IIo BOTANICAL GAZETTE [AUGUST 
here was seen in the lowest point reached during the second week 
when the upland went to 0, while the bog remained 4° warmer. 
The records of the thermographs show wide variations in air 
temperatures. In 1907, during the week April 26—May 3, it ran 
from 21°5 C. to —4°5 C.; in 12 hours it rose from —4°5 C. to 
16° C.; May 11, from 6 a.m. to 8 A.M., the air was —4° C.; May 
13 at 1 P.M. it reached 28° C.; May 16 at 3 A.M. it was only 1°5 C. 
Low temperatures were recorded during the summer. On June 28 
the air got as lowas 4° C. July (1907) was the hottest month, 
judged from the lowest temperatures reached, the lowest for the 
month being 7° C. at 6:15 A.M. the 27th. In August the low records 
Were: the tst.9 C.; 3d,6 C.; ath, 6° C.; 13th, 7° C.; 22d, 3°5C.; 
25th, 5, C. August 6, 1904, a maximum-minimum thermometer 
was hung in the top of an 8-foot tamarack in the sedge zone at 
Dead Lake. It showed a maximum of 37°8 C. and a minimum of 
57s C. 
These figures show that the temperature of the air is compar- 
atively low during the entire summer during the night. The 
coldest time came at 1 A.M. or about 7 A.M. On the other hand, 
day temperatures may run very high. The hottest time of the day 
was about 1 P.M.; it seldom came as late as 2 P.M. Fig. 3 repro- 
duces the air record for the week July 2-9, 1906, taken in the 
floating sedge zone at First Sister Lake. 
The temperature of the soil, on the other hand, shows very 
slow variations during the season. There is great difference in 
soil temperatures at different depths, and they warm up very 
slowly, except for the shallow surface layer; they never get very 
cold. When making contour maps of the bottom of these lakes 
(3, 4) in winter, it was soon learned that although the ice might 
be 10 inches (25.3 cm.) thick over open areas, a good thrust of the 
drill would usually send it through the thin ice near and beneath 
the tamaracks. Even in most severe weather it was necessary 
to wear rubber boots, as the thin ice continually broke under 
one’s weight. What ice is formed, however, lasts long into the 
spring. . 
In taking soil temperatures, a square piece was sawed out of 
the peat and carefully removed. The long bulb of the thermo- 
