376 LECTURE XXIII. 



I will select as examples a few only of the nevertheless considerable number (fifteen 

 genera) so far proved to be insectivorous. 



The ' Venus' Fly-trap' {Dmicea ??iuscipula) is a small member of the Droseraceae, 

 inhabiting the moors of North and South Carolina. The main shoot is a creeping 

 rhizome, from which only a few long and thin roots arise, and at the anterior end of 

 which five or six leaves form a rosette, from the centre of which a vertical flowering 

 stem shoots up subsequently. The leaves may attain a length of six to eight cm. 

 and have the form represented in Fig. 246; c c is the petiole, provided with two 

 green wings, on which the lamina {a b d), consisting of two sharply segmented halves, 

 is situated. In the figure, the half on the side towards the observer has been removed. 

 In the non-irritated condition the two halves of the leaf stand so inclined to one 

 another, that they form almost a right angle at the mid-rib {d b). The lamina 

 contains chlorophyll, and its venation is visible in the figure. Three long, fine, 

 easily overlooked bristles stand on the inner face of each half of the leaf; and any 

 ungentle touch of one of these bristles effects an instantaneous closure of the 

 two halves of the leaf when the plant is sufficiently irritable, which only occurs 

 at high temperatures and during the most vigorous vegetation. The two halves then 

 lie closed like the cover of a thin book. The movement is chiefly effected by the 

 tissues of the mid-rib and neighbouring parts, and is rapid as lightning in the cases 

 mentioned : in feeble plants, however, it takes place slowly. By means of this 

 mechanism small animals in green-houses, such as wood-lice, often a centimetre 

 long, are seized as they creep over the leaf; and the closure of the two halves of 

 the lamina is so firm that even so strong an animal does not succeed in breaking out. 

 Immediately after this closure a second mechanism co-operates in addition— the very 

 stiff outgrowths {d d) at the margins of the leaf. At the instant of closure, these 

 organs interlock somewhat as when the fingers of both hands are pushed between 

 one another, and in this way form a firm closure at the upper convex border 

 of the coincident halves of the leaf. After the closure described the sensitiveness 

 slill goes on acting, and the two halves of the leaf now adapt themselves 

 pliantly around the form of the imprisoned animal, so that its outlines are seen from 

 the exterior. If the bristles have been irritated with some solid body, or if a 

 non-digestible mass has been placed between the halves of the leaf, the closure follows 

 in this case also ; but after some time the two halves of the leaves again diverge from 

 one another. If, however, a thin lamella of hard-boiled prote'id, or a small piece of 

 muscle or similar substance is inserted, or if a suitable animal has been seized by 

 the leaf, the closure becomes more and more complete and tight, and the third and most 

 remarkable mechanism now comes into activity. Hundreds of glandular hairs bearing 

 peltate capitula on very short stalks, and which in the quiescent state were quite 

 dry like the rest of the leaf-surface, now begin to excrete a fluid in relatively very 

 large quantities : I have occasionally seen it exude in dense drops at the anterior 

 fissure between the closed halves of the leaf. This vigorous secretion is evidently 

 a consequence of the stimulus which the animal substance exerts on contact with the 

 glands. The secretion contains an acid, and, in addition, a peptonising ferment. 

 The whole process thus reminds one most vividly of the processes in an animal 

 stomach after a supply of nutritive substance. The ferment, like other peptonising 

 ferments, may be dissolved out by glycerine, and then acts in a test tube in the 



