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 quant.i.ties.

_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 const.i.tuent of common salt (chloride of sodium), and from this source may be obtained in sufficient quant.i.ties for manurial purposes.

[What is the difference between _per_oxide and _prot_oxide 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 cla.s.s const.i.tutes 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 cla.s.ses, those not containing nitrogen, and those which do contain it.

The first cla.s.s const.i.tute nearly the whole plant.

The second cla.s.s, although small in quant.i.ty, 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 cla.s.s 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 cla.s.s?

Under what circ.u.mstances is animal fat decomposed?]

The first cla.s.s of proximates in animals comprise the fat, and like tissues.

The second cla.s.s form the muscle, hair, gelatine of the bones, etc.

In order that they may be perfectly developed, animals must eat both cla.s.ses 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 cla.s.s 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 princ.i.p.ally of _woody fibre_.

Their seeds, and sometimes their roots, contain considerable quant.i.ties 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 coa.r.s.e 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 quant.i.ties 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.