Interaction of the elements.

The carbon dioxide used in photosynthesis was the

original source not only of all carbonate products, but of

all substances such as wood, coal, petroleum, and natural

gas. Combustion of these materials yields heat energy

used to warm dwelling and office, to furnish power for

driving the engines of factory and transportation, and to

generate electricity for both power and light.

Animals themselves are direct bearers of burdens and

drawers of loads. Horses pull tillage implements and

The Plant as a Factory 53

haul farm products to market; camels, llamas, and

burros carry man and goods in regions inaccessible to

wagon and locomotive. Horses and dogs assist in tend-

Ing herds ; cats and birds in the control of mice and in-

sects ; bees and other flying folk pollinate flowers. Not

only are the labors of man lessened by dumb beasts that

live on plants, but his pleasure is also increased by them.

Riding and driving are healthful recreations; ponies,

dogs, and birds gladden the hearts of children who have

them for pets; zoological gardens and aquariums are

places of beauty; and caring for and breeding fancy

animals are avocations of many. Flower gardens and

house plants also beautify the home. Vegetable gardens

and ornamental plants satisfy some men in the same

way that good animals do others.

Many raw products that are transformed by factories

into new forms, whether food, clothing, tools, or books,

are of plant or animal origin. Books, pictures, and news-

papers, so essential in education and in national and

artistic well-being, are made of paper or cloth, both plant

products. Medicines, dyes, and chemicals are supplied

in part by plants. Finally, more people earn their living

by the culture of plants and the rearing of animals than

by any other pursuit. Plainly, man cannot live in and

of himself ; he must be fed, clothed, warmed, and sheltered

from the weather. Since he cannot dispense with plants,

let him not scorn them.

40. Domestication. — When the people who are now

civilized were savages, they lived much as present-day

savages do. Wild fruits, nuts, roots, and tender shoots

fed, clothed, and sheltered them. In the wild, enemies

were frequent and they often prevented man's obtaining

food. Rigorous winters and dry summers also caused

suffering to some, while those in better provided areas

54 The Principles of Agronomy

were less disturbed. Stem necessity drove man to do-

mesticate plants for food and shelter, and animals as

assistants in hunting and in moving about. Originally,

all tame creatures came from native haunts. If they

were useful, the most savage brutes were gradually

brought under subjection by man who alone could use

fire and make machines to throw arrows or stones. Weaker

than many animals and plants, he studied their ways

and found ways of subjecting the useful ones. Seed was

planted in protected places and other plants were kept

out. Then tillage began and man took up a fixed habi-

tation.

Some plants and animals have been so long cultivated

that wild relatives have disappeared. The earliest

records tell us that wheat, barley, and alfalfa were culti-

vated at the dawn of civilization. Constantly new plants

are being used for crops. In the cases of plants recently

domesticated, the wild relatives are still in the fields.

Wild plums and roses, native grasses, and vetches may

still be found, but the plants from which wheat and corn

came have disappeared. Plants not yet known could

doubtless be found that would serve man, and as new

varieties appear, many useful plants will be developed.

41. Plant compounds. — Hundreds of kinds of sub-

stances are found in plants. Some of these man findsr use-

ful and appropriates for his own use. So closely related

aj'e these compounds that they may be included in eight

groups: (1) water, (2) carbohydrates, (3) proteins, (4)

ash, (5) fats and oils, (6) aromatic substances, (7) medic-

inal properties, and (8) acids. In importance the last

three rank far below the first five, yet even these are not

to be neglected.

42. Flavors, perfumes, and other characteristic odors,

such as lemon, mint, and rose-water, have various uses.

The Plant as a Factory 55

Flavors of fruit and nuts serve to distinguish them.

Carbon, hydrogen, and oxygen in various quantities

and arrangement compose these substances. The drugs

and stimulants, such as morphine, strychnine, and quinine,

usually contain nitrogen in addition; while the acids of

fruits, such as malic acid in apples and tomatoes, citric

acid in citnis-fruits and currants, and tartaric acid in

grapes, consist of carbon, hydrogen, and oxygen. These

three classes of compounds promote palatability, give

variety, increase healthfulness, or stimulate the nervous

system rather than serve as constructive foods.

