THE CONCENTRATION FACTOR 



85 



as in decomposition of pure hydrocarbons, the actinomycetes appear 

 to be the more active. 



Tannins are utilized by several common saprophytes (47, 109, 168), 

 presumably after elaboration of an adaptive tannase (Chapter 6). The 

 crude resins of Gnayule are attacked by several fungi (3). 



8. THE CONCENTRATION FACTOR IN CARBON NUTRITION 



As the concentration of carbohydrate in a medium is increased the 

 economic coefficient declines; although more sugar may be utilized, the 

 dry weight does not increase proportionately. Carbohydrate is evi- 

 dently being converted to metabolic products — carbon dioxide, organic 

 acids, soluble polysaccharides, etc. There also occurs at supraoptimal 

 glucose concentrations a simple failure to utilize the sugar present 

 (119), in which case the economic coefficient is not affected. These 

 two related phenomena are surely to be ascribed to the fact that other 

 constituents of the medium, especially nitrogen, become limiting at 

 the higher carbohydrate concentrations. That is, within limits, growth 

 is increased by higher carbohydrate provided that adequate nitrogen 

 is supplied (27). The role of zinc and other metals may be more 

 complicated than that of nitrogen supply (66), but the simple fact that 

 more cellular synthesis will increase the demand for all nutrients 

 should not be neglected in considering the effect of metals on growth 

 and metabolism. 



For many fungi, increase in carbohydrate beyond an optimum 

 point results in an absolute as well as a relative decrease in growth. 

 The data of Figure 2 exemplify this type of response, which is corn- 



Figure 2. The effect of glu- 

 cose concentration on the 

 growth of Psalliota bispora. 

 Drawn from tabular data of 

 Treschow (216) . 



0.1 



Glucose concentration 



1.0 M 



