Development and Cytology of Monosporascus cannonballus

Abstract

Development of the centrum in Monosporascus cannonballus is of the Xylaria type. The perithecium begins development as a curved, multinucleate branch; the ascogonium, from an assimilative hypha. The ascogonium coils, becoming looser as it elongates. Ultimately it is septate, and each segment has one to several nuclei. Branches from the parent hypha and probably from neighboring hyphae develop to cover the ascogonium. These covering hyphae give rise to the perithecial wall cells and to the plectenchyma of the centrum. Paraphyses, apically free from their inception, develop from the plectenchyma before asci are produced. Ascogonial segments give rise to short ascogenous hyphae, which produce croziers terminally. Asci arise from the croziers. After karyogamy and precocious synapsis, two meiotic divisions are followed by a mitotic division. The haploid chromosome number is eight. Some or all of the eight nuclei formed are incorporated into the single ascospore, the remainder being visible in the residual cytoplasm. One or more later mitotic divisions take place within the spore. The single-spored asci are released through a rupture within the periapical ring of the ascocarp and collect in a drop of liquid above the rupture. A portion of the ascus wall breaks down and the spore is released through it, or the entire wall simply dissolves. In either case, the wall dissolves before the drop of liquid disappears.