420 BOTANICAL GAZETTE [DECEMBER 
surface. The sedge zone was covered with 1 to 3 inches (25-75™™) 
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™™) 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 (0.9™) above the surface of the bog. The temperatures for 
the most part were taken on clear afternoons about 3 p. M. when th 
differences are at their maxima. | 
Viiies April |April | April |April | April | May | May | May | May | May Le J ng 
420) 37} a6 | 2 6 G6} 3h ae 
STAT AR in SUE at etna CES Re Soh 
Air temperature 10.5] 2.0 | 10.0} 8.5] 18.0] 2 26.0] 21.0} 26.0] 26.0 
weet ee oh ss ‘ : : : 4.0} 27.0] 15 
pn II.0| 7.0 | 10.0] 10.0] 17.0] 20.0] 23.0] 16.0] 20.5] 21.5) 25-5 = 
Willow-sedge.............. 7.0} 8.0 | 8.0] 9.0] 14.5] 17-7] 10.5| 15.0] 20.0] 22.0) 22 oie 
Peeve eee. Vite T.5| 2.0 | 6.0) 7.5) 11.0] 14.7] 15.5] 13.0] 16.5) 19-0) 20:0) “or8 
Deca pee Ee 0.0, 0.0] 3.0] 4.5| 9.9] 11.7] 15.0] 10.6] 15.0] 17-0] 18.0) Bo-8 
Boe sente cyo2 ee 9.0| 8.0 | 10.0} 9.0] 18.0] 19.0) 22.0] 16.0] 20.0] 23-0) 24-0 ws 
Maple-poplar.............. 7-0} 8.0] 8.0} 8.0} 15 8.0] 19.0] 15.0] 16.0] 15.0) 17-0) Bs 
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 
