ODORS AND LIFE. 191 
by the name of essences or essential oils. In most cases 
the essence is concentrated in the flower, as occurs with the 
rose and the violet. In other plants, as in bent-grass and 
Florence iris, only the root is fragrant. In cedar and san- 
dal-wood, it is the wood that is so; in mint and patchouli, 
the leaves; in the Tonquin bean, the seed; in cinnamon, 
the bark, which is the seat of the odorous principle. Some 
plants have several quite distinct fragrances. Thus the 
orange has three: that of the leaves and fruit, which gives 
the essence known by the name of “ petit-grain;” that of 
the flowers, which furnishes neroli; and, again, the rind of 
the fruit, from which essence of Portugal is extracted. A 
great number of vegetable odors belong exclusively to 
tropical plants, but the flora of Europe furnishes a large 
proportion of them, and almost all the essences used in per- 
fumery are of European origin. England cultivates laven- 
der and peppermint largely. At Nimes, gardeners are par- 
ticularly attentive to rosemary, thyme, petit-grain, and lav- 
ender. Nice has the violet for its specialty. Cannes ex- 
tracts all the essences of the rose, the tuberose, cassia (the 
yellow acacia), jasmine, and neroli. Sicily produces lemon 
and orange; Italy, bergamot and the iris. | 
What, now, is the chemical nature of the odorous prin- 
ciples in plants? The chemistry of to-day reduces almost 
all of them to three categories of well-ascertained sub- 
stances: hydrocarburets, aldehydes, and ethers. We will 
endeavor to give a clear account of the constitution of 
these three kinds of substances, and to mark their place in 
the register of science. The hydrocarburets are simple 
combinations of carbon and hydrogen, as, for instance, the 
petroleum-oils. They represent the simple compounds of 
organic chemistry. As to aldehydes and ethers, their com- 
position is rather more complex; besides carbon and 
hydrogen, they contain oxygen. Every one knows what 
chemists mean by an alcohol; it is a definite combination 
