. A textbook of botany for colleges and universities ... Botany. LEAVES ^33 not so much with increased water accumulation as with the distribution of the water- containing cells. Probably a leaf appears succulent, less because of the large amount of water it contains than because its thickening at the expense of ex- pansion concentrates the water within a compact region; and leaf compactness in contrast to expansion already has been seen to be connected largely with high relative transpiration (p. 598), and thus with cell-sap concentration. Edema. — An explanation of leaf succulence may be sug
. A textbook of botany for colleges and universities ... Botany. LEAVES ^33 not so much with increased water accumulation as with the distribution of the water- containing cells. Probably a leaf appears succulent, less because of the large amount of water it contains than because its thickening at the expense of ex- pansion concentrates the water within a compact region; and leaf compactness in contrast to expansion already has been seen to be connected largely with high relative transpiration (p. 598), and thus with cell-sap concentration. Edema. — An explanation of leaf succulence may be suggested by a consideration of edema, a phenomenon occasionally witnessed when turgor pressure is high and transpiration low, and evidenced externally by the appearance over the leaf sur- face of whitish emergences, known as intumescences (figs. 929, 930). Intumescences develop on the leaves of Hibiscus vitifolius, Solatium tuberosum, and various other. Figs. 929, 930. — Intumescences produced on cauliflower leaves (Brassica oleracea) by chemical stimulation, the leaves having been sprayed with copper ammonium carbonate; 929, a small portion of the lower leaf surface, five days after spraying; i, intumescences: 930, a cross section through an intumescence, highly magni&ed; note the greatly hyper- trophied mesophyll cells (h), which have broken through the lower epidermis (e). — From VoN ScHRENK (929 drawn from a photographic reproduction). plants in moist chambers, and also on isolated leaves of Populus and Eucalyptus and on the inner surfaces of pea pods that are placed in water; in the tomato they have been induced by forcing water into cut stems and by heating the soil in which they grow. In all these cases a surplus of water in the plant causes the hypertrophy of the leaf tissues, which, for lack of space within, are forced to break through the epidermis as intumescences. Probably " water lenticels" (p. 663), the " substitute hydathodes " of Cono
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
