Fig. 3. Phenotype of midA^- during development. (A) Wild-type and mutant cells were deposited in nitrocellulose filter for development under overhead light at 22°C. The underlying cellulose pad was soaked with water and representative photographs are shown at the indicated times. Under these conditions (without buffer) the mutant cells were unable to form fruiting bodies. Bars, 0.5 mm. (B) Cells were deposited on filters as described before, but in this case the underlying pad was soaked with PDF buffer to induce direct culmination. Under these conditions midA^- is able to culminate after a period of migration. Notice the presence of slime-sheath trails left behind at the base of the fruiting bodies. Bars, 0.5 mm. (C) Spores taken from 15-day-old fruiting bodies and photographed with a phase-contrast microscope. Mutant cells are rounder and less refringent than wild-type cells. Bar, 10 µm.