756 Hiley .- — On the Value of Different Degrees of 
bend. Those, however, which were further out in the box would bend 
outwards, and those further in would bend inwards. Thus a point of 
equilibrium could be determined with very fair accuracy, and the centrifugal 
force at this point of equilibrium could be deduced from the number of 
rotations made by the wheel in a known time and the radius of rotation of 
the point of equilibrium. 
3. It was found that if a centrifugal force C, working for a time T , be 
regularly alternated with gravity (mg) working for a time t, then equilibrium 
CT CT 
is only established when = 1. (The actual value of .as deduced 
mg.t v mg.t 
from the average of eighteen successful experiments with radicles of 
Helianthus animus was 0*99.) 
This equation may be expressed thus: CT — mg.t., i. e. the product 
of the force into the time in each direction is the same. The average 
CT 
experimental value of for six experiments with radicles of Cucurbita 
Pepo was 0-97. 
CT 
4. The equation — ■ — = 1 does not hold good if the individual periods 
of exposure to gravity and centrifugal force are long. When (T + 1 ) was 
as much as 20 min. it was found that for the point of equilibrium 
CT 
wgi > 1 * ** e * centrifugal force had to be allowed to act for a longer 
time than would have been expected from previous experiments. This is 
probably connected with the fact, discovered by Jost and Stoppel, that 
radicles may respond negatively to prolonged exposure to centrifugal forces. 
Though, in the case of the present experiments, the period of exposure was 
not sufficiently long to cause a negative response, it may nevertheless have 
been sufficient to allow of a falling-off in the activity of the positive 
response. 
5. The presentation time for Helianthus radicles was determined in the 
usual way, and was found to lie between 3 and 4 \ min., at a temperature of 
i8°-20° C. 
On the intermittent centrifuge, single exposures to gravity might be 
CT 
much longer than this without any failure of the equation = 1. 
6. From theoretical considerations it is clear that, at any rate in many 
of the experiments, actual movement must have taken place in response 
both to gravity and to the centrifugal force ; but as the movement was of 
equal extent in each direction, there was no resultant bending. From this 
fact it is deduced that a given small amount of stimulation, reckoned in 
mg. sec. units, produces the same amount of response in a given radicle, 
however the amount of stimulation may be made up. For instance, 
