CHAPTER XVI.
PINGUICULA.
Pinguicula vulgaris Structure of leaves Number of insects and other
objects caught Movement of the margins of the leaves Uses of this
movement Secretion, digestion, and absorption Action of the secretion
on various animal and vegetable substances The effects of substances
not containing soluble nitrogenous matter on the glands Pinguicula
grandiflora Pinguicula lusitanica, catches insects Movement of the
leaves, secretion and digestion.
Pinguicula vulgaris. This plant grows in moist places, generally on
mountains. It bears on an average eight, rather thick, oblong, light
green leaves, having scarcely any footstalk. A full-sized leaf is about
1 1/2 inch in length and 3/4 inch in breadth. The young central leaves
are deeply concave, and project upwards; the older ones towards the
outside are flat or convex, and lie close to the ground, forming a
rosette from 3 to 4 inches in diameter. The margins of the leaves are
incurved. Their upper surfaces are thickly covered with two sets of
glandular hairs, differing in the size of the glands and in the length
of their pedicels. The larger glands have a circular outline as seen
from above, and are of moderate thickness; they are divided by
radiating partitions into sixteen cells, containing light-green,
homogeneous fluid. They are supported on elongated, unicellular
pedicels (containing a nucleus with a nucleolus) which rest on slight
prominences. The small glands differ only in being formed of about half
the number of cells, containing much paler fluid, and supported on much
shorter pedicels. Near the midrib, towards the base of the leaf, the
[page 369] pedicels are multicellular, are longer than elsewhere, and
bear smaller glands. All the glands secrete a colourless fluid, which
is so viscid that I have seen a fine thread drawn out to a length of 18
inches; but the fluid in this case was secreted by a gland which had
been excited. The edge of the leaf is translucent, and does not bear
any glands; and here the spiral vessels, proceeding from the midrib,
terminate in cells marked by a spiral line, somewhat like those within
the glands of Drosera.
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