Frenching of Tobacco Distinguished from Thallium Toxicity by Spectrographic

Several theories as to the cause of tobacco frenching have been proposed, but each in its turn has been found to be erroneous. Kecently, it has been postulated that frenching is probably a symptom of thallium toxicity. Since the demonstration of the presence of thallium in frenched tobacco tissue in toxic amounts or its absence is essential to an evaluation of the thalhum-toxicity theory, and the quantity of thallium necessary to produce thalhum toxicity under experimental conditions is too minute to be detected by ordinary chemical methods, this theory at first seemed impossible to prove or disprove. However, since spectrographic analysis has been shown by a number of investigators {9, 10, 16y to be applicable to the determination of minute quantities of minerals in plant tissues, the spectrographic method seemed to be applicable to the evaluation of the thallium-toxicity theory. Accordingly, a cooperative study was undertaken in 1937 between the Virginia Agricultural Experiment Station and the Physics Department of the Virginia Polytechnic Institute to determine by spectrographic analysis whether there is any relationship between frenching and thalhum toxicity of tobacco. Preliminary reports on this study have been made by the authors.^