TRANSITIONAL PHYTOPLANKTON 8i 



Antarctic stragglers. Nitzschia seriata was strongly dominant, and the other principal 

 species were Corethron valdiviae in the spineless chain form, Dactyliosolen antarcticus, 

 Chaetoceros atlauticiis and Rhizosolenia alata in that order of importance. Among the 

 rarer forms, indicative of sub-Antarctic influence, R. ciirva, R. polydactyla and 

 Ceratium pentagonum were present. 



The temperature at the next station to the southward was still high, although the 

 position given is normally definitely to the south of the convergence. The phytoplankton 

 at this station was very rich, and in general closely similar to that taken on the first 

 station. Nitzschia seriata was again strongly dominant, and the other more numerous 

 species, in order of their importance were: Corethron valdiviae (spineless chains), 

 Fragilaria antarctica, Dactyliosolen antarcticus and Ceratium pentagonum. The dino- 

 flagellates here reached their maximum for the line, and the typically sub-Antarctic 

 species Rhizosolenia curva and R. polydactyla were both present. 



At St. 635, the next in order as one proceeded south on this line, the quantity of the 

 phytoplankton was moderate, only a trifle over i million organisms being estimated to 

 be present, as against 14 and 40 millions respectively at the first two stations. The 

 quality was also markedly diff"erent, Chaetoceros atlanticus being strongly dominant, and 

 Nitzschia seriata the only other species recorded in appreciable numbers. The dino- 

 flagellates formed but a small proportion of the phytoplankton at this station, and farther 

 south they were not met with on this line. At the next station to the southward, St. 636, 

 the phytoplankton was rich again ; Nitzschia seriata and Chaetoceros neglectus were co- 

 dominant with only a slightly smaller quantity of Ch. atlanticus. Other important 

 forms were Ch. dichaeta and Fragilaria antarctica f. bouvet. 



The three succeeding stations (637-9) were worked roughly south-south-west from 

 the South Orkney Islands ; the temperatures in the upper layers were much lower and 

 the phytoplankton showed an abrupt falling off. At the first of these the high salinity 

 possibly indicates the influence of western Weddell Sea water. Chaetoceros atlanticus, 

 Fragilaria antarctica and Chaetoceros neglectus were the principal forms here among a 

 poor phytoplankton. The two last stations showed minus temperatures and the low 

 salinities suggest that ice had recently melted in the water in which they were worked. 

 At both the phytoplankton was very poor, with the normal spiny form of Corethron 

 valdiviae dominant. 



The next line of stations crossing the Antarctic convergence during this second season 

 (Sts. 644-51), was worked from a point to the north-west of Elephant Island north- 

 wards to Staten Island— across Drake Passage, but farther to the eastward and a month 

 earlier than the corresponding line of the preceding year. The analyses of the phyto- 

 plankton collected on this line are given in Table XXII. 



At the southernmost station C. valdiviae was the most numerous form in an 

 exceedingly poor catch. This station was apparently worked within the "desert" area 

 to the north and east of King George Island which has been noted on other occasions 

 (see p. 72). Proceeding northwards the phytoplankton was somewhat richer at the next 

 two stations, the dominant forms being Chaetoceros neglectus, Nitzschia seriata and 



