Rotten wood. Coloured scanning electron micrograph (SEM) of a piece of domestic plywood infected with dry rot fungus. The vertical structures are xylem tubes that contain large amounts of cellulose, which is the material that provides the wood with its structural support. Thin threads (red) are the fungal hyphae that are destroying the wood by digesting the cellulose. Holes in the wood are seen, especially down centre. Dry rot is a fungus (Serpula lachrymans) that infects damp timber.