mold, name for certain multicellular organisms of the various classes of the kingdom Fungi, characteristically having bodies composed of a cottony mycelium. The colors of molds are caused by the spores, which are borne on the mycelium. Most molds are saprobes and can obtain moisture and nutriment from fruits, vegetables, jelly, cheese, butter, bread, silage, and almost any dead organic matter. Among the commonest forms is the black bread mold (Rhizopus nigricans), which grows on decaying vegetables and fruits as well as on bread. Some molds, e.g., species of Penicillium, are useful in the preparation of Camembert, Roquefort, and other cheeses. Penicillin and other antibiotic substances are also obtained from molds. A few molds are pathogenic, e.g., those which cause ringworm and other skin diseases and several which cause diseases of plants. Some molds produce toxic chemicals called mycotoxins that can cause serious diseases (see ergot). Some organisms traditionally thought to be mold (e.g., slime molds) have now been placed in the kingdom Protista.
See M. K. Matossian, Poisons of the Past: Molds, Epidemics, and History (1989).