Chap. Ill] 



FRESH-WATER VEGETATION 



821 



5. THE VEGETATION OF SNOW AND ICE. 



The perpetual snow and ice of the polar zone and of mountains, here 

 and there, exhibit conspicuous colouring caused by microscopic Algae. 

 These colours, in the case of snow, are of various shades of red, rarely 

 of green, and, in the case of ice, usually brown. The coloured layer of 

 snow may be up to five centimeters thick, whilst ice nourishes its flora only 

 superficially, the phenomena being frequently associated with the presence 

 of fine dust. 



Since its discovery in the Savoy Alps by H. B. de Saussure l , who errone- 

 ously referred it to pollen or to a peculiar mineral substance, the pheno- 

 menon of ' red snow ' has often occupied the attention of the naturalist and 

 traveller. Its true nature was first recog- 

 nized by Elias Fries 2 (1822) and by 

 Agardh 3 (1823), who proved that the red 

 sphericles, so frequently misinterpreted, 

 were individuals of a protococcaceous 

 Alga,to which Agardh gave the name Pro- 

 tococcus nivalis 4 . Sommerfelt 5 , shortly 

 before this, had given to the organism 

 of red snow the name Sphaerella nivalis 

 (Fig. 502, 1-3), which is now in use. 



More recently the occurrence of Algae 

 associated with red snow has been 

 demonstrated on the most distant points 

 in the Arctic and Antarctic zones and 

 on most mountains with perpetual snow 

 (Pyrenees, Alps, Carpathians, Scandi- 

 navian Mountains, Ural, Sierra Nevada in Spain, Equatorial and Chilian 

 Andes), so that the phenomenon may be assumed to be of general distribu- 

 tion. The brown colour of ice has hitherto been observed chiefly in polar 

 districts, and green snow is a rare phenomenon. 



In addition to Sphaerella nivalis — first discovered and exceeding all 

 others in frequency and abundance — numerous other microphytes also con- 

 tribute to the flora of snow and ice. Wittrock 6 enumerates forty-two 

 species, which belong to Cyanophyceae, Diatomaceae, Conjugatae, Volvo- 

 caceae, Pleurococcaceae, and Ulothrichaceae. But among these, besides 

 Sphaerella, only two species are of considerable importance, Ancylonema 

 Nordenskjoldii, Berggr. (Fig. 502, 5, 6), a desmidiaceous organism with 

 violet sap, first discovered in Greenland on ice, to which it imparts a brown 



Fig. 502. Snow and ice Algae. 1-3. 

 Sphaerella nivalis. 4. Raphidium nivale. 

 5, 6. Ancylonema Nordenskjoldii. Mag- 

 nified. After Chodat. 



1 H. B. de Saussure, op. cit. 

 4 Agardh, II. 



2 Fries, op. cit. 3 Agardh, I. 



Sommerfelt. 6 Wittrock, op. cit. 



