Forest Development in the Adirondacks 39 
While edaphically considered sphagnum represents pretty 
uniformly the conditions just described, there are, in fact, 
several species of this important genus which play a more or 
less distinct role in the course of vegetation development of 
this bog. Thus where open water stands between the mounds 
or where after fall rains the bog is partially flooded, the finely 
divided algalike growth of Sphagnum cuspidatum is abundant. 
Its occurrence and abundance consequently fluctuate with the 
season. It may be supposed that this and other species capable 
of growing wholly submerged would figure in the early stage 
of establishing a vegetation cover upon the original constantly 
or seasonally submerged sand plain. The tall, vigorously 
growing sphagnum which makes the deep carpet of the open 
sedge zone is mostly Sphagnum recurvum and this species is 
the active one in forming the rapid upgrowth among heath 
shrubs. Fig. 12. The soft, deep carpet under shade of high 
shrubs and in the conifer bog forest is S. magellanicum and 
this species appears to persist often as the main ground cover 
in the oldest association where balsam, red maple and numerous 
forest floor species of balsam swamp associations occur. But 
in the transition from conifer bog forest to balsam swamp type 
where numerous forest floor species (see previous list, p. 34) 
have entered the association, Sphagnum girgensohni was 
found to be the main ground cover. This was found to be the 
case also in balsam flats outside the bog area.* In the shrub 
zone where the sphagnum blanket is very thick and spongy 
and where mounds are built up so that drying out is a period- 
ical phenomenon, the two so-called mound formers, S. capzil- 
laceum var. tenellum and S. fuscum make a very close, com- 
pact mat. In my observation, however, the mounds them- 
selves are frequently formed by the taller growing species — 
especially S. recurvum and the two previously named species 
then become established upon these mounds. (11, p. 422.) 
* Sphagnum girgensohnii has been observed by the writer to be the first 
of its genus to invade a marsh meadow (Calamagrostis canadenssis and its 
marsh associates) which has for two years been flooded by back water 
caused by beaver dams across Sucker Brook (Cranberry Lake). In this 
case the suggestion arises that this species is a pioneer in the transfor- 
_ mation of a marsh into a bog. : 
