THE STRUCTURE AND MODE OF DIVISION OF THE NUCLEI IN THE YEAST CELLS AND MYCELIUM OF BLASTOMYCES DERMATITIDIS

Abstract

The nuclei in the yeast cells and mycelium of Blastomyces dermatitidis were studied in the living state and in fixed preparations stained by various techniques. Yeast cells and mycelium are multinucleate. Interdivisional and recently divided nuclei migrate into the yeast buds. Nuclear migration also occurs from one cell to another via the pores in the septa of elongated yeast cells and mycelium. Interdivisional nuclei in yeast cells and mycelium are composed of a spherical Feulgen-negative central body enveloped by granular Feulgen-positive chromatin. A nuclear membrane has not been observed surrounding living or stained nuclei either in yeast cells or mycelium. During nuclear division the chromatin condenses, then elongates, and finally pulls apart to form two sister nuclei. The role played by the central body during nuclear division is obscure. However, it was noted that during the division of the chromatin the central body did not divide but became progressively smaller and apparently disintegrated in the cytoplasm. New central bodies are formed in recently divided nuclei. Mitotic figures such as a spindle or a metaphase plate have not been observed in any living or stained preparations. Complexes of chromosome-like elements were noted in some hyphae, possibly those associated with conidial-bearing stalks. Counts made of such "chromosomes" in several of these complexes revealed a minimum number of six and a maximum of eight.