SPECIES HYBRIDIZATION 249 



the reaction system relations. Consequently strict Mendelian analyses 

 may be applied to such phenomena, and the reaction system relations 

 need not be considered. But when species are crossed we must look to 

 reaction system relations to account for the fact that not every set of 

 factors which can be obtained by recombination is capable of establish- 

 ing the harmonious interrelations which are necessary for normal func- 

 tioning in a reaction system. As a consequence species hybrids exhibit 

 a peculiar set of phenomena including sterility, whether partial or com- 

 plete, production of abnormal forms, and apparent lack of conformance 

 to established principles of hybridization. Underlying all these surface 

 phenomena, however, is a behavior essentially Mendelian, if we take 

 Mendelism to include all those phenomena consequent upon the shuffling 

 and recombination of factors which possess at least a relatively high 

 degree of stability. Since any irregularities in the distribution of factors 

 or chromosomes, which may be occasioned by the inharmonious re- 

 lations within the hybrid reaction systems acting upon the chromosome 

 mechanism, can hardly be considered to give rise to results which should 

 not be included under the term Mendelism, it is very evident that simple 

 assumptions such as we have outlined above will account for a con- 

 siderable array of phenomena. 



