197 



Rhododermis Crouan. 



Crouan in J. Agardh, Sp. Vol. II, pars 2, 1852, p. 504. 



1. Rhododermis elegans Crouan. 



Crouan in J. Agardh, Sp. Vol. II, pars 2, p. 505. Crouan, Florule de Finistere, 1867, p. 148, pi 19, fig. 130, 

 Batters, .Mar. Alg. Berw., 1889, p. 91, pi. XI fig. 1 (forma polijstromalica Batters). Kolderup Rosenvinge, 

 Deux, mem., 1898, p. 18, id., Mar. Alg. N. E. Greenl. 1910, p. 104. 



This small arctic and north-atlantic species has been collected in several places 

 in the Danish waters. It forms small, thin crusts of a lilac-rose colour with an 

 irregular outline, the diameter of which scarcely exceeds 5 mm. It resembles in 

 many respects Rh. parasitica of which Kuckuck has given an exhaustive description 

 and splendid figui-es (Beitr. z. Kenntn. d. Meeresalg. 1. Wissensch. Meeresunters. N. F. 

 II, Heft 1. 1897). According to Batters, one of the principal differences is that 

 the cells of the frond in Rh. elegans are broader than long, while in Rh. parasitica 

 they are longer than broad. This difference is in reality general thougli not abso- 

 lute, as may be judged from the figures of Kuckuck and from the fact that cells 

 may be found in Rh. elegans, which are at least as high as broad. Rh. parasitica 

 differs further by its greater diameter, greater thickness and darker colour. A difference 

 exists also in the structure of the border of the frond, this consisting in Rh. para- 

 sitica of distinct filaments (Kuckuck, 1. c. p. 7, Taf. VHI fig. 10) while it is continuous 

 in Rh. elegans (flg. 118 A). 



The basal layer consists of radiating cell-rows, the cells of which are more or 

 less lengthened in a radial direction. In the marginal part of the frond the cell- 

 rows are frequently flabellately radiating towards the irregularly lobed border, here 

 and there showing lateral ramifications (fig. 118 A). The cells are usually 5,5 —7 

 broad, 1^'-' to 3 times as long as broad. In the basal layer lateral fusions between 

 cells belonging to different cell-rows frequently occur, the cells corresponding through 

 a broad open canal. Such fusions may occur at the very margin of the frond. 

 More than two cells may sometimes fuse together (fig. 118 A, B). 



The crust is at first monostromatic, and a rather broad inonostromatic mar- 

 ginal part may often be found. The inner part of the frond was always found to 

 be from 2 to at least 5 cells thick. I have never found it distromatic in a greater 

 extent, and I must therefore suppose that it is only accidentally that Crouan has 

 attributed a distromatic frond to this species, and that there is no reason to main- 

 tain the var. polystromatica Batters. The cells contain several chromatophores as in 

 R. parasitica. In the upper part of the crust the cells are 8—11// broad. In several 

 specimens I found, projecting from the surface, scattered hyaline hairs (fig. 118 C). 

 Their number varied; they were placed between the paraphyses or in the sterile 

 parts of the crust. 



The sori form irregular spots on the surface of the frond; they consist of 

 feebly curved paraphyses, usually 4- or 5-celled, 40 — 50 //. long, at the base 5 — 9 // 

 broad, and between them the sporangia, which are terminal on the vertical filaments 

 of the crust, the upper cell of which has often the character of an upward slightly 



