Where Do Plants Store Essential Oils?
Plants store essential oils either in external secretory structures called glandular trichomes which are located on the surface of the plant, or in internal secretory structures, found imbedded inside the plant material. Usually with plants having an external secretory structure, you can easily identify them by lightly brushing your hand against or on its leaves and notice an aroma imparted on your skin. With plants having internal secretory structures, you may need to break the leaf or seed in order to get to the essential oil.
Most culinary herbs have external secretory structures, especially Lamiaceae (the mint or deadnettle family) plants such as Oregano, Lavender, Rosemary, Spearmint and Peppermint.
Examples of plants with internal secretory structures include: Bergamot, Grapefruit, Lemon, Lime, Orange and Tangerine; Eucalyptus species; Clove bud; Caraway, Carrot seed, Dill, Fennel, Black pepper, Cardamom, Cinnamon, Citronella, Ginger, Lemongrass, Nutmeg, Palmarosa and Patchouli; and resin producing trees such as Benzoin, Frankincense, Fir, Cedar, Pine, Spruce, Juniper, Cypress, Bay laurel, and Myrrh.
In citrus fruits, the internal structure is called the “secretory cavity” and in some tree species, such as Conifers or the Bay laurel, the internal secretory chamber is called the “duct.”