LONG WAVELENGTH RADIATION 435 



Lethality and mutagenic action are not the only effect of irradiation. 

 In particular, irradiated spores may germinate but fail to make con- 

 tinued growth; this phenomenon, reported in several fungi (11, 28, 

 90, 141) is analogous to the delayed effect of X-irradiation on yeast 

 (116) and to the "microscopic mutant" induced in Chaetomium glo- 

 bosum by ultraviolet or ionizing radiation (44, 93). The irradiation 

 of Aspergillus niger spores with low (non-lethal) intensities of a-parti- 

 cles results in the development of asporogenous colonies in an unspeci- 

 fied number (11). These delayed effects are perhaps best described 

 as lethal mutations, but something more than a descriptive analysis 

 would surely be of interest. 



Stimulation of spore germination by ionizing radiation has been 

 reported (15, 154). Other less well-defined stimulatory effects claimed 

 by earlier workers are reviewed by Smith (127). 



The environmental factor most significant in modifying responses 

 of fungi and bacteria to X-irradiation is the ambient oxygen pressure 

 (68, 131): both lethality and mutagenesis are less at low oxygen tension. 

 Sensitivity of Aspergillus terreus to X-irradiation is also increased by 

 previous exposure to infrared radiation (133, 135) and by high spore 

 moisture content (131). The lethality of X-irradiation to Strepto- 

 myces sp. is decreased by various postirradiation treatments (147). 



Radiation biology is undergoing rapid advances at this time, and it 

 is to be expected that generalizations will have a short life. In the 

 fungi it appears that the primary effect of radiation is on the nucleus, 

 and this effect — which may be itself complex — is best visualized on the 

 basis of the target theory so strongly urged by Lea (86). However, 

 there is good evidence — especially in the influence of environmental 

 factors on response — that significant secondary reactions, possibly in 

 the cytoplasm, must be postulated both for ultraviolet and for ionizing 

 radiation (116, 159). 



6. ELECTROMAGNETIC RADIATION OF LONG WAVELENGTH 



Irradiation in the "radio" part of the electromagnetic spectrum may 

 be inhibitory to fungi. Inhibition is, however, a heating effect and 

 does not occur if the temperature is held constant (49, 97, 101, 140). 



BIBLIOGRAPHY 



1. Ames, A. 1915. Phytopathology 5: 11-19. 



2. Arima, K. 1951a. /. Antibiotics (Japan) 4: 232-237. 



3. Arima, K. 1951b. ./. Antibiotics {Japan) 4: 277-280. 



