Heterotrophy in Marine Diatojus 



233 



LIGHT 



+ GLUCOSE I DARK 



CYCLOTELLA sp. 



GLUCOSE I DARK 



01 23456789 10 

 DAYS 



Fig. J. Autotrophic and heterotrophic growth of CijcJotella sp. in aerated 

 cultures. (Light intensity, 300 hix; temperature 20C). 



terium in the dark was about six times as long as that in the 

 hght. The growth curves for the Cyclotella shown in Figure 1 

 illustrate that in the light the presence of glucose in the medium 

 had no effect on the generation time. 



DISCUSSION 



The results obtained so far seem to follow the pattern that 

 one would have predicted, i.e., among marine littoral pennate 

 diatoms, that often inhabit environments rich in organic nutrients, 

 a higher proportion of species are capable of using such nutrients 

 for heterotrophic growth than among the centric diatoms that 

 generally inhabit neritic or pelagic waters with much lower con- 

 centrations of organic nutrients. 



Some diatom species can multiply in the dark in the presence 

 of glucose and nitrate, while othefs require an additional factor 

 present in Tryptone. It remains to be determined which of the 

 components of Tr^'ptone is actixe, and whether it can be replaced 



