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in fungi, a dormant stage that occurs under unfavorable conditions. The sclerotium is a round or elongate body formed by the close intertwining of the hyphae of some ascomycetous, basidial, and imperfect fungi—for example, ergot, sclerotinia, Brazilian polyporous fungus, and monilia. The sclerotium usually ranges in size from a fraction of a millimeter to 2 cm. Some larger forms occur; for example, in the Brazilian polyporous fungus the sclerotium reaches 30 cm in diameter and 20 kg in weight. The cells of the outer part of the sclerotium are dark and thick-walled, whereas those of the interior are colorless and thin-walled.
The sclerotium contains little water (5–10 percent) but is rich in nutritive substances. Under favorable conditions the sclerotium buds and forms fruiting bodies in ascomycetous and basidial fungi or mycelia with conidia in imperfect fungi. The sclerotium may remain viable for several years. The ergot sclerotium contains several alkaloids, including ergotoxine, ergometrine, and ergotamine, which are used medicinally as parturifacients and antihemorrhagics (to treat uterine hermorrhages).