96 BOTANICAL RESULTS OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 



The South Orkneys (lat. about 61 S.) are situated appreciably further south than 

 either South Georgia (lat. about 55 S.) or Kerguelen (lat. about 49 S.), from which 

 most of the previously described material has been derived. This may explain the 

 marked difference in the character of the algal collections obtained from the South 

 Orkneys as compared with those from the other two localities. In the material from 

 the South Orkneys filamentous forms play a very insignificant part, and the bulk of the 

 algae consists of unicellular and colonial species. The total number of species recorded 

 from the South Orkneys in the present paper is 68 (of these 1 genus and 7 

 species are new). The table on p. 97 shows how the different groups are represented. 

 This table, however, gives no idea of the relative part played by the different groups. 

 As a matter of fact (apart from the abundant Prasiola), the lowly unicellular Isokontse 

 and Cyanophycese are the predominant features of the flora, the former being on the 

 whole more abundant than the latter. In this connection we may notice, however, that 

 the complete absence of common cosmopolitian forms like Scenedesmus, Pediastrum, 

 Cosmarium, Closterium, etc., is very striking. The CEdogoniacese, as indeed all fila- 

 mentous forms, are represented only by stray filaments. Only two filaments (one of 

 Mougeotia, the other of Zygnema) of Zygnemaceae were observed. The occurrence of 

 filaments of the various genera nevertheless testifies to the fact that at certain periods 

 their development must be more prominent. Desmids were represented only in two 

 samples by three species. Diatoms are not common, and in some samples (e.g. yellow 

 snow) were almost completely absent. Their determination was in many cases a matter 

 of great difficulty, as frequently only dead fragments of the valves were to be found, 

 and it is probable that a larger number of species actually occurs than is recorded in 

 the present paper. 1 In a number of the samples the unicellular algal flora occurred as 

 a thin covering to numerous muddy particles, and it was necessary to crush the latter in 

 order to find any appreciable number of algal forms. 



The lowly unicellular and colonial forms of alga? are well known to be in many 

 cases among the most difficult forms to determine, and to add to this difficulty a very large 

 proportion of the species in the South Orkneys material were in the resting-stage, or at 

 least in a sufficiently dormant condition to fail to show more than one phase in the life- 

 history. This is particularly true of the forms found on the snow (yellow and red 

 snow), but applies to a lesser extent to practically the whole of the material ; only in 



of the British Antarctic Expedition, 1907-09 (see Reps, on Scien. Investig., vol. i., Biology, part vii., 1911, pp. 

 263-298, pi. xxiv.-xxvi.), while a report on the Freshwater Algse of the British National Antarctic Expedition by the 

 writer is about to appear. These two collections, which come from a latitude appreciably further south than that 

 of the South Orkneys, however, show an algal vegetation of a decidedly different stamp from that described in the 

 present paper. 



1 The republication of this paper has given an opportunity of reinvestigating the diatom-flora of some of the 

 samples in which those forms occurred more abundantly. This reinvestigation was undertaken with a view to 

 determining whether the flora includes any of the new species described by the Wests (loc. cit.), or by the writer in 

 his report on the algae collected by the Discovery, but the result has been a negative one. Common forms like 

 Navicula Shackletmii, N. cymatopleura, etc., which form such a feature in the Ditcovery collections, and in those made 

 by Shackleton's expedition, were found to be quite wanting, and the aspect of the diatom-flora in the South Orkneys 

 is thus quite distinctive. 



