Polarised light micrograph of a tangential section of the mature wood of the English elm (Ulmus procera). Medullary rays are seen running horizontally. Elm is a deciduous tree which can grow up to 35m and its timber is valued for furniture manufacture. Rays are seen running vertically and tracheids (red and blue) and vessels with bordered pits are seen running horizontally. Dutch elm disease, caused by the fungus Ceratocystis ulmi, has had a devastating effect on elm tree populations. Magnification: x68 at 10cm wide.