several days over an object, begin to re-expand, their glands secrete
less freely, or cease to secrete, and are left dry. In this state they
are covered with a film of whitish, semi-fibrous matter, which was held
in solution by the secretion. The drying of the glands during the act
of re-expansion is of some little service to the plant; for I have
often observed that objects adhering to the leaves [page 16] could then
be blown away by a breath of air; the leaves being thus left
unencumbered and free for future action. Nevertheless, it often happens
that all the glands do not become completely dry; and in this case
delicate objects, such as fragile insects, are sometimes torn by the
re-expansion of the tentacles into fragments, which remain scattered
all over the leaf. After the re-expansion is complete, the glands
quickly begin to re-secrete, and as soon as full-sized drops are
formed, the tentacles are ready to clasp a new object.
When an insect alights on the central disc, it is instantly entangled
by the viscid secretion, and the surrounding tentacles after a time
begin to bend, and ultimately clasp it on all sides. Insects are
generally killed, according to Dr. Nitschke, in about a quarter of an
hour, owing to their tracheae being closed by the secretion. If an
insect adheres to only a few of the glands of the exterior tentacles,
these soon become inflected and carry their prey to the tentacles next
succeeding them inwards; these then bend inwards, and so onwards; until
the insect is ultimately carried by a curious sort of rolling movement
to the centre of the leaf. Then, after an interval, the tentacles on
all sides become inflected and bathe their prey with their secretion,
in the same manner as if the insect had first alighted on the central
disc. It is surprising how minute an insect suffices to cause this
action: for instance, I have seen one of the smallest species of gnats
(Culex), which had just settled with its excessively delicate feet on
the glands of the outermost tentacles, and these were already beginning
to curve inwards, though not a single gland had as yet touched the body
of the insect. Had I not interfered, this minute gnat would [page 17]
assuredly have been carried to the centre of the leaf and been securely
clasped on all sides. We shall hereafter see what excessively small
doses of certain organic fluids and saline solutions cause strongly
marked inflection.
Whether insects alight on the leaves by mere chance, as a resting
place, or are attracted by the odour of the secretion, I know not. I
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