differences being, firstly, the presence of minute, almost sessile,
glands, which, like those of Dionaea, do not secrete until they are
excited by the absorption of nitrogenous matter. But glands of this
kind are present on the leaves of Drosera binata, and appear to be
represented by the papillae on the leaves of Drosera rotundifolia.
Secondly, the presence of tentacles on the backs of the leaves; but we
have seen that a few tentacles, irregularly placed and tending towards
abortion, are retained on the backs of the leaves of Drosera binata.
There are greater differences in function between the two genera. The
most important one is that the tentacles of Drosophyllum have no power
of movement; this loss being partially replaced by the drops of viscid
[page 342] secretion being readily withdrawn from the glands; so that,
when an insect comes into contact with a drop, it is able to crawl
away, but soon touches other drops, and then, smothered by the
secretion, sinks down on the sessile glands and dies. Another
difference is, that the secretion from the tall glands, before they
have been in any way excited, is strongly acid, and perhaps contains a
small quantity of the proper ferment. Again, these glands do not
secrete more copiously from being excited by the absorption of
nitrogenous matter; on the contrary, they then absorb their own
secretion with extraordinary quickness. In a short time they begin to
secrete again. All these circumstances are probably connected with the
fact that insects do not commonly adhere to the glands with which they
first come into contact, though this does sometimes occur; and that it
is chiefly the secretion from the sessile glands which dissolves animal
matter out of their bodies.
RORIDULA.
Roridula dentata. This plant, a native of the western parts of the Cape
of Good Hope, was sent to me in a dried state from Kew. It has an
almost woody stem and branches, and apparently grows to a height of
some feet. The leaves are linear, with their summits much attenuated.
Their upper and lower surfaces are concave, with a ridge in the middle,
and both are covered with tentacles, which differ greatly in length;
some being very long, especially those on the tips of the leaves, and
some very short. The glands also differ much in size and are somewhat
elongated. They are supported on multicellular pedicels.
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