F. Børgesen: Rhodophyceæ of the Danish W. Indies. 23 



3. Acrochætium pulchellum nov. spec. 



Thallus minutus, pulviriatus. Pars basalis e filis repentibus 

 ramosis, in parte centrali sensim confluentibus, composita. Spora 

 germinans in duas cellulas fere æquales di visa est, quarum utra- 

 que filum ramosum repens procreat. 



Gellulæ in parte basali irreguläres, breves, 7—10/^ longæ et 

 o—Qfi latæ. Ex his cellulis fila erecta brevia, 1—3 raro plures 

 cellulas continentia, ca. 24 /i alta, egrediuntur ; cellulæ b—Qfx latæ, 

 diametro IV2— 2-plo longiores, chromatophorum stellare pyrenoide 

 centrali instructum continentes. Pili hyalini 

 terminales, ca. 100 /i longi, 2—3 // lati, 

 numerosi. 



Sporangia in filis erectis terminalia, raro 

 in filamentis repentibus sessilia, ovata, 5 — 1 (x 

 lata et 9—10// longa. 



Of the species described by Rosenvinge 

 the present plant seems to come nearest to 

 Acr. (Chr.) hiimile; in its mode of growth 

 and the structure of the cells it also some- 

 what resembles A. (C.) polyblastam Rosenv. 

 but the erect filaments are not so large. 



In agreement with the above mentioned 

 species the germinating spores are divided pig. 14. Acrochætium 

 into two nearly equal cells (Fig. 14); in the ^",^^^4";Ent"37„\Xch 

 young plants these cells are easily recogniz- the original spores, di- 

 able, in the older they are most often not. vided into two cells, 



' , „ . „, . are yet visible. 



From each of these cells a creepmg filament (About 600 : 1). 



is given off in opposite directions ; these 



filaments soon begin to branch, the branches in the middle fusing 

 more or less together. By this method of growing a relatively 

 large disc may be formed (Fig. 15). The cells are rather irre- 

 gularly shaped with more or less sinuated walls, short, about 

 5—6// broad and 7 — 10// long. 



From the cells in the basal layer short erect filaments con- 

 sisting of 1—3 seldom more cells arise. These filaments are 

 terminated by long hyaline hairs or they may bear the sporangia 

 (Fig. 15). Hairs also occur at the ends of the creeping filaments 

 but are soon pushed aside. The hairs reach a length of 100// or 

 more and 2—3// broad. They are, as mentioned above, hyaline; 

 the young hairs are richly provided with protoplasm. 



The chromatophore is stellate with a central pyrenoid 

 (Figs. 15 and 16). 



