424 BOTANICAL GAZETTE [DECEMBER 
In about two-thirds of all the plants placed in a horizontal posi- 
tion in these experiments, there was a bending downward of 1° to 6° 
during the first hour, before there was any observable upward curva- 
ture. This may be partly due to wilting caused by transplanting. 
In general this downward tendency was less in the younger specimens 
where the stipe is shorter, and it was less where the pileus had been 
removed. ‘These facts seem to indicate that it might be the physical 
effect of a new lateral strain rather than a response to a new stimulus. 
For this reason in many cases the pileus was removed, as is shown in 
jig. 4. No. 51 shows this bend downward in the first hour, followed 
by 1° more than complete recovery in the second hour. For the next 
six hours the rate of curvature fluctuated from 3° to 4° per hour; 
this was followed by a steady rate of 2° per hour for five hours; then 
the pileus came to rest at an angle of 32° from horizontal. In No. 56 
the response during the first hour was slight; during the second it 
was greatly accelerated; this was followed by a period of depression 
which lasted for one or two hours; from this time on for the next five 
or six hours the reaction was constant and rapid, then more slow. 
After the vertical line was passed, the curvature took place more 
-and more slowly until, in the case cited here, it came to rest at an 
angle of 98° from its original position. Nine hours later, or 24 hours 
from the start, it remained in the same position and there had been 
no increase in length. There was no neutralization of the 8° of supra- 
curvature. 
In order to determine the exposure period, that is, the length of 
time which the plant must be stimulated in order that reaction may 
follow, several plants were kept in a fixed horizontal position for 15 
minutes and were then rotated on a clinostat about the horizontal 
axis for 24 hours. The plants gave a decided reaction to geotropic 
stimulation for this length of time. There was an upward curvature 
of the stipe varying from 1 5° to 30° from its position during exposure 
to the stimulus. Four records of plants of A. phalloides, stimulated 
by being in a horizontal position for 5 minutes and rotated on Md 
clinostat for 24 hours, showed an upward curvature of 7°, 10°, et 
and 15°, respectively. Eight records of plants of both A. phalloides 
and A. crenulata stimulated for one minute all show an upward 
curvature of either 6° or 7°. In one case of stimulation for 5 minutes, 
