348 POLAR PROBLEMS 



replaced by deeper layers richer in nitrates, thus renewing the food 

 supply of the diatoms; and the abundance of silica in polar seas owing 

 to the low temperature of the water and the great quantities of glacier- 

 swept waste from the land. 



Origin of the Antarctic Land Flora 



An analysis of the scanty land flora of the Antarctic shows three 

 elements, endemic, Arctic, and Fuegian. The high proportions of 

 endemic species, particularly among mosses, can be explained by 

 long isolation and peculiar conditions of environment. Two ex- 

 planations of the Arctic element have been suggested. Carriage of 

 spores and soredia on the feet and plumage of birds like Wilson's petrel 

 and the Arctic tern, which wander through 150° of latitude, might 

 account for some species, but it is difficult to find in this suggestion^" 

 an adequate explanation of the occurrence of half the Antarctic lichens 

 and 30 per cent of the mosses in the Arctic. A more credible explana- 

 tion is either that the species in question are cosmopolitan and have 

 not yet been found in low latitudes or that they have been crowded 

 out by stress of competition in low latitudes where happier conditions 

 lead to more rivalry for location. 



The Fuegian element, ^^ or, it may be said, the Fuegian relationship, 

 of most species shows that the present flora has reached the Antarctic 

 Continent and islands by the prevailing northwesterly winds from 

 South America, birds no doubt playing a part.^^ Ice transport can be 

 ruled out altogether. There is direct evidence of transport from South 

 America in the pollen grains of a Chilean conifer, Podocarpus, which 

 were found among red snow at the South Orkneys. ^^ Probably the 

 present flora first reached Graham Land and adjacent islands, where 

 it shows its richest form, and then spread eastward round the rim of 

 the continent. The migration must have been slow, for it could occur 

 effectively only during a few weeks at midsummer when mosses and 

 lichens "fruit" and there is bare ground for the wind-blown spores to 



1° Jules Cardot: Note sur la flore de I'Antarctide, Compte Rendu Assn. Francaise pour I'Avance- 

 ment des Sci., 366 Session, Reims, 1907, Paris, 1908, pp. 452-460. 



11 On the plant life of Fuegia see, among others: 



Carl Skottsberg: (a) Feuerlandische Bluten; (b) Zur Flora des Feuerlandes; (c) Pflanzenphysiog- 

 nomie des Feuerlandes; (d) Das Pflanzenleben der Falklandinseln (Wiss. Ergebn. Schwed. Siidpolar- 

 Exped., Vol. 4: Botany, Parts I and II, Nos. 2, 4, 9, and 10 respectively), Stockholm, 1908 and 1921. 



Carl Skottsberg, F. Stephani, and T. G. Halle: Botanische Ergebnisse der Schwedischen Expedi- 

 tion nach Patagonien und dem Feuerlande 1907-1909 (five separate monographs), Svenska Vetenskaps.- 

 Akad. Handl., Vol. 46, two numbers, 1910 and 191 1; Vol. 50, No. 3, 1913; Vol. 51, No. 3, 1913; Vol. 56, 

 No. S, 1916. 



P. Dusen: (a) Die Gefasspflanzen der Magellanslander, nebst einem Beitrag zur Flora der Ost- 

 kiiste von Patagonien; (b) Die Pflanzenvereine der Magellanslander nebst einem Beitrage zur Okologie 

 der magellanischen Vegetation (Wissenschaftliche Ergebnisse der Schwedischen Expedition nach den 

 Magellanslandern 1 895-1 897 unter Leitung von Dr. Otto Nordenskjold, Vol. 3: Botany, Nos. 5 and 

 10, pp. 77-266 and 351-523 respectively), Stockholm, 1905. 



1- Carl Skottsberg: Die Gefasspflanzen Siidgeorgiens (Wiss. Ergebn. Schwed. Siidpolar-Exped., 

 Vol. 4: Botany, Part I, No. 3), Stockholm, 1905. 



13 Fritsch, Freshwater Algae of the South Orkneys, p. 119. 



