100 



ELEMENTARY BOTANY. 



for example, in Hypnum, opens by a more or less beaked 

 lid, called the operculum (Fig. 125), which in many species 



Fig. 125. 



is surmounted by a hood, called the calyptra (Fig. 125) ; 

 surrounding the orifice is a single or double row of teeth 

 (Fig. 125), 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 the tube-like protrusion of the deli- 

 cate inner coat or endospore. This continues to grow and 

 gives rise to the filamentous pro-embryo, called the protonema ; 

 from the protonema numerous buds arise, which give origin to 

 the upright, leafy, sexual plants. 



15. No true roots are produced by the Bryophytes ; 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 

 fix the plant in its place, and also to absorb nourishment 

 for its growth. The tissues of the Bryophytes are more 

 highly differentiated 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 parenchy- 

 mous; but in the axial portions of the stem, and in the veins 

 of the leaf, there is, by the elongated bundles of cells, slight 



