90 DISCOVERY REPORTS 



microspores has been observed in the genus by Pavillard (1924), so that in the present 

 instance the theory might apply very w^ell, even though spore formation was not actually 

 observed. The upper limit of the warm deep water at this station lay at a depth of only 

 200-300 m. Lohmann (1928, p. 16) has described a maximum for this genus in January 

 in the Weddell Sea proper, and one would therefore expect to find the species sinking in 

 numbers late in February in the older water farther to the north-east. On the few 

 occasions when this and other Cosciuodiscus spp. were encountered in numbers (which, 

 apart from C. botivet, was almost always under neritic or ice conditions) it was noted that 

 they seemed to have a very limited reproductive period, and once this was over, with 

 their heavily silicified skeletons and small surface-volume ratio, they appeared to sink 

 with great ease. In addition to C. boiivet a form was encountered in some quantity at 

 St. 365 which is to be regarded as an essentially neritic species — Melosira sol. 



A rather similar phytoplankton was encountered at St. 369 between Bristol Island 

 and Southern Thule, though here the approach to typically eastern Weddell Sea con- 

 ditions was more complete, as instanced by the still lower temperature and high salinity. 

 Small Chaetocerids, principally Chaetoceros dichaeta, were again numerically dominant, 

 but the following also occurred in considerable numbers : Rhizosolenia styliformis, Coscino- 

 disaisbouvet, Chaetoceros criophihim and Ch. castracanei, in that order of importance. The 

 Rhizosolenia styliformis found here consisted of large robust individuals in long chains, 

 and it is to the presence of this form, both here and at the following station, that the 

 apparent disproportion between the estimated numbers of organisms and the bulk of 

 the samples is to be ascribed. 



At the most southerly of these stations (St. 368), worked in Douglas Strait in 

 Southern Thule, R. styliformis, Chaetoceros dichaeta and Coscinodiscus bouvet were co- 

 dominant, and other forms of some importance were Chaetoceros criophihim and 

 Fragilaria antarctica. At all these stations the phytoplankton was moderate in quantity, 

 the estimated numbers ranging from 24 to 32 hundred thousand individual organisms. 

 Except for the rich belt to the south-east of South Georgia, however, the hauls might 

 fairly be described as rich in comparison with the majority obtained round that island 

 on the survey of the preceding month. 



It will be obvious from the small number and isolated nature of these stations that 

 little could be gained by discussing them further except in conjunction with other more 

 extensive data from the same area, and accordingly it is proposed to defer consideration 

 of their significance until the results obtained during the following season have been 

 described. 



THE SEASON 1930-1 



The earliest hauls bearing upon conditions in the Weddell Sea during the second 

 season, were taken in the vicinity of Bouvet Island and at a continuous series of observa- 

 tions lasting 24 hours (St. 461) about one-third of the distance between Bouvet Island 

 and the South Sandwich Islands, in October. That the Weddell Sea influence extends 

 as far eastwards as Bouvet Island is shown by the fact that the Antarctic convergence 



