A protoplasmodium of Echinostelium minutum de Bary forms a single fruiting body consisting of a globose mass of whitish spores mounted at the apex of a tapering acellular stalk within 24 to 48 h of the time that it is deprived of a microbial food supply. Sporulation is normally completed within [Formula: see text]. Phase-contrast microscopy indicates that a single, synchronous, intranuclear division occurs during the progressive, centripetal cleavage of the sporangium. This contention is supported by the observation that the number of uninucleate protospores is invariably twice the number of dividing nuclei present in the immature sporangium. Binucleate protospores are occasionally formed by the incorporation of nondividing, pycnotic nuclei.