Carbonic acid is absorbed from the atmosphere by leaves, and decomposed in the green parts of plants under the influence of daylight; the carbon is retained, and the oxygen is returned to the atmosphere.
When plants are destroyed by combustion or decay, what becomes of their constituents?
How does the inorganic matter enter the plant?
Are the alkalies soluble in their pure forms?
Which one of them is injurious when too largely present?
How may sulphuric acid be supplied?
Is phosphoric acid important?
How must silica be treated?
From what source may we obtain chlorine?
When plants are destroyed by decay, or burning, their organic constituents pass away as water, ammonia, carbonic acid, etc., ready again to be taken up by other plants.
The inorganic matters in the soil can enter the plant only when dissolved in water. Potash, soda, lime, and magnesia, are soluble in their pure forms. Magnesia is injurious when present in too large quantities.
Sulphuric acid is often necessary as a manure, and is usually most available in the form of sulphate of lime or plaster. It is also valuable in its pure form to prevent the escape of ammonia from composts.
Phosphoric acid is highly important, from its frequent deficiency in worn-out soils. It is available only under certain conditions which will be described in the section on manures.
Silica is the base of common sand, and must be united to an alkali before it can be used by the plant, because it is insoluble except when so united.
Chlorine is a constituent of common salt (chloride of sodium), and from this source may be obtained in sufficient quantities for manurial purposes.
What is the difference between peroxide and protoxide of iron?
How must the food of plants be supplied?
What takes place after it enters the plant?
What name is given to the compounds thus formed?
How are proximates divided?
Which class constitutes the largest part of the plant?
Of what are animals composed, and how do they obtain the materials from which to form their growth?
Oxide of iron is iron rust. There are two oxides of iron, the peroxide (red) and the protoxide (black). The former is a fertilizer, and the latter poisons plants.
Oxide of manganese is often absent from the ashes of our cultivated plants.
The food of plants, both organic and inorganic, must be supplied in certain proportions, and at the time when it is required. In the plant, this food undergoes such chemical changes as are necessary to growth.
The compounds formed by these chemical combinations are called proximates.
Proximates are of two classes, those not containing nitrogen, and those which do contain it.
The first class constitute nearly the whole plant.
The second class, although small in quantity, are of the greatest importance to the farmer, as from them all animal muscle is made.
Animals, like plants, are composed of both organic and inorganic matter, and their bodies are obtained directly or indirectly from plants.
What parts of the animal belong to the first class of proximates?
What to the second?
What is necessary to the perfect development of animals?
Why are seeds valuable for working animals?
What other important use, in animal economy, have proximates of the first class?
Under what circumstances is animal fat decomposed?
The first class of proximates in animals comprise the fat, and like tissues.
The second class form the muscle, hair, gelatine of the bones, etc.
In order that they may be perfectly developed, animals must eat both classes of proximates, and in the proportions required by their natures.
They require the phosphate of lime and other inorganic food which exist in plants.
Seeds are the best adapted to the uses of working animals, because they are rich in all kinds of food required.
Aside from their use in the formation of fat, proximates of the first class are employed in the lungs, as fuel to keep up animal heat, which is produced (as in fire and decay) by the decomposition of these substances.
When the food is insufficient for the purposes of heat, the animal's own fat is decomposed, and carried to the lungs as fuel.
The stems, roots, branches, etc., of most plants consist principally of woody fibre.
Their seeds, and sometimes their roots, contain considerable quantities of starch.
Name the parts of the plant in which the different proximates exist.
State what you know about flour.
Do we know that different plants have ashes of different composition?
The protein and the oils of most plants exist most largely in the seeds.
The location of the proximates, as well as of the inorganic parts of the plant, show a remarkable reference to the purposes of growth, and to the wants of the animal world, as is noticed in the difference between the construction of the straw and that of the kernel of wheat.
The reason why the fine flour now made is not so healthfully nutritious as that which contained more of the coarse portions, is that it is robbed of a large proportion of protein and phosphate of lime, while it contains an undue amount of starch, which is available only to form fat, and to supply fuel to the lungs.
Different plants have ashes of different composition. Thus—one may take from the soil large quantities of potash, another of phosphoric acid, and another of lime.
By understanding these differences, we shall be able so to regulate our rotations, that the soil may not be called on to supply more of one ingredient than of another, and thus it may be kept in balance.
How are farmers to be benefited by such knowledge?
The facts contained in this chapter are the alphabet of agriculture, and the learner should not only become perfectly familiar with them, but should also clearly understand the reasons why they are true, before proceeding further.
SECTION SECOND.
THE SOIL
CHAPTER I
What is a necessary condition of growth?
In the foregoing section, we have studied the character of plants and the laws which govern their growth. We learned that one necessary condition for growth is a fertile soil, and therefore we will examine the nature of different soils, in order that we may understand the relations between them and plants.
What is a fixed character of soils?
How is the chemical character of the soil to be ascertained?
What do we first learn in analyzing a soil?
How do the proportions of organic or inorganic parts of soils compare with those of plants?
Of what does the organic part of soils consist?
The soil is not to be regarded as a mysterious mass of dirt, whereon crops are produced by a mysterious process. Well ascertained scientific knowledge has proved beyond question that all soils, whether in America or Asia, whether in Maine or California, have certain fixed properties, which render them fertile or barren,