HYDROGEN-ION CONCENTRATION 



159 



satisfactory (not necessarily optimum) for the majority of the fungi. 

 The optimum pH ranges for Blastocladia pringsheimii, Allomyces arhus- 

 cula, and Blastocladiella simplex are rather narrow (Emerson and Cantino, 

 1948) (see Fig. 23). Most of the pH optima reported in the literature 

 are less than 7. Meacham (1918) reported pH 3 to be optimum for 

 Lenzites saepiaria, Fomes roseus, Merulius lacrymans, and Coniophora 

 cerebella. Wolpert (1924) found the pH optimum of various Basidio- 

 mycetes to be in the neighborhood of 5.5. Johnson (1923) reported that 

 the upper pH limit of Penicillium varidbile is 10.1 to 11.1, which is con- 



Blastocladfa 



Allomyces 



Blastocladiella 



Fig. 23. Relation of pH of the medium to growth of Blastocladia -pringsheimii, 

 Allomyces arbuscula, and Blastocladiella simplex. (Courtesy of Emerson and Cantino. 

 Am. Jour. Botany 35: 162, 1948.) 



siderably higher than that of most fungi. The lower pH limits reported 

 vary from 5.3 for B. simplex (Emerson and Cantino, 1948) to 0.5 for 

 Acontium velatum and an unidentified imperfect fungus (Starkey and 

 Waksman, 1943). 



The method used to determine the pH limits of a fungus is to inoculate 

 a series of nutrient solutions having pH values spaced 0.2 to 0.4 unit 

 apart. Growth may be observed visually, or the mycelium may be 

 weighed. Such media should be well buffered. The pH limits for a 

 given fungus as determined in different laboratories are frequently at 

 variance. This is not unexpected, since the composition of the medium 

 and the nature of the buffer influence the tolerance of fungi to hydrogen 

 and hydroxyl ions. The behavior of Marasmius graminum is revealing 

 (Lindeberg, 1944). Calcium ion was effective in overcoming the toxic 

 effect of an initial pH of 3.3. The weight of M. graminum after 12 days 

 was 0.4 mg., but when calcium sulfate was added to the medium, the 

 yield was 8.0 mg. Tamiya (1928) also found calcium ion to protect 

 Aspergillus oryzae to some extent against high concentrations of hydrogen 

 ion. The optimum pH for Gibber ella saubinetti is lower when calcium is 

 present in the medium (Lundegardh, 1924). Wolpert (1S24) also found 



