SPHAGNUM MOSS NICHOLS. 231 



occupied by lakes or ponds, and the same is true of many of the 

 bogs in eastern Canada and the Pacific Northwest. A pond may be- 

 come filled in and replaced by a bog wholly through plant activity. 

 The filling-in very commonly is brought about through the agency 

 of what is known as a floating mat: The vegetation along the edge 

 of the pond grows so vigorously that it spreads away from the shore, 

 out over the open water. In this way there is developed what is 

 commonly referred to as a quaking bog. This raft of vegetation, 

 floating on the surface, rising and falling with fluctuations in the 

 water level, may be underlain by clear water or by soft, bottomless 

 ooze. So firm, however, may the mat become that while the surface 

 trembles and quakes when you walk over it, nevertheless it is quite 

 capable of supporting the weight of a man. A quaking bog is an 

 ideal place to look for surgical sphagnum. 



Bogs can be distinguished from other types of swamp primarily 

 by certain peculiarities in their vegetation, which in turn are attrib- 

 utable to peculiarities in the soil conditions. In certain respects the 

 plant population of all bogs is essentially similar, no matter what 

 section of the country they occur in. One of their outstanding fea- 

 tures is the nature of the bushy element in the vegetation, which, al- 

 most invariably, is made up very largely of membeTs of the heath 

 family: Such plants as the bog laurel and bog rosemary, the cassan- 

 dra, the Labrador tea, and the cranberries. These are mostly absent 

 from swamps of the ordinary description. Bogs frequently are tree- 

 less, and when trees are present they are usually scattered and 

 stunted. In eastern Maine an open, bushy bog is commonly referred 

 to as a heath; in Europe similar areas are called heath or moor. 



In the East the characteristic tree of bogs is the black spruce. In 

 the latitude of southern New England this tree is seldom encountered 

 except in bogs, while farther north, where it is much more generally 

 distributed, the dwarfed bog form of it is so distinct from the form 

 that grows on uplands that the two are commonly treated as distinct 

 species. 1 In the Pacific Northwest there apparently is no tree which 

 is strictly comparable in its habits with the black spruce in the East, 

 but bog specimens of various trees, when compared with specimens 

 growing on better-drained soils, appear noticeably impoverished. 



From our point- of view, however, the most significant feature of a 

 bog is the wonderful development here of the sphagnums. Almost 

 invariably these constitute one of the most prominent elements in the 

 vegetation. To a certain extent the sphagnums may grow in almost 

 any Avet, springy swamp, whether it is open or wooded ; but even in 

 regions such as Nova Scotia and western Washington, where climatic 

 conditions are most congenial to their development, the sphagnums 



1 See the writer's comment on this point in Trans. Conn. Acad. Arts and Sciences 22, 

 p. 257. 1918. 



