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 foliose 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 foliose forms: 
Dermatocarpon mimiatum 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 mimatum 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 
