Mendelian Factors for Flower -Colour. 



305 



treating the digitoflavone, in caustic soda solution, with benzol sulphochloride 

 and crystallising the product from a mixture of chloroform and ether. 

 Melting point, 189° C. 



By treating a specimen of yellow pigment, purified by means of the 

 hydrobromide method and subsequent extraction with ether, in a similar 

 way with benzol sulphochloride, an almost white product was obtained, 

 which crystallised from a mixture of chloroform and ether and melted at 

 188-190° C. 



By hydrolysing a small quantity of the benzol sulphonyl derivative with 

 alcoholic soda for three hours, a sample of luteolin was obtained, melting at 

 324° C. 



There is no doubt that the yellow Antirrhinum pigment is luteolin. The 

 factorial difference between the yellow and ivory varieties can, therefore, 

 be expressed as follows : — The ivory variety has the power to form apigenin 

 throughout the tissues of the flower, whereas the yellow variety has the 

 power to form luteolin, either in addition to, or more probably instead of, 

 apigenin, in the upper epidermis of the lips. It appears most likely that 

 the yellow variety has lost the power to form apigenin in the epidermis 

 and produces luteolin instead, though there does not seem to be any 

 particular reason why the power to form apigenin, instead of luteolin, should 

 be a dominant character.* The different flavones synthesised in either case 

 may be regarded rather as an expression of a fundamental difference in 

 structure of the living molecule in the two varieties, affecting, perhaps, the 

 production of different hydroxybenzoic acids, from which the flavones may 

 be synthesised. Little can be gained at present by postulating the existence 

 of a special organic catalyst or enzyme, representing the " I " factor, and 

 concerned with the removal or addition of an hydroxyl group. 



From the white variety no flavones could be extracted, and this is in 

 accordance with Mendelian evidence. We must suppose, therefore, that 

 either the substances from which the flavones are synthesised are absent, or 

 the power of synthesis fails. 



As regards the yellow patch on the palate, it appears likely that other 

 flavones, having lower melting points and slightly deeper colour than luteolin, 

 are present in this region. 



It seems highly probable that the anthocyanin pigments are derived from 

 the flavones by oxidation, or condensation, or both, though only accurate 

 analyses of the pure pigments can ultimately decide this question. With 

 regard to the suggestion made by one of us as to the mode of formation of 



* There are probably very small quantities of other flavones in the lips of both yellow 

 and ivor_y, but these do not affect the mass colour of the flowers. 



z 2 



