200 DROSERA ROTUNDIFOLIA. [Chap. X. 



have already seen of the impulse travelling less readily in 

 a transverse than in a longitudinal direction. In some 

 other cases, the exterior tentacles did not seem capable 

 of such accurate movement as the shorter and more cen- 

 tral ones. 



Nothing could be more striking than the appearance 

 of the above four leaves, each with their tentacles pointing 

 truly to the two little masses of the phosphate on their discs. 

 We might imagine that we were looking at a lowly organised 

 animal seizing prey with its arms. In the case of Drosera 

 the explanation of this accurate power of movement, no 

 doubt, lies in the motor impulse radiating in all directions, 

 and whichever side of a tentacle it first strikes, that side 

 contracts, and the tentacle consequently bends towards the 

 point of excitement. The pedicels of the tentacles are flat- 

 tened, or elliptic in section. Near the bases of the short 

 central tentacles, the flattened or broad face is formed of 

 about five longitudinal rows of cells; in the outer tentacles 

 of the disc, it consists of about six or seven rows; and in 

 the extreme marginal tentacles of above a dozen rows. As 

 the flattened bases are thus formed of only a few rows of 

 cells, the precision of the movements of the tentacles is the 

 more remarkable; for when the motor impulse strikes the 

 base of a tentacle in a very oblique direction relatively to 

 its broad face, scarcely more than one or two cells towards 

 one end can be affected at first, and the contraction of these 

 cells must draw the whole tentacle into the proper direction. 

 It is, perhaps, owing to the exterior pedicels being much 

 flattened that they do not bend quite so accurately to the 

 point of excitement as the more central ones. The properly 

 directed movement of the tentacles is not an unique case in 

 the vegetable kingdom, for the tendrils of many plants curve 

 towards the side which is touched ; but the case of Drosera is 

 far more interesting, as here the tentacles are not directly 

 excited, but receive an impulse from a distant point; never- 

 theless, they bend accurately towards this point. 



On the Nature of the Tissues through which the Motor 

 Impulse * is Transmitted. It will be necessary first to de- 

 scribe briefly the course of the main fibro-vascular bundles. 



[In n letter (IWS) to Sir III. p. .121. the writer Bpenks of 

 Joneph Hooker. In the ' Life nnd the exUtence In DroHem of " dlf- 

 LetterH of Charles Darwin,' vol. fused nervous mutter," In some 



