4 ;o 'DIFFERENT FORMS OF FLOWERS [1862. 



fertility, that depends on the mutual action of the two sets of 

 individuals. 



The work on heterostyled plants has a special bearing, to 

 which the author attached much importance, on the problem 

 of origin of species." 



He found that a wonderfully close parallelism exists be- 

 tween hybridisation and certain forms of fertilisation among 

 heterostyled plants. So that it is hardly an exaggeration to 

 say that the " illegitimately " reared seedlings are hybrids, 

 although both their parents belong to identically the same 

 species. In a letter to Professor Huxley, given in the second 

 volume (p. 176), my father writes as if his researches on 

 heterostyled plants tended to make him believe that sterility 

 is a selected or acquired quality. But in his later publica- 

 tions, e.g. in the sixth edition of the ' Origin,' he adheres to 

 the belief that sterility 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 dis- 

 tinctness, and that it depends on differentiation of the sexual 

 elements which is independent of any racial difference. I 

 imagine that it was his instinctive love of making out a diffi- 

 culty which to a great extent kept him at work so patiently 

 on the heterostyled plants. But it was the fact that general 

 conclusions of the above character could be drawn from his 

 results which made him think his results worthy of publica- 

 tion. f 



The papers which on this subject preceded and contribu- 

 ted to ' Forms of Flowers ' were the following : — 



" On the two Forms or Dimorphic Condition in the Spe- 

 cies of Primula, and on their remarkable Sexual Relations." 

 Linn. Soc. Journal, 1862. 



" On the Existence of Two Forms, and on their Reciprocal 

 Sexual Relations, in several Species of the Genus Linum." 

 Linn. Soc. Journal, 1863. 



* See ' Autobiography,' vol. i. p. 97. 

 f See ' Forms of Flowers,' p. 243. 