43. Water composes from 60 to 90 per cent of the

weight of green plants. (1) It forms a part of the cell

content keeping the cells full and rigid ; (2) it acts as a

solvent which carries mineral salts and distributes elab-

orated plant-foods; (3) it regulates the temperature of

plants by maintaining a constant stream from root to

leaf where evaporation, which uses much heat, reduces

the temperature to normal. In the animal body, water

performs similar functions. The extra succulence caused

by water in plant tissues increases palatability. Dry

feed and water seem to lack something that green feeds

possess, particularly for the use of milch cows.

44. Carbohydrates consist of carbon, hydrogen, and

oxygen usually in the ratio C,(H20)„. They comprise

from 80 to 95 per cent of the dry weight of plants and are

made from water and carbon dioxide. Starch, sugar, and

cellulose occur in the plant, scattered widely throughout

the tissues. Cellulose makes up all woody tissue and the

strong cell-walls. Starch is the usual form of storage,

while sugar is ordinarily the temporary form, though in

sugar-cane and sugar-beets it is one of the storage com-

pounds. When carbohydrates are digested by man and

beast, they supply work and heat energy and may be

56 The Principles of Agronomy

made into fat. Never, however, do they become a part

of the muscle, ligaments, and connective tissue. Slow

combustion in the cells uses these foods. Starch and

sugars are easily digested, but cellulose, often designated

as crude fiber, is but partly digested. However, it fur-

nishes bulk, which is necessary.

45. Protein compounds contain nitrogen and sulfur

and sometimes phosphorus. Out of these foods, muscu-

lar, connective, and vital tissues of the body are formed.

Flesh, stomach, intestines, lungs, nerves, and brain use

these in direct composition. Man eats meat to supply

these needs because plants are not usually rich in nitrog-

enous substance. Animal bodies must first get them

from plants which contain them in storage. Leaves,

embryo of seeds, and a layer of cells just beneath the seed-

coat are rich in nitrogen. Leguminous plants are much

richer in protein than grasses or cereals ; and legume seed,

such as peas and beans, are composed largely of protein

compounds. Proteins, then, are both scarce and vital;

they cost about three times as much as carbohydrates if

ordinary prices are considered.

46. Ash comprises from a fraction of one to several,

but usually less than 2 per cent, of the dry matter. It

is scattered through the plant as stone cells of the stem

and leaf, in the cell-sap to promote osmosis, and in the

protoplasm itself. A small quantity enters into the

composition of protein. It is called ash because it re-

mains so after burning. Animals concentrate this min-

eral, in the bones and teeth, and use it in smaller propor-

tions in blood and flesh.

47. Fats and oils are simply carbohydrates rich in

carbon and poor in hydrogen and oxygen. Seed embryos

and the flesh of nuts are the storage tissues. All grains

contain some : com about 5 per cent ; seed of flax, sun-

The Plant as a Factory 57

flowers, cotton, mustard, rape, and poppies are about

one-third oil; peanuts, palm-nuts, and coconuts con-

tain from 45 to 67 per cent. Fats and oils, in the animal

body, produce fat and supply energy. In computing

rations for live-stock, they are counted 2.4 times as valu-

able for energy production as sugar and starch.

48. The plant factory. — Since plants and animals use

the same foods, and since the animal is not able to com-

pound its own, the animal draws its food froni the plant.

True, the elements are the same and in the same quantity

before and after photosynthesis, but they are in entirely

different relations. Iron made into pig-iron and then

into watch springs is the same substance in different

forms; but just as the watch-maker could make no use

of the pig-iron, so the animal — and the plant for that

matter — can make no use of carbon dioxide, potassium,

nitrogen, phosphorus, or iron until they have passed

through the factory of the leaf and been made over into

sugar, starch, protein, or oil. Water alone is used in

the compound that exists in nature.

