MARINE ORGANISMS AND ENVIRONMENTAL INFLUENCES 293 



ever, in general It may be stated that the actual effect of the en- 

 vironmental factors upon form has not been analyzed. 



The conditions which induce sexual reproduction and lead to 

 auxospore formation in the various species of diatoms are also 

 obscure. Likewise, are the conditions stimulating cyst formation 

 in diatoms, dinoflagellates, and coccolithophorids. We know that 

 these processes occur regularly in some species, whereas in others 

 they seem to be rarer, presumably occurring as a reaction to rather 

 special env^ironmental conditions. Germination of resting spores 

 has never been studied in cultures, except for the rather unusual 

 type observed by Gross (1940) in Ditylum brightwelU, although it 

 would be of great interest to obtain information on this process 

 in order to further understanding of the annual cycle of many 

 neritic species. 



One of the basic features of behavior in plankton diatoms, their 

 ability to maintain populations in the surface layers even during 

 periods of poor growth conditions, is still one of the dark points. 

 The various species seem to react differently in this case also, as 

 some of them maintain small populations in the euphotic layer 

 throughout the year, while others have brief periods of abundance 

 and then disappear. The field observations call for experimental 

 studies, both to investigate further the interesting theory of Gross 

 and Zeuthen (1948) that flotation is due to the maintenance of a 

 relatively high concentration of monovalent ions in the cell sap 

 and also to explain the specific differences in behavior indicated 

 by the field observations. 



The effect of submarine light upon the phototaxis of flagellates 

 has been subjected to interesting physiological studies by Halldal 

 (1958), but the specific reactions of most species have yet to be 

 described on the basis of laboratory studies. The observations at 

 sea have shown that migrations take place, and have indicated 

 different reaction patterns for the various species (Hasle, 1950), 

 but experimentally very little has been done here. These are a few 

 of the classical problems that must be solved by experimental 

 means, and they are involved in most of the attempts at under- 

 standing the results produced by field surveys. The studies of 

 organic production in the sea by means of Steemann Nielsen's 



