1910] BROWN & SHARP—CLOSING RESPONSE IN DIONAEA 2Q1 
leaf. If, however, a second stimulus was applied either on the same 
or another hair, after an interval of 1. 5 to 20 seconds the leaf 
responded, and in nearly every case by complete closure. The 
leaves of plants which had been kept about the same length of time 
at 35° C. frequently responded to one contact stimulus, while those 
kept at 40° C. closed with the first stimulus about as often as with 
the second. Slight individual differences were sometimes found in 
the leaves tested. These results seem to show that while under ordi- 
hary conditions two mechanical stimuli are usually necessary for 
closure, the number is not fixed, but varies with the environment 
and to some extent with different leaves. 
The question now arises as to whether a certain amount of stimu- 
lation, rather than a certain number of stimuli, is required to effect 
closure. This was first investigated by the use of electrical stimuli, 
the intensity of which could be accurately controlled. MACFARLANE 
(6) was inclined toward the belief that two electrical shocks are 
necessary to cause the closing response. 
Two series of experiments were carried out, in one of which 
the terminals of an induction coil were connected by wires with the 
petiole and keel, and in the other with the petiole and a sensitive 
air. These connections were made by one gentle touch in such a 
Manner as not to cause closure as a result of contact. The leaves 
were allowed five minutes in which to recover from any after-effect 
of the contact stimulus. They were then stimulated with opening 
shocks at intervals of 15 seconds, a single dry cell being used in the 
primary circuit. The result in both series was essentially the same, 
the number of shocks necessary to cause closure increasing as the 
intensity of the stimulus decreased. One strong shock was always 
Sufficient to cause the response, but when weaker shocks were applied 
the number increased until in one case 26 were required. As with 
mechanical stimuli, the leaves showed slight individual variations. 
These results are shown in table I, in which the numbers indicating 
the position of the sliding secondary coil indicate the intensity of the 
induced current produced, the greatest electromotive force corre- 
sponding, of course, to the position marked 0, while the lowest 
Corresponds to position 6. The effect of a stronger current, obtained 
by the use of two cells in place of one in the primary circuit, was 
