3. Carbon Nutrition 



1. PROBLEMS OF METHOD 



Carbon compounds serve two essential functions in the metabolism 

 of fungi, as of all heterotrophic organisms. They supply in the first 

 place the carbon needed for the synthesis of the compounds which 

 go to make up the living cell — proteins, nucleic acids, cell wall ma- 

 terials, reserve foods, and so on; in a typical fungus about 50 per 

 cent of the dry weight is carbon (Chapter 2). Second, the sole source 

 of appreciable amounts of energy is the oxidation of carbon com- 

 pounds, which may account for half or more of the carbon supplied 

 to a culture. 



Knowledge of carbon nutrition, therefore, is fundamental to an 

 understanding of the physiology of the fungi. Much valuable work 

 has been done in this area, but it will be apparent that the data re- 

 quired for confident generalization are usually still lacking, and that 

 much of our knowledge is based on experiments which are open to 

 criticism on the ground of method. 



The study of the carbon nutrition of fungi, or of other microorgan- 

 isms, involves general problems of two sorts: conceptual and meth- 

 odological. 



The concept of utilization may have more than one operational 

 meaning. The commonest usage describes an experiment in which a 

 small inoculum is placed in a medium containing one major source 

 of carbon and all other materials necessary for growth; the organism 



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