. A textbook of botany for colleges and universities ... Botany. LEAVES 631 the centrally placed chlorenchyma occupies less space than does the epi- dermal water mantle (figs. 928, 766, 767). Perhaps the commonest sort of water mantle is represented in Tradescantia, where there is a single or double layer of large turgescent colorless cells. The water tissue com- monly is best developed on the upper side of the leaf, sometimes being confined to that side. In most cases the cell sap is highly acid. In the " ice plant" (Mesembryanthemum crystallinum) a few of the epidermal cells are mu
. A textbook of botany for colleges and universities ... Botany. LEAVES 631 the centrally placed chlorenchyma occupies less space than does the epi- dermal water mantle (figs. 928, 766, 767). Perhaps the commonest sort of water mantle is represented in Tradescantia, where there is a single or double layer of large turgescent colorless cells. The water tissue com- monly is best developed on the upper side of the leaf, sometimes being confined to that side. In most cases the cell sap is highly acid. In the " ice plant" (Mesembryanthemum crystallinum) a few of the epidermal cells are much distended and project considerably beyond the epidermal level, causing the leaves to glisten in the sun- light. Not infrequently plants possess isolated colorless tur- gescent cells in the midst of a tis- sue made up of cells of wholly diJferent character; when such cells have walls with tracheid- like thickenings, they have been called storage iracheids (fig. 772). In many succu- lent monocotyls (as Aloe) the cell sap is very mucilaginous, and in some plants of similar character mucilaginous mate- rial is deposited in the form of wall thickenings. The causes of water acctunulation in succu- lent plants. — Experi- mental data. — Some suc- culent plants ( Sem- pervivum assimile, figs. 1043-1045) when placed for a few weeks in a moist chamber develop slender elongated shoots with thin expanded leaves, having little or no suggestion of succulence, while subsequent removal to dry air results once more in the development of short and stout shoots that bear thick succulent leaves of small size. Such reactions are quite like those previously noted as characterizing habitats that differ in atmospheric humidity and hence in transpiration (see p. 598). But while the xerophytic leaf is in all cases small and thick and the meso- phytic leaf large and thin, the thickness in the succulent xerophyte is due to an increased dorsiventral development of watery tissue, while that in. Fi
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