Chromosome studies of Allium tuberosum and A. cepa were made from one month to eighteen months old calluses. Different types of chromosomal variations like aneuploid number ranging from 28 to 31, tripolarity, lagging, micronuclei, haploid number etc. were noted in A. tuberosum, whereas in A. cepa the cells showed high chromosome numbers such as 32, 64 or more. The normal chromosome number (2n=16) occurred rarely. The selective pressure of the culture media may have led to the manifestation of the genetic control of differential response to chromosome behaviour and growth in the two species of the same genus. © 1980 Springer-Verlag.