EFFECTS OF RADIATION ON FUNGI 905 



for the negative results obtained by Errera (41), Atkinson (1), Berde (5), 

 and Johnson (83). In the cure of certain skin diseases caused by fungi 

 such as athlete's foot and actinomycosis it has been frequently observed 

 that X-rays produce a cure only in certain individuals. The reasons for 

 this difference are not known but the difference may explain why such 

 workers as Lieske (105) and Kleesattel (89) noted no effects of X-rays on 

 actinomycosis, whereas Melchior (120), Levy (104), Sardemann (160), 

 and Jiingling (85) reported positive results. 



The effects of X-rays on fungi are similar in many respects to those 

 which have been reported for green plants. The most conspicuous of 

 these, possibly, is lethal action. Fungi are rather insensitive to X-rays, 

 but large doses produce killing effects. Neidhart (137) was among the 

 first to note lethal action with X-rays. S-shaped survival curves were 

 obtained by Wyckoff and Luyet (196), Luyet (111), and Glocker, Lan- 

 gendorff, and Reuss (58). Lacassagne and Holweck (97) found that the 

 sensitivity of Saccharomyces to soft X-rays is the same for a definite 

 quantity of X-rays regardless of the time and intensity. Very little 

 study has been made of the effects of different wave-lengths. Haskins 

 and Moore (68), however, found that the soft X-rays which they used 

 were 2.1 times as effective in killing Penicillium spores as hard X-rays. 

 The soft X-rays were very nearly monochromatic and were composed 

 chiefly of wave-lengths of 1.5 to 1.3 A, while the hard radiation had its 



o 



greatest intensity between 0.21 and 0.18 A. Careful measurements were 

 made of intensities. The lethal action of X-rays becomes of some 

 practical import in the irradiation of fungi inside of seeds and fruits. 

 Pichler and Wober (146) succeeded in killing Ustilago Tritici in the seeds 

 of wheat, U. nuda in the seeds of barley, and Chrysophlydis endobioticum 

 in potato tubers. They found that X-rays are much more effective 

 than ultra-violet rays for this purpose because of their greater penetrat- 

 ing power. 



Various degrees of injury are produced by X-rays just as by ultra- 

 violet. Yeast loses its ability to multiply with much smaller doses than 

 are required for immediate killing. Such doses may merely retard 

 division or they may cause the production of giant cells which have lots 

 their ability to divide. Some cells may divide only once following 

 irradiation. These various injurious effects have been emphasized by 

 Lacassagne (96), Holweck and Lacassagne (77), Wyckoff and Luyet (196), 

 and Holweck (75). 



The effects of small doses thus far discussed have been either negative 

 or slightly injurious. Lacassagne and Holweck (97) and Wyckoff and 

 Luyet (196) found no evidence of stimulation with small doses of X-rays 

 on yeasts, but Zeller (197) found that under certain circumstances fermen- 

 tation is temporarily increased. Nadson (131) noted that small doses of 

 X-rays may so stimulate the metabolic processes of the cell as to cause 



