SPORULATION 



315 



culture methods came into wide use. The lethal action of ultraviolet 

 light is conditioned by the wave length of the irradiation, by the time of 

 exposure, and by the particular nature of the microorganism. A con- 

 siderable number of investigators have studied the effect of ultraviolet 

 radiation upon sporulation. Both favorable and unfavorable results 

 have been obtained. It should be recognized that length of exposure 



Fig. 61. The effect of light on the production of pycnidia by an isolate of Dendro- 

 phoma obscurans when grown on malt extract-agar plates at 25°C. A, grown under 

 continuous artificial light, .\lternate light and darkness gave similar results. B, 

 grown in continuous darkness. 



is a very important factor in these experiments. In addition, the medium 

 used, the age of the culture, and the temperature rise during irradiation 

 also modify the results. 



Stevens (1928) found that ultraviolet radiation induced the formation 

 of perithecia by various isolates of Glomerella cingulata a few days after 

 irradiation. While old cultures produced a few perithecia without 

 irradiation, many more were produced by young cultures within a short 

 time following irradiation. One effect of such irradiation is the killing 

 of the aerial mycelium. Short exposures allowed the formation of super- 

 ficial perithecia, while long exposures prevented their formation. The 

 majority of the perithecia formed following intermediate dosages were 

 embedded in the medium. It was noted that the age of the mycelium 



