SUMMARYThe somatic chromosome number of 10 varieties of Solanum tuberosum L. has been found to be always 2n = 48; that of Solanum Pearcei Phil. 2n=24. In Solanum pinnatum Cav. the 80% of the metaphases in the root meristems show 2n = 26 chromosomes, two of which evidently smaller than the others. In the remaining 20% of the metaphases aneuploid chromosome numbers (24, 25, 27, 28) occur.Such an aneuploidy has been found to be due to both non congression at methaphase and non disjunction at anaphase.