142 PLANTS WHICH EXHIBIT MOVEMENTS IN THE CAPTURE OF PREY. 



a more profuse elii- ination of mucilage, Tmt also to the secretion of an acid liquid, 

 which has the po\'er of dissolving all bodies of the kind, namely, such as clotted 

 };)loo(l, milk, albumen, and even cartilage. It has been experimentally established 

 (for example) that small solid bits of cartilage placed on a leaf of Pinguicula 

 vulgaris, whose mucilage shows no sign of an acid reaction, cause, after ten or 

 eleven hours, the secretion of an acid li(iuid, and after forty-eight hours are almost 

 entirely dissolved by it. At the end of eighty -two hours the bits of cartilage used 

 in the experiment were completely liquefied, the whole secretion was reabsorbed, 

 and the glands had become dry. When small insects such as midges alight from 

 flight on a leaf of Pinguicula they remain glued by the mucilage, and their 

 struggles to extricate themselves only cause them to sink deeper into it. Thus 

 they generally perish in a very short time, are digested by the acid juice poured 

 from the glands in response to the stimulus, and are absorbed with the exception 

 of the wings, claws, and other parts of the skeleton. 



The acid liquid secreted by the glands is viscous, and when a number of glands 

 are irritated it may exude so copiously as to fill the whole trough of the leaf. If 

 the margin of the leaf alone is stimulated, as when a small creeping insect, or a 

 midge alighting from above, gets upon the slightly up-curved margin of the leaf, 

 not only do the marginal glands, which are comparatively infrequent, discharge 

 their secretion, but in addition the edge curls over; the object of this movement 

 being to cover, if possible, the prey whilst it is held fast by the sticky mucilage, or 

 to push it into the middle of the flat channel, and so, in one way or the other, to 

 bring it into contact with as many glands as possible. The marginal glands alone 

 would not produce the requisite quantity of acid liquid to eflect solution, and, on 

 this account, the glands on a wider area are summoned to assist in the manner 

 described. The involution of the margin takes place very slowly; it is. usually 

 some hours before the animal sticking to the edge is enfolded, or, in the case of 

 the larger specimens, is pushed into the middle of the leaf. After solution and 

 absorption are accomplished, usually by the end of twenty-four hours, the leaf 

 expands again, and its margins assume the position which they had before their 

 involution. 



Besides small insects, pieces of plants, such as spores and pollen-grains brought 

 by the wind, not infrequently fall on the \'iscid surfaces of Pinguicula leaves. 

 These are subjected to the same fate as animal organisms; their protoplasts being 

 dissolved and absorbed like the flesh and blood of insects. 



The action of the acid juice secreted by the glands of butterwort leaves upon 

 albuminous bodies is identical with that of the gastric juice of animals. We may 

 presume therefore that there are in it, as in the gastric juice, two kinds of sub- 

 stance: firstly, a free acid, and, secondly, a ferment completely analogous to pepsin 

 in its action; for, as is well known, it is bj^ means of this combination that the 

 juice of the animal stomach effects the solution of albuminoid compounds. Inas- 

 much as the gland-cells of Pinguicula absorb all the soluble part of the pi-ey, and 

 re-absorb the solvent previously discharged by them, the action of this plant's leaves 



