110 BOTANICAL RESULTS OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 



certainly Choclat's Pteromonas nivalis. 1 The individuals are of an elongated oval shape, 

 and provided with a number of wings, which are rather sinuous and have a more or less 

 marked spiral course (figs. 22-24). The number of wings has been determined as eight 

 in individuals seen from the side, although none were seen in optical section, as Chodat 

 figures them (his fig. 70, H and j). The behaviour of the wings at the two ends of 

 the cells could not be exactly determined, but it would seem (fig. 23) as though they 

 projected somewhat at these points so as to give rise occasionally to the appearance 

 of a terminal papilla (cf. also Choclat's fig. 70, B, c, K) ; all the wings appear to 

 run together to a common point. In the cell-contents an irregularly shaped, more 

 or less central chloroplast with a pyrenoid was often visible, and a considerable 

 amount of the characteristic fat was mostly present. 2 No reproductive or resting 

 stages were observed. 



It seems to me that the reference of this species to the genus Pteromonas is in no 

 way certain. 3 The genus includes a number of species, which are actively motile forms 

 provided with two cilia. In the case of P. nivalis, however, no cilia have been recorded, 

 nor was I able to make out any traces of them in the yellow snow specimens. On this 

 point Chodat (loc. cit., p. 146) remarks, "cellules parfois mobiles, ordinairement immo- 

 biles ; cils inconnus." Wille, 4 in his later description of this species, does not refer to 

 any movement ; in fact, he regards the winged cells as resting-stages (aplauospores), and 

 looks upon certain cells (" spiudelformige, an dem einen Ende etwas abgestumpfte Zellen," 

 p. 168), which he figures on pi. iii., fig. 46 (cf. Chodat's fig. 70, F), as zoospores of the 

 Pteromonas, which had come to rest ; possibly my fig. 31 may correspond to these cells. 

 In view of the fact, however, that neither Chodat nor Wille nor I have seen any trace 

 of cilia on either type of cell, these interpretations appear somewhat forced. A much 

 simpler view would be to regard the typical winged form (as shown in Chodat's fig. 

 70, A, B, c, and my figs. 22-24) as the normal motionless individual, and the unwinged 

 cells (Chodat's fig. 70, F, Wille's fig. 46, and my fig. 31) as young individuals, possibly 

 formed by division of the contents of a mother-individual, and in which wings have yet 

 to arise (cf. Chodat's fig. 70, N) ; the correctness of this view depends mainly on the 

 nature of the movement observed by Chodat. If my interpretation of P. nivalis is 

 correct, it is obviously out of place in the genus Pteromonas, and must be referred to 

 Scotiella as S. nivalis (Chod.), F. E. Fritsch. With the genus Scotiella it agrees in 

 several respects, viz. the single chloroplast with a pyrenoid, the wings (cf. especially 

 the optical section shown in Chodat's fig. 70, J, with my optical section of Scotiella 

 antarctica, fig. 11), the behaviour of these wings at the two ends of the cell ("qui se 



1 Cliodat, Algues vertes de la Suisse, Berne, 1902, pp. 145-146. 



2 Chodat describes the cells of Pteromonas nivalis as " ordinaireraent remplie d'une huile jaune-doree " (p. 146), which 

 may well correspond to the yellow fat observed in the individuals of the yellow snow. Wille (" Algologische Notizen, 

 xi.-xiv.," Nyt Magazinf. Naturmdenshib, xli., 1903, p. 170), however, speaks of the contents of the cells being generally 

 coloured almost quite red by h;ematochrome. This is interesting as indicating that one and the same snow form may 

 exhibit different pigments in different localities. 



3 Cf. Wille, loc. cit., p. 171. 



4 Loc. cit. 



