226 BIOCHEMICAL SYSTEMATICS 



stilbenes, chalkones, asperulosides, and so on, which may be regarded 

 as variants of the basic Ce-Ca-Ce flavonoid nucleus, occur in the plant 

 families which are also notable for the production of anthraquinones. 

 Furthermore, he notes that Trim (1955) found that asperuligenin 

 accumulated in Rubiaceae during development, but only until the 

 synthesis of anthraquinone began. Thus, Hegnauer believes that com- 

 parative phytochemistry points to a relationship between the Ce-C.s 

 and Ce-Cs-Ce groups on the one hand and anthraquinones on the 

 other, so that the acetate theory alone could not satisfactorily 

 account for the facts; possibly phenol-related pathways are involved. 

 The simplest group of quinones, benzoquinones, are rarely 

 found among higher plants, being better known among fungi. Although 

 no attempt is made in this section to give a comprehensive list of the 

 quinones and their sources, there are so few benzoquinones from 

 higher plants, that it is practical to list them all. The following 

 benzoquinones from higher plants are included in Thomson (1957): 



H3CO 



O 



2 : 6-dimethoxybenzoquinone 



Adonis vernalis, Ranunculaceae 



O 



HO-Y^%-CnH 



23 



OH 



O 



embelin 



Myrsine, Embelia and Rapanea, Myrsinaceae 



O 

 HO- 



Rapanea maximowiczii; Myrsinaceae; Oxalis purpurata war. Jacquinii, 

 Oxalidaceae 



