CALDECOTT AND NORTH: RADIO-SENSITIVITY OF SEEDS 403 



Caldecott: They could be, but it is very unlikely. 



Dermen: Does AA AA AA constitution represent an autoploid or an 

 amphiploid condition? 



Caldecott: It could represent either, providing one was dealing with 

 bivalent pairing. 



Garber: On what basis are allopolyploids and allopolyploids to be 

 distinguished when individual loci are involved? When the term "diploid- 

 ization" is used, is it restricted to converting replicate loci (autoploids) 

 to only two loci for alleles or may it be used for converting any poly- 

 ploid to a strictly bivalent type? 



Caldecott: As I am working with allopolyploids I have not concerned 

 myself with this problem. The distinction will, of course, be related to 

 whether or not there is bivalent or quadrivalent pairing. The use of 

 the term diploidization should be generally taken to imply the conver- 

 sion of replicate genes, those which govern the same order of biochem- 

 ical function, to one of their allelic forms so that, after selecting appro- 

 priate genotypes out of F 2 hybrids between the mutated stock and the 

 progenitor, genotypes can be obtained which, when crossed with one 

 another, will give 3:1 ratios. 



Gabelman: Seedlings produced from seeds irradiated with low levels of 

 X-radiation (less than 1,500 r) occasionally show stimulation in growth. 

 What is the nature of this stimulation? How do you rationalize this 

 potential stimulatory effect in evaluating and interpreting the response 

 of seedlings to higher levels of irradiation as used in your experiments 

 on radiosensitivity? 



Caldecott: I am not aware of any reproducible studies with barley 

 seeds that show that low doses of ionizing radiations cause a stimulation 

 in growth, albeit this may be true in other species. I do not know what 

 the nature of the stimulation is in other species and, because it does 

 not exist in barley, have not had the problem of rationalizing the effect 

 with the data presented. 



Osborne: As Doctor Caldecott has mentioned, the Brookhaven coop- 

 erative Program has for some years included preradiation stabilization 

 of seeds at controlled relative humidity which, I believe, is 65 per cent. 



