250 DION-fiA MUSCIPULA. [Chap. XIIL 



of the secretion. So firmly do they become pressed together 

 that, if any large insect or other object has been caught, a 

 corresponding projection on the outside of the leaf is dis- 

 tinctly visible. When the two lobes are thus completely 

 shut, they resist being opened, as by a thin wedge being 

 driven between them, with astonishing force, and are gen- 

 erally 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 irritated, the normal electric current is disturbed. 

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

 dead insect, or 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 slowly 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, sufiices for its final purpose, whilst 

 the movement excited by one of the sensitive filaments being 

 touched is rapid, and this is indispensable for the capturing 

 of insects. These two movements, excited by two such wide- 

 ly diflFerent means, are thus both well adapted, like all the 

 other functions of the plant, for the purposes which they 

 subserve. 



There is another wide difference in the action of leaves 



