(f) Sensitivity varies with mitotic stage (Figure 9-4). Although there 

 is some controversy over which stages are most sensitive, there seems 

 Uttle doubt that dividing cells are more sensitive than nondividing ones, 

 with early interphase being least susceptible (Sparrow. 1951). 



Jk ^ 



^irf^ 



fa) 



(b) 



Figure 9-2. (a) Photomicrograph of First Meiotic Anaphase Chromo- 

 somes of Trillium erectum; (b) Drawing Illustrating the Configuration of a 

 True Two-Side-Arm Bridge. Strands indicated in the bridge are half chro- 

 matids. Plant irradiated at diakinesis with 25 r of X Rays. (From Wilson, 

 G. B., Sparrow, A. H., and Pond. V.. 1959. "Sub-Chromatid Rearrangements 

 in Trillium erectum. I. Origin and Nature of Configurations Induced by 

 Ionizing Radiation," Am. J. Botany, 46, Fig. 2, p. 310.) 



MODIFICATION OF RADIATION EFFECTS 



The question of modifying radiation effects, especially in the direction 

 of minimizing them. is. of course, of practical importance, and conse- 

 quently has received considerable attention. So far. although sensitivity 

 can be modified in both directions by a variety of conditions, there is no 

 real understandins of the mechanism involved. In general, conditions 



RADIATION CYTOLOGY / 197 



