754 Hiley. — On the Value of Different Degrees of 
not even know whether presentation time and reaction time have any 
objective meaning, it came as rather a relief to find that in the experiments 
recorded in this paper, we have to deal with periods which far exceed the 
presentation time, as determined in the usual way, for Helianthus radicles. 
Thus in most of the experiments recorded in Table I there can be no doubt 
that each interval of exposure to gravity or centrifugal force had been fully 
perceived by the radicles, and the machinery had been set going which 
would normally result in response alternately in the two directions. In 
this case one of two things must have happened ; either neutralization took 
place in the motor mechanism so that no movement actually became 
expressed, or movement may actually have occurred first in one direction 
and then in the other, and so on in alternation. It is the second of these 
alternatives, as will be seen below, which most satisfactorily corresponds to 
the facts. 
Zielinski ( 11 ) introduced the term ‘kritische Zeit’ to stand for the 
shortest period of stimulation, the response to which is not inhibited by an 
exactly similar equal-timed stimulation in the opposite direction following 
immediately after. To quote Zielinski’s tables for the radicles of two plants : 
Lepidium sativum 
99 9 9 
Lupinus albus 
99 99 
Temp . Pres. Time. 
i7°-i 8° C. 5.5 min. 
25°-27°C. 1.5 „ 
i7°-i8°C. 8.5 „ 
2 5 °-2 7° C. 2 „ 
Critical Time. Reaction Time . 
6 min. 25.5 min. 
2 „ 12-5 „ 
11 „ 4 6 *5 » 
7 3*3 >» 
This means that if a radicle of Lepidium sativum be kept at a temperature 
of i7°-i8° C. and be placed horizontally for 5-6 min. and then be turned 
through 180 0 and be kept horizontal again for 5-6 min. no movement is 
noticeable. Whereas, if it be kept for 7 min. in each position, a movement 
is noticeable first in one direction and then in the other. 
The critical time for Helianthus has not been determined ; but since 
the presentation time for the temperature at which my experiments were 
carried[out is less than 5 min., the critical time is almost certainly less than 
10 min. Thus in cases such as Experiment 14, there can be no reasonable 
doubt that the radicles actually moved during the course of the experiment 
first in one direction and then in the other, and so on in alternation, and 
that the idtimate equilibrium was due to the neutralization of actual 
movements. 
Now suppose for any such experiment the centrifugal force working for 
time T and gravity working for time t neutralize each other when altei- 
nated, then since movement has actually taken place in response to each 
single stimulus the amount of response that took place to C acting for time 
T must have been equal to the amount of response that took place to mg. 
acting for time t . 
But the experiments described above have shown that under these 
circumstances CT = mg.t , and each of these quantities is of the foim S.t 
