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 thubby horsetail, they are totally wanting. Ludwig defines leaves to be fibrous and cellular processes of the plant, which are of various figures, but generally extended into a plain membranaceous or skiny substance. They are of a deeper green than the foot-stalks 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 confused 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. Desausure, 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... 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 defense 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 shoots. This method is sometimes observed with corn and the esculent grasses; and, in cold years, is practised on fruit-trees and vines, to render the fruit riper and better coloured; but in 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. See PLANT.

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. The preparation of gold-leaf, according to Dr Lewis, is as follows.

"The gold is melted in a black-lead crucible, with some borax, in a wind furnace, called by the workmen a wind-hole: as soon as it appears in perfect fusion, it is poured out into an iron ingot mould, six or eight inches long, and three quarters of an inch wide, previously greased, and heated, so as to make the tallow run and smoke, but not to take flame. The bar of gold is made red-hot, to burn off the unctuous matter, and forged on an anvil into a long plate, which is further extended, by being passed repeatedly between polished steel rollers, till it becomes a ribbon as thin as paper. Formerly the whole of this extension was procured by means of the hammer, and some of the French workmen are still said to follow the same practice: but the use of the flatting-mill both abridges the operation, and renders the plate of more uniform thickness. The ribbon is divided by compasses, and cut with shears into equal pieces, which consequently are of equal weights: these are forged on an anvil till they are an inch square; and afterwards well nailed, to correct the rigidity which the metal has contracted in the hammering and flatting. Two ounces of gold, or 960 grains, the quantity which the workmen usually melt at a time, make 150 of these squares, whence each of them weighs six grains and two-fifths; and as 902 grains of gold make a cubic inch, the thickness of the square plates is about the 766th part of an inch.

In order to the further extension of these pieces into fine leaves, it is necessary to interpose some smooth body between them and the hammer, for softening its blow, and defending them from the rudeness of its immediate action: as also to place between every two of the pieces some proper intermediate, which, while it prevents their uniting together, or injuring one another, may suffer them freely to extend. Both these ends are answered by certain animal membranes.

The gold-beaters use three kinds of membranes; for the outside cover, common parchment made of sheep-skin; for interlaying with the gold, first the smoothest and closest vellum, made of calf-skin; and afterwards the much finer skins of ox-gut, stript off from the large straight gut slit open, curiously prepared on purpose for this use, and hence called gold-beater's skin. The preparation of these last is a distinct business, practised by only two or three persons in the kingdom, some of the particulars of which I have not satisfactorily learned. The general process is said to consist, in applying one upon another, by the smooth sides, in a moist state, in which they readily cohere and unite inseparably; stretching them on a frame, and carefully scraping off the fat and rough matter, so as to leave only the fine exterior membrane of the gut; beating them between double leaves of paper, to force out what unctuousness may remain in them; moistening them once or twice with an infusion of warm spices; and lastly, drying and pressing them. It is said, that some calcined gypsum, or platter of Paris, is rubbed with a hare's foot both on the vellum and the ox-gut skins, which fills up such minute holes as may happen in them, and prevents the gold-leaf from sticking, as it would do to the simple animal-membrane. It is observable, that, notwithstanding the vast extent to which the gold is beaten between these skins, and the great tenacity of the skins themselves, yet they sustain continual repetitions of the process, for several months, without extending or growing thinner. Our workmen find, that, after 70 or 80 repetitions, the skins, though they contract no flaw, will no longer permit the gold to extend between them; but that they may be again rendered fit for use by impregnating them with the virtue which they have lost, and that even holes in them may be repaired by the dexterous application of fresh pieces of skin: a microscopic examination of some skins that had been long used plainly showed these repairs. The method of restoring their virtue is said in the Encyclopædia to be, by interlaying them with leaves of paper moistened with vinegar white-wine, beating them for a whole day, and afterwards rubbing them over as at first with plaster of Paris. The gold is said to extend between them more easily, after they have been used a little, than when they are new.

The beating of the gold is performed on a smooth block of black marble, weighing from 200 to 600 pounds, the heavier the better; about nine inches square on the upper surface, and sometimes less, fitted into the middle of a wooden frame, about two feet square, so as that the surface of the marble and the frame form one continuous plane. Three of the sides are furnished with a high ledge; and the front, which old-Leaf, is open, has a leather flap fastened to it, which the gold-beater takes before him as an apron, for preserving the fragments of gold that fall off. Three hammers are employed, all of them with two round and somewhat convex faces, though commonly the workman uses only one of the faces: the first, called the cutch-hammer, is about four inches in diameter, and weighs 15 or 16 pounds, and sometimes 20, though few workmen can manage those of this last size: the second, called the soldering-hammer, weighs about 12 pounds, and is about the same diameter: the third, called the gold-hammer, or finishing-hammer, weighs 10 or 11 pounds, and is nearly of the same width. The French use four hammers, differing both in size and shape from those of our workmen: they have only one face, being in figures truncated cones. The first has very little convexity, is near five inches in diameter, and weighs 14 or 15 pounds: the second is more convex than the first, about an inch narrower, and scarcely half its weight: the third, still more convex, is only about two inches wide, and four or five pounds in weight: the fourth or finishing hammer is near as heavy as the first, but narrower by an inch, and the most convex of all. As these hammers differ so remarkably from ours, I thought proper to insert them, leaving the workmen to judge what advantage one set may have above the other.

