The cellular slime molds are designated as the order Acrasiales within the phylum Myxomycophyta. Although several genera and many species have been described, the bulk of current investigations have been carried out with Dictyostelium discoideum. This species has a particularly interesting and well-defined morphogenetic sequence and constructs fruiting bodies under a wide variety of environmental conditions. Two related species, Dictyostelium mucoroides and Dictyostelium purpureum, have also benn utilized. A member of another genus, Polysphondylium pallidum, has gained prominence as the first cellular slime mold to be cultivated axenically on defined media (M. Sussman, 1963; Hohl and Raper, 1963). However, as P. pallidum constructs fruiting bodies more slowly than D. discoideum and more fastidiously, the latter has been the species of choice for growth either in association with bacteria and more recently, axenically, (Sussman, 1966; Sussman and Sussman, 1967). A partial listing and classification of the more common slime molds appears below in Table 1.