172 



PROVASOLI 



Table I 



[chap. 8 



Dissolved Organic Matter in Sea-Water" 



a Derived from Duursma's table II (1960), with added concentration ranges found by 

 Duursma. 



of dissolved organic matter by living phytoplankton is not directly demonstrable 

 in the sea. This conclusion is contrary to the finding, under experimental 

 conditions, that several species of algae excrete considerable amounts of 

 organic solutes. This discrepancy deserves further work to find out if the 

 excretions are produced by healthy cells during logarithmic growth or by 

 resting or dying cells, and what are the conditions favoring release of external 

 metabolites. More detailed field studies are also needed to see whether 

 Duursma's findings are general. He determined at the microscope "the relative 

 proportions of the number of several species" (Duursma, op. cit., p. 29), but the 

 plankton populations were not studied in detail ; this could give a more precise 

 meaning to the data on particulate matter and chlorophyll determinations. 



The practical and precise method for analyzing dissolved organic carbon of 

 Duursma allows finally a detailed and more biologically significant definition 



