DEVELOPMENT OF THE PERITHECIUM IN GNOMONIA COMARI (DIAPORTHACEAE)

Perithecia of Gnomonia comari (Ascomycetes) mature within 14 days on cornmeal agar under continuous fluorescent light at 25 C. The perithecium is initiated by a coiled, multicellular ascogonium. Branches from somatic hyphae surround the ascogonium. This hyphal envelope early differentiates into two regions: a centrum of pseudoparenchymatous cells and a peripheral wall of more elongated, flattened cells. The wall produces a long, ostiolate beak by eruption of a column of hyphae from the inner layers at the apex; the cells gradually become thick-walled and brown from the peripheral layers inward. Proliferations from the ascogonial cells near the center of the perithecium form a bowl-shaped mass of ascogenous hyphae which expands centrifugally until it appears in section as a crescentic layer across the middle of the centrum. The centrum pseudoparenchyma above this incipient hymenium disintegrates, and short abortive paraphyses extend upward from the subhymenial pseudoparenchyma into the resulting cavity. The paraphyses disintegrate as the asci develop among them. The hymenium gradually pushes downward into the disintegrating subhymenial pseudoparenchyma until it rests on the perithecial wall. Maturing asci become detached from the hymenium, fill the perithecial cavity, and pass through the ostiole. At the tip of the beak they discharge their ascospores forcibly. Diaporthaceae with abortive paraphyses may occupy an intermediate position in a series leading from forms (Gaeumannomyces graminis) with long delicate paraphyses resembling those in the Sordariaceae to forms (Stegophora ulmea) in which the centrum is entirely pseudoparenchymatous.