240 



PIGMENTS 



occurs with rhamnose in the form of a glucoside in the bark of 

 Quercus tinctoria, in the leaves of the 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, Arctostaphylos Uva-ursi, Acacia catechu 

 and many other plants. 



RJiamnetin, the monomethyl ether of tetrahydroxy-flavonol 

 or quercetin monomethyl ether, occurs in the dried berries of 

 Rhamnus cathartica and R. tinctoria, both of which are used 

 for dyeing cotton. 



CH3O 



OH 



-o- 



OH 



Morin. — This substance, which is isomeric with quercetin, 

 occurs in the wood of Moms tinctoria (yellow wood), where it 

 is accompanied by another colouring matter, maclurin, some- 

 times called moringatannic acid (see p. 190). 



HO 



OH 



Luteolin. — This is the yellow colouring matter of Reseda 

 luteola, known as " weld " ; it is also contained in Genista tinc- 

 toria or Dyer's broom. 



HO 



OH 



o- 



OH CO 



YELLOW COLOURING MATTERS DERIVED FROM XANTHONE. 



There are as yet only three colouring matters known to 

 belong to this group, one of which, euxanthone, does not occur 



