474 Physiology 



stronger competitor. The observations of Brown (37), Dewey and Kidder 

 (93), and Provasoli (462) involve the captor-prey relationship in bacteria- 

 free media. Loefer (325, 326, 328) was dealing with analogous problems in 

 his bacteria-free cultures of Paramecium bursaria, in which conditions 

 optimal for grovv^th of Chlorella paramecii were not those most favorable 

 to growth of the ciliate-algal partnership. 



Experimental data based upon cultures are to be interpreted in terms 

 of protozoan populations. Growth of populations in microorganisms" 

 may consist of several phases (Fig. 8. 4): an initial stationary phase, with 

 no increase in number of organisms; a lag phase, during which the rate 



LOG NUMBER 

 ORGANISMS 



O 



o <y 

 Ti o 



e 



TIME 



Fig. 8. 4. Generalized growth ciir\e for populations of microorganisms. 



of population-growth increases to a maximum; a phase of logarithmic 

 growth, during which the population increases at a constant rate; a 

 phase of negative growth acceleration, in which the growth-rate decreases 

 progressively; a maximal stationary phase, in which the population re- 

 mains essentially constant; and various phases of death, in which the 

 density of population decreases. The first two phases are sometimes 

 lumped together under the one term, lag. 



The early phases in growth of populations have been investigated in 

 Euglena (235, 236) and Tetrahymena (37, 116, 439, 440), while more 



"Recent discussions of bacterial growtli have been published by Hinshelwood (202) 

 and Monod (401). 



