Ultra-thin sections of leaf gall of Thea sinensus infected with Exobasidium vexans were investigated by means of an electron microscope. Materials were fixed with buffered 6.25% glutaraldehyde and post fixation was done by osmium tetraoxide. Dehydration was initiated by 50% alcohol followed by graded series of alcohol and embedd ed in Epon. Sections were cut with glass knives on a Porter-Blum(MT2-B) ultra-microtome and were staind uranyl acetate. Specimens were examined under Hitachi(HU-12) electron microscope operated at 75 KV.
The fungal hyphae were recognized in the inter-cellular spaces, middle lamella, cell walls of the suscept tissue. Cell membranes were not invaginated and the fungal hyphae were not observed within the suscept cells. In the hyphal cells,lipid granules were found, but other organelles were not found. Low electron-dense material was observed in the surrounding part of the hyphae in the inter-cellular spaces. Hypertrophied cell had a large central vacuole and thin peripheral layer of cytoplasm. Electron dense material with osmium tetraoxide during fixation represents a tannin accumulation in the vacuole of the suscept cell. Plasmolysis was not observed and cell membrane was contacted to the cell wall of the suscept. Chloroplast double membranes, grana structures and osmiophilic granules were observed in the chloroplast, but starch grains were not recognized.