leaves to
the Growth and Ripening of the Plant. The Leaves of the
Plant give off Water. How much Rainfall is required by
Crops.

The leaf is in many respects the most important part
of the plant ; it is essentially the manufacturing organ,
and on it depends the whole power of the plant to grow
— i.e. the fundamental process which produces fuel and
food for ourselves and the rest of the animal creation.

As an understanding of the manner in which a leaf
works lies at the very foundation of our science, it will
be necessary to consider a number of experiments to
illustrate every phase of the action.

In the first experiment weigh out a few grains of
mustard seed, and if you have not previously deter-
mined what percentage of water the mustard seed
contains, weigh out a second portion, and put this to
dry in the oven. Then take a pot filled with the
purest sand and mix some of the plant ash you have
previously made with the sand at the top of the
pot, add a suitable amount of water, and sow the

19

20 THE WORK OF THE LEAF [chap.

mustard seeds. When they are well up and showing
green leaves, add one-tenth of a gramme of nitrate of
soda to the water you are giving to the pot, and let the
growth continue for a few weeks longer. Finally, when
the plants show signs of flowering pull them up, wash
away all traces of sand from their roots, put them in the
oven, and weigh them when dry. They will weigh eight
to ten or twenty times as much as the seed from which
they started. It is not even necessary to add to the pot
of sand the plant ash or the nitrate of soda — the weighed
seeds may be sown on a bed of sand or a strip of clean
flannel kept moist in a soup plate, the little plants being
taken off when they will grow no longer. In this case,
however, the increase of weight will not be so great.
Or, again, one of the water cultures to be described
later may be used to afford a comparison between the
weight of the seed and the weight of the plant arising
from it when it has not been in contact with any soil.
Now the point of all these experiments is that the
increased weight of the plant is largely made of carbon
(we have already seen that more than half of the dry
matter of a plant is carbon), yet neither the sand, the
plant ash, the nitrate of soda, nor the water used in the
first experiment, nor the solution used in the water
culture, contain any carbon at all. It is true that the
flannel we have also suggested as a medium on which
the mustard seeds could be grown is a compound of
carbon, but it is such a compound as the plant cannot
feed upon, and is as inert as so much sand. If, then,
the plant gains carbon as it grows, and there is none in
the water or the support" on which it grows, where does
the carbon come from ? There remains only one source
— ^the air which surrounds the plant ; and later experi-
ments will make more evident the fact that plants do
derive their chief sustenance from the air. In these

II.]

CARBON DRAWN FROM THE AIR

21

preliminary experiments we did not use ordinary soil,
because it contains a certain proportion of compounds
of carbon, out of which the plant's increase might
possibly have been made, though we can now show
that such is not the case. Suppose, instead of a
laboratory experiment, we deal with a crop in the open
and make out a sort of balance-sheet ; there is so much
carbon in the soil at starting, and so much in the seed
and the manure, against which we can set off the
amount of carbon in the crop at the finish together
with that in the soil after harvest. Such was the
balance-sheet that Boussingault drew up for the first
field experiments that were ever carried out, and he
showed that, despite the great amount of carbon
removed in a crop, the soil contained no less of this
substance at harvest than at seed time.

Hence followed the inevitable conclusion that since
the carbon had not come from the soil, and could not
have been derived from the rain (water contains
hydrogen and oxygen only), it must have been taken
from the air. We can take an example of this kind of
balance-sheet from the Rothamsted wheat field, choosing
a plot manured only with inorganic salts containing no
carbon (superphosphate, sulphate and chloride of
ammonia, sulphate of potash, etc.), the soil of which
had been analysed in 1881 and again in 1893.

Table III.— Carbon in Soil and Crops, Rothamsted Wheat.
(Plot 7.)

Carbon in Soil, lb. per Acre.

Crops.
Average.

Total
Carbon
in Crop.

Carbon
in Seed.

Gain in Crop
over Seed
and Loss
from Soil.

1881.

1898.

Gain or
Loss.

Grain.

Straw.

61,000

54,000

-7,000

Bosh.
33-5

Cwt.
31-8

25,200

600

17,600

22 THE WORK OF THE LEAF [chap.

Thus, though the carbon in the soil has only lost
7000 lb. during the period under examination, no
less than 25,200 lb. per acre has been taken away in
the crops, and the air is the only source from which it
could have been derived. The air, we know, contains
from 3 to 4 volumes of carbon dioxide in every 10,000,
and small as the proportion may seem, it yet represents
an enormous quantity of carbon dioxide upon which the
plant can draw.

We will now take some experiments showing that
plants have the power to split up this carbon dioxide in
the air and take the carbon from it. As we are dealing
with gases we shall have to put our experimental plants
in water in order to see and collect the gases, and it
will, therefore, be necessary to take well or river water
that has had an opportunity of dissolving a little air, and
especially carbon dioxide, which is rather more soluble
than the rest of the air. By boiling some of the water
in a preliminary experiment it is easy to show that such
water contains dissolved carbon dioxide, which is expelled
in heating. Take a small bunch of young green active
shoots of mint or watercress and put them in a jar of
water, covering them with an inverted funnel the shank
of which leads into a test-tube full of water. Stand the
jar in the brightest light available, and repeat the
experiment with another jar placed in the dark. To
complete the demonstration a third jar should be used,
containing water that had been boiled to expel all gases
and then cooled down ; this also should be placed in the
light. As the light falls on the mint in the unboiled
water little bubbles of gas will begin to appear on the
tips of the leaves ; from time to time they will break
away and ascend into the test-tube above. No such
bubbles appear from the mint in the dark, or from that
which is in the light but immersed in boiled water.

II.] ox YGEN E VOL VED B V PLANTS 23

After a few hours of bright daylight the test-tube will be
nearly full ; remove it carefully, invert it, and bring into
the mouth a chip with a glowing end — the chip bursts
into a flame, proving the gas to be oxygen. Now
oxygen is one constituent of carbon dioxide, and the
experiment is an illustration of the fact that green
leaves in the light split up the carbon dioxide with
which they are in contact and set free the oxygen as
gas, retaining the carbon for themselves. This
continual evolution of oxygen by green plants is the
great agency which is always renewing the vital part of
the atmosphere ; out in the country where the trees and
the grass are growing, the amount of carbon dioxide in
the air keeps at about 3 volumes in 10,000, being rather
less in the summer, when vegetation is active, than in
the winter ; in towns the proportion rises to 4, and even
in dense streets to 6 and 7 per 10,000. On plants
growing in water it is possible to see the bubbles of
oxygen as they are produced ; if you look into any
ditch or pool on a bright day you will see the bubbles of
oxygen entangled in the vegetation, just as you will see
them dotted all over the green algal growth which
covers the bottom of many streams. The surface of
some streams is often covered with little masses of
floating scum ; this scum consists of the algal growth
that has been lifted off the bottom and buoyed up to
the surface by the bubbles of oxygen entangled in it.
It will be noticed that the scum only begins to float up
towards the afternoon and on a sunny day, i.e. after the
light has had time to act and bring about a plentiful
evolution of oxygen.

So far, however, we have only demonstrated that the
plant adds oxygen to the atmosphere ; we can now show
that it will remove carbon dioxide. On a bright day in
spring or early summer take a wide glass tube 5 or 6

24 THE WORK OF THE LEAF [cHAP.

feet long and fill it loosely with freshly gathered leaves
of grass or wheat, taking care only to use young, active
leaves. Now set up the tube horizontally in the
brightest daylight available, and by means of an
aspirator slowly draw air, first through the tube, and
then through a wash-bottle containing some baryta
water. Baryta water is a very delicate test for carbon
dioxide, becoming troubled and milky looking with
a very small quantity of the gas, but if the light is
good there will be no evidence of carbon dioxide in
the air that has been drawn through the tube. Then
detach the tube and let the ordinary air run through
the baryta water ; there is at once a milkiness, showing
what must have been the state of the air before it came
in contact with the green leaves. This experiment
illustrates the fact that green leaves in bright light take
the carbon dioxide out of the air, and, as we have seen
in the previous experiment, liberate the oxygen con-
tained therein.

By using the same apparatus with petals, bracts, and
other parts of a plant which are not green, it can be
shown that only the green portions of the plant have
this power of absorbing and splitting up carbon dioxide ;
in fact, the green colouring matter — the chlorophyll, as
it is called — in leaves and stems effects the first
necessary step in the process, by absorbing the light
which constitutes the motive power. That light is
absolutely essential may easily be seen by repeating
the last experiment after covering the tube containing
the leaves with brown paper. As soon as this has been
done the leaves will be found to add carbon dioxide to
the air passing through, instead of taking it out ; as we
shall see later, all parts of the plant, like germinating
seeds, are breathing as long as they are alive, whereby
they give off carbon dioxide and absorb oxygen, though

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II.] CARBON DIOXIDE SPLIT UP BY PLANTS 25

in bright light this breathing process is masked without
being stopped, by the reverse process of taking in
carbon which we are now considering. The method of
experimenting we have just been describing has been so
modified as to become a means of measuring exactly
the powers of the leaf in splitting up carbon dioxide
under various regulated conditions. In Dr Horace
Brown's experiments, a leaf still attached to the plant is
enclosed in a glass-sided box and a current of air is
drawn through the box, the proportion of carbon
dioxide being determined in the air before it .reaches
the leaf and again when it leaves the box. Working in
this fashion, Dr Brown has shown that a square
decimetre (4 inches square) of active green leaf will
decompose about o-oo8 gramme per hour of carbon
dioxide in ordinary diffuse daylight, which amounts
correspond to a formation within the leaf of about o-oo6
gramme of dry matter. The light may be diminished
considerably without any corresponding falling off in
the power of the leaf, until a certain point is reached
beyond which the action will fall off in proportion to the
reduction in the light. It is easy to see how dependent
plants are upon light by the failure of most of them to
flourish or even to grow in anything approaching dense
shade ; only a few classes of green plants, like ferns and
mosses and those generally of a very slow-growing
character, have adapted themselves to live in compara-
tive shade, whereas all farm crops, which are of course
distinguished by the enormous quantities of dry matter
they manufacture, must be exposed to the fullest possible
light. The process of fixing the carbon of carbon
dioxide and giving off oxygen by the green leaf in sun-
light, which we shall in future call assimilation, may now
be studied by a difTerent method, depending upon the
fact that the first visible product of the action in the

26 THE WORK OF THE LEAF [chap.

leaf is starch. We have already learnt that starch
consists of the element carbon combined with the
elements of water, from which it follows that the plants
must be able to manufacture starch and oxygen out of
carbon dioxide and water, just as in the reverse way
starch and oxygen will burn together to produce water
and carbon dioxide.

Assimilation.
Carbon ) _ , j. . , Carbon^ ^ , _

Oxygen J ^^^^°"^^°^*^® + ^^^^'^ = Water | Starch + Oxygen.

Of course the process of making starch is not so simple
as this diagram makes out, because there must be several
intermediate stages within the plant, still for our pur-
poses we only need to recognise the relationship between
the final products of the change in order to interpret
the various experiments which follow. It is first of all
necessary to learn to identify starch within the leaf;
because the leaf is alive and strongly coloured, it dis-
guises the blue colour which iodine usually produces
with starch. The green leaf must be dipped for a
moment into boiling water to kill it, and then soaked in
alcohol or methylated spirit, until the green colour is
dissolved out. If now the bleached leaf is dipped into a
very weak solution of iodine, the colour of pale sherry, it
will be turned very dark blue, practically black, because
all the starch grains that are diffused throughout the
leaf are intensely stained by the iodine. The leaf can
then be examined under the microscope to see how the
rounded grains of starch are imbedded in all the cells
composing the interior tissues of the leaf

The next step is to show the dependence of starch
formation upon the exposure of the leaf to light ; a
dwarf tropaeolum plant is very suitable for experiment,
if it can be covered completely with a box so as to
exclude the light. The next morning but one, remove

Fig. 5.— Artichoke Leaf, on which the Light Patch was

PROTECTED FROM LiGHT, THE StARCH IN THE LEAF BEING
AFTERWARDS STAINED WITH lODINE.

[Face page 26.

II.] STARCH FORMATION IN THE LEAF 27

the box and pick off one or two leaves, which must be
put away in a box until they can be brought indoors for
testing ; to one or two other leaves still attached to the
plant fasten opaque designs covering part of the leaf, the
simplest plan being to cut two discs of cork and pin them
together with the leaf between. Leave the leaves thus
protected in places from the light until evening, and then
gather them. Follow the same routine as before in
testing the leaves for starch ; it will be found that the
leaves which have been kept in the dark for thirty to
forty hours are quite devoid of starch, from which we
may conclude that any starch present in the leaf when
the plant was covered up has been removed in the dark.
The leaves, however, which were afterwards partially
exposed to the light show a pattern ; the protected
portions still contain no starch, whereas the rest of the
leaf on which the light has fallen has gained starch, and
so will colour up when the iodine solution is applied.
Further experiments depending on the test for starch
can also be tried ; for example, a variegated leaf, white
and green, will show starch in the green parts and not
in the white. Again, a small plant may be kept for a
day or two under a bell-jar over water with some strong
cautic soda solution standing beside it ; the caustic soda
will remove all the carbon dioxide from the air with
which the plant is in contact, and the leaves after a day
or two cease to contain any starch, though they may
have been in full sunlight for some hours before they are
gathered. In this way it is possible to show that the
formation and presence of starch in the leaf is dependent
upon (i) exposure to light ; (2) upon the greenness of the
leaf; and (3) upon the presence of carbon dioxide in the
air with which the leaf is in contact ; all of which
conclusions agree with the views of assimilation that
we had before obtained by other methods.

28 THE WORK OF THE LEAF [chap.

Though starch is manufactured in the leaf it does
not accumulate there, in the darkness it is moved wholly
or partially away and stored in some other part of the
plant : were it not so, leaves would become thick and
swell with the stores of manufactured starch. The
transference of the starch is effected by a similar
mechanism to that which utilises the starch in a seed
for the use of the distant-growing parts of the plant ;
the leaf cells secrete an enzyme capable of dis-
solving starch and transforming it into sugar, which
being soluble in water can move about in the plant.
To show the presence of this diastase we must gather
some young and active green leaves in the early
morning, or after they have been shut up from the light
for some time, as in a previous experiment. Now dry
these leaves very quickly but at a low temperature, best
of all by exposing them over strong sulphuric acid in a
desiccator from which the air has been pumped. Under
these conditions the leaves will dry very rapidly and
their enzymes will suffer no change; when dry, powder
the leaves finely and introduce a little of the powder into
a starch paste solution as before. The starch paste
solution will rapidly become limpid, will lose its power
of turning blue with iodine, and will finally give a
reaction for sugar with Fehling's solution. Clearly the
green leaf contained an enzyme which acts on the starch
paste like that which was present in the extract from
germinated barley — a diastase transforming starch into
soluble sugar capable of diffusing out of the leaf into
such parts of the plant as may require it. So funda-
mental is the process of assimilation that yet another
experiment may be described to illustrate the action.
For this purpose it is necessary to have at hand a plant
or plants possessing a considerable number of large
leaves : the vine, hop, or sycamore are among the most

II.] STARCH FORMATION BY THE LEAF 29

convenient for the purpose. Late at night, when the
removal of starch has been in progress for some time,
about three hundred leaves with their stalks attached
should be gathered and brought indoors. From the
heap of leaves pairs of approximately equal size are
picked out, and as each pair is made up one member of
it is placed in one heap which we will call A, the second
on another heap, B. When a hundred pairs have thus
been divided, the two heaps are weighed and will be
found approximately equal, because the errors of match-
ing each pair of leaves will neutralise one another with
so large a number as a hundred pairs. However, there
will probably be some small difference in weight which
must be noted. The next step is to put one heap (A) of
one hundred leaves into the oven to dry, the other
hundred are set with their stalks in bottles of water in a
position which will expose them to full daylight on the
following morning. At the close of that day they also
are put in the oven to dry. On comparing these sets of
dry weights (making any necessary allowance for initial
differences of green weight) the leaves that have been
exposed to the air for a whole day will be found to have
gained in weight, because of the starch they have formed
under the action of the light

We have already described one experiment to show
that the leaf of a plant is also carrying on a second
process, one of respiration or breathing, which in its
result is exactly opposite to assimilation, in that it burns
up some of its carbonaceous matter, combining it with
the oxygen of the air by which it is surrounded to form
carbon dioxide and water. It is possible to show that
each part ^of the plant is producing carbon dioxide,
merely by gathering such parts in quantity, shutting
them up in a jar for an hour or so, and then testing the
gas within the jar with lime water for carbon dioxide ;

30 THE WORK OF THE LEAF [chap.

though, of course, with leaves and other green parts the
jar must be shielded from the light. Respiration is
most active in the flower, and if the jar is filled with a
lot of young, active tropseolum flowers, a very rapid
evolution of carbon dioxide can be observed. Respira-
tion is always going on, though it is reduced to a
minimum at temperatures below 40° F. ; it is, in fact, a
process essential to the life of all the living cells that
make up either plants or animals. In a leaf, however,
it is never so rapid as the opposite process of
assimilation is in the light ; were not assimilation very
much more active than respiration, the plant would
never increase in weight at all. It is due to the
respiration, which is a necessary accompaniment of their
life, that roots, like mangolds or potatoes, gradually lose
weight when they are stored, for the loss is not only of
water but of dry matter also. Bulbs of tulips or
daffodils are also noticeably lighter in the autumn
when they are planted than in the early summer when
they are first put into store, and if the planting be
deferred for any reason the loss of weight becomes even
more evident.

Another experiment may be carried out to illustrate
further the processes of respiration and assimilation :
About a hundred barley grains are soaked and placed
with a little water in a stoppered bottle holding about a
pint, the stopper is left out and the bottle exposed to
the light until the barley has shot and made a fair
amount of leaf The stopper is then inserted, and the
bottle is put away in a dark cupboard or drawer for
two days ; on taking it out and testing the air in the
bottle by means of a lighted taper, the taper will
be extinguished. In the dark only respiration has been
going on, and so much carbon dioxide has been pro-
duced and so much oxygen used up that the air in the

Fig. 6.— Bottle enclosing Barley Seedlings.

When kept in the dark the enclosed air puts out a lighted taper, but will allow
it to burn after the bottle has been for some hours exposed to light.

[Face page 30.

II.] RESPIRATION AND ASSIMILATION 31

bottle is no longer capable of supporting combustion.
Now stopper-up the bottle again and stand it in the
light for two days ; again test the air it contains with a
taper, and it will be found to support combustion. In
the light the green leaves of the barley have split up
the carbon dioxide and replaced it by oxygen, until the
air will once more support combustion. The bottle may
be replaced in the dark until respiration has again
loaded the air with carbon dioxide, whereupon it may
again be brought into the light and the air reoxygenated
by the assimilation carried out by the green leaves ;
these alterations may be repeated several times, until
at last the barley begins to die for lack of food. Under
slightly more natural conditions, however, such a cycle
of respiration and assimilation can be continued for
very long periods. For example, in the Rothamsted
laboratory a sample of soil weighing several pounds was
put away in a rather moist condition in 1874 i^ 3. gallon
bottle, which it three parts filled. The bottle was corked,
the cork waxed and covered with a lead capsule. A few
years afterwards a fern, Asplenium nigrum^ was noticed
to be growing within the bottle, having developed from
a spore which must have been present in the undried
soil ; this fern has continued to grow, and at the present
time (19 10) it occupies nearly the whole of the vacant
upper part of the bottle. No air can either enter or
leave the bottle ; at first some doubts were entertained
as to the impermeability of the sealed cork, but the
whole of the cork and the neck of the bottle have been
enclosed in a block of paraffin wax, which was melted
and cast on to its present position. The bottle stands
on a low shelf in a building lighted from the roof, the
illumination it receives is only good for a few hours on
summer days, when a little direct sunshine reaches it.
This illumination in the summer is, however, enough to

32 THE WORK OF THE LEAF [chap.

enable the green fronds of the fern to decompose
sufficient carbon dioxide to maintain its slow rate of
growth, and also to give rise to the oxygen required
by the plant for respiration throughout the whole year.
Similarly the plant is always re-creating carbon dioxide
by its respiration, and this carbon dioxide must be
undergoing a perpetual cycle of change — it is split up
by the plant in the light summer days, its oxygen being
returned to the air and the carbon held by the plant,
then in the darkness and the winter this change is more
slowly undone again and the carbon dioxide recon-
stituted. Of course, in such a fashion the fern could
never become any heavier, could not in fact have
reached its present size ; there has also been another
source of carbon dioxide within the bottle due to the slow
decay of the organic matter originally present in the
soil. The development of this enclosed fern with its
quiet annual ebb and flow might be looked upon as a
sort of perpetual motion machine, but we must not fail
to recognise the fact that one external factor — the
incidence of the light — is absolutely necessary to the
process. It is this light, small as its amount may seem
to be, which supplies the energy required to drive the
machine, and this fact may lead us now to consider
the assimilation process from the point of view of the
exchanges of energy which go on during the life of
the plant. It is clear that a plant is a storehouse
of energy, of potential work ; given enough of the
plant — a tree, for example — we can burn it under a
boiler and drive an engine which will do work for us.
To come a little closer, starch will burn when ignited
and supplied with air or oxygen ; in burning it will give
out heat, which can be made to do work. Clearly, then,
starch and oxygen contain more energy than the carbon
dioxide and water into which they are turned by the

i

Fig. 7. — Fern that has been growing inside a closed
Bottle for Thirty-six Years.

[Face page 32.

II.] ENERG V STORED B V THE PLANT 33

burning process. In consequence, when a leaf turns
carbon dioxide and water into starch and oxygen, it is,
as it were, pushing something uphill, endowing the
resulting product with more energy than the original
material possessed, and since energy cannot be created
de novo any more than matter can, this energy must
have been obtained from somewhere outside the leaf.
The energy required to effect the change is, in fact,
obtained from the light ; the green leaf simply acts as a
kind of transformer of the energy coming from the sun
in the form of light, into the stored-up energy possessed
by vegetable material. Stephenson was absolutely right
when he called coal "bottled sunlight," for the vitally
important feature of the coal — its power to burn and
give out heat, whereby it becomes a source of work — is
all derived from the light which fell upon those early
forests in which grew the vegetation that nowadays is
preserved as coal. The plant is not a very efficient
transformer of the energy of sunlight, because it only
picks out and utilises a very small selection from the
numerous rays making up the light ; according to
Dr Horace Brown's researches, the leaf only succeeds
in utilising for the manufacture of starch about Trnnr of
the energy of sunlight and ^V of ordinary diffuse day-
light. Small as this utilisation of the sun's energy may
seem to be, we must not fail to realise that in the
assimilation of the green leaf we see at work the only
great upbuilding process, by which energy is caught and
stored, that can be recognised as going on in the world.
The life of an animal is a down-grade process depend-
ing upon the burning up by respiration of materials
which have been previously built up by the plant, and
though the animal cannot destroy the energy that was
present in his food, he transforms it into low-grade
forms which are not longer utilisable. Decay and

C

34 THE WORK OF THE LEAF [chap.

burning are similarly destructive or down-grade pro-
cesses, and just as the life of the animal is absolutely
dependent on the preliminary life of the plant to build
up its necessary food, so for our engine power we are
largely living upon irreplaceable capital stored up in
the coal and oil that were manufactured in earlier stages
of the world's history.

The fact that the green leaf supplies the driving
power to the whole machinery of the plant finds a good
many applications in practice. It explains, for example,
how it is possible to kill out perennial weeds like thistles
or bearbine by persistent hoeing, which does not give
the leaves an opportunity of working, although the root
keeps throwing up fresh shoots from its latent buds.
Every time it does so, some of the material stored up in
the root is used to make the fresh shoot and get it up
above the ground ; if, however, the new leaves thus arising
are cut off before they have had time to manufacture
any surplus material and send it down to the root for
storage, the original stock is somewhat exhausted, until
by a repetition of the process the plant no longer
possesses any reserve material wherewith to lift a shoot
above ground. Persistence in the cutting-off process is,
however, necessary ; it is no good to spud a thistle once
during the year, because it possesses sufficient reserve
material in its root to get fresh leaves up to the light and
they soon repair the losses.

Again, we see how unwise is the practice of many
gardeners who remove the leaves of tomatoes, vines, etc.,
when the fruit is forming, with the idea of throwing all
the strength of the plant into the fruit or of letting in the
sun to ripen the plant. The removal of the leaves means
that the manufacturing processes of the plant are
stopped; no more carbohydrates are formed, in these
cases no more sugar, and the fruits remain small and

Fig. 8.— Transpiration of Water from Leaf.

[Face page 35.

II.] LEAVES AND RIPENING 35

without their proper sweetness because of the cutting-
ofif of the supply of sugar. Stopping the growing points
of the plant is justifiable, because thereby the material
manufactured together with whatever may be in reserve
in the stems or roots will be thrown wholly into the fruit
and is not wasted in making unnecessary new growth ;
but to the final heaping up of sugar and similar sub-
stances in the fruit the continued action of the leaf is
indispensable. In the. case of grapes, it has been shown
that to cut off any large proportion of the leaves with
the idea of more completely exposing the grapes to the
sun reduces not only the size of the grapes, but their
richness in sugar as well. What ripening action is
caused by the direct rays of the sun is not known, but
probably the increased warmth they cause induces in
apples and pears a quicker change of starch and similar
materials into the sugar and aromatic bodies which mark
the ripe fruit. The sunny side of the fruit is never,
however, very much ahead of the shaded side, so that we
may conclude that the shading is not of much moment
in delaying ripening, whereas the absence of leaves has
a seriously detrimental effect.

Assimilation and respiration do not, however, represent
the whole of the work of the leaf; it has one other
fundamental piece of work to do, that is, to get rid of
water from the plant. We can illustrate this action by
several simple experiments ; for the first, take a test-tube
with a well-fitting soft cork, and slit the cork in two down
its length. Then introduce a long thin leaf (a barley or
a daffodil leaf will do, according to the time of year) into
the tube, and cork up the tube with the leaf between the
two halves of the cork. Leave the tube thus hanging on
to the plant until the next day, when a plentiful deposit
of water will be found inside the tube. For a second
experiment, take a pot containing some actively growing

36 THE WORK OF THE LEAF [chap.

plant possessing only a single stem, a geranium for
example, and tie up the pot in waterproof paper or
rubber sheet so drawn round the stem of the plant that
no water can evaporate from the surface of the pot or
the soil in it. Counterpoise the pot on a large balance,
and note the loss of weight at intervals for the next few
days, comparing the loss per hour by day or by night,
and again during periods of varying temperature, etc.
Instead of weighing the water lost, a form of apparatus
may be devised to render visible the rate at which the
plant is giving off or " transpiring " water, so that com-
parative measurements may be made much more quickly.
An eight-ounce bottle is provided with a rubber cork
pierced with three holes, through the largest of which a
wooden rod passes, while a second carries a horizontal
piece of capillary tubing. A young branch of a plant
or the stem of a large leaf is now passed through the
third opening, the bottle is filled with water, and the cork
is forced in so that no bubbles of air are trapped beneath
the cork. When the apparatus has been left to itself for
a time, until it has become adjusted to the temperature
of the room, the water in the horizontal tube will be
seen to be continually receding because of the water
taken up by the stem and transpired from the leaves.
By means of a scale on the horizontal tube the rate at
which the leaves are transpiring may be measured, and
by putting the apparatus in a cooler room, by shielding
it from the light, etc., the effect of various factors upon
the transpiration process may be gauged. By means of
the wooden rod, the water in the bottle may be forced
back into the capillary tube each time a fresh measure-
ment is required. Measurements should not be made
until some little time has elapsed after each change, in
order that the plant may have adjusted itself to the new
condition. In this way it can be shown that a current of

Fig. 9.— Apparatus for Measuring Rate of Transpiration
FROM Leaf.

[Face page 36.

II.] IVA TER GIVEN OFF B V LEA VES 37

air on the leaves, produced, for example, by a bellows,
increases transpiration if it does not lower the tempera-
ture too much, whereas a close saturated atmosphere
obtained by surrounding the leaves with a bottle and
loosely closing the mouth will reduce and almost suspend
the process. Syringing the leaves, again, by inducing a
saturated atmosphere next their surface, also greatly
reduces transpiration. Again, by smearing with vaseline
first the upper and then the under side of the leaves, we
shall find that with most plants the transpiration takes
place almost wholly from the under sides of the leaves.
We can demonstrate this fact in another way by taking
two clean but cold pieces of glass and putting a freshly
gathered leaf between them ; on taking them apart
after a minute or two, the glass will be so dewed over as to
form an image of the leaf, but the image will be very
thin and faint on the glass which was in contact with
the upper side of the leaf The surfaces of a leaf should
now be examined under a microscope ; either the leaf
can be looked at without any preparation by reflected
light, or the skin on the upper and the under sides can
be torn off and examined separately by transmitted
light. The surface of the leaf will be seen to be studded
with small mouth-like openings, called stomata, and
these openings, except with a few plants, are very much
more numerous on the under than on the upper side.
The stomata, which open and close according to the
illumination, the temperature, the degree of humidity of
the air, etc., form a means of communication between
the outer air and the surface of the active cells in the
middle of the leaf; indeed the cuticle of the leaf, except
for these openings, is composed of cells containing no
chlorophyll, and simply acts as a protecting membrane
practically impervious to gases. Through the stomata
the plant takes in the carbon dioxide it requires for

38 THE WORK OF THE LEAF [chap.

assimilation and in its turn exhales oxygen; through
them again it exhales carbon dioxide when it is respiring,
and gives off its transpiration water in the form of
vapour. As a rule, the water escapes as vapour and
continues to be invisible, but when the surrounding
atmosphere is saturated it may condense as drops upon
the tips or edge of the leaf Thus arises the greater
part of the dew which covers the grass in the early
morning ; were dew only water that had been condensed
from the atmosphere by the ground cooled by radiation,
dew would be as plentiful on a garden path or on a
stone as on the grass.

Many experiments have been made to ascertain how
much water a plant transpires during its growth, and
this information is most easily applied to practical
problems if we establish a connection between the
amount of water transpired by a plant and the increase
of weight (reckoned, of course, as dry matter) which takes
place within the same period. At bottom there is no
real connection between assimilation and transpiration ;
the two processes go on simultaneously, and to some
extent are similarly affected by the same external
conditions, but they are in so many respects inde-
pendent that any ratio we may trace between them can
only be a sort of average, true for the general conditions
prevailing in the place of experiment. For example, in
England, Lawes and Gilbert concluded that for every
pound of dry matter elaborated by such plants as wheat,
barley, clover, and peas, about 250 lb. of water was
evaporated from the surface of the leaves. Hellriegel in
Germany with a drier atmosphere obtained results
about 50 per cent, higher, while Wollny in Vienna and
King in Wisconsin, with still hotter and drier climates,
obtained even higher ratios. In England, however, we
may assume that every pound of dry matter produced

Fig. 10.— Stomata of Sweet Pea, Lower Surface.

[Fac^ page 38.

II.] WATER REQUIRED BY CROPS 39

by a crop has entailed the supply of from 250 to 300 lb.
of water, and this mounts up to a considerable quantity
when the whole production per acre is considered. Of
mangolds, for example, we may expect to grow with
proper treatment 40 tons per acre, about 12 per cent, of
which will be dry matter, i.e. 4-8 tons of dry matter per
acre will be produced. This entails the evaporation of
4-8 X 250, or 1200 tons of water per acre ; and as an inch of
rain is approximately equal to icx) tons of water per
acre, a mangold crop of 40 tons per acre must evaporate
through its leaves as much as 1 2 inches of rain, a very
considerable proportion of the annual rainfall in the
districts in which mangolds are much grown. Other
crops do not produce quite as much dry matter per
acre as the mangold does, but still it will be found that
most of our farm crops necessitate the evaporation
of from 5 to 10 inches of rain. Considering that crops
make their chief growth during the hotter periods of the
year, when evaporation from the soil is also most active,
it becomes evident why the amount of rainfall is one of
the biggest factors in crop production, and why the
operations of the farmer in cultivating the soil are very
largely directed towards conserving for the plant what-
ever water reaches the land.

Because of the large amount of water evaporated by
the plant, a growing crop always keeps the ground
beneath it in a very dry condition ; after harvest it will
generally be found that the subsoil is dry to some
considerable depth. For example, in June 1870 at
Rothamsted after a long drought, determinations were
made of the amount of water in the soil on which a
barley crop was being grown, and on an adjacent piece
of land which was being fallowed and kept bare. Down
to a depth of 54 inches it was found that the bare fallow
soil contained 900 tons per acre more water, an amount

40 THE WORK OF THE LEAF [cHAP.

equivalent to 9 inches of rain. It is often impossible to
lay drains in a clay soil in the autumn on land which
has been cropped, because the subsoil is so dry as to be
unworkable by the ordinary drainage tools. Again, the
drying action of the crop explains the difficulty that is
often met with in the south and east of England in
attempting to secure a second catch crop by sowing on
the stubbles immediately after harvest ; unless there is
timely and continued rain, both soil and subsoil are too
dry to support any satisfactory growth. Even if a stand
of vetches or crimson clover is established, it is apt to
leave the land in spring so depleted of water that the
succeeding crop of roots is jeopardised unless there is
an abundant early summer rainfall. Another example
of the drying power of a growing plant is seen in the
wide circle of stunted growth which extends into a corn-
field round a tree in a hedgerow, should the season have
been a dry one. By its roots the tree has robbed the
subsoil of water much more than it has deprived the
crop of either light or nutriment. The fact that the
growth of a satisfactory crop necessitates the evapora-
tion of a certain amount of water is nowhere more
distinctly recognised than in the practice of alternating
one or two years of crops with a year of bare fallow
which prevails in some of the western districts of North
America, and also in Australia, in regions where there
is but a low annual rainfall of 8 to 12 inches. This
amount of rain is insufficient for more than a very small
crop year after year ; but by leaving the land without
crop for a season and cultivating the surface of the soil
so as to check evaporation, the rainfall of the fallow year
can be so far accumulated that when combined with the
normal rainfall of the following year a profitable crop
can be grown. Over a wide area of semi-arid country
farming can be made profitable without irrigation if the

II.] DEVICES TO REDUCE TRANSPIRATION 41

rainfall of two years can thus be stored up for a single
crop, or sometimes if three seasons* rainfall can be
utilised by two crops only.

It should not be supposed that all plants demand such
great quantities of water for transpiration as do our
ordinary field crops, because they are plants which have
been selected for their rapid growth under favourable
conditions. But in nature we always find that plants
which have adjusted themselves to live either in very
dry situations or in places where it would be injurious
to take in too much water, have always modified them-
selves in some way so as to reduce transpiration.
Whereas in temperate climates the leaves of a plant
arrange themselves to wave in the air and to present as
great a surface as possible to the light, the leaves of the
Eucalyptus and most of the other Australian trees so
dispose themselves as to present only an edge to the
sun, thus reducing both the transpiration and the heat-
ing effect of its rays. Very generally, in such circum-
stances the plant reduces the size of its leaves or even
replaces them entirely by spines, gorse or whin being a
case in point ; sometimes, as in the stonecrops and
houseleeks or the cacti, the leaf is made very thick, so
that its storage capacity is great as compared with
its evaporating surface. A hairy or a waxy glaucous
surface, or the presence of resins and essential oils
(among the plants growing on dry banks there is a
notable proportion of aromatic ones), are all regarded as
mechanisms by means of which the plant has learnt to
reduce transpiration.

Various other consequences also follow from the
continued loss of water at the leaf surface by transpira-
tion, such as the fliow of sap in the stem ; but first it will
be necessary to consider at some length how the water
enters the plant.

CHAPTER III

THE WORK OF THE ROOTS

The Roots as anchoring the Plant. The Roots supply the Plant
with Water. Roots require Air. Roots can only take in
dissolved Material. Etching Action of Roots due to their
Excretion of Carbon Dioxide. Elements necessary to the
Nutrition of Plants. Plants require Combined Nitrogen.

The root of the plant has two great functions to
perform — one mechanical, in keeping the plant firmly
fixed in position ; the other physiological, in supplying
the plant with water and the food it requires from the
soil. In certain cases, notably the mangold and the
carrot among farm plants, the root is also utilised as a
storehouse of the reserve material that is being accumu-
lated in readiness for the formation of flowers and seed.
The books devoted specially to botany must be con-
sulted for details regarding the many shapes taken by
roots, the manner in which they grow, and the devices,
such as the sensitive root-tip, which they possess in
order to make their way into the ground and turn in
the direction of food and water. For our purpose, the
germinated bean and wheat seedlings used for the
previous experiments will afiford sufficient information
as to structure. In the case of the bean, we find a tap-
root running straight down, from the side of which
secondary roots are thrown off; it may further be
observed, when the root has been allowed to grow into
damp air, that all the slender roots near the tip are

42

CHAP. III.] ROOT HAIRS 43

clothed with a down of very fine hairs, though the last
quarter of an inch or so is bare. In the case of the
wheat, instead of a single tap-root a number of fibrous
roots, which branch as they become older, issue from
the embryo ; these likewise are clothed with root hairs
near the tips. By day-to-day observations we shall find
that the root hairs fall off as the root ages ; they occur
only in a region just behind the growing point of the
root. By carefully digging up some young seedlings
from the open ground or from a pot of earth, and wash-
ing away the soil, we shall find that the root hairs cling
very obstinately to some of the fine particles of soil, with
which they are evidently in intimate contact. A good
deal of the holding power of roots is due to this associa-
tion of the root hairs with the finest particles of the soil.
It is possible to show by appropriate experiments that
the primary root of a plant tends to grow straight down-
wards under the direction of the pull of gravity, but that
it may be deflected by its attraction for such necessaries
as water, air, and suitable food. The attraction exerted
by the supply of air is plainly to be seen in the way
roots of trees and any deep-rooting plants force their
way into drains, just as their need for air is shown by
the way roots will not penetrate into undrained soil,
but stop short as soon as the layer is reached which
is saturated with stagnant water and contains no air.
It is also found that wheat develops the best root
system (the foundation of a large crop later) when the
winter is comparatively dry, so as to leave the soil well
aerated ; in a wet winter or wet soil the plant neither
needs so extensive a root system in order to keep
itself supplied with water, nor is it stimulated by the
air to produce roots. The attraction exerted by food
is seen in the way a bone or other fragment of spar-
ingly soluble manure becomes covered and permeated

44 THE WORK OF THE ROOTS [chap.

by the roots of any crop occupying the soil in which
the manure is buried.

Of the power of roots to anchor plants and hold them
firmly in position little demonstration is needed, but it
is interesting to see how many plants actually pull their
crown closer into the ground by contracting their roots.
Examine the young dandelions or plantains which have
established themselves on a lawn ; not only is there no
stem lifting the crown of leaves out of the ground, but
on the contrary this crown is pressed down tightly into
the ground. As a matter of fact it has been pulled
down by the contraction of the main root ; and if this
main root is carefully dug up in the early summer,
washed and examined, it will be seen to be corrugated
and to possess ridges showing where the contraction
has taken place. The crocus affords another interesting
example of contractile roots ; each year the new crocus
corm is formed on the top of the old one, so that after a
few years the corm would find itself on the surface of
the soil. However, the new corm develops a ring of
fleshy contractile roots which draw it down again into
the position occupied by the old one before its decay.
The seedling tubers of the Common Arum (Cuckoo-pint,
or Lords-and-ladies) possess similar contractile roots
which operate each season until the tuber has been
drawn down to its proper level. The habit of many
plants of throwing out adventitious roots from another
part of the stem than that from which the original roots
start should be observed ; in the case of cereals this
throwing out of adventitious roots from a point close to
the surface of the ground, much higher up than the
original crown of roots from the embryo, is a very
important factor in supporting the straw; like the
formation of side shoots, or " tillering," it is promoted
by free exposure to light and air.

Fig. 12. — Contractile Taproot of Dandelion.

[Fuce page 44.

III.] WATER CULTURES 45

In order to demonstrate some of the other actions of
roots, it will be as well at this stage to raise plants in
water culture ; barley or maize form convenient plants,
so a few grains should be germinated in damp sawdust
or between the folds of a roll of blotting paper standing
vertically with the bottom just dipping into water.
Choose some twenty-ounce bottles, fit the necks with
corks, and make up a solution as follows, dissolving the
ingredients separately and mixing them with the bulk
of the liquid in the order given : —

Water .

I litre.

Potassium Nitrate

I gramme.

Magnesium Sulphate .

• 0.5 „

Calcium Sulphate

. 0.5 „

Sodium Chloride

. 0.5 „

Monopotassium Phosphate

o-s „

Ferric Chloride

trace.

Wrap the outside of the bottle with stout brown
paper, and tie it in position so as to keep the contents
in the dark. When the seedlings have grown far enough
to show a little shoot and roots an inch or more long,
split the corks and cut a notch in the split surface, then
fix one of the grains in the notch between the two halves
of the cork, and insert them into the bottle, so that the
tips of the roots just dip into the liquid. If the notch is
too large, a little cotton-wool may be necessary to fix the
grain in position. Put the bottle in the window so that
the little plant gets full light ; if water is added to
the bottle from time to time to restore what has been
lost by evaporation, the barley or maize plant will grow
in a perfectly normal manner and will ripen seed in due
course. It will be obvious from the way in which the
water has to be constantly renewed in the bottle when the
growth is active, that the roots of a plant form the organs
by which the plant takes in water, a fact which might

46 THE WORK OF THE ROOTS [chap.

indeed have been deduced from the continual loss of
water by transpiration from the leaves. By weighing a
bottle and its growing plant on a sensitive balance, and
reweighing after a given time, the loss of water by
transpiration under different conditions of temperature,
illumination, etc., can be readily determined, thus check-
ing the conclusions reached by the previous experiments
upon the leaf It is only by the root that water enters
a plant : when a gardener syringes the leaves or waters
the paths and stages of a greenhouse in which plants are
flagging, he does not thereby add water to the leaf; by
saturating the air with moisture he checks transpiration,
and thus enables the intake by the roots to make up for
the evaporation at the leaf surface. Anything that
checks the development of root, or for a time deprives
the plant of its proper amount of root, renders the plant
more liable to die from lack of water; thus plants after
repotting should be kept for a short time in a close
atmosphere in which little transpiration can take place
until fresh roots have developed, and a transplanted tree
requires special attention in a dry season to maintain a
moist soil round the mutilated root system. Again, crops
on a well-drained soil, even though it is light and little
retentive of moisture, will withstand a period of drought
longer than on a heavy undrained clay, because in the
former case the root system extends deeply into the soil,
whereas in the latter it is cut short near the surface by
the stagnant, airless water. A plant begins to wilt and
will eventually die when the transpiration from the
leaves is greater than the supply brought in by the root
from the soil, and it will be found that roots are not able
to extract the whole of the water present in the soil.
If plants are grown in a pot, and as soon as they begin
to wilt the soil is turned out and a sample weighed and
put to dry, even a sandy soil will be found to contain

III.] DESTRUCTION OF PLANTS BY FROST 47

about 3 per cent., while a clay may contain more than
10 per cent, of water which the soil particles can hold
against the plant, so that it therefore is useless for the
support of vegetation. That the roots themselves take
water from the soil, and do not merely pass on the
suction exerted by the transpiring leaves, may be seen
by the manner in which the supply of water to the plant
ceases when any such cause as cold stops the functioning
of the roots. The vital actions of the root are suspended
at or near the freezing point, and water ceases to be
taken up; consequently if the leaves or stem of the
plant are subjected to any great drying influence while
the roots are thus cold and out of action, the death of
the plant by drying-out may result. Indeed, much of
the destruction by frost of what are known as tender
plants, e.g. tea roses, is due not to drought so much as
to cold. Such destruction will always be found most
severe if a spell of drying wind comes when the
ground is frozen and there is no snow round the plants
to maintain a slightly moist atmosphere and prevent
the access of the drying wind. The shelter of a little
bracken or straw, or of a few spruce boughs, is sufficient
to preserve the plants from injury, not that they are
thereby maintained at any higher temperature, but
because of the protection from wind and evaporation
that has been afforded. The morning sunshine falling
upon a frozen shrub and plant is most destructive, not
because the sudden thaw can exert any direct harm,
but because the sun starts a considerable transpiration
which cannot be met by the roots in the still frozen
ground. We may also use the water cultures to
demonstrate the fact that the roots, like all other parts
of the plant, respire, and therefore must be supplied with
oxygen, in place of which they give off carbon dioxide.
In a water culture the roots obtain the oxygen they

48 THE WORK OF THE ROOTS [chap.

require from the small quantity that the water holds in
solution and constantly renews from the atmosphere
with which it is in contact. For this reason it is advan-
tageous to blow a little air through the culture solution
once a week, especially when the root development has
become at all extensive. The result of cutting off the
oxygen can be shown by replacing the culture solution
in one of the bottles by some water which has been
boiled, to free it from any dissolved air, and then cooled.
Fill up the bottle with this water close to the neck of the
plant, and then pour on it a very thin layer of olive oil,
which will effectually cut off the access of air to the
water in which the roots are distributed. In a day or
so the plant will begin to show signs of ill-health, and
will rapidly die. That the respiration of the root is
accompanied by the evolution of carbon dioxide, can be
seen by placing another plant's roots in distilled water —
not, however, freed from dissolved air — pouring off this
water on the following day, and adding to it lime water.
The milkiness which ensues shows that carbon dioxide
has been given off from the root, and has remained to
some extent dissolved in the water. The same demon-
stration may be effected by letting the plant's roots
themselves dip into lime water.

In addition to the water, it is the function of the root
to take in the various substances required for the
nutrition of the plant. These are obtained from the soil,
and constitute the plant's ash. A simple experiment
can be carried out to demonstrate that any substances
which get into the plant must first of all be dissolved in
the water in contact with the root. Colour the solution
in one of the water-culture bottles a bright pink with
eosin ; to another bottle add carmine or Indian ink. The
eosin, being in solution,willgraduallypenetrate the young
barley plant, and may be seen colouring the veins ; but

III.] ETCHING ACTION OF ROOTS 49

the carmine and Indian ink show no signs of penetration,
because in their case the colouring matter is not dis-
solved, but consists of very fine solid particles suspended
in the fluid. Flowers, especially those from bulbous
plants, which readily absorb water, are occasionally dyed
by thus leaving them for some little time with their stems
dipping into a solution of some dyestuff which makes a
true solution.

If the plant, then, can only take in materials that
have been first dissolved in the water in contact with the
root, how comes it that the plant can make any use
either of the soil or of a great number of manure
substances which are comparatively insoluble in water ?
This point will be more fully dealt with when we are
considering the soil, but at this stage we can show that
the plant itself helps towards bringing such substances
into solution. For the experiment, a thin slab of
polished marble will be wanted; the colour is of no
moment, provided that the surface is nicely smooth and
bright. This slab must be set vertically near the bottom
of a pot filled with ordinary soil in which two or three
dwarf beans are planted, preferably after germination,
in order to save time. When the beans have grown
pretty well and the pot is full of roots, shake out the
contents and wash the slab free from all dirt. The
polished surface will be found to be etched with a series
of markings representing the places where it has been
in contact with the roots, which thus evidently possess
some power of dissolving the carbonate of lime com-
posing the marble. From this experiment and the fact
that the sap contained in the roots of most plants is
acid to litmus paper, it has been somewhat hastily con-
cluded that the plant's roots excrete an acid sap, or
that the sap acts through the walls of the root and so
attacks the solid particles of the soil. Probably, however,

D

50 THE WORK OF THE ROOTS [chap.

this view is erroneous ; there is evidence that the acid
sap can never reach anything outside the unbroken root,
and all the actions, including the etchings of the marble,
are quite explained by the excretion of carbon dioxide,
which, we know, is always taking place from the root.
As a solution of carbon dioxide in water acts like a weak
acid and is much more effective than pure water in
dissolving mineral matter, the roots of the plant have a
distinct effect in rendering the materials in the soil
available as food for the plant ; this point will be
considered later when dealing with the soil.

We may now proceed to make use of the method of
water cultures, to determine what are the mineral sub-
stances, etc., taken by the plant from the soil, and which
of them are essential to its growth. When dealing with
the composition of the plant, we have already seen that a
comparatively small range of elements are to be found
there, and that all plants are alike in containing besides
carbon, hydrogen, and oxygen, also nitrogen, sulphur,
phosphorus, chlorine, and often silica, with potash,
soda, magnesia, lime, and iron among bases. Only
these elements can be essential to the plant : and
whether all of them are necessary can be ascertained
by growing a set of plants in water cultures and
omitting from successive bottles each element in turn.
Taking, for example, in bottle i, the standard
solution which we have already employed ; in 2 the
potassium nitrate may be omitted, thus giving a
solution without nitrogen (the potassium will be still
furnished by the potassium phosphate) ; in 3 the
potassium phosphate is omitted, to get a solution con-
taining no phosphoric acid ; in 4 the potassium
phosphate and nitrate are replaced by the corresponding
sodium salts ; and so on. The seedling barley or maize
plants are inserted in the usual way, with the result

III.] ELEMENTS NECESSAR V TO PLANT GRO WTH 5 1

shown in the illustration, from which it will be seen that
only soda and perhaps chlorine can be omitted without
some injury to the plant. When either nitrogen,
phosphoric acid, or potash is omitted, growth ceases as
soon as the food supply in the seed is exhausted ; in the
absence of sulphuric acid, or magnesia, or lime, growth
continues, though it becomes rather abnormal ; but soda,
silica, and sometimes chlorine can be left out without
causing any difference to the growth. If no iron is
added to the solution, the leaves of the seedling plant
soon become very pale in colour; the new shoots in
particular will be of a pale straw colour and possess no
substance, until in a short time the whole plant perishes.
But if a few drops of ferric chloride are added to the
solution, on the following day the veins of the leaves
will be seen to be turning green again, and the whole of
the leaf will rapidly follow suit. In some way an iron
salt is necessary to the formation of the chlorophyll — the
green colouring matter of the leaf — without which no
assimilation can take place. We may extend the
method of water cultures to ascertain in what state of
combination the various elementary constituents must
be presented to the plant if they are to be utilised by
the plant. In our experiment, for example, we have
used a nitrate as the source of nitrogen, and seen that
the plant can take in this compound of nitrogen and
elaborate from it all the proteins and other complex
nitrogenous bodies it contains ; which of the numerous
other compounds of nitrogen can be similarly utilised ?
As a matter of fact, only a very few, and those of the
simplest type of construction, can be so utilised ; in
addition to the nitrates, plants will take in the salts of
ammonia and a very few bodies like asparagin — i.e., simple
amino bodies such as they build up themselves at a very
early stage from the still simpler nitrates and ammonia

52 THE WORK OF THE ROOTS [chap.

salts taken from the soil. Phosphorus, again, must
enter the plant as a phosphate or phosphoric acid ;
sulphur as a sulphate, for sulphites, sulphides, and many-
other compounds of sulphur are not only useless but
poisonous. The bases found in the plant enter as the
neutral salts of sodium, potassium, calcium, magnesium,
etc. ; in fact, for all the elements except chlorine we may
say that the plant prefers or even requires the ordinary
most highly oxidised compound of each element. It
will thus be seen that the plant behaves towards its
nitrogen and its ash constituents just as it does towards its
carbon compounds — i.e.^ it begins with a simple oxidised
compound, reduces it by splitting off oxygen, and builds
it up into a variety of bodies of great complexity
possessing more potential energy than the initial com-
pounds out of which they have been wrought. It is
easy to understand that a plant must take up the
mineral substances which are found in its ash from the
soil, because it is in contact with no other source of such
a constituent as phosphoric acid. The case is, however,
different as regards nitrogen, because the plant when
growing is surrounded by the atmosphere, four-fifths of
which consists of nitrogen in a free, uncombined state. It
has therefore been a question of much interest — one that
has always been in dispute, and is still not regarded as
settled by some people — whether the plant is not able to
utilise some of this vast stock of free nitrogen and draw
a part, if not the whole, of the combined nitrogen it
contains from such a source. The evidence is, however,
strongly against the view that plants are in any way
able to " fix " or bring into combination the nitrogen gas
of the air, except in one or two special cases where the
process is really effected by certain bacteria living in
partnership with the plants ; the general run of plants
are supposed to be wholly dependent on combined

III.] PLANTS REQUIRE COMBINED NITROGEN 53

nitrogen which they derive from the soil. In the water-
culture experiments, for example, we see how incapable
of growing the plant becomes if the nitrate is omitted
from the culture liquid ; and the same thing occurs if the
conditions are made more normal by growing the plants
in an artificial nitrogen-free soil. Most careful experi-
ments have also been made, in which plants are grown in
prepared soil and the nitrogen present in the seed and
soil at the beginning is compared with the nitrogen
contained at the end in the plant and soil, with the
result that no gain from the atmosphere is detectable.
These experiments, however, are very difficult, and
subject to a large experimental error ; moreover, it has
been argued that the artificial conditions result in such
a diminished vigour that the plant has no longer the
vitality necessary to fix the atmospheric nitrogen.

