Bogs, Their Nature and Origin. 



35 



inating plants whose range is local, chose fifteen species as rep- 

 resentatives of the bogs across North America as follows: Buck-^ 

 bean (Menyanthes trijoliata), tall sedge (Dulichium arundinac- 

 eum), cow-berry (Comarum palustre), Scheuchzeria palustris, tall 

 cotton-grass (Eriophorum polystachyon) , sundew (Drosera ro- 

 tundijolia) , pitcher plant (Sarracenia purpurea), small cranberry 

 (V actinium Oxy coccus), creeping snowberry (Chiogenes hispi- 

 dula), wild rosemary (Andromeda polijolia), leather-leaf (Cha- 

 maedaphne calyculata), Labrador tea (Ledum groenlandicum) , 

 pale laurel (Kalmia glauca), low birch (Betula pumila), and 

 larch (Larix laricina). Of these fifteen species, three, viz., 

 Dulichium a'rundinaceum, Sarracenia purpurea and Kalmia 

 glauca are endemic. The larch and birch are represented in the 

 Old World by closely related forms, while ten of the remaining 

 are present in similar habitats in Europe and Asia. These 

 facts point to their origin as circumpolar species of a preglacial 

 distribution. Some European bogs, according to incontestable 

 proofs, began to form soon after the surface was freed from the 

 snow and ice of the glacial period. In the lower parts of these 

 bogs, are found traces of the arctic flora which then overspread 

 so much of the northern continental areas. Without going into 

 details, it may be said that the relation of these bogs and swamps 

 is a matter of historic development. 



If the wet areas have existed since the time of the glacial 

 tundra, which covered the northern hemisphere, they will show 

 a bog flora today, because the bog flora represents a continua- 

 tion of the arctic tundra flora which existed in glacial times. 

 If the wet area has originated at a date subsequent to the 

 retreat of the continental ice sheet, it will probably show a 

 true swamp vegetation with such plants as cat-tail (Typha 

 latijolia), mat-rush (Scirpus lacustris), rush (J uncus effusus), 

 sedge (Carex riparia), arrow-leaved tear-thumb (Polygonum 

 sagittatum), swamp knotweed (Polygonum emersum), button- 

 bush (Cephalanthus occidentalis) , red-osier dog-wood (Cornus 

 stolonijera), panicled cornel (C. candidissima) , glaucous willow 

 (Salix discolor), red maple (Acer rubrum), elm (Ulmus ameri- 

 cana) and white ash (Fraxinus americana). 



Bogs are formed by the growth of bog mosses (Sphagnum) 

 in temperate and arctic regions on hill tops, on mountain slopes, 

 in valley bottoms, in kettle holes and in lake basins. Here the 



