96 MENDELISM CHAP. 



of the coupling of characters, I have brought together some further 

 data in this Appendix. In the case we have already considered, 

 where the factors for blue colour and long pollen are concerned, we 

 have been led to suppose that the gametes produced by the hetero- 

 zygous plant are of the nature 7 BL : i Bl: i bL : 7 bl. Such a series 

 of ovules fertilised by a similar series of pollen grains will give 

 a generation of the following composition : 



49 BBLL + 7 BBLl + 7 BbLL + 49 BID, 



+ 7 BBLl + 7 BbLL + BbLl 



+ BbLl 



-f 49 BbLl 



177 purple, long 



+ BBll + 7 BUI 4- bbLL + 7 bbU + 49 bbtt 

 + 7 BUI + 7 bbLl 



15 purple, 15 red, 



round long 



and as this theoretical result fits closely with the actual figures 

 obtained by experiment we have reason for supposing that the 

 heterozygous plant produces a series of gametes in which the factors 

 are coupled in this way. The intensity of the coupling, however, 

 varies in different cases. Where we are dealing with another, viz. 

 fertility (F) and the dark axil (/?), the experimental numbers accord 

 with the view that the gametic series is here 1 5 FD : i Fd : i jD : 

 15 fd. The coupling is in this instance more intense. In the case 

 of the erect standard (E) and blueness (B) the coupling is even more 

 intense, and the experimental evidence available at present points 

 to the gametic series here being 63 Eb : i EB : i eB:6$ eb. There 

 is evidence also for supposing that the intensity of the coupling 

 may vary in different families for the same pair of factors. The 

 coupling between blue and long pollen is generally on the 7 : i : i : 7 



