Tori] DACHNOWSKI—CRANBERRY ISLAND I31 
high percentage of atmospheric humidity. The local climate is 
therefore preeminently a deciduous forest climate. The whole 
region was in its recent primitive condition densely forested. On 
the other hand, the marked increase of bog development in area 
and in variety of species in northern localities seems to be corre- 
lated with a decline in extremes of summer temperatures and an 
increase in relative humidity. The general effect is to produce 
a balanced functional relation, though limited in range, between 
the amounts of water absorbed and transpired. This phenomenon 
associated with bog habitats will be discussed in connection with 
a further analysis of the life conditions obtained in bogs from the 
point of view of their physiological aridity. 
If we take the above mentioned climatic factors into account 
in the interpretation of local bog conditions, it will be seen that 
meteorological data in this region are not such as to produce or 
account for xerophily or for persistence of bog floras. The 
climatic changes by which a region varies, if severe and varying 
between wide diurnal and seasonal changes in temperature, humid- 
ity, and light, entail naturally modifications in the functions and 
in the composition of a flora. The vegetation would be tested to 
the limits of its power of adjustment and acclimatization, and 
only the forms which had a greater efficiency of responses and had 
powers of resistance intensified to a new place-function would 
take up the habitat to the extent in which survival under the 
modified conditions would be possible. It has been pointed out 
above that changes in the flora are now occurring and have occurred 
during the development of the bog island. Many of the former 
plants have disappeared and are no longer to be found here, while 
others have survived, hold tenaciously the area under control, and 
are still constituents of the present flora. Their preservation in 
this region would seem to be dependent upon less obvious factors 
than climate. Functional habitat relations, as well as such ecologi- 
cal life relations as are comprised in association, in ecesis, and 
succession, need therefore the more detailed investigation. In 
determining these the first component to be considered is the réle 
of low substratum temperature. The temperature of a soil is a 
phytogeographical factor of great significance, but its weightiest 
