368 MUTATION AND PLANT BREEDING 



phase of Xi plants that were grown to maturity (7). This laborious 

 procedure was used because it avoided the controversy about the 

 accuracy of using root tip cells for determining interchange frequen- 

 cies (4, 30). Seeding chlorophyll mutation data were obtained on X- 

 populations using the method of Stadler (27). 



Experimental Results 

 Relation of seedling height to genetic injury 



After treatment with 5,000 r of X-rays, a large sample of seeds 

 was divided into four lots. Two lots were immediately hydrated for 

 45 minutes, one in the presence of oxygen and the other in the pres- 

 ence of nitrogen. The remaining two lots were stored over phosphorus 

 pentoxide for 8 days at room temperature. After this period one lot 

 was hydrated aerobically and the other lot anaerobically. 



I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 



Seedling Height-cm. 



Figure 1. — Distribution of seedling heights at 7 days from seeds given 

 5 ,000 r of X-rays and then immediately hydrated in the presence of either 

 oxygen or nitrogen. 



