EFFICIENCY OF GROWTH 89 



In relation to utilization of mixed carbon sources, it should be noted 

 that preferential utilization of one compound is common, e.g., the 

 utilization of acetate before glucose (154) and the utilization of soluble 

 sugars before more complex carbon compounds (G2, 109, 188). 



Fungi in nature live as a rule in a dilute solution with more than 

 one carbon source available or potentially available. These conditions 

 do not very closely resemble a single-substrate pure culture. Lignin 

 and cellulose, for example, may be much more rapidly decomposed by 

 the action of induced enzymes than they are when given to an organ- 

 ism in culture as the sole source of carbon. The ecological importance 

 of the ability of fungi to synthesize new enzymes — if this ability proves 

 to be general — justifies much more study of the problem. It is to be 

 hoped, however, that such studies will be guided, more than they have 

 been in the past, by the wealth of experience accumulated in the 

 investigation of induced enzymes in other microorganisms. 



10. EFFICIENCY OF GROWTH 



Several indices of the over-all efficiency of growth in fungi have been 

 proposed. Of these, the economic coefficient has been most frequently 

 determined. It may best be represented as: 



Mycelial dry weight, gm 



X ioo 



Carbohydrate consumed, gm 



Some authors have used the ratio or its reciprocal without multiplica- 

 tion by 100. 



As an approximate index of the efficiency of carbon utilization, the 

 economic coefficient is satisfactory. More elaborate indices, which 

 take account of energy quantities more directly, have been devised 

 (202, 206, 208, 210). 



The economic coefficient can be seen by inspection to be maximal 

 when respiratory carbon dioxide and soluble metabolic products are 

 minimal in quantity. Since both of these are affected by cultural 

 conditions, no one value or even range of values can be set down as 

 characteristic of the fungi as a whole. Fungi grown on dilute media 

 for no longer a time than is necessary to utilize the carbohydrate usu- 

 ally have an economic coefficient in the range 20 to 35; a few higher 

 values have been reported (119, 161, 205, 209). Very low values (77, 

 228, 230) reflect probably the production of significant amounts of 

 soluble carbon compounds in high-carbohydrate media. 



The economic coefficient, although unaffected by temperature (209), 



