terminate in from four to six rigid projections,* each tipped with a
stiff, short bristle. The bilobed leaf, with the midrib likewise tipped
with a bristle, stands in the midst of these projections, and is
evidently defended by them. The lobes are formed of very delicate
tissue, so as to be translucent; they open, according to Cohn, about as
much as the two valves of a living mussel-shell, therefore even less
than the lobes of Dionaea; and this must make the capture of aquatic
animals more easy. The outside of the leaves and the petioles are
covered with minute two-armed papillae, evidently answering to the
eight-rayed papillae of Dionaea.
Each lobe rather exceeds a semi-circle in convexity, and consists of
two very different concentric portions; the inner and lesser portion,
or that next to the midrib,
* There has been much discussion by botanists on the homological nature
of these projections. Dr. Nitschke ( Bot. Zeitung, 1861, p. 146)
believes that they correspond with the fimbriated scale-like bodies
found at the bases of the petioles of Drosera. [page 323]
is slightly concave, and is formed, according to Cohn, of three layers
of cells. Its upper surface is studded with colourless glands like, but
more simple than, those of Dionaea; they are supported on distinct
footstalks, consisting of two rows of cells. The outer
FIG. 13. (Aldrovanda vesiculosa.) Upper figure, whorl of leaves (from
Prof. Cohn). Lower figure, leaf pressed flat open and greatly enlarged.
and broader portion of the lobe is flat and very thin, being formed of
only two layers of cells. Its upper surface does not bear any glands,
but, in their place, small quadrifid processes, each consisting of four
tapering projections, which rise from a common [page 324] prominence.
These processes are formed of very delicate membrane lined with a layer
of protoplasm; and they sometimes contain aggregated globules of
hyaline matter. Two of the slightly diverging arms are directed towards
the circumference, and two towards the midrib, forming together a sort
of Greek cross. Occasionally two of the arms are replaced by one, and
then the projection is trifid. We shall see in a future chapter that
these projections curiously resemble those found within the bladders of
281