BOTRYTIS, a minute fungus which appears as a brownish grey mould on decaying vegetation or on damaged fruits. Under a hand-lens it is seen to consist of tiny, upright, brown stalks which are branched at the tips, each branchlet being crowned with a naked head of pale-coloured spores. It is very common, grow ing everywhere in the open or in greenhouses, and can be found at almost any season. It has a bad record as a plant disease. The fungi placed in one genus Botrytis are in part stages in the life-history of members of the genus Sclerotinia. These are char acterized by the possession of a sclerotium, which is a compact mass of fungal filaments from which a cup-like ascophore arises. (See Ascomycetes in article FUNGI.)