412 



Li: .EN A LEAF. 



same quantity of ore is reduced as in the first 

 ili^rribed process, with the advantage, too, of a con- 

 siderable saving of time, and with one-half of the 

 l.ibour ; but it is attended with the complete loss of 

 the iron, which, in some districts, however, is so cheap 

 as to be of no consideration. Britain produces 

 about half the lead of Europe ; the Elartz, Austria, 

 Prussia and their dependencies nearly all the remain- 

 der. The lead mine of Galena, in Illinois, yielded, 

 in 1829, about 6000 tons of lead. 



It is pretty certain that both lead and tin were 

 employed, in extremely remote ages, in the fabrica- 

 tion of arms, and, above all, in the ornamental parts 

 of them. Homer also alludes to the practice of 

 putting leaden balls at the end of fishing-lines. The 

 custom of writing on lead mounts also into very great 

 antiquity. Frontinus and Dio Cassius assure us, that 

 the consul Hirtius, liesieged in Modena, wrote upon 

 a leaf of lead, respecting his situation, to Decius 

 Brutus, who replied by the same means. Pausanias 

 speaks of certain books of Hesiod written upon 

 sheets of lead ; and, if we may believe Pliny, even 

 public acts were consigned to volumes or leaves of 

 the same material. The poets make frequent allu- 

 sion to leaden coins. Ficorini, in his Piombi Antichi, 

 has collected and represented a vast number of monu- 

 ments of this kind. Caylus conceived them to be all 

 Roman ; and thus, according to that writer, those 

 even which represent Egyptian divinities, or are 

 inscribed with Greek characters, are yet to be re- 

 ferred to the times of the Roman emperors. Statues 

 of lead are very rare. 



Lead; an instrument for discovering the depth of 

 water. It is composed of a large piece of lead, from 

 seven to eleven pounds in weight, and is attached by 

 means of a strap, to a long line, called the lead-line, 

 which is marked at certain distances, to ascertain the 

 fathoms. 



To heave the lead, is to throw it into the sea in a 

 manner calculated to produce the desired effect. 



Deep-sea lead ; a lead of a larger size, being from 

 twenty-five to thirty pounds weight, and attached to 

 a much longer line than the former, which is called a 

 hand-lead. 



LEjENA ; an Athenian hetcera (q. v.), mistress of 

 Aristogiton. Being privy to the conspiracy of Har- 

 modius and Aristogiton against the Pisistratidas, when 

 examined on the subject, she bit oft" her tongue, that 

 she might not be able to speak. A statue was 

 erected by the side of those of the tyrannicides, in 

 hojjour of her, representing a lioness without a tongue, 

 by the side of which was an image of Venus, whose 

 priestess she was. 



LEAF. As it is impossible to give an entirely 

 satisfactory definition of what is meant by the word 

 plant, or animal, so it has equally defied the exertions 

 of naturalists to give a distinct definition of leaf. 

 Leaves are the part of the vegetable world in which 

 vegetable life manifests itself most strongly. Light 

 and air, which so essentially influence the vegetable 

 kingdom, act chiefly on the leaves ; and, in relation 

 to the air, leaves have been compared to the animal 

 organs of respiration to lungs placed externally. 

 They are also organs of nutrition, particularly on the 

 lower surface. The same formation which prevails 

 in the trunk, branches, and roots, has been recognised 

 in leaves, only that what in the former is annular and 

 concentric, in the latter is spread out over an extended 

 plane surface. The spiral vessels and sap vessels, 

 which are observable in the leaf-stalk, are also partly 

 to be traced in the leaf, and form the nerves and 

 veins, which may be considered as the skeleton of the 

 leaf. The spaces between them are filled with a 

 cellular substance, covered by a soft, yet firm cuticle. 

 The cellular substance and the cuticle are different 



on the upper and the lower surfaces ; and, however 

 various the form of the leaves, much conformity 

 always exists in this respect, and is intimately con- 

 nected with the life of the plant. The cellular sub- 

 stance is particularly filled with sap, generally of a 

 green colour. The cells of the upper surface are 

 commonly disposeil lengthwise ; those of the lower 

 surface, breadthwise ; both commonly destitute of 

 sap. The pores, which are generally only on the 

 lower surface (except in plants whose leaves lie on 

 the water, or close on the ground), serve to transmit 

 the air to the internal parts of the plant ; but in some 

 plants they are not discernible, even in some of the 

 more perfect kinds, particularly if the sap is not 

 green. The leaf changes whatever passes through 

 it into the plant from without, or from the plant ; and 

 so essential is the influence of light upon vegetable 

 life, that the gaseous substances given out by plants, 

 in the sun, or in the shade, or by night, are cliemi 

 cally different. Sound and green leaves, in the sun, 

 exhale oxygen and absorb carbonic acid gas ; but 

 by night, or in the dark, they give out carbonic acid 

 gas, and absorb oxygen from the air : sickly plants, 

 and those whose leaves are not green, do this in the 

 sun. The green colour, the almost universal hue of 

 plants, is so intimately connected with light, that 

 young plants do not begin to assume this colour until 

 they come into the light. The importance of leaves 

 to plants is shown by the fact that no plant can grow, 

 nor form blossoms, nor fruits, if deprived of leaves. 

 When fruit has arrived at a certain degree of matu- 

 rity, it may, indeed, be ripened more rapidly by 

 depriving the plant of its foliage ; but this only proves 

 a diseased state. The fine hairs with which leaves 

 are covered, and which sometimes become bristles, 

 contribute considerably to the exhalation and absorp- 

 tion of air and moisture ; so that a plant often owes 

 its nourishment to the atmosphere more than to the 

 ground ; and many plants exhale much more aqueous 

 matter than, on the highest estimation, they can 

 receive from the ground. The leaves, moreover, 

 have often an important part in the secretion of oiiy 

 or other substances. There are whole orders of 

 plants, consisting almost entirely of leaves, as certain 

 mosses, heaths, and others, in which the leaf gives 

 place almost entirely to the stem, so that an interme- 

 diate formation between the two is presented, as in 

 the cactus, euphorbia, stapelia, &c. In many cases, 

 the leaf proceeds only from the joints of the stem, 

 as in the grasses ; and, in this case, it retains much 

 of the nature of the stem. No part of the plant is 

 capable of such an immense variety of forms as the 

 leaf, the description of which would exceed our limits. 

 The leaves form an important characteristic in the 

 subdivision of plants. They are divided into simple 

 and compound, the latter class consisting of those in 

 which several leaves are supported on one footstalk ; 

 and their various subdivisions are formed on the form 

 1. of the apex ; 2. of the base ; 3. of the circumfer- 

 ence ; 4. of the margin ; 5. of the surface ; G. on 

 their position ; 7. their substance ; 8. their situation 

 and position ; 9. their insertion ; 10. their direction. 

 The lobe of a leaf is the segment around the apex. 



We will add here some interesting items of a 

 memoir on the structure of leaves, read quite lately 

 by M. Adolphus Brongniart, before the academy of 

 sciences at Paris. The author states that the leaves 

 of plants that live in the air have a totally different 

 structure from those that are completely submerged, 

 and that this difference in the structure of organs is 

 in direct relation to the two principal functions of 

 leaves respiration and transpiration. In leaves 

 exposed to the air, the surface of the leaf is covered 

 by an epidermis of uncertain thickness, formed of 

 one or more layers of colourless cellules, closely 



