1 74 



MAIZE 



:hap. 



V. 



East and Hayes have shown that two white breeds of 

 maize (Pc and pC), which show not the slightest trace of 

 colour, may bring together the two factors P and C necessary 

 for the full development of purple colour. They also refer to 

 cases in which, owing to the presence of a certain factor, the 

 red or purple colour of the aleurone layer is inhibited from 

 appearing. Such cases are different from mere absence of the 

 colour, for the colour factor is present even though not visible. 

 The following results are obtainable by crossing between an 



allelomorphic pair where such 

 cerned : — 



an inhibiting factor is con- 



132. Repulsion and Coupling of Characters. — This subject 

 is too complex to be discussed at length here, and we can- 

 not do better than quote a few extracts from Professor •Punnett 

 (1, pp. 81-8). "A few cases have been worked out," he says, 

 " in which the distribution of the different factors, to the 

 gametes, is affected by their simultaneous presence in the 

 zygote. And the influence which they are able to exert upon 

 one another in such cases is of two kinds. They may repel 

 one another, refusing, as it were, to enter into the same gamete ; 

 or they may attract one another, and, becoming linked to- 

 gether, pass into the same gamete, as it were, by preference." 

 In the cases of repulsion cited by him, " the original cross was 

 such as to introduce one of the repelling factors with each of the 

 two parents". But "when both of the factors are brought into 

 the cross by the same parent, we get coupling between them instead 

 of repulsion. The phenomena of repulsion and coupling be- 

 tween separate factors are intimately related, though hitherto 

 we have not been able to decide why this should be so. Nor 

 for the present can we suggest why certain factors should be 

 linked together in the peculiar way that we have reason to 

 suppose that they are during the process of the formation of 



