STIMULATION IN THE LEAVES OF DIONAEA 
83 
curvatures, and that there is as great a similarity between these two 
types of movement as there is between those shown by Dionaea and 
by Mimosa. The movement in Dionaea may perhaps be considered 
as intermediate in character between such movements as are exhibited 
in geotropic and hehotropic curvatures, on the one hand, and the 
rapid movement resulting from mechanical stimulation in Mimosa 
on the other. 
Duration of the Effect of Stimulation 
Macfarlane (1902) states that at least two mechanical stimuli are 
necessary to produce closure of Dionaea leaves and that the number 
of stimuli required increases as the time period between successive 
stimuli is lengthened. Brown and Sharp (1910) found that at tem- 
peratures around 2° C. two stimuli are usually necessary for closure, 
but that at 35° C. a single stimulus is frequently sufficient. These 
writers state that if stimuli are applied at intervals of from 20 seconds 
to 3 minutes the number of these necessary to produce closure increases 
with the time elapsing between the application of the stimuli. They 
also showed that if one of the sensitive bristles on the inner surface 
of the leaf of Dionaea is stimulated by more than a very slight touch, 
the effect is independent of the amount of bending of the bristle, each 
such stimulus, regardless of its intensity, producing the maximum 
effect for a stimulus of that kind. It is therefore easy to apply several 
successive stimuli at equal time intervals, and to repeat such a series 
with different time intervals, the intensity of the force applied to the 
sensitive bristle requiring no serious attention in this case. The 
present section deals with the results of a study carried out in the way 
just suggested. 
In each experiment a series of mechanical stimuli were applied 
to a single sensitive bristle, at equal intervals of time, and record 
was made of the number of stimuli required to produce the first 
visible response, and of the number required to produce complete 
closure of the leaf. In different experiments the length of the equal 
time intervals ranged from 20 seconds to 20 minutes. All these experi- 
ments were carried out with a temperature of about 21° C. On 
account of the general importance of this sort of data in the physiology 
of response, and because of the tediousness of such experiments, the 
results of these series are presented in full in Table VII. They are 
summarized by averages in Table VIII. 
