24 ■ Bulletin 392 



The absence of the gene B in either parent precluded, of course, the 

 appearance of any of the blue series in any generation subsequent to 

 the cross. The fact that the genes C and R were intact in both parental 

 types, according to theory, precluded the appearance of tinged whites 

 or plain whites. Magenta, bearing genes for greater intensification of 

 color than mauve, would be dominant to it, as was found to be the case, 

 and in the recombination of genes when Fi plants were selfed, there would 

 be produced such recombinations as would give rise to the three red types 

 and to intervening gradations of color which are difficult to classify 

 as either the one or the other. 



Mauve crossed with light blue. — Four crosses were recorded between 

 mauve and light blue. The Fi offspring were dark blues, light blues, 

 and mauves; the F2 plants were dark blues, light blues, mauves, and 

 pinks. 



According to hypothesis, if a mauve is crossed with a blue the gene B 

 will be brought into the zygotic combination of Fi, and, this being dominant 

 to the genes of the red series, only blue could result. If the light blue 

 parent were simplex for B, some mauves could appear in Fi as follows: 



CCRRbbXX mauve 



X CCRR 



CCRRBbXx Hght blue 



Fi 



g^f XX dark blue 

 \ Xx light blue 



j XX mauve 

 I Xx mauve 



Mauve crossed with dark blue. — Crosses 212 and 213 were made between 

 mauve and dark blue, and in Fi gave only dark blues. They split up 

 in F2 into dark blues and mauves. The numbers were very small, and, 

 had more plants been produced, it is possible that other types might have 

 made their appearance; but it is unlikely that any other types would 

 have appeared in the Fi if both parents were homozygous for all genes, 

 because the blue would have dominated over the red, and the intensifier 

 borne in the dark blue would have been present to give a deeper hue 

 than was found in the mauve. The Fi plants would be simplex for B, 

 allowing members of the red series to appear in Fo. but no tinged whites 

 nor whites could make their appearance because both C and R would 

 remain duplex. The cross may be represented as follows: 



Fi F, 



CCRRbbXX mauve f BBXX dark blue 



X CCRRBbXX dark qCRkI BbXX dark blue 



CCRRBBXX dark blue [ bbXX mauve 



140 



