Perithecial ultrastructure and formation of ascospores of Ceratocystis stenoceras (Robak) C. Moreau

Fine details of perithecial morphology and aspects of ascospore formation of Ceratocystis stenoceras (Robak) C. Moreau are shown in electron micrographs of ultrathin sections. The envelope of the perithecial body proper consisted of two zones of cells which differed morphologically one from another. Loose aggregates of small electron opaque particles were present at the outer wall surface which may be responsible for the characteristic pigmentation of the body and neck. Cells comprising the ostiolate neck may arise as modifications of spindle-shaped cells of the inner zone of the perithecial envelope. Cell walls of the neck and of zones 1 and 2 may be composed in part of periodic acid-reactive polysaccharide. The perithecial envelope and ascogenous cells were separated by a band of several parallel, double-layered membranes which may function in some manner with biosynthetic activities of ascospore production. In general, the mechanics of ascospore formation by C. stenoceras were in most ways in agreement with recent reports of ascospore outogeny in other ascomycetous fungi. Mature ascospores were somewhat lenticular in shape and the outer space wall was finely sculptured.