CHAP. X. MEANS OF MOVEMENT. 255 



its nature, as when leaves are immersed in certain 

 Quids. 



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 arc 

 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 oi 



* Sachs, 'Traite de Bot.' 3rd Lamarck, 

 edit. 1874, p. 1038. This view f Sachs, ibid. p. 919. 



was, I believe, first suggested by 



