time, produced remarkable results. Irradiation 

 increased the frequency of mutations by 17. 1%. 

 These were chromosomal aberrations as a con- 

 sequence of which there developed various mor- 

 phological changes, which received specific 

 names. In addition, among the offspring of the 

 irradiated plants two gene mutations were ob- 

 served: "albino" and "swollen. " The latter had 

 thick, swollen, shiny stems and stalks, thick 

 leaves, and dwarf size. 



A second investigator who began to experi- 

 ment with the action of X rays on plants and who 

 confirmed Muller's results was Stadler. In a 

 whole series of papers (1928, 1929, 1930, 1931, 

 1932, and 1933), he published interesting data 

 that he obtained for corn and barley. In the first 

 experiments he irradiated sprouted seeds. 

 From 26 irradiated plants of barley which gave 

 66 ears in Xj (first generation), three X-ray 

 mutants of recessive type were obtained. They 

 showed various degrees of albinism, which led 

 to the death of these plants. The fact that these 

 mutants appeared only in a few ears indicates 

 that these X-ray mutants arise in the course of 

 ontogeny. The 1243 ears which were examined 

 from Xg (second generation) contained 14 mu- 

 tants, which were also albinos. Stadler imme- 

 diately raised the question of the significance of 

 voltage. He irradiated seeds with high and low 

 voltages. As his experiments showed (Table 15), 

 voltage did not affect the frequency of mutations. 



These experiments also permitted him to 

 make an interesting comparison between the 

 effects of X rays and radium. The latter turned 

 out to be less effective. 



Stadler was also the first to combine the 

 action of X rays with the action of salts of heavy 

 metals (barium, lead, and uranium) for a 6- 

 hour period, 15 hours before irradiation. The 

 author expected to intensify the mutation process 

 on the assumption that the absorption of X rays 

 increases proportionately to the atomic weight 

 of the substance used (Table 16). 



As can be seen from this table, soaking the 

 seeds in the metallic salts increased the number 

 of mutations— one out of 16 ears showed muta- 

 tions — while when X rays were used alone there 

 was only one mutation in 36 ears, i. e. , the 

 preliminary treatment increased the number of 

 mutations by 50%. 



In another of his experiments in 1928 Stadler 

 [1928c] studied the influence of X rays on the 

 frequency of cross overs and the appearance of 

 a mosaic effect in the endosperm of corn. Irra- 

 diation increased the frequency of mutation in 

 the endosperm by [20-fold] ■'^. Stadler attributes 

 this increase partly to intensification of the 

 mutation process in the genes and partly to 

 chromosomal aberration. 



In his paper in 1930, Stadler [1930a] summa- 

 rizes the results of experiments with the genetic 

 effect of X rays on barley and corn. Both dry 

 and sprouting seeds were exposed to radiation. 

 The appearance of mutations in barley was 



'Editor's note: 

 indicated. 



Text in error; correction is as 



Table 15 



The effect of X rays and radium on the frequency of mutations in sprouting barley seeds 



(based on Stadler' s data, 1928a) 



X-Ray treated: 



Total No. of 



Descendants 



Investigated 



[head progenies] 



No. Segregating 



Mutant Seedling 



Characters 



Higher voltage 



Heavy dose , 



Light dose 



Lower voltage 



Heavy dose 



Light dose 



Total .... 



Irradiated by radium, all doses 

 Not irradiated 



210 

 259 



494 

 280 



1243 



6 

 1 



6 

 1 



14 



1039 

 1341 



3 







35 



