chemical knowledge, as elements. The Bodies incapable of decomposition, at present known, are forty-seven; of these, thirty-eight are metals, six are inflammable bodies, and three, substances which unite with metals and inflammable bodies, and form with them acids, alkalies, earths, or other analogous compounds. The chemical composition of Plants has, within the last ten years, been elucidated by the experiments of a number of chemical philosophers, both in this and other countries, and it forms a beautiful part of general chemistry, if the organs of Plants be submitted to a chemical analysis; it is found that their almost infinite diversity of form, depends upon different arrangements and combinations of a very few of the elements, seldom more than seven or eight belong to them, and three, constitute the greatest part of their organised matter."

"All the varieties of substances found in Plants are produced from the sap, and the sap of Plants is derived from water, or from the fluids in the soil, and it is altered by, or combined with, principles derived from the atmosphere."

"Soils in all cases consist of a mixture of dif ferently divided earthy matter, and with animal or vegetable substances in a state of decomposition, and certain saline ingredients. The earthy matters are the true basis of the soil; the other parts, whether natural, or artificially introduced, operate in the same manner."

Sir Humphry also says, "What may be our ul

timate view of the laws of chemistry, or how far our ideas of elementary principles may be simplified, it is impossible to say - We can only reason from facts, we cannot imitate the powers of composition belonging to vegetable structures, but at least we can understand them, and as far as our researches have undergone, it appears that in vegetation, compound forms are uniformly produced from simpler ones; and the elements in the soil, water? the atmosphere, and the earth, absorbed and made parts of beautiful and diversified structures."

Kirwan states, "All Plants, (except the subaqueous) grow in a mixed earth moistened with rain and dew, and exposed to the atmosphere; if this earth be chemically examined, it will be found to consist of silicious, calcareous, and argillaceous particles, often also of magnesia in various proportions, a very considerable quantity of water, and some fixed air. The most fertile also contain a small portion of oil, roots of decayed vegetables, a coaly substance arising from putrefaction, some traces of marine acid, and gypsum. On the other hand, if vegetables be analysed they will be found to contain a large portion of water and charcoal, also of fat and essential oils, resins, gums, and vegetable acids, all which are reducible to water, pure air, inflammable air and charcoal; a small portion of fixed alkali is also found, some neutral salts, most commonly Epsom, tartar vitriolate, common salts and salt of sylvius.”

So far, things are merely reduced to compounds,

and the opinions of these great men accord; but Sir Humphry, farther says " If any fresh vegetable matter which contains sugar, mucilage, starch, or other of the vegetable compounds soluble in water, be moistened and exposed to air, at a temperature of from 50 to 80, oxygene will soon be absorbed and carbonic acid formed, heat will be produced, and elastic fluids, principally carbonic acid, gaseous oxyde of carbon, and hydro-carbonate will be evolved, a dark coloured liquid of a slight sour, or bitter taste, will likewise be formed; and if the process be suffered to continue for a time sufficiently long, nothing solid will remain exceptearthy and saline matter, coloured black by char-coal.

"Animal matters are in general more liable to decompose than vegetable substances, oxygene is absorbed, and carbonic acid and ammonia formed. In the process of their putrefaction they produce compound elastic fluids and likewise azote; they afford dark coloured acid and oily fluids, and leave a residuum of salts and earths mixed with a calcareous matter, the ammonia given off from animal compounds in putrefaction, may be conceived to be formed at the time of their decomposition, by the combination of hydrogene and azote; except this matter, the other products of putrefaction are analagous to those afforded by the fermentation of vegetable substances, and the soluble substances. formed, abound in the elements which are the

constituent parts of vegetables, in carbon, hydrogene, and oxygene.

Again, “The circumstances necessary for the putrefaction of animal substances, are similar to those required for the fermentation of vegetable substances, a temperature above the freezing point, the presence of water and the presence of oxygene, at least in the first stage of the process. He likewise says, "It is probable that as yet we are not acquainted with any of the true elements of matter."

It however appears that both animal and vegetable matters are reducible to the same principles, and so far simplified as to be clearly capable of the different combinations required to reproduce and sustain both animals and vegetables.

Kirwan observes, "Hence we see on the last analysis the only substances common to the growing vegetables, and the soils in which they grow, are water, coal, different earths and salts: these therefore are the true Food of Vegetables; to them we should also add, fixed air, though by reason of its decomposition it may not be distinctly found in them, or at least not distinguishable from that newly formed during their decomposition."

Sir Humphry adds, "Vegetable and animal substances deposited in the soil, as shewn by universal experience, are consumed during the process of vegetation, and they can only nourish * Animal matter containing nitrogene, which vegetable matter does not.

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the Plant by affording solid matter capable of being dissolved by the fluids in the leaves of vegetables; but such parts of them as are rendered gaseous and that pass into the atmosphere, must possess a comparative small effect, for gases soon become diffused through the mass of the surrounding air.

"The great object in the application of manures should be to make it afford as much soluble matter as possible to the Roots of the Plant, and that in a slow and gradual manner, so that it may be entirely consumed in forming its sap and organized parts.

So far the component parts of the Food of Plants seem to be generally understood and admitted; and on the medium of its application and consumption, Kirwan observes, "The agency of water in the process of vegetation, has not till of late been distinctly perceived: Dr. Hales has shewn, that in the summer-months a sun-flower weighing three pounds avoirdupois, and regularly watered every day, passed through it or perspired 22 oz. each day, that is, half its weight. Dr. Woodward found that a sprig of common spearmint, a Plant that thrives best in moist soils, weighing only 28.25 grs. passed through it 3004 grs. in 77 days, between July and October, that is somewhat more than its whole weight each day. He did more, for he found that in that space of time the Plant increased 17 grs. in weight, and yet had no other food but pure rain water, but he also found that it increased more in