Such arguments are, however, disposed of by another
type of experiment, in which a series of plants growing
in sand supplied with the necessary mineral constituents
are given varying amounts of nitrate, with the result
that, up to a certain limit, the growth is strictly propor-
tional to the amount of nitrogen supplied. The same
kind of trial has been made in the field ; for example, at
Rothamsted one plot of mangolds was given a small,
amount of ammonium salts to supply enough nitrogen
to start the plant into full vigour; Table IV., however,

Table IV.— Produce of Mangold Roots, Rothamsted.
27 Years' Average.

Manure.

Tons per acre.

Return for 1 lb.

Nitrogen.
Tons per acre.

Minerals, no Nitrogen
„ 7-8 lb. ,. . .
94 lb. „ .

4-55
14-60

0-l8
o«ii

54 THE WORK OF THE ROOTS [chap.

shows that the extra growth thus produced above that
on the plot wholly without nitrogen was small, and is
closely proportional to the nitrogen supply, when com-
pared with the increase of crop produced by a much
larger amount of nitrogen.

Indeed, the Rothamsted experimental results, taken
collectively, are only consistent with the supposition that
the ordinary farm crop obtains the whole of the nitrogen
it requires from the soil ; on all the plots receiving no
nitrogen whatever, the crop (leguminous plants alone
excepted) has been reduced to a very low level ; indeed,
it is only due to the large stock of nitrogen originally
present in the soil and to certain recuperative actions
at work there that it is maintained at all. The difficulty
about this conclusion — that plants utilise only the com-
bined nitrogen in the soil — is to understand how many of
the rich virgin soils, black with organic matter down to
a depth of nine or ten feet, can have accumulated the
nitrogen they contain. If the plant contains only the
nitrogen it has taken from the ground, there can be no
gain of nitrogen when the plant falls back to the ground,
however numerous the generations in which such a
vegetative cycle may be repeated. Some other agencies
than the mere growth and decay of plants must have
been at work fixing nitrogen, and these will be discussed
later.

While we are dealing with the nutrition of the plant
by means of the root, one other point requires considera-
tion : the analysis of the ash of any given plant shows
a very similar composition, wherever or on whatever
kind of soil the plant has been grown. For example, the
ash of wheat straw (see Table V.) is characterised by a
high percentage of silica and a low one of lime ; this
will be the case whether the wheat is grown on a sandy
or a chalky soil, and is in sharp contrast to the ash of

III.]

COMPOSITION PER CENT. OF ASH

55

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56 THE WORK OF THE ROOTS [chap.

clover, which contains no silica but much lime, or the
ash of mangolds, which, while containing a good deal of
lime, is specially rich in potash and soda. These specific
differences would seem to show that the roots of a plant
possess a power of selection, so that they can in the one
case take in silica and in the other reject it ; or, again,
that they can take in potash in preference to soda, or
both rather than the lime which is so much more
abundant in most soils. It is a mistake, however, to
attribute this selective power to the roots ; it really resides
in the active growing cells of the plant ; the root hairs
(and they are the active absorptive organs of the plant,
both for water and the nutrients coming in with the
water) allow the passage of whatever dissolved substances
are presented to them until the sap within possesses
the same concentration as the water outside the plant.
When this stage has been reached, no more can enter,
until the living cells of the plant by withdrawing some
of the material for constructive purposes lower the
concentration of the sap in that particular substance.
Potash, for example, accumulates in a plant rather than
soda, even though there may be more soda in the soil,
because the plant's cells keep utilising the potash and
taking it out of the sap solution; whereas a small
quantity of soda maintains the plant sap as saturated
as the soil water outside, because so little of it is
required by the plant's cells. But though the active
agency resides in the growing cells, and not in the
roots, the result is the same — the plant as a whole
does exert a selective action on the elements of nutrition
presented to it, so that all plants of the same kind have
a certain characteristic ash composition, in which
differences of soil, season, manuring, etc., do not
cause wide variations. Furthermore, plants of different
species possess sharply differing characteristics in the

III.] COMPOSITION OF CROPS 57

composition of their ash. These differences never
extend to the entire absence from one plant of an
element present in another : all plants contain the same
elements, except silica, which is abundant in some plants
and entirely absent from others, though, as far as is
known, it is unessential to either.

The common idea that certain plants flourish only
in particular soils because they find there some par-
ticular constituent which is elsewhere lacking, is
therefore erroneous ; we might almost say that all soils
contain all the constituents that plants need, so that as
far as food goes, where one plant can grow any other should
be equally possible. It is true that the excess or
deficiency of certain soils in some particular constituent
renders them more or less appropriate to one crop or
another, but the circumstances which determine the
association of a given plant with a particular soil are
more often questions of texture, temperature, and water
supply, than of absolute nutrition, as represented by the
greater or less provision in a soil of a particular con-
stituent of the plant.

Although the composition of different plants does
not vary within very wide limits, and though as we shall
see later the composition does not throw much light on
the suitability of particular soils for certain crops, it is
yet desirable to know what quantities of plant food are
removed from the soil by the ordinary farm crops.

Only average figures can be given because of the
variations set up by season and soil, but in Table VI.
are set out the amounts of the chief nutrient constituents
contained in the usual farm crops, based chiefly upon
analyses at Rothamsted : —

[Table VI.

S8

THE WORK OF THE ROOTS [chap. hi.

Table VI.— Composition

OF Average Crops per

Acre.

Dry

matter.

Nitrogen.

Phosphoric
Acid.

Potash.

Wheat Grain, 30 bushels .
Wheat Straw, i| tons

Total .

Barley Grain, 40 bushels .
Barley Straw, i ton .

Total

Oat Grain, 45 bushels
Oat Straw, 2^ tons .

Total

Maize Com, 50 bushels .
Maize Forage, 3 tons

Total

Meadow Hay, i^ tons

Red Clover Hay, 2 tons .

Swedes, Roots, 20 tons .

Mangolds, Roots, 30 tons .

Potatoes, 8 tons

1530
2650

34
16

14
7

9
20

4180

50

21

29

1750
2080

35
14

16

5

10
26

3830

49

21

36

1630
2350

34
18

13
6

9

37

3980

52

19

46

2500
3000

46
25

17
14

II
50

5500

71

31

61

2820
3760
4700
7900
4480

49

ICO

100

131

61

12
25
23
48

28

51

83

90

290

100

CHAPTER IV

CHANGES OF COMPOSITION WITHIN THE PLANT

The Manufacturing, Resting, and Spending Stages in a Plant's
Development. The Course of Nutrition and Migration in
the Growth of Wheat. The Ripening of the Grain. Storage
and Migration in Root Crops. Removal of Food Materials
from the Leaves of Trees as they Ripen. The Ripening of
Fruit. Effect of Soil and Climate upon the Composition and
Quality of the Crop.

A REFERENCE has already been made to the fact that
the starch manufactured in the chlorophyll-containing
cells of the leaf is not allowed to remain there long, but
is transformed into soluble sugars by the action of
enzymes or ferments also present in the leaf, and is
then moved on to some other part of the plant, where
it is stored as sugar or as starch again until it is wanted.
It is now necessary to consider such processes rather
more generally from the point of view of the whole
economy of the plant, in which operations of manu-
facture, transport, storage, and remigration take place,
giving rise to the stages we call growth or resting or
ripening. In some plants the various operations we
have just enumerated can be seen very distinctly taking
place in succession; this is particularly the case with
bulbous plants, which have evolved the plan of laying

69

6o CHANGES OF COMPOSITION [chap.

up a large reserve store of food to carry the plant in a
resting condition through periods of summer drought.
Perhaps the most instructive example is afforded by the
Autumn Crocus {Colchicmn)^ which, as a wild plant, is
abundant in the west country pastures, and, with its
allies, is also not uncommon in gardens. The noticeable
feature about the autumn crocus is that it throws up
its blossoms without any leaves in the autumn, the
flowers being followed sometime later by the seed pod ;
in March the leaves appear and grow to a considerable
size without any sign of blossom. During the growth
of the leaves, a corm (the equivalent of the bulb
in this case) is formed, and grows to a considerable
size, being packed with starch, etc., which is manu-
factured by the leaf and transferred for storage to
the corm. Towards the end of June the leaves die
down entirely and the plant goes to rest, still, how-
ever, respiring slowly in the corm, such respiration being
a necessary condition of vitality. With the autumn,
however, the corm renews its vigour, the flower stems
are thrown up, but all the material therein, as well as
that required to support the rapid respiration which
attends the flowering period, is drawn from the material
that had previously been stored in the corm. As far as
the plant goes, this is a period of pure spending of its
accumulated resources, because the plant no longer
possesses any leaves or other green organs capable of
assimilation; the corm itself becomes depleted, but
under favourable conditions a quantity of seed is formed,
capable, by its food store, of reproducing the species
and giving it a start in the next generation. The corm
itself also retains enough food material to carry it
through the winter and start new leaves which will
build up the reserve afresh in the spring, thus repro-
ducing the same plant in the following year. With

IV.] DEVELOPMENT OF WHEAT 6i

other bulbous plants the sequence of getting and spend-
ing is not perhaps so clearly seen as in the autumn
crocus : in the common crocus, for example, the leaves
are almost contemporaneous with the flowers ; with the
tulip and daffodil it requires closer observation in
order to realise that the processes of manufacture and
storage are quite distinct from those of flower and seed
formation, because the two are going on almost at the
same time. Just in the same way, even with annual
plants like wheat, we may distinguish the processes and
periods of manufacture and storage, followed by the
later process of migration, when the accumulated
material is stored up afresh in the seed as a reserve
wherewith to give the young plant a start in life. The
course of existence of a wheat plant merits particular
examination from this point of view, and the changes
taking place may be studied in some detail because
they are typical of much of what is going on in all
plants. The starting-point is the seed sown in autumn ;
after it germinates the blades grow 2 or 3 inches high,
but there they generally remain for the rest of the
winter, often indeed appearing to dwindle because of
the way the leaves lie down with the first frost. But
though the growth above ground is almost at a standstill,
the material that is being formed by assimilation is used
up for the formation of roots, which are pushing deeper
into the soil all through the winter. It is at this stage
that the foundation is laid for the future crop, and a wet
autumn and winter, by limiting the aeration of the soil,
causes a restricted root development which is always
followed by a poor yield. For example, if we compare
the crops upon three of the manured plots at Rotham-
sted, we get the following results for the ten wettest
and the ten driest winters (November to January
inclusive) between 1852 and 1904: —

62

CHANGES OF COMPOSITION

[chap.

Rainfall.
Four months,
Nov. to Feb.

Yield of Grain. Bushels.

Mean.

Plot 6.

Plot 7.

Plot 8.

Wet winters .
Dry winters .

13-005
5-786

19-4
28-0

27.1
37-1

32 -o
38-9

26.2
34-7

Thus there was on the average a better crop by 30 per
cent, after the dry than after the wet winters, and this
may largely be set down to the restricted root develop-
ment in the wet seasons. Of course, a wet autumn in
other ways acts very prejudicially to the future crop of
wheat, partly by interfering with the sowing at the
proper time and partly by washing much of the soluble
plant food in the soil down below the reach of the
plant.

When the winter is past and the wheat begins to
grow again, it enters upon its most active period of
drawing nutriment from the soil and of assimilating
carbon from the atmosphere ; the products, as fast as
they are manufactured in the leaf, are moved off and
stored up in the stems of the plants. As the lower
leaves age and begin to yellow off and die, the various
valuable materials they contain, not only the carbo-
hydrates that have been formed by assimilation, but the
nitrogen, phosphoric acid, and potash which are b^ing
employed in the vital processes, are very largely with-
drawn and passed on to some more active part of the
plant. These substances are of too great importance to
the plant to be wasted by being allowed to remain idle
in dead tissue or to be lost to the plant when the leaf
falls, consequently they are taken back into the active
parts of the plant as far as possible before the leaf dies.
Throughout the months of March to June, the processes
of manufacture and storage alone are going forward ; but

IV.] THE FILLING OF THE GRAIN 63

as the wheat comes into flower, these processes begin to
slow down : in particular, the feeding of the plant upon
the soil becomes less. This may be traced in the
diagram. Fig. 15, which shows the amounts of dry
matter, nitrogen, and phosphoric acid contained in the
whole plant and in the grain separately, from the time
when the grain could first be separated — about a
fortnight after flowering — up to the time of harvest. The
curves show that at the starting-point the plant had
reached about 90 per cent, of its ultimate dry weight,
but that it had acquired only about 75 per cent, of the
nitrogen and less than 70 per cent, of the phosphoric
acid that were finally present in the plant. It should,
however, be noted that these figures take no account of
the root, which doubtless itself contained some of the
nitrogen and phosphoric acid that later found their way
into the above-ground parts of the plant. The earlier
experiments of Pierre, conducted in the hotter and drier
climate of France, would indicate that the wheat plant
ceases entirely to take nutriment from the ground at a
much earlier date — soon after flowering ; whereas in the
experiments quoted the processes of nutrition never
stopped until the whole plant was ripening off for
harvest. Assimilation is also shown to be going on as
long as the plant possesses any green leaf tissue ; during
the last fortnight or so before cutting, the dry weight
did not increase at all ; in fact, it decreased because the
burning-up of carbohydrate by respiration continued to
go on and towards the end caused losses which out-
weighed the diminishing gains by assimilation. From the
time of the formation of the grain, the most important
process going forward was the migration into the seed of
the material that has previously been stored in the
stem. It will be seen that the gain of dry matter, and
particularly of nitrogen and phosphoric acid, by the

64 CHANGES OF COMPOSITION [chap.

grain during this period was far greater than would be
accounted for by what the plant had taken up meantime
from either the soil or the air. In fact, at the finish,
although only two-fifths of the whole dry matter of the
plant was collected in the grain, yet 80 per cent, of the
nitrogen and 70 per cent, of the phosphoric acid of the
whole plant had been transferred to it. This, of course,
is only another example of the process which we have
already noted as taking place when the leaves died off
one by one — the valuable materials they contained were
constantly transferred to the still living and active parts
of the plant. In the same way, the seed is just that part
of the plant which has to carry on its life in the next
generation, and it is endowed with as much as possible
of the material that has been with difficulty accumulated
by the parent plant.

During the formation of the grain itself, three stages
may be distinguished ; for about three weeks from the
time of flowering the main process that is going forward
is the formation of what later become the outer
envelopes of the grain, in a thick and fleshy form which
they lose afterwards. This " pericarp," as it is called, is
richer than the ultimate grain in nitrogen and ash,
though the ash does not contain so much phosphoric
acid. There is, of course, no sudden break which marks
the oncoming of the second stage, but towards the end
of the third week the formation of the pericarp has
ceased and the filling in of the endosperm begins to be
the main process going forward ; as this progresses, the
pericarp is denuded of the material already accumulated
there and becomes reduced to the series of tough, dry
membranes, with which we are familiar later as the chaff
and skin of the grain. The filling of the endosperm
continues for nearly three weeks, and the most notable
feature is that the material migrated by the plant from

•bry

I Matter.

Grammes.

MU

^

«4/vr

p^

TTf«

WJVH.

(it

^

^

y

"^

/

V.//V >

ihOLL

;5^

^

^^

/

yo
80
70

60
SO

/

"^

^

t*.-^

t*-

^

^

NT —

P.05_

..*.".'

h?-'-

....-

'••"■"

,^

»''.'

«22

MN

40

30
20

^

X^

^

y-i.

C^

^

y

.-i>

^

^

10

y

^

^

^

0

""^

Kitrogen
and P2O5.

Grammes.
1-3

0.9
0.8

•7

3 6 9 12 IS 18 21 24 27 30 33 36 days.

Fig. 15.— Diagram showing the Migration of Plant Constituents
INTO THE Grain of Wheat during the last Five Weeks before
Harvest.

{Face page 64.

IV.] QUALITY IN WHEAT 6$

day to day possesses an almost constant composition
throughout the process, containing the same proportion
of carbohydrates, nitrogen compounds, phosphoric acid,
etc It is a mistake to suppose that the proteins which
form the gluten are filled in first, and that starch only
enters towards the later stages of filling and ripening.
But though any particular lot of wheat does in this way
pass on a constant mixture of materials from its reserves
to the grain, there will be certain differences in the type
when different varieties or the same variety grown in
different climates or soils are compared. Each plant
in a given field of wheat possesses, as it were, a mould
wherewith to fashion the material it passes on to its
grain, and the form of the mould is determined by the
variety and the environment — soil, climate, season, etc.
Wheats grown in certain climates, such as those prevail-
ing in Kansas, Manitoba, or Hungary, are specially
nitrogenous (glutenous or " strong " wheats), but this is
not due to the hot dry climate shutting down the
migration process prematurely before the later stages
are reached, when starch only enters the grain, but
to the fact that the environment — climate and soil,
together with the varieties appropriate to such con-
ditions— causes the wheat to make that which we
have called its mould on a nitrogenous type. It
should, however, be noted that though variations
due to environment do occur, the composition of the
grain of wheat is singularly constant. It has already
been explained how all plants react against variations
in the composition of the soil and select the particular
constituents appropriate to their nutrition ; so, similarly,
when the migration process begins, the plant again
effects a re-sorting of the material accumulated, and only
passes on its usual constituents to the grain. Thus the
straw will always vary much more in composition from

E

66 CHANGES OF COMPOSITION [chap.

soil to soil, climate to climate, etc., than the grain.
When the filling of the endosperm has been pretty well
completed — which is about a week or a fortnight before
the time at which the grain would usually be regarded
as fit to cut — the ripening process sets in, and this is, in
the main, characterised by a drying up of what has been
previously accumulated. During this last fortnight the
dry matter of the grain increases little, if at all ; certainly
it is stationary in amount, or even declining, during the
last week, and water is being constantly removed. The
main feature, then, of the ripening process is desiccation ;
at the same time, other rearrangements in the chemical
nature of the constituents can be seen : non-protein
nitrogen compounds pass over into the protein state,
and the proportion of sugar falls, but these changes are
not large compared with the drying up which is taking
place. It would appear that it is possible to cut wheat
rather earlier than the usually recognised stage of
ripeness without any loss of weight in the crop, by
which means losses by shedding, birds, etc., might also
be reduced, the only practical question being whether
the final drying process can be better effected while the
wheat is standing, or after it is cut and shocked or even
put into stack.

Certain other practical consequences depend upon
this migration process ; for example, if from any cause
the crop is cut before migration is complete, then the
straw will be so much richer in both fertilising and food
constituents. Similarly, in bad seasons, when ripening
is imperfect, the migration process is always found to be
much less complete, so that a higher proportion of the
accumulated material is left in the straw. Heavy
manuring, again, especially manuring of a nitrogenous
character, is always attended by a less complete migra-
tion, leaving the straw by so much the richer. Straw

IV.]

EFFECT OF SEASON UPON WHEAT

67

from the northern parts of the country, where growth is
more prolonged and ripening less complete, is always
of better feeding value than straw grown where drier
and hotter summers prevail. Some of these points
are illustrated in Table VII., which shows composi-
tion of grain and straw and the ratio between them,
for the wheat grown on three of the Rothamsted plots
in two sharply contrasted seasons — 1852, which was cold
and wet ; and 1863, which was hot and dry : —

Table VII.— Composition of Wheat Crop in Wet and Dry
Seasons.

Plot.

3

Un-
manured.

2

Dung.

7

Artificial
Manures.

Weight per bushel, lb. .

r
■ I

1852
1863

56-6
62.7

58.2
63-1

56-0
62.6

Grain to loo Straw

•{

1852
1863

53-9
70.4

49.6
67-5

41.9
59-4

Nitrogen per cent, in Dry Grain

•{

1852
1863

2.08
1.65

2-02

1-52

2.29

1-53

Nitrogen per cent, in Dry Straw

/

1852
1863

0-57
0-33

0'46
0.25

0-87
0-36

Thus in the wet year, 1852, there is a smaller propor-
tion of grain, and the straw is left much richer in
nitrogen than in the dry year; the heavily manured
plots 2 and 7 also show a greater proportion of straw,
which is richer in nitrogen than that from the
un manured plot. If we compare the wettest season
known at Rothamsted, 1879, with one of the hottest
and driest, 1893, wie find the proportion of grain to straw
on the unmanured plot, which on the average is 70 per
cent., varied from 43 in the wet year 1879, to no in
the dry season of 1893.

As to the effect of heavy nitrogenous manuring, an
example may be taken from some of the Rothamsted

68

CHANGES OF COMPOSITION

[chap.

barley plots in 1905, where a comparison existed
between an unmanured plot, a plot receiving a very-
large amount of nitrogenous wool waste, and a third
plot which had received the same amount of wool waste
a year earlier, so that it had been partially exhausted by
the previous crop : —

Table VIII.— Composition of Barley Crop. Rothamsted, 1905.

Weight

per
Bushel.

Grain to
100 Straw.

Oflfal Corn
to 100
Dressed
Grain.

Nitrogen
per cent,
in Grain.

No Nitrogen
Manured previous year
Manured same year .

58-0
57-3
55-1

I10-4
96.6
72.8

5-9
12.5
34-9

J. 61

1-79
2.42

Here the heavy manuring has evidently given rise to an
excessive proportion of straw, while the grain produced
was so light that much of it had to be dressed out and
regarded as offal.

The principles which have been illustrated in the
migration of the materials forming the grain of wheat
may also be applied to another case — the changes that
go on during the later stages of growth and ripening of
meadow hay. Although the plants composing the
herbage of a meadow are ia the main perennial and
not annual like wheat, the process of nutrition and
migration are essentially similar; carbohydrates are
manufactured from the carbon dioxide in the atmo-
sphere ; nitrogen, phosphoric acid, etc., are taken from
the ground and elaborated, until the flowering season is
reached, when the movement of the previously formed
material into the seed becomes the chief action going
on. This is accompanied by an increasing change of
non-protein nitrogen compounds into proteins, a loss of
sugars by respiration, and a conversion of more soluble

IV.] FOOD STORAGE B V BIENNIALS 69

carbohydrates into fibre — this latter a rearrangement we
did not consider in the case of wheat straw. The
formation of fibre is particularly marked in the final
stages when the seed of the grasses gets ripe, and as
fibre is an inferior food material to starch, not only less
digestible in itself but wasting much more labour in the
process of digestion, there results a considerable loss of
food value in the material. All this points to the
desirability of cutting hay in a young state ; the loss
of weight in the crop will not be great, because for the
bulk of the grasses the later stages of growth are not
attended by much increase of dry matter, since assimila-
tion becomes balanced off by respiration, while there
will be mechanical losses through the shedding of the
seed of many plants ; at the same time the much smaller
proportion of fibre in the early cut hay permits of a far
greater utilisation of the constituents of the hay by the
stock receiving it as food.

The process of storage and migration of the
accumulated materials is perhaps most clearly seen in
the case of the biennial root crops like turnips and
mangolds (or fodder beet); the so-called bulb — an
enlarged stem in the case of swede turnips, a root in the
mangolds — is nothing more than a storage organ, and
the whole work of the first year's growth consists in
filling this with the carbohydrate assimilated by the
leaves and with the proteins which are also there
elaborated. In the mangold the material stored is cane
sugar, which constitutes about 60 per cent, of the dry
matter of the bulb ; the dry matter itself varies from
about 10-5 per cent, in the white-fleshed Globe variety
to over 13 per cent, in the yellow-fleshed and Long Red
varieties. In the sugar-beet, a form of mangold which
for more than forty years has been systematically bred
and selected for its sugar content, the percentage of

70 CHANGES OF COMPOSITION [chap.

sugar in the root has been raised to eighteen or over.
The sugar-content of mangold has not been similarly
raised, because in its case the seed parents have been
selected only on a basis of size and shape and never on
the amount of sugar they contained, as determined by
analysis. The figures just given for the percentage of
sugar and dry matter in the mangold are of course only
averages; certain variations occur due to the soil,
manuring, and also season, but perhaps the largest
variation is that due to size. The larger the root the
more watery it becomes ; mangolds weighing approxi-
mately 2 lb. apiece contain about 2 per cent, more dry
matter than mangolds averaging 7 lb. apiece, above
which weight the falling off in dry matter is not so
marked. The age of the mangold has not much
influence, it possesses much the same composition all
the time it is growing ; just as the wheat grain is filled
up with material of approximately constant composition
from the beginning until the end of grain formation, so
as the mangold bulb swells it is being packed with
materials of a fixed type as regards the proportions of
dry matter, sugars, and nitrogenous matter, this material
being manufactured in the leaf Certain changes do
occur; in the immature mangold, as in those grown
with an excessive amount of manure, there is a slightly
smaller proportion of dry matter, while a much larger
proportion of the nitrogen contained in the root is
combined in the form of nitrates and non-protein
compounds. The nitrates and non-protein compounds
are far from having disappeared when the mangold is
ripe in the late autumn, though they are considerably
reduced in amount. If the mangold is allowed to grow
a second year for seed, a reverse series of changes take
place ; the sugar is removed from the cells of the root in
order to form the flowering stem and eventually the

IV.] CHANGES IN ROOTS DURING STORAGE 71

seed ; when the seed is ripe the former root will be
found almost devoid of sugar or any other easily soluble
carbohydrate or nitrogenous compound, little remains
except fibre. During the storage of the mangold in the
clamp under ordinary farming conditions, the ripening
process proceeds during the closing months of the year;
the roots are of course respiring, and losing in conse-
quence a little sugar, the nitrates and non-protein
nitrogen compounds are also being partially replaced by
proteins, but the loss of material is small as long as the
temperature remains low. As soon as the warmer
weather of the spring sets in, respiration increases, some
degradation of the cane sugar into reducing sugars
takes place, and with sprouting there will also be
change from the protein to non-protein nitrogenous
compounds. When mangolds are kept as late as May
or June, there is a very marked loss of dry matter by
respiration, which may amount to as much as one-third
of the original material, though the loss will be
disguised by the drying-ofif of water which simultane-
ously takes place, so that the stored mangold is
apparently as rich as ever in dry matter.

In swede turnips the percentage of dry matter is about
the same as in mangolds, varying from about 10 to 13
or over, according to the variety, size of root, season and
soil, etc. ; the sugars present are different from the cane
sugars of the mangold, and there is also a considerable
proportion of a class of carbohydrates known as pectins,
bodies which form a mucilaginous jelly when boiled
with water. The changes which the swede turnip
undergoes on storage and when growing a second year
for seed are strictly similar to those taking place in the
mangold, the only difference being that in the forma-
tion of the seed a good deal of oil is built up from the
carbohydrates in the storage material. White turnips

72 CHANGES OF COMPOSITION [chap.

resemble swedes in composition, but are more watery ;
while potatoes contain a much higher proportion of dry
matter, about 25 per cent, and store their carbohydrates
in the form of starch. When a potato set is planted in
spring the starch is converted by a diastatic ferment
into sugar, which is moved off to the growing shoots,
where it is used for constructing the new tissues ; as
growth progresses the cells will be found to be progres-
sively depleted of starch until little more than an empty
husk is left. A slow conversion of starch into sugar is
always going on during the storage of the potato, the
sugar being burnt up in the respiration process which
keep's the plant alive though resting. It is well known
that a potato tastes sweet if it has been frosted or
exposed for some time to a low temperature ; this is
because under such conditions the respiration process
is almost suspended, while the enzyme action forming
sugar still goes on until there is a perceptible accumula-
tion of sugar in the root.

Among perennial plants the movements of the
manufactured materials go on in exactly the same
way as in annuals or biennials ; these movements
are, however, not so apparent, because of the great
permanent store of food material which exists in a
perennial plant. However, it is instructive to cut sec-
tions of the branches of trees at different times of the
year and test them with iodine to show the presence of
starch : in the autumn the wood, or rather that part of
it which is still alive and active, is packed with starch,
but this starch is moved out with the first growth of the
leaves. It is due to the material thus stored that
cuttings can be struck from shoots cut off in the autumn ;
they then contain easily available reserve material out
of which the young roots and the new leaves can be
iijs^nufactured until the cutting attains an independent

IV.]

THE FALL OF THE LEAF

73

existence. As a rule, cuttings cannot be struck from the
young wood in the spring, because it then possesses no
reserve material to draw upon. The leaves of deciduous
trees afford another example of the migration of food
materials ; when the year's growth is over and the tree
is preparing to shed its leaves for the winter, a layer of
comparatively large cork cells forms between the stem
of the leaf and the branch, and it is by the rupture of
this dividing layer that the leaf becomes detached from
the tree. But long before the leaf is detached, as
it begins to get old, the valuable food materials it
contains — the carbohydrates, the nitrogen, phosphoric
acid, and potash — are withdrawn from the leaf and stored
away in the stem, their place being taken by comparatively
abundant and valueless materials like lime and silica.
In consequence, dead leaves, from a manurial point of
view, are much poorer than living leaves, as the following
analyses (Table IX.) of the young, mature, and dead

Table IX. — Materials contained in 500 Leaves of the Plane
Tree, gathered at different dates.

June 18.

July 16.

Aug. 22.

Sept. 7.

Oct. 8.

Oct. 24.

Nov. 6.

Grms.

Grms.

Grms.

Grms.

Grms.

Grms.

Grms.

Dry matter

142-5

1847

182.8

193-8

196-2

148.8

166.I

Nitrogen .

5-9

5-9

4-8

5-0

3-4

1.8

1.4

Ash .

8.7

14-6

17-8

20-I

21.3

18.0

20-3

Phosphoric Acid

1-3

1-3

1-2

1-2

0-9

0-5

0.6

Potash

1.9

2-1

2-1

2-2

1-6

10

0-9

Lime

2-5

5-7

7-7

90

9-5

8.2

9.2

Silica

0-6

1.9

2.9

3-5

4-0

3-9

3-7

leaves of the plane will show. The economy of this
process is obvious ; such substances as the starch formed
by the leaf, the nitrogen, phosphoric acid, and potash
taken from the ground, are required by the active cells in
order to carry out the vital processes of the plant ; they

74

CHANGES OF COMPOSITION

[chap.

are too valuable to be cast aside in the dead leaf, and
are therefore carefully removed into the permanent
storehouse of the stem and roots during the winter
resting period.

In herbaceous plants, which die down to ground level
each winter, the roots form the storage organs ; the stem
and leaves are depleted of their valuable constituents
before death sets in. For example. Table X. shows the

Table X. —Material contained in Upper Growth of Hop-
Plant AT TIME OF Picking and after Dying Down.
Lb. per Acre.

In Hops
Sold.

In Green Leaf

and Bine at

Picking Time.

In Dead Leaf
and Bine in
November.

Returned to
Root.

Nitrogen

Phosphoric Acid .
Potash .
Lime .

Lb.

51
16

39
16

Lb.

38
10
31
92

Lb.

18

5

4

88

T K Per
^^- cent.
20= 53

5 = 50

27 = 87
4= 4

material contained in the parts of a hop plant above
ground (i) at the time of its maximum growth when the
hops — i.e. the seed vessels — were fully formed ; (2) after
the hops had been picked and bine and leaves were dead
down to ground level, and from the table it will be seen
that about one-half of the nitrogen, one-half of the
phosphoric acid, and nearly all of the potash contained
in stem and leaf are removed and sent down to the root
for storage before the winter resting period sets in.

Similar cases of economy, storage, migration, and
retranslation may be traced everywhere in the life-
histories of plants, the guiding fact being the endeavour
of the plant to ensure its continued life and reproduction
by providing a sufficient food supply to start either the
next generation (the seed) or the next phase (in the
case of plants reproducing asexually by bulbs, suckers,

IV.] RIPENING 01 FRUITS 75

etc.), until it has developed adequate roots and leaves of
its own. The broad chemical changes going on in the
plant, such as the migration of the starch from one part
to another, preceded by its conversion into sugar, and
even such changes as the desiccation and the conversion
of ^-proteins into proteins which marks the ripening of
cereals, are recognisable enough; there are, however, a
number of more subtle changes which we are unable in
the present state of knowledge to follow, though they may
often be appreciable in the bulk as constituting what
the practical man calls quality. As an example we
may instance the ripening of fruits such as apples and
pears, which after the migration and filling of the fruit
has been completed, will to a large extent go on
though the fruit has been detached from the tree.
We know the broad outline of the process : the fruit
becomes soft and sweet, often an intense harshness of
taste entirely disappears, in many cases fragrant essences
and aromas develop. Chemically we can recognise
that starch in the unripe fruit disappears because it is
converted in sugars, that some of the tough pectin
bodies are also converted into sugars, as also are the
very bitter tannins, while the agreeable flavoi-rs appear
to be due to ethers produced by the union of some of
the vegetable acids with alcohol derived from the partial
breakdown of sugar. In fact, if the respiration of fruits
is deranged by putting them in a jar containing no
oxygen, the sugars will not be converted into carbon
dioxide and water, but will be broken down part of the
way into the less oxidised form of alcohol, so that the
fruit may become alcoholic without any fermentation in
the ordinary sense of the word taking place. Fer-
mentation by yeast may be regarded as a similar
case of respiration in the absence of free oxygen ; the
yeast cells when placed in a liquid containing sugar

76 CHANGES OF COMPOSITION [chap.

grow and multiply, and in doing so they split up by the
aid of an enzyme the sugar into alcohol and carbon
dioxide. The yeast cells do not feed upon the sugar,
but they derive energy from its splitting up, just as the
ordinary plant cell derives energy from the oxidation of
the sugar to carbon dioxide and water which takes place
during respiration in the presence of oxygen.

In discussing the changes which take place in the
composition of parts of the plant, we have already had
occasion to point out that the changes due to variations
of environment are not very great; the variations
induced by season are much greater than those due to
soil or manuring, as may be illustrated by the figures
for the nitrogen-content of the grain of wheat in
Table VII. In the wet season of 1852 there was about
2 per cent, of nitrogen in the wheat grain, whereas in the
dry year of 1863 there was little more than 1-5 per
cent. ; this season alone has caused a difference of 0-5
per cent, or 25 per cent, of the total, whereas the greatest
difference in nitrogen-content between the grain grown
on the wholly unmanured plot and on that which
receives an annual heavy dressing of farmyard manure
only amounted to 0-2 per cent. As a matter of fact, the
difference in the composition of the crop brought about
by different soils or different manuring may be regarded
as due to the change of climate which the soil and manur-
ing sets up for the particular plant. For example, a heavy
soil will maintain not only moisture about the root but
a moister atmosphere about the leaves, and so become
the equivalent of a wetter season ; on the other hand, a
nitrogenous manure will prolong the growth of a plant
and so cause the ripening process to take place under
other climatic conditions than those prevailing for an
earlier ripening crop. If, however, the differences of
composition induced by environment — soil, manuring,

IV.] QUALITY IN PRODUCE 77

season, etc. — are comparatively small as measured by
such rough analytical factors as the percentage of
nitrogen, etc., they are often of extreme importance
commercially, because they may and generally do affect
those more subtle items in the composition of the
product summed up as quality. We are as yet rarely
in a position to define from a chemical standpoint what
constitutes quality in each particular case, still less to
state the external factors which determine it ; we may,
however, be sure that it is not due to the mere presence
or absence of some particular ingredient in the soil.
We have seen that all plants are fundamentally made
up of exactly the same things in very similar propor-
tions, the differences arise in the style of the architecture
that the plant adopts in each case; and if wheat is
" stronger " when grown in one place than another, it is
not because in the soil of the first place there exists
some element which is absent in the soil of the second
place, but because the habits of the plant are affected
variously by differences in the supply of water, air, or
warmth in the two places. We have, in fact, many
reasons for regarding the supply of water and the
prevailing temperature as the main factors in determin-
ing both the yield and the quality of all crops, and it is
from this point of view that it is most profitable to
regard the soil.

CHAPTER V

THE ORIGIN AND NATURE OF SOILS

The Weathering of Rocks to Soil. Solution of Rock Materials in
Water containing Carbon Dioxide. Action of Frost. Trans-
port of Soil by Rain and Running Water. Action of Worms.
Approximate Analysis of Soils. Properties of Clay and Sand.
Chemical Constituents of Soils. Soils and Subsoils.

Before we take up the question of the composition
of the soil, it will be well to learn something of its origin,
and for this purpose nothing is so instructive as a visit
to a quarry where a clean face of rock can be seen pass-
ing into soil, on the surface of which vegetation may
still be growing. At some distance below the surface
the rock is solid and massive ; in some cases, as in lime-
stone or sandstone, it will be stratified or divided into
parallel layers, which can be distinguished by changes
of colour or texture, even when there is no actual
division along the planes of bedding ; in other cases, as
in granite or basalt, the rock will be massive and show
no sign of splitting into layers. The colour of the rock
will be pretty uniform, and at depth it will often be
some shade of dark green or blue or grey, though of
course there are numerous exceptions, such as red or
yellow sandstones, white or yellow limestones, reddish
granites, etc. Following the rock upwards to the surface,
there comes a point when the rock begins to show signs
of decay ; the divisions that traverse the rock, whether
bedding planes or joints, become somewhat larger and

78

Fig. 1 6.— Formation of a Sedentary Soil.

[Face page 78.

CHAP, v.] SEDENTARY SOILS 79

are discoloured, as though water has been oozing along
them and had caused a certain amount of rusting and
rotting. Higher still, the rock is obviously disintegrated ;
the large fragments, which still are arranged in keeping
with the structure of the unaltered rock below, are
separated by layers of loose sand and stones, or by clay,
and the proportion of this loose material increases the
nearer one gets to the surface. Finally the rock either
wholly disappears, or becomes represented only by
stones in the loose material, which we may now call
the subsoil. A few inches below the surface, this
subsoil gives place to the soil proper, distinguished as a
rule by its darker colour and its admixture with
vegetable matter from the plants that have been grow-
ing upon the surface.

Such a soil passing by insensible degrees into the
rock below is called a " sedentary soil," because it has
grown upon the spot ; but in some quarries and pits we
shall not meet with the sequence described above, but
one in which the surface material turning into soil is
obviously quite distinct from the fundamental rock below,
a sharp line of distinction marking the change from one
to the other. Such cases will be considered later ; it now
remains to examine into the causes which have brought
about the degradation of rock into soil. Water obvi-
ously plays a considerable part in the process ; even the
most solid rock is traversed by certain planes of weak-
ness— bedding planes or joints, along which minute
fissures water slowly percolates, and, as we have observed
in the quarry, begins to degrade and discolour the edges
of the cracks. In pure water itself few of the minerals
constituting rocks are soluble ; but the rain, as it soaks
down through the upper layer of soil pervaded by plants'
roots, dissolves some of the carbon dioxide that is there
being produced, and then becomes a much more effective

8o THE ORIGIN AND NATURE OF SOILS [chap.

solvent. Such water, for example, will dissolve carbonate
of lime, hence limestone and chalk rocks waste away
under the weather, and leave nothing behind but the
2 or 3 per cent, of fine red clay, which is the only
other material making up the rock. Wherever a railway
cutting traverses chalk or limestone, the surface of the
rock will be seen to be let down in places into deep and
tapering pipes ; these represent lines of soakage, along
which the surface water has been continually travelling
to a fissure below, until the rock within the influence of
this gradual current has all been dissolved away. Not
only does carbonate of lime occur in chalk and limestone
in a more or less pure state, but it is found in other
rocks acting as a cement to grains of sand, etc., and as it
dissolves in the percolating rain-water the rock disinte-
grates. Many of the complex minerals which make up
the bulk of the older primitive and volcanic rocks, are
also decomposed by water charged with carbon dioxide ;
for instance, the felspar, which is one of the fundamental
minerals in granite and in all the basaltic rocks, breaks
down to clay under its influence. In Cornwall the
surface of the granite is covered with a white clay thus
formed, in which the still undecomposed grains of quartz
and mica, the other minerals making up the granite,
are lying unaltered ; the basalts and trap rocks similarly
yield a clay, which is red because of the oxides of iron
which are simultaneously formed as the felspar decays
into clay. Iron compounds are very generally diffused
among the rocks ; the greens and browns and blacks of
the unweathered rocks are due to compounds of iron,
which all break up and go into solution under the
action of water and carbon dioxide, eventually becoming
oxidised into something akin to iron rust, and this
oxidised rusty substance is the cause of the yellows,
browns, and reds which predominate in soils. Perco-

v.] THE WORK OF FROST 8i

lating water, then, acts both by pure solution and by
starting more drastic chemical changes by the help of
the carbon dioxide it carries ; its work is often assisted
by the penetration of roots into the cracks and fissures.
The roots, both of the larger forms of vegetation and of
trees, will travel for astonishing distances and will
squeeze themselves in the pursuit of water into the
closest of cracks ; as they grow they exert considerable
pressure to widen the cracks, and when they die and
decay they leave behind a channel for percolation.

The main agency, however, in splitting rocks and
reducing them to the state of soil is frost, or rather
water in the act of freezing. It is well known that
water expands about one-tenth of its bulk in freezing,
and that it will exert enormous pressure on anything
that tends to prevent such solidification and expansion.
Hence the bursting of water-pipes, full bottles, and the
like during a severe frost ; though, as the bursting only
becomes apparent when the water thaws again, it is often
supposed that the thaw does the bursting. Hence also
the constant fracture of stones or bricks exposed to the
weather during winter; they become saturated with
water, and when this water tries to expand within them
they must split to relieve the pressure, thus developing
whatever lines of weakness there were within. The
examination of the face of an old quarry or even an old
wall of brick or stone after a frost will show the ground
at the foot of the face strewn with blocks and fragments
which have been wedged off by the expansion of the
water within the stone or brick. We talk of the
pulverising action of frost on the clods of a stiff clay soil ;
frost is equally if less actively pulverising to the toughest
and most closely grained of rocks. There are other
minor agencies assisting, but in the main, water, roots,
and frost are the tools which are always at work reducing

F

82 THE ORIGIN AND NATURE OF SOILS [chap.

rocks to soil, covering the bare surface of the former
wherever it may be exposed with a slowly formed
coating of its own debris. If the formation of soil
ended at this stage every rock would be covered by its
own appropriate "sedentary" soil, but as soon as the
soil is formed it begins to move. The wind and the
rain are always moving soil downhill ; the wind perhaps
may seem a trivial agency, but in rainless or even semi-
arid climates there are practically no other transporting
agencies at work, and we find vast tracts covered with
fine, uniform, wind-blown soil. The work of the rain is
most apparent when it has been long continued enough
to bring the rivers out in flood ; high up the country
every little gutter, every ditch that bounds the arable
land, is charged with turbid, hurrying water, which is
washing unseen quantities of coarser mud and sand
along its course. Finally the rivers themselves are
charged with sediment, as we can see by filling a large
bottle with the water from one that is running in flood
and allowing it to settle ; along their beds also, gravel
and stones of all sizes are being pushed. Wherever the
velocity of the current is reduced some of the transported
material will be deposited, hence as the streams descend
from the heights into flatter country they discharge the
coarsest part of the material they have washed from the
rocks above, and so give rise to the broad expanses of
gravel, sand, silt, etc., which underlie the water meadows
bordering the lower levels of all rivers. Much of the
suspended mud and clay, however, washes away to sea,
and is thrown down when the velocity of the stream is
entirely checked by the open water, where also the salts
in the sea-water exert their precipitating action upon
the fine particles ; in consequence, beds of newly sorted
soil tend to accumulate in the shallow waters just off
shore, and even to block up the river mouth unless the

V ] DRIFT SOILS 83

tides and currents scour it free. These deposits made
by the river give us a clue to the origin of that other
arrangement of rock and soil that we have noted as
sometimes prevailing, when a clean surface of the
underlying rock is covered by gravel or sand or clay of a
totally different character, without any of the gradual
transition that marks the passage of a rock into a
sedentary soil. The layer which thus rests upon a rock
out of which it has obviously not been formed is never
solid rock, but is an assemblage of divided material that
is generally pretty uniform in character, wholly gravel
or wholly sand, or entirely made up of a uniform silt
like a brick earth. The uniformity is due to the fact
that the material has been transported to its present
position by running water and has undergone a sorting
in the process. Gravels must have been laid down in
the bed of the stream, even though the stream no
longer runs in that spot, but perhaps in a course at a
lower level in the valley. In such cases the gravel is
generally the remains of a much larger tract of gravel
which filled the valley to a higher level at a time when
the stream ran in far greater volume. Similarly the
sand must also have been deposited where the current
still ran pretty sharply, whereas the fine-grained and
uniform silts, such as constitute the brick earth patches,
were either deposited in quiet backwaters and laybyes,
or were dropped by slow degrees on the river meadows
in flood time, just as similar stuff is accumulating to-day
in the same sort of places.

In addition to these non-sedentary soils that have
been moved and redeposited by running water or
by wind, over considerable parts of the country,
especially in the north and the midlands of Great
Britain, and for a hundred miles or more south of
the Great Lakes in the United States, we find the

84 THE ORIGIN AND NATURE OF SOILS [chap.

fundamental rocks covered, often to a considerable
depth, with disintegrated rock that has been moved into
its present position by the action of ice in the imme-
diately previous geological epoch, when a glacial climate
prevailed. These glacial drifts, as they are called, may
be mainly clay or sand, but usually they are considerably
mixed with fragments of rock of all kinds and sizes —
fragments which give clear evidence of the actions they
have been subjected to among the moving ice by the
way they have been rounded off and scored with
scratches and furrows. These glacial drifts form an
exception to what has already been said as to the
general uniformity of the transported soil material.

All soils derived from material that has not grown
up from the rock below, but has been moved by water,
wind, or ice, are known as " soils of transport " or " drift
soils," in contradistinction to the sedentary soils first
discussed. Some idea of the constant state of motion in
which soils still exist may be obtained by considering
the surface of an arable field on such soils as the chalk,
where there are a good many stones. The stones are
always much more abundant upon the top than in the
layers below; they may not be very prominent when
the surface is turned over by the plough, but they
work up again ; they may even be picked off to sell
for road-making, yet in a few years they seem as
numerous as ever, so that the older farmers and
labourers declare they "grow." The clue to their
abundance upon the surface may be obtained by
looking at any garden bed where it happens to receive
the drip from the eaves of a building ; the constant
downpour of water washes all the soil away, and leaves
the ground covered with small stones. The same action
goes on in the stony mixture constituting the soil of the
arable field ; with every rainfall there will be some

Fig. 17.— Section showing Glacial Drift lying on Magnesian
Limestone.

[Face page 84.

v.] ACTION OF WORMS 85

rearrangement of the particles, some washing-down of
the finest material, until the large fragments which are
unmoved by the rain are left on the surface.

Nor are such inanimate agencies as the wind and
rain alone effective in moving soil ; animals play their
part, even ants and moles are capable in time of
bringing about considerable shifting of fine soil from
below to the surface. That some such action does go
on may be concluded from the fact that even when the
soil is stony the surface of an old pasture is quite devoid
of stones, to find which it may be necessary to dig down
for a foot or two. This characteristic of old grass land
is chiefly due to the action of worms, which are always
swallowing the finest soil particles, and then ejecting
them as wormcasts on the surface. At first sight such
an action seems trivial, but one has only to collect and
weigh on some autumn morning the wormcasts from a
square yard of ground to find what a considerable
shifting of earth has taken place. Darwin has shown
that from this cause alone large stones, and even old
buildings of the time of the Romans and later, have
been completely buried ; he found that in one case
burnt marl, spread on the surface of grass land, had been
buried 3 inches in fifteen years, and in another case that
a layer of chalk had sunk 7 inches in twenty-nine years.
A hole cut in an old grass field will often show at some
little depth layers of chalk or ashes or burnt soil, each
layer representing material which had been spread on
the surface years before. Soils of transport are formed
in exactly the same way as sedentary soils, they have
merely travelled a little farther and been subjected to a
certain amount of sorting ; in all cases we have to look
upon soil as the product of the weathering — the dis-
integration and decay — of certain fundamental minerals
out of which the primitive rocks and the earth's crust

86 THE ORIGIN AND NATURE OF SOILS [chap.

are built up. Let us now see what these products are.
It will first be necessary to obtain a certain number of
typical samples of soil ; properly they should be taken
with an auger or other soil-sampling tool, but for the
simple examination that follows they may be obtained
by digging a hole, 2 feet deep, with a smooth vertical
face, and taking off from that face uniform slices down
to 9 inches for the soil, and from 9 to 18 inches for
the subsoil. Samples should thus be obtained of both
soil and subsoil, from a sand, a clay, and an alluvial
pasture, also of the surface soil only from chalky and
peaty land. The samples should be spread out to dry
naturally on trays or sheets of paper, the lumps being
gently crumbled by hand before they get quite dry;
this being most necessary with the clay soils, which can
only be broken down if they are caught at just the right
stage of moisture. When air-dried, they must be passed
through a sieve having round holes, \ inch or 3 mm. in
diameter, the lumps being crushed in a mortar with a
wooden pestle which is not hard enough to break up the
stones. The material passing the sieve forms the fine
earth required for further examination ; the stones are
cast away, though they should first be washed in order
to see of what they are composed. Now take a small
quantity of the fine earth of one of the soils in a little
dish, and heat it over a lamp, gently at first and then
more strongly; at the outset you will notice that it
begins to lose water although it was apparently dry to
start with, then as it becomes hotter it smokes and
gives off a smell of burning vegetable matter ; finally, if
heating is continued for some time, the soil will take a
bright brick-red colour and undergo no further change.
From this we may conclude that soils contain water and
a certain amount of organic matter or humus — the
debris of previous vegetation ; it is most instructive to

v.] COMPOSITION OF SOILS 87

determine how much of each of these constituents is
present in the examples that have been selected. Weigh
out a series of basins, add about 10 grammes of soil to
each, and weigh again ; put the basins in the water oven
for a few hours, and reweigh to find the loss of moisture ;
finally, ignite for two hours over a lamp and make a
last weighing to obtain the loss on ignition, which
includes a little combined water as well as the organic
matter. Considerable differences will reveal themselves
(see Table XL); the moisture that is retained by the
undried soil will vary from about 2 per cent, in the
sandy subsoil to 10 per cent, or more in the peaty soil ;
the loss on ignition will similarly vary from 2 to 6, and
may even run up 30 per cent, in the peaty soil. We
can see clearly enough that the humus present is a
compound of carbon, from the manner in which it chars
and blackens on heating. The humus also contains
nitrogen, as may be seen by heating a little more of
the soil mixed with soda-lime, whereupon the smell
of ammonia, which at once becomes palpable, may be
taken as evidence of the presence of combined nitrogen
in the humus, just as in the plant (p. 3). We can
further show that humus, or rather the humic acid which
can be set free by the action of acids on the humus, is
soluble in alkalis like ammonia or caustic soda. Take
about 20 grammes of the peaty or alluvial soil, and
cover it with dilute (5 per cent.) hydrochloric acid for
half an hour, then pour off the acid and get rid of it
entirely by one or two washings with pure water.
Finally, pour on the soil five or six times its bulk of a
weak solution of ammonia and shake up from time to
time ; a deep brown or even black solution will result,
and the remaining soil will be considerably bleached by
the removal thus effected of the greater part of its
organic matter. We may conclude that humus is one

88 THE ORIGIN AND NATURE OE SOILS [chap.

of the regular constituents of soil, and is the result of
the decay of the vegetation that previously lived on the
soil ; it is a dark brown or black compound of carbon
containing also nitrogen, and is to some considerable
extent soluble in dilute alkalis. It is one of the chief
colouring matters of soils, among the particles of which
it also acts to some degree as a cement.

It is now necessary to make a rough mechanical
analysis of the mineral part of a soil; lo grammes are
weighed out into a dish, a little water is added, and the
contents of the dish are rubbed up into a paste by means
of a pestle made by sticking a rubber bung on to the
end of a glass rod. A beaker about 8 cm. in diameter
and 9 cm. high is now clearly marked on the side at a
point 7-5 cm. from the bottom, and the pulped-up soil is
washed into this beaker through a small sieve made of
brass- wire cloth of lOO meshes to the inch. The sieve
and its contents are put in the oven ; when dry, the
material on the sieve is weighed and counted as " coarse
sand." The dirty liquid in the beaker is now made up
to the 7-5 cm. mark with more water, given a good stir,
and left to stand for exactly twelve and a half minutes,
at which moment the upper turbid liquid is steadily but
quickly poured off from the sediment below into a large
jar. The sediment is now rubbed up afresh with more
water, the water is brought to the mark, stirred, left to
stand for twelve and a half minutes, and poured off as
before into the same jar ; all the processes being repeated
half a dozen times or more, until at last there is nothing
left floating in the clear water at the end of the twelve
and a half minutes' wait. The sediment remaining in
the beaker is dried and weighed ; the contents of the
large jar can also be evaporated down and weighed, but
as this constitutes rather a long operation it will be
sufficient to evaporate a little in order to examine the

v.]

MECHANICAL ANALYSIS OF SOILS

89

character of the deposit, and to arrive at its weight by
taking the difference between the original 10 grammes
and the sum of the two fractions already weighed,
together with the moisture which we have previously
found the soil to contain. By this process, the results of
which are set out in Table XI., the soil has been

Table XI.— Approximate Mechanical Analysis of Various
Soils.

Sand.

Clay.

Alluvial.

Chalk.

Peat.

Sou.

Subsoil.

Soil.

Subsoil.

Sou.

