Spores of Fuligo septica (L.) Weber were studied by light and electron microscopy to determine structural changes during germination. Light microscopic observations indicate that few changes occur prior to protoplast release; however, electron microscopic observations show that a number of changes occur within the protoplast before emergence. An ovoid nucleus becomes irregular and lobed; smooth, cisternal endoplasmic reticulum develops; and concurrent development of dictyosomes and centriole occurs. The dictyosomes and centriole are localized in juxtanuclear sites, and the proximal cylinder of the centriole differentiates into a basal body of a future flagellum. When the spore case ruptures, the inner layer of the wall disappears and the nucleus reverts to its original ovoid form. The protoplast emerges through a wedge-shaped split in the wall and gradually develops into a flagellated cell or, sometimes, a myxamoeba. Simultaneously, contractile and food vacuoles develop, the cisternal endoplasmic reticulum becomes ribosome-coated, and a flagellum develops from the basal body. / Science, Faculty of / Botany, Department of / Graduate