INSECTIVOROUS PLANTS. 55 



figurement of a brain, and we can almost fancy that we detect a trace 

 of disappointment or regret in this admission. 



A wide range of experiment shows that probably all the species 

 of Drosera are adapted for catching and digesting insects by nearly 

 the same means, though not with equal development or completeness. 



Dionma micsoijmla. The form of the bilobed leaf which is the 

 most wonderful feature of this wonderful plant, already described, 

 may be seen from the accompanying sketch. 



Fig. 6. Dionma muscipula. Leaf viewed laterally in its expanded state. 



In the Dionma the locality of sensitiveness is the three filaments 

 which appear on each half of the upper surface of the leaf. It is un- 

 like Drosera in that the filaments are sensitive to sudden impact, the 

 transmission of the impulse is more rapid and the consequent move- 

 ment instantaneous. Another point of unlikeness consists in the 

 power of secretion of the glands, those of Dioncea being only excited 

 by the absorption of nitrogenous matter. When any substance comes 

 in contact with the filaments, the lobes of the disk close instantly 

 upon it, confining it in a concave chamber ; if the imprisoned matter 

 be nitrogenous the lobes are gradually pressed closer together, the 

 glands secrete freely and reexpansion takes place only after from 

 nine to twenty-four days, when nearly all trace of the substance will 

 have disappeared, and sensitiveness is lost, only to reappear after 

 some time has elapsed, if at all. If, however, the closing is the result 

 of sudden impact or of the contact of a non-nitrogenous substance, the 

 leaf shortly opens again and is at once sensitive,, the glands showing 

 no signs of secretion. The constitution and action of the secretion are 

 identical with those of Drosera, as is probably the manner of transmis- 

 sion of the motor impulse. But want of space again excludes many 

 interesting details. 



Aldrovanda, Drosophyllum, Roridula, and Di/blis, four other gen- 

 era of the same order, all are provided with secreting glands and seem 

 to have similar powers, though in a lesser degree. 



Mr. Darwin was also led to investigate the habits of Fingrdcula 



