MINERAL NUTRITION OF FUNGI 13 



nifies or minifies criterion 5. Worley proposes therefore a sector- 

 area method to use in comparing the effect of substrata on growth 

 for any given time interval. 



In making measurements of mycelial growth on semisolid media 

 it must be borne in mind that growth is three-dimensional. On 

 one medium the growth by a given species may be appressed, on 

 another profuse and cottony. Measurements of growth on differ- 

 ent media cannot with fairness be compared, regardless of whether 

 radial measurements, ring increments, or sector areas are used. 



Iron as nutrient. Raulin (1869) w 7 as perhaps the first to main- 

 tain that iron is indispensable for fungi. This hypothesis was con- 

 firmed by Molisch (1892), Benecke (1895), and many others, and 

 as a result it is now firmly established that this element is an 

 integral part of fungus protoplasm. Using Aspergillus niger, 

 Steinberg (1919) secured a scant mycelial mat in solutions lacking 

 iron; he obtained 43.7 times as much in the presence of iron. In 

 similar studies with this fungus Roberg (1928) secured 75 times 

 more mycelium in cultures containing iron. Benecke (1895) 

 found that iron is essential both for growth and for sporulation 

 among species of Aspergillus, Penicillium, and Mucor, an obser- 

 vation which Bortels (1927), using refined techniques, was able 

 to verify. 



Little is known about the functions of iron in fungi. Richards 

 (1899) reported an increased efficiency in the use of sugar by 

 Aspergillus niger and Yemcillium glaiicnm in the presence of 0.1% 

 FeCl 3 . Wehmer (1891) found that in darkness the presence of 

 iron in sugar solutions being fermented by Aspergillus results in 

 decreased production of oxalic acid. Chrzaszcz and Peyros 

 (1935), on the other hand, reported markedly increased produc- 

 tion of citric acid by Aspergillus and Penicillium when the sugar 

 solutions being fermented contain a small quantity of FeCl 3 . Simi- 

 larly, others have recorded contradictory results, and this lack of 

 agreement can be expected to prevail until the proximate function 

 of iron is better understood. 



Copper as nutrient. When the growth of fungi in copper- 

 containing nutrient solutions and in solutions lacking copper is 

 compared, as Waterman [Foster (1939)], Bortels (1927), and 

 McHargue and Calfee (1931) have done, all investigators are in 

 accord in ascribing to copper the role of an essential element. The 

 striking feature of studies of this nature is that minute amounts 



