THE STRUCTURE AND BEHAVIOR OF THE NUCLEI IN SPORES AND GROWING HYPHAE OF MUCORALES: II. PHYCOMYCES BLAKESLEEANUS

Abstract

Nuclei of the sporangiospores of seven strains and the growing hyphae of five strains of Phycomyces blakesleeanus have been examined in fixed and stained preparations. One strain was found to have unusually large nuclei and has been studied in detail. The nuclei in the sporangiospores consist of Feulgenpositive granules and short filaments in a diffuse matrix. In the ordinary strains the nuclei occur in a narrow range of sizes with their largest diameters around 2 microns. In the spores of the unusual culture the nuclei are of several sizes and many have diameters around 4 and 5 microns.Similar differences are found between the nuclei in growing mycelia. The nuclei in hyphae resemble those of Mucor hiemalis. They consist of a shell of tightly packed granules and filaments of chromatin curving around a relatively large nucleolus. The nuclei divide by elongation followed by constriction. The nucleolus divides at the same time and in the same way and half of it passes to each sister nucleus. The possibility is discussed that the strain with the large nuclei may have had its origin in a spore formed by a germinating zygote and containing both haploid and diploid nuclei. The nuclei of the unusual culture, first examined 3 years ago, have preserved their large size through many cycles of vegetative propagation.