Any of about 500 species of primitive organisms that contain true nuclei and resemble both protists and fungi (see fungus). Originally grouped within the kingdom Fungi, some classification systems consider slime molds to be in the kingdom Protista. They typically thrive in dark, cool, moist conditions such as on forest floors. Bacteria, yeast, molds, and fungi provide the main source of slime-mold nutrition. The complex life cycle of slime molds, exhibiting complete alternation of generations, may clarify the early evolution of both plant and animal cells. In the presence of water a tiny spore releases a mass of cytoplasm called a swarm cell, which later develops into an amoebalike creeping cell called a myxamoeba. Both swarm cells and myxamoebas can fuse in sexual union; the resulting fertilized cell, or plasmodium, grows through nuclear division and forms a spore case, which, when it dries, disintegrates and releases spores to begin the cycle again.
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In manufacturing, a cavity or surface in which a fluid or plastic substance is shaped into a desired finished product. A molten substance, such as metal or plastic, is poured or forced into a mold and allowed to harden. Molds are made of various materials, depending on the application; sand is frequently used for metal casting, hardened steel for molds for plastic materials, and plaster for various purposes. Seealso ingot, patternmaking, tool and die making.
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