CALDECOTT AND NORTH: RADIO-SENSITIVITY OF SEEDS 



369 



Immediately after hydration the seeds were plated out in petri 

 dishes and grown for 7 days. At that time individual seedling heights 

 were determined (compare the frequency distributions in Figures 1 

 and 2) and the seedlings were placed in one of three height classes, 

 viz., to 5 cm, 5.1 to 9 cm, and taller than 9.1 cm. The seedlings in 

 each height class were than transplanted and grown to maturity to 

 obtain interchange and mutation data (Figures 3 and 4, Table 1). 



350 r 



Hydroted in presence of 



oxygen ( ) 



nitrogen ( — ) 



II 



12 13 14 15 



.12345678910 



Seedling Height -cm. 

 Figure 2. — Distribution of seedling JieigJits at 7 days from seeds given 

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

 presence of either oxygen or nitrogen. 



It is significant that for those seeds hydrated immediately after 

 X-irradiation (Table 1) the data are not presented in terms of genetic 

 damage in different height classes but rather for the population as a 

 whole. The reason for this is that the distribution of seedling heights 



