Lemon balm oil glands. Coloured scanning electron micrograph (SEM) of the surface of a leaf of Lemon Balm, Melissa officinalis, showing oil glands. On the leaf surface are two types of hairs, called trichomes. Many multicellular hairs serve a protective function for the plant, or reduce evaporation from the leaf. The spherical structures are modified glandular hairs which secrete oils associated with the odour of Lemon balm. Lemon balm is both a herbal and medicinal plant used in perfumes, as a sedative and to treat headache and toothache. Magnification: x585 at 5x7cm size.