Investigations have been carried out on nornicotine content in N. glutinosa during the ontogenetic development of the plant. It has been stated that a 4 weeks old plant does not yet contain this alkaloid, which appears in the leaves of older plants. Young leaves even on the flowering plants do not contain nornicotine. By means of chromatographic method the occurrence of an unknown alkaloid, connected with the presence of nornicotine, has been stated. For this reason the mechanism of the demethylation process of nicotine has been discussed in this paper and a hypothesis has been put forth, that the resistance of. N. glutinosa against the tobacco mosaics is due to the type of oxidation - reduction processes which are essential also for the nornicotine formation.