Cuap. XIII] SENSITIVENESS OF FILAMENTS. 237: 
the tips of the marginal spikes crossing in 2 m. 30 8., and 
the leaf being completely 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 filaments, being 
acted on by exosmose, one leaf was first tried by pouring a 
little of the same svlution in the furrow between the lohes 
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 cell 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 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 discoloured, 
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 
injured, being touched. After a day these three leaves 
opened, and were fairly sensitive when the uninjured fila- 
ments were touched. The sudden immersion of a leaf into: 
boiling water does not cause it to close. Judging from the 
