jmar. XIII. SENSITIVENESS OF FILAMENTS. 293 
I am confirmed in this belief by the effects of 
immersing a leaf of Dionea 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 3m. 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 syringe inserted 
