ABSTRACTSepta of the ascomycete partners of mycorrhizal silver fir (Abies alba) were investigated. Septal pores are accompanied by few Woronin bodies and are usually plugged by dark-staining, membrane-bound material. In one mycorrhizal type, groups of vesicles with electron-dense contents commonly are associated with the pores. They seem to originate from a Golgi-like endomembrane system and appear to contribute to the septal pore plug. In another ascomycete mycorrhiza, plugging of pores by Woronin bodies occurs at septa separating vigorous and dying fungal cells. Pores plugged by Woronin bodies are usually sealed by the vigorous cell with a layer of electron-translucent wall material. Characters of ultrastructure and anatomy suggest that the Ascomycetes belong to the Tuberales or Pezizales.