338 BOTANICAL GAZETTE [May 
be ascribed to temperature as a limiting factor for regions widely 
separated geographically. Except for the fact that growth in local 
bogs begins earlier in spring and continues later in autumn than in 
bogs of more northern regions, the data at hand on the differences 
between air and soil temperatures and on the total temperature 
exposure of plants covering a period of three years, show that low 
substratum temperatures, i.e., winter temperatures below 0° C. at 
the one-foot level (30°™) and below + 3°.C. at the 5-foot level (1.5™), 
do not exist here, and hence play no part in bog structure or bog 
development. The more detailed account of this and other phases of 
the study appears elsewhere. The values of both heat-conductivity 
and heat-diffusion are in general lower in peat than in soils or in 
water, and hence prevent a rapid loss of temperature in the peat 
strata below the surface of vegetation. A persistence of the winter 
cold and ice through the summer months has not been observed im 
this region. Contrary, therefore, to the accepted interpretation, it is 
found that the imperfect decomposition of bog plants is not dependent 
upon supposedly low temperatures. One can readily understand 
that if any influence does exist the process of peat formation and 
preservation must be due to the presence of bog toxins and their 
antiseptic properties. 
Livincston has shown that the evaporating power of the air 
furnishes an extremely valuable criterion for the differentiation 
between great centers of plant distribution, and also for the differ- 
entiation of certain habitats and the succession of plant societies. 
In connection with the problem of the transpiration values of bog 
plants, atmometer readings were obtained from the two stations on 
the bog island during the past year. A third instrument was estab- 
lished on the campus near the University Observatory, in an ope? 
place with an exposure to wind and sunlight similar to that in the 
central station on the bog. The readings of the instrument on the 
campus were taken three times daily, in connection with the climato- 
logical observations called for by the U. S. Weather Bureau Service. 
The data collected on the evaporating power of the air in the bog 
habitat, if compared with the evaporation rate on the campus of the 
University, show that the evaporating power of the air in bogs is pe 
an important limiting factor in controlling bog vegetation, or determn- 
