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.

The roots are short.  Three plants were dug up in North Wales on June 20, and carefully washed; each bore five or six unbranched roots, the longest of which was only 1.2 of an inch.  Two rather young plants were examined on September 28; these had a greater number of roots, namely eight and eighteen, all under 1 inch in length, and very little branched.

I was led to investigate the habits of this plant by being told by Mr. W. Marshall that on the mountains of Cumberland many insects adhere to the leaves.