io8 DISCOVERY REPORTS 



had it been possible to work more stations in the first half of the season. This also applies 

 to a lesser extent to certain other forms with a well-marked spring maximum, e.g. 

 Biddulphia striata. Apart from the forms listed above, the following additional species 

 were encountered in the eddy of western Weddell Sea water at the north-eastern end of 

 Bransfield Strait: Chaetoceros flexuosus at two stations, and the littoral forms Biddulphia 

 (Triceraiium) arcticutn and Lycmophora sp. at one station at which the influence of in- 

 shore water flowing northwards through Antarctic Sound was very apparent. 



From the list it can be seen that despite their wide distribution, such species as 

 Rhizosoleina alata, R. tnmcata and Coscinodiscus spp. were of quite minor importance, 

 while some forms would certainly take a higher place if it had been possible to estimate 

 their numbers satisfactorily and if ice conditions had allowed more hauls to be taken 

 early in the season. From the account already given of the phytoplankton round South 

 Georgia in November 1930, it will be remembered that among the small forms present 

 in vast quantities in old surface water, mainly of western Weddell Sea origin, Chaetoceros 

 socialis, Thalassiosira antarctica and Chaetoceros neglectus took pride of place. There is 

 thus little doubt that in order to make the list fully representative of the phytoplankton 

 of the Weddell Sea as a whole, throughout the year, these three species should be in- 

 cluded in the first half-dozen or so, their precise position relative to the others being, 

 of course, problematical. As it stands, however, the list gives a fairly true picture of 

 the conditions from mid-season onwards, at which time of year most of the obser- 

 vations were taken. The large forms Ch. criophihmi, Rhizosoleriia stylifortnis, and 

 Corethron valdiviae reached an enormous maximum in the older water of the eastern 

 Weddell Sea type in the vicinity of the South Sandwich Islands, while the minute 

 species such as Nitzschia seriata and Fragilaria antarctica owe their high place to their 

 almost complete dominance in the water entering the sea far to the south-east. The com- 

 paratively high position of the spineless chain form of Corethron valdiviae is, of course, 

 entirely due to its complete dominance in the old water between South Georgia and the 

 South Sandwich Islands in the late summer of the abnormally warm year 1929-30. 



From this summary, coupled with the facts previously mentioned of the great increase 

 in quantity of the phytoplankton as one proceeded east-north-east across the mouth of 

 the Weddell Sea in late summer (Table XXXII), one is forced to the following im- 

 portant conclusions. In the region of the South Sandwich Islands and to the east of 

 South Georgia, a rich phytoplankton development takes place lasting on well into the 

 second half of the season in a cold year, and that a rich phytoplankton tends to persist 

 longer in old surface water of the eastern Weddell Sea type than in any of the other 

 types of Antarctic surface water with which we are at present acquainted. 



