STIMULATION IN THE LEAVES OF DIONAEA 87 
From a study of these tables it is seen that if two stimuU are 
appHed with an interval of 20 seconds (0.33 min.) between them, 
closure occurs immediately after the latter stimulus, taking only a 
few seconds. When the interval between the two stimuli is forty 
seconds (0.67 min.) there may be only a partial closure following the 
latter stimulus. As the interval between the stimuli becomes 
greater the number of stimuli required for closure increases, as do also 
the number of stimuli necessary before a visible effect is produced, 
and the number between the first partial closure and complete closure. 
When the intervals are very long closure is so gradual as to be quite 
imperceptible; nevertheless the lobes slowly approach each other and 
complete closure is finally attained, even with intervals of 20 minutes, 
which were the longest intervals employed. In one case 26 stimuli 
were applied, the total period of time between the occurrence of the 
first stimulus and complete closure being 8 hours and 20 minutes. 
In this experiment three hours and 40 minutes elapsed between the 
occurrence of the first visible change and the attainment of complete 
closure. Between this slow movement and the ordinary rapid closure 
there is a gradual intergradation as is shown by the data of Tables 
VII and VIII. 
Here also there is an apparent similarity between the phenomena 
of leaf closure in Dionaea and those of geo tropic curvature; in the 
latter case the reaction time may also be lengthened or shortened. 
Thus Czapek (1895) has shown that by subjecting the roots of Vicia 
faba to varying amounts of centrifugal force the reaction may take 
place in from three fourths of an hour to 8 hours. Fitting (1905) has 
investigated the summation of geotropic stimuli of short duration and 
has found that single short stimuli are not sufficient to produce curva- 
ture but that curvature takes place even though the lengths of the 
individual stimuli are greatly shortened, provided only that the 
length of time between the stimuli is not too great. Brown and Sharp 
(19 10) have shown that in the case of Dionaea there may be a summa- 
tion of individual mechanical or electrical stimuli of low intensities. 
In one case, when feeble electrical stimuli were applied at intervals of 
15 seconds, movement did not occur until after the twenty-eighth 
stimulus. 
The relation between the number of stimuli necessary for the 
closure of Dionaea leaves and the length of the time interval between 
the consecutive stimuli is shown graphically in figure i, in which the 
