MECHANISM OF COMPETITION IN YEAST CELLS 83 



volume. At the same time this is an explanation of the low level 

 of the accumulation of biomass in the separate cultures of Schizosac- 

 charomyces, and the diminished volume of the mixed population in 

 comparison with the volume of Saccharomyces cultivated separately. 



We can now calculate approximately the critical concentrations of 

 alcohol for the separate growth of each species of yeast if we multiply 

 the maximal volumes of these species (K) by the alcohol production 

 per unit of yeast volume. For Saccharomyces we shall have: 

 13.0 X 0.113 = 1.47, and for Schizosaccharomyces: 5.8 X 0.247 = 

 1.43. In other words, the critical alcohol concentrations for both 

 species are about equal. 



Let us now calculate the degree of influence of one species upon the 



unutilized opportunity for growth of another in a mixed population, 



or the coefficients of the struggle for existence. If we take as a unit 



the degree of decrease of the unutilized opportunity for growth of 



Saccharomyces by a unit of its own yeast volume, we have then to 



answer the following question: how much more or less does a unit 



of the yeast volume of Schizosaccharomyces decrease the unutilized 



opportunity for growth of Saccharomyces in the mixed population, 



in comparison with the effect of a unit of the volume of the latter 



species? Then, taking the ratio of the alcohol production per unit 



of yeast volume in Schizosaccharomyces to the alcohol production of 



Saccharomyces we shall find the coefficient of the struggle for existence 



247 

 according to the alcohol production: a = ' = 2.186. Corre- 



U.l lo 



.. . a 0.113 „,,„ 

 spondingly: = ^-^ = 0.457. 



(4) Comparing the results of the examination of the kinetics of 

 growth of a mixed population with the data on the alcohol produc- 

 tion, we observe a certain agreement in the general features. A very 

 strong influence of Schizosaccharomyces upon Saccharomyces made 

 apparent in the analysis of the kinetics of growth proved itself to be 

 connected with the great alcohol production per unit of yeast volume 

 in the former species. However, a strict coincidence of the data of 

 these two independent methods of investigation does not occur here. 

 Thus Schizosaccharomyces excretes a quantity of alcohol per unit of 

 yeast volume 2.186 times as great as Saccharomyces, but influences 

 the growth of the latter 3.15 times as much. Consequently, Schizo- 

 saccharomyces not only produces a greater amount of alcohol, but the 



