Appendix. 55 



oil is, in its various isomers, distributed among plants to an ex- 

 tent not fully understood. It has generally been put down as 

 more especially an educt of three plants, cuminium cyminium 

 (cummin) and cicuta virosa (water hemlock), of the umbellif- 

 erse, and thymus vulgaris 3 , of the mint family ; also sometimes 

 of a fourth, ammi copticum. But a large number of the volatile 

 oils of plants contain hydrocarbons of the composition C 10 H 14 , 

 more and more of which are found by chemical treatment to 

 yield aromatic products and almost certainly to be built upon the 

 benzene nucleus and to fulfil the character of "cymenes." 

 Eucalyptus globulus, the Australian fever tree, which has re- 

 ceived much attention of late years, contains a cymene as well as 

 a terpene. 



Now there appears to be only a short step in composition 

 between cymene, C 10 H 14 , and oil of turpentine, C 10 H 16 , which 

 is found in the coniferous trees, but this short step suffices to 

 throw oil of turpentine out of the homologous series of aromatic 

 hydrocarbons. Now isomeric with turpentine oil proper are 

 " the terpenes" generally, including the essential oils of apricot, 

 bergamot, birch, camomile, caraway, cloves, cubeb, elemi, hop, 

 juniper, lavender, lemon, orange, parsely, pepper, savin, spike, 

 tolu, thyme, and an indefinite number not named or not brought 

 to notice. In fact, a large proportion, probably a majority, of 

 essential oils contain terpenes, generally with other essential oil 

 constituents. To present some approximate indication of the 

 extent of distribution of the volatile oils altogether, a count has 

 been made of the number of plants reported to contain volatile 

 oils in the tabular summary of plant constituents given as the 

 Second Part of Wittstein's Chemischen Analyse von Pflanzen 

 und Pflanzentheilen (1867). This summary includes 576 plants 

 in 114 natural orders. Among these, essential oils are reported 

 in 156 or 27 per cent, of the plants, and in 45 or 39 per cent, of 

 the families. 3 



(2) C. B. A. WRIGHT, Jour. Chem. Soc., 



(3) Of the natural orders, the Labiatse had the largest number of plants 

 containing volatile oils (13 p. c. of all); the Umbelliferse the next largest num- 

 ber; the Synantheriee next, and the Myristicese next (6 p. c. of all). 



