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An account is given of an apparently undescribed virus disease. The virus appears spontaneously in the glasshouse affecting tobacco seedlings in the seed boxes. The symptoms on a number of hosts are described. The chief characteristic of the virus is its failure to become systemic in any host plant so far tested. It is, however, occasionally found in the roots of young tobacco plants, usually in the case of those naturally infected. Certain physical properties of the virus have been investigated. Its dilution end-point appears to be about 1:10,000; its longevity in extracted sap is about 20 days, the thermal death-point is 72° C. The virus shows a strong resistance to alcohol, remaining viable in 99 per cent, alcohol for 71 hours so far as tested. It is not known how the virus is transmitted in nature, and no insect vector has as yet been identified. The virus has been transmitted to healthy cowpeas by spraying them with a suspension of the virus by means of an atomiser. By the Elford method of ultra-filtration the particle size is found to be 20–30μμ. The virus is compared with that of the American tobacco ringspot, and methods of differentiating the two are indicated.
Smith et al. (Wed,) studied this question.