CHAP. X. CONDUCTING TISSUES. 253 



cells are shown to be still more elongated ; and these 

 would form the most direct line of communication from 

 the gland to the bending place of the tentacle. If the 

 impulse travels down the exterior cells, it would have 

 to cross from between twenty to thirty transverse par- 

 titions ; but rather fewer if down the inner parenchy- 

 matous tissue. In either case it is remarkable that 

 the impulse is able to pass through so many par- 

 titions down nearly the whole length of the pedicel, 

 and to act on the bending place, in ten seconds. Why 

 the impulse, after having passed so quickly down one 

 of the extreme marginal tentacles (about T '^ of an 

 inch in length), should never, as far as I have seen, 

 affect the adjoining tentacles, I do not understand. 

 It may be in part accounted for by much energy 

 being expended in the rapidity of the transmission. 



Most of the cells of the disc, both the superficial 

 ones and the larger cells which form the five or six 

 underlying layers, are about four times as long as 

 broad. They are arranged almost longitudinally, 

 radiating from the footstalk. The motor impulse, 

 therefore, when transmitted across the disc, has to 

 cross nearly four times as many cell-walls as when 

 transmitted in a longitudinal direction, and would 

 consequently be much delayed in the former case. 

 The cells of the disc converge towards the bases of 

 the tentacles, and are thus fitted to convey the motor 

 impulse to them from all sides. On the whole, the 

 arrangement and shape of the cells, both those of the 

 disc and tentacles, throw much light on the rate and 

 manner of diffusion of the motor impulse. But why 

 the impulse proceeding from the glands of the ex- 

 terior rows of tentacles tends to travel laterally and 

 towards the centre of the leaf, but not centrifugal! y, ia 

 by no means clear. 



