perithecium

1. (mycology) An ascocarp shaped like a skittle or ball, distinguished by a small pore, the ostiole, through which the spores are released one by one when ripe.Examples: "The Erysiphacae may possibly have given rise to the Laboulbeniales, the only other group in which a single daughter cell of the oogonium is responsible for the asci, and perhaps to the lower Pyrenomycetes also; these, like the Erysiphaceae, have regularly arranged asci, and in Chaetomium fimete the perithecium is without an ostiole."