THE LIFE CYCLE OF PEDIASTRUM SIMPLEX(1)

A sexual cycle and a newly discovered mode of asexual reproduction by azygotes arc described for Pediastrum simplex. In the sexual cycle isogametes from colony cells fuse in pairs, develop into zygotes, which grow and divide, producing motile cells which become angular polyeders. Polyeders may divide internally to form 4-celled colonies, or they enlarge, cleave, and produce zoospores or nonmotile cells. Zoospores are released in vesicles, swarm, adhere to each other, and form, flat colonies I cell thick. The nonmotile cells adhere to each other, enlarge, break out of the polyeder, and become spheroidal colonies. In the asexual cycle, nonfusing gametes, and motile cells derived from colony cells, become 4-spined azygotes which enlarge, divide internally, and release motile cells developing into polyeders. These polyeders develop further like those from zygotes.