Vegetation of Northern Cape Breton. 423 



brownish to nearly black. 6'. magellanicum: in color, pale 

 greenish white, or usually strongly tinged with pink or purple- 

 red. 6". piilchrum might perhaps also be classed here. It may 

 be noted, as of contemporaneous interest, that in the selection of 

 sphagnums suitable for making surgical dressings the full-leaved 

 forms of S. papillosum and, to a lesser extent, 5". magellanicum 

 have been found to furnish the best material (in this connection, 

 see Porter '17). 



Group 5. Plants strictly non-aquatic, growing in moist or 

 relatively dry situations ; erect and mostly slender ; f oniiing 

 dense, compact masses and building up firm cushions. ^. 

 capillaceum tenellum: color commonly a vivid red. S. fuscum: 

 color commonly russet-green. 6". tencnim: color commonly 

 yellowish, or more or less tinged with pink or red. 



As grouped above, the species are arranged approximately in 

 the order of decreasing hydrophytism. For purposes of con- 

 venience, the species of group i may be referred to as aquatic or 

 hydrophytic ; those of group 2 as semi-aquatic ; those of group 

 4 as mesophytic; and those of group 5 as xerophytic. In view 

 of their tendency, of exceeding importance from an ecological 

 standpoint, to form more or less compact cushions, the species 

 in groups 4 and 5 may be distinguished further as "cushion- 

 forming species." The significance of the above classification 

 will be seen presently. 



Outline of methods by zvhich bogs arise in zvater-filled depres- 

 sions. — Bog formation in water-filled depressions is due largely, 

 if not wholly, to plant activity. In general, as has been indicated 

 elsewhere (see discussion of lowland swamps), there are two 

 methods by which the conversion of a pond into a swamp may 

 be accomplished. These may be designated: (i) filling from 

 zvithin, and (2) encroachment from zvithoiit. By the first 

 method the bottom of the pond is built upward toward the sur- 

 face through the gradual accumulation thereon of successive 

 layers of organic debris, derived mainly from the incompletely 

 decomposed remains of various aquatic plants. By the second 

 a mat of swamp vegetation, originating on the banks or in the 

 shallow water near the shore, pushes outward over the surface 

 of the water, roughly speaking, into the deeper parts of the pond. 

 In typical instances these two lines of development are quite 

 distinct from one another, and the filling in of a pond may be 



