356 George E. Nichols, 



ordinarily are best developed in relatively deep, undrained or 

 poorly drained, water filled depressions. For reasons which will 

 be apparent later, however, in humid regions, like the one under 

 discussion, swamps of the undrained type are by no means con- 

 fined to depressions. (<?) Both well-drained and undrained 

 swamps may be underlain by peat ; but in the former the deposit 

 usually is quite shallow and sometimes it is entirely absent. 

 Moreover, in well-drained swamps the peat as a rule is mucky, 

 the plant remains being pretty thoroughly decomposed. 

 Undrained swamps invariably are underlain by peat deposits, 

 which often exceed fifteen feet in thickness ; the peat is more 

 or less spongy, and the plant remains for the most part are well 

 preserved. (j) The soil in practically all swamps in northern 

 Cape Breton is acid to litmus, but it is appreciably more so in 

 swamps of the undrained type than in others. (4) The vege- 

 tation of well-drained swamps is characterized by the moderate 

 abundance of the sphagnums ; by the great variety of herbaceous 

 seed-plants, which in large part are hydrophytes ; by the 

 scarcity of ericaceous shrubs ; and by the presence of several 

 deciduous trees of southward distribution. The vegetation of 

 undrained swamps, on the other hand, is characterized by the 

 luxuriant development of the sphagnums ; by the comparatively 

 small number of species of herbaceous seed-plants, which in 

 large part are bog xerophytes ; by the abundance of ericaceous 

 shrubs ; and by the absence of practically all trees except the 

 black spruce and tamarack. 



b. THE ASSOCIATION-COMPLEXES OF WELL-DRAINED SWAMPS 



Pioneer association-types. — Among the important pioneers in 

 the development of vegetation on springy or wet slopes are the 

 bryophytes, notably the following species : 



Marchantia polymorpha^ Sphagnum squarrosum 



Pellia epiphylla* Philonotis fontana* 



Pallavicinia Lyellii* Mnium punctatufn^ 



Scapania nemorosa* Brachythecium novae-angliae 



Of the herbaceous vascular plants, almost any of the species 

 to be listed later as characteristic of wet meadows may appear 

 at a very early stage in the succession, but the following list 



