FRESHWATER ALGM OF THE SOUTH ORKNEYS. I 1 7 



vegetative reproduction of this form, the threads breaking into two halves, each of 

 which has at first one pointed and one rounded end. The stage shown in my fig. 32 

 undoubtedly shows one of the products of such a division. Subsequently, according to 

 Lagerheim, the round eud grows out into a new hair-like point. Most of the individuals 

 found in the yellow snow were of narrower dimensions than Lagerheim's form, and the 

 cells were rather longer (fig. 33) ; but filaments were found here and there quite agree- 

 ing with Raphidonema nivale, Lagerh., and there is no reason to regard the forms in 

 the yellow snow as distinct from this species. 



In his recent revision of the green algae Wille 1 includes Lagerheim's Raphidonema, 

 in the genus Raphidium, Iviitz. (Anldstrodesmus, Corda) ; this is in agreement with 

 Chodat's earlier view. 2 It seems a little questionable, however, whether this is really 

 warranted. The typical species of the genus Raphidium are unicellular or colonial 

 forms, in which reproduction is effected by transverse division of the contents (frequently 

 into four), followed by elongation of the segments, so that they ultimately come to lie 

 side by side as a number of daughter-individuals within the mother-cell (so-called auto- 

 spore-development). This has not been observed in Raphidonema nivale. On the 

 other hand, although septate Raphidiums have been described (e.g. R. pyreiiogerum, 

 Chod., and R. nivale, Choc!. 3 ), the breaking up of the septate individual into two parts 

 by fragmentation is not known for this genus. The resemblance of Raphidonema to 

 Raphidium therefore appears to be purely superficial, and one must agree with 

 Lagerheim's original view, 4 which regarded this snow alga as a member of the 

 Ulotrichales, probably to be included in the Chfetophoracese ; the peculiar method 

 of vegetative reproduction may, however, indicate a relationship to Sttehococcus, b and 

 until more is known about Raphidonema its exact position must remain doubtful. 



Very rarely forms were found of the type shown in PI. I., fig. 34. This shows a 

 single cell of the Raphidium-typc (diam. 2 M) with a prominent central pyreuoid. 

 This is probably a species of Raphidium, possibly R. pyrenogerum, Chod., which is 

 distinguished by having a pyrenoid, but Chodat's species appears to be much broader. 

 I have seen too few individuals to be sure of the specific determination. 



Filamentous forms are poorly represented in the yellow snow flora. The most 

 abundant is Ulothrix subtilis, Kiitz., of which relatively short filaments were always 

 to be found embedded among the numerous unicellular and colonial constituents 

 (PI. II., phots. 1, 2, /"). Next in abundance comes R. nivale, Lagerh., which has 

 already been considered. Lastly, very occasional filaments of a broad species of 

 (Edogonium (diam. cell = 20 /u) with well-marked caps were observed. 



1 Wille, in Engler-Prautl, Die Xntiirl. I'ftunsenfam., Xachtr. z. 1 Teil, 2 Abteil., 1909, p. 68. 



2 Chodat, "Flore des neiges du col des Ecandies," Bull. Herbier Boissier, iv., 1896, p. 886. It does not aeem that 

 Chodat's Raphidiim nivale is in any way allied to Raphidonema. 



3 Chodat, Algues vertes de la Suisse, Berne, 1902, p. 200, fig. 120. 



4 Loc. cit., p. 523. 



5 Cf. Lagerheim, loc. cit., pp. 523, 524. 



