280 



EVOLUTION OF BRYOPHYTA 



very hygroscopic, assist in forcing off the operculum. After 

 the removal of the operculum the mouth of the capsule is covered 

 by the peristome which now appears as a fringe of teeth radi- 

 ating out from the walls of the capsule (Fig. 210, 4). The 

 teeth of the peristome are always in multiples of two and form 

 one or more, usually two layers, according as only the outer or 

 both surfaces of the peristome cells are thickened. These teeth 



FIG. 212. Germination of the spore: 3, early stage in the germination. 

 4, character of the branching, algal-like filaments that are finally developed 

 from the spore r, rhizoids which penetrate the ground ; b, bud which will 

 develop into a leafy moss plant. 



are so variously marked and fashioned that they furnish one of 

 the most characteristic features of the various genera of the 

 mosses. The peristome closes the mouth of the capsule in wet 

 weather, but on dry days they are constantly twisting and prob- 

 ably assist in the sifting out of the spores somewhat after the 

 manner of the elaters of the hepatics. The dispersal of the 

 spores is also brought about by the contraction and folding of 

 the capsule and also by the seta which is very elastic and often 

 hygroscopic (Fig. 205, D). 



The spores germinate and produce profusely branching chains 

 or filaments of green cells, called the protonema (Fig. 212). In 

 a few instances, thalloid structures are developed as in Sphagnum. 



