. The elements of botany for beginners and for schools. Botany. SECTION 10.] ANATOMY OF LEAVES. 143 green pulp, and is nearly the same as the green layer of the bark. So that tlie leaf may properly enough be regarded as a sort of expansion of the fibrous and green layers of the bark. It has uo proper corky layer; but the whole is covered by a transparent skin or epidermis, resembling that of the stem. 440. The cells of the leaf are of various forms, rarely so compact as to form a close cellular tissue, usually loosely arranged, at least in the lower part, so as to give copious intervening spac
. The elements of botany for beginners and for schools. Botany. SECTION 10.] ANATOMY OF LEAVES. 143 green pulp, and is nearly the same as the green layer of the bark. So that tlie leaf may properly enough be regarded as a sort of expansion of the fibrous and green layers of the bark. It has uo proper corky layer; but the whole is covered by a transparent skin or epidermis, resembling that of the stem. 440. The cells of the leaf are of various forms, rarely so compact as to form a close cellular tissue, usually loosely arranged, at least in the lower part, so as to give copious intervening spaces or air passages, communi- cating throughout the whole interior (Fig. 443, 483). The green color is given by tiie chlorophyll (417), seen through the very transparent walls of the cells and through tlie translucent epidermis of the leaf. 441. In ordinary leaves, having an upper and under surface, the green cells form two distinct strata, of different arrangement. Those of the upper stratum are oblong or cylindrical, and stand endwise to the surface of the leaf, usually close together, leaving hardly any vacant spaces; those of the lower are commonly irregular in shape, most of Ihem with their longer diameter parallel to the face of the leaf, and are very loosely ar- ranged, leaving many and wide air-chambers. The green color of the lower is therefore diluted, and paler than that of the upper face of the leaf. Tlie upper part of the leaf is so constructed as to bear the direct action. of the sunsliine ; the lower so as to afford freer circulation of air, and to facilitate transpiration. It communicates more directly than the upper with the external air by means of Siomates. 442. The Epidermis or skin of leaves and all young shoots is best seen in the foliage. It may readily be stripped off from the surface of a Lily-leaf, and still more so from more fleshy and soft leaves, such as those Fig. 483. I\Iagiiified section of a leaf of White Lily, to exliibit the cellular structure,
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1887
