298 BOTANICAL GAZETTE [APRIL 
if the hairs were thereby bent. The effect of water seems to be entirely 
due, therefore, to its mechanical action. 
It is well known that a slight shaking will cause movement in the 
leaf of Mimosa. Experiments were undertaken to determine whether 
the leaf of Dionaea would also respond to shaking. ‘These were not 
conclusive, but showed at least that the leaves can endure much shak- 
ing without showing response. In one case a long-petioled leaf was 
arranged so that it was struck near the distal end on alternate sides by 
the bar of a metronome beating 200 times per minute; and after 45 
minutes the leaf showed no change. When the leaves of Mimosa 
are shaken, the large leaflets offer a considerable resistance to the 
air, which, together with their inertia, results in the bending of them 
and of the pulvini. The only parts of a Dionaea leaf which could 
be so affected are the cells at the bases of the sensitive hairs, as all 
the rest of the leaf is comparatively rigid. ‘The hairs are so slender 
that they offer little resistance to the air, and on account of their 
small mass have a relatively slight inertia, and so when moved through 
the air can have little tendency to bend the cells at their bases. In 
experiments, however, in which the leaves were shaken under water, 
which offers a greater resistance to the passage of the hairs, the result 
was the same as in a Mimosa leaf shaken in air. It would thus seem 
that the nature of the response is the same in the two cases, the effect 
of the denser medium in the former balancing the effect of the large 
leaflets in the latter. This conclusion is further supported by the 
experiment already noted, in which the leaf closed as a result of bend- 
ing produced in a sensitive hair by jets of air directed against it. 
MACFARLANE (6) found that leaves stimulated twice mechanically 
at an interval of 0.25 second did not close on the second stimulus. 
If, however, the interval was 0.33 second or more they did close on the 
second stimulus. 
Leaves which had been kept for an hour at 15° C. were stimulated 
twice mechanically at intervals of 0.25 to 2 seconds. When the 
interval was less than 0.75 second, response never followed; when It 
was 1 second, response was frequent; while at intervals of 1-5 
seconds or more the leaves invariably closed. At temperatures of 
35° C. to 40° C. the leaves rarely failed to respond to two mechanical 
stimuli separated by an interval of 0.25 second. They always 
