126 MENDELISM chap. 



coupling and repulsion may be much higher. We 

 have already seen that the erect standard in the sweet- 

 pea (p. 78) is dominant to the hooded standard 

 (cf. PI. II., 7), and we assume that the former 

 contains a factor for the erect character (£") which 

 is lacking in the latter {e). Now the factor for 

 erect standard exhibits the phenomenon of coupling 

 and repulsion with the factor for blue {B). If we 

 make a cross between a purple erect sweet-pea and 

 a red-hooded one the offspring are all purple erect. 



Purple erect x Red hooded 



I 

 Purple erect 



A considerable number of F^ plants have been 

 raised from such a cross, and as the appended 

 scheme shows they consist almost entirely of the 

 two parental forms. Nevertheless a few purple 

 hooded and red erect plants make their appearance. 

 The proportions in which they appear fit closely 

 with the assumption that the gametic series produced 

 by the F^ plants is of the nature 12^ BE \ i Be: 

 I bE : 1 27 be. The intensity of the coupling is here 

 very much higher than in the cases considered above. 

 For this reason the cross of the opposite nature 

 — purple hooded x red erect — presents a feature of 

 some interest. If, on analogy, we suppose the 

 gametic series produced by the F^ purple erects to 



