Peppermint leaf. Coloured scanning electron micrograph (SEM) of the surface of a peppermint (Menta piperita) leaf. The leaf surface comprises epidermal cells (green). On the leaf surface are globular oil glands (brown), that secrete mint oil. These are modified hair cells (trichomes). Other leaf processes (grey/purple), including two large hair cells, are also seen. Mint leaves and mint oil are used widely in herbal medicine and cookery. Tea made from mint is taken for digestive problems and flu. The oil can be used externally to treat burns, neuralgia and rheumatism. Magnification: x70 when printed 10 centimetres wide.