SUMMARY
Perithecial development of Chaetomium funicolum is initiated with the formation of a sessile ascogonial coil formed as a specialized hyphal branch from vegetative hyphae having uninucleate cells. Cells of the coil are uninucleate or binucleate and become enveloped by hyphae formed from the base of the coil and from adjacent hyphae. Growth of the perithecium results from divisions and enlargement of the surrounding cells. The ascogenous hyphae develop from the ascogonium and give rise to a conical hymenial layer. The perithecial cavity forms from differential growth of the surrounding tissues and the deliquescence of the cells in the region above the ascogonium and ascogenous hyphae. No paraphyses are formed. A meristematic region in the apical portion of the developing perithecium gives rise to an ostiole lined with periphyses. The ascogenous hyphal cells are binucleate and give rise to typical croziers. The asci develop in the preformed perithecial cavity. The mature asci deliquesce, releasing mature uninucleate ascospores within the cavity. This type of development is typical of the species of Chaetomium studied.