MARINE ORGANISMS AND ENVIRONMENTAL INFLUENCES 291 



demonstrated, and this field calls for experimental work on a large 

 scale. Field observations indicate that there is considerable varia- 

 tion between the species as to the frequency of auxospore forma- 

 tion. Detailed information on this point, required for a satis- 

 factory handling of diatom cultures in autecological work, can 

 be obtained only through laboratory experiments. 



The third large group of plankton algae, the coccolithophorids, 

 has also, one may say rather unexpectedly, disclosed a complicated 

 life cycle. In Coccolithus fragilis Bernard (1939) has suggested a 

 tentative life cycle, which includes the regular occurrence of 

 palmella stages in the sea. Quite recently Parke (1959) has been 

 able to show experimentally that the species Crystallolithus 

 hyalinus represents the motile stage of the well-known Coccolithus 

 pelagicus, which, according to Parke, has the character of a cyst. 

 This is an observation which gives quite a new viewpoint to the 

 understanding of distribution related to environment in these 

 forms. Observations on Coccolithus hiixleyi, the commonest of all 

 marine coccolithophorids, indicate that problems are also in 

 store concerning the life cycle of this species. 



This type of experimental work has been dealt with so exten- 

 sively here because it is essential both in direct interpretation of 

 the observations from the sea and in the introduction of a tech- 

 nique whereby uniform material for culture work may be obtained. 

 The recent achievements give promise of obtaining very important 

 information through continued studies within this field. 



Looking back upon the work which has been done on cultures of 

 marine phytoplankton, we notice that the experimental results 

 have been related to only a few of the many problems facing a 

 field ecologist. For many reasons it was natural to start with 

 environmental factors such as salinity and temperature, which 

 had been used so extensively for interpretation of specific diff"er- 

 ences in distribution. A basic knowledge of the influences of these 

 factors would also seem to be a prerequisite for a closer study of 

 the finer details in distribution pattern and seasonal occurrence. 



As activities have been so restricted and, unfortunately, a 

 great part of the experimental work has been made on species 

 which are not observed regularly in the sea, such as Phaeodactylum 



