EFFECTS OF RADIUM RAYS ON PLANTS 1005 



A percentage of 17.7 chromosomal mutants in over 100 offspring from 

 a single capsule was greater than had been obtained even without the 

 radium treatment. The average number of mutant forms (2n +1) 

 previously arising in a total of 15,417 progeny of untreated normal 

 diploid parents was 73, or 0.47 per cent. These figures were inter- 

 preted as warranting the conclusion that the increased percentage of 

 chromosomal mutations was due to the radium rays. 



From one treated parent, two recessive gene mutations appeared in 

 the offspring of 18 Fi plants tested by selfing. 



Radiation experiments with Datura have been continued by Buchholz, 

 Blakeslee and collaborators and the results of treatment were reported in 

 1928 and later. The parts treated were pollen grains, pollen tubes, 

 and seeds. Radium, radium emanation, and X-rays all produced genetic 

 effects which may be classified under, (A) gene mutations; and (B) 

 chromosome mutations. 



A. Buchholz reported the production of three types of genes which 

 affect pollen-tube growth in heterozygous plants: (a) those which cause 

 the failure of half the pollen grains to germinate; (6) those which cause 

 the early bursting of half the pollen tubes; and (c) those which cause a 

 slower growth of half the tubes, thus forming a second mode of distribu- 

 tion in the style. These genes are transmitted through the egg cells, 

 and in the F2 generation segregation occurs in a 1:1 ratio in respect to 

 normals and plants with the pollen abnormality. 



Cartledge and Blakeslee (16) found genes which are transmitted 

 through the eggs, but which cause the abortion of the pollen grains 

 affected (8 cases), and about a dozen other genes which affect pollen 

 form or behavior. 



Avery and Blakeslee (3) found visible gene mutations of various kinds 

 including 18 albinos, 13 pales, 8 with rough leaves, and 4 male steriles. 



B. Bergner, Satina, and Potter reported frequent chromosomal 

 abnormalities, including: (a) segmental interchange between chromo- 

 somes ; (6) exchange of terminal humps (probably satellites) on chromo- 

 somes; (c) simple translocations resulting from fragmentation of a 

 chromosome, one part of which is left as a free fragment, and the other 

 part of which is permanently united to a nonhomologous chromosome; 

 and (d) deficiencies of a whole or part of a chromosome. 



Races homozygous for modified chromosomes have been called 

 "prime types." Seventy-five prime types have been isolated from 

 radiated Daturae, in 48 of which one or both of the modified chromosomes 

 have been identified. Modified chromosomes from these prime types 

 have been used in synthesizing "compensating types." The latter are 

 plants which have only a single member instead of a pair of a particular 

 chromosome, but in which the missing chromosome is compensated for 

 by parts of two modified chromosomes. In the compensating type, 



