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1 IResults obtained from the germination of mature zygospores of Rhizopus stolonifer support the hypothesis that normal meiotic processes operate in the sexual cycle of this fungus. The mating-type allele and a second allele, sul, segregated independently. When immature zygospores were germinated no such regularity was observed, but recombinant auxotrophic genotypes were recovered indicating a predormancy meiosis. However, prototrophic recombinants were not found. Bisexual heterokaryotic strains were also recovered from immature zygospore germinations but were auxotrophic. When cultures were obtained from outgrowths of both suspensors of a single zygospore the genotypes were not always those of the respective parents. This suggests the occurrence of nuclear movement from the immature zygospore to the suspensor cells.

The progeny resulting from crosses between Rhizopus microsporus and R. rhizopodiformis were analysed for a number of morphological characters and the ability to produce either zygospores or azygospores. The interspecific crosses resulted in relatively stable cultures exhibiting intermediate morphology and producing only azygospores. The results suggest that the progeny are diploid or aneuploid, which leads to heterozygosity, particularly with respect to mating type.