CHAPTER XXXIX. CRYOPLANKTON. 1 VEGETATION ON 

 ICE AND SNOW 



THIS glacial vegetation is most closely allied to plankton. It has 

 long been known that animals and plants live on the extensive snow- 

 fields and glaciers of arctic countries, and such high mountains as the 

 Alps, Pyrenees, and Andes ; they are in the main microphytes, yet, 

 like plankton, they can occur in such countless numbers as to colour 

 the snow or ice. The animals specially include Poduridae (Desoria 

 saltans, and the blue Achorutes viaticus), Tardigrada, Radiolaria, and 

 threadworms. To Wittrock and Lagerheim 2 we largely owe our know- 

 ledge of the vegetation, which consists mainly of aquatic plants, and 

 particularly of algae (Diatomaceae, Chlorophyceae, and Cyanophyceae), 

 Schizomycetes, and mosses in their protonema-stage. Some Phycomy- 

 cetes also occur. In 1892 Lagerheim assessed the number of species 

 at seventy- two. According to colour we may distinguish red, brown, 

 also green and yellow, snow. 



Red snow is the commonest, and has been known for the longest 

 time ; the tint varies from blood-red to rosy red, and from brick-red 

 to purple-brown. It is caused especially by Chlamydomonas (Sphaerella.) 

 nivalis, and C. nivalis var. lateritia. This unicellular, spherical or ovoid 

 alga has red contents, and colours the uppermost layers of snow to 

 a depth of a few centimetres ; in the water derived from melting snow 

 it multiplies by zoospores. In addition there occur, among other species, 

 Gloeocapsa sanguinea, Cerasterias nivalis, Pteromonas nivalis, as well 

 as diatoms, and, in Ecuador, species of Chlamydomonas. 



Brown snow owes its colour to various species, including the desmi- 

 diaceous Ancylonema Nordenskioldii, which contains violet cell-sap and, 

 together with other algae and ' cryoconite ' (very fine mineral particles), 

 has an important action on the ice in the interior of Greenland, as it 

 absorbs the sun's rays more strongly than does the ice and thus melts 

 deep cavities in the latter. In company with it live Pleurococcus vulgaris, 

 Scytonema gracile, diatoms, and other algae. 



Green Snow is a phenomenon due to the presence of Green Algae, for 

 instance Desmidiaceae, also to Raphidium nivale, 3 Cyanophyceae, protone- 

 mata of mosses, and green individuals of Chlamydomonas (Sphaerella) 

 nivalis. Bright yellow or greenish yellow snow is tinted by another alga, 

 possibly Chlamydomonas flavivirens, which is known to occur on snow- 

 fields of the Carpathians. 



These plant-communities provide very evident examples of extra- 

 ordinary powers of resistance on the part of plant-cells : except for the 

 peculiar properties of the protoplasm they seem to be devoid of any 

 means of protection against cold, though perhaps red colouring-matter 

 may enable them to absorb heat. 4 During the greater part of the year 

 they lie frozen in ice or snow and in the lasting darkness of the arctic 

 night ; when the sun's heat melts the ice and snow, they awaken into 

 activity, carrying on their processes of nutrition and reproduction in 



1 Schroter, 1904-8, p. 623. * Wittrock, 1883, p. 883 ; Lagerheim, 1892. 



* Chodat, 1896. Wulff, 1902. 



M 2 



