W. Bateson and R. C. Punnett 297 



It is probable, however, that the case of blue and long pollen' is one 

 in which the repulsion is of the 1 : 7 order. Up to the present time 

 we have had four families of the mating Bl x bL and the 419 plants 

 recorded in F^ were distributed in the four possible zygotic classes as 

 follows : 



Total 226 95 97 1 



Though the evidence for partial repulsion rests here upon the single 

 red round plant which occurred in family 61, it is in reality very much 

 stronger than it appears at first sight, for the following reason. All the 

 plants in the above four families were hooded, i.e. lacking in the factor 

 for erect standard (E). As we have already pointed out^ the three 

 factors E, B, and L constitute a series such that if any two are brought 

 into a zygote by different gametes repulsion occurs between them. 

 Until the present round hooded red plant appeared we had never 

 encountered this combination in any of our experiments. It cannot 

 therefore be regarded as due to a stray seed from another family. And 

 it is evident that if the repulsion between any pair of these three 

 factors were complete such a plant could never arise. For in the 

 normal course the ehl gamete could never be formed. Only two 

 possibilities therefore are open. Either we must look upon it as an 

 unaccountable mutation, or we must consider that the repulsion between 

 B and L is partial. In the light of the evidence afforded by the cretin 

 sweet pea we prefer the latter hypothesis, and we are inclined to regard 

 the partial repulsion between B and Z as of the 1:7:7:1 type. On 

 this hypothesis we should expect one red round in every 256 plants 

 (cf. Table II) whereas experiment gave 1 in 419. At the same time 

 we recognise that the data are not yet sufficient to preclude the 

 1 : 15 : 15 : 1 system. It is worthy of note that the coupling between 

 B and L is usually on the 7:1:1:7 system, and it would be interest- 

 ing if in such cases as these the repulsion and coupling systems for a 

 given pair of factors were shewn to be of the same intensity. In most 

 cases this could not be tested in practice owing to the verj' large 



1 Blue in the flower colour (B) is dominant to red (b), and long pollen (L) is dominant 

 to ronnd pollen ({)• 



« Proe. Roy. Soe. 1911, p. 7. 



