The Elements of Agriculture.

by George E. Waring.

SECTION FIRST.

THE PLANT.

CHAPTER I.

INTRODUCTION.

[What is the object of cultivating the soil?

What is necessary in order to cultivate with economy?

Are plants created from nothing?]

The object of cultivating the soil is to raise from it a crop of _plants_. In order to cultivate with economy, we must _raise the largest possible quant.i.ty with the least expense, and without permanent injury to the soil_.

Before this can be done we must study the character of plants, and learn their exact composition. They are not _created_ by a mysterious power, they are merely made up of matters already in existence. They take up water containing food and other matters, and discharge from their roots those substances that are not required for their growth. It is necessary for us to know what kind of matter is required as food for the plant, and where this is to be obtained, which we can learn only through such means as shall separate the elements of which plants are composed; in other words, we must _take them apart_, and examine the different pieces of which they are formed.

[What must we do to learn the composition of plants?

What takes place when vegetable matter is burned?

What do we call the two divisions produced by burning?

Where does organic matter originate? Inorganic?

How much of chemistry should farmers know?]

If we burn any vegetable substance it disappears, except a small quant.i.ty of earthy matter, which we call _ashes_. In this way we make an important division in the const.i.tuents of plants. One portion dissipates into the atmosphere, and the other remains as ashes.

That part which burns away during combustion is called _organic matter_; the ashes are called _inorganic matter_. The organic matter has become air, and hence we conclude that it was originally obtained from air. The inorganic matter has become earth, and was obtained from the soil.

This knowledge can do us no good except by the a.s.sistance of chemistry, which explains the properties of each part, and teaches us where it is to be found. It is not necessary for farmers to become chemists. All that is required is, that they should know enough of chemistry to understand the nature of the materials of which their crops are composed, and how those materials are to be used to the best advantage.

This amount of knowledge may be easily acquired, and should be possessed by every person, old or young, whether actually engaged in the cultivation of the soil or not. All are dependent on vegetable productions, not only for food, but for every comfort and convenience of life. It is the object of this book to teach children the first principles of agriculture: and it contains all that is absolutely necessary to an understanding of the practical operations of cultivation, etc.

[Is organic matter lost after combustion?

Of what does it consist?

How large a part of plants is carbon?]

We will first examine the _organic_ part of plants, or that which is driven away during combustion or burning. This matter, though apparently lost, is only changed in form.

It consists of one solid substance, _carbon_ (or charcoal), and three gases, _oxygen_, _hydrogen_ and _nitrogen_. These four kinds of matter const.i.tute nearly the whole of most plants, the ashes forming often less than one part in one hundred of their dry weight.

[What do we mean by gas?

Does oxygen unite with other substances?

Give some instances of its combinations]

When wood is burned in a close vessel, or otherwise protected from the air, its carbon becomes charcoal. All plants contain this substance, it forming usually about one half of their dry weight. The remainder of their organic part consists of the three gases named above. By the word gas, we mean _air_. Oxygen, hydrogen and nitrogen, when pure, are always in the form of air. Oxygen has the power of uniting with many substances, forming compounds which are different from either of their const.i.tuents alone. Thus: oxygen unites with _iron_ and forms oxide of iron or _iron-rust_, which does not resemble the gray metallic iron nor the gas oxygen; oxygen unites with carbon and forms carbonic acid, which is an invisible gas, but not at all like pure oxygen; oxygen combines with hydrogen and forms water. All of the water, ice, steam, etc., are composed of these two gases. We know this because we can artificially decompose, or separate, all water, and obtain as a result simply oxygen and hydrogen, or we can combine these two gases and thus form pure water; oxygen combines with nitrogen and forms nitric acid. These chemical changes and combinations take place only under certain circ.u.mstances, which, so far as they affect agriculture, will be considered in the following pages.

As the organic elements of plants are obtained from matters existing in the atmosphere which surrounds our globe, we will examine its const.i.tution.

CHAPTER II.

ATMOSPHERE.

[What is atmospheric air composed of?

In what proportions?

What is the use of nitrogen in air?

Does the atmosphere contain other matters useful to vegetation?

What are they?]

Atmospheric air is composed of oxygen and nitrogen. Their proportions are, one part of oxygen to four parts of nitrogen. Oxygen is the active agent in the combustion, decay, and decomposition of organized bodies (those which have possessed animal or vegetable life, that is, organic matter), and others also, in the breathing of animals. Experiments have proved that if the atmosphere consisted of pure oxygen every thing would be speedily destroyed, as the processes of combustion and decay would be greatly accelerated, and animals would be so stimulated that death would soon ensue. The use of the nitrogen in the air is to _dilute_ the oxygen, and thus reduce the intensity of its effect.

Besides these two great elements, the atmosphere contains certain impurities which are of great importance to vegetable growth; these are, _carbonic acid, water, ammonia, etc._

CARBONIC ACID.

[What is the source of the carbon of plants?

What is carbonic acid?

What is its proportion in the atmosphere?

Where else is it found?

How does it enter the plant?

What are the offices of leaves?]