182 



MUSCINE^:. 



True roots are wanting, but are biologically replaced by rhizoids. 

 These are developed on the stems or thallus : in the Liverworts 

 they are unicellular, but in the Leafy-Mosses generally multicel- 

 lular and branched. In the latter group they are considered 

 identical with the protonema, and may become true protonema, 

 and new plants may be developed from them (Fig. 186 6). 



The internal structure of the sexual generation is very simple. 

 The leaves in nearly all cases are formed of a single-layered plate 

 of cells; in the Leafy-Mosses, however, a midrib is very often 



FIG. 166. -.4 Lower portion of a Moss-plant with rhizoids (r), one of which bears a 

 reproductive bud (1). The dotted line indicates the surface of the ground; tlie portions 

 projecting above this become preen protonema (p); fc is a young Moss-plant formed or. 

 one of these. B Germatining spore of Funaria hygrometrica, with exospore still 

 attached. C, D Older stages of the protonema. 



formed, and sometimes, also, marginal veins ; and along these lines 

 the leaves are several layers of cells in thickness. The stem is 

 constructed of cells longitudinally elongated, the external ones of 

 which ai-e narrower and sometimes have thicker walls than the 

 more central ones. Vessels are not found, but in several Mosses 

 there is in the centre of. the stem a conducting strand of narrow, 

 longitudinal cells, which represents the vascular bundle in its first 



