formers is Solaginalla rpuestris (L.) Spring., often Cover¬ 
ing large areas on the rook surface. It is not uncommon 
to find superposed upon this mat the two common mosses 
already mentioned. The Selaginella mat becomes nearly 1 
dm. thick in plaoes, living plants growing on the dead 
mat of former generations. This paves the way for her^ 
baceous plants, such as Danthonia 3picata (L.) Beauv. (wild 
oat grass), Potenti 11a tridentata Ait. (three-tootiled 
cinquefoil), and even for woody species, such as the bear- 
berry ( Arctostaphylos Uva-ursi (L.) Spreng.) and stunted 
specimens, (2 - 4 dm. high), of staghorn sumac ( Khus typhina 
L.). The roots of the latter creep over the rock surface 
for several decimeters until finally they may become anchored 
in a crevice, arctostaphylos is especially well adapted 
to the severe conditions found on these rock surfaces. Often 
it occurs in large patches, thus aiding in the retention of 
more soil and the conservation of soil moisture. Large 
angular depressions in the rook surface may occasionally 
be found where enough moisture is retained to support even 
shrubby growth without being definitely anchored in a crevice. 
Such a case was illustrated by a low specimen ( 2 - 3 dm. 
high) of Hew Jersey tea ( Oeanothus am eric anus L. ) which had 
adapted itself completely to the shape of the depression, 
but could be pulled out bodily as a dense mat. 
