filaments were touched. Nevertheless two fresh leaves on being dipped
into water at 75 and 62 1/2 (23 .8 and 16 .9 Cent.) instantly closed.
These were then placed with their footstalks in water, and after 23
hrs. partially re-expanded; on touching their filaments one of them
closed. This latter leaf after an additional 24 hrs. again re-expanded,
and now, on the filaments of both leaves being touched, both closed. We
thus see that a short immersion in water does not at all injure the
leaves, but sometimes excites the lobes to close. The movement in the
above cases was evidently not caused by the temperature of the water.
It has been shown that long immersion causes the purple fluid within
the cells of the sensitive filaments to become aggregated; and the
tentacles of Drosera are acted on in the same manner by long immersion,
often being somewhat inflected. In both cases the result is probably
due to a slight degree of exosmose. [page 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 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 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
258