OCR Text |
Show 368 PINGUICULA YGLGARIS. CHAP. XVI. CHAPTER XVI. PINGUICCLA. Pinguicula vulgctris- Structure of leaves- Nu~bcr ~f insects and other objects caught- Movement. of th.e m~rgms of the loa:'es _ uses of this movement- Secretion, d1gestlon, and absorptiOnAction of the secretion on various animal and veg table substances _The effects of substances not containing soluble nitrogenous matter on the glands- Pinguicula g'randiflora - Pingu'icula lusitanica; catches insects-Movement of the leaves, secretion and digestion. PINGUICULA VULGARIS.-This plant grows in moist places, generally on mountain~. It bears on an aver~ge eight, rather thick, oblong, hght green leaves, having scarcely any footstalk .. A fu.ll-sized leaf is about lt inch in lenath and ! Inch In breadth. The young 0 d . central leaves are deeply concave, an 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 circ~lar 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 ~re supported on elongated, unicellular pedicels ( con~aming a nucleus with a nucleolus) w~Ich rest ~n sh?ht prominences. The small glands differ only In ?e~ng formed of about half the number of cells, containm? much paler fluid, and supported on much shorter pedicels. Near the midrib, towards the base of the leaf, the CHAP. XVI. CAPTURED INSECTS. 369 pedicels are multicellular, are longer than elsewh re, 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 f 18 inches; but the fluid in this case was secreted by a gland which had been excited. The edge of the leaf is transluc nt, and does not bear any glands ; ancl her the spiral vessels, proceeding from the midrib, terminate in c lls marked by a spiral line, somewhat like those within the glands of Drosera. The roots are short. Three plants w r dug up in North Wales on June 20, ancl carefully washed; each bore five or six unbranched roots, the longest of which was only 1·2 of an inch. Two rath r young plants were examined on Sept mber 28; these had a greater number of roots, namely eight and ighteen, all under 1 inch in length, and very littl branch d. I was led to investigate the habits of this plant by being told by Mr. W. Marshall that on the mountain · of Cumberland many insects adher to th leaves. A friend sent me on June 23 thirty-nine leaves from North Wales, which were selected owing to objects of some kind adhering to them. Of these leaves, thirty-two had caught 142 insects, or on an average 4·4 per leaf, minute fragments of insects not being included. Besides the insects, small leaves belonging to four different kinds of plants, those of Erica tetrah·x being much the commonest, and three minute seedling plant , blown by the wind, adhered to nineteen of the leaves. One had caught as many as ten leaves of the Erica. Seeds or fruit , commonly of Carex and one of Juncus, be ides bits of mos and other rubbish, likewise adhered to six of the thirty-nine leav~s. The same friend, on June 27, collected nine plant.· bearmg seventy-four leaves, and all of these, with the exception · of three young leaves, had caught insects; thirty insects were counted on one leaf, eighteen on a second, and sixteen on a third. Another friend examined on August 22 some plants in Donegal, Ireland, and found insects on 70 out of 157 leaves· :fifteen of 2 B' |