TEM study of wound-induced vessel occlusions in European Ash (Fraxinus excelsior L.)

Vessel occlusions in branches of Fraxinus excelsior L. were investigated by means of transmission electron microscopy. The vessel occlusions are fanned by exudates released from adjacent ray and axial parenchyma cells through the intact pit membranes. initial stages mostly display balloon-like structures protruding from the pit aperture into the vessel lumen. These inclusions possess a very electron dense outer membrane and dispersed exudates in their interior. Therefore, the vessel occlusions in F. excelsior do not represent true tyloses.