L. EHRENBERG 



different doses of X-rays. The seeds were sown at two different tempera- 

 tures, -|-25° and +12° C. The damage developed is greater at the lower 

 than at the higher temperature. This is in agreement with Gelin's"* findings, 

 that the frequency of chromosomal rearrangements in the root tips is about 

 twice as high in the cold as in the warmth. Figure 3 demonstrates 



Figure 3. Relative growth of seedlings 

 from seeds with 9-3 and 22-0 per 

 cent water, respectively, treated with 

 X-rays and grown at 25° C. ( X ) and 

 12° C. (o). 



28-0 %K0 



further what seems to be a general trend in experiments of this type, viz. 

 that the temperature influence is smaller when seeds of a low water content 

 are irradiated. In Figure 4 a similar experiment, comparing temperature 



100 



20 w eo so 

 fVarmffy, °/cgrou'fh 



WO 



Figure 4. Dormant seeds irradiated with 

 X-)ays and neutrons (■ — ' 8 MeV). 

 Relative growth at 12° C. given as 

 function of relative growth at 25° C. 



100 



80 



\60 



<3 



20 



20 VO 60 80 

 Warmth. % growth 



100 



Figure 5. Germinating seeds [pre-soaked 

 for 24 hours in water) and dormant 

 seeds irradiated with different X-ray 

 doses. Relative growth at 12° C. given 

 as function of relative growth at 25° C. 



effects on seeds irradiated with X-rays and neutrons, is shown diagram- 

 matically : the relative growth at the lower temperature ( + 12° C.) is given 

 as a function of the relative growth at the higher temperature (+25° C). 

 In the case of X-rays, a 25 per cent decrease of the growth in the warmth 

 is found to correspond to as much as 70 per cent decrease in the cold (i.e. in 

 accordance with the result given in Figure 3). For neutron irradiation, the 

 influence of the germination temperature is appreciably smaller. 



In Figure 5 the influence of the germination temperature has been studied 

 for the case of seeds irradiated with X-rays after the start of the germination 



287 



