INDUCED MUTATIONS IN PLANTS 1267 



ficatioii of the germ plasm. Stein reported characteristic modifications 

 of the irradiated plants ("Radiomorphosen") which in general were not 

 transmitted to the progeny. In some instances (49), however, similar 

 defects were noted in the progeny of treated plants, and recent evidence 

 (50) indicates that these may be inherited as if due to recessive gene 

 mutation. 



In the Gramineae several of the economically valuable cereal plants 

 have been used in genetic experimente with X-rays and radium. Barley 

 (Hordeum spp.), oats (Avena spp.), wheat {Triticum spp.), and maize 

 {Zea Mays) have been used by Stadler (38 to 47) and wheat has been 

 used also by Delaunay (10 to 13) and Sapehin (36). 



In the experiments with barley (38, 40, 43, 45a) mutation was induced 

 by seed treatment with both X-rays and radium. In the first series of 

 experiments 53 mutations were found among 2800 progenies tested, while 

 no mutations were found among the 1500 control progenies tested. Since 

 about 90 per cent of the induced mutations could be recognized in the 

 seedling stage, seedling mutations alone were used as an index of mutation 

 frequency in some of the later experiments in which high numbers of 

 mutations were required for significant comparisons. More than 

 800 mutations affecting seedling characters were observed in these 

 experiments. About 95 per cent of these affect chlorophyll characters 

 of diverse types. The remainder include a wide range of morphological 

 abnormalities. Treatment of both dormant and germinating seeds 

 resulted in mutation, but the rate of mutation following treatment of 

 actively germinating seeds was about eight times as great as that follow- 

 ing similar treatment of dormant seeds. In both dormant and germinat- 

 ing seeds the mutation rate was roughly proportional to the total intensity 

 of radiation applied. The frequency of induced mutation was not 

 affected by temperature treatments applied either at the time of irradia- 

 tion or during the period following. X-rays through a wide range of 

 wave-lengths induced mutations of the same general type and at rates 

 approximately proportional to the ionizing intensity of the radiation 

 applied. IMutations were induced similarly by gamma rays of radium, 

 beta rays of radiothorium, and cathode rays. 



Similar treatments applied to common oats and common wheat have 

 little or no effect on the frequency of seedling mutations (42). Common 

 oats and wheat have 21 pairs of chromosomes, while common barley 

 has 7 pairs. Related species of Avena and Triticum with 7 pairs of 

 chromosomes {Avena brevis, A. strigosa, Triticum monococcum) responded 

 to the treatment in the same way as barley. The difference in response 

 between the 7-chromosome and the 21-chromosome species is considered 

 the result of gene reduplication in the polyploid species. 



Induced variations in wheat have been reported by Delaunay and 

 by Sapehin. Delaunay (10 to 13) X-rayed 50 ears of Triticum vulgare 

 albidum, an awnless common wheat, and obtained from the progeny 