SubfloU.

Sou.

Soil.

Moisture .

2.4

1-7

4.4

5-5

2-4

4.6

2-4

8.4

Organic matter .

40

3-0

6.4

4.4

14-3

8-1

6.9

32-8

Coarse Sand

10.3

9.7

.^•P

0.8

O-I

00

20-2

26.6

Fine Sand .

670

68.6

30-1

160

53-3

47-5

21.9

14-2

Clay and Silt .

16.3

I7-0

55-2

73-3

29.7

39-8

9.6*

18.0

* This soil also contained 89 per cent, of carbonate of Ume.

divided into three fractions — the coarse one caught by
the sieve, which casual examination and feel shows to be
sand ; the finer one in the beaker, which is still gritty to
the touch and is seen under the lens to be made of
rounded particles, so that it may be called fine sand ;
and the finest stuff of all that remained suspended in
the water poured into the jar, material which is so fine
that some of it will remain floating for days though left
quite undisturbed. When we have collected a portion
by evaporation or long settlement it will feel quite
smooth and greasy between the fingers, and only under
the higher powers of the microscope will it show the
particles of which it is composed. It is clay, but not so
wholly clay as a finer separation would obtain, being in
fact a mixture of what the soil analyst would call clay
and fine silt, but still for working purposes a very pure
clay. Notice particularly that when it dries it forms a

90 THE ORIGIN AND NATURE OF SOILS [chap.

tough cake which requires some force to break, whereas
both the coarse and fine sand fall to a powder as soon as
they are dry. If we make this partial separation for all
the examples of soil we shall find the greater part of
each of them to be composed of sand and clay in varying
proportions ; however, even the coarsest soil is not free
from clay, while even the heavy clay soil probably contain
50 per cent, of the sand fractions.

Before examining the nature of the sand and clay
fractions there is still one other regular constituent of
soil which must be identified, and this we may do by
putting a few grammes of each soil in a dish and
covering it with dilute hydrochloric acid. In several
cases, especially with the chalky soil, there will be a
visible effervescence, due to the escape of carbon dioxide
from carbonate of lime in the soil, which is being decom-
posed by the hydrochloric acid. Even the soils which do
not effervesce probably contain some carbonate of lime,
small amounts of which (less than i per cent, or so)
show no visible evolution of carbon dioxide gas, because
it dissolves in the liquid as fast as it is set free. The
peaty soil is pretty sure to show no effervescence, and as
a rule this is due to the entire absence of carbonate of
lime from such soils. A further test which should be
applied is to put a little of each soil in a wettish condition
on a strip of blue litmus paper; the peaty soil, and
perhaps some of the others, will show themselves after
standing to be acid, and from acid soils carbonate of
lime is absent except in accidental fragments. These
four substances — humus, sand, clay, carbonate of lime,
constitute the solid matter of all soils ; but only in the
exceptional cases of peats on the one hand or chalky
soils on the other do the sand and clay fail to pre-
dominate greatly over the other two constituents.

To study the properties of sand any ordinary clean

v.] PROPERTIES OF CLA Y 91

sand will suffice, while for the clay a piece of pure tile
or brick clay before it has been mixed with sand is
required, or better still, a sample of modelling clay ; some
will be wanted in its natural moist condition, while a
little should be dried and roughly powdered. Begin by
taking some moist clay and some wetted sand ; the clay
can be moulded into shape and will hold together even
when squeezed into thin sheets, the sand possesses little
or no cohesion. On drying, the sand falls to pieces, the
clay retains its shape and becomes hard. Mould a little
brick of the clay, 6 to 7 inches long and about i inch
square, make two marks on the face exactly 5 inches
apart ; put the clay aside to dry, and then measure the
distance between the marks ; the clay shrinks in drying.
Clay is plastic and coherent when wet, retains its shape
on drying, but shrinks and becomes very hard, none of
which properties are shared by the sand. Take three
funnels, plug their stems loosely with cotton-wool, and
weigh out into one 50 grammes of sand, into each of the
others 50 grammes of the dry powdered clay ; stand each
above a beaker, and pour on to the soils 100 c.c. of water.
On to one of the clay soils, however, pour a little water
to begin with and make it into a paste with the clay,
adding water little by little until all the clay is pulped
up and then pouring on what remains. Now note both
how much water runs through and how long it takes to
drain in each case. The water runs through the sand in
a few minutes, and when measured the sand will probably
not have retained more than i o c.c. of the water. Through
the powdered clay the water may take an hour or more to
pass, and when the drainage is complete the clay may
have retained almost its own weight of water. In the
third funnel, where the clay has been pulped up with
water or "puddled," no water at all will have passed.
As compared with clay, the sand passes water quickly

92 THE ORIGIN AND NATURE OF SOILS [chap.

and retains but a small proportion when thoroughly
drained ; puddled clay is quite impervious to water.

We may make one more experiment with clay :
Work up a few grammes of clay with a gallon or so of
distilled or rain water, and divide the turbid water that
results among several jars. To one add a few grains of
salt, to another a few cubic centimetres of lime water,
to a third a little sulphate of lime dissolved in water, to
a fourth a few drops of ammonia, to a fifth a few drops
of acid, and leave a control without addition ; put them
all aside to settle down undisturbed. The liquid to
which nothing has been added will take a long time to
clear, with the ammonia it will take longer still, days or
even weeks. The acid, on the contrary, causes the
solution to clear in a comparatively short time ; the lime
water and the sulphate of lime also induce clearing,
though not so rapidly, and the salt is still less effective.
The appearance of the quickly clearing liquids gives us
some clue to what takes place ; the acid and the salts,
especially salts of lime, induce the very fine particles of
which the clay is composed to clot together and coagulate,
or flocculate, as we shall prefer to call it. Since each of
the compound particles thus formed must be heavier
than the units of which it is composed, it falls to the
bottom of the liquid more quickly, and generally behaves
as though it were something of the order of a grain of
sand. Clay particles will also flocculate if left to them-
selves and exposed to changes of temperature, wettings
and dryings, freezings and thawings, and this fact has a
very important bearing on the working of clay soils.
On the other hand, any handling or knocking about of
the clay soil when in a wet condition breaks down the
flocculation and sets all the fine particles free once
more, making the clay more characteristically clay than
ever.

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v.] CHEMICAL CONSTITUENTS OF SOILS 93

But though all soils are built up of sand and clay,
humus and carbonate of lime, these materials only
give rise to its physical structure ; they account for
the manner in which the soil works and its relations to
water, but in themselves they have nothing to do with
feeding the plant. In order to get information on that
aspect of the soil it is necessary to try a new experi-
ment. Take a series of funnels, plugged as before
loosely with cotton-wool, and pack each with a different
sample of soil, then pour on to each a small quantity of
hot water and let it percolate through, an operation
which will be hastened if each funnel can be led into a
flask communicating with a filter pump. Take the
liquid which comes through, filter if necessary, and
evaporate it to dryness in a clean basin — a small
residue will be left representing the material in the soil
which was soluble in water. One test only need be
applied to it ; pour on to the residue a solution of
diphenylamine in sulphuric acid and an intense blue
colour will appear, indicating the presence of nitrates in
the extract from the soil. In this nitrate, which is
present in all soils, we have a substance which, as we
have learnt before, will serve as food for plants, supply-
ing them with the combined nitrogen that is necessary
for their existence. Ammonia, the other nitrogen
compound which plants can utilise, may also be detected
in soil, but in such small quantities that a delicate test is
necessary. The small proportion is due to the fact that
ammonia in the soil is constantly being converted into
nitrates by a process which will be explained later.
Indeed the nitrates themselves are only present in the
soil in very small amounts, from two to twenty parts
per million of a dry soil ; how minute a fraction of the
whole soil does the soluble portion constitute, may be
guessed from the residue left in the dishes after evapora-

94 THE ORIGIN AND NATURE OF SOILS [chap.

tion of the soil extract. It is, however, not quite
sufficient to consider the soil materials that are soluble
in water as alone capable of feeding the plant ; we have
already seen reason to suppose that the carbon dioxide
excreted by the plant's roots and also present in the
soil from other sources, adds greatly to the solvent
action of the water, enabling it to attack substances
which are usually regarded as insoluble in water. In
consequence, we have come to regard any substance in
the soil that is soluble in acids as a potential plant food
which may, however slowly and in whatever small quan-
tities, be brought into solution and so reach the plant.

If, then, we attack a soil with strong hydrochloric
acid, which we may be sure will dissolve everything that
is likely to reach the plant within the next century,
we shall find some 5 to 1 5 per cent, of the soil going
into solution, but by far the greater part of this consists
of oxides of iron and alumina, to which (except for a
trace of iron) the plant is indifferent. If we analyse the
soluble material we shall find exactly the elements
we have previously ascertained to be common
to all plants, i.e.^ chlorine, phosphoric acid,
sulphur, and some silica among non - metals,
with soda, potash, magnesia, lime, iron, and alu-
mina in excess ; but the elements that are necessary
to the plant rarely make up i per cent, of even the
most fertile soils. This i per cent, however, is all-
important, constituting as it does a vast reservoir of
potential plant food. Nor is the quantity so small as
might at first sight appear ; a cubic foot of soil in situ
weighs from 90 to no lb., clays being the lighter and
coarse sands the heaviest of all ; at Rothamsted, again,
where the soil is a clay loam, the layer of soil, an acre in
extent and 9 inches deep, weighs about two and a half
million pounds, exclusive of stones, i.e. rather more than

v.] SOILS AND SUBSOILS 95

a thousand tons. If, then, a soil possesses as little as
one-tenth per cent of nitrogen, it still contains about a
ton of nitrogen per acre down to the depth of 9 inches
only; yet, as we have seen earlier (Table VI.), an
ordinary crop does not remove from the soil more than
50 to 100 lb. of nitrogen per acre. There is thus material
for fifty or more full crops in the poorest soils ; but
these questions will be discussed more in detail in a
later chapter.

We may now return to the rough soil analyses we
have made, to see what light they throw on the relative
nature of the soils and subsoils. For purposes of
illustration. Table XII. (page 96) gives more accurate
and detailed analyses of such a series, in which the
soils have been split up into a larger number of frac-
tions than was attempted in our rough analysis ; each of
the fractions in the first case included two of the frac-
tions into which the soil is separated in the full analysis.

Looking down this table we first notice that there is
comparatively little humus in the subsoils ; the humus is
almost wholly confined to the 9 inches in which the
roots are numerous. Exceptions to this rule are
furnished by the alluvial and sometimes by the peaty
soils if the soil has been taken from the top of a peat
deposit of any depth, because peat is nothing more than
an accumulation of former vegetation in a more or less
pure state. The alluvial subsoils always show a con-
siderable amount of humus, because down to their
lowest depths they consist of old soil which has been
washed off the surface into the rivers in flood time, and
redeposited lower down the river. Only when the
alluvial subsoil consists of coarse-grained gravel or sand
will it be poor in humus ; these large particles naturally
carry no humus after rubbing together for a time in
running water. As regards carbonate of lime, soil and

96

THE ORIGIN AND NATURE OF SOILS [chap.

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v.] SOILS AND SUBSOILS 97

subsoil are very much alike, the soil being generally a
little the poorer, because of the constant solution that
is going on in the surface soil. On the other hand, the
surface soil has sometimes been so regularly dressed
with chalk or lime that it shows a higher percentage
of carbonate of lime than the subsoil. Soils on chalk
or limestone formations are often very shallow, so that
the subsoil becomes nearly pure carbonate of lime,
wherever a subsoil can be said to exist. As regards
sands and clay, in the heavier soils — i.e,^ the true clays,
the heavy clay loams, and most alluvial soils — the surface
soil is more coarsely grained than the subsoil ; it contains
more sand and less clay. This difference is due to the
constant action of the rain washing down the finest
particles, especially when the soil is loose after cultiva-
tion. When the rain beats upon the rough surface of
the soil, some of the very finest particles become washed
off and suspended in the water; sometimes they are
filtered out again by the soil at a lower level, sometimes
they are carried away into the ditches ; in either case
the coarser-grained material is left behind on the top.
The subsoil, however, of a sandy soil possesses much the
same composition as the soil ; in this case there is both
less fine material to wash down, and also the whole soil
settles together when beating rain falls, instead of leav-
ing the hollow spaces which occur in a clay soil for a long
time after it has been worked. As to the comparisons
between different kinds of soils, we find that all the
heavy working soils (really the lightest per cubic foot)
are made up of the finer particles, and contain but little
sand ; especially do they contain very little of the coarsest
sand, which tends to keep a soil open and friable. They
are distinguished by a high proportion of clay, though
of what the analyst properly calls clay — material made
up of particles less than one hundred and twenty-five

G

98 THE ORIGIN AND NATURE OF SOILS [chap.

thousandth of an inch in diameter (o-ooo2 mm.), there
is rarely as much as 30 per cent. In some very wet and
heavy working soils, of which No. 8 is an example, the
percentage of true clay is not especially great, but it is
associated with high percentages of the fractions next in
fineness — the fine silt and the silt — and these, in the
absence of coarse sand, are almost as retentive of water
and clay-like as clay itself. Such a soil does not shrink
so much on drying, but it lies wet for a long time ; it is
excessively greasy and sticky after rain, and when
worked down to a fine tilth will run together after rain
and cake on the top in a fashion special to itself. The
difficulty of working all heavy soils is much mitigated if
they contain an appreciable quantity of carbonate of lime,
because that substance constantly dissolves in the soil
water which has gathered carbon dioxide from the
decaying humus, and thus forms a solution of bicarbonate
of lime which keeps the clay particles flocculated. On
some formations marls occur containing a considerable
proportion of very fine-grained carbonate of lime mixed
with clay ; such soils are very sticky and work heavily,
but they crumble readily when dry, and never lie so wet
as the true clay soils. Lastly, the sandy soils vary very
much in character ; some sandy soils, in which the fine
sand and the silt are the predominant fractions, are
amongst the most valuable of soils for tillage purposes.
They are light, and so are cheaply worked ; no time is
lost, because they are fit for the plough almost immedi-
ately after rain, and yet for all the quickness with which
they dry, they do not lose their power of supporting the
crop with water during a drought. Such soils may
contain no more than 10 per cent, of clay, but owe their
good qualities to the general predominance of fractions
of medium coarseness. The really poor sands, which
are often so light (in the farmer's sense) as never to have

v.] BARREN SOILS 99

been brought into cultivation but remain in open
common and waste, may still contain 6 to 10 per cent,
of clay, but the sand fractions and particularly the coarse
sand, constitute something like three-quarters of the
whole soil. Such soils can retain no water for the
service of the crops upon them, nor for reasons that will
be seen later can they retain any plant food : they are
poor in the chemical sense, but barren chiefly because
of their dryness, even with the evenly distributed rain-
fall of Great Britain.

CHAPTER VI
CULTIVATION AND THE MOVEMENTS OF SOIL WATER

Nature of the Film of Liquid surrounding Wet Particles of Soil.
Retention and Movements of Water due to Surface Tension.
Percolation. Rise of Subsoil Water by Capillarity. Value of
Autumn Ploughing. Effect of Spring Cultivations. Cooling
of the Land by Evaporation. Effect of Hoeing and Rolling
upon the Temperature and Water-content of the Soil. Dry
Farming in Semi-arid Regions. Drainage and the Tempera-
ture of Soils. Spring Frosts. Early and Late Soils.

Somewhat earlier in the book an experiment was
described (p. 91) which had for its object the deter-
mination of the relative powers of different soils to
retain water, though the water was given every
opportunity of draining away. It will now be necessary
to ask how the soils effect this retention of water,
because on this depend many of the properties of soils
which are important to the farmer. It is not easy to
observe what is going on in the soil itself, because the
particles are so small, but we can obtain a convenient
illustration by means of a model on a large scale.
Procure a dozen or so large beads and thread them on
three or four strings from a stick, so as to form a little
rectangle of beads hanging vertically and all in contact ;
this may be taken to represent an imaginary section of
the soil greatly magnified. Now dip the beads in oil
and lift them out to drain, or better still, dip them in
melted wax for a few moments, so that after lifting them

Fig. 19. — Photograph illustrating Liquid Film
ROUND Soil Particles.

[Face page 100.

CHAP. VI.] THE WATER FILM loi

out the wax will drain away for a short time before
setting to a solid state. Oil or wax is only used because
it exaggerates and renders more perceptible the results
which would be equally given by water ; the appearances
presented are shown in the photograph. It will be
found that all the beads are covered with a skin of oil
or wax, just as they would have been "wetted'* had
they been dipped in water, but this skin is thinnest on
the upper row of beads, and gets perceptibly thicker
on each lower row. Moreover, wherever two beads are
in contact there is a much thicker layer of liquid in the
angle joining the two surfaces, though again the
accumulations are greater the lower the row; finally,
the lowest row of beads carry beneath them large drops
which are just not big enough to fall off. The whole
set of beads must be considered as enclosed within a film
of oil, which we may regard not so much as sticking to
the material of the beads but as drawn over them,
because the outer surface of the film acts like an
elastic skin— so that we might compare the arrange-
ment to a set of balls tied up in a stretched sheet of
thin indiarubber. This stretched skin on the surface
of a liquid is always pulling inward and trying to shrink
into the smallest possible area ; for this reason drops of
water assume a round shape whenever they reach such
a small size that their weight becomes less effective than
the elastic pull of the film, or the surface tension as we
shall call it. To take another illustration : the hairs of a
dry paint-brush stand out to form a round end ; wet
them, and they are dragged together to a point by the
surface tension of the film of water trying to reduce
itself to the smallest possible area. It is not merely the
contact with the water which causes the pointed end,
because when the brush is dipped below the surface it
retains the rounded shape it possesses when dry, the

I02 THE MOVEMENTS OF SOIL WATER [chap.

point is only in evidence when the brush is partially wet.
Water or other liquids cling to solid bodies which they
'' wet," because they enclose them within the elastic film
formed by their surface, and as the liquid inside the
film is free to move, the film must be equally stretched
at every point when equilibrium has been attained and
the liquid is at rest When the shape of the wetted
body is irregular, the film that encloses it will always
adjust itself to develop its minimum of surface. Coming
back to the beads in oil or wax, the film on the upper
surface is stretched to the thinnest extent that is
consistent with not breaking, because all the liquid
inside that does not form the film itself is free to
move, and sinks by gravity as low as possible. On the
lowest row the film is at its thickest, all the pull of the
elastic skin being employed in holding up the weight of
liquid inside the skin. In the angles between the beads
the layer is thicker, because the skin is, as it were,
stretched across a corner in order to reduce its area to
a minimum. With this idea of a stretched outside skin
in our minds, let us imagine what would happen if
liquid were added or taken away from any point.
Suppose liquid is added at the top, the skin becomes
at once more stretched, and tries to readjust matters by
pressing the liquid down and establishing an equal
stretching all over, and in this downward pressure it is
aided by gravity. Once the liquid has arrived at the
lower layer, the skin there has to carry an increased
weight, too much for its elasticity, so that the skin breaks
and a drop falls. It is in this way that water percolates
downwards in consolidated soil where there are no
actual channels through which to flow ; it is handed on
from particle to particle, until at last it reaches an open
space into which a drop can form and break off. This
open space may be a drain-pipe, which then begins to

VI.] SVRPACn TENSION I03

run. It has often been thought difficult to explain how
drains come to have free water in them at all, being
themselves composed of porous material which clings to
water like the fine-grained soil with which it is in
contact ; but when any of these fine particles gets so
overcharged with water that the elastic skin is stretched
beyond its holding power, the skin will rupture and
detach a drop of free water into any open space that
may be present. Returning now to our original
illustration of the set of beads dipped in oil, what will
happen when liquid is taken away from the top ? The
skin is reduced in thickness, its stretching and therefore
its pressure on the liquid inside is reduced, so that a
rise of liquid takes place from below until the tension is
once more equalised all over. Thus water can rise in a
soil from the lower wet layers in order to replace that
which has been taken away by evaporation at the
surface, but it is necessary that there shall be a con-
tinuous film of water from the evaporating surface to
the wet layer below. If the evaporation continues until
the films become thinner and thinner and more and
more stretched ; at last the stretching becomes too much
for the elasticity of the material, the film ruptures and
shrinks up to a smaller surface with a relieved internal
strain. Similarly, if liquid is taken away at the side
there will be thinner films created at that point with
reduced stretching, which exerts a pull on the liquid
until the tension of the film is once more equalised all
over. Water will move horizontally from 'a wetter
to a drier area, just as it can move upwards against
gravity, or still more readily downwards with gravity ;
as long as the film of water round the particles is
continuous, this motion in order to restore equilibrium
can take place. This property of water and other
liquids to generate a kind of stretched skin on the

104 THE MOVEMENTS OF SOIL WATER [chap.

surface is known as surface tension ; it is only another
way of looking at the property which is sometimes
called capillarity, the power of liquids to move upwards,
downwards, or sideways, along, or into any system of
fine tubes. By means of a few glass tubes drawn out
fine and some coloured water, one may easily see that
water will rise in such tubes above the level outside,
and will rise farther the finer the tube in which the
experiment is tried. When one corner of a sponge or a
towel is dipped into water, the whole soon becomes
wetted, and the behaviour of the water may either be
regarded as a creation of a stretched film from fibre to
fibre, or a motion of the water along the fine channels
formed by the closeness of the fibres. In the same way
water may be conceived to move in the soil along the
fine channels formed between particles which are touch-
ing at their salient points ; it is quite easy to show that
soil is never packed solid, there is always about 40 per
cent, of free pore-space between the particles, like the
spaces which must exist between the spheres making
up a heap of shot, however closely they are packed
together. But just as we have seen that, for any motion
of water to take place in the soil, the film of water must
be continuous from particle to particle, so from this
other point of view there must be no gaps in the soil
destroying the continuity of the fine tubes, because
liquids can move but a small distance along a wide tube.
In interpreting the relations between water and the soil
particles, either way of looking at things — capillarity
or surface tension — may be employed ; perhaps the
stretched film is the more useful, because it fixes
attention on the fact that the surface exposed by the
soil particles is their active and effective part in all such
actions. It is easy to understand that the more
extensive the total surface possessed by the soil

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Fig. 20.— Diagram illustrating Capillary Rise
OF Liquids.

\Face page 104.

VI.] SURFACE OF SOIL PARTICLES 105

particles, the bigger area there is to which water, or
anything else wetting the surface, will cling; further-
more, the smaller the particles into which a given
weight of soil is divided, the greater the total area of
surface. Imagine a little cube, i inch on the side,
divided by three cuts into eight cubes, each \ inch on the
side ; the surface exposed by the solid material has been
doubled, because for one cube with six faces, each an inch
square, there are now eight cubes, each with ^\>l faces a
quarter of a square inch in area, or 12 square inches in
all. In consequence, a really fine-grained soil possesses
an enormous area and a corresponding absorbing power ;
it has been calculated in various ways that the particles
contained in a cubic foot of an average heavy soil
possess surfaces making up a total area of about an
acre, while in a clay soil this is increased to about 4
acres. All surface-tension actions are, therefore, more
powerful in clay and similarly fine-grained soils; they
absorb a greater amount of water, and hold on to it
more tightly. The rate of motion of water, however, in
such soils is slower, whether it be the downward move-
ment due to gravity and surface tension together which
we call percolation, or the upward movement due to
surface tension alone when the surface is losing water.
The slowness of the movements is due to extreme
fineness of the channels between the minute clay
particles; the water in these channels cannot move
freely, because it is never removed from the drag caused
by the attracting surfaces of the solid. Skin friction is
always at work, and there is never anything approaching
free flow.

Applying these principles to the soils themselves, we
see that in a coarse-grained sandy soil percolation will
always be rapid, because the mere motion of water by
gravity in the large spaces between the particles will be

io6 THE MOVEMENTS OF SOIL WATER [chap.

little impeded by skin friction. Drainage will therefore
be good, but since the soil particles possess so small a
surface that can be wetted, the soil will therefore retain
very little moisture, sometimes no more than lo per cent,
when fully saturated but drained. Similarly, the
particles being large the water-films round them are
not extensive, and will not possess much power of lifting
water against gravity ; when evaporation is going on, the
water will rise quickly because it is little impeded, but
to no great distance. The capillary tubes formed by
the interspaces between the sand grains are large, so
motion up them is quick, but for only a short distance.
In the opposite way, in a very finely grained soil like a
clay, percolation will be slow, because the downward
motion is hindered by the clinging of the extensive
surface to the water, and by the fineness of the inter-
spaces through which it has to ooze. This extensive
surface, however, retains a considerable proportion of
water, up to 40 per cent, when drainage is over but
losses by evaporation have not begun. Again, although
the pull exerted by so great a surface is enormous, it is
very ineffective in drawing up water rapidly, because of
the drag exerted by the particles on the water with
which they are in such close contact. When the clay
has been tempered and kneaded so as to reduce it to*
its maximum of fine division and also to pack the
particles together as closely as possible, water will not
move through it at all, because the water particles are
held so tightly by the clay particles with which they are
in contact that to all intents and purposes they cannot
move at all. For practical purposes the most valuable
soils are those which are fine-grained enough to possess
considerable surface, capable of retaining water against
drainage, and also of lifting it from the wetter layers
below when the proportion has been reduced by

VI.] WATER REQUIRED BY CROPS 107

evaporation at the surface, but yet are sufficiently coarse
to admit of the reasonably free movements of water
either downwards or upwards. There is, in fact, a happy
medium of grain which has a large and effective surface
that is yet not too large to shut down the movement of
the water. Such soils are found among some of the
loams and fine sands in which predominate those
fractions which we have previously designated as fine
sand and silts.

We have already discussed the amount of water
required by the growing plant, and have found that
taking the experimental figure of 200 to 300 pounds
of water transpired from each pound of dry matter
elaborated, then the usual crops grown in this country
will evaporate from 6 to 10 inches of rain, and even
more in the case of a heavy crop of mangolds. Con-
sidering that this growth is all made during a portion of
the year only, that evaporation from the bare soil will
also dissipate much of the rainfall, a great deal of which
also runs off the surface or percolates so quickly into
the subsoil as to lead to its permanent loss to the land
by drainage, we can easily understand that where the
annual rainfall is only 30 inches or so, as is the case
over the greater part of England, the crops are often
likely to suffer for want of water. Humid as is the
English climate, the magnitude of the crops in any given
year is more often determined by lack of water than by
any other single factor, and the majority of the
operations of cultivation are directed towards obtaining
and storing as large a water-supply as possible.
Beginning in the autumn, it is desirable to get the
stubbles ploughed early and left rough for the winter ;
much more of the winter rainfall will be absorbed by
such a ploughed surface than by one which remains so
firm and trampled by the harvest operations that water

io8 THE MOVEMENTS OF SOIL WATER [chap.

penetrates with difficulty and largely runs off to the
ditches. Not only is more water collected, but the
exposure of the plough slice to the weather, to the
pulverising action of freezings and thawings, wettings
and dryings, tends to flocculate the clay particles on
heavy soils, so that later they are easily worked down
to a fine tilth. This weathering action has even some
effect on the chemical constituents of the soil ; the potash
compounds in particular are found to become more
soluble after a winter's exposure of the soil to frost
and rain. The autumn ploughing is particularly valuable
on really heavy soils ; they are rarely dry enough during
the winter or early spring to be fit for cultivation ;
in the process they become somewhat tempered and
smeared by the plough, kneaded also by the treading
of horses and man, so that they would dry into tough
and difficult clods were they not afterwards exposed to a
succession of spring frosts to bring them into condition
again. One cultivation of a clay soil in a wet state in
the spring may easily spoil its working and therefore its
productivity for the rest of the year, because there are
no longer any frosts to restore the tilth, whereas a
mistake in the autumn becomes repaired by the action
of the later frosts.

Assuming that the land has been ploughed in the
autumn, it is then desirable to plough once more in
the spring as soon as the land will carry horses safely —
the object of this second ploughing being to conserve
the main supply of water in the subsoil, and also to
enable the layer on the surface to become dry and
warm so as to be ready for the formation of a seed
bed. After the winter rains the plough slices will have
become somewhat closely beaten down and joined up
once more into a compact mass with the earth forming
the subsoil below ; thus the film of water on the particles

VI.] COOLING BY E VAPOR A TION 109

at the surface is joined up to that surrounding the
particles in the subsoil below, with the result that as fast
as water is evaporated from the surface the losses are
repaired from the subsoil. This not only causes a loss
of water to the soil — a loss which may become of
importance later — but the continuous evaporation keeps
the surface moist and cold. It should always be realised
that an evaporating liquid withdraws heat from the
objects with which it is in contact — the heat being
necessary to convert the liquid into vapour. This with-
drawal of heat is well seen in the cold experienced by
the wetted hands or face when a dry east wind is
blowing and causing rapid evaporation ; it may be
illustrated experimentally by wrapping the bulb of a
thermometer in wet flannel or cotton-wool and whirling
it rapidly round and round in the air, whereupon the
temperature indicated by the thermometer may be
made to fall several degrees. Again, the cooling effect
of evaporation may be demonstrated by the cold
experienced when a little alcohol, ether, or petrol is
poured on the hands. Being all readily volatile liquids,
they withdraw a considerable amount of heat from the
hands in order to pass into the state of vapour. The
spring cultivation of the previously ploughed land
breaks up the continuity of the water films between the
plough layer and the subsoil below, water thereupon
travels much more slowly into the surface layer, which
in consequence can become dry, and being dry can also
warm up at an earlier date. The actual drying will
probably take place a little more gently, because the
land is not forced to wait until the parching east winds
set in ; when heavy wet land is dried rapidly under
their influence a hard, steely crust is generally formed
on the surface which is difficult to break down later.
The early spring ploughing before the frosts are quite

no THE MOVEMENTS OF SOIL WATER [chap.

ended is of the greatest importance in getting a heavy
clay soil to break down to a mellow crumbly seed bed.
The remaining operations of early spring are mostly
directed towards obtaining a good seed bed by the use
of cultivators of various kinds, and on heavy soils the
important thing to be observed is never to work the
land when it is in the least wet, or clods of deflocculated
clay must inevitably be the result, clods which dry with
difficulty and then form hard tough masses which can
only be worked down by the action of frost. By
implements alone — cultivators, rollers, or clod-crushers
— it is impossible to reduce the lumps formed by
smeared and deflocculated clay into a fine tilth.

But while the farmer is reducing his soil to a crumb, so
as to secure a fine seed bed in which he can deposit the
seeds at an even depth, he is also careful to keep the soil
consolidated, because if it becomes loose below the
surface there can no longer be any continuity of liquid
films between the water in the subsoil and that round
the particles in contact with the roots of the young
plant. After sowing, the land is generally further
consolidated by rolling, and in a dry spring the rolling
may be repeated just after the seeds have begun to push.
The effect of rolling is to consolidate the whole soil
from the surface downwards ; it brings the soil particles
into more intimate contact and assists the formation of
continuous water films from the wet subsoil below. As
these water films are continuous to the surface there
will be loss of water by evaporation, with a consequent
reduction of temperature ; but these disadvantages have
to be faced, in view of the vital importance of keeping
up the water-supply from below to the germinating
seeds or infant plants in time of drought. By experi-
ment, we can find that land which has been rolled is (i)
moister at the surface but drier at 9 inches or a foot

VI.] ROLLING AND HOEING in

down ; (2) cooler at the surface than is a piece of adjoin-
ing land which has been kept loosely covered with soil.
Too much stress cannot be laid on the importance of
consolidating the soil round the roots of plants,
especially in their earlier stages of growth ; although
gardeners are accustomed to tread over their beds
before sowing small seeds like onions, they often allow
the soil of flower-beds to become altogether loose and
porous down to considerable depth, simply by doing
too much trenching and deep digging.

As soon as the plant has been established the chief
work of the farmer or gardener consists in maintaining
a loose surface of the soil for the remainder of the season.
Not only are the various processes which liberate plant
food from the reserves in the soil promoted by a constant
stirring of the surface, but above all things the stock of
water in the soil is conserved for the uses of the plant
alone. A loose surface tilth soon dries itself, but as it
possesses no close connection with the layer below there
is no continuous water film from the water-bearing layers
to the surface at which loss is suffered by evaporation.
The water is lifted by surface tension as far as the soil
is consolidated, i.e. up to the roots of the plant, but it
cannot get into the layer which is actually exposed to
the drying wind and sun, because this layer is only lying
loosely on the water-holding soil with large gaps
between. The loose, friable layer of soil acts as a screen
on the soil below, protecting it from evaporation : it is in
fact a soil mulch, and serves just the same purpose as a
layer of farmyard manure, or straw, or grass clippings
— any of the materials which a gardener usually calls a
mulch. By keeping it constantly renewed, the soil
mulch may be completely effective in preserving all the
water originally present in the soil until the only loss of
water to the soil is that which the crop takes and utilises.

112 THE MOVEMENTS OF SOIL WATER [chap.

An old gardener was accustomed to say that he watered
his garden with his hoe ; and in this connection it should
be noted that a light watering or a gentle shower of
rain during a drought often causes more loss than gain
of moisture to the soil. The wetting of the surface soil
which ensues may be only sufficient to re-establish the
film of water round the soil particles at the top and make
that film continuous with the permanent film reaching up
from the wetted subsoil. In consequence, as soon as
evaporation begins afresh at the surface, water is lifted
from the lower layers to takes its place, and the process
goes on with considerable loss to the stock of water in
the soil unless the continuity of the film near the surface
is ruptured by cultivation. Waterings should be done
thoroughly or not at all, and they should be followed
up by hoeing as soon as the surface is fit to work again.
The fact that the crop evaporates or transpires con-
siderable quantities of water has already been noted, and
also the consequence that the growth of a crop leaves
the soil very much drier than it was before. The
converse of the proportion is seen in the fact that a year
of bare fallow, in which no crop is grown but the surface
is kept stirred to check evaporation, will accumulate a
considerable proportion of that year's rainfall in the
subsoil for the benefit of subsequent crops. In semi-arid
areas of deficient rainfall such as prevail in many parts
of western America and Canada, in southern Russia,
and in regions bordering the Australian deserts, farming
is rendered possible with a rainfall of lo to 15 inches per
annum by taking advantage of bare fallows. It is
customary to take only one crop in two years, or two
crops in three years ; in the intermediate years the soil
is kept ploughed so as to establish a surface which will
both collect any rain that falls and will also evaporate
but little because of its looseness. The chief features of

VI.] DR Y FARMING 1 1 3

this "dry farming" in arid areas are the insistence on
the establishment of a soil mulch — the loose dry layer
of soil which will prevent evaporation — and on " subsoil
packing," as it is called, i.e., the consolidation of the soil
immediately below the mulch, so that it will continuously
and steadily lift whatever water may have been accumu-
lated in the subsoil as far as the roots of the plant. To
generate the soil mulch, shallow, broad-tined cultivators
and harrows are used, while ring rollers are used to
effect the subsoil packing. These principles of "dry
farming " have been before the mind of the British farmer
from time immemorial, especially when farming upon
some of the light sandy and chalky soils in the east and
south-east of England, where the rainfall is light and the
evaporation active. To grow satisfactory root crops
under these conditions demands great skill in the
preparation of the soil, and the whole art of the farmer
is therefore concentrated on getting a good seed bed.
First of all, if the soil is heavy he has to work it
with judgment to get it to fall down into a crumb at all ;
then he strives to render this crumb deep and uniform,
thoroughly consolidated, and in intimate contact with
the undisturbed subsoil below, but at the same time
possessing a loose, friable surface which will admit air
yet protect the layer in which the roots are growing
from the evaporation that follows exposure to sun and
wind. It is possible to understand the principles under-
lying the farmer's operations and aims, but; only
experience can teach the moment at which a difficult
soil may be moved with success so as to bring it into the
desired condition. Such knowledge, however, of what to
aim at in the cultivation of the soil, of the best tool to
take and the right opportunity to seize for each operation,
lies at the basis of all husbandry. The art of the arable
farmer may be summed up as the proper preparation of

114 THE MOVEMENTS OF SOIL WATER [chap.

a seed bed, for on that depends the future of the crop to
a far greater extent than on the inherent fertility of the
soil or the amount of manure it receives.

The effect of the water-content of the soil upon its
temperature is one of the most important factors which
the cultivator of the soil has to bear in mind : it has
already been explained that the evaporation of water
results in a considerable lowering of temperature, so
that the heat of the spring sun may be largely spent in
drying a soil without raising its temperature at all.
The amount of heat necessary to raise the temperature
of a pound of water by one degree would heat a pound
of dry soil by about seven degrees, whereas it would
require about a thousand times as much heat to
evaporate a pound of water and even then cause no rise
of temperature. Growth does not take place below a
temperature of about 41° F., this being also the limit
below which most seeds do not start nor do the
roots of a plant function, hence before any growth can
take place in the spring, it is necessary to raise the soil's
temperature above this limit. Almost the only source of
heat is the radiation from the sun, which is absorbed by
the soil and converted into heat ; but to ensure that the
heat shall be effective in raising temperature, evaporation,
and therefore the access of the soil moisture to the
surface, must be checked by cultivation. Any method
of diminishing evaporation will, of course, aid in raising
the temperature of the soil ; for example, a rough surface
to the ground, wind breaks, hedges, or belts of trees,
which check the sweep of the wind over the ground, are
very effective in early spring towards getting the soil
quickly into condition for maintaining growth. In
many places the producers of early vegetables on light
land near the sea have learnt how desirable it is to
establish wind breaks by erecting lines of thatched

VI.] DRAINAGE 115

hurdles or temporary reed fences across their land.
Similarly, stones upon the surface of the land both help
the ground to warm up more quickly and maintain the
stock of water later in the season when droughts
set in.

The effects of drainage upon cultivated land afford
several illustrations of the principles underlying the
operations of cultivation. In the first place, the drained
land is warmer and therefore earlier, because as the
level of permanent water is no longer near the surface,
less water will be brought up to be evaporated ; conse-
quently, drying and warming of the surface soil can take
place comparatively quickly. At the same time the
temperature of the air above the soil is also found to be
raised by drainage. In the second place, with the
lowering of the water-level in the soil, air is introduced
to greater depths, the root system of the crops can
extend farther, and in consequence the plant has a
greater soil layer to draw upon, and is thereby better
able to resist a drought. Lastly, the introduction of air
more deeply with the soil and the replacement of the
old stagnant water conditions by a steady movement of
water through the soil, results in the improvement of its
texture ; the clay particles are flocculated both by the
occasional dryings and by the salts that are washed
through ; to a certain extent also the very finest particles
of all are washed down into the drains. The improve-
ment of the texture of the soil by drainage is of course
a question of time, and only becomes apparent some
years after the drains have been put in.

Just as the drainage of a heavy or a waterlogged soil,
by reducing the amount of water with which it is
burdened, causes the soil to warm up more quickly in
the spring, and therefore to become earlier, so the
question of early or late soils is largely determined by

ii6 THE MOVEMENTS OP SOIL WATER [chap.

the quantity of water they retain. Only a light, coarse-
grained soil, possessing a good natural drainage, can free
itself quickly from the winter rainfall, and therefore can
warm up quickly ; but whether such a soil will also be an
early one, depends also upon its situation, aspect, and a
few minor factors like colour. The heating of a soil
is practically wholly due to the sun ; although, if a soil is
made very rich in fresh organic matter, like farmyard
manure, there will be a little heating of the soil owing
to the rapid decomposition of organic matter that ensues.
In this case the soil has been to some degree converted
into a hot bed ; but putting this rare factor aside, the
colour of the soil has a certain influence upon the com-
pleteness with which the sun's rays are absorbed and.
converted into heat within the soil. Black soils will be
the most effective, red soils come next. One practical
application of this fact lies in the use of soot as a top-
dressing for wheat in the early spring ; the soot contains
a little ammonia which acts as manure, it also checks
the attacks of the slugs and small snails which often do
damage to the young corn, but it has a further beneficial
action, because its colour enables the soil to absorb more
heat, enough in fact to raise the temperature by one or
two degrees on a sunshiny day. A very simple experi-
ment will demonstrate this : a small plot of ground, a few
yards square will suffice, must be brought into a state
of good uniform tilth in March or April, and one-half
should be lightly dusted over with soot, so as to blacken
the surface, without protecting it by any such coating as
would act as a mulch. Two ordinary thin-stemmed
thermometers (which should be checked against one
another beforehand), are then plunged in the soil, one
in each portion, care being taken to bury the bulbs at
exactly the same depth of 3 inches and to make the
soil firm round them. On a bright day of continuous

VI.] ASPECT 117

sunshine, the thermometer below the blackened soil will
register from one to four degrees higher temperature
than the other one beneath the uncoloured soil. Aspect
is also a matter of considerable importance — a field
sloping to the south, not only receives the sun's rays
both earlier in the morning and later in the evening,
than another field facing north, but also the intensity of
the rays upon a given area is greater. Since the sun is
never vertically overhead in this country, the area that
has to be covered and warmed by a given beam of sun
is smaller when it falls on ground sloping towards the

Fig. 21.— Distribution of Sun's Rays upon Southerly
AND Northerly Slope.

beam, ue. southwards, than when it slopes the other way.
The diagram. Fig. 21, shows on to how much smaller an
area the sunbeam AB is concentrated when the area
slopes towards instead of away from the beam. An
early soil should also be a sheltered one ; wind always
increases the evaporation from the soil, and therefore
reduces its temperature; the use of hedges and
screens of any kind is of value to the raiser of
early vegetables, provided he does not allow them to
keep the sun off his crops. Height above sea-level is
also a factor demanding consideration ; putting aside

ii8 THE MOVEMENTS OF SOIL WATER [chap.

local variations, there is a steady fall of average tempera-
ture with increasing elevation, so that nearly all the soils
in Britain usually known as early and used for the
productions of the first vegetable crops, are comparatively
near the sea-level. At the same time, soils which lie
at the bottom of valleys are subject to late frosts in the
spring, and early frosts in the autumn ; the frosts always
come more severely and more frequently in the lowest
parts of the valley, and often do not extend many feet
up the sides of the valley. Such frosts arise in still
weather and cloudless nights, and are due to the cooling
down of the earth's surface by radiation into space, when
there are no clouds to act as a blanket. If the atmo-
sphere is also still in such radiation weather, the air in
contact with the ground becomes chilled, whereupon it
contracts and grows denser. Owing to its increased
density it then begins to roll downhill like so much
water and accumulates at the bottom of the valley until
it is displaced by the still colder air which occurs later
in the night. Stillness is necessary, otherwise the cooled
air would not lie in the valleys, but soon become
disseminated. The proximity of the sea or other large
body of water, is also a considerable factor in the pro-
duction of an early soil ; the water, because of its large
specific heat tends to keep temperatures equable, and
does much to mitigate the untimely spring or early
autumn frosts which are so much dreaded by the fruit
and vegetable grower. Nearly all the districts in
which early potato-growing is practised in the United
Kingdom are near the sea, e.g. Jersey, the neighbour-
hood of Penzance, Ayshire, Kerry, parts of West
Lancashire, and a few places on the seaboard of Kent
and Essex, etc.

A soil which is thus early because of its coarse
texture, its dryness, the readiness with which it can be

VI.] HE A VY AND LIGHT SOILS 1 19

worked after rain, its aspect and situation, develops
certain disadvantages later in the season. It is apt to
dry out with even a short drought ; it often reduces the
yield of ordinary crops by thus checking the growth at
critical stages, even if the crop is not forced to ripen off
too early. Such soils, again, often give rise to very rapid
growth in the autumn after the rains ; this growth, how-
ever, is often soft and stands very badly in a severe winter.
A heavy soil which is late to warm up, for the same
reason often holds its temperature until well on into
the autumn ; and crops growing upon such heavy soils
will continue their development far into the winter.
On them the whole course of development is slower
and more uniform, and this results in subtle differences
in quality between the produce of heavy and light soils,
which in the present state of our knowledge can be
better appreciated by experience than explained by
science.

CHAPTER VII

THE LIVING ORGANISMS OF THE SOIL

Formation of Nitrates in the Soil. Bacteria in the Soil which
decompose Organic Matter. Bacterial Loss of Nitrogen from
the Soil. Formation of Humus. Fixation of Nitrogen by
Bacteria associated with Leguminous Plants. Value of Clover
Crops in the Rotation. Inoculation of Soil. Other Bacteria-
fixing Nitrogen in the Soil. Accumulation of Nitrogen in
Virgin Soils. Dependence of Soil Fertility upon Bacteria.

So far, we have considered the soil as though it were
a merely dead medium in which the plant can fix itself,
and from which it can obtain food by processes of solution
and diffusion, as though the whole behaviour of the soil
towards the plant were regulated by chemical and
physical actions of the kind that can be reproduced in
the laboratory. Yet certain facts might serve to suggest
that other changes have their seat in the soil ; for
example, we have ascertained by water-culture experi-
ments that plants can only take in their necessary
nitrogen in the forms of nitrates or ammonia, small
amounts of which are very general constituents of
cultivated soils. But though nitrate of soda and sulphate
of ammonia are employed as manures, their purpose is
equally and more commonly served by other compounds
of nitrogen, such as the animal and vegetable residues
which are found in ordinary dung. Both experiment
and farming experience show that the plant will obtain
nitrogen from whichever of its compounds is put into

120

CHAP. VII.] NITRIFICATION 121

the ground, yet we do not know of any means by which
these nitrogen compounds can be converted into nitrates
in the laboratory except by most difficult and involved
processes. The whole history of nitrates in the soil will,
in fact, repay a little study. It has been known from
time immemorial that nitre in some form or other is a
product of the soil, and in India the men of a whole
caste or guild make their living by gathering nitre. They
scrape away the surface soil from time to time in the
neighbourhood of the villages just beyond the point where
the drainage finds an outlet, extract it with hot water,
and then after clarification concentrate the solution thus
obtained, the result being the nitrate of potash, nitre, or
saltpetre of commerce. Similarly, in Egypt the native
cultivator knows that the earth from deserted villages
— the dust, in fact, into which the old mud-built habita-
tions resolve themselves — forms a valuable fertiliser and
will yield nitre when extracted with water. Again, nitre
used to be obtained in Europe from the earth of cellars,
stable floors, and other fairly dry places near habitations ;
in later times it was expressly manufactured by building
up nitre beds — mixtures of earth with a certain amount
of carbonate of lime and organic matter, over which
urine and similar liquids containing compounds of
nitrogen were poured from time to time. The bed was
protected from the rain, was kept moist but not wet, and
after a period of from three to five years it was extracted
with water and yielded a solution of nitrate of lime,
which could be afterwards converted into nitrate of
potash for gunpowder-making. This well-known process
of nitrification represents the fact that the soil is able to
bring about a change in the organic compounds of
nitrogen and convert them into nitrates, either nitrate of
lime or nitrate of potash, according to the base which
happens to be present. Long before the mechanism of

122 LIVING ORGANISMS OF THE SOIL [chap.

the change was understood men had learnt that it was
forwarded by a proper degree of moisture, by warmth,
and by the presence of a base Hke carbonate of lime.
Not, however, until about 1 877 was it demonstrated that
the agents effecting the change are certain minute
organisms living in the soil and called bacteria, which are
classed with the plants, though they are so lowly in type
that they might almost be regarded as the common
meeting-ground of the lines of plant and animal descent.
At first only the fact was demonstrated that the change
was due to something living, and this was done by
showing that nitrification ceases when the soil is kept
permeated by the vapour of chloroform, which will
inhibit or destroy living organisms. Again, if the soil is
heated to the temperature of boiling water it loses its
power of forming nitrates. The first step having thus
been taken, subsequent investigators cleared up the
various steps in the process and succeeded in isolating
from the soil in an unmixed state two organisms, one of
which will change ammonia into nitrite and the other
will complete the oxidation into nitrate. We can
demonstrate their action by a few simple experiments ;
an ammoniacal solution that also contains the other
elements necessary to the nutrition of bacteria is made
up as follows : —

2 grammes Ammonium Sulphate
0'2 „ Potassium Phosphate
o-i „ Magnesium Sulphate
o-i „ Sodium Chloride

are dissolved in i litre of water, and a few drops of
ferric chloride solution are also added. One hundred
cubic centimetres of this solution are placed in each of
four flasks of about 3CX) c.c. capacity, the mouths of
which are afterwards plugged with cotton-wool. The
flasks and their contents are then sterilised by heating

O 3J V

o a Si.
g.S cl

as,

.2 c

*^ 3
CO
O >

|1
•— in"

CTJ

^ Is-

^ ^g-

t3 rt
C -O

VII.] NITRIFICATION 123

them in a steamer for an hour or so to the temperature
of boiling water. One flask is retained as a check, to
another about a gramme of fresh soil is added, to a
third and fourth a gramme of soil each and half a
gramme of carbonate of lime. One of these latter
flasks is then heated up to boiling again for half an
hour. The four flasks are put aside in a warm and dark
place for a period of three weeks or a month, and the
liquid in each is then tested for the presence of nitrates
by taking out one drop of it on a loop of platinum wire
and introducing it into a solution of diphenylamine in
sulphuric acid. The control — the nutrient solution to
which no soil has been added — will show no nitrate ;
sometimes the solution to which soil only has been
added will also show none, but in the solution to which
both soil and carbonate of lime have been added,
nitrates will be found and the ammonia may have
entirely disappeared. Finally, the fourth flask which
had been boiled after the addition of the soil will also
show no change, only the unaltered ammonia remains
without nitrates. In this simple way it is possible to
demonstrate that some living agency is forming nitrates
in almost all cultivated soils. These agents are, how-
ever, absent from peaty and acid soils, and do not occur
in subsoils taken below a depth which varies with the
nature of the soil. Another instructive experiment may
be made by filling a glass tube about 5 feet long and i
inch in diameter with fragments of chalk, the cork
which closes the bottom of the tube being supplied with
one exit-tube to drain off any liquid, and another rather
longer tube turned over inside, through which air can be
admitted to the interior. The tube is first of all seeded
with the nitrifying bacteria by running some well-water
through it, or by putting a little soil on the top of the
chalk, then a dilute ammoniacal solution or even a liquid

124 LIVING ORGANISMS OP THE SOIL [chap.

like diluted urine or liquid manure or sewage is allowed
to drip very slowly on to the top of the chalk, so slowly
that the liquid takes several days to work its way from
piece to piece of the chalk before it finds its way out at
the exit. When the tube has grown into good working
order the ammoniacal liquid will undergo pretty
complete nitrification as it soaks down the chalk, and
only nitrates will be found leaving the tube, but the
introduction of a little chloroform into the tube will
soon put a stop to the action.

