126 BOTANICAL RESULTS OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 



Cf. p. 117. The forms observed are possibly referable to a distinct species, but the 

 material was insufficient to come to definite conclusions on this point. Width of 

 cells = 2 M. 



20. CCELASTRUM MICROPORUM, Naeg. ex. A. Br., Alg. unicell., 1885, p. 70 ; Rabenh., 

 Fl Europ. Alg., iii., 1868, p. 80. 



Samples 10, 11, and 15, fairly common. 



Forma irregulare, n. f. (text fig. 1, H, p. 122). 



Cellules coenobii irregularissime cohserentes. 



Iii sample 11 there occurred side by side with normal colonies of C. microporum 

 others, in which the cells were very irregularly connected, so that the compact spherical 

 appearance of the normal colony was often quite lost. Frequently the sphere was only 

 half formed ; in other cases, while several cells of the colony showed the usual arrange- 

 ment, others were so disposed that they stood off from the general surface of the colony 

 and completely destroyed the symmetrical character of the latter (fig. 1, H). In other 

 cases again the colonies were very small, consisting of only four or six cells. These 

 peculiar forms may possibly be explained by Senn's observations (" fiber einige colouie- 

 bildeude einzellige Algen," Bot. Zeitung, Ivii., 1899), who found that colonies of 

 Caslastrum tend to dissociate into their individual cells if plenty of oxygen is present 

 in the surrounding medium. This is likely to be the case in water in these Antarctic 

 localities and may account for the numerous irregularities above described. Samples 

 10, 11, and 14 contained numerous isolated cells of the Ccelastrum-type, and these are 

 very probably to be regarded as dissociation-products of normal colonies. 



21. CCELASTRUM SPH^RICUM, Naeg., Gatt. einzell. Algen, Zurich, 1849, p. 98, and 

 tab. v., c, fig. 1. 



Sample 11, rather rare. 



P LEV 'ROCOCO 'AC 'E^E. 



22. PLEUROCOCCUS VULGARIS, Menegh., Monograph. Nostoch., p. 38. 

 Samples 1 and 3 (yellow snow !), rare; samples 10 and 11, not uncommon. 

 This species was occasionally found in Nos. 10 and 11 forming short filaments. 



23. PROTODERMA BROWNII, n. sp. (PI. I., fig. 1 ; PI. II., phots. 1, 2, 3, 5, P). 

 Thallus constat ex uno vel duobus (vel pluribus ?) stratis cellularum et explanatus 



est in summa nive ; margo thalli irregularis. Cellulee multangulares vel angulis modice 

 rotundatis ; membranse cellularurn gelatinosse (?), hyalinte, larnellosas, lamella intermedia 

 paulum granulata. Chromatophora singula, similis disco arcuato, cum pyrenoide. 

 Cellulse interdum continent aliquantum adipis. Propagatio ? Diana, cell. = 5-12 M. 



Samples 1 and 3 (yellow snow !), abundant. 



It is probable that Pleurococcus vulgaris, Men. /3 coheerens, Wittr. (" Om snb'ns och 

 isens Flora," loc. cit.), in part belongs to this species. Wittrock's fig. 17 (on pi. iii.) 

 strongly recalls a patch of Protoderma brownii. 



