220 



PHYSIOLOGY OF THE FUNGI 



By using a series of test organisms of known deficiencies, it is easy to 

 demonstrate that fungi excrete vitamins. It is a common experience to 

 find deficient fungi growing in association with contaminants. The 

 method is simple and consists of inoculating plates of vitamin-free medium 

 with two test fungi (Fig. 44). Not all fungi excrete the same amount of a 



Fig. 44. Test demonstrating the excretion of biotin by Aspergillus 7'ugulosus (right), 

 whengrownwith Sordariafimicola (biotin-deficient) on vitamin-free glucose-asparagine 

 medium. Sordaria (left) made only slight growth until it approached the colony of 

 Aspergillus, where a zone of stimulated growth is evident. 



given vitamin. This may be shown by choosing test fungi such as 

 Sordaria fimicola, which requires more biotin for fruiting than for growth. 

 Some fungi excrete enough biotin to allow grow^th of S. fimicola, while 

 others excrete enough biotin to allow reproduction also. Other com- 

 pounds besides the vitamins may be excreted and favor the growth of 

 other organisms. Further instances of the favorable effect of one fungus 

 on the sporulation of another are discussed in Chap. 14. 



The metabolic products of one fungus may inhibit the growth of 

 another. This phenomenon may be frequently observed on contaminated 

 plates (Fig. 45). Fleming (1929) discovered the action of penicillin in 

 this way. 



Many fungi apparently produce substances which inhibit the germina- 

 tion of their spores. Schopfer (1933) found that spores of Phy corny ces 

 blakesleeanus would not germinate on agar media upon which this fungus 

 had grown. If such a "staled" plate was autoclaved, the medium would 

 then allow germination and growth of P. blakesleeanus. These results 



