1910] BROWN & SHARP—CLOSING RESPONSE IN DIONAEA 299 
responded when the interval was longer than this and failed to respond 
with shorter intervals. This is added evidence that the leaves 
Tespond more readily at higher temperatures than at lower. As in 
the case of animal muscle, there seems to be in Dionaea a short 
interval after one stimulus during which another has no effect. 
THERMAL STIMULI.—MAcFARLANE (6) allowed drops of water at 
temperatures varying from 50° C. to 75° C. to fall upon open leaves. 
At the higher temperature one drop caused closure, while at the lower 
several applications were necessary. Only four of the leaves so 
treated reopened, and he says, “the subsequent fate of most of the 
leaves points to a permanent injury.” It is not stated whether or not 
the water was dropped on the sensitive hairs. The present writers 
found that water at room temperature, dropped directly upon the 
hairs, causes closure, while the gentle application of water at 50° C. 
does not cause the response. When warm water is dropped in this 
manner, it is of course cooled somewhat before it reaches the leaf. 
Since it is possible to interpret the cases reported by MACFARLANE 
as being due either to a heat stimulus, to a mechanical stimulation 
of the sensitive hairs, or to injury, it was thought advisable to 
Teinvestigate the effects of heat. Water at 65° C. was applied in 
some cases to the inner, and in other cases to the outer surface of the 
leaves. In all cases closure resulted. These leaves exhibited no 
appearance of injury, and after reopening responded again quite 
normally. Asa control for these experiments, water at room tempera- 
ture was applied for several minutes to both inner and outer surfaces 
of the leaves without effect. This seems to indicate that heat causes 
the closing response. Water at 75° C. was then applied as above. 
Closure resulted in all cases, but two days later the parts of the 
leaves touched by the water were dead and black. Only small areas 
on some of them had been injured, and in several such cases the rest 
of the leaf responded normally. We can also confirm MACFARLANE’S 
statement that cold water will cause closure. This is true whether it 
be applied to the inner or to the outer surface. 
ELECTRICAL STIMULI.—Experiments already described show that 
electrical stimuli, when applied to various parts of the leaf and petiole, 
cause closure, and that the effect depends upon the intensity of the 
Stimulation rather than upon the number of stimuli. The response 
