CELL-CONTEXTS AND FORMS OF CELLS. 233 



carpaceae, Cistaceae, Turneraceae, Lythraceae, Myrtacese, Aralia- 

 ceae, Umbelliferae, Ericaceae, Primulaceae, Convolvulaceae, Ver- 

 benaceae, Labiatae, Solanaceae, Caprifoliaceae, Valerianaceae, and 

 Compositae. 



COMPOSITION OF VOLATILE OILS. The volatile oils are usu- 

 ally of a very complex composition ; it will be found, however, 

 that they owe their principal characteristics to one or more 

 definite compounds. The following classes of compounds have 

 been derived from the volatile oils. 



TERPENES, hydrocarbons of the formula C 10 H 16 , are found in 

 the volatile oils of the Pinacese, Rutaceae, etc. The terpene pinene 

 makes up practically the entire bulk of turpentine oil. The 

 terpene limonene is found in the oil of lemon to the extent of 

 90 per cent. It is not, however, the characteristic constituent in 

 this oil, the odor of lemon being due to an aldehyde, citral. 



SESQUITERPENES, hydrocarbons of the formula C 15 H 24 , have 

 been isolated from a number of oils, the best known representa- 

 tive of this class being cadinene, occurring in the oils of cubeb, 

 patchouli, savin, etc. 



ALCOHOLS belonging to the aliphatic and aromatic series occur 

 in a number of oils combined as esters with the fatty acids. Both 

 methyl alcohol and ethyl alcohol are found in the aqueous dis- 

 tillates in the preparation of certain oils. This occurrence is 

 usually explained as being due to the decomposition of other sub- 

 stances. Methyl alcohol is thought to be derived from the de- 

 composition of cellulose, while ethyl alcohol is considered to be 

 a product of the fermentation of carbohydrates. That ethyl 

 alcohol may be derived in this manner is probable from the obser- 

 vations of Maze, who obtained alcohol from germinating seeds. 

 Esters of methyl alcohol, especially methyl salicylate, are widely 

 distributed. Among other alcohols, the following may be men- 

 tioned : Linalool constitutes the bulk of lignaloe oil ; geraniol, a 

 diolefinic alcohol makes up the bulk of rose oil ; benzyl alcohol, 

 as an ester, occurs in the oils of jasmine, tuberose, ylang-ylang, 

 etc. ; cinnamic alcohol, as an ester, occurs in cassia oil, storax, and 

 Peru balsam ; menthol (peppermint camphor) , a secondary alcohol, 

 is found in peppermint oil; borneol (camphyl alcohol) occurs 



