Mendelian Factors for Flower -Colour. 



303 



known flavone melting above 300° C. and having at the same time the 

 solubilities and properties of the yellow pigment. 



Proceeding on the assumption that the yellow pigment might be luteolin, 

 a fairly satisfactory separation was brought about by hydrobromic acid, 

 which, according to Perkin,* forms, in glacial acetic acid, a compound with 

 luteolin but not with apigenin. The luteolin hydrobromide remains in 

 solution unless excess of hydrobromic acid is added, when it separates out in 

 ochre-coloured crystals which are decomposed by water into luteolin and 

 hydrobromic acid. The method of procedure in our case was as follows : The 

 ether extract containing the mixed pigments was ground into a thin paste 

 with glacial acetic acid, heated to boiling, and hydrobromic acid added, but 

 not in excess. On cooling, the bulk of the apigenin separated out, while the 

 yellow pigment remained in solution. The apigenin was filtered off, and on 

 addition of much water to the filtrate the yellow pigment separated out and 

 was also filtered off. A repetition of this process ensures greater purity of 

 the yellow. After drying, the yellow was further purified by extraction with 

 ether. 



The pigment prepared in this way, except for its melting point, which 

 varied from 310° to 328° C, resembled luteolin in properties. According to 

 Perkin.f luteolin is a bright yellow crystalline substance, readily soluble in 

 alcohol, fairly soluble in ether, and very slightly soluble in water, even when 

 hot. With ferric chloride solution luteolin gives at first a green, later a red- 

 brown, coloration. The melting point of luteolin was for many years given 

 as " above 320° C." More recently Perkin has obtained luteolin by two 

 different methods of purification, giving, in one case, a product melting at 

 327-329° C, in the other, at 323-326° C. 



Luteolin occurs in Genista tinctorial and in leaves of Digitalis^ and also, 

 together with small quantities of apigenin, in Eeseda hcteola.\\ 



The structural formulas of luteolin and apigenin are as follows : — 



* Perkin, A. G., " Luteolin.— Part I," ' Chem. Soc. Journ., Trans.,' 1896, vol. 69, p. 206. 



t Perkin, A. G., " Luteolin.— Part I," 1 Chem. Soe. Journ., Trans.,' 1896, vol. 69, p. 206 ; 

 " Luteolin.— Part II," ' Chem. Soc. Journ., Trans.,' 1896, vol. 69, p. 799 ; Perkin, A. G., 

 and Horsfall, L. H., " Luteolin.— Part III," : Chem. Soc. Journ., Trans.,' 1903, vol. 77, 

 p. 1314. 



% Perkin, A. G., and Newbury, F. G. " The Colouring Matters contained in Dyer's 

 Broom (Genista tinctoria) and Heather (Callu/ia vulgaris)" ' Chem. Soc. Journ., Trans.,' 

 1899, vol. 75, p. 830. 



§ Fleischer, F., "Digitoflavon, ein neuer Korper aus der Digitalis purpurea" ' Ber. D. 

 Chem. Ges.,' 1899, vol. 32, p. 1184 ; Killiani, H., u. Mayer, O., " Ueber die Identitat von 

 Digitoflavon und Luteolin," ' Ber. D. Chem. Ges.,' 1901, vol. 34, p. 3577. 



|| Perkin, loc. cit. 



VOL. LXXXVII. — B. z 



