CHAP. X. CONDUCTING TISSUES. 251 



rounding tentacles bend almost simultaneously with 

 great precision towards it. Now there are tentacles 

 on the disc, for instance near the extremities of the 

 sublateral bundles (fig. 11), which are supplied with 

 vessels that do not come into contact with the branches 

 that enter the surrounding tentacles, except by a very 

 long and extremely circuitous course. Nevertheless, 

 if a bit of meat is placed on the gland of a tentacle 

 of this kind, all the surrounding ones are inflected 

 towards it with great precision. It is, of course, pos- 

 sible that an impulse might be sent through a long 

 and circuitous course, but it is obviously impossible 

 that the direction of the movement could be thus 

 communicated, so that all the surrounding tentacles 

 should bend precisely to the point of excitement. The 

 impulse no doubt is transmitted in straight radiating 

 lines from the excited gland to the surrounding ten- 

 tacles ; it cannot, therefore, be sent along the fibro- 

 vascular bundles. The effect of cutting the central 

 vessels, in the above cases, in preventing the transmis- 

 sion of the motor impulse from the distal to the basal 

 end of a leaf, may be attributed to a considerable space 

 of the cellular tissue having been divided. We shall 

 hereafter see, when we treat of Dionasa, that this same 

 conclusion, namely that the motor impulse is not 

 transmitted by the fibro-vascular bundles, is plainly 

 confirmed ; and Professor Cohn has come to the same 

 conclusion with respect to Aldrovanda both members 

 of the Droseraceae. 



As the motor impulse is not transmitted along the 

 vessels, there remains for its passage only the cellular 

 tissue ; and the structure of this tissue explains to a 

 certain extent how it travels so quickly down the long 

 exterior tentacles, and much more slowly across the 

 blade of the leaf. We shall also see why it crosses 



