Ultrastructural observations of ascomal development in Melanospora zamiae

An ultrastructural investigation was conducted on ascomal development in Melanospora zamiae to supplement a previous light-microscopic study, with emphasis on centrum structure and development of the ascogenous system. The centrum of young ascomata prior to initiation of ascus formation showed that the centrum was filled with large, thin-walled pseudoparenchymatous cells with a large, oval, multinucleate ascogonial cell situated in the lower region of the centrum. Ascogenous hyphae developed from the ascogonial cell and in turn formed binucleate cells that developed directly into asci without crozier formation. Synaptonemal complexes were seen in the diploid nucleus of young asci. At the stage where the asci elongated, the centrum pseudoparenchymatous cells appeared deteriorated. Two morphologically distinguishable types of mitochondria were present in cells of various tissues during different stages of ascomal development.