320 



PHYSIOLOGY OF THE FUNGI 



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EXPOSURE TIME IN SECONDS 

 Fig. 63. Effect of time of exposure to ultraviolet radiation on the production of 

 spores from scraped and unscraped cultures of AUernaria solarii. (Courtesy of 

 McCallan and Chan, Contribs. Boyce Thompson Inst. 13 : 327, 1944.) 



NUTRITIONAL FACTORS 



The nutritional conditions under which a fungus produces reproductive 

 bodies and spores are often quite different from those which are optimum 

 for vegetative growth. Not all media are equally suitable for sporula- 

 tion. The frequent failure to obtain sporulation of many common fungi 

 in culture, even though they grow profusely, testifies to the extent of our 

 ignorance regarding the necessary nutritional factors. However, the 

 following factors have been shown to be important: concentration of 

 medium, carbon and nitrogen sources, carbon-nitrogen ratio, micro 

 essential elements, specific reproductive factors, and vitamins. 



Concentration of nutrients. Among the early workers, Klebs (1900) 

 gave a great deal of attention to the effect of nutrient concentration upon 

 reproduction. For most of the fungi with which he worked, exhaustion 

 of the food supply favored sporulation. Klebs (1899) kept a culture of 

 Saprolegnia mixta in the vegetative condition for 2^^ years by constant 

 renewal of the nutrient solution. Yet, this fungus produced spores within 

 a few days when the food supply became exhausted. The same principle 

 holds true for the Myxomycetes as well as the filamentous fungi. Camp 

 (1937) grew Physarum polycephalum and studied the effect of the number 



