The action of camphor dissolved in water is remarkable, for it not only
soon induces inflection, but apparently renders the glands extremely
sensitive to mechanical irritation; for if they are brushed with a soft
brush, after being immersed in the solution for a short time, the
tentacles begin to bend in about 2 m. It may, however, be that the
brushing, though not a sufficient stimulus by itself, tends to excite
movement merely by reinforcing the direct action of the camphor. The
vapour of camphor, on the other hand, serves as a narcotic.
Some essential oils, both in solution and in vapour, cause rapid
inflection, others have no such power; those which I tried were all
poisonous.
Diluted alcohol (one part to seven of water) is not poisonous, does not
induce inflection, nor increase the sensitiveness of the glands to
mechanical irritation. The vapour acts as a narcotic or anaesthetic,
and long exposure to it kills the leaves.
The vapours of chloroform, sulphuric and nitric ether, act in a
singularly variable manner on different leaves, and on the several
tentacles of the same leaf. This, I suppose, is owing to differences in
the age or constitution of the leaves, and to whether certain tentacles
have lately been in action. That these vapours are absorbed by the
glands is shown by their changed colour; but as other plants not
furnished with glands are affected by these vapours, it is probable
that they are likewise absorbed by the stomata of Drosera. They
sometimes excite extraordinarily rapid inflection, but this is not an
invariable result. If allowed to act for even a moderately long time,
they kill the leaves; whilst a small dose acting for only a short time
serves as a narcotic or anaesthetic. In this case the tentacles,
whether or not they have [page 228] become inflected, are not excited
to further movement by bits of meat placed on the glands, until some
considerable time has elapsed. It is generally believed that with
animals and plants these vapours act by arresting oxidation.
Exposure to carbonic acid for 2 hrs., and in one case for only 45 m.,
likewise rendered the glands insensible for a time to the powerful
stimulus of raw meat. The leaves, however, recovered their full powers,
and did not seem in the least injured, on being left in the air for 24
or 48 hrs. We have seen in the third chapter that the process of
209