FRESHWATER ALGJE OF THE SOUTH ORKNEYS. 119 



this region does not attain to nearly so abundant a development as yellow snow. 1 The 

 number of species present is also smaller. On the whole sample 4 was richer in 

 individuals than either 5 or G, and showed a somewhat different constitution. Nearly 

 all the forms present were in the resting condition, so that some doubt attaches to 

 certain determinations. The samples of red snow included a good deal of non-algal 

 matter, such as hairs, starch grains, pollen grains of Podoearpiis, etc. 



In comparison with the flora of the yellow snow we have to note certain similarities 

 and certain differences. Among the former we may reckon the occurrence of character- 

 istic forms of the yellow snow flora, such as Scotiella antarctica, F. K. Fritsch, and 

 Raphidonema nivale, Lagerli. The former was found only in samples 5 and 6, 

 especially in the latter; the number of individuals was small, but those present were 

 of exceptionally large size (length of cell about 55 M). They appeared to contain the 

 same yellowish fat as in the yellow snow forms ; no resting-stages were observed. 

 The Raphidonema was quite common (especially in sample 4), and in this case 

 agreed absolutely with Lagerheim's description. Apart from fragments of an 

 (Edogonium it was the only filamentous form present. 



There are two marked differences from the yellow snow flora. These are () the 

 immense preponderance of red spherical cells, no doubt constituting the resting-cells 

 of different members of Chlamydomoiiadacese (see below), and (l>) the occurrence of 

 various diatoms in all three samples. The resting-cells are of two chief types, viz. 

 with and without a broad mucilage-sheath. The latter type are circular, with a 

 smooth, somewhat thickened membrane and granular contents, with a central pyrenoid 

 (text fig. 1, A, p. 122); the diameter of these cells varies between 10 and 20 M. The 

 red colouring matter in the contents had been for the greater part taken up into the 

 preserving fluid, and the cell-contents appeared colourless or slightly greenish ; it is 

 therefore impossible to say what the exact colour of these cells was in nature. A 

 considerable quantity of fat was often present in these resting-cells. They recall very 

 markedly the resting-cells (aplanospores) of Chlamydomonas nivalis (Sommerf.), Wille 

 ( = Sphserella nivalis, Sommerf.), as figured by Wittrock. 2 As very few other stages of 

 this alga were found, the determination must, however, remain somewhat doubtful. 

 In one or two cases subdivision of the contents into a number of parts was observed, 

 but this, of course, scarcely aids in determining the species. 



The second type of resting-cell (observed only in sample 4) closely resembles the 

 other type except that the cells are surrounded by a broad sheath of mucilage often about 

 two to three times the width of the cell in diameter (cf. text fig. 1, C, p. 122 3 ) ; in many 

 cases the mucilage was of a deep red colour, probably owing to the colouring matter of 

 the cell having diffused out and stained the mucilage under the influence of the preserv- 



1 Cf. also the remarks on the distribution of red and yellow snow cited on p. 99, from Dr R. N. Rudmose 

 Brown's letters. 



2 Wittrock, luc. cit., tub. in., fig. 1. 



3 The mucilage-sheath was often considerably broader than is shown in this figure. 



