. A textbook of botany for colleges and universities ... Botany. S68 ECOLOGY. on the upper leaf surfaces in mesophytes and in xerophytes, there are no breaks whatever in the epidermis, which thus contrast strikingly with the chlorenchyma. In most dicotyls the cells are nearly isodiametric (figs. 8ii, 812, 911), while in monocotyls they usually are elongated in the same direction as is the leaf (figs. 796, 804). Commonly the epi- dermal cells of air leaves differ from the mesophyll cells in the absence of chlorophyll (except in the guard cells) and in the presence of a cutinized outer layer, th
. A textbook of botany for colleges and universities ... Botany. S68 ECOLOGY. on the upper leaf surfaces in mesophytes and in xerophytes, there are no breaks whatever in the epidermis, which thus contrast strikingly with the chlorenchyma. In most dicotyls the cells are nearly isodiametric (figs. 8ii, 812, 911), while in monocotyls they usually are elongated in the same direction as is the leaf (figs. 796, 804). Commonly the epi- dermal cells of air leaves differ from the mesophyll cells in the absence of chlorophyll (except in the guard cells) and in the presence of a cutinized outer layer, the cuticle; such an epidermis soon ceases to have any r61e other than that of protection. In submersed plants, however, the epidermis contains chlorophyll and remains uncutinized, thus taking part in absorption and in synthesis. The epidermal cells of hydrophytes and (j of mesophytes usually are larger than are like cells in xerophytes, and the growth of mesophytes in xerophytic conditions commonly results in a decreased cell size. Fig. 808. — a cross section through the leaf epi- y^g gj^^g;. epidermal walls; dermis of the century plant {Agave americana), . . _i showing the ceUulose layer (c"), the cuticular layer CUtmtZaUon. — i he outer (c'). the cuticle (c), and a superficial layer of wax wall of the epidermis, origi- grains (A) which constitute a glaucous bloom; highly n^lly thin, and also perme- magnified. u a c able because composed of cellulose, in the adult leaf commonly is thickened through the deposi- tion of citlifi, a fatty substance highly impermeable to water. Usually the cutinized portion forms a continuous yellowish coat, the cuticle (figs. 807, 810), below which is the slightly modified cellulose portion of the outer wall. In some xerophytes a cuticular layer is interposed be- tween the cellulose and the cuticle, the wall thickening progressively inward before it becomes cutinized (fig. 808). In Pinus the encroach- ing wall finally fills the entire
Size: 2665px × 937px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
