The Ultrastructure of Meiosis in Three Species of Physarum

Abstract

Three spp. of Myxomycetes were investigated with the electron microscope to determine the position of meiosis in these spp. Synaptinemal complexes occur in the nuclei of spores about 20 hours past the cleavage stage in Phvsarum flavicomum, P. polycephalum, and P. globuliferum, indicating that meiosis in these 3 spp. occurs in the spore, instead of prior to spore cleavage. Nuclear division in P. flavicomum is characterized by an intranuclear spindle and by the absence of centrioles at the poles. After meiosis in this sp., all but one of the 4 resulting nuclei degenerate, leaving the spore uninucleate and presumably haploid. Two basal bodies appear within the spore after meiosis.