SEASONAL SUCCESSION 



179 



there is a short continuous period of production, rather than any well-marked succession 

 of forms. 



While nearly all the species reach their maximum during the main outburst, some 

 persist throughout the summer to a much more marked degree than others. Others 

 again, after falling off in January and February, show from the few observations ob- 

 tainable at that season a definite tendency towards a secondary autumnal maximum. 

 Thus it is possible to classify the more important species roughly into four groups: 



Fig. 78. The probable distribution of the dominant species over the area studied at mid-season. 



(i) spring forms, (ii) forms with a spring maximum but which remain more or less im- 

 portant throughout the season, (iii) forms with spring and autumn maxima, and (iv) a 

 few comparatively unimportant forms found most frequently in late summer and 

 autumn. 



One or two important forms do not fall into the grouping very well and may be 

 mentioned separately: 



The minute species Chaetoceros socialis, which has been found to be such an im- 

 portant constituent of the phytoplankton in water of the western Weddell Sea type, 



evidently has its maximum round South Georgia in spring, but as Hardy has shown 



23-2 



