308 DION.T:A MUSCIPDLA. CHAP. XIIL 



resist being opened, as by a thin wedge driven 

 between them, with astonishing force, and are gene- 

 rally ruptured rather than yield. If not ruptured, 

 they close again, as Dr. Canby informs me in a letter, 

 " with quite a loud flap." But if the end of a leaf 

 is held firmly between the thumb and finger, or by a 

 clip, so that the lobes cannot begin to close, they 

 exert, whilst in this position, very little force. 



I thought at first that the gradual pressing together 

 of the lobes was caused exclusively by captured 

 insects crawling over and repeatedly irritating the 

 sensitive filaments ; and this view seemed the more 

 probable when I learnt from Dr. Burdon Sanderson 

 that whenever the filaments of a closed leaf are irri- 

 tated, the normal electric current is disturbed. Never- 

 theless, such irritation is by no means necessary, for a 

 dead insect, or a bit of meat, or of albumen, all act 

 equally well ; proving that in these cases it is the 

 absorption of animal matter which excites the lobes 

 Blowly to press close together. We have seen that the 

 absorption of an extremely small quantity of such 

 matter also causes a fully expanded leaf to close 

 slowly ; and this movement is clearly analogous to 

 the slow pressing together of the concave lobes. This 

 latter action is of high functional importance to the 

 plant, for the glands on both sides are thus brought 

 into contact with a captured insect, and consequently 

 secrete. The secretion with animal matter in solution 

 is then drawn by capillary attraction over the whole 

 surface of the leaf, causing all the glands to secrete 

 and allowing them to absorb the diffused animal matter. 

 The movement, excited by the absorption of such 

 matter, though slow, suffices for its final purpose, 

 whilst the movement excited by one of the sensitive 

 filaments being touched is rapid, and this is indis- 



