Ouar. X. MEANS OF MOVEMENT. 255 
its nature, as when leaves are immersed in certain 
fluids. 
The power of movement which various plants possess, 
when irritated, has been attributed by high authorities 
to the rapid passage of fluid out of certain cells, which, 
from their previous state of tension, immediately con- 
tract.* Whether or not this is the primary cause of 
such movements, fluid must pass out of closed cells 
when they contract or are 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.t In the case 
of Drosera there is certainly much movement of the 
fluid throughout the tentacles whilst they are under- 
going inflection. 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 
* Sachs, ‘Traité de Bot.’ 3rd Lamarck. 
edit. 1874, p. 1038. This view t Sachs, ibid. p. 919, 
was, I believe, first suggested by 
