Ultrastructure of the ascospore wall in Pezizales (Ascomycetes)—I. Ascodesmis microscopica (Crouan) Seaver and A. nigricans van Tiegh

The development of wall layers and ornamentation of ascospores is studied with the electron microscope in Ascodesmis microscopica (Crouan) Seaver and A. nigricans van Tiegh. In both species a primary and a secondary wall are formed in succession. The primary wall differentiates into two layers, an inner endospore and an outer epispore. The secondary wall gives rise to patterns of ornamentation and is composed of membranous structures in a homogeneous matrix; the epiplasm seems to be involved in its formation. The reported differences in the development of ascospore ornamentation between these two species must be denied. Only the final patterns of ornamentation are different.