The glands, with the exception of those borne by the extreme
FIG. 3. (Drosera rotundifolia.) Longitudinal section of a gland;
greatly magnified. From Dr. Warming.
marginal tentacles, are oval, and of nearly uniform size, viz. about
4/500 of an inch in length. Their structure is remarkable, and their
functions complex, for they secrete, absorb, and are acted on by
various stimulants. They consist of an outer layer of small polygonal
cells, containing purple granular matter or fluid, and with the walls
thicker than those of the pedicels. [page 7] Within this layer of cells
there is an inner one of differently shaped ones, likewise filled with
purple fluid, but of a slightly different tint, and differently
affected by chloride of gold. These two layers are sometimes well seen
when a gland has been crushed or boiled in caustic potash. According to
Dr. Warming, there is still another layer of much more elongated cells,
as shown in the accompanying section (fig. 3) copied from his work; but
these cells were not seen by Nitschke, nor by me. In the centre there
is a group of elongated, cylindrical cells of unequal lengths, bluntly
pointed at their upper ends, truncated or rounded at their lower ends,
closely pressed together, and remarkable from being surrounded by a
spiral line, which can be separated as a distinct fibre.
These latter cells are filled with limpid fluid, which after long
immersion in alcohol deposits much brown matter. I presume that they
are actually connected with the spiral vessels which run up the
tentacles, for on several occasions the latter were seen to divide into
two or three excessively thin branches, which could be traced close up
to the spiriferous cells. Their development has been described by Dr.
Warming. Cells of the same kind have been observed in other plants, as
I hear from Dr. Hooker, and were seen by me in the margins of the
leaves of Pinguicula. Whatever their function may be, they are not
necessary for the secretion of a digestive fluid, or for absorption, or
for the communication of a motor impulse to other parts of the leaf, as
we may infer from the structure of the glands in some other genera of
the Droseraceae.
The extreme marginal tentacles differ slightly from the others. Their
bases are broader, and besides their own vessels, they receive a fine
11