IMPLICATIONS 29 



INFLUENCE OF OSMOTIC PRESSURE 



Special attention has been devoted to the concentration of salts 

 and nutrients in culture media because spores can be germinated 

 and mycelium can be grown in solutions having high osmotic 

 equivalents. Ordinarily the media are prepared with their con- 

 stituents in such proportions that the osmotic pressure ranges 

 from 0.5 to less than 10 atm. 



Knowledge of osmotic pressure finds practical application in 

 food preservation with salt or sugar. Increased percentage of salt 

 in brines, for example, is correlated with increased capabilities for 

 preservation. Molliard (1918) found that conidial formation by 

 Sterigmatocy stis nigra is prevented in a nutrient solution contain- 

 ing 1% NaCl; within the range of 2 to 5% mycelial growth is 

 retarded, and with 12% there is complete inhibition. 



Fungi differ greatly in their tolerance to salts with high osmotic 

 pressures. Raciborski (1905) grew Torula sp. in a saturated solu- 

 tion of sodium chloride or of sodium nitrate. Hawkins (1916) 

 grew certain plant pathogens, including Botrytis cinerea, Diplodia 

 tubericola, Fusarium radicicola, F. oxysporum, Sclerotinia cmerea, 

 and Sphaeropsis malorum, in potassium nitrate solutions with a 

 calculated diffusion tension of 47 atm. Certain molds, such as 

 Aspergillus niger and Femcillium glauciim, have been grown in 

 solutions having an osmotic pressure equivalent of 157 atm. 



Similarly the preservation of jelly, jam, syrup, and such foods 

 against molds is correlated with the osmotic concentration of the 

 sugar used. Heald and Pool (1908) found that a mold which they 

 named Torula saccharina achieved optimum growth in Pasteur's 

 nutrient solution containing 45% sucrose. Slight growth occurred 

 in 75 to 80% sucrose solutions. 



IMPLICATIONS 



From the foregoing account it is manifest that species of fungi 

 differ from each other in nutritional requirements. Some grow 

 well on almost any substrate that is employed and for this reason 

 may be regarded as "domesticated" or "tamed" fungi. Others, 

 on the other hand, may barely survive on these same media, may 

 grow poorly on a limited number of substrates only, or may not 



