150 SYSTEMATIC BOTANY. 



surmounted by a hood, called the calyptra (Fig. 262, cat) ; 

 surrounding the orifice is a (single or double) row of teeth 

 (Fig. 262, per), called the peristome (Gr. peri, around ; 

 stoma, mouth) ; the teeth number four, eight, sixteen, 

 thirty-two, or sixty-four. The spores germinate by the 

 rupture of the firm, outer coat, or exospore, and tube-like 

 protrusion of the delicate, inner coat, or endospore, which, 

 by division, gives rise' to the filamentous proembryo, called 

 protonema; from this numerous buds arise, which give 

 origin to the upright, leafy, sexual plants. 



176. No true roots are produced by the Bryophyta; 

 organs functionally (but not structurally) corresponding to 

 them, are the rhizoids, or root-hairs, which grow from the 

 under surface of the thallus, or from the sides of the stem. 

 They serve to support the plant in its place, and also to 

 absorb nourishment for its growth. The tissues are more 

 difierentiated than in previous groups. The epidermis is 

 often quite well defined, and true stomates, absent in the 

 lower groups, here appear. The tissue is mainly paren- 

 chymous ; but in the axial portions of the stem, and in the 

 veins of the leaf, there is, by the elongated bundles of 

 cells, slight indication of a fibro-vascular system. The 

 two classes into which the Bryophyta are divided are (1) 

 the Liverworts {MepaticoR) and (2) the Mosses {Musci). 



I. Hepaticee. In this group, the Liverworts (Fig. 263), 

 the plant-body is generally a true thallus, or thalloid 

 structure, with only slight differentiation into stem and 

 leaves. There are usually well-marked dorsal and ventral 

 surfaces ; when leaves are present, they consist of a simple 

 layer of cells, with no midrib or other veins. The plants 

 are small, of a bright green or brownish color, and grow 

 in moist places on the ground, on rocks, or on the bark 



