268 CONCLUDING REMARKS CHAP. VI 



first crossed and of their hybrid offspring must also 

 be looked at as merely an incidental result, following 

 from the special co-adaptation of the sexual elements 

 of the same species. We can thus understand the 

 striking parallelism, which has been shown to exist 

 between the effects of illegitimately uniting hetero- 

 styled plants and of crossing distinct species. The 

 great difference in the degree of sterility between the 

 various heterostyled species when illegitimately fer- 

 tilised, and between the two forms of the same species 

 when similarly fertilised, harmonises well with the 

 view that the result is an incidental one which follows 

 from changes gradually effected in their reproductive 

 systems, in order that the sexual elements of the dis- 

 tinct forms should act perfectly on one another. 



Transmission of the Two Forms by Heterostyled Plants. 

 The transmission of the two forms by heterostyled 

 plants, with respect to which many facts were given in 

 the last chapter, may perhaps be found hereafter to 

 throw some light on their manner of development. 

 Hildebrand observed that seedlings from the long- 

 styled form of Primula Sinensis when fertilised with 

 pollen from the same form were mostly long-styled, 

 and many analogous cases have since been observed 

 by me. All the known cases are given in the two 

 following tables. 



that, judging from the remark- female elements in the two forms of 



able power with which abruptly the same heterostyled species, or 



changed conditions of life act on in all the individuals of the same 



the reproductive system of most ordinary species, could be acquired 



organisms, it is probable that the only under long-continued nearly 



close adaptation of the male to the uniform conditions of life. 



