238 DION^A MUSCIPULA. [Chap. XIII. 



the leaf having been previously left for 1 hr. 10 m. in water 

 without any eflfect; for now the lobes closed rather quickly, 

 the tips of the marginal spikes crossing in 2 m. 30 s., and 

 the leaf being completely 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 filaments 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 eflfect was produced. So that the cells on 

 the upper sui^uce are not thus aflFected. But when, after 

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

 c''Ag 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 cell of the filaments by exosmose; 

 and that this sets up some molecular change in their con- 

 tents, analogous to that which must be produced by a touch. 



The immersion of leaves in a solution of sugar aflfects 

 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 

 syringe inserted between the lobes, one re-expanded after two 

 days; a second after seven days; and the third after nine days. 

 The leaf which closed, owing to a drop of the solution having 

 adhered to one of the filaments, opened after two days. 



I was surprised to find on two occasions that the heat 

 from the rays of the sun, concentrated by a lens on the bases 

 of several filaments, so that they were scorched and discol- 

 oured, did not cause any movement; though the leaves were 

 active, as they closed, though rather slowly, when a filament 

 on the opposite side was touched. On a third trial, a fresh 

 leaf closed after a time, though very slowly; the rate not 

 being increased by one of the filaments, which had not been 



