An electron microscope study of maturation and germination of sporangiospores of two species of Rhizopus

Immature sporangiospores of Rhixopus iaigricans and R. sexualis were relatively thin-walled, although thickened longitudinal ridges were already discernible. The position of the nuclei suggested that they had recently divided; the mitochondria were globose and similar to those of vegetative hyphae; the protoplast was surrounded by a thin plasmalemma and con-tained numerous food globules. The endoplasmic reticulum was sparse. Mature spores had a thick wall of reticulate structure and contained large contorted mitochondria. The first visible stage in germination was the formation of an inner cell wall of tangential elements resembling that of the vegetative hyphae and contrasting with the original spore wall. The mitochondria increased in number, probably by division of the large con-torted ones of the dormant spore, and were again regularly globose. The original spore wall became considerably stretched and finally ruptured to allow the germ tube enveloped in the newly formed elastic inner wall to emerge