Leaves are of a deeper green colour than the foot-stalks on which they stand; being formed by the expansion of the- vessels of such stalks that produce several ramifications ; mutually intersecting each other, and thus making a kind of net; the meshes of which are filled up with a tender porous substance, variously called the pulp, pith, or parenchyma. This net is provided, chiefly on the surface of the leaf, with a great number of porous or absorbent vessels, which are destined to imbibe the humidity of the air. The upper surface serves as a defence to the lower ; and so essential is this disposition to the vegetable economy, that, if a branch be inverted so as to destroy the natural direction of the leaves, these in a short time will spontaneously resume their former position.
Leaves, therefore, are not merely ornamental to plants, but contribute in a very considerable degree to promote vegetation: thus almost every class of the vegetable creation is furnished with them, excepting mushrooms, and one or two other productions of the earth. Indeed, if any tree be deprived of its leaves, it cannot shoot vigorously ; and, if it be totally divested of them, it speedily perishes. When however, vegetation ceases, these organs of respiration and inspiration become superfluous : hence there are but few plants furnished with leaves throughout the whole year ; the greater part is entirely deprived of them, and remains naked during the winter, producing new foliage with each returning spring.
The utility of leaves, in an economical respect, is very great, even after they cease to be essential to vegetation. Hence they should not be suffered to rot upon the ground, but carefully gathered in autumn; then exposed to a dry air, frequently turned, and thus made subservient to various useful purposes. Such leaves furnish an wholesome winter fodder for cows and sheep, either of which animals devour them eagerly. With this intention, they may be dried in a similar manner, and even mixed, with hay: and, if properly kept free from moisture, they may be easily preserved throughout the winter.
Nor are the leaves of vegetables, especially those of beans, less serviceable as a manure, for clay-soils, because the lower ones are very substantial, and yield, in the opinion of Dr.DARWiN, a considerable portion of carbonic acid ; hence it may be explained, that bean leaves;. by continually dropping on the surface of the land supply the earth with carbon, and thus render it more nutritive to such vegetables as may afterwards be cultivated. In this respeCt, they are greatly preferable to sheep's or cow's dung, because they never stock the soil with weeds, the roots or seeds of which are frequently propagated by the compost of ordinary dunghills.
The leaves of trees may also be advantageously substituted for sawdust, in wine-cellars; and for horse-litter, or tanner's bank, in hot-beds, for which they are eminently calculated; and, if trodden down closely, and properly moistened, they will gradually ferment;" while their heat is more uniform and permanent than horse-dung : besides, there is no danger of burning or suffocating the plants in the frame. Vegetable foliage, likewise, affords an useful material for the stuffing of beds, bolsters, mattresses, and cushions. But, to prevent them from crumbling into dust, when frequently shaken, a correspondent, in the 1st vol. of the Museum Rus-ticum et Commcrcia/e, observes, that they should be moistened while drying.; as their contexture will thus be rendered more, tough and elastic : we are inclined to recommend, with this intention, a weak solution of glue orisinglasz.—. They certainly merit a fair trial; and, as we have no doubt of their salubritv or softness, they might be beneficially employed by the | who mar gather and prepare them with little trouble or expence.
Concerning the physical properties of leaves, in general, we are silent; as we treat of the more valuable medicinal plants in their alphabetical series ; but we cannot conclude this article, without stating an ingenious remark of Dr. Darwin; who is of opinion, that after their bitter particles have been extracted in a hot-bed, the leaves may be selected and converted into a spirituous drink similar to small beer, without possessing any disagreeable flavour : there is every reason to believe that such object may be effected by proper management; and the drink thus produced will doubtless be more wholesome than the adulterated liquors, which are imposed upon the public, by designing and avaricious persons.