RADIATION STUDIES ON FUNGI 443 



much greater energies than in the case of ultraviolet. The much milder 

 processes brought about by ultraviolet or by photodynamic action of even 

 longer wave lengths are entirelj^ adequate, however, to produce the same 

 biological effects which are apparently caused by ionizing radiation. It is 

 to be expected, then, that comparison of the biological effects of different 

 radiations solely on the basis of their energies is singularly uninformative. 

 The major differences are found in comparisons of kinetic experiments 

 with the different radiations, and of environmental modifying factors. 

 Thus the survival of Neurospora microconidia is exponential with ultra- 

 violet (Norman, 1951), but is complex with a higher order component 

 with X rays (Giles, 1951). In yeast the order of the survival curves is 

 similar to the ploid}^ with X rays, but much higher with ultraviolet 

 (Pomper, unpublished; Sarachek and Lucke, 1953). Photoreactivation, 

 the strongest modifying factor with ultraviolet, is not observed with X 

 rays, whereas oxygen tension during irradiation, the strongest modifying 

 factor with X rays, is not influential with ultraviolet. 



A^arious general effects of ionizing radiations on fungi have been 

 reported. With yeast, no stimulation of growth was obser\'ed at low 

 doses with X or a rays (Lacassagne and Holweck, 1930). Cell division of 

 yeasts was retarded (Holweck and Lacassagne, 1930a). After higher 

 dosages of X rays, cells often underwent two divisions before swelling up 

 and dying (Holweck, 1930; Wyckoff and Luyet, 1931; Holweck and 

 Lacassagne, 1930a; Brace, 1950; Henshaw and Turkowitz, 1940). The 

 phenomenon of delayed death has been emphasized (Holweck, 1930; 

 Wyckoff and Luyet, 1931) as a major difference between ultraviolet and 

 X radiation but Oster (1934b) has observed the delay following ultra- 

 violet. It has been reported that some enlarged cells obtained after X 

 irradiation or exposure to radiimi have continued in culture as enlarged 

 cells (Brace, 1950; Bauch, 1943). A suggestion of induced polyploidy has 

 been made but cannot be accepted without genetic proof. Experiments 

 with a rays (Lacassagne, 1930) and cathode rays (Wyckoff and Luyet, 

 1931) suggest that death occurs after a cell division. X-irradiated spores 

 of Chaetomium cochtiodes all germinated but only a fraction survived to 

 maturity (Dickson, 1932). 



Changes in the sexual pattern of certain yeasts and molds have also 

 been reported. In a culture of normally isogamic Mucor genevcnsis, fre- 

 quent heterogamic conjugations were observed after X irradiation 

 (Nadson and Philippov, 1925). Two strains of this mold were isolated, 

 one showing an increased amount of zygote formation with a decrease in 

 sporangia, the second the reverse. Zijgorhynchus moUeri also exhibited 

 the latter behavior (Nadson and Philippov, 1928b). The yeast Nadsonia 

 fulrcsccns, normally heterogamic, responded to X rays by developing a 

 series of abnormal sexual reactions, leading finally to complete loss of 

 sexuality with greater doses (Nadson and Philippov. 1926). 



