These nuts are almost spherical in shape, the size of a small walnut, of a grayish-brown color externally, and usually coated with a faint whitish-gray covering (which is lime). Internally they are reddish-brown, with white marbled spots. Good fresh nutmegs should be dense, heavy, and so oily that when pierced with a needle a drop of oil should follow the withdrawal of the latter. Nuts which are hollow, wormy, and of a faint odor cannot be used in perfumery. Oil of nutmeg is used extensively in perfumery, but is rarely employed pure, more commonly in combination with other strong odors. OLIBANUM. _Latin_—Olibanum; _French_—Encens; _German_—Weihrauch. This gum-resin, employed even by the ancient civilized nations of Asia, especially as incense for religious purposes, comes from East African trees, various species of Boswellia. Fine olibanum appears in light yellow tears, very transparent and hard, whose pleasant though faint odor becomes particularly marked when it is thrown on hot coals. In perfumery olibanum is used almost exclusively for pastils, fumigating powders, etc. Pulverulent olibanum constitutes an inferior quality and is often adulterated with pine resin. OPOPANAX. _Latin_—Resina Opopanax. The root stock of an umbelliferous plant, indigenous in Syria, now recognized at Balsamodendron Kafal, furnishes a yellow milky sap containing an aromatic resin with an odor resembling that of gum ammoniacum. At least the opopanax now obtainable in the market is derived from this source. True opopanax resin, such as used to reach the market formerly, is now unobtainable, and its true source is yet unknown. Opopanax oil is used in perfumery to some extent. ORANGE FLOWERS. _Latin_—Flores Aurantii; _French_—Fleurs d’oranges; _German_—Orangenblüthen. The flowers of the bitter orange tree (Citrus vulgaris), as well as those of the sweet (Citrus Aurantium), contain very fragrant essential oils, which differ in flavor and value according to their source and mode of preparation. See below, under Oil of Orange. The leaves, too, contain a peculiar oil used in perfumery. ORANGE PEEL. _Latin_—Cortex Aurantii; _French_—Ecorce d’oranges; _German_—Orangenschalen. The very oily rinds of the orange occur in commerce in a dried form; such peels, however, can be used only in the manufacture of liqueurs; in perfumery nothing but the oil from the fresh rinds is employed, and this is generally obtained by pressure. ORIGANUM. See Marjoram, and Thyme. ORRIS ROOT. _Latin_—Radix Iridis florentinæ; _French_—Iris; _German_—Veilchenwurzel.