152 MENDELISM CHAP. 



most cultivated varieties are complex heterozygotes. 

 Were the potato plant subjected to careful analysis 

 and the various factors determined upon which its 

 variations depend, we should be in a position to 

 remake continually any good potato without running 

 the risk of losing it altogether, as is now so often 

 the case. 



The application of Mendelian principles is likely 

 to prove of more immediate service for plants than 

 animals, for owing to the large numbers which can 

 be rapidly raised from a single individual and the 

 prevalence of self-fertilisation, the process of analysis 

 is greatly simplified. .Even apart from the circum- 

 stance that the two sexes may sometimes differ in 

 their powers of transmission, the mere fact of their 

 separation renders the analysis of their properties 

 more difficult. And as the constitution of the indi- 

 vidual is determined by the nature and quality of its 

 offspring, it is not easy to obtain this knowledge 

 where the offspring, as in most animals, are relatively 

 few. Still, as has been abundantly shown, the same 

 principles hold good here also, and there is no reason 

 why the process of analysis, though more trouble- 

 some, should not be effectively carried out At the 

 same time, it affords the breeder a rational basis for 

 some familiar but puzzling phenomena. The fact, 

 for instance, that certain characters often "skip a 

 generation " is simply the "effect of dominance in F^ 

 and the reappearance of the recessive character in the 

 following generation. " Reversion " and " atavism," 

 again, are phenomena which are no longer mysterious, 

 but can be simply expressed in Mendelian terms 

 as we have already suggested in Chap. VI. The 



