Cuar. X.] MEANS OF MOVEMENT. 207 
pressed together in one direction, unless they, at the same 
time, expand in some other direction. For instance, fluid can 
be seen to ooze from the surface of any young and vigorous 
shoot if slowly bent into a semi-circle.* In the case of 
Drosera there is certainly much movement of the fluid 
throughout the tentacles whilst they are undergoing inflec- 
tion. Many leaves can be found in which the purple fluid 
within the cells is of an equally dark tint on the upper and 
lower sides of the tentacles, extending also downwards on 
both sides to equally near their bases. If the tentacles of 
such a leaf are excited into movement, it will generally be 
found after some hours that the cells on the concave side are 
much paler than they were before, or are quite colourless, 
those on the convex side having become much darker. In 
two instances, after particles of hair had been placed on 
glands, and when in the course of 1 hr. 10 m. the tentacles 
were incurved halfway towards the centre of the leaf, this 
change of colour in the two sides was conspicuously plain. 
In another case, after a bit of meat had been placed on a 
gland, the purple colour was observed at intervals to be 
slowly travelling from the upper to the lower part, down 
the convex side of the bending tentacle. But it does not 
follow from these observations that the cells on the convex side 
become filled with more fluid during the act of inflection than 
they contained before ; for fluid may all the time be passing 
into the disc or into the glands which then secrete freely. 
The bending of the tentacles, when leaves are immersed 
in a dense fluid, and their subsequent re-expansion in a less 
dense fluid, show that the passage of fluid from or into the 
cells can cause movements like the natural ones. But the 
inflection thus caused is often irregular; the exterior ten- 
tacles being sometimes spirally curved. Other unnatural 
movements are likewise caused by the application of dense 
fluids, as in the case of drops of syrup placed on the backs 
of leaves and tentacles. Such movements may be compared 
with the contortions which many vegetable tissues undergo 
when subjected to exosmose. It is therefore doubtful 
whether they throw any light on the natural movements. 
If we admit that the outward passage of fluid is the cause 
of the bending of the tentacles, we must suppose that the 
cells, before the act of inflection, are in a high state of 
* Sachs, ibid. p. 919, 
