Sclerotia
(from skleros, hard). Small, hard bodies, produced by many Fungi belonging to various groups. They exhibit variations in size, colour, and form, but agree in being made up of very closely interwoven mycelium. The outer layer of the Sclerotium is peculiarly dense, and is formed of hyphae so adherent to one another, and with so many cross walls, as to resemble true parenchyma in appearance. Sclerotia vary considerably in size, from the minute S. cepaevorum (which gives rise to Mucor subtilissimus on Onions), resembling a grain of gunpowder, to the size of a large pea in the Sclerotia of some Agarics. They are usually round or oval but may be irregularly lobed or elongated, as in Ergot of Rye. Many are black, or nearly so; others are brown, dull yellow, or white. By their texture, they are fitted to withstand extremes of temperature, and of drought or moisture, better than ordinary mycelium; and it is by means of them that many Fungi are preserved through the winter. A considerable number of Sclerotia make their appearance only on dead parts of plants in a state of decay, e.g., the very common S. semen (like a small pea, at first white, then changing to black), which produces Typhula; or in dung, e.g., S. stercorarium, from which Coprinus stercorarium is developed. But several are formed on living plants. Among these are the following: In Potato stems, the Sclerotium from Peziza postuma is produced; on most herbaceous stems S. durum appears in long, black ridges or warts, from which arises a mould (Polyactis cinerea), followed, after a time, by Peziza Fuckeliana; S. cepaevorum, which produces Mucor subtilissimus on Onions; S. clavus, the Ergot of grasses, from which Claviceps purpurea is developed; and a Sclerotium which fills the berries of Vaccinium Myrtillus, and gives origin to Peziza (Sclerotinia) baccarum. Sclerotia are not themselves a cause of disease in plants, but are organs by which disease-producing Fungi are propagated. When any cultivated plants are attacked by Fungi that produce Sclerotia, the only safe method of treatment is to burn all parts that bear the latter, to prevent the spread of disease the following year.