MINERAL FOOD OF FUNGI 119 



This is said to be due to their higher specific heat ; thus 

 water has the highest specific heat of all substances, and 

 consequently it can diminish the effects of rapidly changing 

 temperatures upon life. 



The physiological role of mineral nutrients is not known 

 in most instances, but only the experimental proof that 

 certain substances have a more or less marked effect on 

 growth. 



Potassium salts are necessary in most fungi for the 

 production of protein, even when sugar is present. 



Magnesium salts are also indispensable, but a mere 

 trace is sufficient when the nutrient medium has an acid 

 reaction. 



Molisch, in studying the action of iron on the higher 

 plants, also observed that when salts of iron were added 

 to the nutrient medium of Aspergillus m'ger, growth was 

 much more luxuriant. He therefore concluded that iron 

 was as essential to fungi as to the higher plants. Wehmer 

 has verified Molisch's statement, but considers his con- 

 clusion as too general, as it was observed that if nitrate 

 of ammonia is replaced by nitrate of potash, the presence 

 or absence of iron makes no appreciable difference to the 

 vigour of growth, 



Giinther states that even in the case of suitable salts, a 

 diminution of growth takes place as the salts become more 

 concentrated. A combination of salts beneficial to fungi 

 is a salt of potassium and of magnesium, along with a 

 compound containing sulphur and another containing 

 phosphorus. 



Rubidium can replace potassium in the case of Botrytis 

 cinerea, but not in that of Rhizopus nigricans. 



Salts of copper in exceedingly minute proportions favours 



