92 MENDELISM chap. 



factors B and E during the formation of the gametes in 

 a plant which is heterozygous for both. 



Other similar cases of factorial repulsion have been 

 demonstrated in the sweet pea, and two of these are also 

 concerned with the two factors with which we have just 

 been deahng. Two distinct varieties of pollen grains 

 occur in this species, viz. the ordinary oblong form and 

 a rather smaller rounded grain. The former is dominant 

 to the latter.^ When a cross is made between a purple 

 with round pollen and a red with long pollen the Fi plant 

 is a long pollened purple. But the F2 generation con- 

 sists of purples with round pollen, purples with long 

 pollen, and reds with long pollen in the ratio 1:2:1. 

 No red with round pollen appears in F2 owing to repul- 

 sion between the factors for purple (B) and for long pollen 

 (Z). Similarly plants produced by crossing a red 

 hooded long with a red round having an erect standard 

 give in Fi long pollened reds with an erect standard, 

 and these in F2 produce the three types, round pollened 

 erect, long pollened erect, and long pollened hooded, in 

 the ratio 1:2:1. The repulsion here is between the long 

 poUen factor (L) and the factor for the erect standard 

 (£). 



' It should be mentioned that as the shape of the pollen coat, like 

 that of the seed coat, is a maternal character, all the grains of any given 

 plant are either long or else round. The two kinds do not occur together 

 on the same plant. 



