Closed stoma on Kalanchoe leaf. Coloured scanning electron micrograph (SEM) of a leaf from the succulent Kalanchoe blossfeldiana, showing a closed stoma (centre). Stomata are pores that are the site of gaseous exchange in the plant. The opening and closing of the stomata is controlled by semicircular guard cells, which swell and become turgid to close the openings. K. blossfeldiana is adapted to hot, arid conditions and opens its stomata at night, which is the opposite of most plants, to prevent water evaporation. It absorbs carbon dioxide through the stomata at night and converts it to an organic acid for storage. When the plant starts photosynthesising during the day it uses the stored carbon dioxide. The flecks on the surface are wax. Magnification: x400 when printed at 10 centimetres tall.