Though it was the first to be investigated, nitrifica-
tion is only one of the many changes going on in the
soil that are due to bacteria, and some of these changes
are of the utmost moment to the nutrition of the plant
and to the maintenance of the fertility of the soil. As
regards changes in the nitrogenous compounds, another
experiment can be performed which will illustrate the
main features of the cycle that is perpetually being
worked through. A flask is made up as before with
lOO C.C. of nutrient solution, in which, however, the
sulphate of ammonia is replaced by an equal weight of
peptone, this being a complex carbon compound of
nitrogen closely related to flesh, albumen, etc., but more
convenient in this connection because it is soluble. Half
a gramme of carbonate of lime is placed in the flask,
which is then sterilised as before in the steamer ; when
cold, about i gramme of soil is added. The flask is put
away in the dark as before, and at the end of a week it
is examined. It will be found that tlie first change to
take place has been putrefaction ; the liquid possesses a
strong and offensive smell and is turbid with swarms of
organisms it contains, some of which are easily visible if
a little of the liquid is placed under the higher powers
of the microscope. The liquid is then restored to the
dark for another fortnight or so, when the putrefactive

VII.] SOIL BACTERIA 125

smell will have disappeared and been replaced by a
faint smell of ammonia, the next step in the cycle of
transformations. Another month in the dark will show
the third and, as a rule, the final stage well on its way —
the previously formed ammonia is now being converted
into nitrate. Lastly, the fate of the nitrate may be illus-
trated by leaving the flask in the light for a few weeks,
whereupon a bright green growth of algae will appear
from spores introduced with the original soil. In
sunlight the algae will form a scum buoyed up by the
bubbles of oxygen set free, because the algae are green
plants which possess chlorophyll and split up carbon
dioxide like other higher plants. After the algal growth
has made some headway the liquid may be tested, and
will no longer show either nitrate or ammonia; these
substances have been absorbed by the growing algae
and reconverted into proteins by being drawn into
combination with the carbon compounds which the
algae have assimilated from the atmospheric carbon
dioxide. Thus in the flask has been illustrated the
whole cycle of the breakdown by bacteria and the
reconstruction in the living plant of the protein bodies
which are fundamental to both plants and animals.
This all-important set of changes is brought about by
at least three distinct sets of bacteria. The first com-
prises numerous forms or species of the so-called
putrefactive bacteria, which seize upon the complex
nitrogenous bodies like the proteins and break them
down into simpler substances, among which are certain
compounds containing sulphur and possessing character-
istic disagreeable smells, the unpleasantness of the smell
being probably nothing more than a physiological
memory of the fact that intestinal disorders have always
followed the consumption of food possessing such a smell
and therefore swarming with bacteria. After this first

126 LIVING ORGANISMS OF THE SOIL [chap.

putrefactive breakdown another set of bacteria takes up
the resulting nitrogenous compounds and breaks them
down still further into ammonia, whereupon the nitrifying
bacteria can begin to exercise their function. Com-
pounds in the soil are, however, subject to other kinds
of change, as we can show by a further experiment. A
flask of about lOO c.c. capacity is fitted with a good cork
and a single exit-tube leading downwards and then
bent up at the extremity : into this flask about lO
grammes of soil and a \ gramme of sugar are placed,
then the flask is completely filled with a solution
containing i per thousand of potassium nitrate. After
the contents of the flask have been shaken a little to
get the sugar dissolved, the cork and exit-tube are
inserted ; the latter is completely filled with water and
set up so that it dips into water and is directed into the
open end of an inverted test-tube, also filled with water.
The apparatus is then put away in a dark, warm place,
and examined from time to time ; after some days
bubbles of gas will begin to appear and will collect in
the test-tube. When enough of the gas has been
collected it may be examined with a lighted taper, and
by shaking up with lime water it will prove to consist
in the main of nitrogen gas. If at the same time the
liquid remaining in the flask be tested it will no longer
show any reaction for nitrate; this salt has been
decomposed by certain organisms in the soil with the
liberation of nitrogen gas. Obviously this is a very
wasteful process, because nitrates and all forms of
combined nitrogen are valuable, whereas four-fifths of
the atmosphere is made up of nitrogen gas. Any such
change in cultivated soils ought so be checked as much
as possible, and this can only be done by avoiding the
conditions which give rise to the decomposition. Now
the essential conditions of the experiment were the

VII.] DENITRIFICA TION 1 27

presence of organic matter like sugar, which is easily
oxidised, and the exclusion of all air, so that the soil
bacteria in want of oxygen are driven to take it out of
the nitrate which is present. In nature the soil does
lose nitrogen because of bacterial changes of this kind ;
we call the process denitrification, but the losses will
only be large when there is much easily oxidisable
organic matter present in the soil, and when the soil
gets short of air by waterlogging or some similar
accident. That the losses, however, may be consider-
able can be deduced from one of the experimental plots
on the wheat field at Rothamsted, where the large
quantity of 14 tons per acre of farmyard manure are
applied every year for the wheat crop. Despite all this
application of manure the yield of wheat has not
continued to increase ; indeed, for the last forty years
it has been almost stationary, except for seasonal
fluctuations. The amount of nitrogen, however, that is
obtained in the wheat crop is only about one-quarter of
the 200 lb. per acre that was applied in the manure.
Of the remaining three-quarters of the annual supply
of nitrogen, about one-quarter still remains in the
soil, as an unexhausted residue which will very slowly
be converted into plant food. But one-half of the
immense amount of manurial nitrogen applied has been
lost entirely ; it has been dissipated as nitrogen gas by
the bacteria in the soil causing what we have called
denitrification, and the loss has been so great because of
the enormous accumulation of organic matter "in the
soil. Denitrification causing loss of soil capital must
be added, then, to the list of bacterial actions always
going on in the soil, or ready to take place whenever
the conditions become favourable to that particular form
of activity.

So far, however, we have only been considering

128 LIVING ORGANISMS OF THE SOIL [chap.

changes brought about by bacteria in the nitrogen-
ous compounds present in or added to the soil, but
non-nitrogenous materials undergo equally marked
decompositions, often of great practical importance. To
illustrate the nature of these changes, two experiments
may be performed. A tall bottle, which has an inlet at
the bottom, is filled with dry soil, mixed with a small
quantity of finely powdered sugar, about 2 grammes of
sugar per kilogram of soil. The action is the same
with all carbohydrates, but it will take place more
rapidly with sugar, so that it is the preferable substance
to use. Sufficient water is slowly poured in to moisten
the soil, then the bottle is put aside in a warm place,
and once a day the gas it contains is pumped out
through a wash-bottle containing lime water, air being
allowed to enter in its place. It will be found that
quantities of carbon dioxide are given off by the soil,
and in a week or two if the soil be washed and the
solution filtered and tested no trace of sugar will be
detected. It has all been oxidised by the bacteria of
the soil into carbon dioxide, air of course having been
also necessary to the process. In the other experiment
a corked-up flask with an exit-tube, such as was
employed in the denitrification experiment, is required.
The flask is partly filled with a solution of nutrient salts,
such as was used for water cultures, and a number of
strips of clean filter paper, which is nearly pure cellulose,
is introduced together with a small quantity of soil, or
better still, of pond mud. The flask and tube are filled up
with water, and made to lead into an inverted test-tube
over water as before, then the whole apparatus is put
aside in a warm place in the dark. It may be some
days before any action sets in, but eventually bubbles
of gas will arise and will collect in the test-tube, which
can be removed for their examination from time to

VII.] CELLULOSE FERMENTATION 129

time. Carbon dioxide will always be found, but if that
is removed by shaking up the contents of the tube with
lime water or a little caustic soda, some other gas will
also remain, and this gas will take fire if a light be
brought to the mouth of the test-tube. The inflammable
gas is generally marsh-gas, sometimes hydrogen, or a
mixture of the two. At the same time, it will be seen
that the filter paper is being attacked ; the strips get
thinner and begin to break up in places ; finally they
disappear entirely, or give place to a dark brown,
structureless mass. On testing the liquid it will be
found to be acid. In this type of fermentation, which
takes place without any contact with the air, cellulose
and other carbohydrates become split up into carbon
dioxide and either marsh-gas or hydrogen, a certain
amount of humus being formed at the same time. It
should be noted that all the changes described in this
and the preceding experiments will not take place if the
action of bacteria is suspended at starting by intro-
ducing chloroform into the mixture, or by sterilising the
whole by boiling ; they are all processes due to living
agencies, and in most cases we cannot reproduce them
in the laboratory by purely inanimate means. These
two modes of breaking down carbohydrates illustrate
processes which are widespread in nature. The first,
in which the carbon compounds are oxidised in the
presence of air to carbon dioxide, represents the slow
decay which overtakes all organic matter when freely
exposed. A leaf, a branch, even a tree itself, which falls
to the ground in a wood is eventually dissipated into
gas, and leaves behind nothing more solid than the ash
which would have resulted if it had been burnt. The
process of aerial decay is, in fact, neither more nor less
than a slow burning brought about by living organisms ;
not only bacteria effect such actions, but many fungi,

I

I30 LIVING ORGANISMS OF THE SOIL [chap.

and even insects, worms, and other lowly creatures help
to produce the same change. The other change, which
takes place in the absence of air, is seen when a branch
of a tree falls into a pond or a deep ditch and becomes
buried in the mud. Thus cut off from the air it changes
much more slowly, but it does lose carbonic acid, marsh-
gas, and sometimes hydrogen. Thereby it also becomes
gradually black, and on analysis proves to be richer in
carbon than the original wood, because it has been
giving off in the gases that arise from it more of its
hydrogen and oxygen than of its carbon. This process
of an anaerobic (out of contact of air) change is seen
most markedly in the formation of peat from vegetable
matter on waterlogged land, but it has its share in the
production of the humus of all cultivated soils.

We have now reviewed the main types of change
brought about by bacteria in the organic matter of the
soil ; the carbon compounds are being broken down into
simpler bodies and in nearly all cases eventually become
carbon dioxide, the regeneration of which into the
complex organic matter of the carbohydrates, etc., is
effected by the living plant. The nitrogen compounds
are also broken down into successively simpler bodies,
finally into ammonia and nitrates, which the living plant
can again utilise and reconstruct into the more complex
protein forms. Some nitrogen also is always being
thrown out of combination, and passed into the air in
the comparatively useless state of nitrogen gas. It will
be noticed that we have seen no agency at work to
reconvert nitrogen gas into any form of combination,
nothing in fact to account for the original stock of
combined nitrogen in the world. Plants can only make
use of nitrogen when it is already combined as ammonia
or nitrates; they build up successively more complex
bodies from these substances, but not from nitrogen gas

VII.] FIXATION OF NITROGEN 131

itself. The soil bacteria we have been discussing
similarly only cause the circulation of nitrogen from one
form of combination to another ; one type sets nitrogen
free, but none that we have yet examined do anything
to bring it back into combination. But if the combined
nitrogen of the world had only been suffering loss by
change into nitrogen gas ever since the beginning of
things, however small those losses may appear to be, we
should probably have arrived at some evidence of a
diminution of the stock and signs of its ultimate
exhaustion. No indications of the sort, however, exist,
from which it might be concluded that some agency
must be at work replenishing the stock by " fixing "
nitrogen gas and bringing it back into combination.

The discovery of such an agency arose out of the
long-debated question of whether our ordinary plants,
which are always in contact with a boundless store of
nitrogen gas, do not possess in their leaves the power
of thus " fixing " the nitrogen they require. Many
of the earlier investigators were firmly convinced that
plants had such a power, arguing from the difficulty
of understanding how there could be combined nitrogen
in the world from any other source. Moreover, great
refinement of experiment is necessary to demonstrate
that the nitrogen gained by a plant is exactly balanced
by the amount lost by the soil, hence the controversy
lasted for a considerable time, even if it can be regarded
as ended now. However, the weight of evidence, and
notably a series of experiments carried out by Dr Evan
Pugh of Pennsylvania at Rothamsted in 1857-8, coupled
with the experience gained by field trials of the great
value to the crop of a supply of manurial nitrogen, have
led people ever since the middle of last century to accept
as a general principle the opinion that plants do not fix
nitrogen. In 1886, however, two German investigators.

132 LIVING ORGANISMS OF THE SOIL [chap.

Hellriegel and Wilfarth, who had been growing different
kinds of plants in pots containing pure sand supplied
with nutrient salts in solution, and particularly with
varying quantities of nitrogen, noticed that certain
plants which were being nitrogen-starved suddenly
recovered their vigour and began to grow as though
they were freely supplied with the missing element,
nitrogen. Such plants were always of the leguminous
family — peas, beans, clovers, lupins, etc. ; when grown
in the sand with little or no combined nitrogen, they
began by reaching a stage when they had used up all
the nitrogen contained in the seed, after which they
became stunted or took on rather a light yellowish
colour. Some of them, however, would suddenly
recover from this debilitated condition, turn green again,
and begin to flourish as before. When such plants were
shaken out of the sand in which they were growing,
their roots were always found to be studded with small
warty nodules, which varied in size from that of a pin's
head on clover to something as large as a walnut on the
larger perennial leguminous plants. The investigators
at last made certain that the presence of these nodules
upon the roots was accompanied by an increase in the
amount of combined nitrogen in the plant, an increase
that could only have been obtained by the fixation of
some of the atmospheric nitrogen. The nodules were
found to be colonies of a peculiar form of bacterium,
which must have originally come from the soil, because
when leguminous plants were grown on sterile sand with
suitable precautions, no formation of nodules nor fixation
of nitrogen took place until there had been infection of
the plant's roots either by the introduction of a trace of
soil or of an infusion of a nodule that had grown on
another plant. Once, however, inoculation had been
effected, nodules began to appear on the root and fixation

VII.] THE NODULE ORGANISMS 133

of nitrogen took place in the plant as a whole. The seat
of this fixation was then demonstrated to lie in the
bacteria themselves — these bacteria in fact live in
partnership (symbiosis) with the clover or other plants.
They receive from its leaves a certain amount of sugar
which they oxidise in order to obtain the energy
necessary to effect the combination of free nitrogen ; in
their turn they give up to the plant the nitrogen com-
pounds it requires for its life cycle. It has since been
found possible to cultivate these bacteria apart from the
leguminous plant with which they are usually associated
and to get them to fix nitrogen when fed with sugar,
but the amount so fixed is small compared with that
obtainable by them for the living plant. The organism
has also been shown to exist in several different forms ;
in the soil it takes a motile form very much smaller
than the rod-shaped and even branched forms which
may be seen in the nodules, and in this state it is
capable of passing through the fine root hairs of a
seedling leguminous plant, an infection which soon
becomes evident in the growth of a nodule swarming
with the transition forms of the bacterium. The
laboratory evidence for the fixation of nitrogen by these
bacteria was thus rendered very complete ; indeed it is a
simple matter to arrange an experiment to demonstrate
the process. All that is necessary is a series of small
pots, preferably of glazed earthenware, filled with sand
mixed with i per cent, of calcium carbonate, the pots
and their contents being sterilised before starting by
heating in an oven for an hour or so. The seeds of
some leguminous plant — vetches, sweet peas, or lupins are
convenient for the purpose — are sterilised by washing in
alcohol and recently heated distilled water, and are then
germinated on sterile sand or filter paper until the
seedlings are large enough to handle. Meantime the

134 LIVING ORGANISMS OF THE SOIL [chap.

pots of sand are watered nearly up to saturation with a
culture solution made up as on p. 45, but omitting the
sodium nitrate, and the seedling plants are carefully
introduced. The pots must now be either kept in a case
well protected from dust, or the surface of the sand
must be covered over by a thin layer of cotton-wool, in
order to keep away dust which may contain the organism.
After a week or so of growth all the plants will begin to
show the want of nitrogen by a cessation of growth and
the sickly yellow colour of the leaves. To one pot
is then added a few cubic centimetres of a soil extract
made by shaking up soil with rather more than an equal
bulk of water, and filtering ; to a check pot is added
the same quantity of infusion that has been boiled.
Similarly, another pot is watered with an infusion of a
nodule taken from a leguminous plant of the kind
growing in the pot, and as before the check pot is given
the same infusion, boiled. The checks will continue to
get more sickly looking and will shortly die, whereupon
it can be ascertained that they possess no nodules on
their roots ; but the plants inoculated either from soil or
another nodule develop nodules, recover their health,
and will grow into perfect plants if the supply of mineral
constituents be sufficiently renewed. The experiment
should be duplicated, because the check pots are liable
to get accidently inoculated unless dust is most rigor-
ously excluded.

This discovery of the fixation of nitrogen by the
bacteria associated with leguminous plants at once threw
light on a number of facts which had been difficult of
explanation before. For example, farmers had always
known that in some way the growth of clover and similar
plants was beneficial to the soil ; even in the time of the
Romans, Pliny, Virgil, and other writers on agriculture
had instructed the husbandman to prepare his land for

vn.] VALUE OF LEGUMINOUS CROPS 135

wheat by first growing crops of vetches or lupins or
beans. In English agriculture the same idea was
enshrined in the Norfolk four-course rotation, in which
red clover or beans are followed by wheat ; and it was
well known to the practical man that the wheat always
flourished best where the clover had been good in the
previous year, Boussingault, who was the first scientific
man to make field experiments, drew up a kind of
balance-sheet in which the carbon and nitrogen sup-
plied to the land over a term of years was com-
pared with the amounts of the same elements
taken away in the crops. Of course, in all cases the
carbon removed was enormously in excess of that
supplied, because of the assimilation that had taken
place, but when the land was alternately bare fallowed
and cropped with wheat, there was no more nitrogen
obtained in the crop than had been put on in the manure.
But with other rotations including clover and beans,
there was always more nitrogen harvested than was
applied ; and when the land was occupied by lucerne or
alfalfa, more than a hundred pounds of nitrogen were
taken away annually for five years, and yet the soil
showed no sign of impoverishment, rather the contrary.
Another example of the same kind was obtained at
Rothamsted : in 1873 a piece of land was divided, one
part being cropped with barley, the other with clover
which had been sown the year before ; the nitrogen was
determined in the two crops, and showed that in the
barley 37 lb. of nitrogen was removed, in the clover 151
lb. In the following year the whole of the land was sown
with barley, and the crop where barley followed barley
contained 39 lb. of nitrogen per acre, whereas that which
followed clover contained 69 lb. per acre. An analysis
was also made of the soil in 1873, after the first barley
and clover crops had been removed, and the soil after

136

LIVING ORGANISMS OF THE SOIL [chap.

clover, down to a depth of 9 inches, was found to
contain 3915 lb. per acre of nitrogen, against 3540 lb.
after barley. Table XIII. sets out the figures.
Table XIII. — Effect of Growth of Clover on Succeeding Crop.

Nitrogen in Crop and Soil. Lb. per Acre.

Plot A.

Plot B.

In Crop (1873), Barley . . 37-3
In Soil after Barley . . 3540

In Crop (1874), Barley . . 39.1

Clover .
After Clover
Barley .

151-3
3915
69.4

This last experiment illustrates a fact of great
practical importance — that a good crop of clover not
only produces a lot of highly nitrogenous fodder, in
which most of the nitrogen has been won from the air,
but also leaves behind in the roots and stubble such an
additional amount of nitrogen as will be of considerable
benefit to future crops. Another example from Rotham-
sted will illustrate this point : on the Agdell rotation
field, which is farmed on the Norfolk four-course shift,
one-half of the field carries no crop during the year pre-
ceding the wheat, whereas the other half grows clover or
beans. Thus an opportunity is afforded of estimating
the effect of the clover or beans on the succeeding crops
of the rotation. If we take for our example the years
following a specially good clover crop, and compare the
two plots which are manured once in the rotation, we
obtain the figures in table.

Table XIV.— Total Produce per Acre after Clover or Bare

Fallow.

Clover, 1894.

Wheat, 1895.

Swedes, 1896.

Barley, 1897.

Clover Plot .
Bare Fallow Plot .

767 cwt.

5209 lb.
4547 „

389 cwt.
380 „

4913 lb.
3595 n

VII.]

EFFECT OF CLOVER CROP

137

Thus we see that the clover crop not only produced
nearly 4 tons of hay, which was removed from the land,
but left behind residues which increased the next wheat
crop from 4 to 5 quarters, and even caused a large
increase in the barley crop which came two years later,
in spite of the fact that a considerable amount of nitro-
genous manure had been applied to the intermediate
crop of swede turnips. It is, in fact, possible by growing
clover once during the rotation, to maintain the soil at a
moderate level of fertility without bringing in any
external source of nitrogen such as purchased fertilisers
or feeding stuffs, notwithstanding the continual removal
of nitrogen from the farm in the corn and the meat that
are sold away. The following example from the same
Agdell field will illustrate the point : —

On one of the plots, which receives phosphoric acid
and potash but no nitrogenous fertiliser, clover is
grown once in the four years' rotation, and the swede
turnip crop is chopped up and ploughed in, thus re-
turning to the land the fertilising materials contained
in the plant, in the same way as is done when the turnips
are fed off with sheep. The following table (XV.) shows

Table XV.— Conservation of Soil Fertility during
Rotation when no Nitrogen is Supplied. (Rothamsted.)

Nitrogen in Soil, per cent. . 1867
• 1874
. 1883
. 1909

0-138
0-132
0.138
0.150

rWheat . . .
Average yield, J Clover Hay .
1852 to 1903 1 Swedes .

iBarley .

35.1 bushels
47-7 cwt.
9'3 tons
34'5 bushels

that the nitrogen in the soil is not experiencing any
measurable loss, while the crop returns indicate that a

138 LIVING ORGANISMS OF THE SOIL [chap.

fair level of fertility is being maintained through the
nitrogen collected by the growth of clover once during
each four-year cycle.

All these illustrations serve to emphasise the point,
that by the growth of leguminous plants as frequently
as possible the farmer possesses a means of maintaining
and even increasing the stock of nitrogen in his land
without expense, because the crop of valuable fodder
produced in itself pays for the year's farming. Of the
crops commonly grown, lucerne (or alfalfa) seems to be
the most effective in fixing nitrogen ; it is particularly
valuable on poor chalky and sandy soils where it can be
left down for several years, when it will with a minimum
of expense both yield a paying amount of fodder and
prepare the land to carry a short succession of arable
crops with no extraneous nitrogen supply. Lucerne has
proved more difficult to establish on the poor clays, but
even there its benefits are very marked. Sainfoin is
probably as valuable a nitrogen collector, but it has been
less rigorously tested ; while the clovers, particularly red
clover, are especially effective considering the short
time they occupy the soil. Red clover is most valuable
to the soil if it is kept grazed after the first cut ; a second
cut leaves less nitrogen behind, because in the late summer
the nodules on the roots become considerably depleted of
the nitrogen previously gathered from the atmosphere
in order to make the second growth, while a crop of
clover seed is even more exhaustive of anything that
may have been stored in the root. The annual
leguminous plants — beans and vetches — gather less
nitrogen from the atmosphere, and are therefore less
valuable as preparations for succeeding crops ; indeed,
on the rotation field at Rothamsted, a bean crop has
proved no better preparation for wheat than a summer
of bare fallow. At Rothamsted, however, the beans are

VII.] SOIL INOCULATION 139

pulled and not cut, thus depriving the soil of a consider-
able residue of root and stubble. Of course it should
not be forgotten that leguminous plants can, and do to
a large extent, in nature feed upon the combined
nitrogen in the soil, and it is probable that a plant like
a bean utilises the nitrogen of the soil until it is driven
by starvation to make the nitrogen of the nodules its
source of supply.

In view of the enormous importance to practical
agriculture of the nitrogen-collecting power of the
leguminous nodule bacteria, a number of experiments
have been made all over the world to see if anything
could be gained by introducing an increased or possibly
a more vigorous supply of these organisms into the
soil. It has been shown, in fact, that although there is
only one species, as it may be called, of bacterium
associated with leguminous plants, yet that species
possesses a certain amount of racial adaptation, so that
clover which has been infected from a clover nodule
grows better than if it had been infected from a bean
nodule. In some cases this specialisation has gone so
far that the particular leguminous plant can only be
infected from another plant of the same kind or by soil
in which it has been grown ; it responds very indif-
ferently to the neutral form of organism that is present
in cultivated soils and adapts itself to most of the
leguminous crops it meets. Moreover, from time to
time, particularly in new countries or where heath or
bog or salted alkali land is being reclaimed for the first
time, soils are met with which do not contain any
nodule organisms, so that when leguminous plants are
sown they neither develop nodules nor fix nitrogen.
These considerations have led to the artificial inocula-
tion of the soil with the organism appropriate to the
desired crop, either by spreading over the land a small

I40 LIVING ORGANISMS OF THE SOIL [CHAP.

quantity, half a ton per acre or so, of soil taken from a
field in which the crop in question had before grown suc-
cessfully, or by sprinkling on the seed an artificial culture
of the organism. A number of artificial cultures of the
organisms appropriate to such crops as clover, lucerne,
sainfoin, beans, peas, etc., have been prepared and can
now be purchased commercially in an active state.
The practice recommended has been to add the small
pure culture that is purchased to a fair bulk of water
containing sugar and nutrient salts, or to diluted
separated milk, and to keep the mixture for a day or
two in order to allow the bacteria to increase, then the
seeds are dipped in the liquid for a moment immedi-
ately before sowing. The results of such inoculation
trials have, however, been disappointing from a practical
point of view ; in most cases the soil is already so well
stocked with the usual nodule bacteria that the introduc-
tion of a few more in the inoculating liquid does not
affect the growth of the leguminous plant. In the much
rarer cases where the soil is entirely without the
organism, its artificial introduction may prove of
enormous benefit and enable the crop to grow where it
would otherwise have starved. But very often the
absence of the organism is only a sign that the soil is in
some way unfit to carry it, and some improvements
must be effected in the soil before either organism or
leguminous plant can be established. Even when the
soil is not actually in a condition to prevent the
organism growing, the introduction of a particular
bacterium, such as that associated with lucerne, cannot
be done all at once, or with the rapidity and certainty
of growth that is seen when even a single bacterium is
added to a sterile medium. The strongest inoculation
that is practical only introduces a minute new element
into an active flora already in possession of the soil;

VII.] BACTERIA-FIXING NITROGEN 141

to make good their footing they have to compete with
the already overcrowded population of the soil, the
numbers of which are only maintained at a certain level
by the limited extent of the food supply. It has thus
been found necessary to make several inoculations and
renewed sowings before lucerne can be regularly
established in soils to which it was entirely new, though
when one successful crop has been grown there is never
any difficulty later in establishing a second. At present,
however, the practical applications of pure cultures of the
nodule bacteria to the inoculation of soil are distinctly
limited, and the enormous returns that have been
promised for them can only be realised in very
special cases.

Since the discovery of the nitrogen-fixing organisms
associated with the nodules of leguminous plants several
other bacteria have come to light which can fix nitrogen
without any such partnership with a higher plant. For
example, among the typical organisms bringing about
the decay of organic matter in such places as the mud of
ponds and marshes, there occurs a bacterium possessing a
limited power of fixing nitrogen, but which we have reason
to suppose does play some part in keeping up the stock
of nitrogen in soils. But the most actively fixing
organism that has been isolated is a comparatively large
bacterium, called Azotobacter, which has been identified
in virgin soils from all parts of the world. Certain char-
acteristic features possessed by Azotobacter Qmh\Q it to be
readily detected, and the following experiments may be
performed to illustrate its action. A non-nitrogenous
culture medium must be prepared as on p. 122, omitting
the ammonium sulphate, and portions of 100 c.c. are
placed in flasks, i gramme of glucose and half a gramme
of carbonate of lime are added to each, after which the
flasks are plugged and sterilised in the usual way. From

142 LIVING ORGANISMS OF THE SOIL [chap.

one or two of the flasks the carbonate of lime is omitted.
If such a non-nitrogenous medium is inoculated with a
mixture of organisms, only those which are able to draw
upon the atmospheric nitrogen can live and multiply,
because all the usual bacteria depending on a supply of
combined nitrogen are starved out and must remain
dormant until their necessary food comes along. The
series of prepared flasks are then inoculated with about
a gramme of soil each, and put away in a warm dark
place to incubate as usual. After a week or ten days'
time the flasks are examined ; wherever the Azotobacter
was present in the soil the liquid in the flask will be
covered with a dark brown skin, held up on the surface
by a number of bubbles of some gas which is evidently
being freely developed. The flasks containing no
carbonate of lime will often show no brown scum nor
formation of gas, unless the soil sample added is itself
rich in carbonate of lime. An analysis of the contents
of the flasks will show that nitrogen has been gathered
— often as much as 8 milligrams of nitrogen are fixed
for each gramme of sugar in the original solution. The
glucose that has been added is necessary, not merely as
food for the Azotobacter^ but as material which can be
oxidised or burnt up to supply the energy required to
bring the nitrogen into combination. Almost any
carbohydrate will serve the purpose, but glucose and
mannite appear to be most readily oxidised. The
Azotobacter is really a very powerful oxidising agent ;
the gas which is given off" during the first growth in the
culture flasks is carbon dioxide produced in this way.
During, or by means of the rapid process of oxidation,
some of the nitrogen which is present is also drawn into
combination. Perhaps an even more satisfactory method
of demonstrating the fixation — more satisfactory because
it follows the sequence of changes taking place in the

VII.] NITROGEN FIXATION IN VIRGIN SOILS 143

soil in nature — is to put some of the flasks back in the
incubator and leave them there for one or two months.
The other groups of bacteria introduced in the soil
sample resume their activity as soon as they can obtain
some of the combined nitrogen that has been introduced
by the Azoiobacter, and a portion of the compounds
that have been so elaborated is broken down and
successively oxidised into ammonia and nitrates. On
eventually testing the contents of the flask no glucose
will be found, but the presence of nitrates can be shown
by diphenylamine in the usual way. Finally, if the
flasks are put in the light, green algae will begin to make
their appearance, the spores having been introduced
with the soil, and thus a growth of green vegetable
matter is seen which has derived the whole of the
nitrogen it contains from the atmosphere through the
agency of the Azotobacter.

It will easily be seen that so widely distributed and
so active an organism as Azotobacter may have played
a considerable part in maintaining and even in creating
the stock of combined nitrogen possessed by the
world. The one factor necessary for fixation is that
the soil shall be kept supplied with the purely car-
bonaceous material formed by plants from the atmos-
phere by the assimilation process. In the Rotham-
sted wheat field it has been shown that little fixa-
tion has taken place in the soil of the unmanured plot
— only enough to replace the small losses by drainage,
weeds, etc., the amount removed in the crop being
balanced exactly by the reduction in the stock of nitrogen
in the soil during the period under investigation. The
crop being wheat after wheat every year, a very small
residue of roots and stubble are left as material
which the Azotobacter can oxidise. When more carbon-
aceous residues are left behind, as on grass land,

144 LIVING ORGANISMS OF THE SOIL [chap.

particularly where the natural herbage is allowed to fall
and decay, there is abundant material for the purposes
of the organism, and fixation in consequence can become
a marked feature in the history of the soil. Two small
portions of land at Rothamsted have been allowed to
run down from arable into a mass of rough grass and
weeds, nothing having been done to the land for more
than a quarter of a century. The coarse derelict herbage
that has sprung up — natural prairie — falls back to the
soil every year, and an analysis of these soils before and
after the growth of the wild vegetation show a notable
fixation of nitrogen, over 90 lb. per acre per annum for
the twenty-five years during which the land has been
left to itself. This experiment also helps us to under-
stand how forest soils get enriched with nitrogen ; the
autumnal fall of leaf adds a large amount of carbonaceous
matter to the soil and thus enables the Azotobacter to
go to work. The enormous accumulations of nitrogen
in the deep black soils of the prairies, the steppes, and
similar areas, probably also owe their origin to Azoto-
bacter ; for in these soils the requisite conditions are
fulfilled — carbonate of lime exists in the soil, and there
is a steady addition of carbonaceous matter as each
year's growth dies down in the autumn.

We are now in a position to get some general con-
ception of the work of the bacteria in the soil ; the
actual numbers are very great, as many as forty millions
have been estimated in a gramme of a garden soil
fairly rich in organic matter, and the number of species
that can be distinguished is considerable. It is, how-
ever, better to consider them by groups according to
their function, than by species, and the main features of
the chief groups have been set out above. All these
different groups are at work together in the soil, but
which will predominate and what degree of activity it

VII.] BACTERIAL ACTIONS IN SOIL 145

assumes will depend very greatly on external conditions,
such as the cultivation the land receives. Perhaps the
most important are the organisms concerned with
preparing the food for plants ; in the first place the
putrefactive organisms break down proteins and kindred
nitrogenous material into successively simpler com-
pounds, which are then taken in hand by another group
of bacteria and converted into ammonia, though it is
impossible to draw any hard and fast distinction
between these two sets of organisms. The work of
the ammonia - makers is concluded by the nitrifying
organisms, which complete the final stage of oxidation
of the nitrogen compounds and produce the nitrates
forming the chief source of nitrogen for our crop plants.
The nitrifying organisms are on the whole so much
more active than the ammonia-makers that there is
rarely more than a trace of ammonia to be extracted
from the soil ; the rate at which nitrates are ready for
the plant is mostly determined by the rate at which the
ammonia-makers can produce ammonia to be nitrified.
The work of all this group of organisms is promoted by
the same factors as forward the growth of other living
creatures, i.e.^ a proper degree of warmth and moisture
and a due amount of soluble food (in this case the
mineral salts found in plant ashes). It is also
stimulated by such special conditions as an abundant
supply of air, a sufficiency of carbonate of lime, and
cultivation to distribute the bacteria in the soil. On the
other hand, under certain conditions, as when sulphate
of ammonia or nitrate of soda is applied to the soil,
many organisms will seize upon these soluble nitrogen
compounds for their own nutrition and multiply in such
numbers that an appreciable fraction of the nitrogen in
the fertiliser is withdrawn in order to build up the
bodies of the bacteria, which becoming thereby con-

K

146 LIVING ORGANISMS OF THE SOIL [chap.

verted into proteins or substances akin to them, require
to go through the routine of decay and oxidation before
they can reach the plant. Next come the group of
denitrifying organisms which deal wastefully with the
nitrogenous reserves of the soil, converting them into
nitrogen gas, which possesses no value. These become
active when the soil is waterlogged and the supply of
oxygen cut off; their action is also promoted by an
abundance of organic matter. Then we have groups of
organisms working in a contrary sense by fixing nitrogen
gas and so enriching the soil ; some of these organisms
live free in the soil, others enter into symbiotic partner-
ship with the leguminous and a few other kinds of
plants. Similarly, for the non-nitrogenous organic
matter we have one group of oxidising or decay
bacteria, which burn up the carbohydrates to carbon
dioxide and water in the presence of air, and another
group working under anaerobic conditions, which
produce carbon dioxide and marsh-gas or hydrogen ;
both groups, but especially the latter, giving rise to
humus as an intermediary product. The tendency of
these various organisms, which are in many cases
working in opposite directions, is to arrive at some
state of equilibrium appropriate to each given soil and
to the treatment it receives; for example, in an
exhausted soil such as prevails on the unmanured plot
on the Rothamsted wheat field, the activity of the
ammonia-making organisms has been reduced to the
point that the nitrogen thus rendered available for the
crop is practically balanced by the nitrogen gained by
the fixation organisms. On the other hand, on the plot
receiving farmyard manure every year, to which about
four times as much nitrogen is being applied as is being
removed in the crop, there is no longer any increase of
nitrogen in the soil ; the activity of the denitrifying

VII.] GOOD AND BAD SOIL ORGANISMS 147

group has been so increased by the excess of organic
matter that it maintains the balance by getting rid of
all the surplus of nitrogen.

The " condition " of the soil in the farmer's sense of
the word — its capacity to keep the crop steadily and
fully nourished — is in the main determined by the
activity of the ammonia-makers, and this, temperature
and moisture conditions being equal, depends wholly
upon their numbers. The numbers are in the first place
conditioned by the food supply of the soil, and secondly
by another wholly different class of living creatures
which have recently been ascertained to play an
important part in the soil. These are various protozoa
— distinctly animal organisms a thousand times larger
than the bacteria upon which they prey, the numbers of
which they keep down to a certain limit. It is possible
on a small scale to kill off these protozoa and yet leave
the bacteria active, in which case the productivity of the
soil is raised, even to the extent of being doubled, with-
out any additions of manure : whether these small-scale
processes can be adapted to our fields yet remains
to be seen.

Within the soil there are also numerous microfungi
and moulds of all kinds, many of which are breakers-
down of protein and carbohydrate matter like some of
the bacteria, while others are more harmful, because
they compete with the higher plants for food, or even
give rise to diseases like " finger-and-toe " or " club
root" in turnips and cabbages. In a general way it
may be said that bacteria predominate in soils which
are kept neutral by a sufficiency of carbonate of lime,
but that fungi become abundant and harmful as soon as
the soil is allowed to get acid, their activity being
promoted by the use of acid manures like superphos-
phates and sulphate of ammonia. While we are very

148 LIVING ORGANISMS OF THE SOIL [chap. vii.

far from being able to control the bacteria and other
organisms of the soil, we are beginning to realise both
the fundamental importance of the part they play in
the nutrition of the crop and the manner in which
they can be affected by processes and materials which
can be applied to the soil ; and though so far we have
only succeeded in explaining results that the practical
farmer had arrived at by experience, our knowledge
must in time lead to deliberate and conscious advances
in the way of utilising their powers to better effect.

CHAPTER VIII

THE CHEMICAL COMPOSITION OF THE SOIL

Plant Food found in Normal Soils. Dormant and Available
Plant Food. Rotations and Plant Food in the Soil. Systems
of Farming — Wasteful and Conservative. Requirements of
Different Crops for Fertilisers. Types of Soil — Characteristic
Weeds and Crops.

It has already been stated that while the greater part
of the soil consists of sand and clay, materials that are
of no service as food for the plants, there are also
present much smaller quantities of the elementary
substances — nitrogen, phosphoric acid, potash, lime, mag-
nesia, etc. — elements which we have found in plants and
learnt to be necessary to their nutrition. In Table XII.
a series of chemical analyses of characteristic English
soils are set out, and though the number of soils repre-
sented is not great, the examples show almost as wide
variations in composition as may be expected anywhere
in the United Kingdom. The first things that may be
noticed in these analyses is that the range of variation
in composition is not great, in few of the soils does the
nitrogen fall below o-i per cent, in very few arable soils,
on the other hand, does it rise above 0-3 per cent. ;
phosphoric acid may be as low as o-o6 per cent in
exceptional cases, but very rarely will it be higher than
0-2 per cent. ; potash perhaps shows the greatest varia-
tions, ranging between o-i per cent, to i-o per cent.
These comparatively small variations hardly seem to

149

ISO CHEMICAL COMPOSITION OF THE SOIL [chap.

account for the great differences in fertility which we
know to exist between one soil and another, differences
which are reflected in a rent of 5s. an acre in one case
and £^ in another. The next point that requires
consideration is the comparatively large quantities of
plant food present in even the poorest soils, a quantity
which is enormous in comparison with the amount
required by ordinary crops. For example. Table VI.
shows that few crops take more than 100 lb. of nitrogen
per acre from the soil, or 50 lb. of phosphoric acid, or
1 50 lb. of potash ; only heavy root crops will remove as
much as this, crops of cereals require about one-half
As the layer of soil 9 inches deep over an acre weighs
about two and a half million pounds, the one-tenth per
cent, of nitrogen which is to be found in all but the very
poorest of soils would still represent as much as 2500 lb.
per acre, or sufficient for twenty-five full crops of roots
or fifty full crops of corn.

Yet at Rothamsted, where an attempt has been made
to grow both roots and corn continuously without
manure, in a very few years the crop of wheat fell to
about 13 bushels per acre of corn and 10 cwt. of straw,
while the mangold crop averaged no more than 4 tons
per acre. Nor does growing crops in a rotation instead
of continuously help matters much : on the Agdell field
at Rothamsted, where the Norfolk four-course system is
followed, the average production of the unmanured plot
has been 16 cwt. swedes, 16 bushels of barley, 9 cwt. of
clover hay, and 26 bushels of wheat. When grown in a
rotation, the cereal crops have maintained their yield at
a much better level than when grown continously on the
same land, but the preceding crops of clover or sv/edes
are so poor that the land is practically lying fallow for
the year before the corn. Some clue to the explanation
of the difficulty is afforded by the facts which have been

VIII.] DORMANT AND AVAILABLE PLANT FOOD 15 1

considered in the previous chapter, as to the changes
which the nitrogen compounds in the soil have to go
through before they can feed the crop. Proteins and
similar compounds of nitrogen are of no service to the
plant until they have been transformed by bacteria into
ammonia and nitrates ; hence the amount of nitrogen
available for the plant in the soil at any moment may
be but a small fraction of the whole. Just in the same
way, phosphoric acid and potash must be brought into
solution before they can enter the plant, and the rate
at which the compounds of these constituents in the
soil will become dissolved depends greatly on their
nature and physical condition. For rough practical
purposes we may divide the plant food in the soil into a
dormant and an available portion, though it would
probably be nearer the truth to consider the whole as
potentially available, yet differing greatly in its degree
of activity. It is indeed impossible to draw any absolute
line of distinction between the dormant and the avail-
able— only an absolute division can be made among the
nitrogen compounds, of which nitrates and ammonia
might be classed as available and the rest as dormant,
but even then some of the dormant materials might be
rendered available a few days or even hours later.
Again, among the compounds of phosphoric acid we
might regard dicalcium phosphate in the soil as avail-
able and iron phosphate as dormant, but really this only
means that the calcium phosphate would yield a solution
containing perhaps a hundred times as mixh phosphoric
acid as would the phosphate of iron. This shows how
vain it is to hope to separate the available from the
dormant plant food by means of a solvent which will
extract the one and leave the other undissolved ; in any
solvent, however weak, both dissolve up to a point, and
the differences are only of degree and not of kind. . The

152 CHJEMICAL COMPOSITION OF THE SOIL [chap.

point to realise is, that plants feed on the solutions in
the soil water, and when the compounds in the soil can
renew this solution quickly and maintain it at a compara-
tively high concentration, they may be described as
"available" plant foods, whereas the "dormant" plant
foods give rise to soil solutions of low concentration,
which are not speedily repaired when the plant has
extracted the constituent in question. In the case of
nitrogen, the renewal of the solution depends upon the
attack of bacteria upon the nitrogen compounds in the
soil ; as regards phosphoric acid and potash, more
purely physical and chemical actions regulate the rate
of solution. The formation of the soil solutions has
already been discussed, and it was stated that the
carbon dioxide excreted by the roots of the plant has a
considerable effect in aiding the attack of the soil water
upon the mineral constituents of the soil. It is easy to
show in the laboratory that a solution of carbon dioxide
in water is a better solvent of such phosphates and
potash compounds as occur in the soil than pure water
is — almost in proportion to the amount of carbon dioxide
dissolved — and that such a solution must exist in the
soil is evident from the composition of the gases in the
soil. In most soils the actual solid particles only occupy
about 60 per cent, of the total space, the rest being
filled up by water and air. When the soil is saturated
with water the air is expelled, but complete expulsion is
only possible when the soil is saturated very carefully
from below, so as gradually to displace all bubbles.
Under ordinary conditions some air is always entangled
even when the soil is soaking, and as soon as drainage
gets established there will be 20 per cent, or more of
air, even though the soil is apparently very wet. The
air in the soil, however, does not long retain its original
composition; by the respiration of the roots and the

VIII.] CARBON DIOXIDE IN SOIL GASES 153

oxidising action of the decaying bacteria, oxygen is
always being replaced by carbon dioxide, until, as the
various determinations of the composition of the air ex-
tracted from an alluvial pasture soil indicate, there may
be 10 per cent, of carbon dioxide present, despite the
exchanges that are always going on at the surface where
the soil becomes open to the air. Now the carbon
dioxide will dissolve in the soil water in proportion to
its concentration in the air with which it is in contact,
hence a solution with a fair amount of power to attack
minerals is formed as soon as the rain-water has been
lying for some little time in the soil and has taken up
its proper proportion from the soil air with which it is
in contact. In a few cases, as with peaty soil, it is
possible that the organic matter may yield certain acids
to the soil water which give it an extra solvent power,
and the bleaching of stones and sand in peaty soils is
sometimes taken as a proof that this happens ; but it is
doubtful whether carbon dioxide would not equally
effect the solution, aided perhaps by reducing actions
caused by the organic matter. In the same way it has
already been stated that the supposed solvent action of
roots may be put down to the carbon dioxide they
excrete, rather than to any fixed sap acids that exude
from the roots and then attack the soil particles with
which they are in contact. That roots have a powerful
solvent effect, may be learnt from various direct experi-
ments ; in one case it was shown that plants growing in
a mixture of sand and ground rock phosphate could get
a good supply of phosphoric acid, whereas similar plants
starved when growing in the sand alone, though they
were supplied with water that had previously filtered
through a second plot of sand and phosphate. In
another experiment plants were grown in powdered
granite, and when this was washed after growth was

154 CHEMICAL COMPOSITION OF THE SOIL [chap.

over, a certain proportion of it was found to have been
converted into clay. The solvent action, however, in
both these cases can be put down to the carbon dioxide
excreted by the roots.

Many attempts have been made to devise processes of
analysis which should discriminate between the available
and the total plant food present in the soil : it has already
been pointed out that an ordinary straightforward
analysis which determines all the nitrogen in the soil
and all the phosphoric acid and potash which can be
dissolved out by strong hydrochloric acid, shows enough
food material for fifty and even one hundred ordinary
crops. Consequently, when such an excess is revealed
it is difficult to interpret the analysis, or to base upon
it any recommendations to the farmer regarding the kind
of manures he requires. Very dilute acids have, there-
fore, been suggested — a solution of citric acid that shall
be comparable to the acid sap of the root, or a solution
of carbon dioxide that shall be like the soil water — with
the idea that all of the phosphoric and potash which
these liquids would dissolve might be regarded as
available. It cannot be said that these methods of
analysis have provided infallible information ; it is not
possible, for example, to say that if a soil contains less
than a certain limited amount of phosphoric acid
determined by this method it follows that a phosphatic
manuring is required. The limit to be adopted will
vary with the texture of the soil, the water usually
present, the amount of carbonate of lime, the crop under
consideration, and other independent factors. For
example, a sandy soil may contain much less phosphoric
acid than a clay soil and yet feed the plant equally well,
simply because the open, aerated soil induces a much
greater root development. Again, a crop like wheat,
with its long period of growth and deep roots, is much

VIII.] ELEMENTS FOUND IN' SOIL 155

less dependent upon mineral manures than are the
shallow-rooted crops like turnips and barley. Soil
analysis, even by the most refined methods, is chiefly of
value when the analysis of the particular soil under
consideration can be compared with a number of
analyses of similar soils on the same type of land ; so
as to ascertain its relative deficiencies or excesses, and
interpret them in the light of what has been ascertained
beforehand about this type of soil by experience or by
field trials. If, for example, the average percentage of
phosphoric acid in soils of a given type, defined perhaps
by a particular geological formation, is 0-15, and it is
also known that phosphatic manures usually meet with
a fair response on such land, then if the soil of a
particular field on that formation only shows 0-I2 per
cent, of phosphoric acid, it will be safe to predict the
necessity for phosphatic manures on that field, though
on other soils 0-12 of phosphoric acid might indicate
such richness in that constituent as to remove the need
for phosphatic manures.

One other point is brought out in a series of soil
analyses : besides a considerable uniformity in the
proportions of nitrogen, phosphoric acid, and potash, all
soils contain very much the same substances. It is
extremely rare to find that any one of the regular
constituents is missing, i.e., soda, potash, lime, magnesia,
iron, manganese, alumina, chlorine, silica, phosphoric
and sulphuric acids ; and it is almost as rare to find an
appreciable quantity of any other element, though one
or two occur occasionally in small quantities. Now this
fact puts an end to the very common idea that differ-
ences in character or quality in the crops grown on a
given soil are due to specific deficiencies in the soil
which may be made up artificially. Of course, there
are cases where a crop shows certain special features

156 CHEMICAL COMPOSITION OF THE SOIL [chap.

brought about by lack of phosphoric acid or lack of
potash, because these substances affect the whole course
of development of the plant ; yet when the apples grown
on a particular field are always very red or the wheat is
very strong, it is useless to expect to find some substance
in the soil to which the redness or the strength is due.
It seems so straightforward to analyse the "strong"
wheat and ascertain the substance which causes the
strength, and then proceed to find the same substance
in the soil giving rise to strength. Unfortunately,
things do not happen in this simple way : the differences
in quality are usually due to very subtle differences in
the construction of the plants' constituents, and not in
the materials — carbon, hydrogen, nitrogen, oxygen, etc.
— out of which the structures are made. In nearly all
cases, also, the structure is mainly determined not by the
plant food or the manure available, but by the climate, the
water - supply, the temperature, and other physical
conditions of the soil. Just in the same way the old
theory must be erroneous which explained the value of
a rotation of crops by supposing that each plant in
turn extracted one particular substance from the soil,
and so temporarily exhausted the land for itself but
not for other crops requiring a different nutrient.
We see that no single crop can exhaust the soil of any
of its essential constituents, we see also that all crops
take out very much the same elements and in similar
quantities — therefore the value of a rotation depends
on a quite different set of factors. Putting aside the
economic arrangement of the labour which a rotation
permits, its great value lies in the facility it affords for
cleaning the land without any special labour. When-
ever one crop is grown continuously on the same land,
as is done on the Rothamsted experimental plots,
certain weeds which are favoured by the particular crop

VIII.] VALUE OF ROTATIONS 157

always get an extremely strong hold on the land and
become very expensive to keep under. Diseases and
insect pests special to the crop tend to accumulate
until they may unfit the land to carry the crop. The
tilth of the land often suffers when the same crop is
grown continuously on it; for example, when wheat
follows wheat there is very little time to prepare the
land between the crops; again, if swede turnips are
repeated for the second crop the land would miss the
autumn ploughing, which on many lands is a very
necessary element in the preparation of a seed bed for
turnips. And though soil exhaustion in any strict sense
is impossible, yet when any particular crop is repeated
there will always be one particular layer of soil in which
the roots of the plant chiefly reside, and this layer is
somewhat affected either by the removal of its plant
food, or possibly by the addition of some injurious
substance due to the plant. At any rate it is the deep-
rooted plants, wheat and mangolds, which seem to
flourish best when grown repeatedly on the same soil ;
whereas shallow-rooted plants like turnips, barley, and
specially clover, soon begin to fall off in yield if grown
continuously on the same land. The theory that plants
excrete some substances specifically poisonous to them-
selves and that a rotation is necessary to give it time to
decay, has been revived of late years, but the evidence
in its favour seems inconclusive, nor is it necessary to
set up so remote a hypothesis to explain the niain
factors in the virtues of a rotation.

Before we can leave the question of rotations and
the amount of plant food in the soil, it is desirable to
arrive at some idea of what is removed from the land
during an ordinary course of cropping, for on that will,
to some extent, depend the nature and quantities of the
materials which must be returned as manure if the

158 CHEMICAL COMPOSITION OF THE SOIL [chap.

fertility of the soil is to be maintained. As we shall see
later, we cannot wholly gauge the requirements of a
given crop by first ascertaining what it takes away from
the soil, but we can sum up the effect of a given rotation
and learn whether it is likely to leave the land richer or
poorer. We may consider arable land first, and assume
that when farmed on the Norfolk four-course rotation
it is of such fertility as to yield, on the average, 4^
quarters of wheat and 5 quarters of barley, 2 tons of
clover hay and 20 tons of roots. We may also assume
that only corn and meat are sold off the farm, the straw
being trampled down, and some of it fed with the roots
in order to make the dung which comes back. When
farmyard manure is made in the yards we may expect,
for reasons which will be set out later, that only one-half
of the nitrogen contained in the food will find its way
back to the land in the dung, though when roots are fed
off by sheep folded on the land about nine-tenths
will be returned. About three-quarters of the phos-
phoric acid and practically the whole of the potash may
be expected to come back in the dung. On this basis
we should get figures somewhat as shown in Table
XVI. — the annual loss to the land per acre would
amount to about 31 lb. of nitrogen, 9 lb. of phos-
phoric acid, and 5 lb. of potash.

As regards phosphoric acid and potash, there can be
no possible compensating agents at work other than
feeding stuffs or fertilisers brought on to the farm from
some external source ; it will, therefore, be necessary to
use about 240 lb. per acre of superphosphate (33 per
cent, acid phosphate) once during the rotation, say for
the swedes, in order to maintain the fertility of the land.
The draft on the potash is not so great, and on the
stronger soils we may expect that the weathering of soil
particles will render available a sufficient proportion of

VIII.]

MAINTENANCE OF FERTILITY

159

the dormant stock of potash to obviate the necessity
of any specific potash manuring : on the h'ght soils
200 lb. of kainit per acre once during the rotation would
repair all losses. As regards the nitrogen, however, the
figure we have obtained possesses very little value as a
guide to practice, because it ignores the whole group of
gains and losses of nitrogen which are due to bacteria in
the soil. For example, we have assumed that the
nitrogen contained in the clover crop has all been
derived from the atmosphere, so that this crop has

Table XVI.

■Fertilising Constituents per Acre Removed
DURING Four-Course Rotation.

Nitrogen.

rhosphoric
Acid.

Potash.

V^heat, 36 bushels, less 2\ for seed .
Wheat Straw, \ ton fed, rest in dung .
Swede Turnips, 20 tons fed
Barley, 40 bushels, less 3 for seed
Barley Straw trampled into dung
Clover, 2 tons Hay, fed .

Total for four years .

Average loss per acre per annum .

Lb.
37
0.7
56
32

54*

Lb.

14-8
o-S
3-6

I4-0

3-8

Lb.
10.8

CI

0.4
90

0.4

125.7

35-7

20-7

31-4

8.9

5-2

* Nitrogen drawn from atmosphere and not added in.

entailed no loss to the soil ; but we have very sound
evidence that the soil will have gained nitrogen after
the growth and removal of the clover crop. Moreover,
half the nitrogen in the clover-hay fodder is returned to
the soil in the dung, whereby the farm will have been
still further enriched by the growth and consumption of
clover. On the other hand, the soil suffers losses of
nitrogen which cannot be estimated — losses both by
drainage and by bacterial action — and these losses grow
larger the higher the level of richness at which the land

i6o CHEMICAL COMPOSITION OF THE SOIL [chap.

is maintained. A better idea of the requirements of
land under ordinary farming conditions may be obtained
from a study of certain of the Rothamsted plots, for
which a balance-sheet showing the gains and losses of
nitrogen over a period of years can be drawn up.

Taking first the unmanured wheat plot as an ex-
ample of land reduced to a very low level of fertility, we
learn that during the years 1852 to 1902 ityielded on an
average a crop of 13-1 bushels of wheat, which contained
in both grain and straw 18 lb. of nitrogen. During this
period the percentage of nitrogen in the soil had fallen, and
the nitrogen lost by the soil is approximately equivalent to
that removed in the crop. At this low level of fertility,
then, the nitrogen that had also been removed by
drainage and bacterial action (and such losses must
exist) had been replaced by recuperative actions,
doubtless due to Azotobacter and kindred organisms in
the soil. But for the plot receiving farmyard manure
every year, the nitrogen removed in the crop together
with what has been stored up in the soil only accounts for
about one-half of the nitrogen applied as manure. The
wasteful actions due to drainage or bacteria must have
enormously increased and have removed the balance,
any recuperative actions being swamped in such great
losses. Turning now to one of the rotation plots on
Agdell, we find that when clover or beans were grown
once in each four years, and where also the root crop was
returned to the land (see Table XV.), the nitrogen in
the soil remained stationary despite its removal in the
crops of wheat, barley, and clover, or beans. In this case,
then, the recuperative actions (which include the growing
of a leguminous crop) were able to balance the wasteful
processes in the soil and the removal of the grain and
clover crops, without any additions of nitrogen from
outside the farm. The level of production was not, how-

VIII.] THEORIES OF MANURING i6l

ever, high, being only 35 bushels of wheat and 34
bushels of barley, and though it might have been
increased had the straw and clover hay been made into
manure and returned to the soil, only a level of
production below the average can be maintained if the
land is left to natural recuperative actions. As soon as
larger crops are aimed at and the soil is brought into
higher condition to produce them, the wasteful actions
are increased in a higher ratio, as may be seen from the
example of the wheat plot dunged every year. Conse-
quently, to get the land up to the level of 5 qrs. of
wheat, not only the extra nitrogen contained in 5 qrs.
above 4 qrs. must be added, but a great deal more must
be brought in, in order to make up for the increased
rate of loss taking place in land in higher condition.

