PHYTOPLANKTON OF SOUTH GEORGIA 



41 



THE PLANKTON SURVEY OF NOVEMBER 1930 



On this survey forty-nine stations, arranged on seven lines radiating out to a distance 

 of about 100 miles from the island, were made in the course of 15 days by the R.R.S. 

 ' Discovery II '. The arrangement of the lines differed slightly from that adopted on the 

 previous survey (see Fig. 4), but the area was equally well covered. The phytoplankton 

 obtained was exceedingly rich and varied, the main spring diatom increase having ap- 

 parently only just reached its maximum. At some stations the settled volume of the 

 catches exceeded i^ litres, and as small colonial forms, notably Chaetoceros soa'alis, 

 Ch. neglectus and the minute form of Thalassiosira antarctica which occurs in gelatinous 

 colonies, were exceedingly abundant, it will at once be seen that it was utterly impossible 

 to estimate their numbers with even the rough comparative degree of accuracy 

 achieved with the larger species. The ordinary chain form of Th. antarctica was, how- 

 ever, always countable, though unfortunately small numbers of the closely allied 

 Coscinosira antarctica were probably confused with it at a few stations on the Undine 

 South and Cooper Island lines. The general practice adopted was to denote the presence 

 of small colonial forms, when too numerous to be estimated satisfactorily, by a symbol 

 such as + or co, and to count only those forms that could be clearly distinguished under 

 a J in. objective. By this means the expression of the relative abundance of the leading 

 forms diagrammatically is ruled out of court, and tables have therefore been constructed 

 showing both the actual numbers, and the percentages of the total estimated apart from 

 the uncountable forms, which, however, are included in the tables with appropriate 

 symbols so that their great importance can be clearly recognized. 



On the Larsen line (Fig. 4), the catches were uniformly heavy, except for that at 

 St. 494. From Table IX it will be seen that conditions on this line were very uniform, 



