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ON THE FOOD OF PLANTS.
The Food of Plants has for a long time excited an anxious enquiry, and a great variety of conjectures have been formed as to what it consists of, or in what state it is taken up by the Roots. It has been an object of research with men of the greatest talents and learning, and to aid them, the powers of chemistry have been exerted and applied in a variety of ingenious experiments. The earth, as well as vegetables and animals, has been analysed and variously described, and accurate observations have been made and stated; but as yet no one has
l been able to describe a theory that has obtained general concurrence, or to establish a clear and practical rule for ascertaining the quantity and quality of the Food of Plants furnished by particular soils, nor the means of giving fertility, or restoring it when exhausted, by regulated proportions.
Although the earth appears capable of affording and sustaining a spontaneous produce in vegetables and fruit, her powers of production or principles of fertility are found to be limited, and possessed in different degrees by different portions; and it has been clearly proved that they are sooner or later exhausted by the growth of particular vege
tables, according to the nature and situation of the soil ; it therefore became an object essential to the Arts of Horticulture and Agriculture, to ascertain the nature of vegetables and the composition of the soil most congenial to their different productions, in order to be enabled to remedy defects, remove opposing matter, and supply deficiencies, or, in other words, to sustain, increase, or diminish, the powers of production, or principles of fertility.
Vegetables, like animals, vary in their nature and habits, and like them have their peculiar food, for although the Food of Plants may generally be -composed of the same elements, it varies in the proportion of its composition, and thereby becomes adapted to different purposes; thus we find, that a soil which will furnish only Food enough to support one Plant of a peculiar kind, will at the same time furnish sufficient to sustain many others of
: different species.
Bradley, in the work I have before noticed, says, “ Land animals may be likened in general to those Plants which are called Terrene, for that they live only upon the earth, such as oak, elm, beech, &c.; amphibious animals, such as otters, beavers, tortoises, frogs, &c. which live as well on the land as in the waters, may be compared to. the willows, alders, minths, &c. The fish kind, or aquatic race, whether of the rivers or the sea, are analogous to the water plants, such as water lilies, water plantains, &c. which live only in the fresh
waters, or the fuci, &c. which are sea or salt water plants, and not any of these will live out of its proper element; from whence we may conclude how improper it would be to plant a water lily on a dry sandy desert, or an oak at the bottom of the sea, which would be just as reasonable as if we propose to feed a dog with hay, or a horse with fish; however this rule of nature has been so little observed, even by some of our greatest planters, that we can hardly boast of good success in one out of five plantations that have been made.”
He also says, “ I shall beg leave to remark, that as the several land animals have their respective diets, so have the Terrene Plants their
several soils from whence they derive their nourishment, as some animals feed on flesh, others on fish, &c. so do Plants love, some clay, others loam, sand or gravel ; nor is this all we ought to observe, we must consider likewise how beneficial to every Plant is a right exposure, whether in a vale, the sides or tops of hills, exposed to the south or north winds, whether inland or near the sea, for it is a proper exposure that keeps a Plant in health.”
Bradley, Hitt, and Miller, consider the Food of Plants to be salts, which every species of earth. more or less, contains within itself; and that according to the proportion of salts contained in each kind of soil or manure, will its prolificacy be.
That all soils, and all vegetable and animal matter, may be found to produce salts, under certain chemical
processes, I have no doubt; but this does
not prove it to be necessary that every substance, or any substance containing the basis or elements of salts, should undergo this process, and be formed into salts, before it can be in a state to constitute Food fit for the reception and nourishment of Plants.
Salts are various in their nature and general effects, when placed in contact with other substances.
I have made many experiments with sea salt, nitre, soda, barilla, &c. &c. and feel myself justified in concluding, from the results, that salts are not in any degree an essential in the Food of Plants.
The opinions of Drs. Smith and Pearson on this subject, appear rational : they say, that salts, as they operate in promoting vegetation, are analogous to mustard, cinnamon, ginger, &c. which are not of themselves at all, or necessarily nutritious, but contribute to render other things nutritious by exciting the action of the stomach, and other organs of digestion and assimilation. Dr. Pearson
-“I have no doubt of the truth of the position, that no living thing, neither Plant nor Animal, can grow or live in a state of visible action, without supplies of matter that has been alive; in other words, living Animals and Vegetables can only live on dead Animals and dead Vegetables; no Plant nor Animal has ever been known by experience, nor in the nature of things does it seem reasonable, that they can be nourished
by mere water and pure air, as some persons have asserted.”
Notwithstanding all that has been said to establish the opinion that salt is a valuable manure, I am convinced it never can, as an article of food, contribute to the increase of any vegetable, but as a chemical agent, by destroying and hastening the decomposition of animals and vegetables, and by its deliquescence, 'it may in many instances increase the fertility of soils.
Mr. Kirwan, in an Essay on Manures and the Food of Plants, as applicable to Agriculture, takes a very correct and comprehensive view of his subject.
Sir Humphry Davy also has favoured the world with a very luminous work on agricultural chemistry
Both those eminent chemists appear to have maturely considered the nature of Manures and the Food of Plants, and, no doubt, have explained their opinions and detailed their experiments with great clearness and perspicuity.
Were it possible for me, in a work like this, to convey an adequate idea of the information contained in either of those works, it may appear conceited and presumptuous to attempt it; but as I could not claim the merit of having done my
best to elucidate my subject, without a reference to such splendid authorities, and finding it difficult to explain their arguments, experiments, and results, in any language equal to their own, I trust I shall be