ANTHOXANTHINS 



333 



presentative ones will be mentioned here in order to give some 

 idea of the constitution of these compounds. 



Flavone in an almost pure condition is contained in the 

 powder which may be shaken off the surface of the stem and 

 leaves of Primula pulverulenta ; being soluble in benzene 

 this solvent may be used for its extraction. 



Chrysin, or dihydroxy-flavone, is a yellow colouring matter 

 occurring in several varieties of poplar, such as Populus nigra 

 and P. pyramidalis — 



o 



HO 



C— 



CH 



OH CO 



Quercetin, or tetrahydroxy-fiavonol * 



O OH 



HO' ^' c. ( )0H 



OH CO 



is widely distributed in the higher plants ; combined with 

 rhamnose, it exists in the form of a glucoside in quercitron 

 bark, Quercus tinctorius, in onion scales, wallflower petals, 

 leaves of horse-chestnut and hop, and in many other plants. 

 Quercetin, in the uncombined state, also is found in the bark 

 of Pyrus Malus and in the leaves of Thea sinensis, Arcto- 

 staphylos Uva-ursi, Acacia catechu, and many other plants. 



Rhamnetin, the monomethyl ether of tetrahydroxy-fiavonol 

 or quercetin monomethyl ether, occurs in the dried berries of 



* Flavonol is the hydroxyl derivative of flavone ; the relationship 

 between the two substances is shown by the following formulae : — 



O O 



CH 



CO 



Flavone 



COH 



CO 

 Flavonol 



