. Text-book of botany, morphological and physiological. Botany. FIG. 37.—Epidermis of the central vein of the leaf of FIG. of the sclerenchyma in the stem the holly; A transverse section; # superficial appearance of Pteris aquilina (x 550). A a fresh thin transverse (front view). section; B the longitudinal wall between two cells, fresh (a curved pit-canal at the lower end); C transverse sec- tion in concentrated sulphuric acid; D longitudinal sec- tion of the wall in sulphuric acid ; a the central lamella of the wall; b second shell; c third or innermost shell of the cell-wall;
. Text-book of botany, morphological and physiological. Botany. FIG. 37.—Epidermis of the central vein of the leaf of FIG. of the sclerenchyma in the stem the holly; A transverse section; # superficial appearance of Pteris aquilina (x 550). A a fresh thin transverse (front view). section; B the longitudinal wall between two cells, fresh (a curved pit-canal at the lower end); C transverse sec- tion in concentrated sulphuric acid; D longitudinal sec- tion of the wall in sulphuric acid ; a the central lamella of the wall; b second shell; c third or innermost shell of the cell-wall; $ pore-canals; / cavity of the cell. wall of the cells a, which have become entirely converted into mucilage and rendered indistinguishable, their innermost system of layers (b) appearing as a strongly refractive shell. In the dry state the mucilaginous mass is almost horny; it swells up strongly in water with potash solution; with iodine and sulphuric acid it does not become coloured, but the sharply defined inner shell b turns blue. In isolated cells numerous cell-wall-layers may also form a mucilaginous shell which is most beautifully developed in the spores of Pilularia (Fig. 33, p. 32) and Marsilea. In the sporocarp of these plants are certain masses of parenchyma, the cell-walls of which become mucilaginous on the inner side; when dry the mucilaginous masses are firm and horny, but can absorb so much water that they increase in bulk several hundred-fold, and burst the wall of the sporocarp (Book II., Rhizocarpeae). A similar transformation into mucilage of inner layers of cell-wall, while an outer, thin, and cuticularised shell resists, occurs with linseed and quince-seed. The inner thickening-masses of the epidermis of the seed, transformed into mucilage, absorb the surrounding water, swell up violently* and, bursting the cuticle which is incapable D 2. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readab
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1882
