Vegetation of Northern Cape Breton. 



427 



6". fiiscum and .S". capUlaccnm tenellum, which, while they may 

 frequently be present, do not thrive in the wetter situations. 

 These xerophytic sphagnums, at first growing intermixed with 

 the mesophytic species, gradually become more abundant, over- 

 growing and eventually eliminating their less xerophytic competi- 

 tors. The mesophytic cushion-forming sphagnums may be 

 largely responsible for the elevation of the bog surface to a 

 height of a foot or two above the original water level, but any 



Figure 62. — Margin of small undrained pond near crest of raised bog; 

 barrens in mountains west of Ingonish ; in foreground, Andromeda and 

 other shrubs advancing into the pool. 



further upward growth is dependent very largely on the 

 xerophytic cushion-forming sphagnums, which invariably are 

 the predominant species in a mature bog. 



Encroachment from without, with particular reference to the 

 formation of floating mats. — In its essential features, floating 

 mat formation in the highlands differs little from what has been 

 described for the lowlands. The pioneers may be either shrubs 

 or sedges. In the former case (Fig. 62), here as there, unless 

 the framework created by the shrubs becomes overgrown by 

 sphagnums, mat formation proceeds no farther than this incipient 



