Brown Rot Fungi
Brown rot primarily decays the cellulose and hemicelluloses in wood, leaving a brown residue of lignin, the substance which holds the cells together. Wood affected by brown rot is usually dry and fragile, readily crumbles into cubes because of longitudinal and transverse cracks (tending to crack across the grain). Infected wood may be greatly weakened, even before any external evidence of decay can be seen. Brown rot is generally more serious than white rot.
Old infestations of brown rot which have dried out will turn to powder when crushed. They are often labeled as “dry rot.” This common term is deceiving, because dry wood will not rot! Actually, wood kept dry will never decay.