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does not appear. First page follows. Introduction During an attempt to find a weed reservoir of the western celery mosaic, another virus affecting celery was recovered from one of the weeds tested. Poison hemlock, Conium maculatum L., a common umbelliferous weed, was often found naturally infected with a ringspot virus. The symptoms of ring-spot on celery have been described briefly in a previous paper (Severin and Freitag, 1938).4 Celery plants showing symptoms resembling ringspot were collected in celery fields on several occasions, but attempts to recover virus from these apparently naturally infected plants have failed. The ringspot virus occurs commonly on poison hemlock in the Santa Clara, San Benito, Salinas, and Sacramento valleys of California. Experiments were undertaken during 1936 to determine the symptoms, host range, and insect vectors of the poison-hemlock-ringspot virus. Various phases of its transmission by aphids were studied, including the relative importance of the different species as vectors, transmission during short feeding periods, retention of the virus by aphids, loss and recovery of infectivity by aphids on celery, and ability of aphids to acquire virus from plants after infection. Experiments were conducted on mechanical transmission of the virus. A number of virus diseases that produced ringspot symptoms have been described on the following host plants: Tobacco: (Fromme, Wingard, and Priode (1927)); (Henderson and Wingard (1931)); (J. Johnson (1936)); (E. M. Johnson (1930)); (Price (1936)); (Priode (1928)); (Valleau (1932)); (Wingard (1928)) Potato: (Burnett and Jones (1931)); (J. Johnson (1925); (J. H. Smith (1928); (K. M. Smith (1929), (1931); (Valleau and Johnson (1930)) Tomato: (Bald and Samuel (1931)); (Gardner, Tompkins, and Whipple (1935)); (Samuel, Bald, and Pittman (1930)); (K. M. Smith (1932)) Delphinium: (Burnett (1934)); (Valleau (1932)) Clover: (Henderson (1934)); (E. M. Johnson (1933)) Rose: (Nelson (1930)); (White (1930)) Sugar beet: (Hoggan (1933)) Hyoscyamus niger L.: (Hamilton (1932)) Cabbage: (Tompkins, Gardner, and Thomas (1938)) Dahlia: (Brierley (1933)) Plum and peach: (Valleau (1932)) Peony: (Whetzel (1915)) (Johnson and Valleau (1935)) reviewed the literature on virus diseases causing ringspot symptoms, but without mentioning anyvirus that causes chlorotic or necrotic ring and line patterns on celery.

Poison-hemlock-ringspot virus and its transmission by aphids to celery