Utricularia, more especially of Utricularia montana, although this
genus is not related to Aldrovanda.
A narrow rim of the broad flat exterior part of each lobe is turned
inwards, so that, when the lobes are closed, the exterior surfaces of
the infolded portions come into contact. The edge itself bears a row of
conical, flattened, transparent points with broad bases, like the
prickles on the stem of a bramble or Rubus. As the rim is infolded,
these points are directed towards the midrib, and they appear at first
as if they were adapted to prevent the escape of prey; but this can
hardly be their chief function, for they are composed of very delicate
and highly flexible membrane, which can be easily bent or quite doubled
back without being cracked. Nevertheless, the infolded rims, together
with the points, must somewhat interfere with the retrograde movement
of any small creature, as soon as the lobes begin to close. The
circumferential part of the leaf of Aldrovanda thus differs greatly
from that of Dionaea; nor can the points on the rim be considered as
homologous with the spikes round the leaves of Dionaea, as these latter
are prolongations of the blade, and not mere epidermic productions.
They appear also to serve for a widely different purpose. [page 325]
On the concave gland-bearing portion of the lobes, and especially on
the midrib, there are numerous, long, finely pointed hairs, which, as
Prof. Cohn remarks, there can be little doubt are sensitive to a touch,
and, when touched, cause the leaf to close. They are formed of two rows
of cells, or, according to Cohn, sometimes of four, and do not include
any vascular tissue. They differ also from the six sensitive filaments
of Dionaea in being colourless, and in having a medial as well as a
basal articulation. No doubt it is owing to these two articulations
that, notwithstanding their length, they escape being broken when the
lobes close.
The plants which I received during the early part of October from Kew
never opened their leaves, though subjected to a high temperature.
After examining the structure of some of them, I experimented on only
two, as I hoped that the plants would grow; and I now regret that I did
not sacrifice a greater number.
A leaf was cut open along the midrib, and the glands examined under a
high power. It was then placed in a few drops of an infusion of raw
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