Thyme leaf surface. Coloured Scanning Electron Micrograph (SEM) of the underside of a leaf of the herb thyme, Thymus vulgaris. Two types of leaf hairs (trichomes) are seen, and stomata. Stomata appear as small, green circular structures; they serve as pores for the exchange of gases from the leaf surface. Unbranched multicellular hairs (blue) are seen which may have a protective function or reduce evaporation from the leaf. Glandular spherical structures (yellow) are modified hairs; these are the source of the aromatic oil of thyme. Thyme is used as a herb in cooking. It also has medicinal properties. Magnification: x150 at 6x6cm size.