Coloured scanning electron micrograph (SEM) of a fallen leaf (dark brown) from the Northern Black Forest, Germany. It is covered with the hyphae (string-like) of different fungi. There are also some bacteria (blue). Fungi are the first organisms to decompose wood because they can split and utilise lignin, a complex compound in the woody cell walls of plants. Together with bacteria and microscopic animals, they form humus from organic waste. Magnification: x1300 when printed at 15cm wide.