ix REPULSION AND COUPLING 



95 



that actually found by experiment. It will be noticed 

 that in the whole family the purples are to the reds as 

 3:1, and the longs are also three times as numerous as 

 the rounds. The peculiarity of the case lies in the dis- 

 tribution of these two characters with regard to one an- 

 other. In some way or other the factors for blue and 

 for long pollen become linked together in the cell divisions 

 that give rise to the gametes, but the linking is not com- 

 plete. This holds good for all the four cases in which 

 repulsion between the factors occurs when one of the 

 two factors is introduced by each of the parents. 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 between 

 separate factors are intimately related, though hitherto 

 we have not been able to suggest 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 the gametes. Nevertheless the 

 phenomena are very definite, and it is not unlikely that 

 a further study of them may throw important light on 

 the architecture of the living cell. 



APPENDIX TO CHAPTER IX 



As it is possible that some readers may care, in spite of its com- 

 plexity, to enter rather more fully into the peculiar phenomenon 



