208 



WILLIAM S. COOPER 



back of the Ledum zone there is frequently a broad belt where 

 Calliergon covers the surface completely. Investigation in such 

 a case will show that this species is merely a thin carpet over- 

 lying masses of dead sphagnum sometimes a meter in depth. In 

 a few bogs Camptothecium nitens (Schreb.) Schimp. was found 

 invading the sphagnum in a similar way. Hylocomium proli- 

 ferum and Hypnum crista-castrensis, mosses of the climax forest 

 often follow soon after Calliergon. 



Under certain conditions which were not satisfactorily deter- 

 mined, the sphagnum is able to hold its own against the invading 



Fig. 5 Bog near Park Place. A mass of sphagnum invading the bog forest, 

 surrounding trees and logs, and burying the herbaceous vegetation. 



mosses, and even to become an invader itself. Tongues of the 

 moss were frequently found advancing into portions of the bog 

 forest previously free of sphagnum (fig. 5) ; and in one case a mass 

 was discovered actually climbing a slope of 25° into the climax 

 forest itself. It had reached a distance of ten meters from the 

 true bog margin and had attained a height of four and a half 

 meters above its level. It was entirely covered with a thick but 

 stunted growth of Ledum. 



The bog forest develops upon the area previously dominated by 

 the Sphagnum-Ledum combination, and in the " marginal zone" 



