200 DROSERA ROTUNDIFOLIA. [Cuar. X. 
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 ; 
nevertheless, 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 describe briefly 
the course of the main fibro-vascular bundles. These are 
shown in the accompanying sketch (fig. 11) of a small leaf. 
Little vessels from the neighbouring bundles enter all the 
many tentacles with which the surface is studded ; but these 
are not here represented. The central trunk, which runs up 
the footstalk, bifurcates near the centre of the leaf, each 
branch bifurecating again and again according to the size of 
the leaf. This central trunk sends off, low down on each 
side, a delicate branch, which may be called the sublateral 
branch. There is also, on each side, a main lateral branch or 
bundle, which bifurcates in the same manner as the others. 
Bifurcation does not imply that any single vessel divides, 
but that a bundle divides into two. By looking to either 
side of the leaf, it will be seen that a branch from the great 
central bifurcation inosculates with a branch from the lateral 
bundle, and that there is a smaller inosculation between the 
* [In a letter (1862) to Sir Joseph 
Hooker, in the ‘Life and Letters of 
Charles Darwin,’ vol. iii. p. 321, the 
writer speaks of the existence in 
Drosera of “ diffused nervous matter,” 
in some degree analogous in constitu- 
tion and function to the nervous 
matter of animals. Now, that 
through the researches of Gardiner 
(Phil. Trans.’ 1883) and others 
the connection between plant-cells by 
inter-cellular protoplasm has been 
established, we can understand the 
transmission of the motor impulse as 
a molecular change in the protoplasm 
from cell to cell.—F. D.] 
