We may conclude that a small dose of camphor in solution is a powerful
stimulant to Drosera. It not only soon excites the tentacles to bend,
but apparently renders the glands sensitive to a touch, which by itself
does not cause any movement. Or it may be that a slight mechanical
irritation not enough to cause any inflection yet gives some tendency
to movement, and thus reinforces the action of the camphor. This latter
view would have appeared to me the more probable one, had it not been
shown by M. Vogel that camphor is a stimulant in other ways to various
plants and seeds.
Two plants bearing four or five leaves, and with their roots in a
little cup of water, were exposed to the vapour of some bits of camphor
(about as large as a filbert-nut), under a vessel holding ten fluid oz.
After 10 hrs. no inflection ensued; but the glands appeared to be
secreting more copiously. The leaves were in a narcotised condition,
for on bits of meat being placed on two of them, there was no
inflection in 3 hrs. 15 m., and even after 13 hrs. 15 m. only a few of
the outer tentacles were slightly inflected; but this degree of
movement shows that the leaves had not been killed by an exposure
during 10 hrs. to the vapour of camphor.
Oil of Caraway. Water is said to dissolve about a thousandth part of
its weight of this oil. A drop was added to an ounce of water and the
bottle occasionally shaken during a day; but many minute globules
remained undissolved. Five leaves were immersed in this mixture; in
from 4 m. to 5 m. there was some inflection, which became moderately
pronounced in two or [page 212] three additional minutes. After 14 m.
all five leaves were well, and some of them closely, inflected. After 6
hrs. the glands were white, and much mucus had been secreted. The
leaves were now flaccid, of a peculiar dull-red colour, and evidently
dead. One of the leaves, after an immersion of 4 m., was brushed, like
the leaves in the camphor, but this produced no effect. A plant with
its roots in water was exposed under a 10-oz. vessel to the vapour of
this oil, and in 1 hr. 20 m. one leaf showed a trace of inflection.
After 5 hrs. 20 m. the cover was taken off and the leaves examined; one
had all its tentacles closely inflected, the second about half in the
same state; and the third all sub-inflected. The plant was left in the
open air for 42 hrs., but not a single tentacle expanded; all the
glands appeared dead, except here and there one, which was still
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