82 CHEMISTRY OF PLANT LIFE 



of Daphne; and fraxin, CieHigOio (glucose and fraxetin), is 

 found in the bark of several species of ash. 



The structural arrangement of the oxy-cumarin groups which 

 are found in these glucosides is shown in the following formulas. 

 It is not known to which OH group the sugar is attached, in each 

 case. 



Skimmetin ^Esculetin 

 CH=CH-CO CH=CH-CO 

 /\ n_l /\ rvJ 



Daphnetin Fraxetin 



CH-CO CH = CH CO 



HO/N 



HO( N 



OCH 3 



Scopolin, C22H2gOi4, found in Scopolia japonica, contains 

 two glucose molecules united to a monomethyl ether of aesculin; 

 while limettin, found in certain citrus trees, is the dimethyl ether 

 of sesculin. 



THE PIGMENT GLUCOSIDES 



Many, if not all, of the red, yellow, violet, and blue pigments 

 of plants either exist as, or are derived from, glucosides. These 

 are of three types: the madder, or alizarin, reds are derivatives of 

 various oxy-anthraquinones; most of the soluble yellow pigments 

 are glucosides derived from flavones or xanthones; and the 

 soluble red, blue, and violet pigments of the cell-sap of plants 

 are mostly anthocyan derivatives. The four basic groups, or 

 nuclei, which are present in these different types of compounds are 

 complex groups consisting essentially of two benzene rings linked 

 together through a third ring in which there are either two oxygen 

 atoms in the ring, or one oxygen in the ring and a second attached 

 to the opposite carbon in the (C = 0) arrangement, as shown by the 

 following diagrammatic formulas: 



