Ultra-thin sections of the rust of Japanese pear (Pyrus serotina Rehder varp. culta Rehder cv. 'Kikusui') infected by Gymnosporangium horaeanum Sydow were examined with an electron-microscope.
Pathogens were recognized in inter cellular space, middle lamella (Figs. 1, 2, H) and the region of the central vacuole of the suscept tissue. Within the central vacuole and the cytoplasmic area, the hyphae are alway sorrounded by single membrane (probably cell membrane of the suscept cell, Figs. 4 5 CM) and with at least a layer of the suscept cytoplasmic area (Figs. 4,5).
The cell of suscept tissue had a central vacuole (Figs. 1-5 V) and a thin peripheral layer of cytoplasmic area. Nuclei (Fig. 8 N), chloroplasts (Figs. 2 CH, 6, 7), mitochondria (Figs. 2, 5, 8 M) and endoplasmic reticula (Fig. 8 ER) were found in the cytoplasmic area. Starch grains and osmiophilic granules were observed in the all chloroplasts and developed lamellar structures of chloroplasts were not recognized. The disintegrations of double membranes were not seen in nuclei, chloroplasts and mitochondria.