Q. 

 O 



c 

 o 



ST. PH. 



LOG. PH. 



LITE, MIN.OIL 



LITE, CHARCOAL 

 LITE 



DARK 



B. 



6( 



25 X 10^ 



5 X 10" CELLS /ML 

 6 



1.25 X 10 



. X 10^ C. 

 12 3 4 5 6 



Time (hours) 



Fig. 5. 



The influence of various environmental and biological 

 factors on the rate of center formation. The data are 

 plotted as the number of centers per drop (group or 

 colony of cells) against time. Graph A Indicates that 

 cells taken from the stationary phase of growth aggregate 

 sooner and at a faster rate than do logarithmic phase 

 cells. Graph B illustrates that the rate of center forma- 

 tion is faster in the light and in the presence of charcoal 

 and mineral oil than in the dark and in the absence of 

 these two agents. Graph C shows that the rate of center 

 formation is faster at high cell density than at low cell 

 density. 



Figure 5C shows the relationship between 

 the rate of center formation and cell density. 

 The higher the density the faster the rate. This 

 result would be expected if increasing the density 

 of eells also increased the number of cells 

 ontogenetically ready to aggregate. 



CELL 

 DENSITY 



ADSORBANTS 

 LIGHT 



GROWTH 

 PHAiSE 



RATE OP CENTER PORMATION 



f 



DENSITY AND DTSTRTBTITTGN 

 CiV f^KNTF.RS 



CELL POOL SIZE 



Fig. 6. 



The Inter-relatlonshlps between various environmental 

 and biological factors, the rate of center formation and 

 the distribution and density of centers. Note that the rate 

 of center formation and cell pool size are the primary 

 factors In determining center density and distribution. 



Figure 6 summarizes the inter-relation- 

 ships between the various factors that influence 

 the rate of center formation, and the distribution 

 and density of centers. One final variable, not 

 previously mentioned, is "cell pool size", the 

 number of cells available for aggregation. If 

 the pool of cells is large, then after the initial 

 wave of aggregation, the cells remaining could 

 aggregate to form additional centers. This would 

 result in an increase in center density and would 

 favor the establishment of random or clustered 

 distributions since these "secondary" centers 

 could form at any distance from the first. Con- 

 versely, if the pool is small, few if any cells 

 would remain after the first wave of aggrega- 

 tion and no secondary centers could form. This 

 situation would minimize center density and 

 favor a spaced distribution. 



Two models satisfactorily account for the 

 relationship between the rate of center forma- 

 tion, and center density and distribution. In one 



127 



