Ascospore discharge in the annulate form of Hypoxylon truncatum

Abstract

Ascospore discharge in the annulate form of Hypoxylon truncatum (Schw.:Fr.) J. H. Mill, is preceded by the loss of the peridial wall covering of the ostiolar region. This is accomplished by way of a specialized mechanism which involves hyaline spongy tissue located between the outer amorphous and inner palisade wall layers of the perithecium. The exposed ostiolar projection becomes concealed by terminal bulbous cells of short hyphae that arise from nearby peridial cells. Disintegration of the ostiolar projection occurs concomitantly with the disappearance of these bulbous cells. By this time a large part of the pseudoparenchyma and most of the paraphyses in the centrum have degenerated to form a transparent gelatinous mass. Asci deliquesce and release mature ascospores within the perithecium just prior to ascospore discharge. The ascospores ooze out of the ostiole mixed with the gelatinous material and form either a massive spore ball or a spore tendril.