206 BOTANICAL GAZETTE [MARCH 
About this time or often before, young plants of other mosses 
more or less tolerant of shade become established upon the higher 
parts of the sphagnum mass. Polytrichum strictum Banks is the 
first arrival, and Aulacomnium palustre (L.) Schwaegr. and Callier- 
gon Schreberi (Willd.) Grout soon follow. These species form mats 
of continually increasing lateral extent, which put an effectual 
stop to further upward growth of sphagnum. 
Fic. 42.—Sphagnum-Ledum zone, the moss entirely concealed by the abundant 
growth of the latter; the edge of the bog forest in the background; Raspberry Island. 
b) Sphagnum invading the forest 
The fact has been mentioned that the sphagnum frequently 
spreads into the marginal zone as well as toward the center of the 
bog. In some places this invasion is so effective that the marginal 
zone is entirely obliterated. The moss does not always stop even 
here, but occasionally climbs entirely out of the bog, invading the 
climax forest. - A case of this kind was reported by Hott (33) from 
a locality near Siskowit Lake. A far more striking instance was 
discovered on Raspberry Island, near the northeast end of the bog 
(see map, fig. 36 and fig. 43). In a stretch of 50 m. along the margin 
the sphagnum had completely obliterated the marginal zone and 
had ascended the slope for varying distances. At the point of 
