THE ARCHEGONIAT^E 



201 



the vegetative existence of the sporophyte itself. In the more 

 specialized forms like the True Mosses and Anthoceros, spore-forma- 

 tion is subordinated, and the sporophyte develops green assimilative 

 tissue and a system of conducting tissues, and is dependent upon the 

 gametophyte only for its supply of water. 



Biology. The Bryophytes are, for the most part, inhabitants of 

 moist localities, and a few are true aquatics (e.g. Riccia Jluitans, 

 Fontinalis). Their favorite habitat is shaded earth and moist 

 rocks, bases of trees, and similar places. They may, however, be 

 adapted to a dry situation, and become completely dried up without 

 injury. This is strikingly shown by many Calif ornian Bryophytes, 

 which remain dormant through the long rainless summers, resuming 



FIG. 162. Targionia hypophylla. Germination of spores ( X about 200) . C, E, optical 

 sections ; x, apical cell ; r, primary rbizoid ; sp, spore-membrane. 



growth at once with the advent of the autumn rains, and completing 

 their season's growth during the rainy winter. 



Liverworts seldom occur in sufficient numbers to constitute a con- 

 spicuous feature of the flora, but the Mosses are often gregarious, 

 and in the wet northern regions often cover large tracts, almost to 

 the exclusion of other vegetation. This is seen especially in north- 

 ern bogs, where the Peat-mosses (Sphagnum), Hypnum, Polytrichum, 

 etc., are the most important factors in the vegetation. In the 

 northern forests, also, the ground . and the decaying trunks of 

 the fallen trees are covered with dense cushions of large Mosses. 

 Similar conditions prevail in the cooler regions of the southern 

 hemisphere. 



