Development of the Vegetation of New York State 135 
1. The course of vegetation on bare rock. 
Hoel Pond near Saranac Inn Station offers a good field for 
a study of this. A tolerably high, rocky promontory fronts 
southward upon the lake. The surface generally is strewn 
with coarse fragments of the granite-like rock, some worn 
smooth and rounded, some — including numbers of huge 
dimensions — are angular. At one point a few square rods 
of native rock lie with a southern exposure. This outcrop 
is not clifflike but rounded off, although fractured enough to 
present seams or small fissures and the surface is minutely 
roughened in the characteristic fashion of weathering granite. 
Some of this rock is entirely bare of plant life in mid- 
summer at least, though doubtless certain blue green algae 
and perhaps minute lichens cover it in somewhat wet, fogg 
and cloudy weather. But generally a close examination will 
reveal minute crusts of lichen attached to the rock as if a 
part of it. These may be regarded as the beginning of the 
invasion. ‘Their presence may have promoted the formation 
of deeper pits in the rock where dust and some organic debris 
may lie long enough to offer a foothold for the broad disc- 
shaped lichens (Umbellicaria and Gyrophora) which now 
cover most of the rock, being held firmly by root-like hold- 
fasts set in the minute pockets. These relatively large plants 
make a thin interrupted mat which tends to accumulate dust 
and the small amount of organic debris. The lichens are 
extremely tolerant of dessication and are in fact dry and 
brittle most of the day in midsummer. With dewfall or 
fog and especially when it rains they expand and become 
very prominent. 
The seams or fissures present an easier point of invasion 
because of the accumulation of soil and a more constant 
water supply. These seams are occupied by mosses — Poly- 
trichum, and especially by a rock fern (Chezlanthes Feet). 
Larger plants such as blueberry may get a start in these fis- 
sures. At the crest of this rock exposure, a thin body of 
mineral soil and raw humus composed largely of pine needles 
