Dry rot fungus. Coloured scanning electron micrograph (SEM) of dry rot in a piece of domestic plywood. Dry rot is a fungus (Serpula lachrymans) which infects damp timber. As the fungal network, or mycelium, grows, it destroys the cellulose in the wood and weakens its structure. The mycelium consists of strands known as hyphae, the thin threads seen here. The thicker objects are fragments of wood.