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DISCOVERY REPORTS 



sideration of the actual analyses, as it is evident that the observations were not sufficiently 

 numerous to yield results of much value from the latter method of treatment. From 

 the account already given it will have been seen that the characteristic Rhizosolenia 

 plankton in the sub-Antarctic surface water, which had been such a feature of the first 

 week in March of the previous year, and of which traces were still observed as late as 

 April, did not occur in 193 1, the phytoplankton at the comparatively few stations worked 

 within the sub-Antarctic Zone on this occasion consisting mainly of Antarctic stragglers. 

 On the other hand, while in 1930 the comparatively rich phytoplankton with small 

 Chaetocerids and Nitzschia seriata dominant was not encountered until April, and then 

 on the westernmost line, in 193 1 a similar phytoplankton was encountered already half- 

 way across the Scotia Sea early in March. In Fig. 39 the phytoplankton totals are 



Fig. 40. The distribution of Corethron valdiviae (spineless chain form) in the Scotia Sea, February-March 1 93 1 . 



indicated by shading, and the presence of this comparatively rich phytoplankton to the 

 south of the Antarctic convergence is clearly shown. The distributions of the more im- 

 portant species of diatom have also been plotted individually in Figs. 40-45. Fig. 40 

 shows the distribution of the spineless chain form of Corethron valdiviae, which as we 

 have endeavoured to show in the preceding pages, may be regarded as a dominant form 

 of the phytoplankton in the southern sub-Antarctic waters, and also in old Antarctic 

 water, in abnormally warm seasons, in late summer. This is well borne out by the dis- 

 tribution observed during this particular piece of work. It will be seen that it occurred 

 at five out of the six comparatively poor stations worked to the north of the con- 

 vergence, and at four only of the stations immediately to the south, where the phyto- 

 plankton was richer and this species of less relative importance, though the actual 

 numbers in one case were higher. It may be mentioned that this form has occasionally 



