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 (*o8, pp. 10, 

 191) 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. Ill, 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 arid Third Reactions 

 A tentacle is capable of reacting several times in succession. 

 C. Darwin ('08, pp. 11, 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 



