. Cassell's popular gardening. Gardening. 162 CASSELL'S POPULAE G-ARDENING. vary greatly in different cases, and these diver- sities serve, together with those connected with the shape and disposition of the leaf, as means of dis- crimination between different plants or groups of plants. It must suffice here to give one illustration only. In the majority of Dicotyledonous plants, those in which the seedling plant has two cotyledons, the group comprising most of our trees and shrubs, the ribs of the leaf, or their ultimate branches, are arranged in a reticulate or net-like fashion, so that ther
. Cassell's popular gardening. Gardening. 162 CASSELL'S POPULAE G-ARDENING. vary greatly in different cases, and these diver- sities serve, together with those connected with the shape and disposition of the leaf, as means of dis- crimination between different plants or groups of plants. It must suffice here to give one illustration only. In the majority of Dicotyledonous plants, those in which the seedling plant has two cotyledons, the group comprising most of our trees and shrubs, the ribs of the leaf, or their ultimate branches, are arranged in a reticulate or net-like fashion, so that there are angular spaces between them. In the larger number of Monocotyledons (Palms, Lilies, Grasses, &c.) the ultimate veins are not netted, but somewhat straight and nearly parallel, so that the interspaces are either long and narrow, or if angu- lar, then four-sided, not polygonal. Even in cases where from the thickness of the cellular tissue, or the opacity of the epiderm, the veins are not readily conspicuous, the arrangement can be determined by simply tearing the leaf. Where the veins run in a nearly straight direction, as in an Iris-leaf, for instance, the edges of a tear will be nearly straight; but where they form net-like meshes, as in a Cab- bage-leaf, then the edges of the tear wiU be angular and irregular. The Skin of the Leaf.—It remains now to speak of. the epidermis or skin. This, like the other parts of the leaf, is subject to variation in. Pig. 50.—Epidermis of a Leaf (magnified) showing Stomata. different plants, and it is usually somewhat diiferent on the upper and lower surfaces respectively. It most generally consists of a layer of flattened cells, destitute of chlorophyll. Those on the upper sm-- face are closely packed, with no interspaces between them. Those on the lower sm-face are interrupted by a greater or less number, sometimes by an immensely large number, of pores called " stomata " (Eig. 50). These are apertures communicating wit
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Keywords: ., bookcentury1800, bookdecade18, booksubjectgardening, bookyear1884
