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

Abstract

Histological studies were made of roots fixed 2, 4, 6, 8, and 10 days after exposure to 143 r of X radiation. The terminal 3·5 cm. of root was cut into three roughly equal portions and fixed in Bouin's solution. Longitudinal sections were cut 20μ thick, and axial, or nearly axial sections were selected for study and stained by Feulgen's method. Many important changes in the cells of the meristematic region take place within the first two days after irradiation. Indeed, if we are correct in our interpretation of the process of root growth retardation by radiation, the most important primary injuries develop during this period. Thoday's observations (Part IX of this paper) show that the peak manifestation of chromosome aberration occurs during the first ten hours, even in roots exposed to the highest dose of X radiation used in his experiments, which would certainly have greatly delayed the entry of cells into mitosis. We have been concerned to discover how the injuries observed by Thoday can be related to the histological changes observed during the period of peak reduction of growth rate several days later. The changes in the disposition of mitotic and resting cells resulting from exposure to 143 r of X rays is shown in Fig. 15. The curves depict the percentage of cells seen in all phases of mitosis averaged over the complete cross section as a function of distance from the root tip at different times after irradiation.