MENDELIAN THEORY 351 



breed true, but that of the dominant there were two degrees or con- 

 ditions, which it might even be possible to distinguish by structural 

 characteristics : namely, those which were found ever after to 

 breed true (pure dominants) and those which produced both reces- 

 sive and dominant forms (impure dominants). It is thus obvious 

 that selection, from the greater prevalence of impure than pure 

 dominants, may result in unstable forms being experimented with, 

 and thus necessitate years of selection in place of the rapid, one 

 might almost say immediate, results that are possible. 



