1905] TRANSEAU—BOGS OF THE HURON RIVER VALLEY 419 
than the forests of mineral soils. These phenomena have not been 
observed in any of the bogs in this vicinity. 
The same statement holds for the presence of loose floating bogs 
which are driven about on lakes by winds (35). 
2. Temperature.—In its temperature relations both the topography 
and the character of the substratum combine to influence the bog 
habitat. It has long been noted by agricultural writers that reclaimed 
bog areas are particularly subject to late frosts in the spring. One 
of the causes of this peculiarity lies in the fact that on clear and quiet 
nights the cooled air overlying elevations drains into the depressions 
(11). Some recent observations made by SEELEY (45) near Chicago 
show how effective such atmospheric drainage may be even in dis- 
tricts whose range of elevations amounts to but 15 feet (4.5™)- : He 
found that the hilltop averaged, on the night of the observations, 
2.5° F. (1.4° C.) higher than that of the depression while a ther- 
mometer placed -30 feet (9™) above the hilltop averaged 8.8° F. 
(5° C.) above that of the ‘swale.’ On comparing the temperatures 
of atmospherically undrained and drained depressions with that of 
the hilltop, he found that the hilltop temperature was 36.3° F. when 
that of the drained depression was 36° F. and that of undrained 
31.8° F. Here is a particular instance in which frost occurred in 
the undrained depression, but not in the other situations. On quiet 
nights low grounds in general are subject to lower temperatures 
than the adjoining highlands, and it is probable that these effects 
are more pronounced in the case of undrained depressions. — 
A second factor in the production of low temperatures ” bogs 
is found in the nature of the substratum. In the spring the ice whi cm 
has formed beneath the cassandra and tamarack areas melts with 
extreme slowness, when once the surface of the soil has been a 
This is explained by the low conductivity of the loose, ens y 
decayed, vegetable covering, and by the shading a the plants A 
For example, at First Sister Lake, in 1904, the Ice had oanre a ss 
from the water surface on April 10. On April 17, with - . “6 
Perature of ro° C., the temperature of the substi. aes i 
sedge zone averaged 10° C., in the Cassandra zone 6 — a 
tamarack zone 3° C., and the area of willows and sedges Ze i a 
Was found at several points among the tamaracks, an inch belo 