We thus find it impossible to construct a balance-
sheet for the land that sets off the removal of plant food
in the crop against the original stock in the soil and the
additions in the manures, because any such summary is
upset by the unknown gains and losses suffered by the
nitrogen in the soil, nitrogen being the most important
element of plant food. As we began by dismissing the
idea that we could decide upon the manuring of a given
field by finding out by analysis some particular substance
lacking in the soil which could be supplied as manure,
so now we must dismiss in its turn the theory that for
the proper manure we have only to provide what the
crop will take away from the soil. The first theory
made too much of the soil, since it assumed that
different soils possess radical differences which do not
exist ; the second theory fails because it takes no account
of the soil at all, and neglects the enormous reserves of
plant food therein contained. In fact, no general theory
of manuring can be drawn up which will predict the
appropriate treatment for every plant beforehand — we

L

i62 CHEMICAL COMPOSITION OF THE SOIL [chap.

must ascertain by experiment the specific requirements
of each crop, and adjust the manure to them, taking
also into account the character of the soil and the
style of farming, whether high or low.

According to their habits of growth, different crops
possess very different powers of feeding themselves
upon the stock of plant food in the soil — the specific
requirements of each is generally the particular element
the crop finds some difficulty in obtaining for itself.
For instance, wheat is sown without much previous
preparation of the soil, and makes the greater part of its
growth during the cooler portion of the year when
bacterial activity in the soil is low ; as a consequence, the
stock of nitrogen compounds in the soil is being but
slowly converted into ammonia and nitrates available to
the plant, and this particular crop becomes specially
dependent on a supply of some active form of nitrogen
as manure. On the other hand, the wheat plant
possesses a very extensive root system and has a long
period of growth, so that it searches the soil pretty
thoroughly and is well able to pick up the mineral plant
foods — potash, phosphoric acid, etc. — which it requires.
Hence, on the normally fertile soil, wheat requires no
mineral manures, but will respond to active nitrogenous
manure should the land not be in very high condition.
Barley supplies an instructive contrast — it is a spring-
sown crop, and for it the land gets a more thorough
preparation than for wheat. Nitrification and other
bacterial processes rendering available the nitrogenous
compounds of the soil are active in the recently stirred
land as it is warming up in April, May, or early June,
so that the barley crop requires little manurial nitrogen,
though it takes away from the soil as much of this
element as does the wheat crop. Being, however,
shallow-rooted and possessing but a short period of

VIII.] SANDY SOILS 163

growth, it is very dependent on a manuring of
phosphates, potash being less necessary, because it is
fairly abundant on any but the lightest soils. Swede
turnips afford another illustration : they are sown late,
when spring is well advanced, and after a very extensive
working of the soil ; during growth there is also a good
deal of intertillage, which promotes bacterial activity,
with the result that the crop requires very little nitrogen
in its manure though it takes away two or three times as
much as the wheat crop does. But with its shallow root
system the swede crop is greatly in need of phosphates,
and also of potash — perhaps more freqnently than is
suspected. The specific requirements of crops will be
dealt with more particularly in a later chapter ; but soils
show certain real differences, partly chemical and partly
physical, which affect their manuring and management
and may be now considered.

Sandy soils are made up, as we have said before, of
the coarser grades of particles, and contain as a rule but
a small proportion of clay ; it follows that they are easily
and rapidly permeable by water, and as they do not
retain much water they warm up quickly in the spring
and are early soils. Possessing but little clay, they not
only dry quickly, but they can be worked when wet
without any danger of destroying their texture ; this,
again, helps towards early cropping. Their coarseness
of grain, however, prevents them from lifting subsoil
water readily to the surface, so that crops on them
suffer from even short periods of drought, and it is
necessary to keep them as consolidated as possible by
folding with sheep, rolling, etc., in order to help the
capillary uplift of water. Being so warm and well
aerated, all bacterial actions go on rapidly in light soils,
and humus and other organic materials decay quickly :
such soils, therefore, are not retentive of manure but

1 64 CHEMICAL COMPOSITION OF THE SOIL [chap.

must be dressed frequently and heavily if they are to
be made fertile. From the chemical point of view, they
often show certain special deficiencies ; very generally
they are lacking in carbonate of lime, with the result
that turnips and similar cruciferous crops are found
to suffer from finger-and-toe or club root. Lacking
clay, they are also apt to be deficient in potash, and
crops like mangolds, potatoes, clover, and tobacco,
which require plenty of potash, should always receive
potash manures on sandy soils. All sandy soils, from
their warmth and friability, are apt to be very weedy ;
the characteristic weeds are often those associated with
lack of lime rather than with the dryness of the soil.
Good examples of this type of weed are the Spurreys
{Spergula arvensis and Spergularia rubra), Sheep's Sorrel
(Rmnex acetosella), and Corn Marigold {Chrysanthemum
segetum), all common on light sandy soils, but indicating
also great lack of lime if not actual acidity. The
Knawels {Scleranthus annuus and perennis). Knot Grass
{Polygonum aviculare), and some of the wild Poppies
{Papaver dubiuni) and the small Bindweed {Convolvulus
arvensis), are among the most troublesome weeds of
sandy arable land ; sometimes also a form of Bent Grass
{Agrostis alba) is very abundant. On the grass land
various tufted species, Cock's-foot {Dactylis glomerata),
the Oat Grasses {Arrenathemuvt avenescens, Avena
flexuosa), and the Soft Brome {Bromus mollis), are
characteristic. Leguminous plants, except Bird's-foot
Trefoil {Lotus corniculatus), and more occasionally some
of the Vetches like Vicia cracca, are not abundant;
though various weeds — Hardhead {Centaurea cyanus)^
Buttercup {Ranunculus bulbosus), Rattle {Rhinanthus
crista-galli) and Silver Weed {Potentilla anserind) are
common. On the wastes, Gorse ( Ulex europceus and nanus)
Broom {Cutisus scoparius), Heather and the Heaths, the

VIII.] LOAMS 165

Bracken Fern {Pteris aquilina), and the Foxglove
{Digitalis purpurea) are typical, all of them being
associated with lack of lime also ; while the character-
istic trees are the Spanish Chestnut, the Silver Birch,
the Holly, and many Conifers, particularly Pinus
pinaster.

The sandy soils pass by insensible stages into the
loams — indeed many of the most fertile loams are really
sands in which the finer silt fractions predominate.
Properly a loam is marked by an equable distribution
of the various grades of particles, with enough clay and
fine silt to render it retentive of moisture and manure,
but with sufficient sand to keep it open and well drained.
Chemically, also, the loams might be described as well
found, without any specific deficiencies or excesses ;
particularly the proportion of carbonate of lime, though
it may be small, is sufficient to maintain the neutrality
of the soil. The loams might, on the one hand, be said
to have no specific flora; on the other hand, certain
plants are only found on good, free-working soil in fair
condition, so that they may be taken as indicative of
fertile loams. Among trees the Elm is characteristic, as
are clean, well-grown Thorn hedges, and an abundance
of Nettles {Urtica dioica) in the hedgerows and waste
places. On the arable land, Chickweed {Steilaria inedia)^
Groundsel {Senecio vulgaris), Fat Hen {Chenopodium
album)y Annual Nettle {Urtica urens), and Sow Thistle
{Sonchus oleraceus) are weeds indicative of good land.
Goose Grass {Galium aperine), the Speedwells ( Veronica ^
sp.), Pimpernel {Anagallis arvensis), Henbit {La^nium
amplexicaule), and various Spurges {Euphorbia peplus)
etc., are also common. On the pastures. Perennial Rye
will generally be the most characteristic grass, and its
smooth leaf gives a characteristic shine to some of the
best grazing land ; White Clover is also abundant, and

i66 CHEMICAL COMPOSITION OF THE SOIL [chap.

the herbage is generally very varied and forms a thick
close sole. Buttercups are very common on some of
the alluvial pastures, and are sometimes taken as a
sign of overmuch cake feeding ; many Oxeye Daisies
{Chrysanthemum leucanthejnum)^ on the contrary, indicate
that the land has been allowed to get too poor.

Just as the sands pass insensibly into the loams, the
latter grade by degrees into the clays, the most pro-
nounced examples of which are the soils resting upon
some of the formation developed in the East Midlands
and in the east and south-east of England— the Oxford
and Kimmeridge Clays, the London and Weald Clays,
being the most marked. A true clay soil is cold and late,
very retentive of moisture yet suffering severely from
a drought of any duration, not only because of the cracks
it develops, but because of the slowness of the capillary
movement of water from below and the restricted root
development of all crops upon clay, especially when the
land has not been drained. Clays are difficult to work,
the draught of all tools being heavy, and great care
must be taken to catch them at the right moment of
working ; especially in spring it is ruinous to their tilth
to put horses on them when they are in the least wet.
It is most important to plough heavy soils in the autumn
and leave them rough through the winter, so as to get
the beneficial pulverising and flocculating action of
repeated frosts and thaws ; on the heaviest soils an
occasional bare summer fallow is desirable because of
the value of the weathering to the tilth. Being cool and
moist, clay soils are retentive of manure ; long straw and
other bulky manures are of value to open up the texture
of the soil ; it is often indeed of service to burn, or rather
char, some of the clay and incorporate it with the rest
of the soil. Clay soils are very often deficient in
carbonate of lime, so that dressings of lime are of

VIII.] CLA Y SOILS 167

special value both in supplying this needed constituent
and in bringing about the flocculation of the finest
particles, thus improving the texture and render-
ing the soil drier and warmer. Phosphoric acid
is also deficient in many clays, and as plants become
naturally somewhat shallow-rooted on such soils a
good supply of phosphate manure is often extremely
effective ; potash, on the contrary, is usually abundant on
clay soils. The typical crops of clay soils are wheat,
mangolds, beans, and permanent pasture, though the
latter may be very bad unless it is properly managed.
Weeds are not so abundant as on other soils, but a few
are specially troublesome, especially Black Bent Grass
{Alopecurus agrestis) and Field Mint {^Mentha arvensis) ;
the Rest Harrow {Ononis arvensis) is often a bad weed
on the poor pastures ; the Wild Carrot {Daucus carotd),
the Teazel {Dipsacus sylvestris), and the Primrose
{Primula vulgaris) are characteristic. The Oak is the
typical tree of clay land, with Ash in wetter places, and
Hornbeam in the underwood and hedges. Clay land
pastures are often characterised by a very shallow-
rooting vegetation, which may even become largely
stoloniferous (creeping rooting), with such difficulty do
the roots penetrate the stiff, unaerated soil ; a form of
Bent Grass {Agrostis alba) often constitutes the bulk of
herbage; Sweet Vernal Grass {^Anthoxanthemum odor-
atum) and Crested Dog's-tail {Cynosurus cristatus) are
also common.

Calcareous soils may be either light, as when derived
from the Upper Chalk, or heavy and sticky, when they
contain much admixture of clay as they do on the Chalk
Marl and several of the argillaceous limestones in the
Midlands ; but in all cases they possess a very special
and characteristic flora. The wild plants are very full
of flowers, and the copses and hedgerows contain a

1 68 CHEMICAL COMPOSITION OF SOIL [chap. viii.

number of flowering shrubs that are seen on few other
kinds of land — the Traveller's Joy {Clematis vztalba),
the Mealy Guelder Rose ( Viburnum lantana), the
White Beam Tree {Pyrus aria), the Dogwood {Cornus
sanguinea) being most characteristic ; while of the trees,
the Beech, the Yew, and the Cherry are particularly
associated with chalk and limestone soils. Leguminous
plants are abundant both in the pastures and the waste
places, the Horseshoe Vetch {Hippocrepis comosd)
being a very sure indicator of a calcareous soil, while
the natural home of Sainfoin and Lucerne {Alfalfa) is
on the warm, chalky soils of the south and east of
England. The lighter chalky soils are notoriously
weedy. Fumitory {Fumaria officinialis)^ Dove's-foot
Cranesbill {Geranium molle)^ and Field Buttercup
{Ranunculus arvensis) being among the most abundant.

Peaty and waterlogged soils also develop a special
vegetation which need hardly be considered in detail,
since the farmer merely wants to recognise certain plants
and other indications that show the need for drainage
either in spots or over the whole field. Patches of rushes
always indicate stagnant water near the surface, as also
the various sedges known to the farmer as Carnation
Grass {Luzula, sp.). The occurrence of tufts of Aira
ccespitosa also indicates wetness ; and a stagnant, water-
logged condition of the soil is shown by the presence of
brown rusty deposits in the ditches, accompanied by an
iridescent scum on the surface of the water. On digging
into such land a layer of peat is generally found below
the surface vegetation, and below that a layer of rusty
oxides of iron upon the surface of the true soil. The
treatment required in such cases is drainage and liming.

CHAPTER IX

FOODS

Composition of Cattle Foods. Nature of Carbohydrates, Fat,
Proteins, Fibre, Ash. Processes of Digestion in the Animal
Body. Digestibility. Character of various Concentrated
Foods, Cereals, Roots, Straw, and Hay. Valuation of
Feeding Stuffs.

We have already discussed the constituents of plants ;
these constituents in their turn make up the foods, and
have to be considered from a fresh point of view in
dealing with the nutrition of animals. As a rule, the
composition of any given cattle food is expressed as
follows : — Decorticated cotton-seed cake contains —

Moisture

. = 8-2 per cent.

Fat .

. = II-9 »

Proteins or Albuminoids

. = 46-2 „

Carbohydrates (by difference)

. = 21-2

Fibre

• = 5-5

Ash (containing sand=i'5 per

cent.) = 7-0 „

The fat really represents the material which is soluble
in ether; when dealing with oilcakes and similar ripe
foods it will consist almost wholly of pure fat, but in the
case of green fodders various other materials, e.g. chloro-
phyll, are dissolved by the ether in the process of
analysis and counted as fat. Crude fat would be a more
correct title. The proteins (albuminoids of the older

169

I70 FOODS [chap.

books and in trade documents), again, should be called
crude proteins or some equivalent term, because the
figure expressing them is only obtained by multiplying
by 6-25 the total nitrogen contained in the food, thus
including as proteins various non-protein nitrogenous
compounds such as the amides, amino-acids, and other
bodies intermediate between nitrates and proteins. All
green fodders contain a considerable proportion of their
nitrogen in this "amide" or non-protein form, and in
their case the true proteins are sometimes determined
separately. Crude fibre is again a purely conventional
term for whatever remains undissolved when the food
has been digested for some time, first with dilute acid
and then with alkali : it represents very approximately a
part of the food which can only be very imperfectly
digested by the animal, and is therefore of much smaller
value as food. The ash is a figure of value to the
analyst, while the " sand " (that portion of the ash which
will not dissolve in weak acids) provides an index of how
far the food is contaminated with dirt, mud, sand, etc.
Finally, all the rest of the food is reckoned as soluble
carbohydrates ; obviously the figure expressing their
percentage contains the accumulated errors of the
analysis, and is of value only for comparison with other
foods. Indeed in the United Kingdom the seller of
feeding stuffs is under no obligations to state the amount
of carbohydrates in the food he is selling, though he
must state the percentage of moisture, nitrogen, and
fat. In all foods we find these constituents — fats, pro-
teins, carbohydrates, fibre — and though great differences
exist between the various materials thus classed
together, according to the food in which they occur, our
knowledge is still too imperfect to make it worth while
discriminating between them in an ordinary analysis.
We must now consider the processes of digestion

IX ] THE PROCESS OF DIGESTION 171

which these foods undergo in the body in order to
become available for the nutrition of the animal. They
have to reach the blood, this being the circulating
medium which conveys them to every part of the body,
and in consequence they must either be soluble or
become converted into such a state of solubility as will
permit them to pass through the walls of the stomach
and intestines. These organs form the alimentary
canal, from which there is no direct opening into any
other part of the body. The process of digestion takes
place as the food is passing along this alimentary canal ;
whatever is not absorbed by its walls forms the
undigested part of the food, which is excreted as the
faeces. The solution of each of the constituents of food
is effected by one or more of a series of enzymes which
are secreted by the animal ; these enzymes being exactly
comparable in their action and nature to the diastase,
etc., which have previously been described under plants.
Considering first the fat, its digestion is not accom-
plished until the food has left the stomach ; at this stage
the food materials, which had previously been rendered
acid by the gastric juice, are brought into an alkaline
condition by mixture with the bile and the pancreatic
juice. Amongst other enzymes the pancreatic juice,
which is also mixed with the food at this stage, gives
rise to a lipase or fat-splitting ferment, which resolves
the fats into their component fatty acids, and glycerin.
These later bodies are capable of passing through the
walls of the intestine, and by means of the blood and of
the lymphatic system they are distributed about the
body. It is found that fat stored up by an animal, or
excreted as milk, does to some extent partake of the
nature of the fats contained in its food, showing that
the fatty acids (the basal material of the fats) are not
entirely broken down before the fat is reconstructed in

172 FOODS [CHAP.

the animal. On the other hand, there is plenty of evi-
dence that the fat of the food never passes into the body
or into the milk without some change. Once digested,
all fat that is not stored is used by the animal as fuel in
order to maintain its heat and provide it with the
energy by which it is enabled to work. In this process
the fat is completely burnt up, and its elements leave
the body again in the form of carbon dioxide and water,
having undergone just the same change as would have
taken place had the fat been set on fire. The fat is
truly burnt, and has been proved to give out the same
amount of heat inside the animal as if it had been
burnt in a lamp.

The carbohydrates contained in the food also
become soluble as a result of enzyme action ; the sugars
are, of course, soluble to begin with, but starch is first
attacked by a diastase which occurs in the secretion of
the saliva. In consequence, the digestion of starch is
active in the first stomach and during the " chewing of
the cud " in ruminant animals. This salivary digestion
is, however, suspended in the stomach proper, because of
the acid reaction there set up ; but the starch is attacked
again in the small intestine, after the influx of the
alkaline bile and the pancreatic juice, which gives rise
to a second diastatic enzyme. The digestion of cellulose
and the more soluble portions of the fibre is less easy to
follow. All seeds themselves contain an enzyme capable
of attacking cellulose, and this would become active in
the alimentary canal, especially in the long digestive
tract of ruminants, in which the food remains for four or
five days. There is little evidence that animals them-
selves secrete any cytase or cellulose-dissolving enzyme.
The intestinal tract, however, contains bacteria, which
multiply greatly in the food, and are able to break
down the cellulose and fibre into various simpler bodies,

IX.] THE PROCESS OF DIGESTION 173

such as sugars and fatty acids that are capable of
absorption by the blood, together with gases like
methane, and to these bacteria is ascribed the main part
of the work of digesting cellulose and similar carbo-
hydrates.

All carbohydrates — sugars, starches, or soluble cellu-
loses— acts as fuel for the body : having reached the
blood, they are passed on to the living cells, and there
burnt to carbon dioxide and water in order to supply
energy. When more carbohydrates are supplied than
the animal requires, they can be built up into fats either
for storage or for milk production, carbohydrates them-
selves being never stored in the animal body except in
the liver, which contains one special body of this nature
— glycogen. The combustion of the carbohydrates is
not, however, always so complete as that of the fats ; a
certain proportion, especially of the cellulose and fibre,
is excreted in a unoxidised form as methane or marsh-
gas, and to this extent the value of the carbohydrate as
fuel has been reduced.

The digestion of the proteins is a more complex
process. The stomach secretes a gastric juice which is
acid and also contains an enzyme called pepsin, by
which the proteins are first attacked. Then in the
small intestine the partly digested food is mixed with
the pancreatic juice, which possesses an alkaline reaction
and generates a second enzyme called trypsin, which
also attacks the proteins. Both of these enzymes break
down the proteins into peptones, albumoses, and' succes-
sively more soluble amino-acids, which are able to
diffuse through the walls of the intestine. There the
simple nitrogen compounds are once more built up into
proteins, and in that form are passed into the blood and
led to the different parts of the body ; though another
view is that the soluble nitrogen compounds enter the

174 FOODS [chap.

blood, and are only re-formed into proteins by the cells
which remove them from the blood. The greater part
of the nitrogen compounds thus digested is oxidised
into carbonic acid and water, the nitrogen part of the
compound being eliminated from the blood by the
kidneys, chiefly as the urea which is excreted in the
urine. A part, however, of the digested protein — and
this is really the indispensable part to the animal —
is used up for repairing nitrogenous waste in the tissues.
In growing animals some of the proteins of the blood
are stored up as lean meat ; also, when there is an
excess of protein in the diet, some of the carbon will be
stored in the animal as fat, the nitrogen being again
excreted as urea. When an animal is not putting on
weight at all, the whole of the nitrogen that is digested
is excreted again as urea and kindred bodies in the
urine ; the amount of protein required to repair the
daily waste is comparatively small, and the excess is
simply treated by the animal as fuel.

The fibre in the food analysis does not truly
represent the indigestible portions of the food, for
all natural foods except pure oil, sugar, and starch are
only imperfectly digested ; some part of the food resists
the intestinal enzymes and bacterial processes and is
excreted from the body in the faeces. As regards the
nitrogenous compounds of food, it is important to
remember that whatever is digested is afterwards
excreted as soluble urea in the urine, while the
undigested portions remain in an insoluble state in
the dung. The non-protein nitrogenous bodies pos-
sess a much smaller food value than the proteins ;
as fuel they are not so valuable, while it is
still a matter of debate to what extent they can
replace proteins in repairing tissue waste. Appar-
ently they can at least save waste of the proteins, and in

IX.] MINERAL CONSTITUENTS OF FOODS 175

ruminant animals they can become converted into
proteins by the action of the bacteria in the intestinal
tract. Little need be said about the mineral constitu-
ents of the food — the ash — though it is essential to build
up the bones of the animal, and to supply the salts
circulating in the blood. As with the other constituents,
some of the contents of the ash are digested and excreted
in the urine, some are excreted unchanged in the dung.
Salt is one of the most important food constituents,
since from it has to be made the hydrochloric acid
which is secreted in the stomach, and is required for the
digesting processes there proceeding. Phosphate of
lime is also absolutely necessary; from it is built up
the framework of the bones as well as the phosphorus
compounds which occur in all parts of the body.
Young animals soon become diseased if fed upon foods
in which this constituent is deficient. Of course, besides
these main constituents which run the machinery of the
body — the fat, carbohydrates, proteins — foods contain a
variety of other bodies which give flavour, and affect
the disposition of the animal towards its food, although,
as far as is known, they do not actually alter its digesti-
bility. The question of flavour is as yet beyond
scientific treatment, its influence must be left to the
observation and judgment of the skilled feeder of
cattle.

When the value of different foods comes to be
considered, especially with the object of compounding
rations for feeding stock, it is not sufficient to know the
percentage of fat, proteins, etc., which the food contains,
we must also know how much of each is digestible.
For example, pure fat is completely digestible by the
animal so that it is wholly burnt up within the body, yet
the same fat when disseminated through the mass of a
hard seed may, to a greater or less degree, escape the

176 FOODS [CHAP.

attack of the digestive ferments in its passage through
the alimentary tract, and so be in part excreted
unchanged. Obviously the test of non-digestibility is
the occurrence of the material in the faeces, hence if we
wish to determine the digestibility of a given food we
must maintain an animal on a diet consisting of the food
in question over a particular period. During this period
the weight of the food given and the faeces excreted is
exactly observed. Both food and faeces are analysed
by the similar methods ; the difference between the fat
that has been fed and the fat contained in the faeces
gives the proportion of this constituent that has been
digested, similarly for the protein and the carbohydrates.
When concentrated foods which cannot be fed by them-
selves are in question, e.g. linseed cake, a preliminary
diet of hay alone is given and the faeces analysed, then
for a certain period a known amount of linseed cake is
added to the hay diet, and the change in the composition
of the faeces is determined. Certain errors are inherent
in this process ; in the first place, it is impossible to
mark off exactly when the faeces corresponding to a
given diet begin and cease to be excreted. Then a
certain amount of waste tissue containing nitrogen
which had previously been stored in the body is always
excreted into the intestine, and so gets reckoned as
undigested protein. Again, the bile and other secretions
provide matter which is soluble in ether but is not fat.
Still the results obtained are close enough to the
processes going on in digestion to be of real value.
Greater discrepancies are introduced by the fact that the
digestive power of one animal differs considerably from
that of another, and besides this personal idiosyncrasy
one kind of animal possesses greater digestive powers
than another, especially for the cellulose and fibre
portions of the food. It has already been mentioned

IX.] DIGESTIBILITY 177

how much more capable are sheep and cattle, with their
complex stomachs, ruminating habits, and lengthy
intestines, to deal with fibrous foods than are horses or
even pigs, in the intestine of which animals the food
remains for a much shorter period. Hence the digesti-
bility of many foods depends upon the animal to which
it has been fed, but these variations occur much more in
dealing with such bulky foods as hay or straw than
with the concentrated feeding stuffs. Of course, varia-
tions occur in the food itself; for example, hay cut before
it is dead ripe is the most digestible, and the nitrogenous
matter of hay is better digested when the food is
rich in this constituent. In fact, we may say
generally that rich foods are better utilised than poor
ones, without regard to the fact that they contain initially
a higher proportion of valuable constituents. Only when
an excess of food is given does its digestibility decrease,
a starving animal cannot get more than the normal
amount of nutriment out of a given food. Again, the
work that the animal is doing has little or no effect
upon the digestibility of the food given to it. Cooking
does not appear to increase the digestibility of any of
the usual cattle foods ; in fact, the digestibility of the
proteins is reduced. Drying the food, as in making hay
from grass or in curing maize forage, does not diminish
the digestibility if the process is properly carried out.
Making the grass into silage, so far from increasing,
actually reduces the digestibility of such proteins as
escape reduction to ^-proteins by the process; it is a
mistake to suppose that silage-making will convert
worthless grass and similar waste products into valuable
food. It has also been shown that while the addition
of fats or proteins to a comparatively poor diet of
hay and straw and roots causes no reduction in the
digestibility of either the original diet or the additions,

M

178 FOODS [chap.

yet if carbohydrates are added to a hay or straw diet the
digestibility of the proteins in the original diet is reduced
when the added carbohydrates amount to more than lo
per cent, of the fodder. Thus, roots should not be added
to a hay and straw diet in greater proportion than 15
per cent (reckoning both as dry matter), unless some
concentrated protein food be given at the same time in
order to maintain the ratio between nitrogenous and
non-nitrogenous constituents of the food at a higher
level than i to 8.

Table XVII. (page 179), which is copied from a table
compiled by Dr Crowther, of Leeds University, sets out
the average composition of a number of the foods most
commonly in use, together with the percentages of the
same constituents that are in a digestible condition and
one or two other factors which will be explained later.

The most concentrated of all foods are the meals and
cakes, the latter being the residues left after crushing
various oil-bearing seeds in order to extract as much oil
as will come out by pressure alone. The composition of
such cakes will vary with the nature of the seed and its
origin, but the amount of oil in the cake can also be
greatly modified by the extent of pressure put on and
the temperature at which the crushing is conducted.
With linseed cake in particular it is customary not to
extract the oil as fully as would be possible, whereby
the cake is enriched and at the same time rendered
softer and easier of digestion. In some cases the oil is
extracted by chemical means, but the seed residue is
then generally used for manure ; as a rule, rape seed
is treated in this fashion because it is rarely pure
enough to be used afterwards as cattle food, being often
mixed with a considerable proportion of mustard seed.
In the United Kingdom few cakes are used beyond
those derived from linseed and cotton seed, and of

IX.]

COMPOSITION OF FEEDING STUFFS

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i8o FOODS [chap.

recent years from soya beans ; but earth-nut and palm-
nut cakes are sometimes obtainable and many other
kinds of seeds are crushed, though the residues are
usually worked into some of the compound proprietary
mixtures which are so widely sold as oilcakes.
Farmers are recommended to buy pure cakes made
from one kind of seed only. As a rule, such cakes are
cheaper intrinsically even though their price is higher,
and they are much less subject to adulteration. Their
greatest value, however, lies in the fact that the farmer
knows exactly what he is using, and can come to definite
conclusions for the guidance of his future practice.

These oilcakes constitute the richest and most con-
centrated of all cattle foods, in most cases also their
digestibility is very high. At the head stands decorti-
cated cotton cake, since cotton-seed meal still containing
its oil unextracted is rarely seen in the United Kingdom,
though it is commonly employed- for fattening cattle in
the United States. The cake is made from cotton seed
from which the husks have previously been removed,
the undecorticated cake being made from the whole
seed after the cotton fibre has been ginned off.
Decorticated cotton cake is extremely rich in proteins
and oil, and contains but little fibre ; while it is an
excellent food for bullocks fattening and for dairy cows,
it must not be given to the latter anywhere near the
time of calving, nor should it be fed to calves. There is
evidence that it contains some substance which is at
times disturbing or even poisonous to cattle, so that
cotton cake must always be used with discretion.
Undecorticated cotton cake is the favourite adjunct to
the food of cattle fattening upon grass, especially in the
early spring : it has certain astringent properties which
correct the action of the young grass. When fed to
milch cows cotton cake tends to harden and raise the

IX.] OILCAKES i8i

melting-point of the butter made from their milk.
In buying undecorticated cotton cake, care should be
taken to see that it has not got heated or become
mouldy — the smell and taste give fair evidence in this
direction ; of course an analysis is of great importance,
to see that it contains no undue proportion of husk.
The same precautions must be taken over undecorti-
cated cake, of which many very inferior samples are
made containing an excess of husk, sometimes ground
to a powder to disguise it ; an excess of cotton fibre also
occurs, and is undesirable.

Linseed cake is the most highly esteemed of all the
feeding stuffs ; it is always relished by stock and never
disturbs their health in any way, though if fed in large
quantities to milch cows it is apt to render the butter
too soft and oily. Linseed cake is particularly valued
by graziers at the end of the fattening process, because
nothing else will confer the sleek, shining appearance
and kindly feel of the skin which comes to an animal
"finished" on linseed cake. Linseed cake should be
analysed and examined for purity; it should show no
reaction when tested for starch, which would only be
present as an impurity due to the seeds of weeds, for
linseed itself contains no starch. Very hard cakes also
are undesirable, because they are low in oil. There
is evidence, however, that the very high content
in oil which is often attained — 12 per cent, or over — is
rather an expensive luxury, for just as good results can
be obtained with poorer cakes supplemented by a
corresponding amount of carbohydrate.

Soya-bean cake is so recent an introduction that
little can yet be said of its specific actions or character,
but it appears to be an extremely valuable food for all
classes of stock. Gluten meal and gluten feed are
residues obtained in the manufacture of various maize

i82 FOODS [CHAP.

products, such as starch ; they are in consequence foods
specially rich in proteins, and have proved valuable in
feeding milch cows and for young stock growing or in
the early stages of fattening.

Of the cereals, oats are the richest, containing the
highest proportions of both proteins and fat ; they are
valuable for all classes of stock, and always wholesome.
Wheat requires more careful feeding, but barley again
forms a very safe general food, containing a large propor-
tion of carbohydrates. Experience has shown that the
deficiency of barley in protein is best corrected by the use
of cotton cake. Maize is chiefly a carbohydrate-contain-
ing food, and however valuable for work and for fattening,
as regards its proteins it must be considered as rather- a
low-grade type of food. Beans and peas are both rich
in proteins ; they are amongst the most valuable of foods
for either young growing stock, horses, pigs, or sheep ;
an admixture of bean meal is also good in a ration for
milch cows.

Oat straw is generally a little richer than either
barley or wheat straw, but the variations in composition
between oat straw from different fields or different
varieties is greater than the differences between oat and
barley or wheat straw. Only one analysis of straw has
consequently been given in the table. The composition
of hay is also very variable, because differences due to
the making are also added to the differences induced by
the nature of the herbage, the soil, or the season. Of
the different roots, potatoes contain by far the most dry
matter, (25 per cent), then mangolds with about 12 per
cent, swedes with a little less, and turnips with less than
10 per cent They are all in the main carbohydrate
foods : the potato contains starch, the mangold sugar,
while swedes and turnips contain various pectic bodies
as well as sugars. A large proportion of their nitrogen

IX.]

VALUATION OF FEEDING STUFFS

M

is present in the form of non-protein compounds, as it is
also in cabbage and all other green foods.

It is impossible to value feeding stuffs with the same
measure of precision which attaches to comparisons of
fertilisers, but certain estimates may be drawn up which
are useful in considering the purchase of foods of
the same class. Fats and carbohydrates may clearly be
compared together, since both sets of bodies are used
solely as fuel. Experiments which will be discussed
later show that fats ^wo. rise to about 2-3 times as much
heat as carbohydrates, whether compared in the calo-
rimeter or in the body, so that we may value i lb. of fat
at 2-3 times the value of i lb. of carbohydrate. Proteins
besides their value as fuel are also necessary to repair
waste ; while no relation depending upon principle can
be fixed between them and the carbohydrates, for
commercial purposes they may be taken as equal to
fats, Le. at 2-3 times the value of carbohydrates. Thus
if we wish to compare the values of decorticated cotton
cake and of gluten meal, we can proceed as follows : —

Constituent.

Decorticated Cotton
Cake.

Gluten Meal.

Fat . . .

Protein

Carbohydrate

Percentage.

9x2.3

41x2.3

26

Food Units.
20.7

260

Percentage.

4x2.3

38x2.3

45

Food Units.

9-2

87.4

4S-0

141-0

141-6

It would be far more correct to consider the di-
gestible constituents only in such a valuation, in
which case the feeding stuffs set out above would
show 118 and 126 units respectively, figures which
ought not to be too widely departed from in the
relative prices given for the foods. In the market,

1^4 FOODS [chap. IX.

however, it will be found that the prices depend upon
very different conditions, mainly of a commercial
character, hence the grazier who values out the feeding
stuffs on offer before purchase can generally obtain a
substantial advantage. In a subsequent chapter, how-
ever, it will be shown that such a basis of comparison is
only of value when dealing with concentrated foods ; a
more accurate basis of judgment is afforded by the
starch equivalents which will then be explained.

CHAPTER X

THE UTILISATION OF FOOD BY THE ANIMAL

Food as a Source of Energy. Heat Value of various Foods.
Energy consumed in Digestion and Internal Work.
Maintenance Rations. Feeding for Rapid Work or Increase
of Weight. Amount of Food required for a given Amount
of Work. Nitrogenous Materials required to repair Tissue
Waste. Minimum of Protein necessary.

So far, we have only discussed the composition of
various foods and the process of digestion by which
they reach the body ; it is now necessary to consider the
purposes which these foods serve, and their utilisation
within the body. We will begin by looking at foods
from the standpoint of energy : we have already
indicated that an animal is an organisation which has
to be continually fed with some external supply of
energy in order to maintain its warmth and its power
of doing work. It resembles water running down-
hill, in that when once started it runs on of itself; the
transformation of energy continues as long as the
material containing the energy is supplied, and during
the transformation there is a certain wastage through
change into low-grade, unusable forms of energy. The
food and the oxygen together contain stored-up energy ;
like a reservoir of water at the top of a hill, they will run
down into carbon dioxide and water, the energy being
liberated as heat, just as the water will have parted with

185

1 86 UTILISATION OF FOOD BY THE ANIMAL [chap.

its energy as heat by the time it is at rest again at the
foot of the hill. During the running-down process, also,
in both cases a certain proportion of the stored-up
energy can be converted into work or other forms of
valuable energy; moreover, both processes will run of
themselves if the sluice-gate be opened in one case, or
the mixture be ignited in the other. The energy of all
bodies, i.e. their capacity for doing work, is best
measured in terms of heat, the unit usually employed
in this sort of work being the large calorie, which is the
amount of heat required to raise the temperature of
I kilogram of water by i degree. This calorie has
been valued against other kinds of energy ; for instance,
if the heat contained in the calorie were transformed
into work, it would lift 425 kilograms i metre (or 1-4
tons I foot) ; similarly, electricity or light can also be
measured in terms of calories. To take an example, we
can say that a given weight of coal possesses a certain
amount of energy, which would be developed and
measured as heat if the coal were burnt and the heat
communicated to a known weight of water. But if the
coal is burnt in a steam boiler, and the steam made to
drive an engine, less than the whole of the energy of
the coal will be found in the waste heat from the boiler
and steam, because a certain proportion has been
transformed into work. A dynamo will transform this
moving energy into electricity with but a small loss by
friction {j.e. with but a small reconversion into heat),
and the electricity may be changed again into work,
light, chemical energy, or other forms — the ultimate
result being a running down into low-grade heat. The
original stock of energy is never lost or destroyed, the
sum total of the different forms developed being always
that originally present in the coal ; even when finally
degraded into heat, there are still the original number

X.] ENERGY OF FOOD 187

of calories present. The difference is that such low-
grade heat has lost its effectiveness, and can no longer
be transformed into work, light, or electricity. As
another illustration we may take a watch : in the act
of winding a certain amount of energy is communicated
to it, and remains stored in the energy of the coiled-up
spring. Gradually this energy is transformed into the
energy of motion of the parts of the watch, which is just
as continuously rubbed down by friction into heat which
leaks away. There is no loss of energy; the world
when the watch runs down contains a little more evenly
distributed heat, exactly balancing the energy com-
municated to the coiled spring at the outset.

The total energy possessed by any food — that which
is often called its fuel value — can be measured in the
simplest fashion by actually burning in oxygen a given
weight of the food in a vessel surrounded by a known
quantity of water and observing the rise of temperature
that ensues. This gives the maximum amount of
energy available from the food, but the animal does
not realise the whole of it except in the case of a pure
fat or oil which is as completely burnt in the body
as it is in the calorimeter. Most foods are not
completely digested, hence the excreta contain some
energy and must also be burnt separately in the calo-
rimeter, the heat evolved being deducted from the
total energy of the food in order to estimate what is
available for the animal. The nitrogen of proteins,
again, is excreted as urea, which is combustible and
contains energy ; this also must be burnt and the heat
deducted from the fuel value of the food ; also from all
carbohydrates, and particularly from fibre a certain
proportion of methane and hydrogen is produced in
the intestine, and these unburnt gases represent losses
of energy to the animal. For example, with oxen,

1 88 UTILISATION OF FOOD BY THE ANIMAL [chap.

Kellner obtained the following fuel values and heat
values for certain typical foods, expressed in calories
per gramme of food : —

Table XVIII.— Energy Developed by Various Foods.

Fuel

Value

per grm.

Losses of Energy.

Heat

Value to

Ox.

Excreta.

Urine.

Marsh.
Gas.

Earth-nut Oil (Fat)
Wheat Gluten (Protein) .
Starch (Carbohydrate) •
Meadow Hay
Wheat Straw .

8.8
5-8
4-1

3-6

1-75

2-1

...

I'l

0-2I
O'l

0.4

0-23

0-3

8-8
4-7
3-7
1-8
i-i

This table shows us that though in the calorimeter

fat will develop — =2-15 times as much heat as starch,

8-8
yet in the ox it will develop — 1 = 2-4 times as much,

because in the digestion of the starch some of the
material is excreted as methane which is still com-
bustible and contains energy.

in the calorimeter have a heat value

4.1

Similarly proteins, which

5-8

— 1-4 times

that of starch in the animal, possess — = 1-25 times

the value of starch, because of the comparatively large
proportion of undeveloped energy still contained in the
excreted urea. We can then take as a basis these
experimentally ascertained facts, that the heat value
to the animal of a pure digested fat is 2-4 times that
of starch, and that of digested protein is 1-25 times that
of starch, and proceed to calculate the heat value of

X.]

HEAT VALUE OF FEEDING STUFFS

189

mixed feeding stuff in terms of starch. For example,
ICK) lb. of meadow hay (Table XVII.) contains : —

Constituent.

Percentage
Digestible.

Heat Value to

Animal
compared with

Starch.

Total SUrch
Units.

Fat

Protein ....
Carbohydrates and Fibre .

I X

4 X
41 X

2.4
1.25

2.4

5.0

41.0

48.4

Thus, 100 lb. of meadow hay are equivalent to 48-4 lb.
of starch by calculation from the constituents, whereas
Kellner found by experiment, as shown above, that when
I of starch gave 37 calories, i of meadow hay gave
1-8 calories, or 100 of meadow hay give as much heat as

- — ^^-^ = 487 of starch, a sufficiently close agreement.

If the animal is at rest, either fattening or on a mere
maintenance diet {i.e. the minimum diet which will
keep it stationary in weight), then the whole of the heat
values of the foods expressed in the last column, less
what is stored as fat and flesh, will be developed in the
animal's body, and will go to keep it warm. If, however,
the animal is at work, then the amount of energy thus
developed will not appear as heat inside the animal. It
is, of course, true that even when at rest in the stall the
animal is doing a certain amount of internal work, but
this internal work being done inside the body is there
reconverted into heat without loss ; it is only work
outside the body, as in drawing a cart or turning a mill,
that is lost as animal heat, because it is converted into
some other form of energy that can be stored outside
the body. But as regards the internal work of the

I90 UTILISATION OF FOOD BY THE ANIMAL [chap.

body, we must make a distinction between the work
done in carrying on such movements as breathing, the
circulation of the blood, etc., which are bound up with
the life of the animal, and the other work of digestion —
mastication, swallowing, the motions of the stomach and
intestines — which will vary in amount with the nature
of the food supplied. Pure fats and carbohydrates like
sugar can be digested with a minimum of exertion, but
when the same substances are found in food-stuffs
entangled among the fibres of tough materials like hay
and straw, the animal may have to do a good deal of
work in breaking down the food before the enzymes can
get at the digestible constituents, and this work has to
be derived from the combustion of some previously
digested food stored up in the body, i.e. eventually
from the energy contained in the food itself. If, then,
for any food-stuff we begin by estimating a certain
number of calories as its heat value, which heat value
is the measure of the energy it can liberate in the body,
we shall have to make a deduction for the energy used
up in digestion before we can get at the energy remain-
ing that is available for work or for such purposes as
putting on fat. If, indeed, the work spent in the
digestion of a given food is very large, it may approach
or even exceed its total heat value, and so leave no
margin for either the internal or external work of the
body. Of course, the energy thus spent either in
digestion or internal work is still transformed into heat,
whereby the animal is kept warm ; hence an animal at
rest on a maintenance diet, the heat value of which just
supplies enough energy for both digestion and internal
work, will still maintain its animal heat, and will
even be able to increase it by a greater consumption of
food if it is forced to make up for greater losses of
heat by being put to live under colder conditions. But

X.] WORK EXPENDED IN DIGESTION 191

if all the energy derivable from the food is spent in
effecting digestion and internal work, there will be no
margin left either for external work or the production of
increased weight, hence, however much food the animal
ate, it can never do any work nor grow any heavier.
This condition, when the energy derived from the food
is wholly or even more than balanced by the energy
required for digestion, is realised in the case of a horse
feeding upon straw, which is very fibrous, so that the
work required is great and a large proportion remains
undigested, while of the digested carbohydrate about
one-fifth is lost as methane. Zuntz found that the
horse actually consumes more energy in digesting
straw than is contained in the portion digested, and
this is confirmed by an experiment of Miintz, who fed a
horse on straw alone. Although the horse was allowed
an unlimited amount of straw it died at the end of about
two months, thoroughly exhausted because it had been
compelled to draw upon its body. Again, Kellner, in
experiments with oxen, which are better able than
horses to deal with foods like straw, found that more
than four-fifths of the energy contained in the digested
part of the straw was consumed in the digestion
processes, leaving less than one-fifth available for work
or increase. When, however, the straw was made into
a pulp by the processes employed by papermakers,
who disintegrate the cellulose by boiling with an alkali
under pressure, as much as 88 per cent, of the straw was
digested, and of this digestible matter a little more than
a third only was consumed in effecting digestion.

So fundamental are these considerations regarding
the total and available energy of foods, that we may
recapitulate : the total energy resident in any food is
measured by the heat it will evolve on burning, and is
called its fuel value. From this fuel value must be

192 UTILISATION OF FOOD BY THE ANIMAL [chap.

deducted the fuel value of the undigested excreta, and also
of the incompletely oxidised urea and the gases evolved in
the intestine, in order to obtain the energy available for
the animal — the heat value of the food. All this energy is
available for the maintenance of the heat of the animal,
but a certain proportion is spent in the work of digestion,
and it is only the surplus that is available for the internal
and external work performed by the animal or for the
increase of weight that it may be putting on. If the
food is being added to the maintenance ration, all the
surplus will be available for external work or for
increased weight. We can now define the surplus
energy which a food will give out over and above the
work required for its own digestion, as the " dynamic "
energy of the food, and it is this dynamic energy alone
which is available for performing work or for giving
rise to increased weight. Thus we distinguish the total
energy or fuel value of the food, the heat value or
thermal energy, and now the dynamic energy or value
for work and production.

One or two examples may perhaps make this more
clear.

Taking decorticated cotton cake we may on its
analysis calculate the " fuel value " from the experiment-
ally determined facts that i gramme of oil (in such seed
cakes) produces 9-2 calories on combustion, i gramme
of protein and i of carbohydrate producing 5-8 and
4- 1 calories respectively. From 100 grammes of decorti-
cated cotton cake we therefore obtain a fuel value of
460 calories as follows : —

Oil, 9 grammes x 9*2 calories . . = 82*8

Protein, 41 grammes x 5-8 calories . = 237*8

Carbohydrates and Fibre, 34 grammes

X 4-1 calories . . . . = 139-4

460-0

X.] ENERG V A VAILABLE FOR WORK 193

Deductions must now be made for the undigested
part of the food, for the urea and the methane excreted,
as follows : —

Undigested Oil, 0-5 grammes at 9-2 cals. . = 4*6
Undigested Protein, 7 grammes at 5-8 cals. . = 40-6
Undigested Fibre, 14 grammes at 4-1 cals. = 57*4

Urea from 34 grammes digested protein at

I- 1 calories . . . . . = 37'4

Methane from 20 grammes digested carbo-
hydrates, etc., at 0-4 calories . . = 8-o

148-0

Deducting these 148 calories from the fuel value,
460 calories, we get 312 calories as the heat value of the
cotton cake. We have now to make a further deduc-
tion of 3 per cent, (or 9 calories) as the internal work
spent in digestion, leaving 303 calories as the dynamic
energy of 100 grammes of decorticated cotton cake avail-
able for transformation into work or storage as fat in the
animal ; though, as will be seen later, only a certain frac-
tion of this can be so converted or stored.

Let us now compare meadow hay, calculating on the
same lines : —

2-5 grammes fat at 8«2 calories . . = 20*5

10 grammes protein at 5-8 calories . . = 58-0

68 grammes carbohydrates and fibre at 4-1 cals. = 278'8

Calories, fuel value 357*3

Deductions : —

Undigested Fat, i'5 grammes at 8-2 calories . = I35'3
Undigested Protein, 6 grammes at 5-8 cals. . = 34-8
Undigested Fibre, 27 grammes at 4' I cals. . = 1107
Urea from 4 grammes digested protein, at

M calories . . . , = 4*4

Methane from 41 grammes digested carbo-
hydrates, etc., at 0-4 calories . . = i6'4

178-6

N

194 UTILISATION OF FOOD BY THE ANIMAL [chap.

Deducting this from the fuel value we get 357-3 —
178-6= 178-7 calories as the heat value of 100 grammes
of meadow hay. But from this we have to deduct 40 per
cent, for internal work spent in digestion, or 71-5
calories, leaving only 107-2 calories as the dynamic energy
of 100 grammes of meadow hay. Thus the meadow
hay, while it possesses more than half (178 compared
with 312) the heat value of the cotton cake — i.e, is more
than one-half as effective in keeping up the heat of the
animal on a maintenance ration — has yet only about
one-third of the value of cotton cake (107 as against 303)
towards doing work or putting on increased weight.

Bearing these principles in mind, we may trace
certain simple practical consequences. Rough, coarse
fodders like hay or straw, poor grass, roots, etc., serve
perfectly well for keeping animals in store condition, for
though they require a considerable expenditure of energy
for their digestion there is enough margin to carry on
the internal work of the body and the whole energy is
afterwards available as heat, while the animal has only
to be kept warm and is neither working nor increasing
in weight. Similarly, animals that are at slow work and
are never called upon for any great output of energy in
proportion to their weight, can be fed upon bulky low-
grade fodders which do not develop any great surplus
of energy. But when animals are growing rapidly or
are performing heavy and rapid work, then comparatively
rich and concentrated foods are necessary, foods which
develop a large surplus of energy over that which is
required for their digestion. A horse standing in the
stable may be fed on nothing but hay, just as a horse
out at grass needs only a little hay besides the old grass
even in severe winters, but as soon as the horse is
worked, instead of more hay it must be given corn of
some kind ; and a racehorse, on which great calls are

X.] VALUE OF CONCENTRATED FOODS 195

made for a sudden and excessive output of energy, must
have the most concentrated and digestible foods that
can be obtained. No increase in the amount of the
lower-grade foods will compensate for their lack of
concentration, because so much time would be spent by
the animal in heaping up the necessary surplus energy.
To take another example, cattle or sheep will never
grow fat in one season on the grass growing on the
majority of fields, however great an area they may be
given to graze ; it is only on certain choice fattening
pastures that the increase is rapid enough to prepare an
animal for market without artificial assistance. On the
ordinary grass lands the animal spends so much of the
energy obtained from its food in digesting it that the
surplus left for production does not permit of rapid
growth ; on the fattening fields the grass possesses a
smaller proportion of fibre, and therefore less of its heat
value is wasted in the digestion processes.

Similarly, in the last stages of fattening animals in
stalls carbohydrates are of much less value than they are
at an earlier period, because they call for an expenditure
of energy in digestion which is disproportionate to the
increase they produce at that stage, when the increase
bears a very small ratio to the food consumed, whereas
much less of the energy of fats and proteins is wasted
in the digestion process.

