THE PROBLEMS OF ANTARCTIC PLANT LIFE. 13 



discoloured by diatoms, and I am not aware that other recent expeditions have recorded 

 this occurrence ; but Dr W. S. Bruce, in the cruise of the Balsena in 1892-93 between 

 62 and 63 S., off Louis Philippe Land, frequently remarked that the sea was olive- 

 green or olive-brown from this cause, and that the most usual species in these dis- 

 coloured parts was Corethron criophilum. This phenomenon is of much commoner 

 occurrence in Arctic seas. 1 Plankton collections well within Antarctic seas and over a 

 wide area are largely confined to the collections of the Scotia, which fortunately was 

 able to traverse some 10,000 miles of unexplored south polar waters. The other recent 

 expeditious, Discovery, Antarctic, Gauss, Frangais, and Nimrod, did comparatively 

 little marine exploration within truly polar waters. The Belgica's results in this de- 

 partment should, however, be of great interest, and will be supplemented by those of 

 the Pourquoi Pas?, while the Vnhlivia's collections, though in more or less extra-polar 

 waters, have important relation to Antarctic plankton. A detailed report and discussion 

 of the Scotia's plankton is in process of completion. 



While freshwater algae appear to be comparatively abundant, they are not nearly 

 so plentiful as in north polar regions. In the collections which I made at the South 

 Orkneys, Dr Fritsch has found 68 species (of which 5 are new) : most are uni- 

 cellular and colonial. 2 With the exception of the Belgica, the Southern Cross, the 

 Discovery, and the Nimrod, other expeditions have not yet published their results 

 in this branch of botany. A number of forms, however, have been recorded from 

 Kerguelen and South Georgia. 



Among the South Orkney collections very few reproductive stages were found even 

 in material collected about midsummer, and Dr Fritsch believes that many species only 

 reproduce during very limited periods under specially favourable conditions. The 

 rarity of diatoms and infrequence of desmids in this freshwater flora are noteworthy 

 None of the new forms of diatoms in either the Discovery or Nimrod collections occur 

 at the South Orkneys. 



Red and yellow snow occur at the South Orkneys, though neither is abundant. Red 

 snow has been recorded from Arctic regions, as well as other parts of Antarctic regions, 

 including Graham Land and Victoria Land : it is also recorded from extra-polar regions. 

 Yellow snow is much rarer, and I am not aware that other Antarctic expeditions came 

 across it. Dr Fritsch has reported in considerable detail on these coloured snows (he. cit.), 

 and he finds that yellow snow is due to an association of 1 8 species of algae and 2 of fungi ; 

 most of the algas are green forms, but few diatoms occur. The whole of this flora has a 

 plankton character, and Dr Fritsch suggests that this and other snow floras may have 

 arisen by wind carriage of plankton forms to the snow surface. Most of the constituent 

 members of this flora have a quantity of fat in their cell contents, in which yellow 

 pigment occurs. This fact seems to be an adaptation to the severity of the habitat. 



1 "On the Nature of the Discoloration of the Arctic Seas," Robert Brown, Trims. Bot. Soc. Ediii., ix. p. 244. 



2 See this volume, pp. 95-134, and "Freshwater Algre collected in the South Orkneys," Joan/. Linn. Soc. Land 

 xl., 1912, pp. 293-338. 



