1911] DACHNOWSKI—CRANBERRY ISLAND 137 
maples still less. Plants imbedded in the peat at a depth of 1 
foot (0.3 m.) are within ranges of temperature from o° C. to 27° C. 
The underground growth of the plants continues when the winter 
temperature in the substratum rises and reaches the gradient from 
4 to 8° C. When these soil temperatures prevail during winter 
for a sufficient length of time, the different stems and buds shoot 
upward and develop leaves and lengthen their internodes rapidly 
in the warmer weather of spring. The absorbing organs at 3 
inches (7.5 cm.) depth in the peat substratum encounter a mean 
average of 13°5 C. with an amplitude of more than 30°. In all 
cases, however, the range of temperature in the maple-alder zone 
is less than that of the central zone by a difference of at least 6°. 
These observations and facts disclosed as to the actual tempera- 
tures in the peat substratum of Cranberry Island, and the seasonal 
changes therein point to the following conclusions: 
1. The soil temperature of two plant associations formed about 
the bog island are slightly different, and each association has its 
own characteristic temperature range. 
2. Of the two plant associations in the bog area, the one more 
liable to extreme low temperatures in the spring and during the 
growing season is the maple-alder zone along the border of the lake, 
and not the more xerophytic central zone. 
3. The substratum temperatures as phenomena of the local 
peat deposits are not favorable to the preservation of bog types, 
if low temperature is considered to be an edaphic criterion; in 
connection, therefore, with an analysis of the life conditions in this 
bog area low temperature is not a limiting factor. 
4. A persistence of the winter cold and ice through the summer 
months is a point not proved either by observation or by register- 
ing instruments. The persistence of northern forms in this bog, 
therefore, has some other cause than low temperature of the sub- 
stratum. In arctic latitudes, no doubt the most significant factor 
in determining the character and the distribution of plants, as 
well as in the formation and preservation of humus material, is 
low temperature. In the latitudes of Ohio, temperature is not 
a factor in the process. Neither does the accumulation of humus 
finally bring about edaphic conditions ‘‘too cold and too acid.” 
