Southeastern Washington and Adjacent Idaho. 65 



About the foliaceous species, water not only has a better chance 

 to collect and be absorbed but evaporation is also less rapid. In- 

 deed, it is probable that the change from crustose to f oliose lichens 

 is as great a change of habitat as happens anywhere in the sere, 

 although too minute in extent to be impressive. 



Gyrophora-Parmelia Associes 



This community is in general less marked than the preceding 

 and is characterized by the following f oliose forms : 



Dermatocarpon miniatum Parmelia conspersa 



Gyrophora phaca Parmelia pubescens 



Lecanora rubina 



Gyrophora phaca may easily be found invading the areas of 

 the preceding crustose forms and because of its growth-form 

 actually causing them to disappear on account of decreased light. 

 Thus it comes to dominate areas of greater or lesser extent. 

 Parmelia conspersa takes possession of new areas in a similar 

 manner. Dermatocarpon miniatum is characteristically found in 

 situations where water seeps out of the rock ledges during a part 

 of the year. . 



As soon as soil and humus begin to accumulate in the crevices 

 and larger pores of the rock, the more xerophilous mosses begin 

 to appear. The pores in the basalt vary from those microscopic 

 in size to those several inches or even feet in diameter. On a 

 single rock one may come across an infinite variety of stages from 

 the dry exposed top of the rock with its crustose lichens to the 

 creviced or roughened lower portions where foliose forms are 

 mixed with mosses, grasses, and other flowering plants. 



Grimmia-Tortula Associes 



The moss of most common occurrence on the rocks and the one 

 which is able to live in the most xerophytic situations is the black 

 moss, Grimmia montana. This moss, with its minute rhizoids and 

 power of withstanding desiccation, quickly follows the lichen stage 

 and even precedes several species of the foliose lichens in point 



65 



