C. p. SWANSON 



indirect energy transfer. Phase II consequently corresponds to Phase II 

 of Figure 1 where the fate of the potential breaks is considered to be deter- 

 mined, and the influence of oxygen is greater at the left than at the right end 

 of the spectrum of chromosomal damage, as demanded by the data in 

 Table II. 



(3) Phase III — Primary breaks are distinguished from actual breaks only 

 by a time factor, and the transformation may be immediate or only after an 

 interval of time as indicated. The Tradescantia data suggest that oxygen is 

 ineffective at this level, but we cannot be certain that this is true for breakage 

 in other organisms. 



{4) Phase IV — The Tradescantia data again suggest that the fate of actual 

 breaks is not influenced by oxygen, but the possibility is included since it 

 may be important in other organisms. 



ACKNOWLEDGEMENTS 



This paper was uritten at the Institute of Genetics, University of Stockholm, where 

 the author was in residefice as a Guggenheim Fellow. The author wishes to acknow- 

 ledge his indebtedness to Professor Gert Bonnier for the facilities placed at his disposal, 

 and for the many courtesies extended. Figure 2 and the discussions revolving around 

 it are to be considered part of a collaboration with Dr. A . G. Liining, and they are 

 included here with his kind permission. 



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* SwANSON, C. P. ibid, in press. 



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1^ Thoday, J. M. Heredity (Symp. on Chromosome Breakage, Springfield, 111., 

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261 



