. College botany; structure, physiology and economics of plants. Botany. 78 COLLEGE BOTANY They also contain the chlorophyll, which is the important factor in the absorption of sunlight and in the making of carbohydrates. The epidermis consists of a layer of cells covering, both upper and lower surfaces of the leaf. These cells have lost their proto- plasmic contents and the outer wall has become very much thick- ened and infiltrated with a waxy substance, which makes the leaf water-proof (Figs. 59 and 60). The outer wall is called the cuticle and is composed of cutin, which is very similar to
. College botany; structure, physiology and economics of plants. Botany. 78 COLLEGE BOTANY They also contain the chlorophyll, which is the important factor in the absorption of sunlight and in the making of carbohydrates. The epidermis consists of a layer of cells covering, both upper and lower surfaces of the leaf. These cells have lost their proto- plasmic contents and the outer wall has become very much thick- ened and infiltrated with a waxy substance, which makes the leaf water-proof (Figs. 59 and 60). The outer wall is called the cuticle and is composed of cutin, which is very similar to suberin. Fig. 59. Fig. 60. Fig, 59.—Cross-section of leaf showing: (u) upper epidermis; (p) palisade cells; (m) mesophyll cells; (0 lower epidermis; (s) stomata. Fig. —Lower surface of leaf allowing stomata. (page 52). They protect the more delicate cells within but permit the free transmission of light. On the lower surface we find great nmnbers of minute openings or stomata (singular, stoma) (Fig. 60). The stoma is the opening between two crescent-shaped guard cells through which the air passes into a cavity in the mesophyll of the leaf. The guard cells are crescent- shaped and differ from the other epidermal cells in being well supplied with protoplasm and chloroplasts. These stomata ai-e usually found in much smaller numbers on the upper surface of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Cook, Melville Thurston, 1869-1952. Philadelphia and London, J. B. Lippincott Company
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