. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. STKUCTURE OF LEAVES. 79 Leaves and theie Appendages. Structure of Leaves. Leaves are expansions of the bark, developed in a symmetrical manner, as lateral appendages of the stem, and having a connection with the internal part of the ascending axis. They appear at first as small projections of cellular tissue, continuous with the bark, and closely applied to each other. The points from which they arise are called nodes. In the early stages of their development they are
. A Manual of botany : being an introduction to the study of the structure, physiology, and classification of plants . Botany. STKUCTURE OF LEAVES. 79 Leaves and theie Appendages. Structure of Leaves. Leaves are expansions of the bark, developed in a symmetrical manner, as lateral appendages of the stem, and having a connection with the internal part of the ascending axis. They appear at first as small projections of cellular tissue, continuous with the bark, and closely applied to each other. The points from which they arise are called nodes. In the early stages of their development they are undivided. The cellular papiUse, from which they originate, gradually expand in various ways, acquire vascular tissue, and ultimately assume their permanent form and position on the axis. They may be divided into aerial and submerged leaves, the former being produced in the air, and the latter under water. Aerial Leaves.âThese leaves consist of vascular tissue iu the form of veins, ribs, or nerves, of cellular tissue or parenchyma filling up the interstices between the veins, and of an epidermal covering. The Vasctjlae System of the leaf is continuous with that of the stem, those vessels which occupy the internal part of the stem becoming superior in the leaf, while the more ex- ternal, become inferior. Thus, in the upper part of the leaf, which may re- present the woody layers, there are spiral vessels (fig. 141 t), annular, reticulated, and pitted vessels, â ;;, and ligneous fibres, /; whilst in the lower side, which may re- present the bark, there are laticiferous vessels and fibres, resembling those of liber, I. There are usually two layers of fibro-vasoular tissue in the leaf, which may be separated by maceration. They may be seen in what are called skeleton leaves, in which the cellular part is re- moved, and the fibro-vascular tissue is left. The vascular system of the leaf is distributed through the cellular tissue in the form of simple or branching veins. The Epidekm
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectbotany, bookyear1875
