Radiosensitivity and rate of cell division: "law of Bergonié and Tribondeau".

The rate of cell division decreases as tobacco leaves grow, and older leaves grow without any cell divisions. Disks were cut from leaves having differing degrees of cell division at various developmental stages. In the chlorenchy, induced susceptibility to photodestruction of chloroplasts was used to measure sensitivity to gamma radiation as a function of the rate of cell division. The same biological effect can thereby be studied both in dividing and in nondividing tissues of the same morphological and physiological cell types. The radiosensitivities were approximately the same, irrespective of the extent of cell divisions.