IIo BOTANICAL GAZETTE [AUGUST 
even lower. It is noted also that the time element of this period 
varies greatly in the two seasons. In 1915 it is comparatively 
short, while for both series in 1916 it is extended over a consider- 
able period. It has been proved by the work of SHREVE (34) that 
plants grown under different environment not only have different 
anatomical characters but also have a different rate of transpira- 
tion. 
On the basis therefore of a possible change as a result of 
environment, it can safely be asserted that this is the reason for 
the short span in 1915 and the long one in 1916. Why or how 
the plant establishes such an apparent equilibrium cannot be 
stated. This equilibrium represents the greatest force or tension 
which can be applied before a plant assumes the condition of 
permanent wilting. A plant such as Aériplex will necessarily have 
an extended period when this equilibrium is maintained. The 
exact wilting will be when there is a serious rupture in the water 
columns. 
If this interpretation is correct, the 1915 and 1916 series should 
exhibit a difference in the foliar transpiring power values during 
the so-called equilibrium stage. It would be expected that the 
1915 series would have a higher minimum than the 1916 series. 
This is evident, for in 1915 the lowest point reached at any time 
is never below 0.15, while for the 1916 series it is as low as 0.09 in 
one case and 0.10 in the other. There would thus seem to be a 
direct relation between the time of the equilibrium, the lowest point 
in the index of foliar transpiring power, and the evaporating power 
of the environment. The point at which wilting occurs is defi- 
nitely marked out. This point appears graphically to better 
advantage for the plants of 1915 than for those of 1916; but the 
plants of 1915 were larger and were grown in smaller containers 
than those of the following year. For the series of 1915 the 
permanent wilting occurs on August 21, while for series la (1916) 
the wilting occurs on August 7, and for series Ib of the same year 
the wilting occurs on August 4. 
In this study the same conception of wilting is advanced as 
before. The present study is really more or less of an elaboration 
of the former. It is assumed here that Drxon’s (16, 17, 18) con- 
