INDUCED MUTATIONS IN PLANTS 1265 



has been concerned primarily with the analysis of the chromosomal 

 effects of irradiation. The results of these studies are discussed in 

 Paper XLI. Additional instances of mutation induced by radium 

 treatment are reported by Avery and Blakeslee (1) and Buchholz and 

 Blakeslee (7, 7a). 



Buchholz and Blakeslee studied abnormalities of pollen and pollen- 

 tube growth in plants from radium-treated parents. The strain of 

 Datura Stramonium used in their experiments was a diploid line derived 

 from a haploid plant. Such a line is absolutely homozygous except 

 for genes which may have mutated subsequent to the establishment 

 of the diploid line. The radium treatments were applied to the mature 

 pollen before pollination or to the pollen tubes growing in the style after 

 pollination. Among the plants of the next generation 192 were tested 

 for abnormal pollen-tube growth, by examining the styles of normal 

 plants pollinated from the plants under test. Forty-eight plants showing 

 abnormal pollen behavior were found. Two of these cases are described 

 in detail. In one, about half of the pollen ordinarily fails to germinate 

 or in some instances gives rise to pollen tubes which burst near the stigma. 

 In the second case, the pollen germinates normally, but half of the grains 

 produce slow-growing pollen tubes which commonly fail to accomplish 

 fertilization. In both cases the variation is transmitted normally 

 through the female germ cells. Since the chromosomes of the affected 

 plants are apparently normal, the abnormalities are considered to be 

 due to recessive genes, resulting from mutation induced by the radium 

 treatment. 



Genetic variations are induced in Datura similarly by X-ray treat- 

 ment. Blakeslee et al (6) have briefly described various genetic effects 

 of X-ray treatment of seeds of Datura Stramonium, including the produc- 

 tion of a number of gene mutations. 



A comprehensive series of investigations of the cytogenetic effects 

 of both X-ray and gamma-ray treatments in Nicotiana has been carried 

 out by Goodspeed (16 to 19), following the discovery of X-ray induced 

 variation in Nicotiana by Goodspeed and Olson (20). Treatments 

 were applied to young buds, mature pollen, dormant seeds, and young 

 seedlings. Various species and varieties were used. In addition to a 

 wide variety of chromosomal variants (which are discussed in Paper XLI), 

 many gene mutations were found in the progeny of treated plants. 

 Goodspeed (17) has described three apparent mutants of A^. Tabacum 

 purpurea. Two of these, pink-flower color and pistillody of the androe- 

 cium, occurred in progenies of plants in which young buds were X-rayed, 

 the third, albino seedlings, in the progeny of a plant grown from radium- 

 treated seed. Later investigation (18, 19) indicated that the pink-flower 

 variation resulted from the loss of a chromosome segment rather than 

 from gene mutation. 



