Scanning electron micrograph of oil glands on the surface of a sepal of English lavender, Lavandula angustifolia. The picture shows oil glands (cyan), 80 microns in diameter, mainly grouped within a groove on the sepal. The branched (pale green) structures arising elsewhere on the surface are trichomes.The oil glands produce an essential oil; a complex mixture of more than 100 phytochemicals. Essential oils are thought to have evolved as a way for plants to control predators, though their presence may act both as repellant and attractant. In Brassica species for example, mustard oil repels many animals, but attracts cabbage white butterflies. Lavender oil attracts humans. It is used in cosmetics, as a food flavouring, and as a mild sedative. The oil mimics the effects of the female hormone oestrogen, but is Generally Regarded As Safe (GRAS) by the US Food & Drug Administration (FDA)