Treating food from this point of view as supplying
energy to the animal, we may now proceed to consider
the animal's requirements under different conditions.
The simplest case is, of course, that of the animal at
rest on a maintenance diet, so that it is neither increasing
nor diminishing in weight. As the temperature of the
animal is always higher than the surrounding atmo-
sphere (from 100° to 104° R, varying with the animal),
a constant loss of heat is going on from the surface of

196 UTILISATION OF FOOD BY THE ANIMAL [chap.

the body, and the food supply must be sufficient to
repair this loss or the animal will be forced to consume
some of its previously stored-up fat or flesh. All
internal work, including that done during digestion,
reappears as heat, so that as long as the food is
above the grade of straw and contains more available
energy than is required for the digestive process, the
food is only called upon to repair the losses of heat and
maintain the body temperature ; the work required for
digestion, respiration, and other bodily processes being
performed by the way without interfering with the final
production of heat, because it is work done inside the
animal. In other words, the maintenance diet con-
tains just enough energy to drive the machine when it is
running idly with the animal at rest, and in the running
of the machine the food energy is transformed into heat
which keeps up the body temperature. Actually on
most diets, even maintenance rations, the energy re-
quired by the resting animal to maintain its temperature
is greater than that required for internal work ; some of
the food is burnt simply and solely as fuel for warming,
and the amount of food required will be determined
only by the heat lost by the animal. The magnitude
of this factor will vary with the size of the animal, or
rather with the surface it possesses, because heat is lost
only from the surface. Now the smaller the animal the
greater is its surface in proportion to its weight (a cubic
foot of water weighs 62-5 lb. and has a surface of 6
square feet ; a cube 2 feet on the side would weigh eight
times as much, but only have a surface of 24 square feet,
i.e. four times as much as before) ; hence small animals
will require for maintenance more food in proportion to
their weight than large ones. Of course, the greater the
difference in temperature between the animal and its
surrounding air the greater will be the loss of heat and

X.] ENERG V REQUIRED B V ANIMALS 197

the consumption of food to repair the loss ; hence the
truth of the old saying that shelter is as good as a meal.
Heat may also be required, and, therefore, food consumed
in raising the temperature of the food and water to the
body temperature, and this may be considerable when
large quantities of very cold water, or roots which
contain nearly 90 per cent, of water are consumed
at a freezing temperature. This, however, would only
affect animals on a maintenance ration when the food
is reduced to the minimum necessary to keep the
animals warm ; on fattening rations there is always a
surplus of heat that cannot be utilised in any other way.
Leaving, however, such cases out of account, Kellner
has drawn up the table from which the diagram. Fig.
23, has been constructed, showing the heat value of
the food required for the maintenance of store bullocks
of various weights when they are kept at rest at a
temperature of about 60° F. The solid line expresses the
number of calories which the digestible part of the food
must give out per day in order to keep the animal in a
stationary condition ; these calories can be converted
into terms of food by calculating that i lb. of digestible
organic matter in an ordinary ration will evolve about
1600 calories, and i lb. of starch about 1 700 calories ; the
dotted line gives the equivalent in starch of the solid
line. A fat bullock weighing about 1750 lb. requires
about 20,000 calories heat value in its daily food in
order to keep it going. The maintenance requirements
of a horse are very similar to those of a bullock ;' accord-
ing to Zuntz, the maintenance ration of a horse at rest
must evolve about 12,100 calories per diem, and not
more than two-thirds of this energy must be expended
in the work of digestion. Sheep have rather greater
requirements in proportion to their weight, because of
their smaller size and therefore larger proportional

198 UTILISATION OF FOOD BY THE ANIMAL [chap.

surface, and also because of their higher temperature;
a sheep weighing lOO lb. requires digestible food which
will develop about 2000 calories, ix. 1000 lb. of sheep
requires 20,000 calories, whereas 1000 lb. of lean cattle
only require about 11,000 calories. All these figures,
however, refer only to maintenance diets, when the
animal is doing no work and not putting on flesh. As
soon as work has to be performed the number of calories
required jumps up : for example, a horse weighing iioo
lb., and carrying harness weighing about 20 lb., will
perform about 11 50 foot-tons of work in walking 10
miles at a pace of 2\ miles an hour ; this will be
increased to about 1440 foot-tons at l\ miles an hour,
and to about 2200 foot-tons when trotting at 7 miles an
hour. Foot - tons can be transformed into calories
directly on the basis that 1-4 foot-tons of work will
yield i calorie when degraded into heat by friction,
but the converse change cannot be made so readily,
because a large proportion of the heat must always be
left unutilised in its conversion into work. A steam
engine, for example, is a machine for transforming heat
energy into mechanical energy, yet at its utmost
efficiency we can barely get out in work one-seventh of
the energy contained in the coal, the rest being evolved
in waste, low-grade heat From this point of view the
animal is a much more efficient machine than a steam
engine, for it is able to convert into mechanical work
about one-third of the available energy it derives from
its food, i.e. of the "dynamic" energy of the food.
According to Zuntz's experiments, a horse can turn out
about 770 foot- tons of work for each pound of available
food, reckoned as usual as starch, given in addition to
the animal's maintenance diet — the available food being,
however, the equivalent of what we have hitherto called
dynamic energy, or the value of the food for work, i.e.

Heat

Value
of Food

Calories.

20,000

15,000

Starch
Equiva-
lent.

iLb;

Live weight,

lb. 900

^

H

ej:J

alU^^

^fj^

D^^^^

-

STAPi^.

f 0JI

/AL£N

r

looo iioo 1200 1300 1400

[500 1600 1700 1800

Fig. 23.— Diagram showing the Energy required from the Food
BY Oxen of Different Weights.

[Face fage 198.

X.]

FOOD REQUIREMENTS OF HORSES

199

after deductions have been made for energy spent in
digestion, etc. As different foods possess different
amounts of available energy, Zuntz has constructed the
following table for the horse : —

Table XIX.— Available Energy of Various Foods.

Value as

Sterch

of Digested

Portion.

Used for

Digestion

Work, as

Starch.

Foot-tons of
Work avail-
able per lb.
of Food.

Equivalent

Quantities of

Food for

Work
Purposes.

Starch .
Maize .
Beans .
Oats

Lucerne Hay
Meadow Hay
Straw .

ICX)

78-5

72-0

61.5
45-3
39-1
18.1

0

8-2
II-I
12.4
21.9
20-0
29.7

542
470

379
180
140

Nil.

10

I-I5

1-43

3-OI

3-87

This table means that the digestible portion of a
pound of maize has a heat value to the horse equal to
that of rather more than three-quarters of a pound of
starch; nearly 10 per cent, of this heat value is used up
in the work of digesting the maize, but from the
available energy remaining the horse can put out 542
foot-tons of work. On meadow hay, however, although
it contains just half the quantity of digestible food, yet
so much energy is consumed in digestion that the
balance only enables the horse to put out 140 foot-tons
of work, or only one-quarter the work that can be done
on the maize, though the food yields half as much
digestible matter. In the case of straw there is no
margin at all left for work. We also see that if the
addition of i lb. of maize to a horse's diet enables him
to do a certain amount of work, 1-43 lb. of oats or 3 lb.
of lucerne hay would be necessary to replace the maize
and turn out the same amount of work. Similarly, it was
found that when a horse walked 12^ miles a day, 20 lb.

200 UTILISATION OF FOOD BY THE ANIMAL [chap.

of hay would keep it in condition ; if it drew a load that
added 1943 foot-tons to its work, 26-4 lb. of hay were
needed ; while 24 lb. were insufficient if the horse trotted
without a load. The load meant 6-4 lb. extra of hay,
and according to our table a better effect would have
been produced by substituting 2 lb. of maize.

It is difficult as yet to apply these kind of calcu-
lations to practice because of the impossibility of
estimating with exactitude the amount of work
performed by a horse in any operation, but we may
assume that at ordinary heavy work like ploughing, a
horse will be doing about 1000 to iioo foot-tons of work
per hour. To do this work, 2 lb. of maize, 2\ lb. of
beans, or nearly 3 lb. of oats will be required ; or for an
eight-hour day's work, about 20 lb. of mixed corn. To
this must be added, not the whole maintenance require-
ment of the horse, because his heat requirements will be
satisfied by the development of heat from the muscular
work spent in the body and in digestion, but instead
about a third of the whole amount in order to do the
work of respiration and circulation, i.e. about 3 lb. more
of corn. If some of this corn is replaced by its
equivalent in hay we get a fair approximation to the
ordinary working rations of a farm horse, and these can
be adjusted on the principle that every hour's work is
equivalent to between 2 lb. and 3 lb. of corn. These
figures are contained more exactly in the following table,
derived from Kellner, where the horse is made to work
under experimental conditions, walking at the rate of
about 2\ miles per hour, against the draught indicated,
for eight hours a day.

The concentrated foods like oats, beans, or maize yield
very nearly their full value in starch equivalents for all
the digestible constituents of the food, i.e. nearly all the
digestible constituents are available for work. But, as

X.]

HORSE RATIONS

20I

we have explained before, with the coarse fodders much
of the energy is spent in the work of digestion, so that
only a portion is available for work, though all the heat
value is available for maintenance. In the ordinary
horse ration, we may deduct about lo per cent, from the
digestible food constituents reckoned as starch in order
to obtain figures comparable to those given in the
bottom line of the table. In a later chapter more exact
figures will be given for the starch equivalent.

Table XX.— Energy Requirements of Working Horses.

Live weight of horse, lb.

675

900

1125

1350

1575

Draught in lb. weight .

lOI

126

151

175

220

Daily work in foot-tons

4200

6000

7200

8400

9600

Calories required for maintenance

9000

10900

12600

14300

15800

„ „ for work .

10400

12900

15500

18000

20600

Starch equivalent for mainten-

ance, lb

5-3

6.4

7-4

8.4

9-3

Starch equivalent for work, lb. .
Total Starch equivalent, lb.

6-1

7-6

9.1

10-6

I2-I

1 1.4

14-0

16.5

190

21-4

So far, the food has only been considered as a source
of energy, and this is much its most important function,
so that the best measure of the value of a food is the
amount of available energy it possesses. Food, how-
ever, has also to effect the renewal of the tissues of the
body, and this function must be considered indepen-
dently of the supply of energy.

An animal cannot be maintained without a certain
minimal supply of protein containing nitrogen, and
though the protein can supply energy and when in
excess can even give rise to fat, its prime purpose is to
repair the nitrogenous waste of the tissues, and for this
no other nutrient will suffice. Proteins give off heat
when burnt in the body and so can take the place
of fats or carbohydrates, but as these two latter con-

202 UTILISATION OF FOOD BY THE ANIMAL [chap.

tain no nitrogen they cannot do the special work of
the proteins. We have already briefly indicated
the metabolism suffered by the proteins in the
diet; they are broken down by the enzymes of the
stomach and the intestine into comparatively simple
amino-acids and amides, and in this form are ab-
sorbed by the walls of the stomach and intestines.
It is still in doubt whether they are there recon-
verted into proteins which pass into the blood, or
whether the blood is given the simple split products
resulting from the enzyme action. The end result is
the same in either case, the nitrogenous compounds are
carried always in the blood-stream and so reach succes-
sively every cell in the body where such materials . are
absorbed as are required to maintain the structure of
the cell ; at the same time the cell hands over to the
blood the waste nitrogen products excreted by the cells.
The amount of nitrogen compounds thus taken up for
tissue repairs and renewals is only a small portion of
the nitrogenous compounds entering the blood from the
food, unless the animal has been placed on a minimal
ration which barely maintains a nitrogen equilibrium.
As a rule, the animal is receiving more protein than is
absolutely necessary, but when the blood containing the
digested protein products passes through the kidneys
the nitrogen part is split off in the form of urea and
only non-nitrogenous compounds are passed on, to
be used for generating energy or forming fat as need
may be. This accounts for the rapid excretion of urea
after a meal, when it cannot be supposed that time
enough has elapsed to give rise to an amount of tissue
waste equivalent to the urea excreted. Thus we must
distinguish between the excreted nitrogen compounds,
which are due to tissue waste and represent the
indispensable nitrogen requirements of the body if

X.] PROTEIN REQUIRED BY ANIMALS 203

its equilibrium is to be maintained, and the other
nitrogen compounds (urea only, probably) split off
from proteins which are being used as mere sources
of energy, though both kinds are excreted together
in the urine. The former quantity of nitrogen, the
minimum required to repair tissue waste, can be
measured either by putting the animal on a purely non-
nitrogenous diet and seeing how much nitrogen is
excreted under such conditions of nitrogen starvation,
or, more accurately, by gradually reducing the protein in
a ration supplying the proper amount of energy until a
limiting condition of nitrogen equilibrium is reached
when any further diminution in the protein fed results
in the excretion remaining greater than the intake,
after the first disturbance due to the change of diet has
passed away. In this way the minimum requirements
of protein for oxen or horses on a maintenance diet
appear to be about \ lb. per day per 1000 lb. live
weight ; for sheep this quantity must be nearly doubled,
because of the comparatively large draught on protein
for the growth of wool, which cannot be brought to a
standstill like the formation of flesh. It is, however,
never safe in feeding animals to get down to this
minimal limit ; the digestibility of the carbohydrates in
the ration is reduced if the proteins are low, especially
when the rations are large, because the animal is then
called upon to secrete an increased amount of enzymes
which are themselves nitrogenous bodies. Moreover, it
has been shown that respiration is quickened, the
circulation is more vigorous, and the temperature is
raised a trifle, if the supply of proteins is above the
absolute minimum. There is another point of view
also to be considered : though the proteins form a great
natural group of substances having many characters
in common, which can be further grouped into smaller

204 UTILISATION OF FOOD BY THE ANIMAL [chap.

classes of still more similar substances, yet it is probable
that each species of animal and plant builds up a protein
special to itself and differing somewhat from all others.
In order to build up its special body protein an animal
must be supplied with the right units, />., the simple
amino-acids, amides, etc., which are produced by the
splitting-up of proteins by enzymes, and those units
which the animal does not require will be useless to it as
nitrogenous food, though they will be burnt as usual to
supply energy. Some food proteins also may be with-
out a unit that is essential to the building-up of the
body protein ; thus it has been shown that zein, the
particular protein of maize, will not maintain the
nitrogen equilibrium of rats or mice. However, much
of it is fed, they eventually die of nitrogen starvation,
because the zein molecule lacks a particular constituent
which is an essential part of the body protein of these
animals. If, however, a very small quantity of this
particular substance is also supplied, then the animal
begins to utilise the zein split products and form its
necessary body protein, because it has also obtained the
necessary keystone of the structure. Thus we see that
the animal must have more products of protein digestion
presented to it than it actually uses, because it has to
pick them over in order to select the indispensables in
the right proportions ; moreover, the diet should contain
some variety in the proteins supplied, in order to make
certain that no essential constituent is deficient.

The food of an animal not increasing in weight should
therefore be considered from two points of view — it
must supply sufficient energy for the calls upon the
animal for work, and at the same time it must contain
sufficient protein to repair the tissue waste that an
animal always experiences even during starvation.
Energy is supplied by all kinds of food that are com-

X.] ALBUMINOID RATIO 205

bustible — most by fat, less by proteins, less still by
carbohydrates and crude fibre as far as it is digestible —
and the amount of energy that must be supplied by the
food depends simply upon the amount of work done by
the animal. In animals at rest energy is only required
to perform the operations of mastication and digestion,
internal work like breathing, and to maintain the
temperature of the body, though the heat developed in
performing the former functions may be sufficient to
keep up the bodily heat. When an animal is at work
combustion is going on so rapidly that far more heat is
developed than is necessary to the maintaintence of the
normal temperature, and the excess is got rid of by an
increased evaporation of water from the lungs and the
skin, for the animal's temperature never rises sensibly
as long as it is healthy. In addition to food supplying
the necessary energy, the animal must also receive at
least a minimal amount of protein which it can utilise
for tissue formation ; any excess is rapidly reduced to
non-nitrogenous combinations and then burnt up for the
development of energy like any other food.

From the point of view of the food, we must consider
that it contains first of all a certain store of energy
measured by its value as fuel, from which to begin with
we must deduct the energy of the indigestible portions,
and the energy still possessed by excreta like urea and
marsh-gas, in order to get the heat value of the food to
the animal. Further still, we must deduct from this
value the work spent by the animal in masticating and
digesting the food if we are to obtain the energy value
of the food to the animal — i.e, the surplus remaining out
of which it can do work. We now want an expression for
the protein value of the food, and to do this we are
accustomed to calculate the ratio between the non-
nitrogenous food constituents and the protein. To make

2o6 UTILISATION OF FOOD B V THE ANIMAL [chap. x.

the comparison fair, the non-nitrogenous food con-
stituents must be reckoned in terms of carbohydrates
by multiplying the fat by 2-3 and adding it to the
carbohydrates and digestible fibre ; the ratio of the sum
of these constituents to the digestible protein is known
as the albuminoid ratio. If the albuminoid ratio is
to be a figure of the slightest value in judging of a
food ration, it must be calculated on the digestible
constituents only and not on the analytical composition
simply, as is so often done. An albuminoid ratio of 5 : i or
less is said to be narrow ; when it approaches 10 : i or
12:1 it is called wide. The ratio is of comparatively
little importance in connection with the cases we have
just been discussing — animals at work and not increasing
in weight ; but when we are dealing with animals which
are growing and increasing in weight, which, therefore,
especially in the younger stages, are adding to the amount
of body protein they contain, or again with animals
which are secreting milk, the albuminoid ratio becomes
of more value in forming a judgment of a ration. This
most important side of feeding will be considered in the
following chapter.

CHAPTER XI

FOOD REQUIRED BY THE GROWING AND
FATTENING ANIMAL

Composition of Lean and Fat Animals. Food required to Produce
a given Increase of Live Weight. Starch Values of Foods.
Albuminoid Ratio. Food Rations for various Purposes
based upon Starch Values.

In the previous chapter we have only considered food
as a source of energy to the animal, maintaining its
temperature, and then supplying it with energy by
which it may carry out its bodily functions and perform
work. But the farmer is usually concerned with animals
which are growing and increasing in weight, and we
have now to ask ourselves to what extent the food is
utilised in these processes. The foundation of our
conclusions must rest upon the knowledge of the
composition of the animal's carcass in different stages
of its life, and this knowledge was obtained at Rotham-
sted, where Lawes and Gilbert had a number of animals
slaughtered in different stages of fatness, and determined
stage by stage the composition of the body of each.
The following animals were selected : — a fat calf, a half-
fat and a fat ox ; a fat lamb, a store sheep, three other
sheep in a half-fat, fat, and very fat condition ; a store
and a fat pig. The animals after slaughter were care-
fully divided, and the weights of the different parts of
the carcass and the offal were determined ; afterwards

2o8

FOOD REQUIRED

[chap.

the proportions of water, fat, protein, and ash in each
part were determined, with the results set out in Table
XXI. and further illustrated in Diagram No. 24. On

Table XXL— Percentage Composition of Carcasses of
Animals in Different Stages of Fattening.

i

li

bS

^1g?

11

II

t

1

Contents

tomachs

Intestin

Moist sta

S

tn ^->

Fat Calf

3-8o

15-2

14-8

33-8

63-0

3-17

Half-fat Ox .

4.66

16-6

19.1

40-3

51-5

8-19

Fat Ox.

3-92

14-5

30-1

48.5

45-5

5-98

Fat Lamb .

2.94

12.3

28.5

43-7

47-8

8-54

Store Sheep .

3-16

14-8

18.7

36.7

57-3

6-00

Half-fat Old Sheep

3-17

I4-0

23-5

40.7

50-2

9-05

Fat Sheep .

2.81

12-2

35-6

50-6

43-4

6 -02

Extra Fat Sheep .

2.90

10.9

45-8

59-6

35-2

5-i8

Store Pig . . .

2.67

137

23-3

39-7

55-1

5-22

Fat Pig .

Mean of all

1.65

I0'9

42.2

54-7

41-3

3-97

3-17

13-5

28.2

44.9

49-0

6.13

PERCENTAGE COMP

OSITIO^

r OP IN

CREASI

] IN F^

iTTENI

NG.

Oxen ....

1.67

9-i6

75-36

86-19

13-81

Sheep ....

2-34

9-47

79.87

91-68

8-32

...

Pigs ....

o-o6

6-50

78-00

84.56

15-44

...

looking at these results, it will be seen that the process
of fattening is very much what its name implies. As
the animal puts on weight, there is little or no increase
in the proportion of either the ash or the protein, but
the fat gains steadily at the expense of the water. Of
course, as an animal is increasing in weight during
the fattening, the actual amount of protein matter it

XI.] COMPOSITION OF FATTENING ANIMALS 209

contains does also increase, but not so rapidly as the
fat, so that its percentage of the total weight actually
falls off. It should also be noticed that the fat animal
contains a smaller proportion of water than the same
animal in a store condition, lean meat is a much more
watery substance than fat, so that the accumulation of
fat tends to reduce the proportion of water in the whole
body. If we can assume that the different animals
slaughtered in the various stages of fatness fairly
represent the kind of changes that the single animal
would have gone through while it was being fattened,
we can use these figures of Lawes and Gilbert to
ascertain the composition of the increase in live weight
which the animals put on in passing from the store to
the half-fat, and from the half-fat to the fat condition.
It will then be found that in the case of oxen which are
being steadily fattened from the time they are young,
the increase of weight will consist of about one-third
water and two-thirds dry substance, about three-fourths
of the latter consisting of fat. In the final finishing
stage, when the animal is fully grown, about three-fourths
of the increase will be dry matter, 90 per cent, of which
will consist of fat. In the case of sheep, there is more
mineral matter in the increase because of the amount of
alkaline salts in the wool ; but despite the nitrogenous
nature of the wool, the live weight increase of sheep is
even less nitrogenous and more fatty than that of oxen.
In fact, about 75 per cent, of the increase of weight in
fattening sheep is made up of fat itself In the case of
heavy fat pigs the increase put on is still less nitro-
genous and more fatty, there being about 80 per cent, of
fat and only 7 per cent, of nitrogenous matter in the
increase. While these figures give us a pretty clear
idea of the nature of the changes that are going on
when the animal is fattened, they do not tell us how the

O

2IO

FOOD REQUIRED

[chap.

food gets utilised nor what proportion of it is stored
up within the animal. It is obvious that the animal
by no means adds to itself the whole of its food, or even
the whole of what it digests. We have already seen
that a considerable proportion of food is required simply
for maintenance, being burnt as fuel to keep up the
heat of the body and carry on the internal work of the
organs. But even if we make deductions of the matter
used for maintenance, we shall not find that the rest of
the digestible food is stored up in the body of the fatten-
ing animal. Lawes and Gilbert put together a large
number of statistics relating to animals being fattened
in the ordinary way upon the farm ; determining their
weight from time to time, and the weight and composi-
tion of the food which they had been receiving. From
these results Table XXII. was constructed, which shows

Table XXII.— Relation of Food consumed to Live
Weight Increase.

Dry Substance of Food

.

■»3

42

a

9n-

Consumed.

it

Si

o a

u

0

sis

tl!

Sag

1!

11

1^1

Days.

Lb.

Lb.

Lb.

Lb.

Lb.

Oxen .

27

112

87

I46i

121

I3-0

9.4

50

Sheep .

19

307

143

20\

159

9.2

17.2

54

Pigs .

33

104

5«

48

270

4.8

56.2

63

Dry matter of solid excrement and urine, exclusive of litter.

that to make i lb. of increase in the live weight of
oxen, 1 3 lb. of dry food material was necessary, while
about 9 lb. were wanted in the case of sheep and

XI.] RELATION OF FOOD TO INCREASE 211

5 lb. in the case of pigs to produce the same increase
of I lb. in the live weight. Of course, these results are
only very approximate, particularly as they do not take
into account the nature of the food, but express the kind
of results which may be expected on the very mixed
diet prevailing in England. We have already seen that
not only do foods differ very greatly in composition, but
that much more of the digestible part of the food is
available for the service of the animal in the case of
concentrated foods than with coarse fodders, which
require a large expenditure of energy for their diges-
tion. Moreover, these figures by Lawes and Gilbert
are average figures spread over the whole period of
fattening, and if we examine more closely the rate of
increase, we shall find that a given weight of food is
much more effective in producing live weight in the
earlier than in the later stages of fattening. This was
well brought out in some other experiments of Lawes
and Gilbert, in which pigs were fattened for a period of
ten weeks. In the first month, less than 4 lb. of food
produced an increase of i lb. in the live weight ; during
the second month, 5 lb. of food were required to produce
the same increase ; while in the last fortnight, as much
as 6 J lb. of food were consumed for each pound of weight
put on. Thus a farmer who is fattening animals for
market should always remember that it is the last few
pounds which are the most expensive to produce, and
that he may easily spend very much more than he
obtains in getting up the final finish of the animal.

The exact value of the various constituents of
fattening stuffs in producing increased live weight has
been worked out, since the experiments of Lawes and
Gilbert, by the much more elaborate investigations which
demand the use of a respiration chamber. By these
means an exact balance-sheet is obtained for the period

212 FOOD REQUIRED [chap.

during which the animal is under investigation, the
composition of the food is known, the composition of
the excreta is determined, and also the amount of
carbon dioxide and methane given off by the animal.
The difference between the carbon in the food and the
excreta will represent the carbon stored up in the body
as fat and lean meat, and as the amount of nitrogen
stored is similarly determined, we can further calculate
how much of the carbon has been stored in the form
of fat. From this kind of experiment it has been
determined that of i lb. of pure digested fat about \ lb.
is stored in the body, supposing that the fat is given in
addition to a maintenance ration and none of it is
needed by the animal for general purposes. The
proportion varies somewhat with the nature of the fat,
the range being from about 47 per cent, to about 60
per cent, as a maximum. Of pure digested protein
about 23 per cent, could be stored as fat. Digested
starch and crude fibre can give rise to about 25 percent,
of their weight as fat, while sugar gives rise to less than
19 per cent. These proportions, however, refer only to
the pure food constituents in their digested form. In
many feeding stuffs the digestible constituents do not
attain these full values, a large and varying proportion
being spent in the work of digestion. Roughly speaking,
in the various cakes and meals the digestible constituents
possess their full value for making fat, such as is shown
by the pure constituents themselves. It is in the case
of the coarse fodders, such as bran, hay, and roots like
mangolds, that a deduction must be made from the full
value to express the value to the animal in producing
increase. We can, in fact, attach to each feeding stuff
which has been under investigation a factor showing the
percentage of their full value which the digestible
constituents will possess in that particular feeding stuff.

XI.] VALUATION OF FEEDING STUFFS 213

For example, the factor for meadow hay is about 70 per
cent., which means that the digestible protein in the
meadow hay, instead of being capable of yielding 23 per
cent, of its weight of fat stored up in the animal (suppos-
ing the hay is added to the diet required for maintenance
so that it can all be utilised for making increase), will
only yield 70 per cent, of its full value of 23 per cent, i.e.
the digestible protein of the meadow hay will only be
converted into 16 per cent, of its weight of stored up
fat. In the calculations in the preceding chapter
(p- 193) we deducted 3 per cent, of the energy con-
tained in the digested part of cotton cake, but 40 per
cent, of the energy contained in digested meadow hay,
in order to find the dynamic energy available for work
or increase.

We can make use of the values which have been
deduced for the digestible constituents in the feeding
stuffs so as to obtain a single figure which sums up the
relative value of the feeding stuff. We have already
attempted to do this in a somewhat imperfect fashion
when discussing the analysis of the feeding stuffs. We
have taken as a kind of guide the fact that the fats are
about two and a quarter times as valuable for fuel
purposes as the carbohydrates, and have also made the
assumption that the proteins are worth about as much
as fats (a commercial assumption which takes into
account the value of its nitrogen as well as the fuel
value of the protein). Thus, we can add to the per-
centages of carbohydrates the percentages of fat and
protein multiplied by 2-3, and so obtain the number of
units which represent the value of the food in terms of
carbohydrates. Such a valuation, which is all or more
than the market takes account of, possesses little exact
value, because it neglects the digestibility of the various
constituents. But if we base our calculations upon the

214 FOOD REQUIRED [chap.

digestible portions only of the food, the results are still
vitiated by failing to take into account the work that is
spent in the digestion of the food. Such a unit system
is not greatly in error when we can confine it to com-
parisons between the highly concentrated foods that
possess nearly full value (p. 183), but breaks down when
the comparison is made between a concentrated and a
comparatively low-grade fodder.

For example, working from Table XVII. the crude
analysis shows for decorticated cotton cake 41 per cent,
of protein and 9 of oil, 50 in all, which, multiplied by 2-3,
give 115. Add 26 per cent, of carbohydrates, and the
total food units amount to 141. Meadow hay, with 10
of protein and 2-5 of fat, to be multiplied by 2-3, give .28
units, which, added to 42 of carbohydrates, give 70 food
units ; making the hay just about half as valuable as the
cotton cake. If we consider the digestible constituents
only, the cotton cake shows 34 per cent, of protein and
8-5 of oil, which, multiplied by 2-3, give 98, to which must
be added 20 of carbohydrates and fibre, making a total
of 118 digestible food units. Meadow hay contains 4
of digestible proteins and i of fat, 4-I- 1 X 2-3 = 1 1 ; adding
41 digestible carbohydrates and fibre we get 52 total food
units, considerably less than half the figure for cotton
cake. The soundest method of comparison which we
have now to explain would give figures of 7 1 and 3 1
respectively, bringing the meadow hay still further
below the cotton cake.

The basis of comparison is derived from considera-
tions— (i) of the digestible constituents of the food; (2)
of the facts we have just stated, that a pound of fat in
the food will be stored to the extent of about 50 per
cent, whereas a pound of protein only gives rise to less
than a quarter of a pound of fat, and a pound of starch
to about the same ; and (3) of the value that these

XI.] STARCH EQUIVALENTS 215

constituents possess in each food when deduction has
been made for the work spent in digestion. In order to
arrive at a convenient number for our comparisons, we
shall take starch as a basis and reduce the digestible
constituents of the other foods into terms of their
equivalents of starch. For example, we have just seen
that a pound of digested fat in the food will give rise to
half a pound of fat in the increase, whereas a pound of
starch only gives rise to a quarter pound of fat in the
increase ; so that if we call 100 the value of starch, then
we should have to express the value of fat by 200.
Similarly, pure protein has a fat-making value about 90
per cent, of that of starch, so that the equivalent in
starch of 100 of protein would be 90. In this case we
are dealing with pure food constituents, but exactly the
same principle may be followed for each feeding stuff as
a whole. We can obtain a single number which repre-
sents the number of pounds of starch which would have
the same fattening effect as 100 lb. of the food
in question. This starch equivalent represents the
summing up of the value of the fat, protein, carbo-
hydrates, and fibre respectively in the food, after the
deduction brought about by the work spent in digestion.
Table XVII., with its list of food compositions and
digestible constituents, also gives the starch equivalents,
which range from as high as 120 for linseed to as low as
1 1 for wheat straw. Such a table of starch equivalents
forms the only sound basis for the comparison of the
value of feeding stuffs, and though there are many other
factors to be taken into account in making up rations
for farm animals, these figures should be considered in
deciding which are the cheaper of the concentrated
feeding stuffs which can be purchased, and also in what
quantities they should be used to replace one another
in a ration. Of course they refer only to the fattening

2i6 FOOD REQUIRED [chap.

increase, and they are based upon experiments with
ruminant animals — sheep and oxen. They do not hold
exactly for fattening pigs, nor do they refer to the
production of energy in working horses. However, the
energy which becomes available for work purposes is
derived from the digestible constituents after deduction
of the work spent in digestion in just the same way as
the materials available for increase, so that no consider-
able error is introduced if we take the starch equivalent
of a food as representing the energy that would be
available for work purposes as well as the surplus that
will be available for making increase of live weight.

One other point, however, we must bear in mind. The
starch equivalent takes into account only the fat-making
power of the food, and pays no attention to the nitrogen
it contains nor the requirements of the animal for
nitrogen. Suppose we have arranged a certain ration
that will supply the requirements of the animal as
regards energy or fat production, basing the ration upon
the starch equivalent of the foods ; we have then also to
make a second calculation of the albuminoid ratio of the
ration in order to make sure that the animal is getting
the proper amount of nitrogen. But with all the know-
ledge that has been derived from the experiments upon
feeding animals, knowledge which is summed up in the
starch equivalents, it would be extremely unwise to
begin to construct rations for farm animals on a priori
principles, considering that they require a certain number
of starch equivalents per diem and a particular
albuminoid ratio, and assuming that it is a matter of
indifference how these units are arrived at. The better
plan is to take as our starting-point certain well-
recognised rations which have been justified in practice
for the particular purpose in view, and see how they can
be modified to secure equal efficiency but greater

XI.] FOOD RATIONS i\1

cheapness. Sometimes also we find that animals are
being grossly overfed, and this we can detect by finding
that the total number of starch equivalents fed is greatly
in excess of the number in a standard ration.

This system of starch equivalents to represent the
relative value of the different feeding stuffs is really the
return to one of the earliest methods by which it was
proposed to bring these substances into comparison.
Early in the nineteenth century Thaer, one of the first
of the German agriculturists to apply science to the
feeding of animals, attempted to draw up a table of
what he called " hay values " for the different foods then
available, these hay values being the equivalents in
good hay of ICXD lb. of the food in question. Thaer's
hay values, however, were almost entirely based upon
the amount of nitrogen contained in food, and it is
rather characteristic of the change that has passed over
the science of feeding stuffs to find that the new starch
equivalents upon which we now base our comparisons of
foods take no account of the nitrogen the food contains.

A few examples may now be given of the use of the
starch equivalents in compounding rations.

The following ration was given to heavy dray horses
working long journeys : —

Lb.

Oats ....

Peas ....

Beans ....

Bran ....

Clover and Rye Grass Hay .

17

and it became desirable to replace the peas, which were
no longer obtainable cheaply. From Table XVII. we
learn that peas possess a starch equivalent of 70 and an
albuminoid ratio of i : 3J. Now maize possesses a
starch equivalent of 68, so that they could be substituted

2l8

FOOD REQUIRED

[chap.

for peas without any serious loss in the supply of energy ;
to be exact, 5 lb. 2\ oz. of maize would be equivalent to
5 lb. of peas. But the albuminoid ratio of maize is
much lower than that of peas, so it is necessary to know
if the albuminoid ratio of the new ration is below what
might be considered safe. This may be calculated as
follows, still using Table XVII. : —

Digestible Constituents.

Food.

Weight.

Protein.

Oil.

carbohydrates.

Food
Units
(X2-3).

Per

Food

Per

Per

Food

Cent.

Units.

Cent.

Cent.

Units.

Lb.

•-

Oats .

5

9

45

5-2

60

45

225

Maize .

5

7

35

4-5

52

68

340

Beans .

5

19

95

1-2

14

48

240

Bran .

4

10

40

3

28

45

180

Meadow Hay

^'%

4

34

I

20

41

348

Clover Hay .

8.5

5*5

47

1-5

29

35

323

296

203

1656

1859

By multiplying the percentages of digestible protein by
the weight of each food we obtain in the third column a
total of 296 digestible protein food units in the ration.
To obtain the number of digestible non-protein units we
must similarly multiply their percentages by the weight
of food, but the oil percentages must be further multi-
plied by 2-3 to make them equivalent to the carbo-
hydrates. Thus we get a total of 203 food units from
the oil in the ration and 1656 from the carbohydrates,
making 1859 non-protein food units in all. This total
must be divided by 296, the number of protein units, in
order to obtain the albuminoid ratio of the whole. As
in the case in question, this is still as narrow as i : 6, we

XI.] FOOD RATIONS 219

may assume that the ration is well above the safety
limit, and that the maize can be substituted for the
peas without affecting the horses. Instead of calculat-
ing out the albuminoid ratio of the whole, we might
have found how much digestible protein the new ration
contained, as follows : —

Lb.

Oats, 5 lb. at 9 per cent.

=

•45

Maize, 5 lb. at 7 „

=

•35

Beans, 5 lb. at 19 „

=

•95

Bran, 4 lb. at 10 „

. =

•40

Meadow Hay, 8i lb. at 4 per cent.

=

•34

Clover Hay, 8J lb. at si „

. =

•47

2-96

Thus the horse would be getting nearly 3 lb. of digestible
protein per diem, and Table XXIII. shows that a horse
in heavy work requires 2 lb. per diem per 1000 lb.
live weight. Thus, 3 lb. would be sufficient if the horses
in question did not weigh more than 1500 lb. To take
another case, a fattening ration for cattle contained : —

Lb.

Swedes . . . .84

Hay .... 12

Linseed Cake ... 5

and it was desired to substitute cotton cake and barley
meal for the linseed cake. Five pounds of linseed cake
is equivalent to 5x76-^100=3-8 lb. starch; it also
contains 5x25-^100=1-25 lb. protein. Barley has a
starch equivalent of 74 and 9 per cent, of digestible
protein, so that 2 J lb. of barley meal would be equivalent
to 2jx-74= 1-65 lb. starch, and would contain -22 lb. of
digestible protein. Three pounds of decorticated cotton
cake with a starch equivalent of 71 and 34 per cent, of
digestible protein would have a starch equivalent of

220

FOOD REQUIRED

[chap.

2-13 lb., and would contain i-02 lb. protein. Thus the
two would together have a starch equivalent of
1-85 4- 2- 13 = 3-98, and would contain •22 + 1-02= 1-24 lb.
protein, or the fattening value of the ration has been
increased a trifle, while the amount of protein remains
the same, so that probably \ lb. could be taken off the
barley meal, as the amount of protein is already pretty
high.

Dairy cows were receiving : —

Lb.

Beans

4

Oats

3

Linseed Cake

2

Bran

4

Straw Chaff

5

Hay

6

Straw

6

and it was desirable to substitute gluten meal and maize
as much as possible for the other concentrated foods,
which had become dear. We may calculate as
follows : —

Starch Equivalent.

Protein.

Beans, 4 lb. .
Oats, 3 lb. .
Linseed Cake, 2 lb.

Per cent.
67
63
76

Lb.
2-68
1-89
1-52

Per cent.

19

9

25

Lb.

•76
•27

•50

Total .

...

6-09

...

i^53

Thus we have to make up 6- 1 lb. of starch equivalent
and 1-5 lb. of protein. Gluten meal has a starch
equivalent of "JJ and 33 per cent, of digestible protein ;
maize has a starch equivalent of 84, but only 7 per cent-
of digestible protein ; thus rather a smaller weight of

XL]

FOOD RATIONS

221

these foods will serve, but the gluten meal must pre-
dominate in order to keep up the protein. We may
try:-

Starch Equivalent.

Protein.

4 lb. Gluten Feed

gives
4 lb. Maize gives .

Per cent.

77
84

Lb.

308
3-36

Per cent.

33
7

Lb.

1-32
0-28

Total .

...

6.44

...

I -60

and obtain rather more both of starch equivalent and of
protein. It would now be wise to replace 2 lb. of the
gluten feed by decorticated cotton cake, both to give
variety and impart consistency to the butter fat.

We then have —

Starch Equivalent.

Protein.

2 lb. Decorticated
Cotton Cake .
2 lb. Gluten Feed .
4 lb. Maize .

Per cent.

71
77
84

Lb.

1.42
1.54
3-36

Per cent.

34

33

7

1
Lb.

0-68
0.66

0-28

Total .

...

6.32

...

1-62

so that we could reduce the amount of the mixture by
about \ lb. per head in order to obtain an almost exact
equivalent to the original ration both in the supply of
energy and of protein.

One more example will suffice to illustrate the
method ; fatting pigs per 100 lb. live weight
received : —

Lb.

Barley Meal ... 4

Pea Meal . . . , i

222 FOOD REQUIRED [chap.

which have to be replaced by maize and decorticated
cotton cake. Four pounds barley meal will supply 2-96 lb.
starch equivalent and 0-36 lb. digestible protein ; i lb.
pea meal will add 070 lb. starch equivalent and 0-17 lb.
protein : total, 37 lb. starch and 0-53 lb. protein. Four
pounds maize will supply 3-36 starch and 0-28 protein,
to which \ lb. of cotton cake will add 0-35 of starch and
0-17 protein, making a total of 3-71 lb. starch
equivalent and 0-45 digestible protein. The protein is
a little lower in this ration than in that which it was
intended to replace, but the albuminoid ratio is still
narrow enough for pigs that have made a good deal of
growth and are chiefly putting on fat. Another ounce
or two of cotton cake and a little less maize would make
the ration almost exactly equivalent to the old one.

Such are the uses to which the following tables can
be put by a practical farmer. In Table XXII I. are given
certain standard rations which have been worked out by
Kellner from the results of a very large number of
exact experiments ; from these he may learn the weight
of starch equivalent and protein that is appropriate to
various farm animals. By the aid of Table XVII. the
farmer can calculate the starch equivalents and digestible
protein in the rations he is using, and correct them if
they depart widely from the quantities given by
Kellner. Finally, if, to suit the fluctuations of the
market or the materials available on the farm, he
wishes to modify his current ration, he can from this
same table calculate the quantities of other foods
necessary to replace those to which he has hitherto
been accustomed.

XI.]

STANDARD RATIONS

223

Table XXIII.— Standard Rations (Kellner),
per 1000 lb. live weight per day.

Dry Matter in
Total Ration.

Digestible.

Animal.

Protein.

starch
Equivalent.

Horse, light work .
Horse, medium work
Horse, heavy work •

18—23
21—26

23—28

10
1.4
2-0

9.2
II.6
15-0

Fattening Cattle-
At 550 lb. live weight
At 770 lb. live weight
At 950 lb. live weight

26
26
26

2-8
2.2
1-5

14.4
11.2
100

Milch Cattle-
Yielding 10 lb. milk per

1000 lb. live weight .
Yielding 20 lb. milk •
Yielding 30 lb. milk .
Yielding 40 lb. milk .

22-27
25—29
27—33
27—34

1.0 — 1.3
1.6— 1.9

2.2—2-5

2.8—3-2

7-8-8-3
9.8— 1 1 -2

11-8-13-9
13-9- 16-6

Fattening Lambs —
65 lb. live weight
no lb. live weight
Full grown ....

31
28
24-32

3-5
2-5
1.6

17
15
14-5

Fattening Pigs—
44 lb. live weight
no lb. live weight
200 lb. live weight

28

6.2
4-5
3-0

33-8

32

24-5

CHAPTER XII

FARMYARD MANURE

Composition of Animal Excretions. Litter. Changes taking place
during the Making and Storage of Manure. Losses of
Nitrogen in Manure-making — Unavoidable or due to
wasteful Methods. Composition of Farmyard Manure from
various Sources. Care of Farmyard Manure. Farmyard
Manure as a Fertiliser. Value of Farmyard Manure. Valua-
tion of Manure Residues derived from the Consumption of
Purchased Feeding Stuffs. Cost of Farmyard Manure.

In the preceding chapter we have learned that the food
of animals contains various substances which are also
food for plants. The fat, the fibre, and the carbo-
hydrates in a feeding stuff are useless, because being
only compounds of carbon, hydrogen, and oxygen, they
are as far as they are digested resolved into carbon
dioxide and water, and even their indigestible portions
when they reach the soil cannot feed the plant. The
nitrogen, however, that the feeding stuff contains is of
the first importance to the plant, and the phosphoric
acid and the potash which are also present in the ash
are equally indispensable elements of the plant food.
We have further learnt that the animal only retains in
its body a comparatively small proportion of the
nitrogen and other valuable constituents of the food.
The actual proportion retained depends upon the age
of the animal ; a young animal putting on flesh, or a
cow in full milk, take from the food more of the nitrogen

224

XII.] ORIGIN OF MANURES 225

and the phosphoric acid than animals which are stationary
in weight, while animals in the last stages of fattening
hardly retain anything at all. It is because the animal
thus keeps back so little of the plant food which was, in
the first place, taken from the soil for the production
of the vegetable feeding stuff, that the excrements of
animals has always been regarded as the most valuable
of fertilisers since any settled agriculture began. In
fact, it is only comparatively recently that any other
fertiliser has been known, for though various industrial
residues, such as woollen rags, clippings of hoofs and
horns, bones, and malt dust have been utilised as
manures for the last two or three hundred years, their
efficacy was very limited, and the business of crop-
raising centred round the proper use of farmyard
manure. The great range of artificial manures now
available, which are either derived from industrial pro-
cesses or represent the accumulated fertility of some
other country, have all come into use since about 1840.

Farmyard manure consists essentially of the excreta
of the various animals, horses, cattle, and pigs kept in
the farmyards, mixed with the litter — straw or other-
wise— which is used to absorb the urine and keep the
animals clean. Very slight consideration shows us,
however, that in the farmyard manure that goes on the
land we are dealing with a very different product from
the fresh mixture of straw and excreta. The mixture,
in fact, undergoes great changes during the time it is
under the feet of the animals, and these changes are
mainly brought about by bacteria. The first change
taking place while the manure is being " made," as a
farmer would say, is continued to a greater or less
extent when the manure is afterwards removed from the
yards or the boxes and made up into heaps. At first
the straw of the manure shows little alteration, but

P

226 FARMYARD MANURE [chap.

as the making process proceeds it is partly broken down
by the hoofs of the animals and partly by bacterial
decay, which latter change proceeds still further during
the storage process until no trace of the straw structure
may remain, but the whole material has passed into a
uniform brown or black mass. The farmer is accustomed
to speak of the fresh straw in manure as " long," while
the old fermented material he calls " short."

Before considering in detail the changes which go on
during the processes of making and storage, we must
refer back to what we have already learnt concerning
the fate of the valuable materials in the feeding stuffs,
fixing our attention for the time being upon the
nitrogen. It will be remembered that portions of the
nitrogenous compounds in the food are indigestible, and
are excreted by the animal in the faeces ; that part,
however, which is digested is excreted in the form of
urea in the urine, except for a small portion which the
animal may retain in the body. This division of the
nitrogen in the food represents a great difference in its
value as a fertiliser. The nitrogen compounds in the
faeces, since they have resisted the attack of the digestion
processes, will be very slowly attacked in the soil by
the bacteria which have to break down and convert
them into ammonia and nitrates before they can feed
the plant. Such materials, then, are slow in their action
as fertilisers, and remain for a very long time unchanged
in the soil. The nitrogen, however, in the liquid portion
of the manure in which it is present in the shape of
urea, will change very rapidly into ammonia, so that it
is an extremely active fertiliser, and far more valuable
than the solid parts of the manure which would contain
the same amount of nitrogen. The same considerations
apply equally to the phosphoric acid and potash ;
whatever part of these constituents in the food is

XII.] MANURIAL VALUE OF EXCRETA 227

digested gets excreted in a liquid and soluble form, and
is therefore in an available state for the plant, whereas
the same constituents in the faeces are insoluble, and
only reach the plant after the lapse of some considerable
time. We have also learnt in the previous chapter that
the richer and more concentrated a food is, the greater
is the proportion of its nitrogen that is digested. For
example, decorticated cotton cake contains nearly 7 per
cent, of nitrogen, and about nine-tenths of that nitrogen
is digested and reappears in the soluble active form of
urea; whereas hay only contains about i\ per cent, of
nitrogen, of which barely half is digestible, while the
other half is excreted in a solid form and will form but
a slow-acting fertiliser. Thus an animal which is fed
with concentrated cakes and meals, such as a bullock
during the fattening process, will be giving rise to much
richer manure than animals which are being kept in a
store condition and only receiving such low-grade foods
as hay, straw, and roots, even though the same amount
of nitrogen is being consumed in the two cases. We
have thus a number of factors affecting the composition
of farmyard manure. Young growing stock take
nitrogen from the food in order to make flesh, and
phosphoric acid in order to make bone ; milch cows take
both phosphoric acid and nitrogen for their milk ; store
stock and working horses do not receive very concen-
trated food, and in their turn give rise to comparatively
poor manure. The animals themselves induce a certain
amount of difference, and though the composition of the
excreta varies so much with the age and food that
analyses are not of much information unless large
numbers are given, it will be found that the urine of
sheep and horses is more concentrated than that of
cattle and pigs, and similarly, that the solid excreta
of the two former are also drier. It is this greater

228 FARMYARD MANURE [chap.

dryness and richness which causes the gardener to
describe horse manure as " hotter " than that produced
by cattle and pigs. Bacterial changes take place in it
more rapidly, and both a greater amount of ammonia
and a greater rise of temperature are produced by the
fermentation. The composition of the resulting farm-
yard manure also varies, to a certain extent, with the
litter employed. Straw is, of course, most general, and
though there are differences in composition between
wheat, oat, and barley straw, these differences are not
great, and are indeed less than the variation in the
composition of any one of them in different seasons.
Speaking generally, the straw is richer in cool seasons
and in more northern climates. The only other sub-
stance at all widely used for litter is peat moss; it is
both somewhat richer in itself in nitrogen than is straw,
and possesses a greater absorbing capacity for the
liquid portions of the manure. It is doubtful, however,
whether the extra nitrogen in the peat moss is of much
service to the plant, nor do the bacterial changes in
making the manure go on so readily as with straw.

The changes we shall now discuss refer to ordinary
farmyard manure made with straw, and these changes
may be divided into two groups — those taking place in
the carbon and the nitrogen compounds respectively.
So far as the carbon compounds — the fibre and other
carbohydrates in straw — are concerned, the chief change
that takes place is the anaerobic fermentation which we
have discussed when dealing with soils. A number of
organisms are present in the air and in dust, which at
once attack the carbohydrate material of the straw and
begin to burn it up, with the production of carbon
dioxide. The organisms, however, soon use up all the
oxygen that is contained in the air entangled in the
manure, whereupon the work is taken up by the

XII.] LOSS OF WEIGHT IN DUNG-MAKING 229

anaerobic organisms, which give rise on the one hand
to carbon dioxide and marsh-gas or hydrogen, and on
the other hand to the dark brown substance of indefinite
composition which we call humus. Analysis of the gas
derived from a newly made dunghill showed that at
first a good deal of hydrogen was being produced, but
when the dunghill was kept tight and moist the most
characteristic fermentation was that giving rise to
carbon dioxide and marsh-gas. Only when the mass
was allowed to get dry, so that air could enter, did the
aerobic fermentation, giving rise to carbon dioxide
alone, begin to take place. It will be seen, however,
that a considerable loss of dry material must take place,
because whether the fermentation takes place in the
presence or absence of air, solid carbohydrates are being
converted into gases like carbon dioxide and marsh-gas.
We find, as a matter of fact, that during the making of
dung, something like a quarter of the original dry matter
is burnt up, and that by the time the dung has been
made and stored, this loss of dry matter has been
increased to one-half, and may easily become greater
with very old short manure.

Turning now to the nitrogenous compounds which
form the chief fertilising elements of the manure, we
have already said that the most important is the soluble
urea contained in the urine. This substance is at once
attacked by bacteria which are always present in cattle
stalls, stables, etc., and by a very slight chemical change
is converted into carbonate of ammonia. Carbonate of
ammonia is a substance which spontaneously splits up
into the two gases carbon dioxide and ammonia, so that
when any liquid containing carbonate of ammonia is
exposed to the air and dried up at all, the valuable
ammonia is at once converted into gas, and escapes. In
this way a great loss of fertilising material can easily

230 FARMYARD MANURE [chap.

arise, and we find as a matter of practice that, despite
the utmost care that can be taken in making dung, there
will always be a loss of nitrogen due to the volatilisation
of the ammonia derived from the fermentation of the
urea. This loss, furthermore, falls upon the most
valuable of the nitrogen compounds, i.e. upon those
which are soluble in water and readily available as food
for plants. A large number of experiments have been
made in which the amount of nitrogen supplied to the
animals was carefully determined and compared with
the amount which was afterwards found in the dung
that had been made, and under the most favourable
conditions of practice the loss amounted to about 15 per
cent, during the making of the manure. The best
conditions are found to be attained by keeping the
straw and manure tightly trodden down beneath the
feet of the animals, and in a fairly moist condition so as
to exclude the action of air. If the straw was allowed
to remain in the yard or box in a loose, open condition,
or if the litter was cleared from under the animals and
simply thrown into a heap day by day, then the losses
of ammonia were very much increased, and often rose to
half of the nitrogen that had been given in the food.
All disturbances of the manure should be avoided,
because they result in very active fermentation, with a
corresponding increase in the evaporation of ammonia.
For example, when fresh strawy manure is repeatedly
turned, it is well known that the temperature of the
whole mass rises to 70° or 80° through the fermentation
that sets in, and quantities of ammonia are given off
during the turning, as may be detected by the smell.
The heat that is generated by the active bacterial
fermentation is utilised by gardeners in the preparation
of a hotbed, and it is well known that only fresh strawy
manure, which contains plenty of easily fermentable

XII.] FERMENTATIONS IN THE DUNG-HEAP 231

urea and soluble carbohydrates in the straw, will get up
heat quickly and serve as material for a good hotbed.
A gardener is also accustomed to let manure in this
way get hot and turn it repeatedly before using it for
such purposes as the growing of mushrooms. Such a
process the gardener calls "taking the fire out" of the
manure, whereby he means that he has got rid of, in
fact burnt up, the easily fermentable material, and at
the same time he has reduced the amount of ammonia,
which otherwise might easily have become injurious to
the roots of tender plants. The fermentation of urea is
not, however, the only change in the nitrogenous
compounds that takes place. The undigested proteins
in the faeces and similar bodies contained in the litter
are attacked by the putrefactive bacteria ; they are
resolved into simpler substances, and may eventually
break down as far as ammonia. At the same time,
however, certain reverse changes take place ; the
bacteria which develop in the dung are so enormous in.
number that they take for themselves an appreciable
percentage of the soluble compounds of nitrogen there
present and convert them into insoluble proteins
forming part of their own tissue. The various changes,
which we have thus indicated as taking place during
the making of farmyard manure while it is still under
the feet of the animals, are also continued during the
storage process. After the manure has been made up
into a mixen or dung-heap, the changes become much
slower, and the loss of nitrogen is comparatively small if
the heap is kept moist and tightly packed. Losses of
nitrogen, however, are constantly occurring, and under
ordinary working conditions we must expect that only
about half of the nitrogen originally contained in the
food finds its way back to the land in the farmyard
manure ; of the other half some will have been retained

232 FARMYARD MANURE [chap.

by the animal, but the greater part will have been
evaporated as ammonia during the making of the
manure and any turning it may have received, while
some will have been set free as nitrogen gas. At the
same time the more fermented the manure becomes,
and the shorter and more rotten its condition, the less
of the nitrogen will be present in soluble form, and the
more of it will have been reconverted into substances
akin to a protein.

