92 CARBON NUTRITION 



chapter, it has been assumed that carbon sources are utilized by path- 

 ways involving hexoses or hexose phosphates as intermediates. How- 

 ever, the data of Table 1 afford several instances in which glucose is 

 inferior to some other carbon compound, xylose, gluconic acid, disac- 

 charides, or polysaccharides. None of these cases has been studied. 

 The superiority of xylose or gluconate could mean that the phospho- 

 gluconate oxidation pathway (Chapter 7) is more active than others. 

 Or, a compound may be superior to glucose for accidental reasons — 

 pH relations, accumulation of intermediates, contamination with 

 metals or growth factors, etc. This second explanation has been 

 suggested earlier for the superiority of particular disaccharides and 

 polysaccharides. It must be admitted, however, that the question is 

 still open. 



Looking at the whole field of carbon nutrition of fungi, one is 

 struck with the gaps in our knowledge. Certain groups — the Mu- 

 corales and the Peronosporales are examples — have been more or less 

 neglected. Comparative studies of species within a genus, particularly 

 species of different habitat, might prove most valuable. The bio- 

 chemical basis of nutritional capabilities is largely a matter of in- 

 ference at present; failure to utilize fructose or mannitol, for example, 

 probably has a simple enzymatic basis. As just discussed above, in- 

 duced enzyme synthesis in the fungi is still largely a matter for specu- 

 lation. Some of the data reported in this chapter, and more which 

 have been omitted, are difficult to accept, and important points of 

 this nature should be reinvestigated. Finally, the understanding of 

 nutrition in nature, with numerous substrates present in low concen- 

 tration, is a long-range goal progress toward which will require 

 radically new techniques of investigation. 



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