182 



PHYSIOLOGY OF THE FUNGI 



fimbriata show absolute total deficiencies for thiamine. No environ- 

 mental condition is known to allow the synthesis of this vitamin by these 

 fungi. In the case of a conditioned deficiency, the synthesis of the 

 vitamin may be influenced by certain environmental conditions, such as 

 temperature, composition, concentration, and pH of the medium. 



Pythium hutleri failed to grow in a mineral salts-asparagine medium 

 containing 16.4 g. of salts per liter unless thiamine was added (Robbins 

 and Kavanagh, 1938). When the salt concentration was reduced to 1.64 

 g. per liter, this species grew without the addition of thiamine. A defi- 



30 35 40 45 



Temperature 

 Fig. 39. Growth-temperature relations for wild-type Neurospora and a temperature- 

 sensitive mutant deficient for riboflavin. Amounts of riboflavin are indicated on the 

 curves in micrograms per 20 ml. of medium. Below 25°C. growth was good without 

 riboflavin, while no growth occurred above 28°C. without added riboflavin. (Courtesy 

 of Mitchell and Houlahan. Am. Jour. Botany 33: 31, 1946.) 



ciency for riboflavin conditioned by temperature was reported by Mitchell 

 and Houlahan (1946) for a mutant of Neurospora (Fig. 39). Growth was 

 poor or none at temperatures above 25°C. unless riboflavin was added. 

 Below 25°C. the fungus was able to synthesize riboflavin. The partial 

 deficiency of Sclerotinia camelUae for inositol was influenced by tempera- 

 ture, particularly in the above-optimum range (Barnett and Lilly, 1948). 

 Low pH of the medium resulted in partial thiamine deficiency of 

 Sordaria fimicola, while no deficiency for thiamine was apparent at initial 

 pH 4.0 or above (Lilly and Barnett, 1947). Within the range of 3.8 to 

 3.4, growth was quite slow, but the addition of thiamine overcame the 

 inhibition due to the high acidity (Fig. 40). These results indicate that 

 pH 3.8 or lower inhibits the synthesis of thiamine by S. fimicola. In a 

 similar way, the availability of p-aminobenzoic acid to a mutant of 



