82 MENDELISM CHAP. 



One of the best illustrations of repulsion between 

 factors occurs in the sweet-pea. We have already 

 seen that the loss of the blue or purple factor (B) 

 from the wild bicolor results in the formation of the 

 red bicolor known as Painted Lady (PI. IV., 7). 

 Further, we have seen that the hooded standard 

 is recessive to the ordinary erect standard. The 

 omission of the factor for the erect standard (E) 

 from the purple bicolor (PI. II., 5) results in a 

 hooded purple known as Duke of Westminster (PI. 

 II., 7). And here it should be mentioned that 

 in the corresponding hooded forms the difference in 

 colour between the wings and standard is not nearly 

 so marked as in the forms with the erect standard, 

 but the difference in structure appears to affect the 

 colour, which becomes nearly uniform. This may 

 be readily seen by comparing the picture of the 

 purple bicolor on Plate II. with that of the Duke 

 of Westminster flower. 



Now when a Duke of Westminster is mated with 

 a Painted Lady the factor for erect standard (E} is 

 brought in by the red, and that for blue (B} by the 

 Duke, and the offspring are consequently all purple 

 bicolors. Purples so formed are all heterozygous 

 for these two factors, and were the case a simple one, 

 such as those which have already been discussed, 

 we should expect the F 2 generation to consist of the 

 four forms erect purple, hooded purple, erect red, 

 and hooded red in the ratio 9:3:3:1. Such, how- 

 ever, is not the case. The F,, generation actually 

 consists of only three forms, viz. erect red, erect 

 purple, and hooded purple, and the ratio in which 

 these three forms occur is 1:2:1. No hooded red 



