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Electron microscopy of pea (Pisum sativum L. cv. English Sabre) leaf cells, infected with three strains (N, S and O) of red clover mottle virus, revealed membranous inclusions characteristic of many comoviruses. The inclusions contained membranous vesicles with fine fibrils, osmiophilic globules and microbodies. The inclusions were not present in dark-green regions of systemically infected leaves (strains N and S). Membranous structures were also seen inside a few nuclei. In the chloroplasts of chlorotic regions of systemically infected leaves (strains N and S) phytoferritin was frequently observed. Chloroplasts in cells infected with strain O had no phytoferritin crystals, but were deformed by very large starch grains. Cell wall modifications were common in mesophyll regions infected with all three strains. Virus-like particles were found in all cell types, scattered or in crystals but not in the aggregated form in dark-green regions of systemically infected leaves (strains N and S).