[Chap. XLVIII 



MOSSES AND LIVERWORTS 



639 



Fig. 292. Earlier and later stages in the development of alpine tundra on Mt. 

 Robson, British Columbia. Vegetation starts in the crevices of the glaciated rock 

 surface (A); ultimately rock and plant debris covers the entire surface; and sedges, 

 grasses, creeping willows, heath plants, and Drxjas (in flower) form a continuous 

 association (B). Photos by W. S. Cooper. 



pied the farm site, it is often amazing to see the extent to which the 

 species of bryophytes that foiTnerly hved in the forests of the region 

 have reappeared. 



In tropical and subtropical forests, where rainfall is ample, mosses 

 and liverworts grow profusely in glades and on stream banks. Many 

 grow as epiphytes, forming spongy cushions on tree trunks and branches 

 in the forest canopy. Some even grow on the surfaces of leaves. 



Certain aquatic species live attached to rocks in swift clear streams, 

 and even in waterfalls. Most species of bryophytes are land plants, in 

 contrast to the algae, most of which are aquatics. 



