Lectures on Botany, as Delivered in the Botanic Garden at Lambeth (Volume 1) (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1805. Excerpt: ... SECTION VIII. On Leaves. WE come in the next place to give you a general idea of the structure of leaves, and to point out to you the principle different kinds as they are botanically considered. Leaves are defined to be fibrous and cellular procefiess of plants, which are of various figures, but generally extended, with a flat, membranous, or Urinny substance. In their structure they considerably resemble the stalk, and hence they may in some degree be considered as a stalk flattened. The generality of leaves are obviously composed of, ist, The lignous, or woody substance, distributed in innumerable ramifications through the middle of the leaf, and which gives it firmness and durability. 2d. The parenchyma, fleshy or pulpy substance, placed on each side of, and in the interstices of the woody net-work, forming the principle substance, and giving to the leaf its green colour; this substance, which is very tender, from its cellular structure, is quickly destroyed by maceration, leaving the woody substance or skeleton of the leaf behind. These two parts are covered on each side by a membrane or skin, which is considerably tougher than the parenchyma, and not so soon destroyed by maceration. Insects frequently destroy one of the skins of the leaf, generally the under one, as being the most tender, together with the parenON LEAVES. chyma, leaving the woody ramifications and upper skin entire; and sometimes in herbaceous plants, where the woody ramifications are tender, a small caterpiller or grub, hatched from an egg deposited by a fly, between the two coats, will destroy both the woody and parenchymateous substances, leaving the two skins colourless. The skeletons of leaves, made by maceration, are usually exhibited by Lecturers on Anatomy; the best we have ...