As has been already stated, it is not strictly correct that this or that kind of vegetable is more fitted to sustain animal life, simply because of the larger proportion of nitrogen it contains; but it is wisely provided, that along with this nitrogen in all plants, a certain proportion of starch or sugar and of saline and earthy matter are always associated—so that the quantity of nitrogen may be considered as a rough practical index of the proportion of some of the important saline and earthy ingredients also.
An important practical lesson on this subject is taught us by the study of the wise provisions of Nature. Not only does the milk of the mother contain all the elements of a nutritive food mixed up together—as the egg does also for the unhatched bird—but in rich natural pastures the same mixture uniformly occurs. Hence, in cropping the mixed herbage, the animal introduces into its stomach portions of various plants—some abounding more in starch or sugar, some more in gluten or albumen, some naturally richer in saline, others in earthy constituents; and out of these varied materials the digestive organs select a due proportion of each, and reject the rest. Wherever a pasture becomes usurped by one or two grasses—either animals cease to thrive upon it, or they must crop a much larger quantity of food to supply the natural waste of all the parts of their bodies.
It may indeed be assumed as almost a general principle, that whenever animals are fed on one kind of vegetable only, there is a waste of one or other of the necessary elements of animal food, and that the great lesson on this subject taught us by nature is, that, by a judicious admixture, not only is food economised, but the labour imposed upon the digestive organs is also materially diminished.
SECTION VIII.—CONCLUDING OBSERVATIONS.
In this little work, now brought to a close, I have presented the reader with a slight, and I hope plain and familiar, sketch of the various topics connected with practical agriculture, on which the sciences of chemistry and geology are fitted to throw the greatest light.
We have studied the general characters of the organic and inorganic elements of which the parts of plants are made up, and the several compounds of these elements which are of the greatest importance in the vegetable kingdom. We have examined the nature of the seed,—seen by what beautiful provision it is fed during its early germination—in what form the elements by which it is nourished are introduced into the circulation of the young plant when the functions of the seed are discharged,—and how earth, air, and water are all made to minister to its after-growth. We have considered the various chemical changes which take place within the growing plant, during the formation of its woody stem, the blossoming of its flower, and the ripening of its seed or fruit,—and have traced the further changes it undergoes, when, the functions of its short life being discharged, it hastens to serve other purposes, by mingling with the soil, and supplying food to new races. The soils themselves in which plants grow, their nature, their origin, the causes of their diversity in mineral character, and in natural productiveness, have each occupied a share of our attention—while the various means of improving their agricultural value by manuring or otherwise, have been practically considered, and theoretically explained. Lastly, we have glanced at the comparative worth of the various products of the land, as food for man or other animals, and have briefly illustrated the principles upon which the feeding of animals and the relative nutritive powers of the vegetables on which they live are known to depend.
In this short and familiar treatise I have not sought so much to satisfy the demands of the philosophical agriculturist, as to awaken the curiosity of my less instructed reader, to shew him how much interesting as well as practically useful information chemistry and geology are able and willing to impart to him, and thus to allure him in quest of further knowledge and more accurate details to my larger work,[27] of which the present exhibits only a brief outline.
J. P. Wright, Printer, 18 New street, N. Y.
Wiley & Putnam’s New Publications.
LIBRARY FOR THE YOUNG.