of five holes each at a given temperature. The 

 bottles were illuminated from below through 

 plastic windows in each hole. The continuous 

 fluorescent light was attenuated with fogged 

 photographic film filters placed below each 

 window. Thus, at each of six temperatures, five 

 light intensities were achieved. The light 

 intensity in each hole was measured by an 

 International Rectifier I2BM silicon photocell 

 which was calibrated against a Weston Model 

 756 footcandle meter and an Eppley radiometer 

 using the same fluorescent light source. 



Counts of cells in each culture were made at 

 daily intervals by taking 1-ml aliquots and 

 counting all the cells in a 0.1-ml portion using 

 a Palmer-Maloney counting chamber. Cell num- 

 bers were plotted against time in days on 

 semilogarithmic paper. Grov^h rates during 

 the exponential phase of growth were calcu- 

 lated by the equation: 



1^^ 



10g2 ^2 - l0g2 Ni 



to- tl 



where Ni and N2 are cell counts at times ti and 

 ^2. .W2 is expressed as doublings of cell numbers 

 per day. 



Results and Discussion 



Three experiments were performed. The first 

 two were terminated after only 4 days of 

 growth because of failure of the temperature- 

 controlling equipment and because of contami- 

 nation of some of the cultures with a small, 

 colorless flagellate. Nevertheless, these pre- 

 liminary experiments served to establish that 

 growth of G. sple)ide}is was optimum at 

 moderate temperatures and light intensities. 



This result was confirmed in the third experi- 

 ment in which growth was followed for 8 days. 

 Figure 1 shows the growth rates that were 

 achieved during the exponential phase of growth 

 at different temperatures and intensities in 

 this experiment. No growth occurred at 10° and 

 30°C and was suboptimal at 15°C. Growth was 

 maximal at 20-27 °C and at a light intensity of 

 2-9 kilolux. These are rather wide ranges of 



0.050 



en .t 

 Z E 



UJ •^ 



X -J 



0.025 



C- 



1,000 



- 500 



15 



10- 



o 

 5 



o'- ql 



0.000 

 0.000 



0.000 



0.000 



10 



15 



20 

 TEMPERATURE {°C) 



25 



0.000 



0.3001 

 ,0.200\ 

 0.100 



QOOO 



I I i_ 



30 



Figure 1. — Growth rates of Gyinnodinmm splendens at various light intensities and temperatures. 

 The numbers are rates in doublings per day at each intensity and temperature and the data are also 

 contoured to show similar rates. 



600 



I 



