Rotten wood. Micrograph of a piece of wood infected with dry rot fungus. The structure of the wood is seen here, with large spaces (xylem vessels) and smaller spaces (xylem parenchyma). Thin threads are the fungal hyphae that are destroying the wood by digesting the cellulose that provides the wood with its structural support. Dry rot is a fungus (Serpula lachrymans) that infects damp timber.