F. Børgesen: Rhodophyceæ of the Danish W. Indies. 



201 



This beautifully purple-rose plant was found upon the pikes 

 of Eiicidaris tribuloides, often covering these quite densely ; the 

 tufts reach a height of ^h cm. 



The basal creeping filaments (Figs. 189, 190 A) are irregularly 

 branched; they are about 30,« broad, having a very thick wall 

 (often 8 — 10// thick). The filaments are fastened to the pikes of 

 the Echinoderm by means of rhizoids. 



These are shorter or longer without any transverse walls, 

 but having very thick peripheral walls, the 

 lumen of the cells is, in this way, reduced 

 to very little. At the bottom end the 

 rhizoids for the most part broaden out to 

 a flat, roundish, irregularly lobed disc. 



The erect filaments are very straight 

 and not much branched ; the branches 

 issue alternatingly, but seldom oppositely. 

 The filaments are from 16 — 25// broad; 

 the cells from 3 — 5 times as long as the 

 diameter. The last mentioned contain 

 many small, oblong, parietal chromato- 

 phores more or less growing together, 

 forming irregularly lobed, parietal plates 

 and having several nuclei especially in the 

 apical cell where often more than ten 

 are to be found. Only plants with tetra- 

 sporangia were found. These are situated 

 terminally upon a short one-celled branchlet 

 growing out singly (very rarely in twos) from 

 the upper end of the mother-cell (Fig. 

 190 C). Only seldom the branchlet may 

 have two cells; sometimes, too, it has a 

 lateral sfcalk-cell with a sporangium (Fig. 

 190 B). The sporangia are tetrahedrally 

 divided, ovate roundish, about 46 — 52 /i 

 long, and 44—46/7. broad; the wall of the 

 sporangia is very thick, 6 — 8/^ or more. 



Fig. 190. Spermothamnion 



investiens (Crouan) 

 Vickers, var. cidaricola 

 Borgs. A, piece of a plant 

 with creeping and erect 

 filaments (25:1); 5 and 

 C, pieces of erect fila- 

 ments with tetraspores 

 {B, 50:1; C, 70:1). 



The original specimens upon which the 

 brothers Crouan have based the description of their species were 

 found upon Galaxaura lapidescens and Stromhiis gigas. In Schramm 

 et Maze, "Essai de classification des Algues de la Guadeloupe" ^) 



») During a stay in Paris I saw this rare book in the library of Dr. Bor- 

 NET, and he allowed me to take a copy of it. 



