334 PHYSIOLOGY OF THE FUNGI 



A reduction in sugar alone may be effective. (2) A change in the source 

 of carbon. Replacing glucose by the same amount of sucrose, lactose, 

 starch, or other carbon source may favor reproduction. (3) A change 

 in the source of nitrogen. (4) A change in the carbon-nitrogen ratio. 

 (5) The addition of an adequate supply of vitamins for vitamin-deficient 

 fungi. (6) The addition of certain micro elements to the medium, if it 

 is made up of highly purified chemicals. (7) The addition to the medium 

 of certain natural products, such as pieces of stems or leaves. (8) The 

 addition of culture filtrate containing metabolic products from the same 

 or other fungus. (9) The addition of special compounds, such as glutaric 

 acid, which has been shown to be effective in a few cases. (10) The 

 addition of certain specific sexual factors, or hormones, known to be 

 effective for certain Phycomycetes. (11) The addition of certain chem- 

 icals, such as hydrogen peroxide, to the mycelium. (12) Exposure of 

 cultures to ozone. (13) The use of spores instead of mycelium as inocu- 

 lum. Flooding of agar plates with spore suspension has given excellent 

 results with some fungi. (14) The sterilization of media by means other 

 than heat. (15) Transfer of certain parasitic fungi to their living hosts. 

 (16) Growing the fungus in the presence of certain bacteria or other 

 fvmgi. (17) A change in pH of the medium, (18) A change in the 

 temperature of incubation. (19) Adequate aeration. (20) Exposure to 

 light or alternate light and darkness. (21) Short exposures to ultraviolet 

 radiation. (22) Variation in the intensity and wave length of light. (23) 

 Mechanical injury to the mycelium. (24) Gradual desiccation of the 

 cultures. (25) Allowing the cultures to age. (26) The proper combina- 

 tion of any two or more of the above factors. The secret of the sexual 

 reproduction of many fungi no doubt lies in the proper combination of 

 factors which singly are known to favor reproduction in other fungi. 



REFERENCES 



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development of perithecia, asci and ascospores by Sordaria fimicola Ces. and 



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 *Barnett, H. L., and V. G. Lilly: Nutritional and environmental factors influencing 



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