ix REPULSION AND COUPLING 87 



complete, and the examination of a large quantity of 

 similarly bred material shows that the purple longs 

 are about twelve times as numerous as the purple 

 rounds, while the red rounds are rather more than three 

 times as many as the red longs. Now this peculiar 

 result could be brought about if the gametic 

 series produced by the F l plant consisted of 

 7 BL+ i Bl+ i bL+ 7 bl out of every 16 gametes. 

 Fertilisation between two such similar series of 16 

 gametes would result in 256 plants, of which 177 

 would be purple longs, 1 5 purple rounds, 1 5 red 

 longs, and 49 red rounds a proportion of the 

 four different kinds very close to 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 

 distribution of these two characters with regard to 

 one another. 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 complete. This holds good 

 for all the four cases in which repulsion between the 

 factors occurs when one of the two factors is intro- 

 duced 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 



