CALDECOTT AND NORTH: RADIO-SENSITIVITY OF SEEDS 



371 



350 



5 9 



Seedling Height- cm. 



Figure 3. — Relation of seedling height at 7 days to interchange frequency 

 at microsporogenesis. (Plants grown from dormant barley seeds subjected 

 to 5,000 r of X-rays and stored for 8 days before hydration in the presence 

 of either oxygen or nitrogen.) 



and gnenetic injury under the two conditions of hydration. In this 

 connection, a study was set up wherein seeds were subjected to one 

 of a wide range of doses of X-rays and then immediately hydrated, 

 either aerobically or anaerobically, and planted in the field. Immature 

 inflorescences were collected from the Xi plants and microsporocytes 

 were examined to determine the frequency of interchanges induced 

 in the material (Figure 5). At maturity up to five heads were removed 

 from each plant and the seeds grown to determine the X 2 chlorophyll 

 mutation frequency (Figure 6). 



These genetic data demonstrate that when seeds are hydrated 

 aerobically after X-irradiation there is an exponential relation 



