Ultrastructure of the ascospores of some species of the Torulaspora group.

Development and germination of the ascospores in species of the Torulaspora group of yeasts have been described. Most species had warty spores which, in sections, showed a dark outer layer consisting of the outer unit membrane of the prospore wall and a layer underneath formed at an early stage of development of the spores. In mature spores the light inner layer of the wall was delimited at the outside by a thin dark layer. The warts often contained dark material. The ascospores of two Pichia and three Debaryomyces species were studied for comparison; they differed in sections from the Torulaspora spores. The taxonomic implications of the ultrastructural observations have been discussed.