1911] DACHNOWSKI—CRANBERRY ISLAND 135 
areas are found in the central zone bordering the Rhus-Alnus 
thickets where ice never forms in winter. Such temperature 
conditions would not attract special attention were it not for the 
fact that usually the temperature is so much lower in the adjacent 
areas. From a biological standpoint this fact is significant because 
these conditions favor isolation of habitats and produce a promi- 
nent floristic difference. Wolfella floridana commonly occurs in 
these “‘warm”’ pools. 
Plants are not dependent so ‘memeh upon the mean annual tem- 
peratures as upon the minima and maxima of temperature encoun- 
tered, and upon the duration of the vegetation season. To throw 
some light on the characteristic temperature range occurring 
throughout the year and within a growing season, the temperature 
data of the monthly extremes for the seasons of 1908, 1909, and 
for the autumn and winter of 1907, and the spring of 1910 are 
appended. As far as the writer is aware, no observations of minima 
and maxima temperature records within a bog, covering a period 
of three years, have been carried out thus far. On account of 
the fact that the present data were obtained at a station whose 
ecological significance is especially interesting, table VI of the 
temperature data is deemed worthy of a closer consideration. 
We see again that the temperature of the substrata at the differ- 
ent levels is affected less by the alternate heating and cooling at 
the surface, but in a far greater degree by the progression of the 
seasons. It increases slowly during May, is stationary more or 
less during August and September, and begins to decrease fairly 
rapidly in November. The maximum temperature occurs in 
July and August, and the minimum temperature is registered in 
January for the central zone. That of the maple-alder zone occurs 
in February. Observations have shown that the lake freezes to a 
depth of 8-15 inches (20-37 cm.), while the bog is covered by ice 
to a thickness varying from 3 to 5 inches (7.5-12.5 cm.), except 
for a few places where ice never forms. Consequently, the strata 
in the bog area below the one-foot level (30 cm.) are well protected 
from lower temperatures and from sudden temperature changes. 
When the sun’s heat melts the ice and snow, the percolating water 
derived from the melting ice lowers the temperature of the deeper 
