370 



MUTATION AND PLANT BREEDING 



Table 1. — Height of Seedlings at 7 days After 5,000 r Irradiation in Relation to 

 Survival, Interchange Frequency, and Mutation Frequency. * 



*Nonirradiated control populations evidenced no interchanges in 383 Xi spikes and an X? 

 chlorophyll mutation frequency of 0.001 mutant seedling per 100 X? plants. 



about the mean was close to normal (Figure 1). Accordingly, too few 

 seedlings fell in either the tall or short height classes to give a reliable 

 estimate of the injury in those classes in comparison with those which 

 fell within plus or minus one standard deviation of the mean. 



From the data presented it is apparent that there is a good 

 correlation between the extent of injury, as measured by seedling 

 height, and the degree of genetic injury as measured both in terms 

 of mutations and interchanges. It is also apparent (Table 1) that 

 populations of individuals can be selected from seeds that have been 

 X-rayed and stored which evidence no increase in genetic injury 

 resulting from storage. 



Relation of oxygen to manifestation of genetic injury 



The demonstration that post-irradiation hydration in the pres- 

 ence of oxygen resulted in greater seedling injury to dormant seeds 

 than post-irradiation hydration in the presence of nitrogen (5, 10) 

 necessitated a critical analysis of the relation between dose of X-rays 



