96 



MUTATION AND PLANT BREEDING 



y RAYS 



■@ e 



-©- 



X RAYS 



SOFT 

 X RAYS 



a PARTICLES 



Figure 14. — Separation of ion clusters in relation to the size of virus 

 particles 27 myc in diameter. After Gray (57). 



molecules of the tissue, i.e., the higher the linear energy transfer 

 (LET). (See Section I.) 



The biological consequences of variations in LET have been 

 studied for many years and are of great importance in radiogenetics. 

 Certain qualitative differences and many quantitative differences in 

 cytogenetic responses can be attributed to differences in the ioniza- 

 tion density of the radiation used. The relative biological effect (RBE) 

 for many responses increases with increasing LET but may go through 

 a maximum (Figure 15) and then decrease. This saturation effect can 

 be explained, in some cases at least, by the production of surplus 



