The, Formation of the Anthocyan Pigments of Plants. 115 



have reference to the soluble sap pigments of the wallflower {Gheiranthus 

 cheiri). Of these pigments, A. G. Perkin* has already investigated the 

 hydroxyflavones present in the deep yellow flower of the variety of wallflower 

 known as " Cloth of Gold." He has shown that when the extract of sap 

 pigment is hydrolysed by boiling with dilute sulphuric acid an olive yellow 

 precipitate of the pigment separates on cooling. The precipitate is a mixture 

 of quercetin 



OH 



\/\/ 0H 

 OH CO 



and its monomethyl ester iso-rhamuetin 



O OCH s 



oh /y \_/ — \ OH 



OH CO 



Of these substances quercetin is distributed very widely in plants, but 

 iso-rhamnetin has been met with only in the Indian dye, asbarg (from 

 Delphinium zalil).f 



The general characters and distribution of the pigments of the flowers of 

 Cheiranthus cheiri are as follows : — 



The petals contain both sap and plastid pigments. In the deep yellow 

 varieties the colour is due to a plastid pigment which accompanies and 

 masks a pale yellow (cream) sap pigment. Purple flowers contain a purple 

 (anthocyan) pigment, together with a little plastid yellow. The same 

 pigments occur in the brown wallflower, which owes its colour to the large 

 amount of yellow which occurs, together with purple. Eed flowers contain 

 anthocyanin, together with xanthein, the yellow of which masks to some 

 extent the blue constituent of the anthocyan pigment. In certain primrose- 

 yellow varieties the colour changes with the age of the flower. The buds 

 and newly opened blossoms are of a rich yellow, but as the flower grows 

 older the yellow fades gradually till the petals are cream or almost white. 

 The full yellow is due to the plastid pigment which occurs together with 

 the pale primrose-coloured xanthein in the buds of young flowers. The 

 plastid pigment disappears as the age of the flower increases, and the pale 

 colour of the full blown flower is due to the persistence of the soluble sap 

 or xanthein pigment. 



* ' Chem. Soc. Trans.,' 1896, p. 1566. 



t Perkin and Pilgrim, 'Chem. Soc. Trans.,' 1898, p. 267. 



