W NUTRITION OF FUNGI 



of solutions giving the best yields were as follows: KH 2 P0 4 , 

 0.019 M; MgS0 4 -7H 2 0, 0.002 M; and NaNO s , 0.019 M. 



Difficulties encountered in studies of mineral nutrition. 

 Lest it be thought that the elements potassium, phosphorus, mag- 

 nesium, sulphur, and calcium comprise all the minerals requisite 

 for the proper nutrition of fungi, it is pointed out at this juncture 

 that evidence has been gradually accumulating that iron, zinc, 

 manganese, and copper are among other elements now known to 

 be absolutely essential for the normal physiological processes of 

 fungi. The experiments from which these conclusions are drawn 

 will be considered subsequently. It should first be pointed out 

 that the amounts of these elements, as Raulin (1869) first showed 

 for iron and zinc, are so minute that the term trace elements has 

 come to be applied to them. This terminology does not serve any 

 useful purpose, since the amount of a particular element is no 

 index or measure in determining essentiality. 



The conclusions from studies of the nutritional use of these ele- 

 ments—for example, iron, calcium, zinc, manganese, and boron- 

 are, as mi^ht be expected, contradictory. This situation has come 

 about because it is now known that certain of the elements occur 

 in distilled water or come into solution from test tubes, Petri 

 dishes, and culture flasks in amounts sufficiently large to meet the 

 metabolic needs of the organism. Water redistilled from Pyrex- 

 glass stills should be utilized. Pyrex glass may be quite satisfac- 

 tory, particularly if it has previously been used in such a way as 

 to leach out the zinc. In addition, the sugars and C.P. nutrient 

 salts contain various elements as impurities. By spectroscopic 

 methods Steinberg (1937) identified in C.P. reagents commonly 

 used in nutritional experiments with fungi the elements listed in 

 Table 4. 



The presence of appreciable quantities of various elements in 

 C.P. chemicals constitutes an important difficulty, especially in 

 studies that involve elements utilized by fungi in small amounts, 

 as are iron, zinc, boron, copper, and manganese. Repeated re- 

 crvstallization of the nutrient salts has proved to be wholly un- 

 satisfactory [Roberg ( 1928) ] in purifying them. Steinberg (1919, 

 1935) has devised methods to effect practically complete removal 

 of such elements. He heats the nutrient solution in the presence 

 of excess CaCO l3 for 15 minutes at 15-lb pressure. The increased 

 alkalinity in the presence of heat causes the undesirable heavy 



