CHAPTER 5 

 ESSENTIAL METALLIC ELEMENTS 



The fungi need about 17 elements to supply their nutritional require- 

 ments. These elements are utilized in the form of specific compounds, as 

 ions, and as free elements. Some of the essential elements are required by 

 all fungi. Other elements are required only by certain species. In a 

 general way, the elements required by the fungi are the same ones 

 required by bacteria, green plants, and animals. There are, however, 

 striking differences in the essential-element requirements of different 

 groups of organisms (Table 15). Differences in ability to utilize specific 

 compounds containing these essential elements are common in the fungi 

 and bacteria. 



BIOLOGICALLY ESSENTIAL ELEMENTS 



Before seeking to determine which elements are essential, it is necessary 

 to define what is meant by the term hiologically essential element. An 

 essential element is indispensable in that no other element may entirely 

 replace it. Without these essential elements life is impossible. An ele- 

 ment needed in extremely small amounts may be just as essential as car- 

 bon, which comprises almost half the weight of a fungus. 



There are some 92 chemical elements (if we exclude the recently 

 isolated trans uranic elements), most of which are known to exist, or may 

 exist, as a mixture of isotopes. So far as is known, all the isotopes of an 

 element (with the possible exception of the isotopes of hydrogen) have the 

 same chemical and biological properties. Even radioactive isotopes, 

 before they decay, exhibit the same biological properties as the stable 

 isotopes. The biological effects of radiation in inducing mutations are 

 considered briefly in Chapter 18. In spite of the limited number of ele- 

 ments, the question of essentiality is not settled completely for all. 



The problem of determining which elements are essential for the fungi 

 has been approached from the standpoint of ultimate analysis of mycelium 

 and spores. If certain elements, such as carbon, potassium, and mag- 

 nesium, are always found in all samples analyzed, irrespective of the sub- 

 strates upon which these fungi grew, it may be concluded with a high 

 degree of probability that these elements are essential for the fungi. 

 Some of the analytical results of ultimate analyses of mycelium and spores 

 have been collected by Buchanan and Fulmer (1928) and Foster (1949). 



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