334 Dansk Botanisk Arkiv, Bd. 3, Nr. 1. 



trali, subcomplanatus,in juvenili statu ex una cellula central! et quat- 

 tuor pericentralibus compositus, postea cortice tectus. 



Crescentia terminalis; cellula apicalis major, transverse septata. 

 Filamenta in inferiori parte decumbentia, rhizoideis substrato adfixa 

 dein assurgentia, subrecta, in superiori parte arcuata. 



Thallus infra nudus, supra in latere dorsali (convexo) ramulis 

 monosiphoneis in duas series alternantibus, instructus. Cellulæ ramu- 

 lorum cylindricæ. 



Ramificatio adventitia, ramis sæpe prope ab latere ramulorum 



ortis. 



1. Cottoniella arcuata nov. spec. 

 Frons ca. 8 cm alta. Rami adulti ca. 200—250 ^ lati, ramulis 

 usque ad 1 mm longis, ex cellulis cylindraceis ca. 175 n longis et 

 7 — 20 |.i latis compositis. 



The basal part of the plant consists of decumbent filaments 

 fixed to the substratum {Halimeda etc.) by means of rhizoids (Fig. 

 336 h). The rhizoids are not separated by walls at their outgrowth 

 from the mother-cell, but walls occur in the more or less cylin- 

 drical stalk; they end in a small multilobed disc. The rhizoids are 

 rather vigorous with thick undulated walls; the cylindrical part is 

 about 30 \i\ the wall about 12 \.i broad. 



The decumbent filaments show no marked differences from the 

 erect ones, their summits often bending upwards and those of the 

 erect filaments bending downwards. The decumbent filaments as 

 well as the erect ones with the exception of the youngest parts are 

 covered by a cortical layer. The thickest filaments I have met with 

 had a diameter of 200—250 \x. 



The erect filaments are arch-shaped in their upper ends 

 (Fig. 334), bearing a series of branchlets with limited growth 

 placed in zigzag in two rows along the dorsal, convex sides (336 a). 

 The filaments increase by means of a large, conical-cylindrical 

 apical cell (Fig. 335 a, b) from which disc-shaped, thin segments 

 gradually are cut off. These segments remain undivided for some 

 time, I have counted about 6 of them. They increase gradually in 

 length and are then divided into a central and four pericentral cells. 

 Shortly after the segments have begun to be divided the branchlets 

 with limited growth begin to grow out from the central cells (Fig. 

 335 a, h) and are seen as small cupola-outgrowths on the convex side 



