378 LECTURE XXIII. 



they all become applied to the prey with their heads, and completely envelope it in the 

 fluid secretion. After some time (10-20 hours) the lamina itself also becomes curved, 

 and all the movements of the leaf called forth by the stimulus may be approxi- 

 mately imitated by laying a small body on the palm of the hand while the five fingers 

 are outspread, and then curving the fingers in such a way that they all touch the 

 body with their tips, while the palm itself becomes at the same time curved round 

 the body. The chemical action in the case of Drosera consists in that the secretion 

 of the glands (which is already present and contains a peptonising ferment, but 

 was hitherto neutral in reaction) now becomes acid in consequence of the stimulus. 

 The digestive fluid is thus rendered complete, since it, like pepsin, only acts as 

 a peptonising agent in an acid liquid. Rees and Will ' were the first to extract the 

 peptonising ferment out of the leaves o^ Drosera by means of glycerine, and to establish 

 its digestive action on blood-fibrin — a fact which is the more deserving of mention, 

 since this was the first demonstration of the existence of a peptonising ferment in 

 plants. After complete digestion and absorption of the products of solution, the 

 tentacles of ihQ, Drosera leaf again return to their original position, and the lamina 

 becomes extended and flat. On the leaves of Drosera in the open the empty remains 

 of numerous small insects are to be found at any time. Nevertheless the plants 

 may easily be cultivated in a room under a bell-glass until the ripening of the 

 seeds, without their catching insects : this, however, does not prove that the latter does 

 not act favourably for nutrition, and the researches of Francis Darwin and Rees 

 make it at least very probable that Drosera plants fed artificially flourish more 

 vigorously than those not so fed. 



The course of affairs in our native species of Pinguicula (Utriculariae), which 

 inhabit moist shady spots, is unusually simple. Here also there is a rosette formed 

 of a few tongue-shaped leaves, from the midst of which the flowering stalk subse- 

 quently arises. These plants also may be easily cultivated and observed in pots. The 

 surface of the leaves, which contain abundance of chlorophj'll, presents a velvety 

 appearance, owing to very numerous epidermal glands, which possess approximately 

 the form of a mushroom, some with long and others with short stalks. The capitula of 

 the glands are moistened by the secretion which they exude, and hold fast any very 

 small insect, or bread-crumb, or piece of proteid laid on. After one or a few hours 

 the small body is noticed to be enveloped in a drop of fluid of considerable size, and 

 with an acid reaction; at the same time the margin of the leaf begins to curve 

 upwards, and in the course of several hours the digestible body is completely covered 

 by the leaf margin arched in over it. After a few days, when the products of diges- 

 tion have been completely absorbed, the leaf again opens out flat. 



Finally, we may shortly describe another of the most complex and remarkable 

 mechanisms for the purpose of digesting insects. The so-called ' Pitcher-plants ' of 

 the genus Nepenthes, which are extended over Madagascar, Ceylon, and elsewhere in 

 South-Eastern Asia, are thin-stemmed climbing plants, provided with large simple 

 leaves abounding in chlorophyll. From the apex of a leaf, a filiform tendril slowly 

 developes, which, like other tendrils, is able to wind round the branches of neighbouring 



1 Rees and Will, 'Einige Bemerkungen über fleischfressende Pflanzen' (Bot. Zeitg. 1S75, 

 p. 713)- 



