The Elements of Agriculture. George Edwin Waring

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      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.

      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 is the protein of wheat called?

      Why is flour containing much gluten preferred by bakers?

      Can protein be formed without nitrogen?

      If plants were allowed to complete their growth without a supply of this ingredient, what would be the result?

      The second class of proximates, though forming only a small part of the plant, are of the greatest importance to the farmer, being the ones from which animal muscle8 is made. They consist, as will be recollected, of carbon, hydrogen, oxygen and nitrogen, or of all of the organic elements of plants. They are all of much the same character, though each kind of plant has its peculiar form of this substance, which is known under the general name of protein.

      The protein of wheat is called gluten—that of Indian corn is zein—that of beans and peas is legumin. In other plants the protein substances are vegetable albumen, casein, etc.

      Gluten absorbs large quantities of water, which causes it to swell to a great size, and become full of holes. Flour which contains much gluten, makes light, porous bread, and is preferred by bakers, because it absorbs so large an amount of water.

      What is the result if a field be deficient in nitrogen?

      The protein substances are necessary to animal and vegetable life, and none of our cultivated plants will attain maturity (complete their growth), unless allowed the materials required for forming this constituent. To furnish this condition is the object of nitrogen given to plants as manure. If no nitrogen is supplied the protein substances cannot be formed, and the plant must cease to grow.

      When on the contrary ammonia is given to the soil (by rains or otherwise), it furnishes nitrogen, while the carbonic acid and water yield the other constituents of protein, and a healthy growth continues, provided that the soil contains the mineral matters required in the formation of the ash, in a condition to be useful.

      The wisdom of this provision is evident when we recollect that the protein substances are necessary to the formation of muscle in animals, for if plants were allowed to complete their growth without a supply of this ingredient, our grain and hay might not be sufficiently well supplied with it to keep our oxen and horses in working condition, while under the existing law plants must be of nearly a uniform quality (in this respect), and if a field is short of nitrogen, its crop will not be large, and of a very poor quality, but the soil will produce good plants as long as the nitrogen lasts, and then the growth must cease.9

ANIMALS

      That this principle may be clearly understood, it may be well to explain more fully the application of the proximate constituents of plants in feeding animals.

      Of what are the bodies of animals composed?

      What is the office of vegetation?

      What part СКАЧАТЬ