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TERPENOIDS AND STEROIDS 



The most important and widely distributed triterpenoids are the pentacyclic com- 

 pounds. They have been found in plants as primitive as Sphagnum (14) but are most com- 

 mon among the seed plants, both free and as glycosides (see also under "Saponins"). 

 The nonglycosidic triterpenoids are frequently found as excretions and in cuticle where 

 they may have a protective or waterproofing function. Zimmerman (15) has proposed 

 the interesting generalization that monohydroxy triterpene alcohols are not accompanied 

 by pigments in the plant whereas triterpene diols occur along with carotenoids, and tri- 

 terpene acids with flavonoids. 



Three basic ring skeletons are recognized, derived from three hypothetical hydro- 

 carbons. 



ursane type 



oleanane type 



lupane type 



