AROMATIC COMPOUNDS 



47 



HC=0 



OCH- 



HC=0 



Vanillin 



Methyl Salicylate 



Piperonal 



Urushiol and similar phenols with long aliphatic side-chains are responsible for the vesi- 

 cant action of poison ivy, poison sumac and other members of the Anacardiaceae. Kavain 

 and similar compounds of kava-kava root (Piper methysticiun) are responsible for the 

 sedative and intoxicating action of this plant. What, if any, function that the simple aro- 

 matic compounds have in plants is unknown although two suggestions seem most worthy of 

 consideration. The fungicidal activity of phenols makes it reasonable that they may act 

 to protect against fungus attack. There is no question but that the presence of protocatech- 

 uic acid in certain varieties of onions increases the resistance of these varieties toward 

 attack by certain fungi (1). Another possibility is that by acting as germination inhibitors 

 phenols prevent premature sprouting of certain seeds. Varga and Koves (2) have shown 

 that all the germination inhibitors of dry seeds are phenolic acids and derivatives. The 

 coumarins, to be discussed later in this chapter, are also important plant growth inhibi- 

 tors. 



BENZOQUINONES 



Benzoquinones are common fungal pigments but rarely encountered in higher plants. 

 Some of the more important ones (e. g. plastoquinone) seem structurally related to the ter- 

 penoids and are therefore included in Chapter 8. Hydroxy- and methoxybenzoquinones 

 are found in a few higher plants and are of some economic importance. 2-methoxybenzo- 

 quinone appears as a pink coloration in whole wheat flour after long-standing as the result 

 of hydrolysis and oxidation of a glucoside present in wheat germ. The dried fruit of 

 Embelia ribes is used in India for treatment of tapeworm and skin diseases. Its active 

 ingredient, embelin is a dihydroxyquinone. Other alkylhydroxyquinones similar to embelin 

 are found in a few other plants which have been used for many years as vermifuges. 



OCH. 



2-Methoxybenzoquinone 



Embelin 



