Lemon balm leaf hairs. Coloured scanning electron micrograph (SEM) of the underside of a leaf of the herb lemon balm, Melissa officinalis. Numerous hairs (trichomes) cover the undersurface of the leaf. These unbranced multicellular hairs may have both a protective function against predators and serve to reduce evaporation from the leaf. Stomata or pores appear as small, green rounded structures; they serve to exchange gases and water from the leaf surface. Lemon balm is both a herbal and medicinal plant used in perfumes, as a sedative and to treat headache and toothache. Magnification: x900 at 6x7cm size.