308 



PART IV. CLASSIFICATION. 



FIG. 189. jl A fruticosa Lichen, TJsnea larbata, with apothecia. a. B A foliaceous Lichen, 

 Sticta pulmonacea, with apothecia, a (nat. size). (After Sachs.) 



Many species of crustaceous 

 Lichens inhabit the highest 

 peaks of the Alps, and other 

 lofty mountains, on which there 

 is no other vegetation, and they 

 contribute materially to the 

 weathering of the rocks and to 

 the formation of a vegetable 

 soil. When they grow on the 

 trunks of trees, they occur more 

 especially upon those which 

 have a smooth surface ; the 

 formation of a rough bark seems 

 to interfere with their growth. 

 Lichens may become completely 

 dried up without losing their 

 vitality. 



FIG. 190. Crustaceous Lichens. A and B 

 Qraphit elegans : B slightly magnified. C Per- 

 tusaria, Wulfeni, slightly magnified. (After 

 Sachs.) 



