ZHAP. XIII. SENSITIVENESS OF FILAMENTS. 293 



I am confirmed in this belief by the effects of 

 immersing a leaf of Dionaea in a moderately strong 

 solution of sugar ; the leaf having been previously left 

 for 1 hr. 10 m. in water without any effect ; for now the 

 lobes closed rather quickly, the tips of the marginal 

 spikes crossing in 2 m. 30 s., and the leaf being com- 

 pletely shut in 3 m. Three leaves were then immersed 

 in a solution of half an ounce of sugar to a fluid 

 ounce of water, and all three leaves closed quickly. 

 As I was doubtful whether this was due to the cells on 

 the upper surface of the lobes, or to the sensitive fila- 

 ments, being acted on by exosmose, one leaf was first 

 tried by pouring a little of the same solution in the 

 furrow between the lobes over the midrib, which is the 

 chief seat of movement. It was left there for some time, 

 but no movement ensued. The whole upper surface of 

 leaf was then painted (except close round the bases of 

 the sensitive filaments, which I could not do without 

 risk of touching them) with the same solution, but 

 no effect was produced. So that the cells on the upper 

 surface are not thus affected. But when, after many 

 trials, I succeeded in getting a drop of the solution to 

 cling to one of the filaments, the leaf quickly closed. 

 Hence we may, I think, conclude that the solution 

 causes fluid to pass out of the delicate cells of the 

 filaments by exosmose ; and that this sets up some 

 molecular change in their contents, analogous to that 

 which must be produced by a touch. 



The immersion of leaves in a solution of sugar 

 affects them for a much longer time than does an 

 immersion in water, or a touch on the filaments ; for in 

 these latter cases the lobes begin to re-expand in less 

 than a day. On the other hand, of the three leaves 

 which were immersed for a short time in the solution, 

 and were then washed by means of a svringe inserted 



* > 



