xxm 



meaningless diversities of floral structure, his attention was keenly 

 alive to any other interesting phenomena of plant life which came in 

 his way. In his correspondence, he not unfrequently laughs at himself 

 for his ignorance of systematic botany ; and his acquaintance with 

 vegetable anatomy and physiology was of the slenderest. Neverthe- 

 less, if any of the less common features of plant life came under his 

 notice, that imperious necessity of seeking 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 accom- 

 panied by an equally strong need to test them by well-devised 

 experiments, and to acquire all possible information before publishing 

 his results, the effect was that he touched no topic without elucida- 

 ting it. 



Thus the investigation of the operations of insectivorous plants, 

 embodied in the work on that topic published in 1875, was started 

 fifteen years before, by a passing observation made 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." (I, p. 95.) 



The researches thus 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 process 

 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 reading a short paper by Asa 

 Gray, published in 1858. He sent me some seeds, and on raising 

 some plants I was so much fascinated and perplexed by the revolving 

 movements of the tendrils and stems, which movements are really 

 very simple, though appearing at first sight very complex, that I 

 procured various other kinds of climbing plants and studied the whole 

 subject .... Seme of the adaptations displayed by climbing plants 



