300 DR. F. E. FRITSCH ON FRESHWATER ALGJE 
In most сазез the organisms found on snow and ice contain some 
characteristic pigment (red heematochrome in the case of Chlamydomonas 
nivalis; violet or purple phycoporphyrin in the case of Ancylonema Nor- 
denskiéldit), although green snow (due to filamentous Alge, Desmids, and 
Cyanophycee) has also been described. Similar pigments are found in 
members of many other types of algal floras, but there is certainly 2 
prevalence of pigmentation in forms occurring on the snow. It has been 
pointed out that these pigments are capable of absorbing the heat-rays 
of the sun*, and it is also possible that they may serve to screen the 
chlorophyll during the long summer f. It is difficult to express ап opinion 
on the funetion of the yellow pigment colouring the organisms of the 
yellow snow, but it is possible that it acts in one or both of these ways. In 
support of this it is noticeable that the Protoderma, which presumably forms 
a sheet on which the other forms settle down, is on the whole very poor in 
fat and pigment, perhaps because it is screened by the overlying forms 
from the light. 
We may next proceed to consider the various organisms that are distin- 
guishable in the yellow snow flora. Apart from a number of resting-stages, 
which could not be determined, 18 species of Algæ and two Fungi are 
concerned in the production of this association. The Algæ observed are the 
following :— 
Protoderma Brownii, Е. E. Fritsch, n. sp. | Spherocystis Schroetert, Chod., f. nivalis, 
(p. 301). Е. E. Fritsch, n. f. (p. 314). 
Chlorosphera antarctica, Е. E. Fritsch, | Trochiscia antarctica, Е. Е. Fritsch, n. sp. 
n. sp. (p. 302). (p. 916). 
Scotiella antarctica, V. E. Fritsch, n. gen. | Raphidonema nivale, Lagerh. (p. 317). 
et sp. (p. 304). Raphidium pyrenogerum, Chod.? (р. 318). 
Scotiella polyptera, Е. E. Fritsch, n. sp. | Ulothrix subtilis, Kutz. 
(p. 908). | Œdogonium sp. 
Pteromonas ntvalis, Chod. (р. 309). | Pleurococcus vulgaris, Menegh. 
Chodatella brevispina, F. E. Fritsch, n. sp. | Chlamydomonas caudata, Wille. 
| 
(p. 311). | " sp. * (p. 318). 
Oocystis lacustris, Chod., f. nivalis, Е. E, | Mesotenium Endlicherianum, Naeg. 
Fritsch, n. f. (p. 313). | Nostoc minutissimum, Kitz. 
A considerable number of these forms will be considered in detail in the 
following paragraphs. 
* Cf. V. B. Wittrock, * Die Flora des Schnees und des Eises besonders in den arktischen 
Gegenden," in Bot. Centralbl, xiv. 1883, p. 159 ; Warming, Joc, cit. p. 163. 
t Cf. Chodat, * Algues vertes de la Suisse, 1902, p. 74. Hmatochrome certainly acts as 
a screen to the chlorophyll in other Alge (e. g. Trentepohlia), cf. Oltmanns, Morph. u. 
Biol, d. Algen, ii. 1905, p. 200. 
