Thus we see that the plant obtains its food in the following manner:—
| Carbon. | — | In the form of carbonic acid from the atmosphere, and from that contained in the sap, the oxygen being returned to the air. |
| Oxygen & Hydrogen. | — | From the elements of the water constituting the sap. |
| Nitrogen. | — | From the soil (chiefly in form of ammonia). It is carried into the plant through the roots in solution in water. |
| Inorganic Matter. | — | From the soil, and only in solution in water. |
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.
PROXIMATE DIVISION OF PLANTS, ETC.
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.