312 BOTANICAL GAZETTE [APRIL 
a relatively high water loss as on the dunes, is growing in the 
very opposite environment in reference to its physical factors. 
The growth water and relative humidity are greater here than at 
any other station, while soil temperature, evaporation, and atmos- 
pheric temperature are lowest. Of these factors, measured soil 
moisture might be cited as the causal factor leading to increased 
transpiration, but it seems improbable that this factor can be re- 
sponsible for the higher water loss. It is more probably associated 
with structural features, the correlation of root and leaf develop- 
ment, or the greater exposure to light. 
12. The variation in average transpiring power from day to day 
as recorded for the same leaves is greater for the mesophytic forest 
than is the difference between the average rates for the most 
mesophytic and most xerophytic stations, if we consider the clay 
series only and disregard the prairie record. The converse is true 
for the dune series. 
13. Daily variations in the transpiration stream are most 
pronounced in the xerophytic situations, and least so in the strongly 
mesophytic ones. 
14. The average transpiring power is less in deep forests and 
moist ravines than in open woodlands, and less in open forests 
than in exposed positions on clay. The greatest transpiring ability 
was recorded on the open sands where there was no humus, and on 
the prairie. 
15. The transpiration curve characteristic of the prairie station 
is closely similar in its essential features to the curves representing 
the open dune sands. There is a more rapid morning rise as com- 
pared with the forest, owing to the greater light exposure at that 
period, a tendency to an earlier maximum due to a greater water 
reserve, a more frequent recurrence of a saturation deficit, and 
finally a steeper afternoon decline than is commonly recorded for 
the clay environments. 
16. The highest transpiration rates are found to be ocched 
with a low growth water, which is not interpreted as being in any 
way causal, but as evidence that growth water is of relatively little 
significance so far as transpiration is concerned until it approaches 
the wilting coefficient. 
