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. 
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