199 
with the fact that it has been found with ripe sporangia in March (Lille Belt) and 
with empty sporangia in April (Limfjord, Samso waters). On the other hand it has 
also been found with ripe sporangia in June, July and September, and it seems 
thus that it may produce ripe sporangia at all seasons. 
The species occurs on stones (flint, limestone, granite), shells and carapaces 
of animals (Mytilus, Serpula, Hyas) and Algæ (Polysiphonia elongata, Chondrus crispus, 
hapters of Laminaria digitata), in 5,5—19 meters depth. 
Localities. Sk: YN?°, S.E. of Bragerne, 10,5 m. — Lf: XX in Nissum Bredning, 5,5 m. — Kn: 
TG, north of Læsø, 9,5 m. — Ke: VY, Fladen, 18 m. — Ks: OP, Lysegrund, 6 m. — Sa: Northside of 
Refsnæs, 19m. — Lb: NV and XQ, near Middelfart, 15—19 m; CC, south side of Hornenæs, 7,5 m. 
2. Rhododermis Georgii (Batters) Collins. 
F. S. Collins in Phycotheca Bor. Amer. No 1299; id., Notes on Algae, III, Rhodora, August 1906, p. 160. 
Rhodophysema Georgii Batters, New or critical Brit. mar. Algæ. Journ. of Botany, Vol. 38, 1900, p. 377. 
Kylin, Algenfl. schwed. Westk., 1907, p. 194—196, fig. 41. 
Rhododermis Van Heurckii Heydrich, Über Rhododermis Crouan, Beihefte z. Botan. Centralblatt, Bd. 14, 
1903, p. 243, Taf. 17. 
Strange to say this characteristic little species was first described in 1900, though 
it has later proved to be widely distributed. It has also been recorded in’ several 
places in the Danish waters, always growing, as elsewhere, on Zostera-leaves, but it 
has further been found growing on uncovered roots of Zostera. 
The plant begins as a thin monostromatic crust much resembling that of Rho- 
dodermis elegans, and with the same marginal growth. The marginal part is usually 
continuous with an irregularly undulating outline, and consisting of radiating fila- 
ments which are 4—6y broad; more rarely the ends of the filaments are free, not 
laterally connate. Lateral fusions between cells of these cell-rows not unfrequently 
occur (fig. 119 A). The crust is early divided by horizontal divisions, which advance 
from the centre towards the periphery, with the result that the crust usually becomes 
polystromatic to the margin. The radial growth has meanwhile ceased, so that the 
diameter of the crust rarely exceeds 300 y. 
As shown by Heypricu, CorLıns and Kyrın, the species occurs in two 
forms, a disc-shaped and a globose or pear-shaped or irregularly lobed. In the 
disc-shaped form, the frond is usually 4 to 5, at most 7 cells thick, when fully 
developed and fructiferous. The cells of the erect cell-rows are 4—6y thick. As 
shown by HEypricH and Kyrın, some of the superficial cells may produce long, 
vigorous hyaline hairs of the usual type in the Florideæ; they are 5—7 a thick 
near the base, and contain a nucleus near the top. The cells of the frond contain 
a nucleus and several chromatophores. 
In the disc-shaped specimens the sorus often originates shortly after the for- 
mation of the first horizontal walls. The upper cell produced by these divisions 
in the central part of the frond develops then in a paraphyse or in a sporangium 
with its stalk cell, and there is only one layer of vegetative cells under the sorus. 
When the surrounding cells now continue growing in a vertical direction and dividing 
