112 



THE STRUGGLE FOR EXISTENCE 



utilization of the food resources, P. caudatum has an advantage over 

 P. aurelia; but if the resistance to waste products is the essential 

 point, then P. aurelia will take place of P. caudatum. 



It is interesting to note also that in the complicated situation of 

 these experiments the superiority of one species over another in com- 

 petition did not simply reflect the properties of these species taken 

 independently, but was often essentially modified by the process of their 

 interaction. 



P.cauditum 

 (tS.pust) Q 



pays 



Fig. 26. The growth of the number of individuals of Sttjlonychia pustulata 

 cultivated separately, and in the mixed populations with Paramecium cau- 

 datum and Paramecium aurelia (on the medium of Osterhout). 



(2) If we turn to the population growth of Stylonychia pustulata 

 and its competition with two species of Paramecium, we shall en- 

 counter extremely complicated processes. The corresponding data 

 are given in Table 5 (Appendix) and Figure 26. These experiments 

 were made with Osterhout's medium containing Bacillus pyocyaneus, 

 simultaneously with those mentioned above. Therefore, the data 

 on the separate growth of P. caudatum and P. aurelia given in Appen- 

 dix Table 3 serve as a control for these experiments. 



First of all, the separate growth of Stylonychia pustulata is very 



