DICTOSTELIUM DISCOIDEUM
This species hormone secretion is very similar to plants, but instead of producing a fruiting body a large rounded cyst is formed which, after a series of cytological events (now believed to be fertilization and meiosis), produces a mass of postconjugation amoebae encased in a thick, spherical cellulose wall. It is known that certain environmental conditions, notably darkness and an excess of surface water, favor the formation of macrocysts. There is excellent evidence that some species are heterothallic, and macrocysts are only produced where the amoebae of the two mating types are present. Here we show in Dictyostelium discoideum that, if the opposite mating types (NC-4 and V-12) are put on opposite sides of a dialysis membrane, macrocysts always form among the V-12 amoebae and their formation is induced by a substance that diffuses through the membrane from the NC-4 amoebae.