ALLIED AND MISCELLANEOUS PRODUCTS 



191 



are due the reds, blues, and violets of most fruits and flowers, of 

 red cabbage, beets, red autumn leaves, etc. They are glucosides 

 composed of a sugar and an anthocyanidin nucleus of the funda- 

 mental structure. 



O 



X 



The anthocyans are ampholytes and react with bases and acids 

 to form basic and acid salts, which vary in color from the bright 

 reds, when acid, to the blues, when alkaline, according to Will- 

 statter. The neutral anhydride salt is purple. Buxton and Dar- 

 bishire (1927) found the sap of red flowers generally had a pH value 

 of about 5.5 and that of blue flowers about 8.0. These different 

 salts may be thus represented: 



CI CI o- 



I I 



o o 



K— \ 



blue 



purple 



Intermediate colors may be produced by mixtures of different 

 anthocyans or by mixtures of anthocyans with other pigments 

 such as the anthoxanthins. Because of the change in color with 

 acidity, the anthocyans are used as indicators in hydrogen ion and 

 acidity studies in much the same way as litmus. When blue and 

 red flowers die, they commonly change color owing to the changes 

 in the acidity of the cell sap and protoplasm which accompany 

 death. In Ipomdea learii the pink buds (pH 6.0) change to full 

 blue (pH 7.8) as the flower opens in 30-40 minutes. As the blossom 

 dies, the blue changes back through violet to pink. 



The formation of the anthocyans depends primarily upon the 

 presence of sugars. Other factors are more or less secondary. Light 

 is important because of its importance in sugar formation, but the 

 work of Shantz and of Arthur tends to show that this effect is 

 indirect rather than direct; although the long rays are the most 

 important in sugar formation, the short rays, notably the ultra- 

 violet, are more essential to the immediate formation of the red 

 pigment in flowers and fruits. Apples, peaches, etc., will not 



