. Botany for high schools and colleges. Botany. THE EPIDERMAL SYSTEM. 91 portion of the underlying mass is also removed. In many of the Thalloj^hytes there is absolutely no differentiation of an epidermal portion. 118.—In the Bryophytes there is in general a poor epider- mal development ; it is composed for the most part of one or more weakly defined layers of smaller cells, which, how- ever, pass by insensible gradations into the inner tissue mass. Here, however, the first true epidermal hairs make their appearance. 119.—In one group of the Liverworts—the MarchantiacecB. Fig. 78.—Longitudinal
. Botany for high schools and colleges. Botany. THE EPIDERMAL SYSTEM. 91 portion of the underlying mass is also removed. In many of the Thalloj^hytes there is absolutely no differentiation of an epidermal portion. 118.—In the Bryophytes there is in general a poor epider- mal development ; it is composed for the most part of one or more weakly defined layers of smaller cells, which, how- ever, pass by insensible gradations into the inner tissue mass. Here, however, the first true epidermal hairs make their appearance. 119.—In one group of the Liverworts—the MarchantiacecB. Fig. 78.—Longitudinal section of erect portion of thallus of Marchantia polymor- pha. 0, epidermis ; S, walls between air-spaces, the latter filled with rows of chloro- phyll-bearing cells, chl; sj), a stoma; g, a large parenchyma-cell, x 550.—After Sachs. —there is an epidermal system of a high degree of perfection, and composed of epidermis proper and stomata (Fig. 78). The epidermis consists of a single layer of somewhat tabu- lar cells arching over the air-cavities which occupy the upper surface of the plants ; it is perforated here and there by sto- mata or breathing pores, composed of four to eight circular rows of cells placed one above the other {sp in the figure). These chimney-like structures originate by the division of a single cell into four or six radiating daughter-cells ; in the centre of this group an intercellular pore is formed by the lateral growth of the cells (Fig. 79) ; and by a subsequent. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bessey, Charles Edwin, 1845- [from old catalog]. New York, H. Holt and company
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