. Physiological botany; I. Outlines of the histology of phænogamous plants. II. Vegetable physiology. Plant physiology; Plant anatomy. EPIDERMIS. 65 sooner or later thrown off, and replaced by a subjacent protective tissue, — cork. 218. Except at peculiar openings (stomata, etc.), the epider- mal cells are in close apposition. Upon their exposed surface the}' are cutinized, and thus a continuous hyaline film is formed, known as the Cuticle?- 219. Sometimes the epidermis may be torn off without much disturbing the underlying tissues. 220. Besides the cells which compose the proper tissue of the
. Physiological botany; I. Outlines of the histology of phænogamous plants. II. Vegetable physiology. Plant physiology; Plant anatomy. EPIDERMIS. 65 sooner or later thrown off, and replaced by a subjacent protective tissue, — cork. 218. Except at peculiar openings (stomata, etc.), the epider- mal cells are in close apposition. Upon their exposed surface the}' are cutinized, and thus a continuous hyaline film is formed, known as the Cuticle?- 219. Sometimes the epidermis may be torn off without much disturbing the underlying tissues. 220. Besides the cells which compose the proper tissue of the epidermis, there are certain ap- pendages or accessory structures, mainlj' hairs or analogous pro- ductions (together called tri- chomes), and peculiar cells which constitute the stomata. 221. Epidermal cells proper are in uninterrupted contact. They are usuallj' of a tabular or pris- matic form. The lines which mark their outlines as viewed from above are sometimes straight, but oftener sinuous, at least on the longer sides of the cell, which here as elsewhere correspond with the direction of growth. Near stomata and trichomes the cells frequently assume very irregular forms. 222. Their upper or free surface is generally slighth" convex, and often has minute outgrowths, for instance, in velvety petals ; when these arc larger and longer, thej' constitute the simplest form of plant hairs. 223. Delicate epidermis possesses thin walls; but in a large number of fleshy and tough plants the walls have considerable thickening, j'et not always on the same part. Thus in the leaves of Cycads the upper wall is the thicker; in many Bromeliaceae, the lower and side walls. In a few cases the cell-cavit}' is nearly filled by the thickening material. Stratification, striation, and pitting of the cell-wall may also occur, great diversity existing in all these respects. 224. When tlie epidermis is ver}' delicate, the demonstration of the thiu film of cuticle requires great care in the e
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