CHAPTER V
Of what does a perfect young plant consist?
How must the food of plants be supplied?
Can carbon and earthy matter be taken up at separate stages of growth, or must they both be supplied at once?
Having examined the materials of which plants are made, it becomes necessary to discover how they are put together in the process of growth. Let us therefore suppose a young wheat-plant for instance to be in condition to commence independent growth.
It consists of roots which are located in the soil; leaves which are spread in the air, and a stem which connects the roots and leaves. This stem contains sap vessels (or tubes) which extend from the ends of the roots to the surfaces of the leaves, thus affording a passage for the sap, and consequently allowing the matters taken up to be distributed throughout the plant.
What seems to be nature's law with regard to this?
What is the similarity between making a cart and raising a crop?
In the growth of a young plant, what operations take place about the same time?
It is necessary that the materials of which plants are made should be supplied in certain proportions, and at the same time. For instance, carbon could not be taken up in large quantities by the leaves, unless the roots, at the same time, were receiving from the soil those mineral matters which are necessary to growth. On the other hand, no considerable amount of earthy matter could be appropriated by the roots unless the leaves were obtaining carbon from the air. This same rule holds true with regard to all of the constituents required; Nature seeming to have made it a law that if one of the important ingredients of the plant is absent, the others, though they may be present in sufficient quantities, cannot be used. Thus, if the soil is deficient in potash, and still has sufficient quantities of all of the other ingredients, the plant cannot take up these ingredients, because potash is necessary to its life.
If a farmer wishes to make a cart he prepares his wood and iron, gets them all in the proper condition, and then can very readily put them together. But if he has all of the wood necessary and no iron, he cannot make his cart, because bolts, nails and screws are required, and their place cannot be supplied by boards. This serves to illustrate the fact that in raising plants we must give them every thing that they require, or they will not grow at all.
In the case of our young plant the following operations are going on at about the same time.
The leaves are absorbing carbonic acid from the atmosphere, and the roots are drinking in water from the soil.
What becomes of the carbonic acid?
How is the sap disposed of?
What does it contain?
How does the plant obtain its carbon?
Its oxygen and hydrogen?
Its nitrogen?
Its inorganic matter?
Under the influence of daylight, the carbonic acid is decomposed; its oxygen returned to the atmosphere, and its carbon retained in the plant.
The water taken in by the roots circulates through the sap vessels of the plant, and, from various causes, is drawn up towards the leaves where it is evaporated. This water contains the nitrogen and the inorganic matter required by the plant and some carbonic acid, while the water itself consists of hydrogen and oxygen.
Thus we see that the plant obtains its food in the following manner:—
What changes does the food taken up by the plant undergo?
Many of the chemical changes which take place in the interior of the plant are well understood, but they require too much knowledge of chemistry to be easily comprehended by the young learner, and it is not absolutely essential that they should be understood by the scholar who is merely learning the elements of the science.
It is sufficient to say that the food taken up by the plant undergoes such changes as are required for its growth; as in animals, where the food taken into the stomach, is digested, and formed into bone, muscle, fat, hair, etc., so in the plant the nutritive portions of the sap are resolved into wood, bark, grain, or some other necessary part.
The results of these changes are of the greatest importance in agriculture, and no person can call himself a practical farmer who does not thoroughly understand them.
CHAPTER VI
We have hitherto examined what is called the ultimate division of plants. That is, we have looked at each one of the elements separately, and considered its use in vegetable growth.
Of what do wood, starch and the other vegetable compounds chiefly consist?
Are their small ashy parts important?
What are these compounds called?
Into how many classes may proximate principles be divided?
Of what do the first class consist? The second?
What vegetable compounds do the first class comprise?
We will now examine another division of plants, called their proximate division. We know that plants consist of various substances, such as wood, gum, starch, oil, etc., and on examination we shall discover that these substances are composed of the various organic and inorganic ingredients described in the preceding chapters. They are made up almost entirely of organic matter, but their ashy parts, though very small, are (as we shall soon see) sometimes of great importance.
These compounds are called proximate principles,7 or vegetable proximates. They may be divided into two classes.
The first class are composed of carbon, hydrogen, and oxygen.
The second class contain the same substances and nitrogen.
Are these substances of about the same composition?
Can they be artificially changed from one to another?
Give an instance of this.
Is the ease with which these changes take place important?
From what may the first class of proximates be formed?
The first class (those compounds not containing nitrogen) comprise the wood, starch, gum, sugar, and fatty matter which constitute the greater part of all plants, also the acids which are found in sour fruits, etc. Various as are all of these things in their characters, they are entirely composed of the same ingredients (carbon, hydrogen and oxygen), and usually combined in about the same proportion. There may be a slight difference in the composition of their ashes, but the organic part is much the same in every case, so much so, that they can often be artificially changed from one to the other.
As an instance of this, it may be recollected by those who attended the Fair of the American Institute, in 1834, that Prof. Mapes exhibited samples of excellent sugar made from the juice of the cornstalk, starch, linen, and woody fibre.
The ease with which these proximates may be changed from one to the other is their most important agricultural feature, and should be clearly understood before proceeding farther. It is one of the fundamental principles on which the growth of both vegetables depends.
The proximates of the first class constitute usually the greater part of all plants, and they are readily formed from the carbonic acid and water which in nature are so plentifully supplied.
Why are those of the second class particularly important to farmers?
What is the general name under which they are known?
What