198 CHARLES DARWIN. 



" Insectivorous Plants " was published July 2nd, 

 1875, but I consider it last, as the subject stands some- 

 what apart from the rest of his botanical works. 

 The subject was^ suggested to him by noticing the 

 insects caught by the leaves of the Sun-dew (Drosera} 

 near Hartfield. He then studied in great detail the 

 causes of the movement, and the sensitiveness of the 

 gland-tipped hairs, finding that a piece of hair 

 weighing T 4oo f a g ra i n causes one of them to 

 curve inwards, and alters " the condition of the con- 

 tents of every cell in the foot-stalk of the gland." 



The greater part of the work deals with the 

 experiments on Drosera, which were extremely 

 numerous and detailed. The remainder treats of 

 other insectivorous plants, such as Dionsea, Pingui- 

 cula, Utricularia, etc. The methods of capture, the 

 movements of the plants under the stimulus supplied 

 by the living insect (or other animal), and the re- 

 sulting changes in the plant-cells were not the only 

 points studied. He also investigated the digestive 

 secretion and its action upon the food absorbed by 

 the leaves. 



