246 



PIGMENTS 



state, also is found in the bark of Pyrus Mains and in the 

 leaves of Thea sinensis, Arctostaphylos Uva-ursi, Acacia catechu, 

 and many other plants. 



Rhamnetin, 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. 



o 



CH3O 



OH 



COH 



OH CO 



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

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

 is accompanied by another colouring matter, maclurin, some- 

 times called moringatannic acid (see p, 193). 



O 



HO 



OH 



OH 



HO 



OH CO 



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. 



CH 



/ 

 OH CO 



Other members of this group of substances are Apigenin, 

 occurring in Apiuni petroselinum, and Fisetin, occurring in 

 Quehi'acho colorada, and Rhus cotinus or Dyer's sumach. 



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 



