principle; but heat is not the vital principle of organized bodies, though, probably, a consequence of that principle. Living bodies of animals and plants produce heat; and the phenomenon has not, I think, been entirely explained on any chemical principles, though, in fossils, the production of heat is, in most cases, tolerably well accounted for.

"In animals it seems to have the closest possible connexion with the vital energy; but the effects of this vital energy are still more stupendous in the operations constantly going on in every organized body, from our own elaborate frame to the humble moss or fungus." (p. 7.)

I venture to dissent from the opinion of this excellent man, that if vegetables be endued with sensations, their enjoyments, upon the whole, abundantly counterbalance the sufferings they experience from depredations of various kinds; for, not to say anything of the ravages of animals which feed upon herbage, if we consider the arts and inventions by which man is enabled to bring the vegetable creation under his absolute control; if we take into the account the operations of amputation, deracination, cutting, pruning, ringing, and the variety of instruments whereby these operations are effected, where is the mind of sensibility, believing plants to be endued with sensation, that would not revolt from the daily and hourly infliction of torture upon the most innocent and beautiful of the Creator's work, and turn with disgust from those horticultural pursuits, which might otherwise constitute one of its most gratifying sources of enjoyment?

It surely appears more consistent with benevolence and philosophie truth, to look upon plants as organized beings, endued with a species of life, wholly dependent upon electrical currents; and so constituted, as to be the chief intermedia between the surface of the earth, and the atmosphere which surrounds it; and by whose instrumentality, chemical changes of the highest order are effected, among the most important of which may be ranked, the attraction of aqueous vapours, and the condensation of the dew. (No. 198).

382. Progress of vegetation. The structure of the seed has been described somewhat at large in paragraph 254. "The matter of the seed," observes Sir Humphry Davy, "when examined in its common state, appears dead and inert; it exhibits neither the forms nor the functions of life. But let it be acted upon by moisture, heat, and air, and its organized powers are soon distinctly developed. The cotyledons expand, the membranes burst; the radicle acquires new matter, descends into the soil, and the plume rises towards the free air. By degrees the organs of nourishment of dicotyledonous

plants become vascular, and are converted into seed leaves, and the perfect plant appears above the soil. Nature has provided the elements of germination on every part of the surface; water, and pure air, and heat are universally active, and the means for the preservation and multiplication of life, are at once simple and grand." (Agric. Chemistry.) When a matured seed, therefore, has been deposited in the ground, at such a depth as to exclude light, (though this is not always an indispensable condition,) and yet to admit of the access of air and of moisture, the vital functions, stimulated by electro-chemical agency are excited, and germination commences. The young root or radicle, a, (Fig. 18, 1,) first appears, and is sent downwards in search of nourishment, as well as to fix the plant to the ground. The next step in the vegetative process, is the expansion and bursting of the cotyledons, or seed-lobes, cc; and to this

follows the advance of the plume, or embryo, p.

The expanding embryo resembles, in some degree, a little feather, and has, for that reason, been named by Linnæus, plumula; it soon becomes a tuft of young leaves, with which the stem, if there be any, ascends. In the garden bean, exhibited at No. 1, the cotyledons do not emerge from the soil; but in the dwarf kidney-bean,-in the radish, No. 2,

and in all the subjects of the Brassica tribe, as well as in many other plants, the cotyledons ascend, and form the leaves first developed, styled the seed leaves. Thus, ff, represent these seed leaves of the radish, which, when enclosed in the husk, or testa of the dry seed, constituted the two cotyledons: g, is the radicle, now become a fusiform spindle, or tap root (see 242-c); h, is the tuft of leaves and young stem rising between the seed leaves.

383. The chemical phenomena of germination, "consist chiefly in the changes that are effected in the nutriment destined for the support and developement of the embryo till it is converted into a plant. This nutriment either passes through the cotyledons, or is contained in them; because the embryo dies when they are prematurely cut off. But the farinaceous substance of the cotyledons, at least in exalbuminous seeds, is a proof that they themselves contain the nutriment. They are regarded, therefore, as the repositories of the food destined for the support of the embryo in its germinating state. And if the seed is furnished with a distinct and separate albumen," (see 254-3,) "then is the albumen to be regarded as the repository of food, and the cotyledons as its channel of conveyance. But the food thus contained in the albumen or cotyledons, is not yet fitted for the immediate nourishment of the embryo. Some previous preparation is necessary; some change must be effected in its properties: and this change is effected by the intervention of chemical agency. The moisture imbibed by a seed placed in the earth, is immediately absorbed by the cotyledons, or albumen, which it readily penetrates, and on which it immediately begins to operate a chemical change, dissolving part of their farina, or mixing with their oily particles, and forming an emulsive juice. The consequence of this change is a slight degree of fermentation, induced, perhaps, by the mixture of the starch and gluten of the cotyledons in the water, which they have absorbed, and indicated by the extrication of a quantity of carbonic acid gas, as well as by the smell and taste of the seed. This is the commencement of the process of germination, which takes place even though no oxygen gas be present; but if no oxygen gas be present, then the process stops; which shows that the agency of oxygen gas is indispensable to germination. Accordingly, when oxygen gas is present, it is gradually inhaled by the seed; and the farina of the cotyledons is found to have changed its savour. Sometimes it becomes acid, but generally sweet, resembling the taste of sugar: consequently is converted into sugar, or some substance analogous to it. This is a further proof that a degree of fermentation has been induced; because the result is precisely the same in the process of malting called the saccharine

