1901 | GENETIC DEVELOPMENT OF FORESTS 309 
If the lichens be on not too steep a slope they will in them- 
selves furnish soil enough to maintain a higher form of plant 
life. Xerophytic mosses gain a foothold as soon as a slight soil 
is made. These, too, by decay aid the lichens in forming a soil 


1 Cladonia rangiferina, Moss, and 
Fic. 5.—A granite rock covered by the licher 
herbaceous plants. To the right are conifers growing in the crevices of rocks 
that will support still higher forms. /ig. 5 shows such a society. 
It is even possible, in time, without the aid of inorganic proc- 
esses of weathering to establish a soil capable-of supporting a 
tree vegetation. However, inorganic processes of weathering 
4 . 7. > 1 } Z 
are going on continually. Changes of temperature, etc., crumble 
the rocks and form crevices in which soil lodges. Since most of 
