378 



MUTATION AND PLANT BREEDING 



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 20 

 15 



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[] Heot * I5,000r + oerobic hydrotion (x = 7. 6 cm.) 

 Heot * I5,000r ♦ onoerobic hydration (x = 11.4 cm.) 



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] Heot + I5,000r t 48hrs. storage - oerobic hydrotion (x=8 5cm.) 

 Heot + I5,000r + 48 hrs. storage + anaerobic hydration (x = 1 1.0 cm.) 



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6 7 8 9 10 



SEEDLING HEIGHT (CM) 



12 



14 



15 



Figure 10. — Elimination of sensitivity to storage but not to oxygen result- 

 ing from a pre-irradiation temperature treatment at 75°C. 



parts B and D). Third, while pre-irradiation heat treatment elimi- 

 nated storage injury, it did not modify the sensitivity of the seeds to 

 aerobic hydration, even when they were stored for 48 hours before the 

 initiation of hydration (Figure 10). This particular observation is 

 considered to be of especial significance and will be dealt with in the 

 discussion. 



Post-irradiation temperature extreme and oxygen and storage 

 effects. — The demonstration that the injury to seeds could be 

 increased by storing them at room temperature after X-irradiation 

 emphasized the need to determine to what extent the injury progres- 

 sion, as a function of time, was temperature dependent. To elucidate 

 this problem, an extensive two phase study was set up. In the first 

 phase seeds were irradiated and then immediately stored at one of 

 three temperatures (—78° C, 20° C, and 85° C) for different periods of 

 time before they were hydrated either aerobically or anaerobically 

 (Figure 11 A). In the second phase, after X-irradiation, the seeds were 



