backs of the leaves, and the spikes, with a few on the upper surface of
the lobes. These octofid projections are no doubt homologous with the
papillae on the leaves of Drosera rotundifolia. There are also a few
very minute, simple, pointed hairs, about 7/12000 (.0148 mm.) of an
inch in length on the backs of the leaves.
The sensitive filaments are formed of several rows of elongated cells,
filled with purplish fluid. They are a little above the 1/20 of an inch
in length; are thin and delicate, and taper to a point. I examined the
bases of several, making sections of them, but no trace of the entrance
of any vessel could be seen. The apex is sometimes bifid or even
trifid, owing to a slight separation between the terminal pointed
cells. Towards the base there is constriction, formed of broader cells,
beneath which there is an articulation, supported on an enlarged base,
consisting of differently shaped polygonal cells. As the filaments
project at right angles to the surface of the leaf, they would have
been liable to be broken whenever the lobes closed together, had it not
been for the articulation which allows them to bend flat down.
These filaments, from their tips to their bases, are exquisitely
sensitive to a momentary touch. It is scarcely [page 289] possible to
touch them ever so lightly or quickly with any hard object without
causing the lobes to close. A piece of very delicate human hair, 2 1/2
inches in length, held dangling over a filament, and swayed to and fro
so as to touch it, did not excite any movement. But when a rather thick
cotton thread of the same length was similarly swayed, the lobes
closed. Pinches of fine wheaten flour, dropped from a height, produced
no effect. The above-mentioned hair was then fixed into a handle, and
cut off so that 1 inch projected; this length being sufficiently rigid
to support itself in a nearly horizontal line. The extremity was then
brought by a slow movement laterally into contact with the tip of a
filament, and the leaf instantly closed. On another occasion two or
three touches of the same kind were necessary before any movement
ensued. When we consider how flexible a fine hair is, we may form some
idea how slight must be the touch given by the extremity of a piece, 1
inch in length, moved slowly.
Although these filaments are so sensitive to a momentary and delicate
touch, they are far less sensitive than the glands of Drosera to
prolonged pressure. Several times I succeeded in placing on the tip of
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