XIX 



DARWIN'S WORK ON THE MOVEMENTS 

 OF PLANTS 



By Francis Darwin, 



Honorary Fellow of Christ's College, Cambridge. 



My father's interest in plants was of two kinds, which may be 

 roughly distinguished as Evolutionary and Physiological. Thus in 

 his purely evolutionary work, for instance in The Origin of Species 

 and in his book on Variation under Domestication, plants as well as 

 animals served as material for his generalisations. He was largely 

 dependent on the work of others for the facts used in the evolu- 

 tionary work, and despised himself for belonging to the "blessed 

 gang" of compilers. And he correspondingly rejoiced in the employ- 

 ment of his wonderful power of observation in the physiological 

 problems which occupied so much of his later life. But inasmuch as 

 he felt evolution to be his life's work, he regarded himself as something 

 of an idler in observing climbing plants, insectivorous plants, orchids, 

 etc. In this physiological work he was to a large extent urged on by 

 his passionate desire to understand the machinery of all living things. 

 But though it is true that he worked at physiological problems in 

 the naturalist's spirit of curiosity, yet there was always present to 

 him the bearing of his facts on the problem of evolution. His 

 interests, physiological and evolutionary, were indeed so interwoven 

 that they cannot be sharply separated. Thus his original interest 

 in the fertilisation of flowers was evolutionary. "I was led 1 ," he 

 says, "to attend to the cross-fertilisation of flowers by the aid of 

 insects, from having come to the conclusion in my speculations 

 on the origin of species, that crossing played an important part in 

 keeping specific forms constant." In the same way the value of his 

 experimental work on heterostyled plants crystalised out in his mind 

 into the conclusion that the product of illegitimate unions are 

 equivalent to hybrids — a conclusion of the greatest interest from an 

 evolutionary point of view. And again his work Cross and Self 

 Fertilisation may be condensed to a point of view of great import- 

 ance in reference to the meaning and origin of sexual reproduction 2 . 



1 Life and Letters, i. p. 90. 



2 See Professor Goebel's article in the present volume, p. 401. 



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