PREVIOUS WORK: DISCOVERY INVESTIGATIONS 273 



adjacent coastal areas — the most complicated region in the Antarctic zone. It was shown 

 that here the main diatom increase began in late spring or early summer, the time of 

 incidence falling later in the year as one proceeded pole-wards (p. 183). Stress was 

 laid on the important fact that throughout the whole of the region studied polar 

 influences extend very much farther towards the equator than in the northern hemi- 

 sphere. An attempt was made to group the species according to their seasonal abund- 

 ance and to distinguish the phytoplankton communities^ (' floras ') in Antarctic surface 

 waters of differing past history. These findings still hold good for the most part but 

 stand in need of some modification in the light of our more numerous and widespread 

 observations obtained subsequently. 



Areas with exceptionally rich phytoplankton were observed off South Georgia, other 

 more or less coastal waters round the southern half of the Scotia Arc and in the channels 

 of the Palmer Archipelago ; also, to a lesser extent, in Bransfield Strait. 



It was shown that the phosphate content of the surface waters was never reduced to 

 such as extent that one could regard it as a factor limiting phytoplankton production 

 (Hart, 1934, p. 184). The hypothesis that silica might prove to be limiting to some 

 extent was put forward on the suggestion of Professor W. H. Pearsall, though at that 

 time no direct observations on silica content were available (p. 185). The major mi- 

 portance of various interrelated physical factors in determining the extent of phyto- 

 plankton production was emphasized. Chief among these were the influence of light, 

 the degree of stability of the surface layers, and the effects of pack-ice (pp. 186-93). 



Observations in Cumberland Bay, South Georgia (Hart, 1934, Appendix I) showed 

 the phytoplankton to be very scanty, in striking contrast to the rich catches obtained 

 20-100 miles offshore round that island. The adverse factors responsible for this 

 appeared to be extreme turbulence of the surface layers due to the strong and variable 

 winds, combined with the vast amount of very finely divided inorganic detritus brought 

 down by land drainage (mostly morainic mud). This last must have greatly hindered 

 the penetration of light. The same unfavourable factors have since been found to be 

 responsible for a similar unexpected scarcity of phytoplankton in some regions of the 

 northern hemisphere (Bay of Fundy, Gran and Braarud, 1935, p. 322; coastal waters 

 round Iceland, Nielsen, 1935, pp. 42-8). 



The great value of Hendey's work (1937) lies in his thorough revision of the syste- 

 matics of the plankton diatoms. He has cleared up many vexed questions concerning 

 nomenclature and priority with a thoroughness only possible to one with long ac- 

 quaintance with the extraordinarily voluminous and contradictory literature on the 

 subject. The most helpful features to the plankton worker are his decisions to 'lump' 



1 In some sense the idea of this grouping approximates more closely to that of Gran and Braarud's 

 'phytoplankton societies' (1935, p. 332). Since the groups varied mainly in the proportions of the same 

 species present, not in specific constitution, and the water masses concerned gradually lose their individuality 

 as they move to the east and north, it seems safer to use the wider term. It is just such differences as these 

 due to the much greater rate of change in the aqueous as distinct from the terrestrial environment, that 

 makes it so hard for the plankton worker to describe his observations in terms with rigidly conventionalized 

 meanings. 



