980 BIOLOGICAL EFFECTS OF RADIATION 



Rearrangement or translocation and losses of portions of the chromo- 

 some complement occur with very high frequency as a consequence of 

 X-ray treatment — thus, Stadler (64) concluded from his studies on Zea 

 Mays. In both translocation and dej&ciency, a part of a chromosome 

 is separated from the remainder; in deficiency, this section is lost, while 

 in translocation it becomes attached to another chromosome or section. 

 Deficiency may involve a section of an entire chromosome and may be 

 single or multiple; translocation, whether simple or reciprocal, may 

 involve one or more transfers or interchanges. Combinations of defi- 

 ciency and translocation also may occur. 



Recent work by Narimatsu (45) on V. Faba, which confirmed results 

 of certain authors mentioned previously, indicated that with weak 

 irradiation there was no marked abnormality in cell arrangement as 

 compared with the nonirradiated group. The most marked change 

 was in the cell nucleus where mitoses were decreased. Degenerative 

 changes and swelling of the cell body were more pronounced with medium 

 irradiation, and abnormal cell arrangement occurred. With strong 

 irradiation, swelling of the cell body took place and almost no structure 

 was observed in the protoplasm. No mitoses were observed and the 

 nuclei were swollen and degenerated. Narimatsu (45) concluded that the 

 change in cell arrangement was not a direct result of irradiation but was 

 secondary to change in the nucleus, since the part first affected is the 

 nucleus. 



Bersa (7a) concludes that so-called ray-resistant and ray-susceptible 

 plants behave similarly cytologically. X-rays cause depression in 

 frequency of nuclear division; the stronger the rays, the greater the 

 depression. Prophases suffer only temporarily a stronger depression, 

 which indicates that the rays delay appearance of division phases from 

 the resting nuclei. Bersa did not observe abnormal mitoses until 36 hr. 

 after irradiation. 



There seems to be general agreement that cells of the growing tip are 

 more sensitive to the action of the rays than those of other regions. The 

 nucleus is more ray-sensitive than the cytoplasm; hence it is suggested 

 that there may be an alteration in the nucleus-cytoplasm ratio when 

 mitoses are decreased without a proportional decrease in the amount of 

 protoplasm. Mitotic irregularities occur in the leaves as well as in the 

 growing points of stems and roots. Numerous chromosomal irregulari- 

 ties, including rearrangement or translocation of portions of chromo- 

 somes, are evident after heavy irradiation. 



GENERAL SUMMARY 



The investigations reviewed in this paper have dealt with the physio- 

 logical, morphological, histological, and cytological aspects of the effects 

 of X-radiation on green plants. In spite of the large number of publica- 



