480 THE ACCESSORY PIGMENTS CHAP. 17 



them is quercetin (Formula 17.IV). Information on flavones can be 



O 



OH II 

 O 



Formula 17.IV. Quercetin CisHioO? 



found in the books and reviews of Mayer (1935), Karrer (1932), and 

 Perkin and Everest (1918), and in an article by Link (1938). 



Anthocyanins are red reduction products of yellow flavones. Nor- 

 mally, leaves do not contain anthocyanins, but they occur in certain 

 varieties (purpurea leaves), and also in certain development stages of 

 ordinarily green leaves (e. g., in very young leaves, which often appear 

 red before they turn green). Noack (1922) suggested that flavones and 

 anthocyanins may form reversible oxidation-reduction systems which are 

 somehow related to photosynthesis. This system is normally in the 

 oxidized state (flavones) but may be transformed into the reduced state 

 (anthocyanins) when photosynthesis is inhibited. This suggestion is 

 purely speculative; but it is noteworthy that in flavones and antho- 

 cyanins, we encounter another example of pigments which can occur in 

 an oxidized and a reduced form, similarly to the chlorophylls, the carote- 

 noids, and the phycobilins. 



Bibliography to Chapter 17 

 Accessory Pigments 



A. Carotenoids 

 1837 Berzelius, J. J., Ann. Chemie {Liehig), 21, 257. 



Berzelius, J. J., Ann. Physik, 42, 422. 

 1889 Arnaud, F., Compt. rend., 109, 911. 

 1907 Molisch, H., Die Purpurbacterien. Fischer, Jena, 1907. 



Willstatter, R., and Mieg, W., Ann. Chemie {Liehig), 355, 1. 



1913 Willstatter, R., and Stoll, A., Untersuchungen iiber Chlorophyll. 



Springer, Berlin, 1913. 



1914 Willstatter, R., and Page, H. J., Ann. Chemie {Liehig), 404, 237. 

 1918 Willstatter, R., and Stoll, A., Untersuchungen icher die Assimilation 



der Kohlensdure. Springer, Berlin, 1918. 

 Ewart, A. J., Proc. Roy. Soc. Victoria, 30, 178. 

 1922 Palmer, L. S., Carotenoids and Related Pigments. Chemical Catalog 

 Co., New York, 1922. 



1928 Karrer, P., Helfenstein, A., and Widmer, R., Helv. Chim. Acta, 11, 



1201. 

 von Euler, V., von Euler, H., and Hellstrom, H., Biochem. Z., 203, 370. 



1929 Karrer, P., Z. angew. Chem., 42, 918. 



