SUMMARYThe haploid chromosome number ofHypoxylon fuscumis 4, based on counts at stages before full pachytene (prepachytene), diakinesis, and metaphases I, II, III. Early synapsis of homologous chromosomes occurs. The nucleolus persists through metaphase, being lost in the cytoplasm following its separation from the organizer chromosome at anaphase. A centriole-astral ray mechanism of spore formation was not conclusively demonstrated. Maturing ascospores normally are uninucleate. Several kinds of aberrant asci and spores are described.