CniP. X.] MEANS OP MOVEMENT. 207 



passes through them. When the gland of one of the long 

 exterior tentacles is excited, the upper cells are not in the 

 least affected; about half-way down there is a slight bend- 

 ing, but the chief movement is confined to a short space near 

 the base; and no part of the inner tentacle bends except the 

 basal portion. With respect to the blade of the leaf, the 

 motor impulse may be transmitted through many cells, from 

 the centre to the circumference, without their being in the 

 least affected, or they may be strongly acted on and the blade 

 greatly inflected. In the latter case the movement seems to 

 depend partly on the strength of the stimulus, and partly 

 on 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 contract.' 

 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 vigor- 

 ous 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 in- 

 stances, after particles of hair had been placed on glands, 

 and when in the course of 1 hr. 10 m. the tentacles were in- 

 curved half-way towards the centre of the leaf, this change 

 of colour in the two sides was conspicuously plain. In an- 

 other 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 



"SachB. 'Trnlt<' dp Bot.* .'Idortlt. Sachs, Traits de Dot.' 3d 



1874. p. 1038. This vlow was. I he- edit. 1874, p. Oia. 

 lieve, first suggested by Lamarck. 