As described in paragraph 32, carbon dioxide and water

are imited into sugar by the chlorophyll of the leaf. This

green substance is found throughout the green part of

the plant, but it is abundant in the palisade cells of the

leaf. Small green bodies arranged along the side walls

of these cells intercept rays of sunlight and make use of

this energy to do the work of combining water and carbon

dioxide. The water within the cell touches the chlorophyll

bodies on one side, while the carbon dioxide comes into

intimate contact with them on the other, as it diffuses

against and through the cell-walls from the stomata.

Chlorophyll, by means of energy in the sunlight, causes

this chemical combination to take place. Plants make

no outward demonstration, yet, in quietness, they have

58 The Principles c^ Agronomy

caused the moat important reaction known. This is

the beginning of the food which feeds all. The whole

problem of feeding the world must ultimately be solved

by chlorophyll and sunshine. Figure 15 represents appa-

ratus showing aeration of the leaf.

Fig. 15. — Apparatus showiDg aSratioa of the leaf. (Aft«r Detmer.)

Without green plants, it would be simply a matter

of time until life could not exist on earth. First plants

would die and animals would feed upon them. Grad-

ually these would use up the food and then die. Equally

essential is sunshine, which not only enables plants to grow,

but vaporizes water, lifting it into clouds which return

The Plant as a Factory ^ 59

the water as rain, letting it run down hillside and hollow.

In this journey, it washes soil and grinds rock, it floods

meadows and turns water-wheels, it grinds grain and saws

lumber, it dissolves mineral for plants and generates

electricity. Sunshine, then, is the source of water power

as well as the original power of warmth and food. In this

whole world, only chlorophyll is able to make use of it

for food manufacture.

Just what this strange substance is, has not yet been

found out. Plants growing in the shade continuously

have none, but as soon as they are exposed to sunshine,

it develops. Sunshine and the living cell can bring this

vital substance into action and perhaps into being. Truly

the plant is a factory : sunshine furnishes the power to do

work ; chlorophyll seems to be the machinery ; and water,

dissolved salts, and carbon dioxide are the raw products.

49. Animal concentration. — Proteins occur only in

small percentages in plant tissue. When the plant is

eaten and digested, carbohydrates and oils are " burned "

in doing work and the refuse excreted. Water is the

same in plant, animal, and stream. Some ash is used,

but save in young animals, it is mostly discarded in the

manure. Protein is also partly excreted when fed in

abundance, but part of it is retained and made into flesh,

blood, and sinew. The animal has gradually accumulated

a body composed largely of the vital tissue. When it is

butchered, man gets a concentrated food which began in

the plant cell, but which was refined in the plant and in

the animal, and when cooked is adapted to bis use. Brain

and brawn, which have so changed the world, must look

far back to find the beginning of their working power and

of their tissues.

60. Storage. — Man and other animals must do some-

thing besides eat; hence they eat a quantity and gain

60 . The Principles of Agronomy

reserve energy to carry them till the next meal. Should

the following meal and still others be omitted, they live

on stored food. Finally, fat and muscle waste away and

starvation results.

Something quite similar to this occurs in the plant when

storage is made. During the fruiting period, plants use

food more rapidly than they manufacture it. Perhaps

it would be more accurate to say that the plant moves

the food, or part of it, to the seed from the stem, root,

or leaf. In annuals and biennials, the seed gets most

of the food, while in perennials, it gets only part. The

method of storage is almost identical whether in the

seed, root, or stem.

When sugar is first made it changes into starch. At

night, starch can usually be found in healthy leaves, but

usually not early next morning. Enzymes have changed

it to sugar and the plant has transported it to the place

of storage. Here it is again changed by enzymes into

starch which now fills the white plastids of the cell just

as chlorphyll did the green. A microscope shows this

starch to be in rings with the center of formation on one

side in the potato, and in the middle in beans. Plastid

after plastid may be laden until the whole cell seems to be

composed of starch. Here it remains until transloca-

tion to the seed begins, when enzymes turn it to sugar and

the plant carries it upward through the tracheal tubes.

