Serological Studies of Plant Viruses

The juice from virus-diseased plants contains, in addition to the antigenic constituents of a normal healthy plant, an antigenic fraction which, by the methods employed, is inseparable from the virus itself. This holds true in the case of Tobacco Virus I whether the virus is grown in tobacco or in tomato. This antigenic factor not only accompanies the virus but is specific for a particular virus, in that the antibodies induced by one virus are qualitatively different from those induced by other viruses. 2. Viruses may be freed from the antigenic constituents of healthy plants by several methods of purification. A new method by use of a Seitz filter is described. Regardless of the method of purification, however, it was not possible to separate the virus, as judged by infectivity, from the specific antigenic factor which accompanies it. 3. Close association of the antigenic factor with infectivity and the specific nature of the antigenic fractions accompanying the different viruses strongly suggest that this specific antigenic factor is either the virus itself or a virus-plant-protein complex in which the virus plays the rôle of a haptene. Whatever the true explanation of the nature of the specificity of the reaction may be, the reaction seems to be specific for the virus. The precipitin test should prove to be a valuable aid in the further classification of plant viruses.