900 BIOLOGICAL EFFECTS OF RADIATION 



the number of exposures is more effective than increasing the length of 

 exposure. 



There have been several investigations to determine which wave- 

 lengths are most effective in stimulating spore production. Both 

 Stevens (173) and Bailey (2) found that only wave-lengths in the ultra- 

 violet are effective. Ramsey and Bailey (154) obtained the greatest 

 stimulation of spore production in Macrosporium Tomato and Fusarium 



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Cepae with wave-lengths between 2535 and 2800 A and exposures of 

 15 to 30 min. at 60 cm. from a mercury arc. There is slight stimulation 

 with wave-lengths between 3120 and 3334 A. With wave-lengths of less 



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than 2535 A there is a stimulation of spore production, but there are 

 also some lethal effects and an inhibition of mycelial development. All 

 this work was done with filters. Bailey (2) irradiated 59 varieties of 

 Fusarium with a Cooper-Hewitt quartz-mercury arc. Most species tested 

 give maximum spore production under vita glass which transmits to 



o 



2650 A. Bailey as well as Ramsey and Bailey reported a stimulation of 

 spore production with old cultures. 



Certain environmental factors may affect the amount of stimulation 

 of spore production produced by radiation. Stevens (175), for example, 

 found that in Glomerella cingulata those sugars which greatly favor growth 

 also increase perithecial production on irradiation. Smith (169) found 

 that the temperature at which Fusarium cultures are irradiated markedly 

 affects the number of spores produced. Temperature alone may affect 

 the number of spores produced, but the effects of temperature and 

 radiation are not additive since the amount of stimulation over the 

 controls with ultra-violet is different in cultures grown at different 

 temperatures. This is in contradiction to the work of Ramsay and 

 Bailey (154) who reported that temperature is not an important factor in 

 determining sporulation in Macrosporium Tomato and Fusarium Cepae. 

 However, they considered the effects of ultra-violet and of temperature 

 in separate experiments and did not consider the effects of temperature in 

 conjunction with ultra-violet radiation. Stevens (173) regarded the 

 rise in temperature of a culture during irradiation as unimportant with 

 regard to its effect on spore production. Smith (169) found, however, 

 that the number of spores produced by Fusarium Eumartii can be so 

 increased with a 2-min. exposure to ultra-violet in the absence of a 

 temperature control that the whole culture becomes distinctly blue in 

 color. The blue color is due to diffraction by a very large number of 

 spores and not to pigmentation. The blue color was not obtained when 

 the cultures were irradiated in ice water or in a water bath at room 

 temperature. With this fungus, at least, an accurate measure of spore 

 production under the influence of ultra-violet radiation cannot be 

 obtained without temperature control. 



Ultra-violet radiation may not only increase the number of spores 

 produced but may also hasten their formation. When the spectrum of 



