Rosemary leaf. Coloured scanning electron micrograph (SEM) of the surface of a young rosemary (Rosmarinus officinalis) leaf. The leaf surface comprises epidermal cells (green). On the leaf surface are two types of trichome (hair process). Globular oil glands (yellow) secrete oil. Hair cells (grey), which may be branched or unbranched, may protect the leaf against water loss, or against insects. Rosemary is used widely in cookery and herbal medicine. It is used to treat depression, migraine, rheumatism, arthritis, neuralgia and muscle injuries. Magnification: x400 when printed 10 centimetres wide.