LEA
LEA-
The whole government of the works is in the hands of certain lords, who proportion the quantity to he worked by thefe lead waitings to the feveral perfons who work it. At Namptwich, in Chefhire, two hundred and Sixteen lead wait- ings belong to all the owners of the pit, and no tradefman, batchelor, or widow, can rent more than eighteen lead wallings. All is under the directions of four iworn officers, chofen every year, and thefe appoint how much fait ihall he made each year, and how many houfes lhall work at a time. Rays EngliSh Words, p. 142.
LEAD-Wort. See Plumbago.
LEADERS, in the military art. See FlhE-leaders.
LE./ENA, the lionefs. See Lioness.
-LEAF {Cycl.) — -The leaves of trees and plants afford the cu- rious in microfcopic observations many very beautiful ob- jects.
All leaves are full of innumerable veSTels, which convey perfpirable juices to the pores for their difcharge. Whether there be any circulation in them, is not yet determined ; but as their juices all become ftiff and coagulated, when let out, it is probable that they have fome motion, which keeps them fluid while in the veitcls of the plant. The pores in the leaves of plants are almoft innumerable. Mr. Lewenhock found an hundred and feventy two thoti- fand and ninety pores on one fide of a leaf of box. The leaves of rue feem full of holes, like a honey comb; all the kinds of St. John's wort appear likewife fluck full of pin holes to the naked eye, but the microfcope difcovers, that the places where thole holes feem to be, are really covered with a very thin and white membrane. The backhde of the herb mercury looks as if rough cafl with filver, and all the ribs are full of white round transparent balls, fattened by flender Stalks, like fo many grapes. A (age leaf appears like a rug, or fhag, full of knots and tufts of filver thrums, and em- bellished with fine round cryftal beads, or pendants, and thefe fattened by flender foot Stalks. The back fide of a rofe leaf and particularly of that kind called fweet briar, appears diapered with filver. Every one knows, that the leaves of flinging nettles are thick fet with fharp prickles, which penetrate the (kin when touched, and occafion heat, pain, and fwelling. Thefe fymptoms were imagined for- merly to be owing to the prickles being left in the wounds they make, but the microfcope difcovers fomething much more wonderful in this plant, and fhews that its prickles are formed for acting, in the fame manner as the flings of animals. For every one of them is found to be a rigid body, hollow, and terminating in a very fine point, with an open- ing near its end. At the bottom of this prickle there lies a pellucid bag, containing a limpid liquor, which, upon the leaft touching the prickle, is fquirted out at the little out- let, and if it enters the fkin, produces the mifchiefs before- mentioned by the pungency of its falts. And hence it is, that the leaves of nettles, when they have been dried a little in the Cun, Sling fcarce at all. Baker 's Microfcope, p. 259. ■ The leaves of plants are of the utmoft confequence to the life of the whole. Air evidently paffes in at the leaves, and goes through the whole plant, and out again at the roots. If the leaves have no air, the whole plant will die, as is ea- fily proved by the air pump ; but in thefe experiments, if the leaves be left on the outfide of the receiver, and parted by a hole cemented with wax, and have air, the plant will thrive, and grow, though its roots and ftalk are kept in vacuo in water. The leaves of plants perform the necefTary work of altering the water received in at the roots, into the nature of the juices of the plant ; and hence it is, that the life of the plants depend fo immediately upon their leaves. The hufbandman often flitters for want of this knowledge. A crop of faint foin is a very valuable thing, and its root being perennial, will yield him encreafe many years ; but it is often deftroyed at firft, by fufFcring it to be indifcreetly fed upon by the fheep, which eating up all the leaves, the root remains without the means of a fupply of air, and the whole perifhes.
Leaves being thus neceftary to plants, nature has, in all pe- rennial plants, provided a reverlionary flock of them. The leaves of thefe plants are always formed in autumn, though they are not unfolded till the following fpring. They then open and encreafe gradually, in proportion to the motion of the fap, and the quantity of pabulum it then receives to be circulated. Thefe leaves may alfo, though not wholly appearing out of the bud, be fufficient for the extremely fmall motion of life, which the fap of perennial plants, that drop their leaves, has in winter. TulPs Horfe-hoeing Hufbandry, p. 10.
