232 Marine Microbiology 



(a) enriched sea water, (b) enriched sea water + glucose, (c) 

 enriched sea water + Tryptone, and (d) enriched sea water + 

 glucose + Tryptone. The results are summarized in Table 2. 



TABLE 2 

 Effect of Tryptone on Heterotrophic Growth of Marine Diatoms 



Glucose Tryptone Glucose + Tryptone 



+ 

 + 



+ 

 + 

 + 

 + 



+ 

 + 

 + 



Rate of Growth of Diatoms Under Heterotrophic Conditions 



The experiments reported above were of a qualitative nature, 

 telling us only whether heterotrophic growth was possible. In 

 order to determine actual rates of growth under heterotrophic 

 conditions, the generation ( doubling ) times of three species were 

 determined both in the dark and in the light. The results, shown 

 in Table 3, indicate a wide variation between the species. 

 Nitzschia marginata can multiply as rapidly in the dark as in the 

 light. The generation time of CycJotella sp. in the dark was more 

 than twice as long, while the generation time of Nitzschia clos- 



TABLE 3 



Generation Times of Three Species of Marine Diatoms in Light and 

 Darkness at 20 C (The Basal Medium Consisted of Sea Water, Sup- 

 plemented with Nutrient Minerals, Vitamins and 0.1% Tryptone) 



