The Relative Biological Effectiveness of Tritium β-Radiation with the Broad Bean Root (Vicia faba) as a Test System

Beans used in this study were Sutton's Exhibition Longpod broad beans. They were obtained from Sutton and Sons, Ltd., Reading, England, and were genetically the same as those used by Gray. With three exceptions, the methods used for bean root culture in the present study were the same as those described by Gray and Read (2). Two culture tanks with bean capacities of 80 and 96 beans, respectively, were used. The tanks were provided with a constant flow of water at a temperature of 20 + 3oC throughout the year, and each tank was covered with a Lucite lid to keep the relative humidity directly over the beans constant and somewhat higher than that of the laboratory. The indicator of radiation effect on the apical cell mass of the primary root was reduction or cessation of root elongation, and the criterion for death was cessation of root elongation for 4 consecutive days. A preliminary study was desirable to determine the sensitivity of the bean root to