64 DISCOVERY REPORTS 



The comparative scarcity of species towards the end of the season is indeed well shown 

 by the material from this line as a whole, only nineteen different phytoplankton 

 organisms being encountered as against twenty-seven earlier in the year in the same 

 area. Moreover, it would seem, from a few stations worked on the arrival and departure 

 of the research ships on more extensive investigations, that towards the end of this 

 season the phytoplankton elsewhere round South Georgia was even scantier. The 

 remnant of the formerly abundant flora apparently persisted longest in the old mixed 

 water, mainly of eastern Weddell Sea origin, to the east and north of the island. 



One other feature of this repetition of the Prince Olaf line was interesting — the 

 presence of Peridinium antarcticum in numbers which, though insignificant as compared 

 to the rest of the phytoplankton present, still amounted to over one-third of the numbers 

 recorded for the same species over the whole of the survey worked earlier in the year. 

 Here we have a suggestion of the usual slight increase in dinoflagellates towards the end 

 of the season, which reached such exceptionally large proportions on the survey con- 

 ducted in the late summer of the previous abnormally warm year. 



SUMMARY 



On the plankton survey of November 1930, the spring diatom increase was at its 

 height, and very heavy catches were obtained. The influence of the three types of surface 

 water on the character of the phytoplankton was very clearly shown, and the richest and 

 most varied flora was found in the water, mainly of western Weddell Sea origin, to the 

 south and south-west of the island. Here the dominant forms were Chaetoceros socialis, 

 Thalassiosira antarctica and Chaetoceros neglectus. The cold tongue of eastern Weddell 

 Sea water running up the north-east coast of the island, was populated mainly by the 

 large forms Ch. criophiliim and Rhizosolenia styliformis, and in the older water 

 farther north by Coretliron valdiviae. The poorest hauls on the whole survey were 

 obtained in the old Bellingshausen Sea water to the north-west. 



There is also evidence that during the latter half of the 1 930-1 season, the phyto- 

 plankton did not decrease to anything like the same extent as in previous years. The 

 season was an exceptionally cold one with a lot of ice about. There was pack around the 

 island only a week before the survey was begun, and throughout the season ice was re- 

 ported in comparatively low latitudes to the southward. 



An idea of the richness of the phytoplankton encountered on the November survey 

 may be gathered from the following list, in which the species are arranged in order of 

 their total abundance. The figures in brackets immediately after the specific names 

 denote the number of stations at which each occurred. 



Thus, taking the survey as a whole, sixty separate forms were recognized, including 

 eight species of Chaetoceros, Coscinodisciis boiivet and others that were not taken at 

 all in the scanty phytoplankton of the previous summer, when only twenty-four forms 

 were distinguished. The striking disparity between the two surveys, as regards the 

 quality apart from the quantity of the phytoplankton, was also shown by the fact that 

 the normal spiny form of Corethron valdiviae was present at every station, while the 



