MARINE ORGANISMS AND ENVIRONMENTAL INFLUENCES 285 



that in this respect also we may find important specific difi^er- 

 ences, but much basic work is required in order to obtain a 

 satisfactory method for further studies. 



The possibiHty of different responses to varying concentrations 

 of inorganic nutrients was brought into the spotlight by Rodhe 

 (1948) through his observations of extremely low maximal values 

 for various freshwater species. For the truly marine forms experi- 

 ments are not available to judge whether this ecological factor is 

 responsible for exceptional distribution patterns in certain species. 

 So far, the experimental approach in studying the environmental 

 influences on marine phytoplankton has been for orientation pur- 

 poses. In future special attention should be paid also to the in- 

 teraction of the various factors. 



The technique of the experiments has been simple. The cultures 

 have not been bacteria-free. The media have been enriched sea 

 waters, with or without soil extract as a supplement, and conse- 

 quently not well defined. As long as this was the case, problems of 

 more special nutritional requirements could not be approached. 

 These defects have been obvious to workers in the field and may 

 be partly responsible for the restricted nature of the activities. 



Since the pioneer research on cultures of marine phytoplankton 

 initiated by Miquel (1890-93) and especially by Allen in Plymouth 

 more than half a century ago, a great number of attempts have 

 been made to introduce synthetic media by using artificial sea 

 water. Allen himself, partly in collaboration with Nelson, made 

 experiments of this kind (Allen and Nelson, 1910; Allen, 1914) and 

 made the important observation that only with the addition of 

 small amounts of natural sea water could satisfactory growth be 

 obtained. Subsequent work proved that in most cases growth in 

 artificial sea water was not as good as in Allen or Schreiber sea 

 water with soil extract, or that no growth at all took place. The 

 importance of the organic components of natural sea water for 

 diatom growth was demonstrated by Harvey (1939), but it was 

 not till the general occurrence of auxotrophy in marine phyto- 

 plankton had been discovered that the basis was laid for introduc- 

 ing well-defined media of a satisfactory composition. Through the 

 contributions by Provasoli, Hutner, and their collaborators in 



