104 BOTANICAL RESULTS OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 



of the above-mentioned fat were nearly always present in both kinds of cells, although 

 certainly more abundant in the larger ones (PL I., figs. 2, 4, 5, 6). In a few cases the fat 

 was apparently diffused rather equally throughout the contents of the cells, but it mostly 

 formed very characteristic, highly refractive lumps at one or more points immediately 

 beneath the cell-wall. Frequently it appears in the form of concavo-convex lumps on 

 one side of the cell, the mass of fat fitting like a cap over the protoplasmic contents 

 (PI. I., figs. 2, 6) ; occasionally this cap may even grow out of all proportion and give rise 

 to a huge bulging mass on one side of the cell, which thus acquires an unusual shape. 

 More rarely the fat forms a complete sheath, with a rather irregular inner boundary 

 around the protoplasmic contents. Apart from the cases as yet described, in which the 

 fat exhibits an obvious connection with the cell-contents, a number of cells were always 

 to be found in which there were a number of rounded or oval lumps of fat com- 

 pletely segregated from the somewhat contracted protoplasm of the cell, and lying in a 

 more or less well-marked space between the latter and the cell-wall (PI. I., figs. 4, 5). The 

 cells concerned were always somewhat oval in shape, and showed the pyrenoid and the 

 characters of the chloroplast very prominently. In a few cases (PI. I., fig. 5) two pyre- 

 noids were visible through the drawn-out aperture in the chloroplast, and this seems to 

 indicate that these oval cells were about to divide. On the whole, such cells contained 

 a relatively smaller amount of fat than the ordinary spherical cells do, and it would thus 

 appear as though this segregation and diminution in the amount of fat precedes cell- 

 division. Some uncertainty, however, naturally attaches to this interpretation until the 

 actual process of cell-division has been observed. The conclusion that the large spheri- 

 cal cells, with their transparent mucilage-sheath, and the groups of smaller cells belong 

 to one and the same species may also be challenged ; but apart from the identical struc- 

 ture of the cell in the two cases, I have found practically all transitions between the 

 two sizes, and I think there can be little doubt that they all belong to the same species. 

 The genus Chlorosphasra 1 is characterised by its chloroplast and the power of vegetative 

 division (which distinguishes it from the allied genus CJilorococcum), and by reproduc- 

 ing by subdivision of the cell-contents to form zoospores 2 ; the absence of the latter 

 method of reproduction in C. antarctica is not astonishing in view of the dormant 

 character of the whole of the yellow snow flora. The new species seems to come nearest 

 to C. angulosa, Klebs, 3 in which Artari states that reproduction principally takes place 

 by vegetative division ; C. antarctica, however, differs in the often appreciably smaller 

 size of the cells after division, in the mucilage-sheath around the larger cells, and in the 

 faculty of storing up large quantities of fat. 4 



1 Ctdorosphami is included by G. S. West (British Freshwater Alyx, p. 202) and some other authorities in the 

 genus Pleurococcus, which is not in agreement with the views of Klebs, Artari, Wille, Oltmanns, etc. 



2 Klebs, " Ub. d. Organisation eiuiger Flagellatengruppen, etc.," (filters. But. Inst., Tubingen, 1881-85, p. 343 ; 

 Artari, Unters. iib. Entwickl. u. ,S'yst einiger Protococcoideen, Diss., Moscow, 1892, p. 35. 



3 Cf. Artari, loc. cit., p. 36. 



4 Storage of fat is also found in Pleurococcus rufescens (Kutz.), Breb., which appears to be a species of Chlorosphsera. 

 A full diagnosis of Ghlorosphxni antarctica is given on p. 123. 