In making farmyard manure, the loss of valuable
nitrogen is therefore inevitable, but it is possible to keep
the loss down by taking suitable precautions. In the
first place, it is desirable to keep the manure as long as
possible under the feet of the animals. The least loss
occurs when the manure is made in deep boxes in which
the cattle are fed, and the manure is not removed until
it is ready to go straight out on the land. The turning
of the manure, which must be done when it is carted out
of the yard in order to form the mixen, always results in
loss. Of course, another source of loss in manure-
making arises through washing or leakage of the liquid
manure away. We have already stated that the most
valuable nitrogen compounds are those contained in the
liquid portions of the manure, which is also rich in
potash, so that if this material is allowed to drain away,
the solids that are left behind possess but little value.
The dark brown liquid which we often see oozing from
the dung-heap or leaking from the drains of a badly
kept yard constitutes one of the finest of fertilisers, and
in the management of a yard or cattle stalls the utmost
care should be taken to keep this material soaked up in
the litter. For this reason a partly covered yard is
desirable, so that too much rain is not allowed to wash
through the manure. On the other hand, the wholly
covered yard may easily let the manure get too dry, and

XII.] LOSS OF NITROGEN IN DUNG-MAKING 233

so result in a large evaporation of ammonia. With an
entirely covered yard it is often necessary to pump the
liquid over the litter again in order to maintain it in
a proper condition. Various materials have been sug-
gested to reduce the loss of ammonia. Gypsum, super-
phosphate, kainit, and other substances are sometimes
strewn about the cattle stalls and over the litter with the
idea of absorbing the ammonia whenever it is set free.
All these substances, however, possess but little practical
value; either they are too expensive, or they set up
some secondary injurious action which renders them
unsuitable. The only practical method is to keep the
manure tight and move it as little as possible during
either the making or the storage. It has been shown
that the loss on storage can be reduced by making a
foundation to the new dung-heap of a few inches of old
and well-rotted manure.

It will thus be seen that the changes during the
making of farmyard manure are of a very complex
character. In the first place, we have the purely carbon
compounds of the litter turning into humus — this change
being accompanied by a loss of nearly half of the dry
matter. Secondly, the nitrogenous compounds are
being broken down in one or several stages into the
form of ammonia, some of which escapes. Lastly, other
bacterial changes under certain conditions of free
aeration causes part of the nitrogen to be lost by con-
version into gas, while at all times a certain amount of
reverse change from the soluble to the insoluble protein
state is taking place through the multiplication of the
bacteria themselves. No preservatives are of any avail,
but the loss of nitrogen can be best reduced by moving
the manure as little as possible and getting it on to the
land at the earliest available time. With these general
principles in mind we may now consider a little the

234

FARMYARD MANURE

[chap.

composition of farmyard manure as met with in practice.
It is naturally extremely variable according to the
nature of the animal, and of the food, and again
according to the method of making adopted, and the
age of the product. The average of a large number of
analyses at Rothamsted would show that ordinary
farmyard manure contains about three-quarters of its
weight of water, about 6 parts per thousand of nitrogen,
2 to 3 of phosphoric acid, and 3 to 4 of potash, or
about 15 lb. of nitrogen, 5 lb. of phosphoric acid, and
7 lb. of potash per ton. Thus, farmyard manure is in
the main a nitrogenous fertiliser, and as an all-round
manure it is somewhat deficient in phosphoric acid for
the majority of crops. The effect of feeding and
management is well seen in the first four analyses given
in Table XXIV.

Table XXIV.— Composition of Farmyard Manure.

Nitrogen.

Water.

Phos-
phoric

Potash.

In-

Acid.

Total.

Soluble.

soluble.

I. Made from Roots and

Hay only .

747

0-59

0-l8

0.41

...

...

2. Made from Roots and

Hay and Cake .

74-5

0-82

0-41

0-41

...

3. Made from Roots 'j (

and Hay . • I Ji J

78-0

0-47 ; o-o6

0.41

0-20

0-37

4. Made from Roots (2 |

and Hay and Cake J "^ I

75-7

0-69

0-15

0-54

0.52

0.48

5. Fresh long Straw .

66-2

0-54

0.32

0-67

6. „ „ after

rotting

75-4

o-6o

...

0-45

0-49

7. Very old . .

53-1

o-8o

...

...

0.63

0-67

8. London— Peat Moss .

77-8

0-88

0-51

0-37

0-37

1-02

9. „ Straw .

70-0

0-62

O-IO

0.52

0-48

0-59

No. I shows that fresh manure taken from under the
feet of the animals contained about 0-59 per cent, of

XII.] RICH AND POOR MANURE 235

nitrogen, of which 70 per cent, was in an insoluble
condition, when the animals had been fed upon roots
and hay only. When, however, linseed and cotton cake
had been used in addition, the percentage of nitrogen
had risen to 0-82 per cent, of which less than half was in
the insoluble state. These two analyses refer to
manure taken straight from the boxes ; the next two
refer to manure made in exactly the same way, but
thrown out into the mixen and stored for a month to six
weeks before being analysed. It will be seen that where
roots and hay only had been fed, the manure then
contained much less total nitrogen, only 0-46 per cent.,
though the amount of insoluble nitrogen is about the
same as before, thus showing that the losses had been
falling chiefly upon the soluble nitrogen. Where cake
has been fed the total loss of nitrogen due to storage had
also been great, and had again fallen upon the soluble
portions of the manure ; for whereas, in the fresh
manure more than 50 per cent, of the nitrogen was in
the soluble state, in the stored manure little more than
20 per cent, existed in that state. Thus the difference
between manure made by animals receiving concentrated
foods and those getting only roots and hay, lies chiefly
in the amount of ammonia and other soluble nitro-
genous substances the dung contains. This difference
is well seen in the effect of the manure upon the crops
grown with it. For example, it was found in the field
experiments made with the manures of which the
analyses have just been quoted, that whereas the manure
from the poorly fed animals brought about an increase
of crop amounting to about 30 per cent., the manure
from the richly fed animals gave an increase of over 80
per cent In the second year after the application,
however, both lots of manure gave much the same
return, the manure made from the animals receiving

236 FARMYARD MANURE [chap.

cake only showing a superiority of 7 per cent, over the
other. In slow- acting nitrogenous constituents the
two lots of manure were alike ; the difference chiefly lay
in the ammonia, which had its effect in the first year,
but was not effective afterwards.

Analyses Nos. 5, 6, and 7 show the change of com-
position that dung undergoes on storage. There is a
gradual increase in the percentage of nitrogen, because
the original material has lost carbon compounds more
rapidly than nitrogen, so that the percentage of nitrogen
in the remaining material shows an increase. At the
same time, from other analyses we learn that in very old
short dung but little of the nitrogen remains in a
soluble form or combined as ammonia. Analyses 8 and
9 show the composition of the manure that is obtainable
from London, in the one case made with peat-moss
litter and in the other with straw. The peat-moss
manure is not only richer in nitrogen because of the
nitrogen in the peat moss itself, but it retains a much
higher proportion of the nitrogen in an ammoniacal state
because of the absorptive power of the peat for
ammonia.

From a consideration of the origin of the losses of
nitrogen which take place during the making of dung,
and of the above analyses, a good deal of guidance can
be obtained as to the practical management of farmyard
manure, which remains the fundamental fertiliser in
the ordinary course of farming in this country. In the
first place, since it is clear that the most valuable part
of the manure resides in the liquid, far more care should
be taken to preserve this than is usually the case.
Whether the dung is made in boxes or in yards, there
should be sufficient depth to allow the manure to
accumulate under the animal for the whole winter if
need be, and the floors should be rammed with clay to

XII.] THE MANAGEMENT OF MANURE 237

render them watertight. Yards, in particular, should
be so constructed that the accumulated manure is not
above the general ground line outside, in which case
there will always be a gradual soaking away of the
liquid. On the other hand, yards made thus below the
general ground level are apt to flood in heavy rain, so
that the excess of liquid containing the soluble part of
the manure has to be run off to waste by means of a
drain ; this can, however, be avoided by cutting drains
outside to keep land water from running into the yard,
and by seeing that all the surrounding sheds are
properly provided with guttering. For real economy of
litter, part at least of the yard should be covered ; if the
whole yard is covered, a certain amount of care is
necessary to prevent the dung from getting at times too
dry. Only just enough litter should be used to soak up
the urine, and in order to prevent the liquid working up
to the surface with the trampling, the floor of the yard
should run down to a slight hollow, filled at first with
something stiff like bean haulm or coarse peat moss, in
which the excess of liquid may collect. Above all, the
manure should be kept tightly trampled ; the greatest
amount of loss takes place when the urine falls on a thin
layer of loose strawy litter. The yards and boxes should
be deep enough to carry the animals through the whole
winter, so that they need not be cleaned out except
when dung is wanted to go straight on the land. A box,
for example, 8 feet by 10 feet in area, with an available
depth of 3 feet, would hold about 9 cubic yards, or 8
tons of dung when well trodden down. This would
accommodate two beasts, each receiving 10 lb. of straw
in food and 12 lb. in litter per diem, for four months.
As far as possible, manure in the spring should be left
undisturbed until the autumn, it may then be carted out
on to the stubbles and ploughed in where potatoes or

238 FARMYARD MANURE [chap.

roots are to be taken in the following spring. Even
on the lightest soils the land will be more benefited
thus, than if the manure is made up into a mixen and
only put on immediately before the roots are grown.
Sometimes, of course, a potato grower must have a
supply of well -rooted manure to put in the drills
immediately before planting ; this can often be got
from the lower layers of the earliest used boxes or
yards, since a mixen should be avoided as much as
possible. The principle to keep in mind is that every
disturbance of farmyard manure results in loss, and that
the shorter the time which elapses between the dropping
of the dung and its application to the land, the less this
loss of fertilising material will become.

In considering the value of farmyard manure as a
fertiliser, one has to keep in mind that it is an essential
product of the farm, and that it must constitute the
main source of manure for the land under the conditions
of ordinary mixed farming, where artificial manures will
only be used as supplements and not as rivals. It is
only in certain special cases, such as potato or hop
growing, where the ordinary course of farming does not
supply as much farmyard manure as is wanted, that the
question has to be decided whether artificial manures or
dung from the towns shall be purchased, or again,
whether stock shall be fattened solely with the view of
making manure.

As a fertiliser, the chief value of farmyard manure
lies in the fact that it contains all the elements of a
plant's nutrition — nitrogen, phosphoric acid, and potash
— though for a well-balanced manure the phosphoric
acid is comparatively deficient. Moreover, the nitrogen
is present in various forms of combination, varying from
the rapidly acting ammonia compounds, down to some
of the undigested residues, which will remain for a very

XII.] USE OF FARMYARD MANURE 239

long period in the soil before becoming available for the
plant. In consequence, dung is a lasting manure, which
accumulates in the soil to build up what a farmer calls
"high condition" — the state of affairs which prevails
when the reserves of manure in the soil are steadily and
continuously passing into the available condition in
sufficient amount for the needs of the crop, so that
there is no necessity for freshly applied active manure —
a mode of nutrition which results in healthy growth and
good quality. But however marked the farmer's prefer-
ence is for such lasting manures, the delay in realising
the capital they represent means a certain amount of
loss ; besides which, some of the constituents of farm-
yard manure are so slowly acting as to be hardly
recoverable during the lifetime of the tenant.

An examination of the records at Rothamsted show^
that when farmyard manure was put on at the rate of
14 tons per acre every year for the wheat crop, at the
end of fifty years only 26 per cent of the nitrogen applied
had been recovered in the crop, and less than 20 per cent,
remained stored up in the soil ; more than half had
been wasted either by bacterial processes giving rise to
nitrogen gas in the soil, or by the washing out of nitrates
into the drains. This, of course, is a very extreme case,
both because wheat is a plant taking a comparatively
small amount of nitrogen out of the soil, and also
because the land had become so laden with farmyard
manure, that all the processes of bacterial decay and
destruction of the nitrogenous compounds had been
increased far beyond the normal. On the mangold plot,
about 32 per cent, of the nitrogen in the dung has been
recovered when the dung had been put on year by year,
but when the manure was only put on once in four years,
about three-quarters of the total nitrogen applied was
recovered in the four crops grown with that manure and

240 FARMYARD MANURE [chap.

no other fertiliser. Other experiments at Rothamsted
show how lasting is the effect of farmyard manure, ie.
how very slowly some of the nitrogenous compounds
get oxidised by bacteria and converted into a form
available for the plant. In two cases, on the grass field
and on the barley field, farmyard manure at the rate of
14 tons to the acre was applied for eight years and
then discontinued. The effect of that application can
still be traced more than forty years later, in the higher
crop given by these manured plots than by the plots
which had remained unmanured the whole time. Of
course, these long-continued effects of farmyard manure
are not great in themselves, and will only be perceptible
when the land has been reduced to the lowest ebb of
fertility by continual cropping without manure. Since
the greater part of the nitrogen contained in farmyard
manure is not in a condition to be utilised by the plant
until it has first been attacked by bacteria and converted
into ammonia or nitrates, it may happen that the plant,
though it has been well supplied with farmyard manure,
cannot obtain the nitrogen therein quickly enough,
when the season is otherwise favourable to growth.
For example, we see from the Rothamsted experiment
with mangolds that in years of large crop the plant
which receives some active source of nitrogen like
nitrate of soda will grow heavier crops than those which
receive farmyard manure alone ; although the amount
of nitrogen in the manure applied to the latter, in
addition to that which is already stored up in the soil,
may be far in excess of the plant's requirements. From
many experiments it can be demonstrated that when
the grower is aiming at a very large crop, for example
of potatoes or mangolds, it is more economical to obtain
this by using a mixture of dung and active fertilisers
than by increasing the amount of dung alone. The

XII.] PHYSICAL EFFECTS OF FARMYARD MANURE 241

slowness with which dung can yield up its contents of
nitrogen is particularly noticeable in the early spring,
when the land is cold and bacterial actions in conse-
quence go on very slowly. However rich the soil may
be in farmyard manure and its residues, the gardener
who is in a hurry to push on early production, finds it
very necessary to use an immediately active nitrogenous
manure like nitrate of soda.

The value of farmyard manure to the land is by no
means confined to its fertilising action ; its physical
effects upon the texture and water-holding powers of
the soil are equally important ; indeed, for some crops,
and particularly in droughty seasons, these factors count
for more than fertilisers towards ensuring a good yield.
The farmyard manure, as it rots down in the soil, goes
to restore the stock of humus, which otherwise is always
tending to oxidise and diminish, and the humus,
considered merely from the physical side, contributes
largely to the fertility of the soil. In the first place, it
improves the texture of all soils ; to sands it gives
cohesion and water-retaining power, while by loosely
binding together the finest particles of clay soils it
renders them more porous and friable. When a piece
of old grass land, even on the stiffest of soils, has been
ploughed up, it is easy to see the beneficial effect of the
humus that has been accumulated ; after the winter the
plough slice will crumble naturally so as to harrow down
at once to a mellow seed bed, whereas a neighbouring
piece of the same soil that has long been under arable
cultivation will only show a number of harsh, intractable
clods. The importance of a good seed bed to the future
well-being and ultimate yield of the crop can hardly be
exaggerated ; it is the basis of all good farming, so that
even when the fertilising properties of farmyard manure
have been replaced by artificial manures, some other

Q

242 FARMYARD MANURE [chap.

means, such as the ploughing-in of green crops, must be
employed in order to maintain the stock of humus.
The effect of dung upon the soil is seen in two ways.
In the first place, it will cause the surface soil to absorb
more of the rainfall and to hold it up near the surface,
so that cases may be found in which the subsoil is
actually drier where farmyard manure has been used,
because the rain has been held near the surface and
therefore within reach of evaporation. But the chief
value of the humus which the farmyard manure con-
tributes to the soil lies in the better texture that it
induces. It is particularly noticeable in the number of
plants that are obtained when growing turnips and other
root crops. When soils have long been farmed without
organic manure, however rich they may be in the con-
stituents of plant food, there will be great difficulties and
even total failures in obtaining a proper stand should
the weather conditions have been unsuitable soon after
sowing.

In ordinary mixed farming, undoubtedly the best
way of utilising farmyard manure is to apply it to the
root crops, and especially to mangolds and potatoes.
Swedes require much less nitrogen than do the other
root crops. They also require a firm but fine tilth ; in
consequence, not more than lo to 12 tons of dung per
acre should be given for swedes, and it should be applied
in the autumn, in order that it may become well rotted
down before the spring cultivation begins. But up to
20 tons of dung per acre can be profitably employed for
mangolds and potatoes, and it can, if necessary, be
applied immediately before sowing. In America where
corn (maize) takes the place of root crops, the farmyard
manure may most profitably be applied to that crop. Any
surplus dung, after the requirements of the root crops
have been satisfied, is probably best given to the young

XII.] MANURING BY FEEDING 243

seeds in the early winter, to act both as a fertiliser and
as a mulch. The seeds benefit greatly, and at the same
time much of the added fertility is retained for the corn
crop that follows ; manuring the young seeds is certainly
preferable to the very general custom of manuring the
old ley before it is ploughed up for wheat or oats. A
certain amount of the farmyard manure made on the
farm should, however, always be reserved for the
meadow land, especially on light soils and on land
comparatively newly laid down to grass. Of course,
dung would be wasted on rich grazing land ; it is the
thin light soils that are cut for hay, or grass land that
has only been laid down for a few years and has had no
time to accumulate a stock of humus, which are most
benefited by an occasional dressing of farmyard manure
— once in every four or five years.

In Great Britain many farmers use but little fertiliser
for their land beyond the farmyard manure that they
make, but this farmyard manure contains not only the
fertilising constituents which have been drawn from
the soil of the farm and are contained in the roots and
hay fed to the stock and the straw that has been
trampled down as litter, but they also enrich the dung
by the consumption of imported feeding stuffs, such as
oilcakes, maize, and feeding meals, etc. It therefore
becomes a question of some importance to determine
what extra value is imparted to the manure by these
purchased feeding stuffs. Specially is this important
when the tenant is about to leave a farm, when the
dung that has been made during the last year of his
tenancy still remains in the yard and has not produced
a crop. If purchased linseed cake, cotton cake, maize,
and similar foods have been fed to the stock which
made the manure, there will be left on the farm nitrogen
and other valuable constituents which are just as much

244 FARMYARD MANURE [chap.

unused fertilisers as if they were contained in bags still
unopened from the manufacturer. We have seen in the
analysis that the manure made from rich feeding stuffs
is very superior to that made from low-grade materials
like roots and hay alone. From the records of the
experiments upon fattening animals, we can obtain
some idea of how much nitrogen contained in the food
eventually reaches the soil. We have seen, for example,
that the animal only retains perhaps lo per cent, of
that which was given to it in the food, but that in
making the manure, considerable losses set in even
under the best conditions — losses due to the volatilisation
of ammonia and to the setting free of nitrogen gas by
bacteria. Though these losses are variable, and depend
both upon the nature of the stock and the care taken in
managing the manure, we can assume as a working
compromise that half of the nitrogen contained in the
food fed to the different classes of animals upon the
farm will eventually reach the land again. Of the
nitrogen and phosphoric acid, the losses are confined
to the proportion retained by the animal and whatever
may be lost by drainage, but we may again assume
that about three-quarters of the phosphoric acid and all
of the potash contained in the food will come back to
the land. Acting upon these assumptions, we may
proceed to calculate the value of the materials which
the consumption of a ton of any given food-stuff will
add to the manure made during its consumption. To
take a concrete example — the decorticated cotton-seed
cake contains about 6-9 per cent, of nitrogen, and we
assume that half of this (3-45 per cent.) finds its way
into the manure. If, on the principle explained before,
we reckon that the unit, i.e. i per cent, of nitrogen, is
worth I2S., then the value of the nitrogen added to the
dung by the ton of cake will be £2^ is. 6d. The cake

XII.] COMPENSATION FOR PURCHASED STUFFS 245

also contains 3-1 per cent, of phosphoric acid, three-
quarters of this at 3s. a unit would amount to 7s. ; lastly,
there is 2 per cent, of potash, which at 4s. a unit would
add 8s. to the value of the manure. The total value,
then, that the consumption of a ton of decorticated
cotton cake adds to the manure is ;£"2, is. 6d. + 7s. + 8s.
= £2^ 1 6s. 6d. Again, in the case of maize there is only
1-7 per cent, of nitrogen in the food, the value of half of
which at 12s. a unit would be los. ; there is 0-6 of
phosphoric acid, three-quarters of which would add
IS. 6d., and there is 037 per cent, of potash, which would
add a further is. 6d., making 13s. in all as the value
added to the manure by the consumption of a ton of
maize. It will be seen that these two foods differ very
greatly in the value of the manurial residues they leave
behind when they have been consumed by stock,
the maize being a food rich chiefly in oil and carbo-
hydrates, which possess no fertilising value. The value
of these foods for manure-making purposes again bears
no relation to their cost, which is determined by the oil
and carbohydrates present as much as by the proteins.
The figures that we have thus deduced for the addition of
fertilising material to the dung due to the consumption
of purchased foods, represent what is sometimes called
the compensation values to be attached to these foods,
because they represent the price which should be paid
to a tenant leaving the farm for the purchased food-
stuffs which had been consumed during the last year
of his tenancy, from the manure made by which, of
course, he has as yet reaped no benefit. They are,
however, we have said before, only rough approxima-
tions to the real truth. On many farms the farmyard
manure is so neglected that the loss of nitrogen becomes
much more than the 50 per cent, that we have assumed,
and the longer the manure remains out of the land and

246 FARMYARD MANURE [chap.

lies about in the yard, the greater will this loss become.
On the other hand, when food is fed upon the land and
is not used for making manure in yards or stalls, as,
for example, when the sheep are folded on the land or
cattle are given cotton cake while they are grazing, the
losses of nitrogen would be much reduced, because
the urine which contains the valuable part of the
nitrogen is at once absorbed by the soil, and none of
the usual wasteful actions are set up. On the other
hand, a farm producing much milk takes rather more,
both of phosphoric acid and nitrogen, out of the food than
the proportions we have been assuming, so that dung
made by milch cows is never very rich. But taking
all these things into account, we shall not be far
wrong in assuming a loss of half of the nitrogen under
the ordinary conditions of mixed farming, and in
thereby deducing compensation values in the manner
we have set up above.

We can apply the same principles to obtain the
value of a ton of farmyard manure. Of course, as a
rule, the farmyard manure is a normal product of the
farm, and the only problem is to make it as carefully as
possible, and apply it to the best purpose afterwards.
But there are occasions, especially in growing of crops
like market garden produce, potatoes, hops, when it
becomes a question of whether it is more profitable to
buy farmyard manure or artificial fertilisers, or to keep
stock in order to make the farmyard manure that is
required. It will be found that if the farmyard manure
account is charged with the litter, and the compensation
values of the foods calculated in the fashion described
above, on the assumption that half of the nitrogen,
three-quarters of the phosphoric acid, and all the potash
contained in the food found its way into the manure,
then the farmyard manure will cost from 8s. 6d. to 12s.

XII.] COST OF FARMYARD MANURE 247

the ton by the time it is ready to go on the land ; the
difference in price representing a real difference in value,
according to whether much concentrated food has been
consumed during its manufacture or not. The farmer,
then, who is faced with the problem of specially making
farmyard manure, or on the other hand, buying artificial
fertilisers or town dung, ought to reckon that such
manure of fair quality will cost about los. a ton to
make. In experiments dealing with fertilisers, this
figure should be taken as an average valuation of well-
made farmyard manure. It is noticeable also that if
we proceed to a valuation of farmyard manure on the
basis of the fertilising constituents it contains at the
usual unit rates, its price would work out to about
the same figure of los. a ton.

CHAPTER XIII

ARTIFICIAL MANURES AND FERTILISERS

Nature of a Fertiliser. Fertilisers containing Nitrogen — Nitrate
of Soda, Sulphate of Ammonia, Soot — their Use and Value.
Fertilisers containing Phosphoric Acid. Bones, Superphos-
phate or Acid Phosphate, Basic Slag or Phosphate Powder,
Ground Rock Phosphate. Potash Fertilisers. Guanos.
Industrial Residues. Tankage. Action of Fertilising
Ingredients upon Crops. Expenditure on Fertilisers.
Character of Fertiliser required for particular Crops.
Valuation of Fertilisers.

It has already been explained that of the elements
found in a plant, a certain number are absolutely
essential to its development, but that most of these are
ordinarily to be found in the soil in sufficient quantities
for the plant's requirements. There are, in fact, only
three of these substances in which the soil shows any
deficiency, and the bodies which we call manures or
fertilisers are substances containing one or more of
these three elements — nitrogen, phosphorus, or potash.
At the present time the terms artificial manure and
fertiliser are used indifferently to indicate such com-
mercial materials as are of value to the plant, whatever
their origin ; from the farmer's point of view an artificial
manure is any concentrated plant food which he
purchases and receives in bags. In reviewing these
substances we must begin by drawing a distinction
between the fertilisers which contain only one ingredient

248

CHAP. XIII.] ESSENTIAL CONSTITUENTS 249

of value to the plant — the single manures, as we may
call them — and the compound manures which contain
two or more fertilising ingredients. We may again
divide these materials into nitrogenous, phosphoric, and
potassic manures, according to the elements which
predominate in them. The next most important factor
to be taken into account is the actual percentage of
fertilising material which the manure contains. With
certain exceptions to be dealt with later, i lb. of
nitrogen possesses the same value in whatever fertiliser
it may be contained, so that we must compare all
nitrogenous manures on the basis of the amount only
of nitrogen they contain. Thus, if sulphate of ammonia
contains 20 per cent, of nitrogen, and soot only 4 per
cent., then sulphate of ammonia is five times as valuable
as the soot, if we leave out of account certain other
considerations which may give an extra value to one
or other of these substances. In the case of sulphate of
ammonia, only the 20 per cent, of nitrogen possesses any
value to the soil or plant, the remaining four-fifths,
however indispensable to the constitution of the manure,
must be regarded as surplusage. It should not, however,
be considered that there is any necessary waste, though
the manure does only contain a proportion of the
pure fertilising constituent, for these bodies must be
combined to be of any use. Pure nitrogen gas, for
example, as we have already stated, exists in air in
enormous quantities, but is of no value to the plant
until it has been brought into combination. Pure
phosphoric acid, again, though it does exist and would
act as a fertiliser, is a very scarce material, of interest
only in the laboratory. Thus the surplusage which
may be present in a manure, in addition to its percentage
of nitrogen or phosphoric acid, must be regarded as the
vehicle necessary to carry these valuable constituents.

250 ARTIFICIAL MANURES [chap.

Among the fertilising constituents nitrogen must be
given the first place. Not only is combined nitrogen
much more expensive than either potash or phosphoric
acid, I lb. costing about 6d. (12 cents), but as a
fertiliser it seems to have a much more direct and
immediate action upon a plant than the other two
substances, which are at bottom equally indispensable.
We find that nitrogen pushes on the first vegetative
development of the plant, promotes its growth in fact,
thus enabling it to search the ground more thoroughly
for phosphoric acid and potash which may there be
present. For some little time, indeed, crops may be
grown by the aid of nitrogenous fertilisers alone, and
there is always some tendency to use an excess of these
substances in comparison with manures containing
phosphoric acid and potash, which make less immediate
show. Of the purely nitrogenous fertilisers there are
five which are commonly employed ; sulphate of
ammonia, the most concentrated, contains about 20 per
cent, of nitrogen, and nitrate of soda contains about 15^
per cent. To these concentrated fertilisers two new
rivals have recently arisen in the shape of calcium
cyanamide or nitrolim, containing about 18 per cent, of
nitrogen, and nitrate of lime, containing about 1 3 per
cent. These latter materials are manufactured artificially,
the nitrogen they contain being derived from the
atmosphere. Lastly comes soot, a waste material which
contains a small quantity of ammonia, showing from i
to 5 per cent, of nitrogen according to its purity and the
nature of the material from which it has been derived.

Sulphate of ammonia is a product recovered in
the manufacture of coal-gas, coke, and other industries
involving the destruction of coal. It is a pale grey,
crystalline substance that is freely soluble in water,
though it remains dry, and does not naturally run down

XIII.] SULPHATE OF AMMONIA 251

into a liquid by absorption of water from the air.
Although it is so soluble in water, it can be applied to
the soil without any danger of washing out, because it
there interacts with the humus and clay, and is converted
into substances which are for the time insoluble. It
should not, however, be used as a manure long before
the plant is ready to take it up, because it is readily
converted by the bacteria we have spoken of before into
nitrates which do wash out of the soil. Sulphate of
ammonia is therefore best employed as a top-dressing
or for root crops, in which case it is put in the soil at the
time of year when there is very little danger of any
washing out. It is found by experience that when a
concentrated nitrogenous fertiliser is needed, sulphate of
ammonia is most suitable for shallow-rooted crops, like
barley, swedes, turnips, potatoes. On chalky soils and
on very heavy clays it is the most useful nitrogenous
fertiliser, but it should not be used on light sands nor on
peaty and other soils which have any tendency to get
sour. Being such a concentrated fertiliser, only small
quantities are, as a rule, required. It should be
remembered also that when used as a top-dressing it
will scorch and kill the foliage of any green plant on
which it happens to rest. This is not because it is
poisonous, but merely because any soluble salt in contact
with the green leaf of a plant will draw water from the
tissues, and eventually kill the leaf by so doing. For
this reason sulphate of ammonia mixed with sand is
often used to kill out weeds on lawns ; when sprinkled
over the lawn the soluble material lodges in the crowns
and rests on the broad leaves of weeds like plantains,
buttercups, and daisies, eventually killing them, whereas
it does not touch the upright leaves of grasses but slips
down to their roots and acts as a fertiliser. If a satis-
factory result is to be obtained, however, the weather

252 ARTIFICIAL MANURES [chap.

must remain dry ; should rain come the sulphate of
ammonia dissolves, washes down into the lawn, and
fertilises weeds and grass alike. A more effective plan
is to choose a fine morning and put a pinch of sulphate
of ammonia into the crown of the plantains and other
flat-leaved weeds.

Nitrate of soda is a substance obtained from certain
extensive natural deposits in Chili, and has been
brought to this country since about 1835. It forms a
grey or pinkish soluble salt which easily picks up water
from damp air, and will even pass into a liquid state
when left to itself. It is not retained in any way by the
soil, and is most commonly employed as a top-dressing.
Since it has to undergo no change but can feed the
plant directly, it is the most active of all fertilisers, and
is particularly effective in forcing on a plant into very
rapid growth. Because of its immediate availability, it
is also a specially valuable manure in early spring, when
the natural processes producing ammonia and nitrates
are so slowed down by the cold, that even in rich soils
the plant is not obtaining sufficient nitrogenous food.
Thus, nitrate of soda is particularly useful to the
market gardener who needs to force on his crops rapidly
or to get them growing specially early, and very large
quantities are thus employed with profit. Nitrate of
soda is particularly valuable as a top-dressing for wheat
and maize, for grass land that is being laid up for hay,
for mangolds, and for cabbages. On heavy soils it often
forms an unsatisfactory manure, because it leaves the
land in a state of bad tilth, very wet and sticky after
rain, and then drying into hard clods. In such cases a
mixture of equal parts of sulphate of ammonia and
nitrate of soda is even more effective than either separ-
ately, and does not interfere with the texture of the soil.
It is because of this bad effect upon the tilth that

XIII.] NITRATE OF SODA 253

nitrate of soda gets called a stimulant or a scourge, and
is considered to rob the land. This, however, is no
more the case with nitrate of soda than with any other
single manure. Whenever crops are grown with nitrate
of soda alone, we are removing in the crop nitrogen,
phosphoric acid, and potash, only one of which is being
replaced, so that the land must inevitably become
poorer in the other two constituents. But when nitrate
of soda is employed with the potash and phosphoric
acid that are equally required by the plant, the fertility
of the land is maintained unimpaired, as may be seen
from the Rothamsted experiments, where crops have
been grown with such a mixture on the same land for
nearly seventy years without showing any decline in the
average yield. The other two fertilisers, nitrolim and
nitrate of lime, are not so widely known. Nitrolim
behaves in much the same way as sulphate of ammonia,
but is slower in its action, and ought to be put on the
land before a crop is sown. Nitrate of lime is very
similar to nitrate of soda, though it has not the same
injurious effect upon the texture of the soil. It should
be mentioned that nitrate of soda is poisonous to stock,
and deaths have been reported through animals licking
the bags, or drinking water in which nitrate of soda had
been dissolved.

Soot, the other manure which has been men-
tioned as containing nitrogen and no other fer-
tilising ingredient, is chiefly used as a top-dressing
for wheat in the spring. For this purpose it is very
valuable, not only because of the fertilising effect
of the small amount of nitrogen it contains, but also
because it helps to protect the wheat from the attack
of slugs and snails, which are very active at that time of
the year. Moreover, the dark colour the soot imparts
to the soil is of value, because it causes an increased

254 ARTIFICIAL MANURES [chap.

absorption of the sun's rays, and on sunny days will raise
the temperature of the soil by one or two degrees.
Soot is very variable in composition, and cannot, as a
rule, be purchased with any guarantee as to the amount
of nitrogen it contains. The best guide is its lightness.
A good sample should be free from all admixture of
cinders and similar refuse, and should not weigh more
than 28 lb. per bushel.

The second of the great groups of fertilisers is made
up of those which contain phosphoric acid as their
valuable constituent. Of these, bones in various forms
constitute the oldest and still among the most widely
used of fertilisers. A bone consists of a mineral frame-
work containing phosphate of lime mixed with a little
carbonate. This mineral framework we can see left
behind if we put an ordinary bone into the fire or in a
muffle furnace. On the other hand, if we immerse a
similar bone in dilute hydrochloric acid, after a day or
two all the mineral matter will become dissolved in the
acid, and there will be left behind the cartilaginous
framework of the bone, consisting of material contain-
ing nitrogen, which will be converted into gelatine when
heated up with water at high temperatures. At one
time the bones were only roughly broken up, and then
proved to be only a slow-acting, if effective, fertiliser.
Nowadays it is customary to remove as much of the fat
as possible, and then grind the bones to a fine powder,
which is sold as " bone meal." Owing to the toughness
of the organic matter contained in the bones, the bone
meal is never really fine, and though it is highly valued
on pastures and on some of the lighter arable soils, it is
comparatively slow in its action and unremunerative in
its results.

In addition to bone meal, various other manures are
prepared from bones ; sometimes they are treated with

XIII.] SUPERPHOSPHATE 255

oil of vitriol, and yield a soluble acid phosphate, similar
in its action to the superphosphate to be dealt with
later. These dissolved bones or vitriolised bones, as
they are called, form rather a damp mass, which is not
very easily sown from a machine ; they offer no special
advantage over a mineral superphosphate which is
cheaper, even after making allowance for the nitrogen
the bone manure also contains. Again, the bones are
sometimes submitted to the action of superheated
steam before grinding, thus taking out of them most of
the material containing nitrogen ; the resulting steamed
bone flour is a friable powder rich in phosphates but
containing only about i per cent, of nitrogen, and
forming a valuable manure on light soils. Bone
manures, however, no longer possess their former
importance when they were almost the only source of
phosphates. For many years deposits of mineral
phosphates of lime have been worked for manurial
purposes. Sometimes these rock phosphates are
ground to a very fine powder, which is practically
insoluble in water but which does slowly become
available to the plant in soils rich in organic matter and
well provided with moisture. In the United Kingdom,
however, such ground rock phosphates are rarely
employed ; as a rule, the mineral is treated with oil of
vitriol and converted into the soluble phosphate known
as superphosphate or acid phosphate. Superphosphate
of lime, which, for manurial purposes, was invented by
the late Sir J. B. Lawes, is the most widely employed of all
the phosphatic manures. Being soluble in water, it
becomes disseminated throughout the soil, and is there
reprecipitated wherever it comes in contact with
particles of carbonate of lime or humus. Thus the
surface soil gets mixed with precipitated phosphate of
lime in a very fine state of division, and it is to the fact

256 ARTIFICIAL MANURES [chap.

that this precipitated material is so much finer and
more thoroughly mixed with the soil than any ground
insoluble material can be, that the activity of the super-
phosphate is due. Superphosphate is manufactured in
several grades of concentration ; it is adapted to all crops
for which phosphatic manure is wanted, except for
turnips on an acid soil where " finger-and-toe " occurs.
Nowadays the great rival to superphosphate is a
fertiliser called basic slag, which is obtained as a by-
product in the manufacture of steel from pig-iron,
contaminated with phosphorus. As it occurs in
commerce, basic slag is a very fine dark powder,
insoluble in water, containing about 40 per cent, of
phosphate of lime and also a certain amount of free
lime. This free lime, together with an excess of loosely
combined lime, gives the manure its basic character ; it
is alkaline in contradistinction to the acid nature of
superphosphate, and it adds lime to the soil, whereas
superphosphatic takes it away. The phosphates of
basic slag are insoluble in water, but they are easily
attacked by the carbon dioxide contained in the soil
water, and it is found in practice that they are readily
available to plants, especially upon soils that are damp
and sour. Basic slag has proved of particular value as a
fertiliser for all pastures on clay land, in which case the
free lime that is also present adds greatly to the value
of the manure. Its value as a fertiliser on arable land
of a light and dry character has hardly been enough
recognised in the United Kingdom. Basic slag is also
sometimes known as Thomas's phosphate powder or
basic cinder. It should be carefully distinguished from
the ordinary slag of ironworks, which contains no
phosphoric acid to make it valuable. Many of the
compound fertilisers to be dealt with later also contain a
considerable quantity of phosphoric acid ; indeed some

XIII.] POTASH MANURES 257

of the guanos contain so little else that they may be
practically regarded as phosphatic manures, whose
action is very similar to that of the steamed bone flour
and bone meal mentioned above.

The third group of fertilisers are those which supply
the element potash, but as this substance is naturally
abundant in many soils, especially those containing much
clay, the need for potassic fertilisers is not so much recog-
nised, and they are less generally employed by farmers
than either nitrogenous manures or phosphates. For a
long time the only source of potash was the ashes of
wood and other vegetable matter like kelp, but these
sources have been entirely superseded by the opening
up during the last half century of enormous mines of
potash salts near Stassfurt, in Germany, whence the
world's supply of potash is now almost wholly derived.
Various grades of manures are put upon the market,
the most common being an impure material containing
about 12 per cent, of potash, which is called kainit,
though nowadays it has little right to the title, since it
consists almost entirely of chlorides of potash, soda, and
magnesia. As a rule, kainit is just as valuable, potash
for potash, as the more concentrated fertilisers, because
the salt and other impurities wash out of the soil
without doing any harm. In some cases, however, it is
desirable to use pure materials, and sulphate of potash
of two grades of purity, and muriate of potash, the most
concentrated of all, can then be obtained. There is a
general idea that with crops like potatoes, for which
potash salts are largely employed, the sulphates give rise
to better quality of the product than do the chlorides.

Of the compound fertilisers the oldest and
still the most widely employed are the guanos, of
which the Peruvian guanos, obtained from some of the
rainless islands off the west coast of South America, are

R

258 ARTIFICIAL MANURES [chap.

by far the most important. These guanos consist of
the excrements of the sea-birds which frequent these
islands in enormous numbers during the breeding
season. Owing to the absence of rain, the material
accumulates from year to year with very little change, and
can be excavated and readily reduced to a fine powder.
It, however, undergoes some slow process of decay and
washing, so that while the recent deposits contain as
much as 1 5 per cent, of nitrogen and only about 20 per
cent, of phosphates, in the oldest deposits the nitrogen
is reduced to less than 3 per cent., while the phosphates
have risen to nearly 60 per cent. It is thus very
important to purchase a guano according to its analysis,
and not by its name alone. In any case these fertilisers
will be found to be dearer than the same amount of
nitrogen and phosphoric acid in other forms, the extra
price representing the farmer's long experience of their
kindly action upon his crops. The richer guanos, con-
taining 6 per cent, of nitrogen and upwards, are
extremely active fertilisers, the nitrogen being in forms
which readily get converted into ammonia, and the
phosphates being comparatively soluble in water. They
are also very safe, well-balanced manures, containing
nitrogen and phosphoric acid in much the same pro-
portions as are required by plants, and also a little
potash. Moreover, many different compounds of
nitrogen are present which differ in the rate at which
they will decay, so that the plant is fed continuously, and
suffers from no excess of available nitrogen in the soil at
any time. Such a fertiliser leads to a steady, equable
growth, which is generally attended by superior quality
in the product Thus the Peruvian guanos become
excellent fertilisers for crops where the quality is of
importance, and where it is not necessary to cut down
the expenditure on fertilisers to the lowest limit.

XIII.] MEAT AND FISH MANURES 259

Somewhat similar in their composition and in their
action to the Peruvian guanos are a number of manures
which are manufactured out of residues of meat and
fish that accumulate in various processes of preserving,
canning, and packing these articles for food. It is
customary to extract as much as possible of the fat of
these materials, and then reduce them to a very fine
powder, which will contain nitrogen varying from 4 to
10 per cent, and phosphates which lie between 10 and 50
per cent. These fertilisers decay in the soil, and yield
ammonia in the same steady, continuous fashion as the
nitrogen compounds of the Peruvian guano, and we
may take it as a rule that the richer they are in
nitrogen the more active will that nitrogen be. Meat
and fish guanos, as they are called, form valuable
fertilisers for perennial crops like fruit and hops, and
may also be mixed in small quantities with purely
mineral manures to form fertilisers for root crops.
Rougher manures of this class are sometimes known as
tankage, or as greaves, and are comparatively slow
acting, some of them approach closely the bone meal
described above. The nitrogen they contain should be
reckoned as of less value than in the more concentrated
fertilisers. Naturally all these classes of meat and fish
residues can only be valued at the basis of their analysis.
A meat guano, for instance, may be a highly nitrogenous
fertiliser worth ;^8 or £g a ton, or on the other hand,
little better than a bone meal costing half the price.

Very similar in their actions to meat and fish
residues are certain vegetable residues which from time
to time can be purchased as fertilisers. The best
known of them is rape dust, which consists of ground-
up residues of impure rape seed from which the oil has
been extracted by chemical processes. As a rule, such
seed residues from which oil has been extracted are

26o ARTIFICIAL MANURES [chap.

employed as cattle food, but sometimes they contain
substances injurious to stock, like the rape seed we
have just mentioned and the cake which is derived
from pressing castor-oil seeds, or they have become
damaged in some way and are only utilisable as manure.
Such materials contain, as a rule, about 5 per cent, of
nitrogen and comparatively small quantities of phos-
phoric acid and potash, but when cheap they form very
valuable manures, especially on light soils. Many
other industrial residues get occasionally employed as
fertilisers, in fact, anything of animal origin, like wool
and silk, fur, hair, etc., contains nitrogen, and is thereby
valuable as a fertiliser. Residues from the textile
factories dealing with wool and silk, and fur or feathers,
are sold in the United Kingdom under the general term
of shoddies ; they are extremely variable in composition,
ranging from 3 to 13 per cent, of nitrogen, and they are
always slow in their action, partly because the material it-
self is not readily attacked by bacteria, and partly because
of the difficulty of getting the material finely divided
and disseminated through the soil. But when they can
be bought cheaply, such residues form valuable fertilisers
for perennial crops. It should be kept in mind that
vegetable fabrics like cotton, linen, and jute contain no
nitrogen, so that their residues are valueless as manure.
In dealing with fertilisers it is necessary that the
farmer should bear in mind the very different action of
the three constituents upon the plant, for although all
three substances — nitrogen, phosphoric acid, and potash
— are equally necessary to the growth of the plant, as
we have seen when considering water cultures, yet they
possess very different functions in its development.
Nitrogen is mainly concerned with the vegetative
development of the plant, and increases the tendency to
form leaf and stem ; thus if a plant is given an excess

XIII.] SPECIFIC FUNCTION OF FERTILISERS 261

of nitrogenous manure, the leaf system becomes exces-
sive, a great number of shoots are formed, and the plant
tends to go on growing rather than to turn to the
production of flowers and fruit. Large quantities of
nitrogen are thus valuable for leafy crops of fodder such
as grass, kale, cabbages, etc. At the same time it is
always found that the rapid growth promoted by
excess of nitrogen is both soft and long-jointed, and is
very susceptible to attacks of fungoid disease. Cereal
crops grown with an excess of nitrogen are readily laid
by wind or rain, and the susceptibility to disease of plants
overdosed with nitrogen is often well seen under green-
house conditions. If nitrogen promotes the vegetative
side of the plant, phosphoric acid, on the other hand,
hastens maturity and favours the reproductive side of its
development, as, for instance, the production of fruit and
seed. It is found by experience that the ripening of
crops can be accelerated by a liberal use of phosphatic
manures ; perennial plants like fruit trees can be
similarly induced to fruit rather than to grow. All
these actions of phosphoric acid are most apparent on
heavy soils and in wet seasons, when the natural con-
ditions make for slow maturity. Phosphatic manures
never give rise to the immediate burst of growth and
the dark colour and look of vigour which follows the
application of nitrogen ; their effect is only to be seen at
harvest time, and particularly in the proportion the
fruit bears to the rest of the produce. In consequence,
the use of phosphates is often ignored, while nitro-
gen has been too much employed because its effects
are so manifest. Potash is particularly concerned in the
manufacture of carbohydrates by the plant ; it is there-
fore particularly valuable to crops which, like mangolds,
contain a good deal of sugar or, like potatoes, a good
deal of starch. Being so necessary to the assimilation

262 ARTIFICIAL MANURES [chap.

by the plant, potash tends to keep them growing,
especially on light soils and in dry climates, under which
conditions it exerts its maximum effects. It is also
found to help in stiffening the straw of cereals and grass,
and it increases the disease-resisting powers of all plants.
But though we can thus distinguish between the
effects of the different fertilising constituents, we are
rarely able to argue from this knowledge as to the
requirements of the particular plants. That we must
ascertain by practical experiments, and as an outcome
of our fifty years' experience with fertilisers, we now
know pretty well the special requirements of our various
farm crops. To some extent the manurial treatment of
a crop is determined by the place it occupies in the
rotation that is being followed. It is comparatively
rare to find the same crop occupying the same land year
after year, and under ordinary farming conditions the
soil very often receives a fertiliser, the effect of which has
to extend over several succeeding crops. Again, in con-
sidering the amount and nature of the fertilisers to be
purchased, the farmer has to take into account the style
of his farming, whether high or low. Wherever the
land is not naturally rich and the markets are such that
the farmer cannot obtain a large return per acre for his
crops, he must cut his expenditure down to low limits,
and only indulge in purchased fertilisers to a very
limited extent. He must follow a conservative system
of farming,. being content with comparatively low yields,
the material for which has in the main been derived
from the soil. We should always remember that the
first application of manure is the one which produces
the largest increase in the crop, and that if we double
the manure bill we shall not obtain a double yield or
even a double increase over that which is given by one-
half the manure. In fact, if we go on increasing the

XIII.] FERTILISERS FOR WHEAT 263

amount of manure, we shall soon reach the stage when
the last addition has no effect at all. This "law of
diminishing returns," as it is called, means that a
farmer cannot recoup himself for low prices by forcing
big crops with the aid of fertilisers. The increase thus
bought is the dearest part of the crop. For every farm
there is a sort of level of expenditure on materials like
fertilisers, and the more profitable and the richer the
land, and the more valuable the crops that can be sold,
the higher will this level become. Bearing this fact in
mind, we find that in Britain the wheat crop rarely
receives any fertiliser, except perhaps a small top-
dressing of nitrate of soda or soot in the early spring.
Wheat has a long period of growth and an extensive
root system, whereby it is able to forage for itself pretty
thoroughly, and obtain all the phosphates and potash it
requires from soil in ordinary good conditions. As,
however, it makes its growth during the period of the
year when the soil is comparatively cold, and as the soil
has received very little cultivation before the wheat is
sown, and none at all while it is growing, the processes
which produce ammonia and nitrates out of the nitro-
genous residues of the soil cannot be very active at the
time the wheat chiefly requires its nitrogen. Hence the
value of nitrogenous fertilisers to wheat in the spring,
whereas phosphates and potash meet with very little
response. If nitrogen is the dominant fertiliser for
wheat, barley, on the other hand, chiefly demands
phosphates. It is a comparatively shallow-rooted plant,
and makes its growth in the late spring on land which
has been much more thoroughly prepared than that on
which the wheat crop is sown. In the United Kingdom
barley is very often grown on land which is already com-
paratively rich because the ground has been previously
occupied by the turnip crop, which may even have been

264 ARTIFICIAL MANURES [chap.

consumed in situ by sheep. In such cases the land is
already rich enough ; in fact, it contains too much readily
available nitrogen to give rise to the best quality of
malting barley. But when barley follows wheat on
some of the poor soils, a fertiliser is required, and this
should be composed of a little nitrogen and a fair
amount of phosphates. Oats can be treated in much
the same way as barley, but they are often grown on
land which has just been broken up from pasture and
grass, in which case they are rarely likely to require
much fertiliser. Of all the cereal crops, maize will
respond most freely to fertilisers ; to it should be given
all the farmyard manure that is available, 200 or 300
lb. per acre of acid phosphate, and perhaps a later
dressing of some active nitrogenous manure like nitrate
of soda. Of the root crops, swedes are specially
dependent upon phosphoric acid, and, whether this
crop is grown by the help of farmyard manure or by
artificial manures alone, it will be found necessary on
all classes of land to use for it 4 or 5 cwt. to the acre of
superphosphate or basic slag. Little nitrogen is wanted,
because the crop is growing in the warmer period of the
year and after a very thorough preparation of the soil,
so that the production of available nitrogen compounds
is going on actively in the soil. Mangolds, on the other
hand, are more deeply rooted plants, and are sown at a
cooler time of year; it is found by experience that
they respond to very considerable quantities of nitrogen,
and that they also pay for application of manures
containing potash, though phosphatic manures are less
necessary. Clovers, beans, lucerne or alfalfa, and other
leguminous crops are rarely manured ; they should not be
given nitrogen, but they will respond to dressings of
phosphates and potash, especially upon the lighter and
sandier soils.

XIII.] FERTILISERS FOR GRASS LAND 265

The manuring of grass land is too big and
complicated a subject to be dealt with here in any
detail. Very often indeed the grass land receives no
artificial manure at all; the farmer trusts to the
fertilising effects of the cake and other foods consumed
by stock on the land to maintain its fertility, even when
he grazes it one year and lays it up for hay the next.
It will, however, be found more profitable to hay the
same land every year and keep up its fertility by
manuring because in that way the growth of the
stronger grasses which go to make a big hay crop is
encouraged, whereas they are repressed by a summer's
grazing and their place more or less taken by smaller
bottom herbage which cannot figure largely in the hay
crop. Speaking generally, when supplying manure for
hay we want to remember that nitrogenous manures
will promote the growth of grasses at the expense of the
other constituents of the herbage, until, as we see on
some of the Rothamsted grass plots, the continuance of
a nitrogenous manure year after year for a long period
will cause the whole herbage to be made up of grass
alone. On the other hand, phosphates and potash
without nitrogen stimulate the development of clovers
and other leguminous plants. The herbage is not so
bulky, but weight for weight is more valuable as food for
stock. Thus a manure for hay should contain nitrogen
in order to get bulk, but should also contain a due
proportion of phosphates and especially of potash, to
keep up the clovers and to give feeding value to the
products. On pasture land we want chiefly to encourage
the clovers, and therefore use fertilisers containing no
nitrogen — either basic slag alone when the land is rich
in potash which the lime in the basic slag will liberate,
or basic slag and kainit on the lighter soils. If we can
only encourage the growth of the clovers in the pastures

266 ARTIFICIAL MANURES [chap.

sufficiently, the nitrogen they collect from the atmo-
sphere, which mostly comes back to the land when the
herbage is grazed off, will be sufficient to keep up the
fertility of the soil.

As to the time of application of artificial manures,
it has already been said that nitrates are not retained
by the soil, so that nitrate of soda and sulphate of
ammonia, which so readily changes into nitrate, can only
be employed as top-dressings in the spring, when the
crop already occupies the ground and is ready to utilise
them. Practically there is very little danger of even
the most soluble of quick-acting manures washing down
beyond the reach of the plant in spring or summer.
Consequently all kinds of fertilisers may be safely
ploughed into the ground from the month of March
onwards, except on the very lighest soils. The applica-
tion of spring manures is often needlessly delayed from
a mistaken apprehension that materials like super-
phosphate can be washed out of the land. Insoluble
fertilisers like the shoddies amongst the nitrogenous
manures, and basic slag amongst the phosphatic, should
be put on as early as possible, and may be ploughed or
dug into the soil in the autumn or early winter.

Table XXV. at the end of this chapter gives a
number of analyses of the fertilisers with which a farmer
is most likely to meet, but it should be borne in mind
that many of these substances vary naturally in their com-
position, so that any particular sample can only be
properly judged by the analysis of that actual parcel.
In the United Kingdom, and indeed in all other civilised
countries, the vendor must supply an analysis of the
article he is offering for sale, which analysis has the
force of a guarantee. Given such analyses of a series
of suitable fertilisers, the farmer should then learn to
value them one against another. The most ready way

XIII.] VALUATION OF MANURES 267

of doing this is by what is called the unit system, the
unit being i per cent, of a ton of the fertilising con-
stituents— nitrogen, phosphate of lime, and potash. The
value of a unit of each of these constituents will vary
with market fluctuations, and to a certain extent with
the place of delivery. Thus the exact values prevailing
at any moment can only be obtained by special calcula-
tions, but for purposes of comparing one fertiliser
against another in the United Kingdom it will be
sufficiently accurate to consider that the unit of nitrogen
is worth 14s., the unit of phosphate of lime 2s. if it is
soluble, and I5d. if insoluble, while the unit of potash
may be reckoned as worth 4s. Working on these
principles, fish guano containing j\ per cent, of nitrogen
and 1 3 per cent, of phosphate, should be worth about
1 2 IS., made up as follows : —

^\ of nitrogen at 14s.
+ 13 of phosphate at is. 3d.

