. A textbook of botany for colleges and universities ... Botany. 630 ECOLOGY green cells (as in various thin-leaved succulents), quite as in most leaves except for the evident fleshiness of the organ; or the leaf may be thick with the chlorophyll gradually decreasing toward the center, the cells otherwise being essentially similar in aspect, as in most Crassulaceae (figs. 924, 925); or the leaf may be thick with chlorophyll decreasing toward the center, but with the outermost chlorenchyma cells elongated, representing true palisade cells, while the cells toward the center become more and more
. A textbook of botany for colleges and universities ... Botany. 630 ECOLOGY green cells (as in various thin-leaved succulents), quite as in most leaves except for the evident fleshiness of the organ; or the leaf may be thick with the chlorophyll gradually decreasing toward the center, the cells otherwise being essentially similar in aspect, as in most Crassulaceae (figs. 924, 925); or the leaf may be thick with chlorophyll decreasing toward the center, but with the outermost chlorenchyma cells elongated, representing true palisade cells, while the cells toward the center become more and more isodia- metric and also poorer in chloro- phyll (as in the century plant and in various cacti). Another kind of water tissue char- acterizes more ex- treme succulents (as Salsola and other forms with cylin- drical leaves) and may be regarded as more representa- tive ; in these plants the water tissue, which is composed of large isodiamet- ric cells, is centrally placed and is more. Fig. 926. —A cross section through a succulent xerophytic leaf, that of the Russian thistle {Salsola Kali tenuifolia), illus- trating peripheral palisade chlorenchyma (p) and central water tissue (w); note the relatively thin cuticle (c), and the sharp delimitation between the chlorenchyma and the water tissue, the latter being characterized by the large size of the cells and by the absence of conspicuous air spaces; such a leaf is equilateral and approximately radially sym- metrical, thus having a small surface exposure in proportion to the leaf volume; dorsiventrality is exhibited alone by the vascular bundle, the hadrome or xylem (h) lying above the leptome or phloem (/); highly magnified. or less sharply delimited from the peripheral chlorenchyma cylinder whose cells usually are relatively small and of palisade shape (figs. 926, 927). A third kind of water tissue differs from all the rest in its peripheral position, the cells belonging to the epidermis rather than to the meso- phyll. All gradat
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
