Potato leaf. Coloured scanning electron micrograph (SEM) of a transverse section of a potato leaf (Solanum tuberosum). The upper and lower surfaces of the leaf are covered in a single layer of closely packed cells called the epidermis. Below the upper epidermis is a layer of palisade parenchyma cells containing many chloroplasts. Beneath this layer is the spongy mesophyll which has large intracellular spaces for gaseous exchange. At the bottom is the lower epidermis, a single layer of closely packed cells where the stomata control gas exchange within the spongy mesophyll. Magnification x1260 (x262 at 10cm wide).