THE INFLUENCE OF POST-RADIATION FACTORS ON EFFECTS PRODUCED IN BARLEY 



process and there is no influence of the temperature, contrary to the effect 

 obtained with dormant seeds irradiated simultaneously (see Figure 4). 



Effect of storage after irradiation — In Figure 6 the relative growth of seeds 

 sown after storage for two weeks at room temperature is given as a function 



Figure 6. Dormant seeds irradiated with neutrons and 



X-rays. Relative growth after storage for 6 weeks at 



20° C given as function of relative growth obtained after 



immediate sowing. 



20 ¥-0 60 80 



% Growth at zero time 



too 



of the relative growth of parts of the same irradiated samples sown immedi- 

 ately after irradiation. The storage is found to lead to an increase in damage 

 with X-rays, but not with fast neutrons. The storage effect is relatively 

 greater when seeds of a high water content [i.e. equilibrated with moist air) 

 irradiated and when the seeds are stored at about 25° C. than at about 

 12°C. When germinating seeds are irradiated and afterwards dried again 

 and then stored, no change of the degree of radiation damage is observed. 



CONCLUSION 



Although the data presented (and summarized in Table I) do not suffice to 

 explain the mechanism of radiational action, they provide a foundation for 



Table I 



State of barley seeds 



Dormant, equilibrated to ' 



dry 

 air 



moist 

 air 



Germinating 



Effect on radiation damage {growth inhibition) of : 



lowered growth temperature 



X-rays 



small increase 



large increase 



none 



neutrons 



small 



or 

 none 



storage {esp. high temp. 



X-rays 



small increase 



large increase 



none 



neutrons 



small 



or 

 none 



further work on the biochemical level. The relative absence of post-irradia- 

 tion effects in the case of neutron irradiation indicates that the damage is 

 fixed at the moment of energy absorption, and is in agreement with the 

 finding^ that the neutron damage is confined chiefly to nuclear material. 



288 



