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. Linnæus 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 suckers 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 divested of them. In general, plants stript of any of their leaves, cannot shoot 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 fruits. This method is sometimes observed with corn and the eculent grapes; and, in cold years, is practised on fruit trees and vines, to render the fruit riper and better coloured; but in this this case it is proper to wait till the fruits have acquired their full bulk, as the leaves contribute greatly to their growth, but hinder, when too numerous, that exquisite rectifying of the juices, which is so necessary to render them delicious and palatable.

When vegetation ceases, the organs of perspiration and inspiration become superfluous. Plants, therefore, are not always adorned with leaves; they produce new ones every year; and every year the greater part are totally divested of them, and remain naked during the winter.

**Leaf Insects.** See Cimex, Entomology Index.

**Leaf-Skeletons.** One help for acquiring a knowledge of the anatomy of plants, is the art of reducing leaves to skeletons, which may be done by exposing the leaves to decay for some time soaked in water, by which means the softer will be separated from the internal harder parts. By carefully wiping, pressing, and rinsing them, the harder parts may be obtained from the rest alone and entire. Some have been able to separate the outer covering on both sides from the woody net, and even to split the latter into two. A naturalist in the year 1645 first conceived the idea of making leaf-skeletons by employing decomposition for that purpose, afflicting it by several ingenious operations of art. When the method of producing these skeletons was publicly known, numberless preparations of them were everywhere attempted. So much did leaf-skeletons afterwards engage the attention of philosophers, that one Seligmann wrote a treatise on the various methods which may be employed in their preparation.

The art also of raising trees from leaves has been long known, the first account of which was published by Agostino Mandriola, an Italian of the Franciscan order, who affirms that he produced trees from the leaves of the cedar and lemon tree. In the garden of Baron de Munchhausen, a young tree was obtained from a leaf of the *limon a Rio*, which yielded fruit the second year: It is more than probable that the multiplication of the *opuntia* or Indian fig, first suggested the idea of such experiments, for every joint of that plant when stuck into the earth, and properly nurtured, throws out roots and grows.

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

**Gold Leaf**, usually signifies fine gold beaten into plates of exceeding thinness, which are employed in the arts of gilding, &c. See GOLD Leaf.

**League**, a measure of length, containing more or fewer geometrical paces, according to the different usages and customs of countries. A league at sea, where it is chiefly used by us, being a land measure mostly peculiar to the French and Germans, contains 3000 geometrical paces, or three English miles. The French league sometimes contains the same measure, and in some parts of France it consists of 3500 paces: the mean or common league consists of 2400 paces, and the little league of 2000. The Spanish leagues are larger than the French, 17 Spanish leagues making a degree, or 20 French leagues, or 69½ English statute miles. The Dutch and German leagues contain each four geographical miles. The Persian leagues are pretty near of the same extent with the Spanish; that is, they are equal to four Italian miles, which is pretty near to what Herodotus calls the length of the Persian parasang, which contained 30 stadia, eight whereof, according to Strabo, make a mile. The word comes from *leuca* or *leuga*, an ancient Gaulish word for an itinerary measure, and retained in that sense by the Romans. Some derive the word *leuca* from *albus*, "white;" as the Gauls, in imitation of the Romans, marked the spaces and distances of their roads with white stones.