Coloured scanning electron micrograph (SEM) of wood debris from the soil of the Northern Black Forest, Germany. At top are the remnants of the bark (orange-brown), with mite faeces (grey) below. The decomposing wood is beige. At lower centre are roots that have grown into the wood. The white threads are fungal hyphae.. 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: x65 when printed at 15cm wide.