42O 



BOTANICAL GAZETTE 



[DECEMBER 



surface. The sedge zone was covered with i to 3 inches (25-75 mm ) 

 of dark colored water. The other soils were wet, but their loose 

 texture was effective in preventing a rise of temperature. 



It follows that of the various situations in bog areas those most 

 liable to extreme low temperatures in the spring are in the cassandra 

 and tamarack zone. Since their maximum temperatures are con- 

 siderably below those of neighboring areas, on quiet nights the plants 

 there are but little protected by radiation from the soil as compared 

 with plants of other situations. 



In the following table it is shown that the soil temperatures of 

 the several plant societies formed about a bog are different, and that 

 each society has a characteristic temperature range. The records 

 were made at First Sister Lake. The temperatures, given in C, 

 are averages of readings made in the second inch (25 mm ) below the 

 surface. The " willow-sedge " conditions correspond to those of the 

 ordinary swamp. The " maple-poplar " is an area of these trees on 

 the peat substratum. The " upland" is a sandy, sod- covered area 

 3 feet (o.9 m ) above the surface of the bog. The temperatures for 

 the most part were taken on clear afternoons about 3 P. M. when the 

 differences are at their maxima. 



In the accompanying diagram (fig. 5) it will be seen that the 

 upland, bog-sedge, and willow-sedge soil temperatures do not deviate 

 widely from those of the air, while the temperatures of the cassandra 

 and tamarack areas range considerably lower. The high temper- 

 ature of the bog-sedge zone finds its explanation in that the brown 

 bog water overlying its surface absorbs heat. I have tested this point 

 many times in various bogs and have always found such bog water to 

 have a higher temperature than that of the saturated substratum 

 adjoining it. In its ability to absorb heat rays it approaches that of 

 drained sand. Its range, however, is much less and it retains its 



