Light micrograph of a transverse section through the phellem (cork) of the cork oak Quercus suber. The section shows the large cell size of cork. This is the result of the deposition of suberin in and around the cell walls which, although killing the cells, forms a protective outer layer called the phellem on trees. The impermeability of the phellum cells (cork) has led to its use as stoppers in liquid storage, such as wine bottles. The main supply of this comes from Spain and Portugal. Magnification: x40 at 35mm size. Dark field illumination.