300 BOTANICAL GAZETTE [APRIL 
that growth water influences the transpiring ability of the foliage 
leaves to a less extent than do the atmospheric factors. The only 
critical evidence of growth water influence during these studies 
was when it diminished until it approached the wilting coefficient. 
Visible wilting may then occur, accompanied by a rapid reduction in 
transpiration until it becomes almost entirely cuticular. Repeated 
reduction to the wilting coefficient was found to induce early abscis- 
sion of the leaves, a phenomenon found to take place earlier in the 
dune forest than upon the open sands of the same region. The 
effect of abscission upon the foliar transpiring ability has already 
been shown to be similar to that occasioned by the development of 
a wilting coefficient in the soil. Thus while it is essential that 
growth water be available for the plant, there was little evidence 
that it exerts a conspicuous influence in the daily variation and 
hourly fluctuation of the transpiration stream, for differences in 
average available water ranging from 2.5 to 157 per cent show no 
corresponding variations in transpiring power. 
SOIL TEMPERATURE.—It was not determined in the field to what 
extent soil temperatures influenced the transpiration stream. 
few very significant features are evident from the data, however, 
as when the average foliar transpiring power for each of the 
stations is considered, and correlated with the average soil temper- 
atures for the same stations, taken on the same days. This com- 
parison is indicated in fig. 7 by the heavy solid and dotted curves, 
the latter being the curve for soil temperature. It will be noted 
that the temperature of the soil is high where the transpiration is 
high and low where the transpiration is low. There was but one 
instance when a decrease in soil temperature was not accompanied 
by a corresponding reduction in the transpiration index, this being 
registered for the swamp habitat. A close parallel was found 
between average soil temperatures and average transpiration 
indices. 
A second feature is recorded in the relations of growth water 
and soil temperature. It will be noted that the soil temperature 
decreases as the growth water increases, so that the lowest soil 
temperatures are found where the water is most abundant and the 
highest temperatures where the water is least. The records for 