"A hundred and fifty of the pieces of gold are interlaid with leaves of vellum, three or four inches square, one vellum leaf being placed between every two of the pieces, and about 20 more of the vellum leaves on the outsides; over these is drawn a parchment case, open at both ends, and over this another in a contrary direction, so that the assemblage of gold and vellum leaves is kept tight and close on all sides. The whole is beaten with the heaviest hammer, and every now and then turned upside down, till the gold is stretched to the extent of the vellum; the case being from time to time opened for discovering how the extension goes on, and the packet, at times, bent and rolled as it were between the hands, for procuring sufficient freedom to the gold, or, as the workmen say, to make the gold work. The pieces, taken out from between the vellum leaves, are cut in four with a steel knife; and the 600 divisions, hence resulting, are interlaid, in the same manner, with pieces of the ox-gut skins five inches square. The beating being repeated with a lighter hammer till the golden plates have again acquired the extent of the skins, they are a second time divided in four: the instrument used for this division is a piece of cane cut to an edge, the leaves being now so light, that the moisture of the air or breath condensing on a metallic knife would occasion them to stick to it. These last divisions being so numerous, that the skins necessary for interposing between them would make the packet too thick to be beaten at once, they are parted into three parcels, which are beaten separately, with the smallest hammer, till they are stretched for the third time to the size of the skins: they are now found to be reduced to the greatest thinness they will admit of; and indeed many of them, before this period, break or fail. The French workmen, according to the minute detail of this process given in the Encyclopédie, repeat the division and the beating once more; but as the squares of gold, taken for the first operation, have four times the area of those used among us, the number of leaves from an equal area is the same in both methods, viz. 16 from a square inch. In the beating, however simple the process appears to be, a good deal of address is requisite, for applying the hammers so as to extend the metal uniformly from the middle to the sides: one improper blow is apt not only to break the gold leaves, but to cut the skins.

"After the last beating, the leaves are taken up by the end of a cane instrument, and, being blown flat on a leather-cushion, are cut to a size, one by one, with a square frame of cane made of a proper sharpness, or with a frame of wood edged with cane: they are then fitted into books of 25 leaves each, the paper of which is well smoothed, and rubbed with red-bole to prevent their sticking to it. The French, for sizing the leaves, use only the cane-knife; cutting them first straight on one side, fitting them into the book by the straight side, and then paring off the superfluous parts of the gold about the edges of the book. The size of the French gold leaves is from somewhat less than three inches to three and three quarters square; that of ours, from three inches to three and three-eighths.

"The process of gold-beating is considerably influenced by the weather. In wet weather, the skins grow somewhat damp, and in this state make the extension of the gold more tedious: the French are said to dry and press them at every time of using; with care not to overdry them, which would render them unfit for farther service. Our workmen complain more of frost, which appears to affect the metallic leaves themselves; in frost, a gold-leaf cannot easily be blown flat, but breaks, wrinkles, or runs together.

"Gold-leaf ought to be prepared from the finest gold; as the admixture of other metals, though in too small a proportion to sensibly affect the colour of the leaf, would dispose it to lose of its beauty in the air. And indeed there is little temptation to the workman to use any other; the greater hardness of alloyed gold occasioning as much to be lost in point of time and labour, and in the greater number of leaves that break, as can be gained by any quantity of alloy that would not be at once discoverable by the eye. All metals render gold harder and more difficult of extension: even silver, which in this respect seems to alter its quality less than any other metal, produces with gold a mixture sensibly harder than either of them separately, and this hardness is in no art more felt than in the gold-beater's. The French are said to prepare what is called the green gold leaf, from a composition of one part of copper and two of silver with eighty of gold. But this is probably a mistake: for, such an admixture gives no greenness to gold; and I have been informed by our workmen, that this kind of leaf is made from the same fine gold as the highest gold-coloured sort, the greenish hue being only a superficial teint induced upon the gold in some part of the process: this greenish leaf is little otherwise used than for the gilding of certain books.

"But though the gold-beater cannot advantageously diminish the quantity of gold in the leaf by the admixture of any other substance with the gold, yet means have been contrived, for some particular purposes, of saving the precious metal, by producing a League, kind of leaf called party-gold, whose basis is silver, and which has only a superficial coat of gold upon one side: a thick leaf of silver and a thinner one of gold, laid flat on one another, heated and pressed together, unite and cohere; and being then beaten into fine leaves, as in the foregoing process, the gold, though its quantity is only about one-fourth of that of the silver, continues everywhere to cover it, the extension of the former keeping pace with that of the latter.