Cryoplankton 447 



represented. A few species of desmids are occasionally present, mostly one 

 or two of the pond- or ditch-types of Closterium and Cosmarium. The 

 Peridinieae are sometimes represented by large numbers of Glenodiniwm and 

 more rarely by Geratium hirundinella and one or two species of Peridiniiiin. 



CRYOPLANKTON. 



This name is applied to the flora and fauna of perpetual ice and snow. 

 On the great snow-fields and glaciers of polar countries and high mountain 

 ranges there lives an association of organisms which in many respects 

 resembles the plankton-communities of lakes arid rivers. The vegetable 

 organisms, although including moss-protonema and a few Fungi, are mainly 

 Algae and they may occur in such great abundance as to give a distinct 

 colouration to the snow or ice. The algal groups represented in these snow- 

 floras are the Myxophyceae, Bacillariese and Chlorophycese, and according to 

 the dominance of certain species it is possible to distinguish between red, 

 yellow, green and brown snow. The chief investigators of snow-floras have 

 been Wittrock ('83), Lagerheim ('83; '92; '94); Chodat ('96; '02; '09); 

 Scherffel (10) and Fritsch (12). 



Red Snow has been most frequently observed and described in the past, 

 probably owing to the fact that it stands out so conspicuously, the tint 

 varying from a delicate rosy red to a deep blood-red or sometimes a dark 

 brick-red colour. It occurs extensively in the Arctic countries, in the Alps, 

 the Carpathians, the Andes, and to a limited extent in the Antarctic; it 

 has also been observed in the Appenines and the Pyrenees. It is caused 

 chiefly 'by the rounded resting-cells of Chlamydomonas nivalis which contain 

 a large amount of hsematochrome. These cells colour the upper layer 

 of snow to a depth of several centimetres and layer after layer may 

 become buried. A few diatoms are found in the red snow, and Glceocapsa 

 sanguinea, Scotiella nivalis, Chionaster nivalis and Rhaphidonema nivale 

 have been observed as subsidiary constituents. The species of diatoms vary 

 with the geographical area, and in both Arctic and Antarctic regions the 

 fragmentary remains of marine diatoms are not infrequent. 



Yellow snow is quite distinct from red snow and it may cover extensive 

 areas. In colour it is a pale bright yellow and the algal constituents are 

 more numerous than in the case of red snow. The best account of it has 

 been given by Fritsch (12) who examined in detail yellow snow collected 

 in the South Orkneys. This association included Protoderma Brownii, 

 Chlorosphtera antarctica, Scotiella antarctica, S. polyptera, S. nivalis, Proto- 

 coccus viridis, Chodatella brevispina, Rhaphidonema nivale, Ulothrix subtilis, 

 Mesot&niiim Endlicherianum, Nostoc minulissimum and several other Algse. 

 Some of these Algae are identical with those found in red or other coloured 



