The Effect of Ionizing Radiations on the Broad Bean Root

Abstract

Broad bean roots have been irradiated with α particles by immersion in radon solution. Tips were fixed three hours afterwards and the number of cells seen in mitosis compared with control roots. When the logarithm of the percentage residual mitosis is plotted against the dose, the points define a straight line. These results are compared with similar results obtained previously with neutron and γ rays. The ratio of the slopes of the neutron and α ray lines is the inverse of the ratio of the linear ion densities, suggestive of an effect brought about by a single recoil proton or α particle, but this explanation is not pressed owing to the lack of supporting evidence. The relative efficiencies of γ rays, neutrons, and α rays in reducing the number of cells seen in mitosis in the bean root three hours after irradiation are 1 : 2·1 : 0·6, whereas the corresponding figures for the lethal effect are 1 : 9 : 9.