I 



AROMA OF PLANTS. H 



fragrance to alcohol or ester coinpoiinds, or to both, since these com- 

 pounds are usually found accompanying- one another in the oils. 

 Owing- to their particularly agreeable fragrance, the esters and the 

 alcohols form a class of the so-called desirable constituents. 



Esters represent a group of constituents which are formed by the 

 interaction of alcohols and plant acids (esterification), an ester re- 

 sulting by the elimination of water in the reaction. Almost in- 

 yariably these esters possess a pleasant odor and conyey the charac- 

 teristic mellowness and fragrance to many of the essential oils from 

 plants. Indeed, a number of oils are yalued according to the per- 

 centage of esters which they contain. The largest number of pleas- 

 ant-smelling esters usually occur in oils as formates, acetates, or 

 butyrates. the acetic-acid esters preyailing. The oil of layender 

 flowers, for instance, owes its agreeable aroma to the acetic-acid ester 

 of the alcohol linalool or to linalyl acetate. The oil is yalued ac- 

 cording to the percentage of linalyl acetate Avhich it contains, al- 

 though the free alcohol linalool also exists in the oil. In this con- 

 nection it may be mentioned that the ester menthyl acetate imparts 

 fra'grance to peppermint oil. menthol being also an important con- 

 stituent in this case. 



Another striking example of an ester compound as the odor bearer 

 of an oil is the methyl ester of anthranilic acid, which carries the odor 

 of orange flowers. Further examples are not necessary to emphasize 

 the importance of esters and alcohols in determining the aromatic 

 yalue of oils or plants. 



In yiew of the fact that certain constituents may be classed as 

 odor bearers, the desirability of these constituents in yolatile oils 

 being eyident, attention should be giyen to the possibility of increas- 

 ing this class of substances by proper conditions of climate and 

 cultiyation. 



LOCALIZATION OF ODORS. 



Volatile oils, although found in all parts of plants, are localized 

 more or less generally in certain portions. The leayes, possibly on 

 account of their extensiye area, often carry a large proportion of oil. 

 In many plants, indeed, the leaves serve as the chief source of the 

 oil. ]\Iention may be made here of the oils obtained from leaves of 

 such plants as the eucalyptus, bay, Avintergreen, pine, lemon grass, 

 citronella. and ginger grass. On the other hand, in some plants the 

 oil is obtained principally from other parts, the leaves possessing 

 little or no odor, as in the oil-vieldinc: roses. 



The flowering tops of aromatic plants as a rule yield oils of rich 

 aroma, excelling the oils produced from any other portion of the 

 plant. The exquisite bouquet of such oils as rose, lavender, cassie. 

 orange flower, and ylang-ylang is well known, all of these oils being 

 obtained from the flowers or flowering tops. 



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