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does not appear. First page follows. Introduction One of the viroses found in the course of the investigations of aster yellows on perennial delphiniums (4)3 proved to be transmissible by juice inoculation and showed symptoms resembling those of calico on celery. Calico was reported by Severin and Freitag in 1935 (5). In a later paper (6) they described and figured the symptoms of the disease. But the disease has not hitherto been reported on delphiniums or any other species of the family Ranunculaceae. An investigation was accordingly undertaken to determine whether one of the naturally occurring viroses of perennial delphiniums was caused by the celery-calico virus. Studies were made of the variable symptoms of the disease on this host plant, the incubation period of the disease, the recovery of the virus, and the vectors. A number of hybrids and horticultural varieties of perennial delphiniums were tested for susceptibility to celery calico. A few other host plants of the virus are reported in this paper. Delphiniums in the field in California were found to be frequently infected with more than one virosis—as, for example, with aster yellows and the disease reported in this paper. This situation greatly complicates the problem, especially since the symptoms of these viroses are extremely variable, even when they occur singly. Little progress can be made unless multiple viruses can be separated, and attempts were therefore made to work out methods for doing this in delphinium and also in tomato. Much confusion in the literature dealing with delphinium viroses is caused by the failure of some plant pathologists to recognize and separate multiple viruses in naturally infected plants. Heald and Burnett (2), working with delphiniums infected with what they called “stunt” (aster yellows) (4), reported that some of the symptoms were reproduced by juice inoculation to healthy transplants and seedlings grown in the greenhouse, but that the inoculated plants did not develop the proliferated inflorescence and virescence shown by the naturally infected plants.

Celery calico on perennial delphiniums and certain other host plants