Aromatherapy essential oils are synthesised and stored in many parts of the plant, and in several different types of secretory structures.
Essential oils of eucalyptus and tea-tree, for example, occur in oil sacs within the leaf, while those of peppermint and clary sage are found in glands on the leaf surface. Rose oil is extracted from the petals of the flower, and clove oil, from the dried flower buds.
In the case of marjoram oil, the flowering tops are used-including petals, sepals, upper stalks, and leaves; while to produce oil of yarrow, the entire herb is distilled. Juniper yields an essence from both its berries and twigs, and orange, from its flowers, leaves, and the rind of its fruits.
Plants that belong to the umbelliferae family, including fennel, caraway, and coriander bear their oil in the seeds, just as frankincense and myrrh occur in the bush’s resin.
Essential oils produced from the chopped wood of trees include cedarwood and sandalwood while those of pine and spruce are distilled mainly from the needles or leaves. Vetiver is an example of an aromatherapy oil extracted from the root, and ginger from the fragrant rhizome.
It is not completely understood why plants manufacture aromatherapy essential oils, but it is becoming clear that they fulfil some important ecological function. There is evidence, for example, that the essences of some plants attract pollinating insects, while others serve a repellent function.
Just as essential oils possess, on a therapeutic level, powerful antimicrobial properties, so in nature do they often display the potential to prevent attack by fungi and bacteria.