116 BOTANICAL RESULTS OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 



(i) TROCHISCIA ANTARCTICA, n. sp. (PI. I., fig. 30). 



I have already referred to the abundant occurrence of species of Trochiscia in the 

 material from the South Orkneys ; one of them is characteristic for the yellow snow 

 flora (PL I., fig. 30), although not particularly common. It consists of isolated spherical 

 cells with a thick and rather gelatinous-looking wall, which is uniformly covered with 

 small processes. The latter have typically the shape of truncated wedges with the 

 truncated surface outermost, so that the cell presents the appearance of a cogged wheel. 

 There is, however, considerable variety in the degree of differentiation of these processes, 

 all transitions having been found from cells in which the processes are but feebly indi- 

 cated (probably young daughter-cells?) to such as have very prominent processes; in 

 the latter case they are often of slightly unequal length. The processes appear to be 

 interconnected by a network of ridges. The cell-contents were always a little con- 

 tracted ; they appeared granular and often showed a well-marked central pyrenoid. 

 Starch is always present, but fat is rare in this form, although now and again cells 

 were found with quite a large quantity of it. 



This species of Trochiscia appears to show some resemblance to T. halophila, Hansg., 

 and T. reticularis (Reinsch), Hansg., 1 but both these species have larger cells, and there 

 are differences in the character of the membrane. The yellow snow form may pro- 

 visionally be regarded as a distinct species, T, antarctica, n. sp., characterised by the 

 peculiarly shaped processes on the membrane, the thick walls, and the faculty of fat- 

 storage. 2 Attention may, however, be drawn to the similarity between this form and 

 the zygospores of two species of Chlamydomonas, viz. C. nivalis (Sornmerf. ), Wille, 3 

 and C. globulosa, Perty ; * especially in the latter case there is some considerable 

 resemblance. The character of the contents of Trochiscia antarctica was, however, not 

 at all like that of a zygospore, since as a general rule no great quantity of food-reserves 

 was present ; and nothing to indicate any relation to a species of Chlamydomonas was 

 observed in the material. In fact, T. antarctica presents more the appearance of an 

 independent alga than many other species of the genus do. 



(j) RAPHIDONEMA NIVALE, Lagerh. (PI. I., figs. 32, 33). 



A not uncommon member of the yellow snow flora consists of short filaments of 

 three or four (but occasionally many) cells running to a point at one or both ends (PI. I., 

 figs. 32, 33). The cells are provided with a very thin membrane, and contain but a 

 single chloroplast without a pyreuoid. The filaments were generally more or less curved 

 (fig. 33), and when only one end was pointed the other was rounded oft" (fig. 32). These 

 filaments are undoubtedly referable to Lagerheim's genus Raphidonema. 5 He observed 



1 Hansgirg, Prodromus d. Algenflora v. Bohmcn, ii., Prague, 1892, pp. 240, 241. 



5 A full diagnosis of Trochiscia antarctica will be found on p. 123. 



3 Wille, " Algologische Notizen, ix.-xiv.," Nyt Magazinf. Naturvidenskab, xli., 1903, pi. iii., fig. 45. 



4 Cf. Chodat, Algues vertes de la Suisse, Berne, 1902, p. 132, fig. 60, D. 



6 Lagerheim, " Schneeflora des Pichincha," Ber. Deutsch. Bot. Oes., x., 1892, p. 523, and pi. xxviii., figs. 15-21. 



