The perithecial development ofHypoxylon serpens(Pers. ex Fr.) Kickx in artificial culture is described. Perithecia develop from initials formed within the vegetative mycelium. Perithecial initials include an ascogonium and surrounding envelope. The ascogonium gives rise to ascogenous elements and eventually asci. The envelope gives rise to all sterile structures, including paraphyses and pseudoparenchyma. Features ofHypoxylon serpensperithecia are representative of theXylaria-typecentrum. The relationship of theXylaria-typecentrum with some other centra is discussed.