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 
