ON DROSERA ROTUNDIFOLIA 23 
tion or a slower rate of growth (ibid., p. 255, fig. 12) on the concave 
side. Drosera tentacles are characterized by a contraction of the 
convex side during expansion; this occurred in one case of a leaf 
of Impatiens parviflora (ibid., p. 242, fig. 2). 
iv. Conductivity 
The reaction time represents the interval necessary for the 
latent period and the conduction of an impulse from the gland 
to the region where the reaction commences. This region has 
been shown to be a basal portion of the pedicel, so that the impulse 
is conducted the entire length of the tentacle. The reaction time 
usually varies from one to two minutes. C. Darwin (’08, pp. Io, 
I9I) saw movement ten seconds after stimulation. This shows 
that the rate of conduction can be quite high, for assuming the 
length of the tentacle (which Darwin does not give) to be 2 mm., 
the rate of conduction would be 0.2 mm. per second, which is faster 
than any instance given for the haptotropic reaction of tendrils 
(Fitting, 04, p. 424). The rate of conduction in tentacles is 
generally much less (cf. Pfeffer, ’06, Vol. III, pp. 93, 94). It 
should be emphasized that in Drosera tentacles stimuli are per- 
ceived by cells which are fully grown, and which undergo no 
further development. 
It has not been definitely settled through what tissue impulses 
are conducted in Drosera, but in any case an impulse, in being 
conducted from the gland to the base of a tentacle, must pass 
through cells which later react, without producing a response in 
them. These cells apparently respond only to a secondary im- 
pulse released in the basal cells by the impulse conducted directly 
from the gland. This secondary impulse is conducted in the 
reverse direction, from the base toward the apex. 
v. Second and Third Reactions 
A tentacle is capable of reacting several times in succession. 
C. Darwin (’08, pp. II, 19) observed a leaf inflected three times 
over insects, and suggested the possibility of more reactions. It 
is probable, however, that a leaf can clasp insects a greater number 
of times than any individual tentacle can react, because the 
capture of such prey does not always necessitate the cooperation 
