242 PIGMENTS 



to form a compound C 40 H 54 O 6 I 4 . Unlike carotin and xantho- 

 phyll, which are neutral substances, fucoxanthin has basic pro- 

 perties, and forms blue salts with hydrochloric and sulphuric 

 acids. 



FURTHER LITERATURE. 



Perkin and Everest : " The Natural Organic Colouring Matters," London, 

 1918. 



Schryver: " Science Progress," 1909, 3, 425. 



Stahl : " Zur Biologic des Chlorophylls," Jena, 1909. 



Willstatter and Stoll : " Unters u. Chlorophyll," Berlin, 1913. 



ANTHOXANTHINS. 

 FLAVONES AND XANTHONES. 



Under the headings of Flavones and Xanthones (two words 

 derived from the Latin and Greek for yellow) are included a 

 number of yellow pigments occurring in the vegetative organs 

 and in the petals of many plants. Owing to their close re- 

 lationship to the blue colouring matters known as Antho- 

 cyanins, Willstatter and Everest,* have proposed the adoption 

 for them of the generic te"m, Anthoxanthin, at first suggested 

 by Marquart in 1835. These yellow pigments are often of con- 

 siderable economic value as dye-stuffs. They occur naturally 

 in combination with rhamnose or glucose as glucosides and in 

 some cases uncombined, and frequently are also associated 

 with tannins. 



The anthoxanthins are widely distributed amongst the 

 higher plants ; they are most abundant in plants which grow 

 under conditions of high insolation, unless there be a protec- 

 tion in the form of hairs or thick cuticle. For this reason 

 they are looked upon as affording a protection against the 

 light rays of shorter length. There is sometimes an inter- 

 change between the anthoxanthins and anthocyanins, thus 

 young plants often contain red anthocyanin, which gives place 

 to a colourless flavone in the mature stage ; at leaf-fall the 

 anthocyanin may reappear. f 



The mother substances from which all these compounds 

 are derived and from which they derive their name are the 

 two compounds Flavone and Xanthone, both of which con- 

 tain the pyrone nucleus (see p. 246). 



* Willstatter and Everest : " Annalen," 1913, 401, 189. 

 f Shibata and Nagai : " Bot. Mag. Tokio," 1916, 30, 149. 



