a part of a plant extended into length and breadth in such a manner as to have one side distinguishable from the other. This is Miller's definition. Linnaeus denominates leaves "the organs of motion, or muscles of the plant."—The leaves are not merely ornamental to plants; they serve very useful purposes, and make part of the organs of vegetation.

The greater number of plants, particularly trees, are furnished with leaves: in mushrooms, and shrubby horse tail, they are totally wanting. Ludwic defines leaves to be fibrous and cellular processes of the plant, which are of various figures, but generally extended into a plain membranaceous or skinny substance. They are of a deeper green than the footstalks on which they stand, and are formed by the expansion of the vessels of the stalk, among which, in several leaves, the proper vessels are distinguished by the particular taste, colour, and smell, of the liquors contained within them.

By the expansion of the vessels of the stalk, are produced several ramifications or branches, which, crossing each other mutually, form a kind of net: the meshes or interstices of which are filled up with a tender cellular substance, called the pulp, pith, or parenchyma. This pulpy substance is frequently consumed by certain small insects, whilst the membranous net remaining untouched exhibits the genuine skeleton of the leaf.

The net in question is covered externally with an epidermis or scarf skin, which appears to be a continuation of the scarf skin of the stalk, and perhaps of that of the stem. M. de Saussure, a judicious naturalist, has attempted to prove, that this scarf skin, like that of the petals, is a true bark, composed itself of an epidermis and cortical net; these parts seem to be the organs of perspiration, which serve to dissipate the superfluous juices.

The cortical net is furnished, principally on the surface of the leaf, with a great number of vessels or absorbent vessels, destined to imbibe the humidity of the air. The upper surface, turned towards heaven, serves as a defence to the lower, which looks downward; and this disposition is so essential to the vegetable economy, that, if a branch is overturned in such a manner as to destroy the natural direction of the leaves, they will, of themselves, in a very short time, resume their former position; and that as often as the branch is thus overturned.

Leaves, then, are useful and necessary organs; trees perish when totally deprived of them. In general, plants stript of any of their leaves, cannot thoot vigorously: witness those which have undergone the depredations of insects; witness, likewise, the very common practice of stripping off some of the leaves from plants, when we would suspend their growth, or diminish the number of their shoots. This method is sometimes observed with corn and the elculent grapes; and, in cold years, is practised on fruit trees and vines, to render the fruit riper and better coloured: but in this

in clocks and watches, an appellation given to the notches of their pinions.

Gold LEAF, usually signifies fine gold beaten into plates of an exceeding thinness, which are well known in the arts of gilding, &c. See GOLD LEAF.