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does not appear. First page follows. Primula obconica is a popular, attractive, ornamental potting plant which has commonly been found to be infected with a mosaic disease in commercial greenhouses in San Francisco. The losses of infected seedling plants have ranged from 5 to 25 per cent. A study was undertaken on aphid transmission of the mosaic virus of Primula obconica. Tests were made both with species of aphids that breed on this host plant in the greenhouse, and with species that do not. Other aspects investigated include the efficiency in the transmission of the virus by single unfasted, infective aphids. A comparison was made of the transmission of the virus by lots of 20 unfasted, infective aphids with lots of 20 fasted aphids in short infection-feeding periods on a diseased plant. A comparison was made of the symptoms of P. obconica mosaic with those of common-cucumber, celery-calico, and western-cucumber-mosaic viruses. An attempt was made to experimentally infect P. obconica with the ordinary-tobacco-mosaic virus. Tests were made on the susceptibility of this species of Primula to the California-aster-yellows and spotted-wilt viruses. Review of Literature Tompkins and Middleton (1941)4 reviewed the literature on mosaic diseases of Primula species, and reported the experimental host range and properties of a mosaic virus of P. obconica. Since the publication of that paper, other references to virus diseases aifecting the genus have appeared in the literature. (Moore (1947)) lists a mosaic of Primula in his report on diseases of crops in England.

Aphid transmission of a mosaic virus and symptoms of other virus diseases ofPrimula obconica