398 MUTATION AND PLANT BREEDING 



determined whether or not the added pair of chromosomes carried 

 a factor or factors of economic significance. In cases where some eco- 

 nomic worth was apparent, irradiation studies could be undertaken 

 to translocate a region of the chromosome carrying the gene or genes 

 of significance into the T. vulgar e background of chromosomes. Once 

 this had been achieved it would be a simple matter to eliminate the 

 extra pair of chromosomes from the related genus by backcrossing 

 to T. vulgare and selecting only those progenies with a complement 

 of 42 chromosomes. 



Concluding Remarks 



In recent years a great deal of attention has been given to the use 

 of one acute dose of ionizing radiation for inducing mutations of a 

 beneficial nature. At the same time, relatively little consideration has 

 been directed to other possible approaches, involving both mutations 

 and chromosome structural modifications, which would appear to 

 have great potential promise. The present report is an attempt to 

 emphasize proved and theoretical considerations which suggest that 

 effectively utilized ionizing radiations will likely become of increasing 

 significance to the applied geneticist. 



References 



1. Adams, J. D., and Nilan, R. A. 1958. After effects of ionizing radia- 



tion in barley: II. Modification by storage of X-irradiated seeds 

 in different concentrations of oxygen. Radiation Res., 8: 111-122. 



2. , , and Gunthardt, H. 1955. After effects of ionizing 



radiation in barley: I. Modification by storage of X-rayed seeds in 

 oxygen and nitrogen. Northwest Sci., 29: 101-10S. 



3. Alper, T. 1956. The modification of damage caused by primary 



ionization of biological targets. Radiation Res., 5: 573-586. 



4. Caldecott, R. S. 1955. The effects of X-rays, 2 Mev electrons, thermal 



neutrons, and fast neutrons on dormant seeds of barlev. Ann. Neiu 



York Acad. Sci., 59: 514-535. 

 5. . 1958. Post-irradiation modification of injury in barley — its 



basic and applied significance. Proc. 2nd Intern. Conf. Peaceful 



Uses of Atomic Energy. New York: United Nations, 27: 260-269. 

 6. and Smith, L. 1952. The influence of heat treatments on 



the injury and cytogenetic effects of X-rays on barley. Genetics, 37: 



136-157. 