Proteins are deposited in the cytoplasm as crystals or

globules, or as both. Less storing is done than in the

case of starch, but it is handled in nearly the same way.

Fats and oils usually enmesh themselves in the cytoplasm.

Much seed storage is in the form of oil since most energy

can be so stored in a given space. Embryos are rich in

oil, supposedly on this account.

Plants that store sugar deposit it as false crystals in the

The Plant as a Factory 61

vacuoles when the cell-sap dries, leaving the sugar too

concentrated to remain dissolved. Less soluble sugars

are foiuid in storage than in the sap of the same plant.

This is natural, since insoluble starch and cellulose, and

slightly soluble saccharose (cane sugar) are much less

easily disturbed than the highly-soluble glucose (grape

sugar) of the sap.

51. Harvest. — Plants vary in composition as age

advances because nitrogen and ash are taken up early

and carbohydrates are manufactured later. The place

of storage changes, leaving a plant part rich in food at

one time and almost devoid of it at another. Man must

know for what he wishes the plant. He must also know

what part he wishes to harvest and when he will find what

he wants in that part. Wheat makes the best hay at

bloom or in the soft dough, but is useless for grain until

nearly mature. Beets and carrots yield roots at the end

of the first year, but seed only at the end of the second.

It is rather general for stems, roots, and leaves to lose food

material rapidly as the seed forms.

If hay is the crop, let the grass or legume be cut when

the leaves andВ«stems are rich in delicious, digestible food.

They must be cured in such a way as not to lose value by

leaching with rain or by shattering. When seed is desired,

the plants advance to maturity. Care that seed does

not shell out is all that is' necessary. If roots are required,

biennials are harvested the first autumn; if seed, then

the tops are cut the second. Fruit is picked when full

grown and mature enough to be delicious, yet when firm

enough to withstand handling. Cotton is picked after

the bolls break, but before the lint weathers from the seed.

Man cuts short the life of the plant when it is in the

condition that will best fit his purpose. Curing begins

at once and goes on in sunshine or shade, hastily or gradu-

62 The Principles of Agronomy

aUy> by air or by heat according to the product expected.

Considerable knowledge of plants and effects of treat-

ment are required. He who does this work must know

his ground and work with precision.

52. Control of the harvest. — As civilization has ad-

vanced, man has gained more and more control over na-

ture. More and better machines, propelled more effec-

tively, have given him an enormous power to harvest

large fields within a short time. Orchard-grass must be

cut within a few days of bloom ; timothy may be mown

any time within two or three weeks. American farmers

have chosen to grow timothy. This enables them to tend

much larger hayfields. Some wheats shell more easily

than others; some potato varieties ripen earlier than

others; and alfalfa is richer in protein than grass. All

these factors enable man to control the harvest by choosing

his crop wisely.

Better cultivation, more thorough manuring, and wiser

irrigation produce greater yields. The Utah Station

found that the time of application and the quantities of

irrigation water affected the proportion of stem, leaves, and

grain, and also the chemical composition of these parts.

It was found that moderate irrigation produced better

qualities of grain, potatoes, and fruit than did excessive

water which promoted woodiness and stem development.

Thick planting yields slender, straight flax stems bear-

ing long fiber but little seed ; thin planting, which allows

branching, begets short fiber but much seed. Pruning

may direct food from small useless growth to fruit, and

thinning gives fewer but larger fruits.

If man will but learn the ways of his crop, he may have

largely within his grasp the power to get what he desires

from the plant world. He may set certain forces in

action ; and then, at the right moment, gather a harvest

The Plant as a Factory 63

superior in yield and quality to that of his less diligent

neighbors. The Bible says :

" And God blessed them and God said unto them, Be

fruitful, and multiply, and replenish the earth, and sub-

due it ; and have dominion over the fish of the sea, and

over the fowl of the air, and over every living thing that

moveth upon the earth.

" And God said. Behold, I have given you every herb

bearing seed, which is upon the face of the earth, and every

tree, in which is the fruit of a tree yielding seed ; to you