PIGMENTS 117 



The anthocyanin pigments are soluble in water, alcohol, and 

 ether, the solutions being red or blue in color according to the 

 acidity or alkalinity of the medium. Their presence in many 

 species of plants is hereditable, as these plants come true to color 

 from seed, as in the case of red beets, red cabbage, several species 

 of blue berries, etc. In other cases, the anthocyanin development 

 depends largely upon the conditions of growth, particularly those 

 which prevail during the later stages of development; as in the 

 case of apples, where the amount of red color in the skin depends 

 to a large extent upon the conditions under which the fruit ripens. 



Anthocyanin pigments often make their appearance late in the 

 season; in fruits, etc., as the result of the normal ripening process, 

 but in leaves as the result of shorter daylight illumination accent- 

 uated also by sharp frosts. 



THE ANTHOXANTHINS 



The yellow plant pigments, other than the carotinoids, are 

 almost without exception glucosides having a xanthone or flavone 

 nucleus. These typical nuclei are illustrated on page 83. In 

 these nuclei, as in the anthocyan one, the oxygen atom is strongly 

 basic and combines with mineral acids to form salts (the oxygen 

 becoming quadrivalent) and the color of the pigment depending 

 upon the nature of the combination formed in this way. 



The anthoxanthin pigments are yellow, crystalline solids, 

 which are only slightly soluble in water. They dissolve readily 

 in dilute acids and alkalies, giving yellow or red solutions which are 

 of the same color in either acid or alkaline media. They are 

 extensively used as yellow dyes. 



Many of the common members of this group have been men- 

 tioned in the chapter dealing with the glucosides. The charac- 

 teristic pigment nucleus of several of these is as follows: 



Chrysin, found in various species of poplar and mallows, 



H 







