PHYTOPLANKTON OF THE WEDDELL SEA AREA 



99 



on the return voyage within these limits can be considered along with those of the out- 

 ward passage without further explanation. The southernmost station was worked at the 

 edge of pack-ice, encountered when the 'William Scoresby ' had penetrated to a point 

 within about lOO miles of the probable position of Coats Land. Lack of fuel 

 prevented further progress, but as by this time the ship had penetrated into the region 

 of the distinctive type of plankton found in the water which flows round the inside of 

 the bight of the Weddell Sea, the observations obtained are just as valuable, from the 

 point of view of plankton investigations, as they would have been had an even higher 

 latitude been attained. 



Proceeding southwards from St. WS 542, the hauls from the next five stations show 

 yet another great change in the nature of the phytoplankton. The full analyses of this 

 material are contained in Table XXX, and in addition the relative proportions of the 

 leading forms are shown in Table 18. 



Table 18 



These five stations were worked between 60 and 65° S, 15 and 20° W and are arranged 

 in north to south order. It will be seen that the very rich phytoplankton with Rhizo- 

 solenia styliformis dominant, which was encountered at the southernmost of the last 

 described series of stations, culminated in an enormous catch of this type at St. WS 543. 

 The next great change in the character of the phytoplankton was, however, fore- 

 shadowed in the fairly large numbers of Nitzschia seriata recorded at this station. 

 Another interesting species which occurred here was N. closterium. Except in the im- 

 mediate vicinity of ice or close to the Antarctic Continent this form has rarely been 

 encountered during the course of the investigations. Its occurrence here in open water 

 in about 60" S, to the extent of i per cent of this very rich haul, was probably a legacy 

 of pack-ice which had recently passed away to the north. 



At the next station to the southward, St. WS 545, Rhizosolenia styliformis was still 

 the most numerous of the phytoplankton organisms, but it is evident that the catch at 



13-2 



