ESSENTIAL METALLIC ELEMENTS 83 



SUMMARY 



The role of the essential metallic elements is primarily functional rather 

 than structural. Presumably these ions usually function in ionizable 

 combinations, but some compounds containing metals in non-ionizable 

 compounds have been isolated from fungi. It may be assumed that 

 many of these metallic ions activate enzyme systems, while others are 

 integral parts of enzymes and other essential organic compounds. An 

 element is essential because some of its vital functions cannot be replaced 

 by any other element. Some functions may be performed by other closely 

 related elements. 



The concentration of an essential element affects many life processes 

 besides growth, which is the usual criterion of essentiality. The concen- 

 trations of various essential ions influence the formation of pigments, the 

 synthesis of vitamins and other products, and the dissimilation of carbo- 

 hydrates. While the essential elements may be supposed to participate 

 uniquely in certain life processes, the concentrations of other ions, both 

 of essential and nonessential elements, modify the action of a given ele- 

 ment. The phenomenon of ion antagonism no doubt exists among all 

 ions, and in evaluating the effects of any element it is necessary to con- 

 sider the other constituents present in the medium. It is probable that 

 the mechanism involved is one of modified adsorption rather than any 

 direct chemical reaction in the medium. 



The widespread use of Aspergillus niger as a test fungus in micro- 

 element studies has had the advantage that the work in many laboratories 

 may be compared. The careful and long-continued studies by Steinberg 

 are especially valuable. The almost exclusive use of this fungus has also 

 had its disadvantages. Comparatively little is known about the need of 

 other species for micro elements. Other fungi may require some of these 

 elements in amounts which make it comparatively easy to demonstrate 

 deficiency. The evidence for the essentiality of iron, zinc, copper, 

 manganese, molybdenum, and calcium is impressive in most instances, 

 but the need for the elements on the part of all fungi under all cultural 

 conditions has not been established. In a few instances the evidence is 

 confined to a single fungus. The micro-element nutrition of a wide range 

 of species needs further study. 



REFERENCES 



Bertrand, D.: Le Vanadium comme facteur de croissance pour V Aspergillus niger, 



Bull. soc. chim. biol. 23: 467-471, 1941. 

 Bertrand, D.: Le Vanadium chez les champignons et plus sp^cialement chez les 



Amanites, Bull. soc. chim. biol. 25: 194-197, 1943. 

 Blank, L. M.: Response of Phymatotrichum omnivorum to certain trace elements, 



Jour. Agr. Research 62: 129-159, 1941. 



