APPENDIX 351 



These in the second year of experiment are united again with the 

 pollen cells abc, and we obtain the series 



AaBbCc + AaBbc + AabCc + aBbCc + Aabc + 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 experi- 

 mental plants, even were these raised in a smaller number, and the 

 transformation would be perfected already by a second fertilisa- 

 tion. 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 

 transformation 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 differentiating characters. 



Gartner found by repeated experiments that the respective 

 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, how- 

 ever, that Kolreuter does not merit this criticism, but that Gartner 

 rather has overlooked a material point, to which he himself else- 

 where draws attention, viz. that " it depends which individual is 

 chosen for further transformation." Experiments which in this 

 connection were carried out with two species of Pisum demon- 

 strated that as regards the choice of the fittest individuals for the 

 purpose of further fertilisation it may make a great difference which 

 of two species is transformed into the other. The two experi- 

 mental plants differed in five characters, while at the same time 

 those of species A were all dominant and those of species B all 

 recessive. For mutual transformation A was fertilised with pollen 

 of B, and B with i)ollen of A, and this was repeated with both 



7?" 



hybrids the following year. With the first experiment — there were 



A 



eighty-seven plants available in the third year of experiment for 



