1911] DACHNOWSKI—CRANBERRY ISLAND 139 
great periodic seasonal changes. In winter and in summer the 
minimum temperature of the peat substratum is considerably 
higher than that of the air. Consequently, the annual mean 
temperature of the soil greatly exceeds that of the air. The 
monthly and annual fluctuations of temperature affect the peat 
area to a depth of 2 m., but they are at no time greater or with a 
wider range than those of the air. At what depth the mean tem- 
perature would remain constant has not been determined. 
That the differences between the temperatures of the air and 
that of the substratum are not as great as is generally supposed, 
is a fact upon which it is needless to elaborate further. They 
cannot be looked upon as factors in bog development or in the 
characteristic xerophily of the sphagnum-covered area in this 
region, and hence neither the substratum temperature nor the 
differences between soil and air temperature are of sufficient 
importance to enter into the problem of bog flora, and zonation 
or ecesis and succession. The records show that on the basis of 
temperature as the initial factor the central zone conditions are 
somewhat more rigorous, and that these conditions are mitigated 
in the maple-alder zone; but it cannot be claimed that the differ- 
ences of the plant covering in the two zones are directly correlated 
with the differences of temperature. With no attempt to minimize 
its influence, it is evident that for a comparison of habitats, tem- 
perature, at least as a single physical factor, is a matter of very 
subordinate importance on which to establish a causal relation. 
Those factors acting in conjunction with it demand the greater 
emphasis. It is questioned, therefore, even for regions where 
bogs reach their optimum development, whether the coefficient 
of the differences between the soil and air temperatures is to be 
looked upon as having a greater value than here in the selection 
of plants for bog areas, or the production of xerophilous characters. 
Whether or not important correlations between the temperature 
differences and the transpiratory activities of bog and other plants 
may be expected, a study of the transpiration quantities will 
doubtless reveal. Work of this character is now in progress and 
will be published as soon as opportunity permits. 
