318 



PHYSIOLOGY OF THE FUNGI 



abundant sporulation. Forced aeration of the culture flasks at the rate 

 of 4 ml. of air per minute per milligram of oats-sorghum medium was 

 found to be optimum for sporulation. Mader (1943) discussed the 

 factors inhibiting fruiting of Agnricus campestris and concluded that 

 volatile substances are important, and that they must be removed by 

 aeration of mushroom cellars. 



Hydrogen-ion concentration. The early workers recognized that the 

 acidity of the medium influenced sporulation. Lock wood (1937) studied 

 the formation of perithecia and asci by Penicillium javanicum, Aspergillus 

 herhariorum, and Chaetomium. globosum in buffered media of various 



Fig. 62. The effect of glutamic acid on gametic reproduction of Phycomyces hlakes- 

 leeanus at 26°C. Left, basal medium; right, basal medium plus 10 mg. d-glutamic 

 acid, neutraHzed with CaCOs. Note the line of progametes in the plate on the right. 

 Age, 6 days. (Courtesy of Robbins and Schmitt, A7n. Jour. Botany 32 : 321, 1945.) 



hydrogen-ion concentrations and found that the perithecia produced in 

 the more acid solutions contained few if any asci with ascospores. The 

 percentage of fertile perithecia increased as the pH was increased to 7 or 

 8. Similarly, in our laboratory, we have noted that A . rugulosus produces 

 many perithecia and few conidia at an initial pH value of 6 to 8, while 

 conidia but no perithecia form at pH 3 to 4. 



Robbins and Schmitt (1945) studied the sexual reproduction of Phyco- 

 myces hlakesleeanus on glucose-asparagine medium and found that mature 

 zygospores did not form at 26°C. Zygospores formed when various 

 protein hydrolysates, amino acids (especially glutamic acid), or various 

 organic acids were added to the medium. These buffers prevented the 

 pH from falling low enough to inhibit zygospore formation (Fig. 62). 

 These authors also noted that P. hlakesleeanus on glucose-asparagine 

 medium produced zygospores at 20°C. This is evidence that the com- 

 position of the medium has a profound effect on reproduction. In this 



