ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 391 



many other dry and sterile and unpromising situations. 

 The gray encrusting species are commonest, but many forms 

 occur. The well known "reindeer moss" is a lichen. For 

 the purpose of the following study, one of the gray Parme- 

 lias (fig. 22ya) and one of the chimney lichens that grow on 

 decaying stumps in damp woods (fig. 2296) will answer our 

 needs. 







FIG. 227. Lichens, a, a common 

 ules;6, a "chimney lichen," whc 

 white lichen buds (soredia). 



:ncrusting lichen, showing fruiting cup- 

 ;e "chimneys" are covered with powdery 



