36 BOTANICAL GAZETTE JANUARY 



The bog as a habitat for plants differs widely from the other plant 

 habitats of the region in that its substratum has been built by fore- 

 runners of the present vegetation. Owing to the influence of the 

 wind in the production of waves, the bogs are largely wanting on the 

 eastern shores of lakes, and in the case of basins which have been 

 almost completely filled with peat, the open water lies toward the 

 eastern margin. 



It is well known that bog areas are more liable to late spring 

 frosts than adjoining uplands. This is due to the topography as it 

 affects air drainage, and to the low conductivity of the substratum 

 covering. Under natural conditions it has been found that the areas 

 of cassandra and tamarack dominance are more exposed to late frosts 

 than other societies. 



Observations in bog areas show that the soil temperatures beneath 

 the several plant societies differ markedly in range. The records 

 indicate that the areas of bog sedges have temperatures correspond- 

 ing closely with those of the upland and approximating those of the 

 atmosphere. The willow-sedge (swamp) and maple-poplar areas 

 have slightly lower temperatures during early spring. When the 

 trees leaf out, however, the shade produced causes the maple-poplar 

 area to have the lowest temperatures recorded. The bog shrub and 

 tamarack societies show the lowest average temperature throughout 

 the spring months. 



Low soil temperatures retard chemical action, diffusion, solution, 

 and osmosis, and render the substratum unsuited to soil bacteria. 

 When coincident with higher air temperatures, plants having a low 

 transpiration ratio are favored in .the competition between species. 



In so far as southern Michigan is concerned, the substratum 

 temperatures prevailing in bog areas do not seem to be adequate to 

 account for the presence or absence of bog plants or their xerophilous 

 structures. Experiments suggest, however, that farther north this 

 factor is of prime importance. 



In texture the bog substratum shows every gradation from the 

 coarse fibrous peat of the bog-sedge zone to the black powdery muck 

 of cleared land. Bog soils in general do not afford as good a foothold 

 for trees as do the mineral soils. 



Peat is very resistant to the diffusion of mineral salts, hence bog 



