MECHANISM OF COMPETITION IN YEAST CELLS 81 



the coefficient /3 in the experiments of 1931 was equal to: 0.501, 0.349, 

 0.467, with an average of 0.439. The fluctuations of the coefficient 

 a were more considerable, but the experiments of 1932 give more 

 constant values for a also: 3.11, 3.06, 2.85, etc. 



The fluctuations in the values of the coefficients of the struggle for 

 existence are due in this case in a considerable measure to an imper- 

 fect method of their calculation. 4 However, this is of no serious 

 consequence, as we have a good method for verifying the average 

 values of the coefficients of competition. This method consists in 

 constructing a curve corresponding to the differential equation of 

 competition (the details of this calculation are to be found in the 

 Appendix). A close agreement of the calculated curve of growth of 

 each species in a mixed population with experimental observations 

 represents a good proof of the correctness of the numerical values of 

 the coefficients of the struggle for existence. As regards the yeasts 

 Saccharomyces and Schizosaccharomyces here concerned, their calcu- 

 lated curves of growth are given in Figures 14 and 15. 



In a mixed population of Saccharotnyces and Schizosaccharomyces 

 under anaerobic conditions the coefficients of the struggle for exist- 

 ence have the following values : a (showing the intensity of the influ- 

 ence of Schizosaccharomyces on Saccharomyces) = 3.15; /3 (intensity 

 of the influence of Saccharomyces on Schizosaccharomyces) = 0.439. 

 In other words, one unit of volume of Schizosaccharomyces decreases 

 the unutilized opportunity for growth of Saccharomyces 3.15 times as 

 much as an equal unit of volume of Saccharomyces itself. The species 

 Schizosaccharomyces with its comparatively small volume takes up 

 "a great number of places" in the microcosm. The reverse action of 

 Saccharomyces on Schizosaccharomyces is comparatively weak. One 

 unit of volume of Saccharomyces decreases the unutilized opportunity 

 for growth of Schizosaccharomyces as much as 0.439 unit of the latter 

 species' own volume. 



(3) We now pass on to the most important part of this chapter, i.e., 

 to the comparison of the empirically established coefficients of the 

 struggle for existence with those which are to be expected on the 

 basis of a direct study of the factors controlling growth. The values 

 of the coefficients of the struggle for existence mentioned above are 

 founded upon an analysis of the kinetics of growth of a mixed popula- 



4 In Chapter V we shall meet a more complicated situation. 



