Ergot is a disease of cereal grasses caused by the fungus Claviceps purpurea. It is characterized by the growth of dark sclerotia on the grains of rye and other cereals, which can cause severe poisoning if ingested. ERGOT has been known since ancient times and was once thought to be caused by supernatural forces. It is now known to be caused by a fungus that infects the grain and produces toxic alkaloids.