The Effect of Ionizing Radiations on the Broad Bean Root. Part III

Abstract

This paper forms part of a series1, 2 which record the results of a quantitative experimental study of one particular biological reaction to a variety of ionizing radiations. The various radiations differ among themselves, particularly in regard to the number of ions formed in a given length of track of the ionizing particles, and it is with this factor that any difference in biological response is probably to be correlated. In this respect neutron radiation occupies an intermediate position, as shown in the following table. An earlier investigation of the lethal effects of neutron radiation on broad bean roots3 showed that the ionization produced by 2·7 million volt neutrons is about ten times as effective as γ-ray ionization in killing the root. Only a small number of beans were irradiated on that occasion; moreover, since that time the technique of dose measurement has been improved. It was therefore considered worth while to irradiate a considerably larger number of beans, using the improved methods. The method of growing broad bean roots, the general effects of radiation, the region of the root tip specially sensitive to radiation, the criteria of death, and the method of treating the mortality data statistically have already been described.1 The roots used in these experiments were between 4 and 10 cm. long at the time of irradiation.