Dr. Grew observed the formation of thefe autumnal leaves ; but befide thefe, there is another fet of them formed in the fpring, and expanding about Midfummer. Thefe are of in- finite fervice to many particular trees, particularly to the mulberry, as they fave its life when the fpring leaves have been all eaten up by the filk worms. People who flrip that tree for the food of thefe animals find, however, that fome caution is neceflary, in order to make the new fupply of fpring leaves fave the life of the tree. For if they pull off the old leaves downward, Gripping away italic and all,
the tree often dies, but if they pull them upwards, the tree' lives without hurt; becaufc the ftalk, in this cafe, is left, and often a piece of the bottom of the leaf upon it. Thefe ferve, in fome degree, in the place of the whole leaves, till the new ones are formed.
It is certain that no plant, to which nature has allotted leaves, can live without them, but will certainly die if they are pulled off as foon as they appear. The common grais of our meadows and paftures might feem an exception to this general rule ; but it is to be confidered, that though the fheep eat this down very clofe, and take oft" its leaves as foon as they grow, yet when it is thus devoured by cattle, it is only in the leaf, very little of it growing up into ftalk at that time, and therefore lefs fap is to be purified, and confequently lefs of the operation allotted to the leaves re- quired ; and there is a conftant fucceffion of new leaves growing up in the place of the old ones, and many of thefe being too fhort to be bitten oflj ferve in the place of thofe which are eaten. The figure of the leaves of plants may be reprefented by holding one in the fmoke of refin, camphor, a can- dle, &c. whereby the leaf acquires a blacknefs, which when prefled on white paper, gives the exact fize, fhape, and particular ramifactions of the fibres. This method may be of ufe to botanifts, when they have no fkill in drawing. Boyle's Works Abr. Vol. 1. p. 132. The leaves of plants have feveral distinctions among bota- nifls, according to their fhape and divifion, each of which has its peculiar name. See Tab. of Leaves. Aculcated Leaf, is that whofe furface is covered with cartilagi- nous points, fharp, rigid, and flrong enough to wound any tender part of the flefh ; and which adhere but Slightly to the leaf, and may be eafily feparated from it. Acuminated Leaf, one terminated by a pointed and fharp ex- tremity, like an awl. Acute Leaf, that which terminates in a fnarp point. Alated Leaves, are thofe divided into, or compofed of feve- ral compleat pinnated leaves, whether equal or unequal uniform or difform, as in the orobus, and other the like plants. Alternate Leaves, thofe which do not Stand oppofite, but one
over another, all the way up the flalk, Amplexicaule Leaf, exprefles a leaf, the bafe of which ex- tends itfelf in fuch a manner, that it environs, and furrounds the ftalk every way. In this cafe, the leaf is generally of a fagittated, or heart-fafhioned Shape, and is feflile. Articulated Leaves, thofe which grow one on the top of
another. Bifid Leaf, one divided into two parts at the top. When a leaf is thus divided into three parts, it is faid to be trifid; when into four, auadrifid, and fo on. Multifid exprefles a leaf divided into a great number of fegments. Bigeminate Leaf, one formed of a double conjugation of
lefTer leaves. Binated Leaf, binatum folium, a kind of compound leaf,
formed only of two folioles on one petiole. Bipartite Leaf. See £htinque partite Leaf, infra. Canaliadated Leaf, one which is hollowed all the way of
its length with a channel. Carrions Leaf, one which is full of pulp, or of a flefhy fub- ftance, contained between the membranes which form the upper and under furface. Cartilaginous Le af ', that whofe edge is furrounded with a kind of cartilage, or border, thicker than the reft, but of the fubflance of the leaf. Cauline Leaf, that which grows not immediately from the
root, but on the ftalk of a plant. Ciliated Leaf, one furrounded all the way with parallel hairs, or filaments, fo as to give fome refemblance of the hairi- nefs of the eye-lids. Compound Leaf, is that which is divided to the middle rib into feveral fegments, and feems made up of feveral fmaller leaves, as in liquorice, &c.
Compound leaf exprefles, in general, a leaf that is formed of feveral other lefler ones. In this large fenfe, however, it is divifible into feveral kinds, r. The compound ones, pro- perly and distinctly fo called. 2. The decompound. And 3. The fupradecompound. Of each of which in its place. In defcribing thefe kinds of leaves, the whole leaf, which is the refult of the combination, is called folium, and the fmall leaves, which together compofe it, are called foliola. Compound leaf, properly fo called, is only formed of one feries of foliola, or of one compofition. Compreffcd Leaf, one with the mark of an impreflion on both
Sides. Concave Leaf, one whofe middle is funk or hollowed. Conferta Foua, leaves placed in clufters, or fo clofe to one another, that it is not eafy to difcover their exact fitua- tion. Connata Folia, leaves cohering together, or whofe bafes
unite, fo as to form but one body. Convex Leaf, one whofe middle rifes into a protuberant form.
Cgrdatid
