208 



ANTHOCYANINS AND GENETICS 



vapour. Hence we may assume that the white variety contains no 

 flavone. 



Now let us see how this information can be connected with the 

 facts of Mendelian inheritance. It has been assumed that the yellow 

 plant contains a factor, Y, and when this is absent, the flower is white, 

 whatever other factors may be present. The ivory contains an addi- 

 tional factor, I, which is dominant to yellow. Thus ivory is YY(y)II(i) 

 and may, if heterozygous, throw either yellow or white, or both. Yellow 

 is YY(y)ii and may throw white. Hence the factor which has been 

 termed Y must represent the formation of luteolin in the epidermis, 

 and apigenin in the inner tissues of the corolla, while the factor, I, 

 represents the inhibition of the formation of luteolin. A better under- 

 standing may be reached, perhaps, by considering the constitution of 

 the flavones, apigenin and luteolin : 



HO CO 



Apigenin 



HO CO 



Luteolin 



It will be seen that luteolin contains one more hydroxyl group than 

 apigenin, and this number and special grouping of hydroxyls accounts, 

 it is said, for the greater intensity of colour. The behaviour also of 

 the flavones, on heating with caustic alkali, indicates that each flavone 

 can be considered to be built up of phloroglucin and an oxybenzoic 

 acid; thus apigenin decomposes into phloroglucin and p-oxybenzoic 

 acid: 



COOH 

 and luteolin into phloroglucin and protocatechuic acid 



OH OH 



/\ 



iOH 



COOH 



