Anisogramma virgultorum, a pathogenic Ascomycete on Betula pubescens. A sexual form of this Diaporthaceous fungus, consisting only of isolated perithecia was found on the youngest twigs. It is compared with the stromatic form which is more frequent. The systemic disease caused by this organism is expressed by a necrosis and the development of canker-like growths. Perhaps, because of unsuccessful isolation and cultural development, the fungus is an obligate parasite.