Total .

As this fertiliser was offered to a farmer at 146s., it must
be regarded as dear when compared with the meat meal
containing 7 per cent, of nitrogen and 30 per cent, of
phosphate, which was offered at the same time at 127s.
6d. Valued on the same principle, this later manure is
worth, 7 of nitrogen at 14s. = 98s. + 30 of phosphate at
IS. 3d. = 37s. 6d., or a total of 135s. 6d. By making
valuations in this fashion of the manures on offer in the
market, the farmer is often able to buy much more
cheaply than he would if he stuck to the same kind of
fertiliser year by year, independently of their fluctua-
tions in market value. For some kinds of fertilisers
which are subject to natural variations it is very
necessary that the farmer should obtain an analysis
after the delivery of the bulk, in order to compare it

£

s.

D.

=

5

5

0

=

0

16

0

6

I

0

268

ARTIFICIAL MANURES

[chap. XIII.

with the guarantee upon which he has bought. Such
analyses are rarely necessary when dealing with
reputable merchants for such standard articles as nitrate
of soda, sulphate of ammonia, superphosphates, and
potash salts, but all residual materials like meat and fish
guanos and basic slag are subject to variations in com-
position which may not have been recognised by the
vendor. When a farmer purchases large quantities of
any of these articles it will always pay him to get the
deliveries checked by analysis. However, as the
material varies naturally, it is of the first importance that
the farmer should sample the bulk very carefully so as to
get a portion thoroughly representative of the whole.

Table XXV.— Composition of Various Fertilisers-.

Phosphoric Acid

expressed as

Nitrogen.

Tricalcium Phosphate.

Potash.

Soluble.

Insoluble.

Sulphate of Ammonia

20-5

Nitrate of Soda .

15-7

...

...

...

Nitrolim (Cyanamide)

20«0

...

...

...

Nitrate of Lime

12.7

...

...

Soot* . . . .

3-2

...

Wool Waste* .

7.20

...

...

Greaves * .

4-19

...

4-75

Peruvian Guano (rich) * .

8.4

28.7

2.85

„ „ (phosphatic)*

2-37

47.12

2.90

Fish Meal* .

8-68

...

22-11

...

Meat Meal * .

6.51

28.82

...

Dried Blood .

9-65

...

1.82

...

Rape Dust

4.84

...

3-8

1.4

Superphosphate

26

2

n

37

1-5

...

Basic Slag

...

26

...

M ?> •

...

48

...

Bone Meal * .

4-50

...

46-92

...

Dissolved Bones *

3-21

1 1 '64

26-69

...

Kainit

...

...

12-8

Subject to considerable variation.

CHAPTER XIV

MILK, BUTTER, AND CHEESE

Composition of Milk. Variations to which the Composition of
Milk is subject. Effect of Individuality, Breed, Food, Time of
Milking, Period of Lactation. Feeding for Milk. Composi-
tion of Butter. Nature of the Churning Process. Effect of
various Foods upon the Quality of the Butter. Composition
of Cheese. Changes taking place during the Cheese-making
Process. The Ripening of Cheese. Importance of Cleanli-
ness in all dealings with Milk.

Milk is not a simple substance, but a mixture of a
large number of different bodies which are present in
fairly definite quantities, though they are , subject to
certain variations to be discussed later. By weighing
out a small quantity of milk into a dish so that the milk
only forms a thin layer over the bottom, and putting
the whole into an oven to dry, we can show that the
greater part of milk consists of water, there being, as
a rule, not more than 1 2 per cent of total solids in the
milk. This important figure — the amount of total
solids in the milk — can only be determined exactly by
getting the milk spread out into a very thin layer before
drying it, so readily does a skin form over the surface
and cause the drying of the rest of the milk to proceed
with difficulty. Among the milk solids at least three
are characteristic. In the first place there is the fat,
present to the extent of 3 per cent, or more; then
proteins to the extent of about 3 J per cent, the greater
part of which is commonly called casein ; then lactose or

270 MILK, BUTTER, AND CHEESE [chap.

milk sugar forms another 4J per cent. In addition to
these three carbon compounds, the milk solids contain
certain inorganic materials, chiefly phosphates and
chlorides of calcium and potassium and sodium, some
of which inorganic materials are, however, combined
with the proteins.

Milk Fat. — The fat of milk is there present in a
state of finely divided globules varying in size from
o-oi mm. to o-ooi mm., i.e, from 25^60 of an inch to yV
of that diameter. When examined under the micro-
scope these minute globules appear to have a skin upon
the surface, but this skin probably consists of nothing
more than adhering particles of the casein, which also
is not truly dissolved in the water of the milk. The fat
globules vary in size, the milk of Jersey cows contain
the largest, in the Guernseys and in the other Channel
Island breeds they are almost as large, and they are
also well above the average size in the milk of Kerrys.
In the milk of the Shorthorns, globules of various sizes
may be found, but the small predominate ; the Welsh
and South Devon, the Dutch and Holstein races,
yield milk containing rather small globules. In these
globules the fat is present in the liquid state, although
the temperature of the milk may have cooled down
below the temperature at which the fat solidifies in
bulk. In such small particles, however, the fat remains
liquid in a supercooled state, only assuming a solid
condition when the globules are beaten together, as in
the act of churning. The fat is lighter than water,
possessing a specific gravity of 0-93. In consequence,
the globules tend to rise upwards through the heavier
milk serum, and they are only hindered from rising
rapidly by their smallness and the high viscosity of the
milk serum. The larger the particles, however, the
more quickly do they rise, as may be seen in the quicker

XIV.] THE COMPOSITION OF BUTTER FAT 271

and more thorough creaming of the milk from Jersey
cows. When the milk fat is separated and examined it
proves to be a complicated substance, consisting, like all
fats, of a combination of glycerin with certain so-called
fatty acids. In butter fats there are a large number of
these fatty acids present, differing from one another in
their physical constituents, some members being volatile
and strongly smelling liquids, while others are solid
substances, possessing little smell or taste. We can
obtain an idea of these acids of butter fat by taking
about a gramme of the clarified fat and warming it with
20 C.C. of a solution of potash in alcohol. If the fat is
stirred up it will eventually dissolve, the glycerin being
set free, while the acids combine with the potash to form
a soap. The mixture is now dried up to get rid of the
alcohol, and treated with dilute sulphuric acid, which
decomposes the soap and sets free the fatty acids.
These substances will then be found to possess a very
powerful smell of rancid butter, the smell being due to
butyric and one or two of the other volatile acids. As
the liquid cools the non-volatile acids, which are also
insoluble in water, will solidify to a cake on the surface
of the liquid. The flavour of butter is due to the
liberation of a very small trace of some of these volatile
fatty acids through the action of bacteria upon the
butter fat. If too much is liberated the smell and taste
become too pronounced, and we call the butter rancid.
The composition of the butter fat itself is not constant,
but varies with the season of the year, the nature of the
food, and the period of lactation. Hence follows a
variability in the composition of pure butter fat which
constitutes the chief difficulty in detecting adulterations
of butter, for most of the methods of analysing butter
depend upon determinations of the proportion of volatile
and insoluble fatty acids.

272 MILK, BUTTER, AND CHEESE [chap.

Protein. — Of the proteins of milk the chief is a body
called casein, which is distinguished by its property of
forming a firm curd when treated with the enzyme of
rennet, or a flocculent curd when treated with acids.
The casein is a compound of carbon containing 15-7 per
cent, of nitrogen and about -8 per cent, of sulphur and
phosphorus respectively. It is present in milk
probably combined with calcium ; the resulting salt is
not soluble in water, but exists in normal milk in a
finely divided state diffused through the serum, forming
what is known as a colloidal suspension. Rennet,
which consists of a solution of the enzyme which is
present in the fourth stomach of a calf, causes the
casein to coagulate and form a firm curd, in which are
also enclosed the fat globules of the milk. The rapidity
of the action of the rennet and the firmness of the
resulting curd are increased at higher temperatures, but
the presence of a soluble lime salt is necessary before
the curd will form. For this reason, perfectly fresh
milk will not curdle with rennet, a certain amount of
acid must first have been developed, which formation of
acid takes place naturally when the milk stands, by the
action of certain bacteria, which always find their way
into the milk and convert the milk sugar into lactic
acid, the substance characterising sour milk. It will be
seen later that the development of acidity and the
establishment of a suitable temperature are very
essential to obtain the curd of proper consistency for
cheese-making. After the casein has been precipitated
from milk by the action of rennet or acids, the milk still
contains about o-6 per cent, of other proteins, chiefly of
albumen, which begins to coagulate when the whey is
heated to temperatures above 70°.

Milk Sugar. — The solid body which is present in
largest amount in milk is a particular sugar known as

XIV.] MILK SUGAR 273

lactose, which differs from ordinary sugar in its lesser
solubility and in its lack of sweetness. Milk sugar may
be obtained by evaporating down the whey after the
casein has been coagulated and the albumen
removed by heating up to boiling-point Milk sugar
does not ferment with ordinary yeast, ' but can be
fermented into alcohol and carbon dioxide by certain
special yeasts such as those employed in making kephir
and koumiss — fermented liquids used by the Mongol
races. The most characteristic fermentation of milk
sugar, however, is that brought about by the lactic acid
bacteria, which are always about in cows' stalls, etc., and
find their way into the milk ; they multiply with great
rapidity in the warm milk, and split up the sugar into
lactic acid, while at the same time they oxidise some of
it into carbon dioxide and water. These organisms are
responsible for the usual natural souring of milk, in
which the casein is precipitated as soon as the acidity
reaches a certain degree. It is because the development
of the lactic acid .bacteria is so much accelerated by
warmth, that it is important to cool milk down by the
refrigerator immediately after it has been drawn from
the cow, if the milk is to be sent any distance by rail
and not used immediately.

Composition of Milk. — The average composition of
milk in England is given by Droop Richmond as
follows, the figures being the average of about 200,000
analyses : —

Fat

3-90

Protein .

3-50

Lactose

475

Ash

075

Water .

87-10

Total .

I GO-GO

274 MILK, BUTTER, AND CHEESE [chap.

Though this average composition is very well main-
tained when a large number of analyses are considered,
the milk from a given cow may vary very widely from
the average, and these variations are governed by the
factors set out below. It will, however, be found that
the chief variable is the amount of fat; though the
solids also vary, the differences are never so great as
those of the fat.

1. Individuality. — In the milk of the cows compos-
ing any given herd, although they may be all animals
of the same age belonging to the same breed and all
treated alike as regards food and housing, there
will be found considerable variations in composi-
tion. In an ordinary mixed herd of Shorthorns,
cattle not specially selected, it will generally be found
that some of the cows habitually yield milk containing
less than 3 per cent, of fat, while in others the percent-
age is well over 4. These differences are known to be
hereditary, so that not only can the average composition
of the mixed milk of the herd be considerably raised by
weeding out the animals yielding poor milk, but by
steadily breeding only from those cows which yield
milk possessing a high percentage of fat, a very consider-
able and permanent improvement may be effected in
the milk.

2. Breed. — It has already been mentioned that the
Jerseys and other Channel Island cattle yield milk in
which the fat globules are above the average size. It is
also found that these races produce milk containing a
higher proportion of fat. The following table shows the
average analyses of the milk of a number of races of
cows which are usually kept in milk in the British Isles.
The effect of individuality must also be superimposed
upon these average figures, so that single, cases occur in

XIV.]

VARIATIONS OF FAT IN MILK

275

which the butter fat in the milk of Jerseys rises to 6 or
7, and even 10, per cent.

Table XXVI.— Percentage of Fat in Milk of
Different Breeds.

Veith,

New Jersey,

R.A.8.E. Show,

England.

U.S.A.

1909.

Jersey ....

5.66

4.78

4.29

Guernsey

5-02

4-47

Kerry ....

4.72

...

4-13

Red Poll .

4-34

..

2.99

Shorthorn .

403

3-65

3-07

A3rrshire
Holstein

3-68

3-79

3-51

3. Food. — It is commonly supposed that the per-
centage of fat in the milk of a given herd can be raised
by feeding concentrated foods rich in fat. Experiments,
however, show that the difference which can be brought
about in this way is very small ; the proportion of fat
contained in the milk yielded by a given cow being a
physiological function of the cow itself, it is compara-
tively unaffected by the food. If the amount of food
given be insufficient for the average requirements of the
cow, the animal will begin to lose weight, and will draw
the material from its own tissues in order to keep the
yield of milk and the proportion of butter fat up to its
normal percentage; only when the cow has lost an
appreciable amount of weight will both the yield and
the richness of the milk begin to fall off more markedly.
On the other hand, an excess of rich food will cause the
cow to put on fat, and as the cow gets very fat the milk
will again begin to fall off both in quality and quantity.
A high proportion of fat in the food does not make the
milk any richer in fat. The chief effect of a liberal but
not excessive diet appears to be to maintain the milk
yield somewhat longer during the period of lactation

276 MILK, BUTTER, AND CHEESE [chap.

than would otherwise be the case. Nor do particular
foods have any permanent effect upon the richness of
the milk. It is generally found that a slight change of
food exerts a stimulating action for a short time upon
the milk yield, though drastic changes may have the
reverse effect and temporarily reduce the yield and
quality of the milk ; in any case the effect does not
persist for many days. Certain classes of succulent
foods which are very rich in ^-proteins, such as brewer's
grains, green fodder, and especially fresh grass at its
first shoot in the spring, have an exciting effect in
promoting the flow of milk. Particularly does the first
grass, after the cows are turned out, ^\mq rise to an
abundant production of comparatively poor milk. Lack
of green food is also apt to result in a falling-off both in
the yield and the quality of the milk, and a large
quantity of watery foods eventually results in thin and
poor milk.

The quality of the butter is, however, considerably
affected by the nature of the food, because the composi-
tion of the butter fat varies with the material out of
which it is manufactured by the cow; in some cases
indeed the fatty acids contained in the food can again
be identified in the butter fat. An excess of fibrous
foods — hay and straw or over-ripe forage crops — gives
rise to hard, tasteless butter ; peas and beans and cotton-
seed meal or cake also harden the butter. On the other
hand, linseed cake gives rise to a soft and oily butter,
and maize and gluten feeds, oats and rice, also tend to
soften the butter. The feeding of turnips and swedes,
except some time before milking, communicates a
characteristic and disagreeable flavour to the butter,
while it is well known that the flavour of certain strongly
smelling plants like wild garlic is carried over to the
butter.

XIV ] VARIATIONS OF FAT IN MILK 277

4. Period of Lactation. — Immediately after calving
the cow yields milk of abnormal composition, the
product being a thick yellowish liquid, which coagulates
on boiling and is known as colostrum or beastings.
The colostrum at first contains only about 70 per cent,
of water and something like 20 per cent, of proteins, of
which albumen is by far the most abundant, the casein
being present in only about the normal proportion. After
four or five days the colostrum, which is necessary for
the first nutrition of the calf, passes into ordinary milk.
During the first month or two after calving the yield of
milk is at its greatest, and then gradually falls off until
the cow becomes dry, after nine or ten months. During
the first flush of milk the proportion of butter fat is at
its lowest, it then reaches its average amount, and after-
wards rises again as the cow begins to dry off. The
influence of the period of lactation may be to some
extent disguised by the time of year at which the cow
calves down, and the effect of such changes as turning
the cow out to grass.

5. Age, — While it is difficult to obtain strictly com-
parable results, there is evidence that the milk yield
improves up to about eight years of age, after which a
decided falling-off begins to set in about the twelfth
year. The percentage of butter fat drops a little for the
first few years, and then remains constant until the
eleventh year or so, after which it begins to fall
rapidly.

6. Time of Milking. — As a rule, in Great Britain
cows are milked twice a day, at intervals separated by
very unequal lengths of time. It is not uncommon, for
example, to find cows milked at five or six o'clock in
the morning and again about two o'clock in the after-
noon, thus dividing the day into one period of sixteen
and another of eight hours. It is always found that

278

MILK, BUTTER, AND CHEESE

[chap.

after a long interval, i.e., generally in the morning milk,
the yield is larger, but there is a corresponding falling-
ofif of quality. The morning's milk very often contains
less than 3 per cent, of fat, when the evening's milk may
contain well over 4, and the average milk of the herd is
something like 3J per cent. The following table will

Table XXVII. — Variation of Yield and Composition of
Milk with Interval of Milking.

Morning Milk.

Evening Milk.

Yield.

Per cent.
Fat.

Yield.

Per cent.
Fat.

Thirteen and eleven hours .
Fifteen and nine hours .

1-2

1-5

3-18
2-87

I
I

3-8
4.26

Equal intervals ....
Sixteen and eight hours

1-05
1-5

3-64
2-33

I
I

3-45
4-47

show an example in these variations in yield and com-
position. It is impossible to get over these variations
by any alteration in the food of the animals, although,
as a consequence, the morning's milk often falls below
the legal standard of butter fat. In order to avoid
trouble on this score it is necessary to milk at intervals
of twelve hours, and hold back the evening's milk in a
refrigerated condition for the morning delivery. Milking
three times a day is sometimes resorted to, and there is
some evidence that the secretion of milk is thereby
stimulated.

The milk that is first drawn from the udder is always
poorer than the last drawn, or the strippings. Conse-
quently, the milker can seriously lower the average
composition of the milk unless care is taken to
thoroughly strip the cow and make her yield all the

XIV.]

VARIATIONS OF FAT IN MILK

279

milk that is possible. Table XXVIII. shows the amount
of butter fat in the successive portions of milk taken
from the cow.

Table XXVIII.— Composition of Successive Portions of
Milk taken from the Cow.

Total solids .
Fat . .

10-47
1.70

IC'75
1.76

10-85
2-10

11-23

2-54

11-63

3-14

12-67
4-08

7. Other causes of disturbance. — It is found that
cows are extremely susceptible animals, easily disturbed
both in the yield and composition of their milk by any
external causes which excite the animals. Change of
location into a new building, going out to grass, any
sudden fright, a thunderstorm, or a marked change of
temperature, will often be found to exert a considerable
influence upon both the yield and the composition of
milk. In fact, if the composition of the milk of a single
cow be examined day by day, it will be found to show
a number of irregular variations both in amount and
composition, which are to be accounted for by minor
disturbances of this kind. It is thus necessary, when
one wishes to ascertain the average composition of the
milk produced by a given cow, to make up a composite
sample representing the milk yielded during at least
one week. This should be done by putting aside after
each milking a small quantity proportional to the yield
on that occasion, a preservative being added to the
mixed sample in order to retain it in a condition for
analysis up to the end of the week.

From these particulars it will be seen that- the farmer
engaged in the production of milk should first of all pay
attention to the yield and composition of the milk
produced by each individual cow. By keeping his

28o MILK, BUTTER, AND CHEESE [chap.

records of the milk yield of each cow from day to day,
and by occasional analyses, he will be enabled to obtain
the most profitable returns from his cows. Cases are
on record where the milk yield of a herd has been
raised by lOO or 200 gallons per cow per year by the
keeping of careful records and the weeding out of the
poorer animals. If the farmer is selling milk it will be
sufficient for him to obtain occasional analyses of the
mixed milk in order to see that it keeps above the legal
standard ; but if he finds it is falling too low, it may be
necessary to examine into the composition of the milk
of the single cows, in order to weed out those who are
reducing the percentage of fat to a dangerous degree.
When, however, a farmer is making butter from his
milk he is less concerned with the total amount of milk
yielded than with the amount of butter fat itself, and it
is to such a farmer that a knowledge of the average
composition of the milk yielded by each animal is of the
first importance. As regards the feeding, we have seen
that this should be liberal but not excessive, if either too
high or too low the cow will begin to fall off in both yield
and quality after a certain time. Perhaps the best test
that the food is being maintained at a right level, is to
weigh the cows from time to time. If they are slightly
gaining in weight we may be sure that the food is at
about the right level. Very often in this country cows
are fed excessively and wastefully owing to the mistaken
idea that the greater and richer the amount of food the
better will be the production of milk. Perhaps the
greatest economy in feeding cows can be effected by
roughly adjusting the amount of food to the weight of
the cow and the yield of milk. Properly speaking, a
cow's rations should be made up of the amount of food
required for maintenance, which will vary simply
with the weight of the cow, together with the

XIV.] FOOD REQUIRED BY COWS 281

amount required for the production of the milk she
yields, which may be taken to bear approximately the
same relation to the food as the live weight increase
does in the case of the fattening animals. For practical
purposes considerable economy can be effected in the
feeding of the herd if the cows are divided into three or
four groups, according to their weight and their milk
yield. The cows should have first a basal ration, supply-
ing each with about 25 lb. of dry food per 1000 lb.
live weight, this food to contain about i lb. of digestible
protein and J lb. digestible fat. Next, for each 10 lb. of
milk, food with a starch equivalent of about 5 J lb. and
containing about \\ lb. of protein, is necessary. The
cows can easily be divided into three groups according
to their milk yields (allowing also a little for their live
weight), and given one, two, or three measures of con-
centrated food in addition to the basal ration which all
receive alike.

Butter

The essential feature of butter-making consists in
agitating either the whole milk or the cream until the
fat globules coalesce and form clots the size of shot, at
which stage the butter is said to have " come." Whole
milk is very rarely churned nowadays; instead, the milk
is first of all set for twenty-four or forty-eight hours and
the cream skimmed off, or the cream is separated by
some mechanical separator, as in all modern dairies.
In the old-fashioned methods of making butter, the
milk, when still warm, is poured into shallow pans, which
are left to stand in a cool dairy, whereupon the fat
globules slowly rise to the surface, and the layer of
cream is skimmed off. The separation, when effected
in this way, is not very perfect, about 0-8 per cent, of the
fat being left in the skimmed milk. Instead of shallow

282 MILK, BUTTER, AND CHEESE [chap.

pans, deep metal vessels jacketed with ice were some-
times employed, by which means a very effective
separation of cream was brought about, but an even
larger quantity of fat, over i per cent, was left in the
milk. The only real gain in this process was that the
cream was protected from the influx of the harmful
bacteria. Where any large quantity of butter is made,
the mechanical separator is now invariably used.
These instruments depend for their action upon
bringing the milk into a violent whirling motion by
making it flow into a bowl revolving at the rate of
about 6000 revolutions per minute. Under these
conditions the force of gravity, which tends to separate
the lighter fat globules from the denser milk serum, is
exchanged for a centrifugal force many times greater,
which draws the heavier serum to the outside of the
bowl and leaves the lighter cream at the centre, suitable
ducts being arranged to take away the two liquids which
have thus been separated. The cream which is obtained
from the separator may contain anything from 15 to 50
per cent, of fat, according to the velocity at which the
separator is run. The separated milk, which is the
name given to the liquid from which the cream has
been removed, contains as little as o- 1 5 per cent, of fat
when the separator is working properly ; the rest of the
serum possesses the same composition as it does in
uncreamed milk. After the cream has been separated
it may be churned at once, in which case the product
is known as sweet-cream butter, but the flavour is
then somewhat inferior and the yield of butter is lower.
It is customary to put aside the cream for at least forty-
eight hours in order to develop a certain amount of
acidity before churning. While the cream is thus
ripening it should stand in a warm place, as nearly as
possible 65° F. and should be stirred from time to time

XIV.] CHURNING 283

in order to aerate it. Unless the cream is kept aerated
the bacteria making lactic acid may give place to others
producing butyric acid, to the great detriment of the
flavour of the resulting butter. When the cream is
properly ripe it should be brought to an appropriate
temperature before churning, this temperature being
about 60° in the vi^inter and 55° in the summer. The
length of time occupied by churning will depend upon
getting a proper proportion of cream and water and a
correct adjustment of temperature. When the churning
begins, it is necessary with sour milk in a closed churn
to open the ventilator in the churn from time to time
during the first five minutes of churning. The agitation
of the cream liberates a certain amount of carbon
dioxide which had been formed by the lactic acid
bacteria and was dissolved in a supersaturated condition
in the serum of the cream, and unless this carbon
dioxide is liberated from the churn the whole of the
cream will pass into a frothy or whipped condition. As
soon as the granules of butter have reached the size of
small shot the process is nowadays stopped, and the
butter is washed to free it from all adhering milk serum
before it is worked up into pats. Unless this washing
is thorough the butter will not keep, because the small
amount of casein and milk sugar left in when the
washing is imperfect provides a very favourable nutrient
medium for the development of bacteria, which will split
up the butter fat and set free some of the disagreeably
flavoured fatty acids. The resulting butter is not pure
butter fat but contains a proportion of water depending
on the velocity and the temperature of the churning,
and also upon the method of working the butter after-
wards. Rapid churning at high or at very low tempera-
tures will give rise to a number of very finely divided
globules of water inside the butter fat, and these cannot

284 MILK, BUTTER, AND CHEESE [chap.

be removed by any subsequent working. What visible
water there is in butter has been left in through
imperfect work on the butter table. Well-made butter
should not contain more than 15 per cent, of water,
though as much as 18 may be not unfrequently found.
In addition to the water a certain amount of curd, i.e.,
coagulated casein, and of lactose derived from the cream
serum, are always present, together with whatever salt
has been added to the butter in the process of making
up. From this account it will be seen that no chemical
action takes place during the making of butter ; it is a
mechanical process whereby the fat globules are made
to coalesce by being beaten together until the surface
layer which prevents them from uniting in milk has
been broken down. Success in churning depends upon
obtaining the right degree of acidity at starting, and then
working at the proper temperature. In the further
treatment of butter, cleanliness is the chief essential.

Cheese

The process of cheese-making is much more elabor-
ate than that of making butter. Moreover, from the
very large number of different kinds of cheese whose
characteristics are developed by special methods of
making and curing, it would be beyond the scope of
this book to discuss the working details of the processes
which result in any particular cheese ; instead, it will be
sufficient to consider very broadly the principles involved
in the making of one variety, Cheddar, because these
principles apply to all other cheeses. Cheese-making
may start with either whole milk, separated milk, or
milk from which a portion of the cream has been
removed ; but it is desirable that the milk should be
derived from Ayrshires, Shorthorns, or Dutch cows,
which do not give rise to large globules of fat readily

XIV.] CHEESE-MAKING 285

separating from the serum. It is necessary to begin
with a certain degree of acidity in the milk. This is
obtained by leaving the vats to stand at a proper
temperature, stirring from time to time, both to
introduce air and to keep the cream mixed with the
milk. When the proper acidity has been attained — and
this will vary with each kind of cheese, and must be
determined by chemical means before the cheese-
making is embarked upon — the milk is then brought
to a particular temperature and mixed with a certain
quantity of rennet. Speaking generally, the more acid
the milk, the higher the temperature at which the
rennet is added ; and the more rennet is added, the more
quickly will the curd come and the firmer consistency
will it attain. The necessary degrees of acidity, the
most desirable temperature, and the proper strength of
the rennet have been worked out for most of the cheeses
made on a large scale. When the curd has formed the
vat is left to stand until the curd begins to separate from
the serum or whey. The curd consists of the casein, in
which are entangled the globules of fat contained in the
original milk ; the whey contains the albumen of the
original milk, all the lactose, and a certain proportion of
the salts, some of the calcium phosphate being retained
in the casein in the curd. The next stage in cheese-
making consists in getting up a suitable consistency in
the curd. In the case of a hard cheese like Cheddar,
the curd is allowed to contract or shrink in the whey.
It is then cut up to facilitate the removal of whey, and
the whole mass is raised in temperature to increase still
further the consistency of the curd and expel the whey.
Finally the curd is lifted out, allowed to drain, and put
through the mill in order to reduce it to small pieces.
During all these processes the lactic acid bacteria are
actively at work, and the curd becomes more and more

286 MILK, BUTTER, AND CHEESE [chap.

acid. In the making of softer cheeses like Stilton, the
curd is formed at a lower temperature and is not allowed
to contract so much in the whey, but is removed and
placed in the cheese moulds when still in a soft condition
and before it has developed much acidity. In all cases,
however, the curd, when it has reached its appropriate
consistency, is packed into tin vessels lined with a thin
cloth, and perforated at the sides to allow of the
expulsion of the whey. At this stage, too, a certain
amount of salt is usually mixed with the curd. In
making Cheddar cheese, a considerable pressure is then
applied to the curd in the moulds, and this pressure is
continued two or three days until the mass is thoroughly
consolidated. In the softer cheeses no pressure is
applied, and the mass of curd has to consolidate by its
own weight. The cheese is now made and is a soft
mass possessing a slightly sour flavour, the true cheese
flavour is only developed during the ripening. The
ripening processes which cheese undergoes are extremely
various, thus giving rise to the special and very distinct
flavours which the different kinds of cheese possess.
We may distinguish three distinct processes going on.
I. Certain enzymes contained in the original milk
attack the casein and gradually soften or even liquefy
it, breaking it down into a number of simpler nitrogen
compounds of the amino-acid type, some of which are
strongly flavoured.

2. Though the lactic acid bacteria die out, other
bacteria develop, and some of them form highly
characteristic flavouring products out of the casein or the
butter fat. In some case special bacteria are introduced
into the curd, as in the making of Gruyere, Dutch, and
Roquefort cheeses. Sometimes the bacteria associated
with the special flavour of the cheese also give rise to
gas, and blow round holes in the cheese, as in Gruyere.

XIV.] THE RIPENING OF CHEESE 287

3. Certain moulds, such as Penicillium, the blue
mould of cheese, begin to grow in the curd, and these
likewise split up the casein and the butter fat, forming
from them bodies possessing strong flavour and smell.
The particular set of organisms which will develop in
any make of cheese depends entirely upon the processes
of manufacture, and in many cases upon the actual
place in which the manufacture is carried out. The
walls and the vessels of dairies which have for a long
time been devoted to the manufacture of a particular
kind of cheese become impregnated with the organisms
associated with that cheese and communicate them to
the new curd. Furthermore, the many details in the
management which experience alone has taught the
cheesemaker, can be shown to bring about the
encouragement or depression of particular groups of
organisms which affect the flavour of the resulting
cheese. The curing process is also accompanied by a
gradual shrinking of the cheese and an expulsion of the
whey which is still contained in the curd. For this
reason it is necessary to change the cloths surrounding
the cheese rather frequently at first, and to turn the
cheeses constantly when they have been put into the
storage-room. It is also necessary to maintain the
storage-room at the constant temperature which
experience has shown to be appropriate to the develop-
ment of the special flavour of the cheese. As the
manufacture of cheese is thus dependent upon the
development of particular groups of organisms, it is clear
that it may very easily be turned in a wrong direction,
should any of the encroaching putrefactive or otherwise
undesirable organisms, which are abundant in dust,
dirt, foul water, etc., establish themselves in the curd.
It is to these intrusive organisms that defects in the
flavour or texture of cheese are usually due, and they

288 MILK, BUTTER, AND CHEESE [chap.

can only be avoided by careful attention to cleanliness
and to the purity of the materials employed. The
wrong kind of organisms may have already obtained a
hold in the milk itself at starting, generally through
want of cleanliness in the milking. Next, they may be
introduced by imperfect cleaning of the utensils in which
the milk stands ; the water used is also often a source
of danger, and has frequently been found to be a cause
of various troubles in the final product. When natural
souring is trusted to, a not very satisfactory flora of the
various lactic acid making, bacteria may become estab-
lished in the dairy. For this reason it is sometimes
customary both in cheese- and butter-making on a large
scale to begin by pasteurising the milk ; that is, by heating
it up to a temperature of about 170° R, which kills
practically all the bacteria present. After cooling, the
pasteurised milk is then mixed with a "starter," con-
sisting either of a pure culture of the desired bacteria or
of the good but mixed culture contained in the butter-
milk or the sour whey derived from a previous churning,
or from another dairy turning out products of an
appropriate flavour. In this way the development of
acidity in the milk can be controlled, and this is the
first step towards obtaining a standard product.

In all the farmer's dealingswith milk and its products it
is important to remember that the milk itself provides an
almost ideal feeding-ground for bacteria ; and as bacteria
of all kinds are particularly prevalent in dust and dirt,
specially in the organic dirt that collects in cow stalls
and cattle sheds, or in a dairy which is not kept most
scrupulously clean, milk will deteriorate more readily
than almost any other natural product. The only way
to overcome this difficulty is to exercise the most
scrupulous cleanliness, and to keep the temperature as
low as possible. In the case of milk and milk products,

XIV.] CLEANLINESS 289

dirt does mean disease, sometimes even disease for
those who consume the products ; more often, perhaps,
the dirt gives rise to defects lowering the value of those
products. To ward off the growth of these foreign
bacteria recourse should not be had to antiseptics
which inhibit the development of bacteria. The proper
remedy is cleanliness, and cleanliness alone is sufficient
for practical purposes.

INDEX

Acid, sap, 49 ; vegetable, 75 ; soils,
90, 123, 147 ; manures, 147 ; soil
water in peaty soils, 183 ; fatty,

171. 173
Adulteration of foods, 180
Air, required in germination, li ;

carbon dioxide in, 22 ; in the soil,

152
Albumen, 272, 285
Albuminoid ratio, 206, 218
Albuminoids, 66, 70, 71, 125, 169,

173, 177

Albumoses, 173

Alcohol, 75

Alfalfa, 138, 141, 168, 199

Alimentary canal, 171

Alkali land, 139

Alluvial, soils, 86, 97, 166 ; sub-
soils, 95

Alumina in soils, 94

Amides, 6, 170, 204

Amino-acids, 170,173,204, 276, 286

Ammonia, absorbed by plants, 51 ;
in soil, 93 ; in nitrification, I22»
125 ; as a product of putrefaction*
125 ; sulphate of, 250

Analysis, of soil, mechanical, 88 ; of
various arable soils, 96

Antiseptics, 289

fl-proteins, 6 ; converted to protein,
66, 70; proteins converted to, 71,
177 ; in animal food, 175 ; in
silage, 177 ; in root crops, 183
291

Artificial manures, 225, 248 ; nitro-
genous, 250 ; phosphatic, 254 ;
potassic, 257 ; valuation of, 267 ;
composition of, 268

Ash, in plants, 2 ; of crops, com-
position of, 55 ; in foods, 169 ;
digestion of, 175

Asparagin absorbed by plants, 51

Aspect of land, 117

Assimilation, 25 ; potash required
for, 261

Available, plant food, 151 ; energy
converted into mechanical work,
198 ; energy of various foods,
199

Azotobacter, 141

Bacteria, nitrifying, 122, 145 ;
putrefactive, 125, 145 ; ammonia
producing, 125, 145 ; denitrifying,
126, 146 ; aerobic, 129, 146 ;
anaerobic, 130, 146 ; nodule, 132 ;
nitrogen fixing, 141 ; conditions
necessary to growth of soil, 145 ;
in intestinal tract, 172, 174 ; in
farmyard manure, 228 ; in milk,
273 ; cheese, 286 ; in the dairy,
288

Barley, manurial requirements of,
162, 263 ; as food, 182

Barren soils, 99

Basalt, 78, 80

Basic slag, 256

292

INDEX

Bean, germination of, 7 ; root of the,
42 ; as a recuperative crop, 138 ;
soya, 180 ; as food, 182

Biennials, food storage, 69

Bile, 171, 172, 176

Blood, the circulating medium, 171,
173, 202

Bone meal, 254

Bones^ 254

Boussingault, carbon balance-sheet,
21 ; on leguminous crops, 135

Brick earth, 83

Bulbous plants, 59

Bullocks, on maintenance diet, 195,
197 ; on fattening, 195 ; minimum
protein requirements, 203

Butter, 281 ; fat, 271, 276

Cakes, oil, 178

Calf, composition of fat, 207

Calorie, 186

Capillarity, 104

Carbohydrates, in plants, 5 ; in
foods, 169; digestion of, 172;
proteins and fats in terms of, 183 ;
dependence on potash, 261

Carbon, in plants, 2 ; increased
weight of plants largely made
of, 20; drawn from the air, 21 ;
in humus, 27

Carbon dioxide, evolved in germina-
tion of seeds, 11 ; in air, 22 ; split
up by plants, 22 ; excreted by
roots, 48, 50 ; dissolved in rain-
water, 79; in soil gases, 153;
product of combustion in animal
body, 172, 173, 174

Carbonate of lime, dissolved by soil
water, 80 ; in soils, 90 ; in sub-
soil, 95 ; in heavy soils, beneficial
effect of, 98, 167 ; absence in soil
inhibits bacterial action, 144, 147

Carcass weight, 208

Casein, 269, 272, 285

Castor cake, 260

Cellulose, in plants, 5 ; fermentation
by soil bacteria, 129 ; digestion
of, 172

Cereals, as foods, 182

ChaflF, 64

Chalk, formations, 97 ; soils, 90,
167

Cheese, 284 ; ripening of, 286

Chewing of the cud, 172

Chlorine, in plants, 50 ; in soils, 94

Chlorophyll, assimilation, 24 ; iron
necessary to formation of, 51

Churning, 281

Citric acid as a soil solvent, 154

Clay, derived from felspar and
basalt, 80 ; obtained in mechanical
analysis, 89 ; properties of, 91 ;
soils, 97, 106, 108, 166

Clover, on succeeding crop, effect of
growth of, 135 ; manures for, 265

Colostrum, 277

Colour of soils, 116

Combustion in animal body, 173

Compensation for food - stuflfs con-
sumed, 243

Condition of the soil, 147, 239

Cooking does not increase digesti-
bility, 177

Corm of colchicum, 60

Corn, place in diet, 194, 200

Cotton -seed cake, 169, 178, 180,
183, 192

Cotyledons, 7

Cows, breeds of, 270, 274

Cream, 281

Crocus, contractile root of, 44 ;
autumn (colchicum), 60

Crops, water required by, 39 ; dry-
ing action of, 39 ; eff'ect of catch,
40 ; composition of, 57

Cultivation, 107

Curd of milk, 272, 284

Cuticle, 37

Cuttings, 72

Cyanamide, 250

INDEX

293

Cytase, 172

Dandelion, contracted root of,

44

Decay of organic matter, 129

Denitrification, 126

Desiccation, 66

Dew, 38

Diastase, 16, 72 ; function in leaf,
28 ; in saliva, 172

Diet, in digestibility experiment,
176 ; maintenance, 189

Digestibility, of foods, 175 ; experi-
ments, 176

Digestion, 170; work expended on,

190

Diminishing returns, law of, 263
Diphenylamine, test for nitrates, 93
Disease, susceptibility of plants to,

261
Dormant plant food, 151
Drainage, I15
Drift soils, 82 ; glacial, 84
Dry farming, 113
Dung, short and long, 226 ; London,

236
Dynamic energy, 192, 198

Early soils, 116

Earth-nut cake, 180

Embryo in seed, 7

Endosperm, 8, 64

Energy, stored by plants, 33 ; in
animal body, r72, 173, 185 ; trans-
formed to heat and work, 185 ;
available for work, 190, 199 ;
dynamic, 190, 192 ; thermal, 188,
192 ; total, 187, 192

Enz)rmes, 16, 72, 76, 171, 203, 272,
286

Equivalents, starch, 184, 215

Essential oils, 6

E^ch'ng, action of roots. 4

Ether, in fat extraction, 169

Ethers, 75

Evaporation, cooling effect of, 109 ;
loss of water by, 109, no ; checked
by hoeing, in ; checked by
wind breaks, 1 14

F.ECES, 171, 174, 226

Fallow on soil moisture, effect of,
40, 112

Farmyard manure, 158, 224; com-
position, 234 ; use of, 238, 242 ;
duration of, 240 ; physical effects
of, 241 ; cost of, 246

Fats, in plants, 5 ; in foods, 169 ;
digestion of, 171 ; heat value of,
188 ; in terms of carbohydrates,
183 ; fuel value of, 187 ; in milk,
270

Fattening, animals, 195, 207 ; com-
position of increase in, 208

Fehling's solution, 15

Felspar, 80

Fermentation, 75 ; aerobic, 128, 129 ;
anaerobic, 129, 130; of farmyard
manure, 228

Ferments, 16

Fern, growing in air-tight bottle, 31

Fertilisers, 248 ; nitrogenous, 250 ;
phosphatic, 254 ; potassic, 257 ;
nitrogenous, effect of, 260 ; phos-
phatic, effect of, 261 ; potassic,
effect of, 257 ; valuation of, 267 ;
composition of, 268

Fertility, maintenance of, 158

Fibre, in plants, 5, 69 ; in foods,
169 ; digestion of, 172, 174

Film, in soils, the water, lOl

Fine earth, 86

Finger-and-toe, 147, 256

Fish manures, 259

Fixation of nitrogen, 131

Flocculation, 92, 108, 115

Food, used as fuel, 172, 174 ; more
digestible than poor, rich, 177 ;
valuation of, 183 ; as a source of
energy, 185 ; fuel value of, 187 ;

294

INDEX

in relation to live weight increase,

210; rations, 217; manure value

of, 243
Frost, distribution of plants by, 47 ;

disintegration of rocks by, 81 ;

valleys specially liable to, 117
Fuel value of food, 187
Fungi in the soil, 147

Gases, soil, 153

Gastric juice, 171, 173

Gelatin from bones, 254

Germination, conditions necessary
to, 9

Gluten, 6, 65 ; meal, 181, 183

Glycerin, 271

Glycogen, 173

Grain, the filling of the, 63

Granite, 78, 80

Grass, composition of meadow, 4 ;
land, manures for, 265 ; character-
istic, 164, 165, 167

Gravel, deposition of, 82, 83

Greaves, 259

Growth, elements necessary to plant,
5 1 ; changes of composition during,
59 ; temperature required for, 114

Guanos, 257

Hay, growth and ripening of
meadow, 68 ; digestibility of, 177 ;
composition of, 182 ; heat value
of, 189 ; dynamic value of, 194,
199 ; place in diet, 194 ; values,
Thaer, 217 ; manures for, 265

Heat value of foods, 188

Heating of soils, 114, 116

Heavy soils, 97, 1 18

Hellriegel, on transpiration, 38 ;
and Wilfarth on nitrogen fixation,
132

Hoeing, 112

Hops, 74

Horse, fed upon straw, 191 ; on
maintenance diet, 194, 197 ; avail-

able energy of various foods fed
to the, 199 ; energy requirements
of working, 200 ; minimum pro-
tein requirements, 203

Humus, 86 ; soluble in alkalis,
87 ; in subsoil, 95 ; product of
cellulose fermentation, 129, 130;
value of, 241

Hydrochloric acid, solvent action on
soils, 94 ; in stomach, 175

Hydrogen, 173, 187

Ice as a transporting agency, 84
Inoculation of nodule organisms,

132, 139
Intestines, 171, 176
Iron, in plants, 50 ; in rocks, 80 ; in

soils, 94

Kainit, 159, 257

Kellner, on fuel values, 188, 191 ;
on the maintenance of store
bullocks, 197 ; energy require-
ments of working horses, 200 ;
standard rations, 223

Kelp, 257

Kephir, 273

Kidneys, 174, 202

King on transpiration, 38

Koumiss, 273

Lactation, period of, 277

Lactic acid, 273, 283, 285

Lactose, 269, 272

Lawes and Gilbert, 255 ; ori trans-
piration, 38 ; on the composition
of farm animals, 207

Leaf, work of the, 19 ; starch forma-
tion in the, 26 ; removal of, 34 ;
stomata in, 37 ; the fall of
the, 73

Lean meat, 174, 189, 209

Leguminous crops, 54, 132, 135 ;
plants and soils, 164, 165, 168

Light, assimilation and, 24, 26 ;
soils, 98, 116, 118

INDEX

295

Lime, in plants, 50, 73 *» in ash of
crops, 54 ; in soil?, 94 ; nitrate
of, 250, 253 ; in basic slag, 250

Limestones, 97

Linseed cake, 176, 178, 181

Lipase, 16, 171

Litter, 228

Liver, 173

Loam, 107, 165

London dung, 236

Lucerne, 138, 141, 168, 199

Lymphatic system, 171

Magnesia, in plants, 50 ; in soils,

94
Maintenance diet, 189, 195
Maize, gluten meal, 182 ; as food,

182; d)mamic value of, 1 99;

manures for, 264
Malt, 16
Mangold, yield proportional to

combined nitrogen supplied, 53 ;

food storage, 69 ; composition of,

69, 182 ; manures for, 264
Manure, farmyard, 224 ; artificial,

325, 248 ; required by crops, 263 ;

value of foods, 243
Manuring, theories of, 161
Marl, 98, 167

Marsh-gas, 127, 173, 187, 229
Meals, 178
Meat guanos, 259
Metabolism, of proteins, 66, 70, 71,

173, 202 ; of carbohydrates, 172 ;

of fats, 171 ; of starch, 14,26, 172
Methane, 127, 173, 187 ; in farm-
yard manure, 229
Mica, 80
Micropyle, 9

Migration of plant food, 60, 63
Milk, fat in, 171, 173 ; composition

of, 269, 273 ; souring of, 273 ;

morning and evening, 278 ;

analysis, 280
Moisture in foods, 169

Moulds in cheese, 287
Mulch, III ; soil, 113
Mummy wheat, 13
Miintz on digestion, 191
Muriate of potash, 257
Mustard seed in rape cake, 178

Nitrate, of soda, 250, 252 ; of
lime, 250, 253

Nitrates, in water cultures, 51 ; in
soil, 93, 121 ; lost in denitrification,
126

Nitre, 121

Nitrification, 12 1

Nitrites formed in process of nitri-
fication, 122

Nitrogen, in plants, 3 ; required in
combined state by plants, 53 ;
accumulation in black virgin soils,
54 ; in plant food, 66, 70 ; in
humus, 87 ; in soils, 95, 149 ;
cycle illustrated, 125 ; lost by
denitrification, 127 ; fixation by
bacteria, 131 ; losses and gains
during a four-course rotation,
159; excreted by kidneys, 174;
losses of, in manure-making, 230 ;
in fertilisers, 250

Nitrolim, 250

Nodules, on roots of leguminous
plants, 132 ; organisms, racial
adaptation of, 1 39

Oats, as food, 182, 199; manures

required by, 264
Offal, weight of, 208
Oils, in plants, 5 ; cakes, 169, 178 j

digestion of, 171, 174
Organic matter, in soils, 86, 116 ;

promotes denitrification in soils,

126, 146
Oxen, composition of, 207
Oxygen evolved by plants, 23

Palm-nut cake, 180

296

INDEX

Pancreatic juice, 171, 172, 173

Papain, 16

Pastures, fattening, 195 ; manures

for, 265
Peas as food, 182
Peat, 130 ; moss litter, 228 ; moss

manure, 236; soils, 86, 90, 95,

123, 153, Its

Pectins, 71, 75, 182

Pepsin, 16, 173

Peptone, 124, 173

Percolation, 105

Pericarp, 64

Peruvian guanos, 257

Phosphate of lime, a5 a food con-
stituent, 175

Phosphoric acid, necessary to plant
growth, 50 ; in soils, 94, 149 ;
removed in four-course rotation,
159; deficient in clays, 167; in
fertilisers, 254

Physical effects of farmyard manure,
241

Pigs, composition of, 207

Plant, food, migration and storage
of, 60, 63 ; food, dormant and
available in soil, 151 ; excretions,

157
Ploughing, autumn, 107 ; spring,

108 ; work done by horses in, 200
Pore space, 104
Potash, in plants, 50, 53 ; in soils,

94, 149 ; removed in four-course

rotation, 158 ; abundant in clays,

167 ; manures, 257
Potato, 72; districts, early, 118;

composition of, 182 ; manures for,

257

Prairie soils, 144

Preservatives in dung-heaps, 233

Protease, 16

Protein, in plants, 6 ; and a-proteins,
66, 70, 71, 177 ; breakdown and
reconstruction, 125 ; in foods,
169 ; digestion of, 173 ; in silage,

177 ; heat value of, 188, 201 ; in
terms of carbohydrates, 183 ; fuel
value of, 187 ; requirements, 174,
201

Protozoa, 147

Puddled clay, 91

Putrefaction, 124

Quality in produce, 77
Quartz, 80

Rape, cake, 178 ; dust, 259

Rations, construction of food, 217 ;
for milch cows, 281

Rennet, 272, 285

Respiration, in plants, 29, 60, 63 ;
of roots, 47 ; during storage of
root crops, 71 ; chamber, 211

Ripening, of grain, 66 ; of fruits,
57

Rock, 78 ; primitive, 80 ; volcanic,
80 ; phosphate, 255

Rolling, no

Root, 22 ; hairs, 43 ; adventitious,
44 ; source of water supply to
plants, 46 ; effect of frost on, 47 ;
absorbs soluble substances, 48 ;
etching action of, 49 ; part played
in weathering, 81 ; nodules, 132

Root crops during storage, changes
in, 71 ; digestibility of, 178 ; com-
position of, 182

Rotations, value of, 1 56

Ruminants, 172, 174, 177

Sainfoin, 138, 168

Saliva, 172

Salt as a food constituent, 175

Sand, deposition of, 82, 83 ; in
mechanical analysis, 88 ; pro-
perties of, 91 ; in foods, 170

Sandy soils, 98, 107, 163

Sap, 50 ; acidity, 49

Sea, temperature in proximity to,
118

INDEX

297

Seed, 6 ; " hard," 9 ; vitality of,
13 ; depth of sowing, 13 ; test-
ing, 17

Seed-bed, 18, 108, 113, 241

Separation of milk, 281

Sheep, on maintenance diet, 195,
197 ; on fattening diet, 195 ;
minimum protein requirements,
203 ; composition of, 207

Shoddy, 260

Silage, digestibility of, 177

Silica, in plants, 50, 54, 73 ; in soil,

94

Silt, deposition of, 83

Slag, basic, 256

Soda, in plants, 50 ; in soils, 94 ;
nitrate of, 250, 252

Soil, origin of, 78 ; sedentary, 79 ;
of transport, 82 ; motion of the,
84 ; chemical constituents of, 93 ;
relation to subsoil, 95 ; water,
movements of, 100 ; colour of,
116; inoculation, 139; chemical
composition of the, 149 ; gases,

153

Soot, 116, 250, 253

Souring of milk, 273

Soya bean cake, 180, 181

Standard rations, 223

Starch, in plants, 5, 14, 26 ; iodine
test, 14; digestion of, 172; heat
value of, 188 ; equivalent, 184,
215 ; use of, 219

Starters, milk, 288

Stassfurt potash deposit, 257

Steppe soils, 144

Stomach, 171

Stomata, 37

Stones, growing on arable soils, 84 ;
in soil samples, 86 ; check evap-
oration, 115

Storage, of plant food, 60 ; of fats in
animal body, 173 ; of protein in
animal body, 174

Store condition, 194, 197

Straw, digestibility of, 177 ; com-
position of, 65, 182 ; food value,
191, 199 ; as litter, 228

Strippings, milk, 278

Subsoil, 79, 95 ; packing, 113

Sugars, in plants, 5 ; test for, 15 ;
in mangolds and beet, 69 ; in
turnips, 71 ; action of yeast on,
76 ; digestion of, 171, 174

Sulphate of ammonia, 250 ; potash,
257

Sulphur, in plants, 50 ; in soil, 94

Sun, source of heat to soils, 114

Superphosphate, 158, 255

Surface tension, 100 ; of soil par-
ticles, 105

Swede turnip, food storage, 69 ;
composition of, 71, 182 ; manurial
requirements of, 163, 264

Symbiosis, 133

Tankage, 259

Tannins, 75

Temperature, soils, 114; dung-heap,
230; body, 196

Test, for starch, 14 ; for sugar, 15 ;
seed, 17 ; for carbon dioxide,
24

Texture of soil, 108, 115, 241
252

Thaer, 217

Thermal energy, 193

Thomas's phosphate powder, 256

Tillering, 44

Tilth, 108, 157, 252

Transpiration, 36 ; devices to re-
duce, 41

Transport, soils of, 84

Trees, characteristic, 165, 167, 168

Trypsin, 173

Turnips, food storage, 69 ; composi-
tion of, 182

Urea, 174, 187, 202, 229
Urine, 174, 203, 225, 229

298

INDEX

Valuation, of feeding stuffs, 183,

213; of fertilisers, 267
Vetches, 138
Virgin soils, 54, 144.

Water, in plants, 2 ; required by
crops, 39, 107 ; cultures, 45 ; as
a weathering agency, 79 ; as
a transporting agency, 82 ; in
animal body, 171, 172, 174

Waxes, 5

Weathering of soils, 79

Weeds, 34 ; seeds in oilcakes, 181

Wheat, root, 43 ; development of,
61 ; effect of wet autumn on, 62 ;
"strong," 65, 156; in wet and
dry seasons, 67 ; manurial require-
ments of, 162, 263 ; as food, 182

Whey, 273, 285

Wilting, 46

Wind, as a transporting agency, 82 ;
breaks, 1 14

Wollny, 38

Wood ashes, 257

Wool, 203

Work, done in animal body, 172,
I73> 189; energy converted to,
186 ; done in walking and trot-
ting, 198

Worms, action of, 85

Yeast, 75

Zein, 204

Zuntz, 191, 197, 198

OLIVER AND BOYD, EDINBURGH.

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