88 DISCOVERY REPORTS 



all the species of the genus commonly found in Antarctic surface waters, it is not sur- 

 prising to find it prominent among the Antarctic stragglers into the sub-Antarctic Zone. 



The distribution of Fragilaria antarctica observed on these stations is shown in Fig. 44. 

 Like most of the other Antarctic forms it was evidently coming through the southern 

 half of Drake Passage into the Scotia Sea. North of the convergence it occurred at two 

 stations only, all so close to the convergence as to lie most probably with the zone of 

 great vertical mixing which is found immediately to the north. The occurrence of this 

 species in sub-Antarctic surface waters may therefore reasonably be regarded as 

 fortuitous. 



Fig. 45 shows the distribution of Dactyliosolen antarcticiis, a species whose occurrence 

 especially to the north of the convergence closely agrees with that of Chaetoceros at- 

 lanticus. Like the latter it may be regarded as an autumn form of northerly range 

 (see also p. 69). 



THE PHYTOPLANKTON OF THE WEDDELL SEA AREA 



A brief account of the stations worked in this area has already been given (pp. 13, 14). 

 As stated, the material obtained during the first season's work was very scanty, being 

 confined to a few stations worked rather late in the season in the extreme north-east of 

 the Weddell Sea proper, in the vicinity of the South Sandwich Islands. This material 

 has been treated separately, small as it is, with a view to avoiding confusion and bringing 

 out the abnormality of the conditions obtaining to the north-east during the latter half 

 of the season 1929-30. 



The positions of all the stations worked in the northern part of this area are shown on 

 the same reference chart (Fig. 32) as that used for the previous section (p. 70). 



THE SEASON 1929-30 



On the completion of the plankton survey round South Georgia, course was laid for 

 the South Sandwich Islands, and while on this passage phytoplankton samples were 

 collected at four stations, at which full hydrological data were also obtained. The first 

 of these, St. 359, was worked in the lee of a very large tabular berg, over 60 miles in 

 length. At this station a first attempt to employ the centrifuge method of estimating the 

 phytoplankton was made, but beyond gaining useful experience the results were not of 

 much value, as the phytoplankton appeared to be homogeneous in both quality and 

 quantity down to a depth of 80 m. This was doubtless due to violent vertical water 

 movements caused by the presence of this vast mass of ice. The analysis of the net haul 

 from this station, together with those of the others obtained en route to the South 

 Sandwich Islands, will be found in Table XXIV. It will be seen that the results from 

 St. 342 of the South Georgia survey have also been included, as by this means it be- 

 comes possible to show that the moderately rich belt of phytoplankton met with to the 

 east of South Georgia on that occasion extended for a considerable distance to the south- 

 east. 



