Chap. XL GENERAL SUMMARY. 277 



be called a reflex action, though probably very dif- 

 ferent from that proceeding from the nerve-ganglion 

 of an animal ; and it is the only known case of reflex 

 action in the vegetable kingdom. 



About the mechanism of the movements and the 

 nature of the motor impulse we know very little. 

 During the act of inflection fluid certainly travels from 

 one part to another of the tentacles. But the hypo- 

 thesis which agrees best with the observed facts is 

 that the motor impulse is allied in nature to the 

 aggregating process ; and that this causes the mole- 

 cules of the cell-walls to approach each other, in the 

 same manner as do the molecules of the protoplasm 

 within the cells ;* so that the cell-walls contract. But 

 some strong objections may be urged against this view. 

 The re-expansion of the tentacles is largely due to 

 the elasticity of their outer cells, which comes into 

 play as soon as those on the inner side cease con- 

 tracting with prepotent force ; but we have reason to 

 suspect that fluid is continually and slowly attracted 

 into the outer cells during the act of re-expansion, 

 thus increasing their tension. 



I have now given a brief recapitulation of the chief 

 points observed by me, with respect to the struc- 

 ture, movements, constitution, and habits of Drosera 

 rotuiidifolia ; and we see how little has been made out 

 in comparison with what" remains unexplained and 

 unknown. 



