Glands in contact with pollen, the leaves of other plants, and various kinds of seeds, pour forth much acid secretion, and afterwards absorb matter probably of an albuminous nature from them. Nor can the benefit thus derived be insignificant, for a considerable [page 390] amount of pollen must be blown from the many wind-fertilised carices, grasses, &c., growing where Pinguicula lives, on to the leaves thickly covered with viscid glands and forming large rosettes. Even a few grains of pollen on a single gland causes it to secrete copiously. We have also seen how frequently the small leaves of Erica tetralix and of other plants, as well as various kinds of seeds and fruits, especially of Carex, adhere to the leaves. One leaf of the Pinguicula had caught ten of the little leaves of the Erica; and three leaves on the same plant had each caught a seed. Seeds subjected to the action of the secretion are sometimes killed, or the seedlings injured. We may, therefore, conclude that Pinguicula vulgaris, with its small roots, is not only supported to a large extent by the extraordinary number of insects which it habitually captures, but likewise draws some nourishment from the pollen, leaves, and seeds of other plants which often adhere to its leaves. It is therefore partly a vegetable as well as an animal feeder.
PINGUICULA GRANDIFLORA.
This species is so closely allied to the last that it is ranked by Dr. Hooker as a sub-species. It differs chiefly in the larger size of its leaves, and in the glandular hairs near the basal part of the midrib being longer. But it likewise differs in constitution; I hear from Mr. Ralfs, who was so kind as to send me plants from Cornwall, that it grows in rather different sites; and Dr. Moore, of the Glasnevin Botanic Gardens, informs me that it is much more manageable under culture, growing freely and flowering annually; whilst Pinguicula vulgaris has to be renewed every year. Mr. Ralfs found numerous [page 391] insects and fragments of insects adhering to almost all the leaves. These consisted chiefly of Diptera, with some Hymenoptera, Homoptera, Coleoptera, and a moth. On one leaf there were nine dead insects, besides a few still alive. He also observed a few fruits of Carex pulicaris, as well as the seeds of this same Pinguicula, adhering to the leaves. I tried only two experiments with this species; firstly, a fly was placed near the margin of a leaf, and after 16 hrs. this was found well inflected. Secondly, several small flies were placed in a row along one margin of another leaf, and by the next morning this whole margin was curled inwards, exactly as in the case of Pinguicula vulgaris.
PINGUICULA LUSITANICA.
This species, of which living specimens were sent me by Mr. Ralfs from Cornwall, is very distinct from the two foregoing ones. The leaves are rather smaller, much more transparent, and are marked with purple branching veins. The margins of the leaves are much more involuted; those of the older ones extending over a third of the space between the midrib and the outside. As in the two other species, the glandular hairs consist of longer and shorter ones, and have the same structure; but the glands differ in being purple, and in often containing granular matter before they have been excited. In the lower part of the leaf, almost half the space on each side between the midrib and margin is destitute of glands; these being replaced by long, rather stiff, multicellular hairs, which intercross over the midrib. These hairs perhaps serve to prevent insects from settling on this part of the leaf, where there are no viscid glands by which they could be caught; but it is hardly probable that they were developed for this purpose. The spiral vessels pro- [page 392] ceeding from the midrib terminate at the extreme margin of the leaf in spiral cells; but these are not so well developed as in the two preceding species. The flower-peduncles, sepals, and petals, are studded with glandular hairs, like those on the leaves.
The leaves catch many small insects, which are found chiefly beneath the involuted margins, probably washed there by the rain. The colour of the glands on which insects have long lain is changed, being either brownish or pale purple, with their contents coarsely granular; so that they evidently absorb matter from their prey. Leaves of the Erica tetralix, flowers of a Galium, scales of grasses, &c. likewise adhered to some of the leaves. Several of the experiments which were tried on Pinguicula vulgaris were repeated on Pinguicula lusitanica, and these will now be given.
[(1) A moderately sized and angular bit of albumen was placed on one side of a leaf, halfway between the midrib and the naturally involuted margin. In 2 hrs. 15 m. the glands poured forth much secretion, and this side became more infolded than the opposite one. The inflection increased, and in 3 hrs. 30 m. extended up almost to the apex. After 24 hrs. the margin was rolled into a cylinder, the outer surface of which touched the blade of the leaf and reached to within the 1/20 of an inch of the midrib. After 48 hrs. it began to unfold, and in 72 hrs. was completely unfolded. The cube was rounded and greatly reduced in size; the remainder being in a semi-liquefied state.
(2) A moderately sized bit of albumen was placed near the apex of a leaf, under the naturally incurved margin. In 2 hrs. 30 m. much secretion was excited, and next morning the margin on this side was more incurved than the opposite one, but not to so great a degree as in the last case. The margin unfolded at the same rate as before. A large proportion of the albumen was dissolved, a remnant being still left.
(3) Large bits of albumen were laid in a row on the midribs of two leaves, but produced in the course of 24 hrs. no effect; [page 393] nor could this have been expected, for even had glands existed here, the long bristles would have prevented the albumen from coming in contact with them. On both leaves the bits were now pushed close to one margin, and in 3 hrs. 30 m. this became so greatly inflected that the outer surface touched the blade; the opposite margin not being in the least affected. After three days the margins of both leaves with the albumen were still as much inflected as ever, and the glands were still secreting copiously. With Pinguicula vulgaris I have never seen inflection lasting so long.
(4) Two cabbage seeds, after being soaked for an hour in water, were placed near the margin of a leaf, and caused in 3 hrs. 20 m. increased secretion and incurvation. After 24 hrs. the leaf was partially unfolded, but the glands were still secreting freely. These began to dry in 48 hrs., and after 72 hrs. were almost dry. The two seeds were then placed on damp sand under favourable conditions for growth; but they never germinated, and after a time were found rotten. They had no doubt been killed by the secretion.