26 CULTIVATION AND GROWTH 



as 100 atmospheres (28, 282). Most fungi cease growth or are 

 markedly inhibited when the concentration of soluble sugar exceeds 

 about 2.0 M (109, 129, 159). 



Obligate halophily — an absolute salt requirement — has been re- 

 ported for several fungi (194, 225, 315, 316), although at least some 

 marine fungi do not require salt (8). Further quantitative studies 

 on halophily in marine fungi would be of great interest. 



Protoplasm is presumably always more concentrated than the ex- 

 ternal solution, and limited data support this assumption for the 

 fungi (35). The indications are that the internal concentration, as 

 measured by freezing point depression or by plasmolysis methods, 

 increases as the external concentration is raised (195, 225, 231). In 

 Aspergillus niger the relative amount of bound water is greater when 

 the organism is grown in concentrated glucose (304). Ohtsuki (225), 

 relying on the cryoscopic method, reports an osmotic concentration in 

 Aspergillus glaucus var. tonophilus equivalent to approximately 250 

 atmospheres, i.e., the freezing point of the expressed cell sap was 

 -21°C. 



Thatcher (296, 297), using plasmolytic methods, found that the 

 osmotic pressure of plant pathogenic fungi exceeds that of their hosts 

 and may be a factor in parasitism. Osmotic pressure of hyphae was 

 found in this study to be 15.5-41.3 atmospheres, that of haustoria of 

 rust fungi to be 18.6-21.9 atmospheres. 



Fungi are more active at moderate than at high soil moisture (287); 

 this is presumably to be ascribed to the effect of excessive soil water on 

 aeration. 



11. BIOLUMINESCENCE 



The phenomenon of bioluminescence in organisms generally is re- 

 viewed by Harvey (125); Wassink (324) critically reviews its occur- 

 rence in fungi, and the biochemistry of the process is summarized by 

 Johnson et al. (153). Bioluminescence occurs in at least 17 species of 

 the basidiomycetes, possibly in one ascomycete, and has not been 

 reported from phycomycetes (125, 324). Within a species, both lu- 

 minescent and non-luminescent strains occur in nature (24, 42); in 

 Panus stipticus luminescence is governed by a single gene (190). Lumi- 

 nescence occurs in sporophores, rhizomorphs, sclerotia, and vegetative 

 hyphae (42, 125, 241). As Robert Boyle discovered almost three cen- 

 turies ago, oxygen is necessary; modern work shows that the oxygen re- 

 quirement for fungal luminescence is much higher than that for bac- 

 terial (128). The reaction is temperature sensitive and is reversibly 



