( cxiv ) 



is an incidental rather than a selected quality. The result of 

 his work on heterostyled plants is of importance as showing 

 that sterility is no test of specific distinctness, and that it 

 depends on differentiation of the sexual elements which is 

 independent of any racial difference." * 



The different forms of a heterostyled plant are adapted for 

 cross-fertilisation by insects, and each individual of each form 

 is by the same means excluded more or less completely from 

 fertilisation by another of the same form. In the former case 

 the sexual cells and the accessory apparatus have been kept 

 by selection during long generations of syngamy in a high 

 state of mutual compatibility : in the latter asyngamy, partial 

 or complete, has produced a large measure of the sterility 

 which is its inevitable even if long-delayed result. 



This argument has, I admit, can-ied me much further than 

 I originally intended, and it will be a pleasure to me if the 

 following criticism can be overthrown. 



If the sjjecial adaptation of heterostyled plants for particu- 

 lar lines of syngamy has incidentally resulted in lessened 

 fertility, when the unions discouraged by these adaptations 

 are artificially secured, and in this case without appeal to the 

 physiologically injurious effects of self-fertilisation, why should 

 Ave not similarly explain these effects whenever manifest in 

 the self-bred f offspring of any plant especially adapted for 

 cross-fertilisation 1 



Darwin tells us in the Autobiography that as soon as his 

 "attention was thoroughly aroused to the remai'kable fact 

 that seedlings of self-fertilised parentage are inferior, even 

 in the first generation, in height and vigour to seedlings of 

 cross-fertilised parentage," | he entered upon a series of 

 experiments which lasted eleven years, appearing in 1876 as 

 "Effects of Cross and Self-Fertilisation in the Vegetable 

 Kingdom." Of this work he wrote in 1881, "the results 

 there arrived at explain, as I believe, the endless and Avonder- 

 ful contrivances for the transportal of pollen from one plant 

 to another of the same species." § It is here suggested that 



* "Life and Letters," vol. iii, p. 296. 



t See Francis Darwin on "Tlie Knight Darwin Law," Nature, October 

 27, 1898, p. 630. 

 X "Life and Letters," vol. i, p. 96. § Ibid., vol. i, p. 97. 



