1910] BROWN & SHARP—CLOSING RESPONSE IN DIONAEA 207 
the protoplasm of these cells is more sensitive than that of the other 
cells of the leaf. Inspection of table I will show that when electrical 
shock was conducted through the keel to the petiole, and therefore 
not passed through the region at the base of the hair, it was just as 
effective, or perhaps slightly more so, than when passed through the 
sensitive hair itself. 
It was found that water at room temperature when carefully 
applied to either surface of the leaf blade does not cause it to close. 
Water at 65° C., however, will cause closure without harming the leaf, 
and this response is just as marked, so far as could be determined, 
when the water is applied to the back of the leaf as when applied to 
the inner surface or to the bases of the sensitive hairs. These experi- 
ments with heat and electricity seem to indicate that the other cells 
of the blade are just as sensitive as those at the bases of the hairs. 
Contrary to Darwin’s opinion, the petiole is also sensitive, as we 
have found that passage of electrical shocks through it will cause 
closure of the valves. In this case, however, a much stronger stimu- 
lation is required to effect closure than when the shock is applied 
directly to the blade. This difference may very well be due to loss 
in conduction of the stimulus from the petiole to the region of bending. 
Stimuli of various forms 
In the experiments already recorded, it has been shown that 
closure may result from the application of mechanical, electrical, and 
thermal stimuli. Darwin (3), MACFARLANE (6), and others have 
shown that the leaf may also be closed as the result of chemical stimu- 
lation. For convenience, these various kinds of stimuli may be 
discussed separately. 
MECHANICAL STIMULI.—It has been seen that all parts of the leaf 
are sensitive to mechanical stimulation, and that this acts through 
compression of cells. DARwin (3) states that water falling on the 
Sensitive hairs does not cause closure, while MACFARLANE (6) observed 
that a steady stream directed against a hair, or the gradual immersion 
of the leaf, does cause the response. In our experiments it was found 
that the leaves could be filled carefully with water, or wholly immersed, 
without causing the response, but that the dropping of water on the 
hairs, or the movement of the leaf while immersed, caused it to close 
