These results led me to inquire whether Drosera possessed the power of
dissolving solid animal matter. The experiments proving that the leaves
are capable of true digestion, and that the glands absorb the digested
matter, are given in detail in the sixth chapter. These are, perhaps,
the most interesting of all my observations on Drosera, as no such
power was before distinctly known to exist in the vegetable kingdom. It
is likewise an interesting fact that the glands of the disc, when
irritated, should transmit some influence to the glands of the exterior
tentacles, causing them to secrete more copiously and the secretion to
become acid, as if they had been directly excited by an object placed
on them. The gastric juice of animals contains, as is well known, an
acid and a ferment, both of which are indispensable for digestion, and
so it is with the secretion of Drosera. When the stomach of an animal
is mechanically irritated, it secretes an acid, and when particles of
glass or other such objects were placed on the glands of Drosera, the
secretion, and that of the surrounding and untouched glands, was
increased in quantity and became acid. But, according to Schiff, the
stomach of an animal does not secrete its proper ferment, pepsin, until
certain substances, which he calls peptogenes, are absorbed; and it
appears from my experiments that some matter must be absorbed by the
glands of Drosera before they secrete their proper ferment. That the
secretion does contain a ferment which acts only in the presence of an
acid on solid animal matter, was clearly proved by adding minute doses
of [page 269] an alkali, which entirely arrested the process of
digestion, this immediately recommencing as soon as the alkali was
neutralised by a little weak hydrochloric acid. From trials made with a
large number of substances, it was found that those which the secretion
of Drosera dissolves completely, or partially, or not at all, are acted
on in exactly the same manner by gastric juice. We may, therefore,
conclude that the ferment of Drosera is closely analogous to, or
identical with, the pepsin of animals.
The substances which are digested by Drosera act on the leaves very
differently. Some cause much more energetic and rapid inflection of the
tentacles, and keep them inflected for a much longer time, than do
others. We are thus led to believe that the former are more nutritious
than the latter, as is known to be the case with some of these same
substances when given to animals; for instance, meat in comparison with
gelatine. As cartilage is so tough a substance and is so little acted
on by water, its prompt dissolution by the secretion of Drosera, and
239