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CHARLES DARWIN 133 



for causes which nature had laid upon him, impelled, and 

 indeed compelled, him to inquire the how and the why of 

 the fact, and its bearing on his general views. And as, 

 happily, the atavic tendency to frame hypotheses was 

 accompanied by an equally strong need to test them by 

 well -de vised experiments, and to acquire all possible 

 information before publishing his results, the effect was 

 that he touched no topic without elucidating it. 



" Thus the investigation of the operations of insecti- 

 vorous plants, embodied in the work on that topic, 

 published in 1875, was started fifteen years before, by a 

 passing observation during one of Darwin's rare holidays. 

 ' In the summer of 1860 I was idling and resting near 

 Hartfield, where two species of Drosera abound ; and 

 I noticed that numerous insects had been entrapped by 

 the leaves. I carried home some plants and on giving 

 them some insects saw the movements of the tentacles, 

 and this made me think it possible that the insects were 

 caught for some special purpose. Fortunately, a crucial 

 test occurred to me, that of placing a large number of 

 leaves in various nitrogenous and non-nitrogenous fluids 

 of equal density ; and as soon as I found that the former 

 alone excited energetic movements, it was obvious that 

 here was a fine new field for investigation/ 



" The researches then initiated led to the proof that 

 plants are capable of secreting a digestive fluid like that 

 of animals, and of profiting by the result of digestion ; 

 whereby the peculiar apparatuses of the insectivorous 

 plants were brought within the scope of natural selection. 

 Moreover, these inquiries widely enlarged our knowledge 

 of the manner in which stimuli are transmitted in plants, 

 and opened up a prospect of drawing closer the analogies 

 between the motor processes of plants and those of 

 animals. 



" So with respect to the books on Climbing Plants 

 (1875), and on the Power of Movement in Plants (1880), 

 Darwin says : ' I was led to take up this subject by 



