COLLECTED IN THE SOUTH ORKNEYS, 301 
(а) Proroperma Вво\ухи, F. E. Fritsch. (Pl. 10. fig. 1 ; 
Pl. 11. phots. 1, 2, 3, 5, P.) 
The main ground-mass is constituted by a form which I somewhat doubt- 
fully refer to the genus Protoderma as a new species, P. Brownii (Pl. 10. 
fig. 1). This Alga probably forms broad sheets of cells with an irregular 
margin spread out on the surface of the snow, and may possibly serve as 
а basis for the growth of some of the other forms (cf. p. 298). А rough 
examination discloses merely a number of more or less rounded green 
protoplasmic masses, regularly arranged with reference to one another and 
separated by marked colourless intervals, The latter are due to the cell- 
walls, which are markedly gelatinous; a careful examination (especially 
of material stained with gentian-violet or methylene blue) reveals the 
polygonal (sometimes rather rounded) network due to the middle lamelle of 
the wails and the (occasionally stratified) mucilage, which intervenes between 
middle lamella and cell-contents. The middle lamelle frequently exhibit a 
granular character. Where the cell-contents are not obscured by the above- 
mentioned fat (which was frequently quite wanting in the cells of the 
Protoderma, cf. p. 300), it is possible to make out a single chloroplast, which 
generally takes the form of a curved plate and may frequently be almost 
hemispherical. In preparations stained with gentian-violet a single pyrenoid 
was often to be distinguished in the chloroplast, while iodine generally 
showed the presence of a limited number of starch-grains in the cells. In 
rare cases, adjoining cells of relatively small size were separated by thin 
and delieate walls; such cells are по doubt daughter-cells produced by 
division prior to preservation of the material. These young daughter-cells 
nearly always contained fat. Оп the whole, however, the Protoderma 
seemed in as inactive a condition as the other constituents of this snow flora. 
The cells vary considerably in size, from 5-12 p or even more, but small cells 
are the rule; in most places they form but a single layer, but where 
extensive patches of the Protoderma were observed they appeared to lie in 
two (or more?) layers above one another.—The remaining species of the 
genus Protoderma are characterised, according to recent descriptions *, by 
the thallus eonsisting of a central group of irregularly arranged cells, from 
which short filaments radiate out at the periphery. Of this feature Proto- 
derma Brownii shows nothing, the edge of the thallus in all cases presenting 
just as irregular an arrangement of the cells as obtains in the middle. 
P. Brownit also differs from the other species of the genus in not being an 
* G. S. West, ‘The British Freshwater Alge,’ 1904, p. 204 and fig. 83 д-с; №. Wille, 
“Conjugate and Chlorophycezs," in Engler and Prantl, Die natürl Pflanzenfamilien, 
Nachtr. z. Teil I. Abt. 2 (1909) p. 89; cf. also Hansgirg, * Prodromus d. Algenflora v. 
Böhmen, i. (1886), p. 224. 
