in Hybridisation 377 



characters which are united by the fertilisation. Let us, 

 for instance, assume that the plants selected for experiment 

 differed in three characters, and the species ABC is to 

 be transformed into the other species abc by repeated 

 fertilisation with the pollen of the latter ; the hybrids 

 resulting from the first cross form eight different kinds 

 of egg cells, viz. : 



ABC, ABc, AbC, aBC, Abc, aBc, abC, abc. . 



These in the second year of experiment are united again 

 with the pollen cells abc, and we obtain the series 



AaBbCc + AaBbc + AabCc + aBbCc 



+ A abc 4- aBbc + abCc + abc. 



Since the form abc occurs once in the series of eight 

 terms, it is consequently little likely that it would be 

 missing among the experimental plants, even were these 

 raised in a smaller number, and the transformation would 

 be perfected already by a second fertilisation. If by chance 

 it did not appear, then the fertilisation must be repeated 

 with one of those forms nearest akin, Aabc, aBbc, abCc. 

 It is perceived that such an experiment must extend the 

 farther the smaller the number of experimental plants and 

 the larger the number of differentiating characters in the 

 two original species ; and that, furthermore, in the same 

 species there can easily occur a delay of one or even of two 

 generations such as Gartner observed. The transforma- 

 tion of widely divergent species could generally only be 

 completed in five or six years of experiment, since the 

 number of different egg cells which are formed in the hybrid 

 increases as the powers of two with the number of differen- 

 tiating characters. 



Gartner found by repeated experiments that the respec- 

 tive period of transformation varies in many species, so that 

 frequently a species A can be transformed into a species B 

 a generation sooner than can species B into species A. He 

 deduces therefrom that Kolreuter's opinion can hardly be 

 maintained that "the two natures in hybrids are perfectly 

 in equilibrium." It appears, however, that Kolreuter does 

 not merit this criticism, but that Gartner rather has over- 

 looked a material point, to which he himself elsewhere 



