Differential interference contrast (DIC) light micrograph of a green alga Closterium sp. and a round diatoms Stepahnodiscus sp. The genus Closterium, living exclusively in freshwater environments, is one of the closest single cell relative to land plants. Crystals of barium or calcium sulphate can be seen in the vacuoles at the cell ends. The function of these crystals is unknown. Magnification: x225 when printed at 10 centimetres wide at its longest edge.