For many years Professor KOLLER has possessed an international reputation in the fields of cytogenetics and karyology, both in their fundamental aspects and in their relation to the problems of tumour causation, especially to the role of heteromromatin, and few men have made a greater contribution. The role of the mromosome complex in carcinogenesis has exerted a natural fascin- ation for many decades, but there can be little doubt of the great advances in know- ledge and understanding whim have accrued of recent years. Although it is probable that the key event in the inception of particular...