Liverworts and Mosses 279 



successful adjustment of simple green plants to the land 

 environment. 



Life history of the moss. Mosses reproduce by vegetative 

 propagation and by both 

 sexual and asexual spores. 

 A study of each of these 

 methods will make clear the 

 somewhat complicated life 

 history of the moss plant. 



Vegetative multiplication. 



When a mOSS Spore germi- FIG. 164. Moss spores (A) and protonema 



nates on the soil, it produces (B) ' with f bud (C) from which an upright 



stem develops. 



a branching, filamentous 



body, the protonema, which resembles some of the branching 

 forms among the green algae. The protonema spreads over 

 the soil for some distance and then develops numerous buds 

 (Fig. 164). The buds give rise to the upright leafy branches 

 which we commonly call the moss plant. Because of the 

 numerous buds developed on the protonema, the moss plants 

 stand in thick clusters or masses. 



The upright leafy stems of the moss also have the power 

 of producing protonema-like branches which spread still 

 farther over the soil, thus serving to multiply the plants and 

 to make the plant mass denser and larger. In some mosses 

 with horizontal or inclined stems, the stem tips when in con- 

 tact with the soil develop rhizoids and give rise to new branches, 

 much as the stems of the raspberry develop new plants (page 

 217). These methods of vegetative propagation are com- 

 mon among the mosses, and some mosses are not known to 

 multiply in any other way. 



Sexual reproduction. The upright stems of most mosses 



