120 BOTANICAL GAZETTE [FEBRUARY 
This opening was about 50m. long by half as wide, and was 
surrounded by the climax forest, which ended rather abruptly at 
its edge. The surface of the rock was very smooth, little 
weathered, with very few crevices. A mat composed of mosses 
and cladonias covered it except for scattered irregular areas which 
bore only a few foliose and crustose lichens. The mat had started 
from numerous centers, forming at first more or less circular patches 
which later had partially coalesced. The thickest portions were 
composed principally of Cladonia rangiferina, C. sylvatica, and 
1G. 18.—Rock opening in the climax ee near Siskowit Lake: cladonias 
ass patches) are dominant; masses of the moss Rhacomitrium (darker areas) 
border th onia patches; a few small areas so bare rock; Cryplogramme acro- 
stichoides and other plants growing upon the m 
C. alpestris, and around the edges of the patches and making up the 
thinner portions was a growth of the moss Rhacomitrium canescens 
ericoides (Web.) Schimp. Growing upon the thicker portions were 
scattered plants of Cryptogramme acrostichoides, Diervilla, Arcto- 
staphylos, and a few others. The whole mat could be lifted from the 
rock, there being absolutely no connection except where the younger 
plants of the moss (Rhacomitrium) were feebly attached. This 
species was evidently the pioneer, and the cladonias later had 
become superimposed upon it. From this area we learn that 4 
