Cause of tumor formation inNICOTIANAhybrids. Further serological studies. —Additional researches have been carried out about genetical tumors in genusNicotiana.By means of serological procedure the affinity among pairs of species that give rise to tumorous and non-tumorous hybrids has been tested, considering also their phyletic interrelation. Using ion exchange chromatography a qualitative analysis of the total proteins of tumorous and non-tumorous tissue of hybrids and of normal leaves taken from hybrids and their parental species was carried out. Serological analysis of affinity between the species tested gave following results: