As for the seed transmission of tobacco mosaic virus, most investigators denied the facts under the existing condition, though some of them proved the existence of the virus in the seeds by inoculation experiments and microscopical observation. After considering the copper-sulphate reaction test the writers conclude that the virus exists positively in tobacco seeds, though the seedling has no active virus. The seeds from the virus-affected radish seems to have the virus in small quantity and the seedlings from the diseased seeds have no active virus. The seed transmission of the mosaic virus of tobacco and radish is not to be worried about.