PLANT STRUCTURE AND COMPOSITION 199 



example of (he (!:i\oncs. It is found as the glucoside. Quercetin, a 



CH:iO 



HO 



O O 



H 



citronetin 



eomponcnt of oak bark and yellow coloring agent in corn plants, is 

 illustrated as an example of the flavonol class. The flavonols have 



OH 



HO— 



i— OH 



quercitin 



been reported to possess vitamin activity in the animal. Extracts of 

 citrus peel and other sources of flavonols appear to supplement vita- 

 min C in the prevention of capillary fragility. Rutin, a diglycoside 

 of quercitrin, contains galactosylglucose and rhamnose and is isolated 

 from buckwheat for medical purposes. 



The inheritance of the anthocyanins has been studied in a number 

 of higher plants. Particular genes are known to cause the replacement 

 of pelargonidin anthocyanins by the corresponding cyanidins. The 

 change requires the addition of a hydroxyl group in the 3' position 

 of the basic nucleus. No biological function, other than possible at- 

 traction of insects for pollination purposes, has been ascribed to the 

 water-soluble plant pigments. 



Essential Oils 



Essential oils have been so named because of their odor or essence. 

 The fraction may be recovered from plant material by extraction with 

 the usual fat solvents or by steam distillation. If the former method 

 is used, distillation is necessary to separate the terpene derivatives from 

 the phospholipides, carotenoids, and other components of the lipide 

 fraction. Essential oils are members of a large group of compounds 

 •vvhich may be considered as derivatives of isoprene, a 5 carbon diene. 



