Leaf tissue structure. Coloured scanning electron micrograph (SEM) of a section through the edge of a leaf from the Common Box (Buxus sempervirens). The surface of the leaf is covered in closely packed circular cells (brown) that make up the epidermis. Below the epidermis are palisade mesophyll layers, made up of elongated column-like cells (green) containing chloroplasts. Chloroplasts (not seen) contain a green pigment called chlorophyll, which the plant uses to harness energy from the Sun (a process known as photosynthesis). At the centre of the leaf (red) is the spongy mesophyll, which has large intracellular spaces for gaseous exchange. Magnification: x200 when printed 10 centimetres tall.