1911] DACHNOWSKI—CRANBERRY ISLAND 3 
ent peat soils under cultivation examined by the writer, and lays 
stress not alone upon structural characteristics in plants but also 
upon limiting habitat conditions as conducive to the development 
of place-functions. That various factors enter into the problem, 
and possibly many others not yet discovered have a part directly 
or indirectly, is clearly recognized. 
Further field work on the bog plant societies has been carried 
out especially with a view to test the reference made by several 
writers to the part played by low substratum temperature and by 
the evaporating power of the air. In addition, studies on the 
physical, chemical, and biological problems of the substratum were 
continued. 
It is obvious that the physical conditions, whether temperature 
or evaporation, if sufficiently great in their differences, must have 
an important bearing on the question of distribution and of xero- 
phytism in bog plants. The larger part of the body of bog plants 
is imbedded in the peat at various depths. The various functions 
take place only within lower and upper critical conditioning fac- 
tors. For instance, the germination of seeds, the activity of 
roots and rhizomes, the permeability of protoplasmic membranes, 
the rate of absorption and chemical action during growth in under- 
ground organs, must be greatly affected by the actual extreme 
temperatures encountered, as well as by the rapidity with which 
changes in temperature occur. The diurnal and seasonal temper- 
ature changes in the peat soil, and the differences in temperature 
between the aerial and underground portions of plants cannot fail 
to be of equally great importance in the physical and chemical 
Processes, in the activity of the soil organisms on those biological 
changes which modify soil productiveness, and in the reciprocal 
Physiological influences upon which absorption, transpiration, and 
transport of solutions from one part of the plant to another depend. 
The task of securing.a coordination between these functions must 
be indeed a complicated one, varying greatly in different species 
according to their capacity of endurance. It is therefore clear 
that conditions as regards efficient temperature determine greatly 
the phy siognomy of the individual plant and of the whole of the 
vegetation in habit of growth and distribution. But the rdle 
