199 



with the fact that it has been found with ripe sporangia in March (Lille Bell) and 



with empty sporangia in April (Linifjord, Samso waters). On the olher 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 (Mytihis, Serpiila, Hyas) and Algae {Polysiphonia elongata, Cliondius crispiis, 



hapters of Laminaria digitata), in 5,5 — 19 meters depth. 



Localities. Sk : YN'-, S.E. of Brageriie, 10,5 m. — Lf: XX in Nissum liredning, 5,5 m. — Kn: 

 TG, nortli of La;s0, 9,5 m. — Ke: VY, Fladen, 18 m. — Ks: 0I^ Lysegrund, (5 m. Sa : Nortlisidc of 

 Refsnses, 19m. — Lb: NV and XQ, near Middelfart, 15— 19m; CC, soutli side of Hornenaes, 7,5m. 



2. Rhododerrais Georgii (Batters) Collins. 



F. S. Collins in Phycotheca ISor. Amer. No 1299; id.. Notes on Algae, III, Hliodora, August 190(;, p. KiO. 

 Rhodoplujscina Georyii Batters, New or critical Brit. mar. Alg;e. .Journ. of BotanAS Vol. 38, 1900, p. 377. 



Kylin, Algenfl. schwed. Westk., 1907, p. 194 — 196, fig. 41. 

 Rhododermis Van Heiirckii Heydrich, Uber Hhododermis Crouan, Beiliefte 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 Zos/era-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 i)art is usually 

 continuous with an irregularly undulating outline, and consisting of radiating fila- 

 ments which are 4 — 6/.! 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 peripliery, 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 ju. 



As shown by Heydrich, Collins and Kylin, 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 — 6// thick. As 

 shown by Heydrich and Kylin, some of the superficial cells may produce long, 

 vigorous hyaline hairs of the usual type in the Florideae; they are 5—7 // thick 

 near the base, and contain a nucleus near the top. The cells of the frond contain 

 a nucleus and several chromalophores. 



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 



