Olive leaf. Coloured scanning electron micrograph (SEM). of a freeze fracture through the mid rib of an olive leaf (Olea sativa). It has a thickened epidermis for water retention. The large central vascular bundle has contains xylem surrounded by phloem. Below the upper epidermis and surrounding the vascular bundle is a layer of palisade parenchyma cells containing 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: x80 when printed at 10 centimetres wide.