fermentation, in which oxygen gas is absorbed, heat and carbonic acid evolved, and a tendency to germination indicated by the shooting of the radicle. The effect of oxygen, therefore, in the process, is that of converting the farina of the albumen, or cotyledons, into a mild saccharine food, fit for the nourishment of the infant plant, by diminishing the proportion of its carbon, and in augmenting, by consequence, that of its oxygen and hydrogen."

If the foregoing almost literal, but abbreviated, quotation, from KEITH'S Third Section, book iv., and from No. 724 of the Encyclopædia of Gardening, be compared with that from the Agricultural Lectures, given at No. 382, and with what now follows from the same work of Sir Humphry Davy, the reader will be enabled to form a pretty correct idea of the opinions entertained by modern philosophers, concerning the exciting causes of incipient vegetation.

384. Agency of Oxygen.-" Seeds are incapable of germinating, except when oxygen is present. In the exhausted receiver of the air-pump, in pure azote, in pure carbonic acid, when moistened, they swell, but do not vegetate; and, if kept in these gases, lose their living powers, and undergo putrefaction. If a seed be examined before germination, it will be found more or less insipid, at least not sweet; but after the germination it is always sweet. Its coagulated mucilage, or starch, is converted into sugar in the process; a substance difficult of solution is changed into one easily soluble; and the sugar carried through the cells or vessels of the cotyledons, is the nourishment of the infant plant."

"In the production of a plant from a seed, some reservoir of nourishment is needed before the root can supply sap; and this reservoir is the cotyledon, in which it is stored up in an insoluble form, and protected, if necessary, during the winter, and rendered soluble by agents which are constantly present on the surface. The change of starch into sugar, connected with the absorption of oxygen, may be rather compared to a process of fermentation than to that of respiration; it is a change effected upon unorganized matter, and can be artificially imitated; and in most of the chemical changes that occur when vegetable compounds are exposed to air, oxygen is absorbed, and carbonic acid formed or evolved."

"It is evident that in all cases of tillage, the seeds should be sown so as to be fully exposed to the influence of the air. And one cause of the unproductiveness of cold, clayey, adhesive soils is, that the seed is coated with matter impermeable to air.

"In sandy soils the earth is always sufficiently penetrable by the atmosphere. Any seed, not fully supplied with air, always pro

duces a weak and diseased plant. The process of malting is merely a process in which germination is artificially produced, and in which the starch of the cotyledon is changed into sugar; which sugar is afterwards, by fermentation, converted into spirit.”—(Agric. Chem. Leet. 5.)

It appears from what has been quoted, that philosophers believe the developement of the plantlet, and its subsequent nourishment, to be effected by the agency of oxygen upon one or more of the constituents of the seed,-chiefly the carbon, the results of which are the production of a saccharine, nutritive substance, and the formation of carbonic acid, both of which are fitted to become the food of the plant, when taken up, by introsusception, into its absorbent vessels. But what, it may be asked, is the primary exciting agent; -from whence is this oxygen produced, which effects such surprising changes? In paragraph 103-c, I have endeavoured to show, that the chemical union of the constituents of water, and of vegetable substances, being disturbed by divellent attraction, oxygen and other gases are evolved, and electricity developed. This electricity not only induces the formation of fresh compounds, but propels the nutritive matters into the vessels of the roots. To this it may be added, that air and water, fluids which are indispensable to the primary excitement of the vital functions,-are essentially the same in their constituent elements, (see 141,) that is to say, both the one and the other are composed solely of hydrogen and oxygen; but these elements are united in different proportions, and their union is maintained by peculiar and specific electric attractions. Hence, it results, that fluids of very different gravities and densities are produced. Seeds are composed chiefly of the elements of oxygen, hydrogen, and carbon; substances which appear to be identical with the elements of water, or to be produced from it; for, it is certain, that plants which occasionally grow in, and are supported by water alone, such as hyacinths in glasses, and mustard and cress, when grown upon flannel, moistened by water alone,

It may be doubted, by some, whether electricity is in reality developed; but upon what ground can this be questioned? If every process of decomposition be effected by electric agency, the view of the subject will, I think, be much simplified. Every substance in nature is a compound substance; its constituents are held together by some mysterious cement; that cement I conceive to be light-the grand vivifyer-the supporter, if not the prime agent, of the vital principle; all matter is replete with it, and in definite, specific, and determinate proportions. When this is disturbed, decompositions are effected, and, as in the ordinary chemical processes, without the revealment of any electric current, which, therefore, passes and combines invisibly.