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Chapter I.


It is not possible to conceive of an intelligent solution of the complex problems offered by plant life in the open air and cultivated fields without first considering the innumerable experiments that have been made by experimental botanists. It is therefore necessary for the student and the practical man alike to know something of the laws of growth, as presented in the elaborate treatises by Sachs, Vines, Goodale, and others. I will at present simply collate those special results that bear upon crops as the final object of agriculture and confine myself very closely to the relation between the crop and the climate, in order to avoid being drawn into the discussion of innumerable interesting matters which, although they may affect the crop, yet are understood to be outside the province of climatology. By this latter term I understand essentially the influence on the plant of its inclosure, i. e., the sky or sunshine, soil, temperature, rainfall, and the chemical constitution of the air, either directly or through the



The growth of a plant and the ripening of the fruit is accomplished by a series of molecular changes, in which the atmosphere, the water, and the soil, but especially the sun, play important parts. In this process a vital principle is figuratively said to exist within the seed or plant and to guide the action of the energy from the sun, coercing the atoms of the soil, the water, and the air into such new chemical combinations as will build up the leaf, the woody fiber, the starch, the pollen, the flower, the fruit and the seed.

A climate that is favorable to a special crop is one whose vicissitudes of heat and rain and sunshine are not so extreme but that they can easily be utilized by the sunbeams in building up the plant. An linfavorable climate is one whose average conditions or whose extreme vicissitudes are such that the vitality of the plant-namely, its power to grow-can not make headway against them. In extreme cases, such as frosts, sudden thaws, and great droughts, the climate may even destroy the organic material that had already been formed in the plant.

No plant life, not even the lowest vegetable organism, is perfected except through the influence of the radiation from the sun. It may need the most intense sunlight of the Tropics, or it may need only the diffuse and faint light within dark forests or caves. Heat alone may possibly suffice for the roots and certain stages of growth, but a greater or less degree of light-i. e., energy delivered in short-wave length or rapid periodic oscillations—is necessary for the eventual maturity. The radiation from any artificial light, especially the most powerful electric light, will accomplish results similar to that of sunlight; therefore, it is not necessary to think that life or the vital principle is peculiar to or emanates from the sun, but on the contrary that living cells utilize the radiations or molecular vibrations so far as possible to build up the plant.

We know nothing about the nature of this vital principle, but we can, by the microscope, demonstrate that the essential ultimate structure of the plant or seed is a minute cell, namely, a very thin skin or film or membrane inclosing a minute portion of matter consisting of mixed liquids and solids. This skin is called the wall of the cell; in the early growth of the cell its inclosed liquid is called the protoplasm. By crushing many such young cells we may obtain enough of either part to make a chemical examination and find that the cell wall is a complex chemical substance called cellulose, composed of carbon, hydrogen, and oxygen. By molecules this compound is C18H..; by weight cellulose has C 44.44, H 6.17, O 49.39 per cent. As the cells become older their walls become thicker and are incrusted internally with additional matters, such as gums, resins, etc., until the cell wall refuses to perform its original functions. Such old cells are not easily digested by man or animals and are not considered as food or reckoned among the food crops, but young cells in succulent stems, leaves, and fruits, or the crushed cells of seeds and grains, are nutritious food. Flax, cotton, jute, straw, wood pulp, and many other mature dried cells form the important crops of textile fibers.

The protoplasm within the cell is generally an albuminous compound or albuminoid, viz, besides having carbon, hydrogen, and oxygen, it also contains considerable nitrogen and a little sulphur or phosphorus or iron or other substances, thus forming albumen, whose chemical constitution is expressed by the approximate molecular formula C .

H N, O.S,, or by weight C53, H 7, N 16, () 22, S 1 per cent. Possibly this molecular formula is more properly written 3(C24H.. NGOs), plus the addition of sulphur compounds such as to make the whole become as before written. Mulder supposed that a certain substance which he called proteine, and whose composition is supposed to be Cz.H26N,010, is the basal molecule of albumen; two such molecules, with additional quantities of nitrogen, hydrogen, and oxygen, combined with a little sulphur, phosphorus, iron, or other mineral, make up, according to him, the constitution of the ordinary albuminoid. But his views are not considered altogether acceptable.

The constituent chemical elements contained in cellulose are precisely the same as those of starch, whose formula is C,H2,0., but the arrangement of the atoms and molecules among themselves is

ties of starch and cellulose are very different. Starch, diastase, and cellulose may be considered as substances composed of molecules whose internal structures are respectively more and more complex; in the molecules of each of these substances the carbon, hydrogen, and oxygen are in the same proportions relative to each other both by number and by weight, but a molecule of diastase has twice and one of cellulose three times as many atoms as a molecule of starch. The composition of pure water is represented by the molecular formula H,0,, or by weight H 11, O 89, so that starch may be considered as a compound of 6 atoms of carbon with 5 molecules of water. From the same point of view diastase would be compounded of 12 atoms of carbon and 10 molecules of water, while cellulose would consist of 18 atoms of carbon and 15 molecules of water. These three substances are therefore called carbohydrates, as though carbon combined with water were to be considered as carbon combined with hydric acid. This term is not to be confounded with the word “hydrocarbon,” which is applied to any compound of hydrogen and carbon, which, when combined with water or other molecules, forms a very different series of chemicals, such, for example, as C,H,, which is a hydrocarbon and when combined with 4 molecules of water or hydric oxide forms alcohol, making the latter, as it were, a hydrate of a hydrocarbon.

The approximate percentages by weight of the cellulose found in plants and vegetables dried at a temperature of 212° F. and the per

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centage of albuminous compounds for air-dried crops are given as follows:

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This crude chemical analysis of the walls and of the contents of the crushed cells tells us nothing of the life that had previously resided in the uncrushed organisms, but prepares us for the statement that the development of a plant implies a great amount of work done among the molecules in rearranging them into the places where they are needed. These molecules come from the simpler atoms in the soil, the air, and the rain water, but the force and energy that does the work of building them up comes, so far as we know, from the sunshine. It is a case of the transformation of energy. Within the cells of a plant the molecular energy, or the so-called “radiant energy," that would otherwise produce the phenomena of heat and light is transformed into chemical activity and produces the new molecular compounds that we use as food. We and other animals can not produce these compounds in our own bodies, but we can utilize them if they are not injured in the process of cooking.




It is known that in the act of germination the seed absorbs oxygen from the air contained in the interstices of the soil and that very few seeds will germinate when the soil and the water are deprived of air or free oxygen.

As to the full-grown plant, it is commonly said to absorb carbonicacid gas from the air through its leaves and to exhale oxygen. The investigations of Moisson tend to modify this statement and show that at low temperatures there is more oxygen absorbed than there is carbonic-acid gas produced, while at high temperatures the reverse is true. For each plant there is a certain temperature at which each volume of carbonic-acid gas absorbed is replaced by an equal volume of oxygen exhaled by the leaves. Thus in the case of the Pinus pinaster for every 100 volumes of oxygen absorbed there are 50 volumes of carbonic-acid gas exhaled at 0° C. temperature, but 77 volumes at 13° C. and 114 volumes at 40° C.

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