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



31 



The base (Fig. 23 d, e, /) consists of creeping filaments irregu- 

 larly ramified and more or less fusing together into a pseudo- 

 parenchymatous disc. 



From most of the cells in the creeping filaments erect ones 

 are given off. These filaments are composed of ceils nearly twice 

 as long as broad, 8 — 9 jj. thick and 16 — 18^ long; the lowest 

 are nearly cylindrical, higher up in the filaments the cells are 

 more barrelshaped being somewhat swollen in the middle (Figs. 

 23 a, 24). 



The cells contain a large parietal chromatophore with long 

 lobes along the walls of the cells (Fig. 24) and with a pyrenoid 

 lying near the middle of the cell. The shape of the chromato- 

 phore seems to come near to that Rosenvinge found in A. 

 (C.) leptonema. The cells are mostly very rich in 

 starch filling up the greater part of the lumen 

 making it difficult to see the shape of the 

 chromatophore. 



The filaments are mostly slightly ramified, 

 often not at all. However, the more vigorously 

 developed filaments sometimes give off branches 

 like themselves. Short branchlets on the other 

 hand are often present (Fig. 23 a). 



The cells bear often long, hyaline, unicellu- 

 lar hairs (Fig. 23 b, c). These are at first termi- 

 nal on the end of the filaments but later on 

 they are pushed to the side by the next new 

 cell in the way described for several species by 

 Kylin and Rosenvinge, and the sympodial na- 

 ture of the filaments was clearly visible in this 

 species. 



The hairs are thickest near the base, here 

 about 4/^ broad, tapering towards the summit 

 where their diameter is only about 2 // long ; they reach a length 

 of about 200 — 300^. The hairs are quite hyaline with the ex- 

 ception of the uppermost end which is richly provided with 

 contents. They seem to be rather early shed. 



The monosporangia are mostly sessile, arranged in series 

 upon the upper end of each cell in the filaments, some are 

 pedicellate, placed upon the short branchlets mentioned above 

 (Fig. 23 a). The sporangia are oval-obovate in shape (Fig. 24 a), 

 about 1 fjt broad and 10// long. 



This species is certainly nearly related to Acrochætium leptonema 



Fig. 24. Acrochæ- 

 tiumSancti Thomæ 

 nov. spec, a, sum- 

 mit of a filament 

 with sporangia. 

 6, cells from lower 

 down in a fila- 

 ment with chro- 

 matophores and 

 nuclei. (About 

 500 : 1). 



