[NTERPRETATION OF REVERSION 119 



are from plants belonging to pure pink-flowered and 

 pure white-flowered races respectively; and the 

 purple flower is from a plant of the first hybrid 

 generation produced by crossing these two races. 



These purple-flowered hybrids produce, when 

 self-fertilised, a second hybrid generation which 

 consists of purple-flowered, pink-flowered, and white- 

 flowered plants in the ratio of 9:3:4 respectively. 

 The explanation of this case is precisely similar to 

 that suggested to account for the result of crossing 

 a grey- with a white-seed-coated pea. But it was not 

 so obvious in the present case, for a reason which 

 will be given shortly. The two pairs of characters 

 in this case are supposed to be '' blue " and '' absence 

 of blue," and " pink " and " absence of pink " ; but 

 the blue, like the purple spot, cannot be manifested 

 in the absence of the pink ; so that the composition 

 of the second hybrid generation which, if the blue 

 could be manifested in the absence of pink, would 



be— 



9 Pink and Blue . . . [= Purple] 



3 Pink and not Blue , . [= Pink] 



3 Blue and not Pink * . [= Blue] 



1 not Blue and not Pink • [= White] 



is, as a matter of fact — 



9 Pink and Blue . . [= Purple] i.e. 9 Purple 



3 Pink and not Blue . [= Pink] i.e. 3 Pink 



3 Blue and not Pink . [= White] \. a w] a- 



1 not Blue and not Pink [= White] ) 



The type of second hybrid generation which has 

 been met with twice in this chapter deserves further 



