ESSENTIAL METALLIC ELEMENTS 



77 



shown by McHargue and Calfee (1931). The full effect of copper was 

 dependent upon the presence of other essential elements. The coloration 

 of conidia of A. niger has been shown to depend upon the copper content 

 of the medium (Javillier, 1939). 



Although copper is an essential element, it is a constituent of many 

 fungicides (Chap. 12). The concentration, therefore, is a very important 

 consideration in studying the effect of this element. The phenomenon of 

 ion antagonism must also be considered, for the effect of a given amount 

 of copper is dependent upon the other constituents of the medium. 

 Marsh (1945) investigated the antagonistic effects of three salts upon 

 copper as it affected germination of conidia of Sclerotinia fructicola 



Table 12. The Antagonistic Effect of Three Salts on Copper as Shown by 



THE Germination of Conidia of Sclerotinia fructicola 



(Marsh, Phytopathology 35, 1945.) 



(Table 12). It was shown that the mechanism of the protective action of 

 these salts was to decrease absorption of copper. There is no reason to 

 assume that the absorption and utilization of copper from nutrient solu- 

 tions would not be affected similarly. Thus, the amount of copper added 

 to a nutrient solution may reflect only imperfectly the amount absorbed 

 and used by a fungus. 



It was noted in Chap. 4 that copper is an essential constituent of certain 

 enzymes, including tyrosinase, which occurs in many fungi. Nelson and 

 Dawson (1944) suggest that tyrosinase functions in the respiration chain 

 as an oxygen shuttle. 



Manganese. The classification of this element as essential rests upon 

 the experimental findings that omission of this element from media 

 results in decreased yields. The multiplication of examples strengthens 

 the validity of this conclusion, although most investigators have confined 

 their attention to a relatively few species. The results of Robbins and 

 Hervey (1944) with Pythiomorpha gonapodyoides indicate that investiga- 

 tion of fungi other than Aspergillus niger with regard to micro-element 



