Potato leaf. Coloured scanning electron micrograph (SEM) of a potato leaf (Solanum tuberosum) showing its underside and a transverse section through its structure. The surface is covered in hair-like growths called trichomes that protect the plant against predators and water loss. The trichomes with spheres at their tips secrete oils that are irritating to predatory insects. The upper and lower sides of the leaf are covered in a single layer of closely packed cells called the epidermis. Below the upper epidermis (bottom here) is a layer of palisade parenchyma made up of cells containing many chloroplasts. The next layer, the spongy mesophyll has large intracellular spaces for gaseous exchange. Magnification: x310 at 10 centimetres tall.