Let us now examine plants with a view to learning the _location_ of the various plants.

The stem or trunk of the plant or tree consists almost entirely of _woody fibre_; this also forms a large portion of the other parts except the seeds, and, in some instances, the roots. The roots of the potato contain large quant.i.ties of _starch_. Other roots such as the _carrot_ and _turnip_ contain _pectic acid_,[J] a nutritious substance resembling starch.

It is in the _seed_ however that the more nutritive portions of most plants exist, and here they maintain certain relative positions which it is well to understand, and which can be best explained by reference to the following figures, as described by Prof. Johnston:--

[Ill.u.s.tration: Fig. 1.]

"Thus _a_ shows the position of the oil in the outer part of the seed--it exists in minute drops, inclosed in six-sided cells, which consists chiefly of gluten; _b_, the position and comparative quant.i.ty of the starch, which in the heart of the seed is mixed with only a small proportion of gluten; _c_, the germ or chit which contains much gluten."[K]

[Is the composition of the inorganic matter of different parts of the plant the same, or different?

What is the difference between the ash of the straw and that of the grain of wheat?]

The location of the _inorganic_ part of plants is one of much interest, and shows the adaptation of each part to its particular use. Take a wheat plant, for instance--the stalk, the leaf, and the grain, show in their ashes, important difference of composition. The stalk or straw contains three or four times as large a proportion of ash as the grain, and a no less remarkable difference of composition may be noticed in the ashes of the two parts. In that of the straw, we find a large proportion of silica and scarcely any phosphoric acid, while in that of the grain there is scarcely a trace of silica, although phosphoric acid const.i.tutes more than one half of the entire weight. The leaves contain a considerable quant.i.ty of lime.

[What is the reason for this difference?

In what part of the grain does phosphoric acid exist most largely?]

This may at first seem an unimportant matter, but on examination we shall see the use of it. The straw is intended to support the grain and leaves, and to convey the sap from the roots to the upper portions of the plant. To perform these offices, _strength_ is required, and this is given by the _silica_, and the woody fibre which forms so large a proportion of the stalk. The silica is combined with an alkali, and const.i.tutes the gla.s.sy coating of the straw. While the plant is young, this coating is hardly apparent, but as it grows older, as the grain becomes heavier, (verging towards ripeness), the silicious coating of the stalk a.s.sumes a more prominent character, and gives to the straw sufficient strength to support the golden head. The straw is not the most important part of the plant as _food_, and therefore requires but little phosphoric acid.

[Why is Graham flour more wholesome than fine flour?

Are the ashes of all plants the same in their composition?]

The grain, on the contrary, is especially intended as food, and therefore must contain a large proportion of phosphoric acid--this being, as we have already learned, necessary to the formation of bone--while, as it has no necessity for strength, and as silica is not needed by animals, this ingredient exists in the grain only in a very small proportion. It may be well to observe that the phosphoric acid of grain exists most largely in the hard portions near the sh.e.l.l, or bran.

This is one of the reasons why Graham flour is more wholesome than fine flour. It contains all of the nutritive materials which render the grain valuable as food, while flour which is very finely bolted[L] contains only a small part of the outer portions of the grain (where the phosphoric acid, protein and fatty matters exist most largely). The starchy matter in the interior of the grain, which is the least capable of giving strength to the animal, is carefully separated, and used as food for man, while the better portions, not being ground so finely, are rejected. This one thing alone may be sufficient to account for the fact, that the lives of men have become shorter and less blessed with health and strength, than they were in the good old days when a stone mortar and a coa.r.s.e sieve made a respectable flour mill.

Another important fact concerning the ashes of plants is the difference of their composition in different plants. Thus, the most prominent ingredient in the ash of the potato is _potash_; of wheat and other grains, _phosphoric acid_; of meadow hay, _silica_; of clover, _lime_; of beans, _potash_, etc. In grain, _potash_ (or _soda_), etc., are among the important ingredients.

[Of what advantage are these differences to the farmer?

Of what are plants composed?]

These differences are of great importance to the practical farmer, as by understanding what kind of plants use the most of one ingredient, and what kind requires another in large proportion, he can regulate his crops so as to prevent his soil from being exhausted more in one ingredient than in the others, and can also manure his land with reference to the crop which he intends to grow. The tables of a.n.a.lyses in the fifth section will point out these differences accurately.

FOOTNOTES:

[J] This pectic acid gelatinizes food in the stomach, and thus renders it more digestible.

[K] See Johnston's Elements, page 41.

[L] Sifted through a fine cloth called a bolting cloth.

CHAPTER VIII.

RECAPITULATION.

We have now learned as much about the plant as is required for our immediate uses, and we will carefully reconsider the various points with a view to fixing them permanently in the mind.

Plants are composed of _organic_ and _inorganic_ matter.

[What is organic matter? Inorganic?

Of what does organic matter consist? Inorganic?

How do plants obtain their organic food?

How their inorganic?

How is ammonia supplied? Carbonic acid?]

Organic matter is that which burns away in the fire. Inorganic matter is the ash left after burning.

The organic matter of plants consists of three gases, oxygen, hydrogen and nitrogen, and one solid substance carbon (or charcoal). The inorganic matter of plants consists of potash, soda, lime, magnesia, sulphuric acid, phosphoric acid, chlorine, silica, oxide of iron, and oxide of manganese.

Plants obtain their organic food as follows:--Oxygen and hydrogen from water, nitrogen from some compound containing nitrogen (chiefly from ammonia), and carbon from the atmosphere where it exists as carbonic acid--a gas.

They obtain their inorganic food from the soil.

The water which supplies oxygen and hydrogen to plants is readily obtained without the a.s.sistance of manures.

Ammonia is obtained from the atmosphere, by being absorbed by rain and carried into the soil, and it enters plants through their roots. It may be artificially supplied in the form of animal manure with profit.

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 const.i.tuents?

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 const.i.tuents pa.s.s away as water, ammonia, carbonic acid, etc., ready again to be taken up by other plants.