of fully .1 of an inch (2.54 mm.), that is, across between one-third
and one-fourth of the space between the edge and midrib. Any object,
such as a moderately sized insect, would thus be brought slowly into
contact with a far larger number of glands, inducing much more
secretion and absorption, than would otherwise have been the case. That
this would be highly serviceable to the plant, we may infer from the
fact that Drosera has acquired highly developed powers of movement,
merely for the sake of bringing all its glands into contact with
captured insects. So again, after a leaf of Dionaea has caught an
insect, the slow pressing together of the two lobes serves merely to
bring the glands on both sides into contact with it, causing also the
secretion charged with animal matter to spread by capillary attraction
over the whole surface. In the case of Pinguicula, as soon as an insect
has been pushed for some little distance towards the midrib, immediate
re-expansion would be beneficial, as the margins could not capture
fresh prey until they were unfolded. The service rendered by this
pushing action, as well as that from the marginal glands being brought
into contact for a short time with the upper surfaces of minute
captured insects, may perhaps account for the peculiar movements of the
leaves; otherwise, we must look at these movements as a remnant of a
more highly developed power formerly possessed by the progenitors of
the genus.
In the four British species, and, as I hear from [page 380] Prof. Dyer,
in most or all the species of the genus, the edges of the leaves are in
some degree naturally and permanently incurved. This incurvation
serves, as already shown, to prevent insects from being washed away by
the rain; but it likewise serves for another end. When a number of
glands have been powerfully excited by bits of meat, insects, or any
other stimulus, the secretion often trickles down the leaf, and is
caught by the incurved edges, instead of rolling off and being lost. As
it runs down the channel, fresh glands are able to absorb the animal
matter held in solution. Moreover, the secretion often collects in
little pools within the channel, or in the spoon-like tips of the
leaves; and I ascertained that bits of albumen, fibrin, and gluten, are
here dissolved more quickly and completely than on the surface of the
leaf, where the secretion cannot accumulate; and so it would be with
naturally caught insects. The secretion was repeatedly seen thus to
collect on the leaves of plants protected from the rain; and with
exposed plants there would be still greater need of some provision to
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