The distribution of gametangia on gametophores ofPhyscomitrella (Aphanoregma) patensin culture

Gametangial distribution patterns on gametophores of Physcomitrella (Aphanoregma) patens were studied. Plants were grown axenically under controlled laboratory conditions. Some gametophores produced clusters of archegonia at their apices or in the axils of their uppermost leaves. Of these gametophores, some possessed a few antheridia located at the periphery of the archegonial clusters. Other gametophores produced apical and axillary antheridial clusters unadulterated by archegonia. Thus, this P. patens isolate, ‘maintained in culture since 1962, is paroicous or autoicous depending upon which gametophores are considered. Typically, filiform paraphyses were associated with archegonial clusters and clavate paraphyses with antheridial clusters. Archegonia, solitary or in clusters, also developed from internodal surface cells of the gametophores. Such ectopic archegonia had no associated paraphyses. Many immature sporophytic stages were noticed within archegonia but their development into mature sporophytes occurred only rarely. A possible explanation for the truncation of sporophytic development is discussed.