314 



DISCOVERY REPORTS 



numerous it was present at 62% of the stations, and dominant at 16%. In February 

 and March it fell off in quantity so that it did not obviously predominate over the 

 diatoms anywhere, but was still present at more than half the stations. In April 

 (autumn) it was only observed in very small quantity at three out of twenty-seven 

 stations. 



THE SOUTHERN REGION 

 Except for the three months immediately after midsummer this region is almost 

 inaccessible, and we have only isolated observations in spring and autumn. It may be 

 that wherever Polynas exist in the pack-ice, some production takes place from November 

 onwards, but this can only be a very local effect. From the known climatic and ice 

 conditions it is obvious that large-scale production can only begin when the first large 

 areas of open water are formed in January, and as new ice begins to form in March it 

 follows that the annual production must be crowded into three summer months with no 

 possibility of a secondary autumnal increase. Our observations fully bear this out, the 

 main increase evidently begins very suddenly in January and rises to a high maximum 

 (as the oceanic values go) in February. A few moderately high values have been re- 

 corded in the early days of March, but taking that month as a whole the falling off was 

 most marked. The relevant figures are given in Table 6 and are also plotted on the 

 same scale as for the Northern and Intermediate Regions in Fig. 12. 



Table 6 



There is nothing exceptional about the qualitative sequence in the Southern Region. 

 The results are summarized in Table 7 and follow a very similar course to those found 

 in the Intermediate Region over the period of the main increase. The most noteworthy 

 differences from the conditions farther north, allowing for the difference in time scale, 

 are: Group I showed maximum relative importance at the maximum (quantitative) 

 period instead of before and after the maximum, and was less important than it is farther 

 north throughout the year. Group II was more important here than in either of the 

 more northerly oceanic regions, especially before and after the maximum. This was 

 almost entirely due to dense local concentrations of Chaetoceros criophilum and more 

 especially Corethron criophilum, with Rhizosolenia alata gracillima phase in lesser 

 amounts. At the single autumn observation Dactyliosolen antarcticus was the most 



