268 



CONCLUDING REMARKS 



Chap. VI 



ently spontaneous manner or from slightly changed 

 conditions of life. Gartner also has shown * that the in- 

 dividual plants of the same species vary in their sexual 

 powers in such a manner that one will unite with a 

 distinct species much more readily than another. But 

 what the nature of the inner constitutional differences 

 may be between the sets or forms of the same varying 

 species, or between distinct species, is quite unknown. 

 It seems therefore probable that the species which 

 have become heterostvled at first varied so that two 

 or three sets of individuals were formed differing in 

 the length of their pistils and stamens and in other 

 co-adapted characters, and that almost simultaneously 

 the irreproductive powers became modified in such a 

 manner that the sexual elements in one set were 

 adapted to act on the sexual elements of another set; 

 and consequently that these elements in the same set 

 or form incidentally became ill-adapted for mutual 

 interaction, as in the case of distinct species. I have 

 elsewhere shown f that the sterility of species when 

 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 heterostyled plants and 

 of crossing distinct species. The great difference in the 

 degree of sterility between the various heterostyled spe- 



* Gartner, ' Bastarderzeugung 

 im Pflanzenreich/ 1849, p. 165. 



t ' Origin of Species/ 6th edit, 

 p. 247 ; ' Variation of Animals and 

 Plants under Domestication,' 2nd 

 edit. vol. ii. p. 169 ; ' The Effects 

 of Cross- and Self-fertilisation/ p. 

 463. It may be well here to re- 

 mark that, judging from the re- 

 markable power with which ab- 

 ruptly changed conditions of life 



act on the reproductive system of 

 most organisms, it is probable that 

 the close adaptation of the male to 

 the female elements in the two 

 forms of the same heterostyled 

 species, or in all the individuals 

 of the same ordinary species, could 

 be acquired only under long-con- 

 tinned nearly uniform conditions 

 of life. 



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