22 



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



the summit where their diameter is only about 4 — 5^ while the 

 length of the cell is about 6 — 7^. The basal cell and the lower- 

 most cells in the filaments are about as long as broad, often 

 even a little shorter than broad. 



The principal filaments are as in the var. ty pica mostly very 

 curved (Fig. 13 a, c) ; along the upward side of the filaments 

 all the cells may bear sporangia, or in the more vigorous plants 

 short branchlets ; more rarely some of the cells are provided 

 with branches on the opposite side (Fig. 13 c). 



The cells contain a stellate 

 chromatophore with a central 

 pyrenoid (Fig. 12) quite in ac- 

 cordance with that found in the 

 var. ty pica. 



At the ends of the filaments 

 long hyaline hairs occur (Figs. 12, 

 13), these are about 1 — 2fi thick 

 and reach a length of about 50 ^. 

 The sporangia are always 

 monosporous ; they are oval- 

 obovate, about 5 // broad and 

 Y'lg.l'i. AcrochætiumcrassipesBøvg?,. 6 — Ifi long. They are mostly 



var Zonnsem nov. var. a, ^, c, habit ^ ^iui sometimes also pedi- 



01 plants, a, a young plant, e, base ' ^ 



of a plant showing the immersed cellate or placed upon short 



nethermost part. \a, b c, about branchlets; now and then such 

 250 •.l\d,e, about 800 : 1). ' 



branchlets have two sporangia. 



The length of the larger specimens without hairs is about 60^. 



This species seems to be nearly related to Acrochætium {Chan- 

 transia) moniliforme Rosenvinge and Acrochætium catenulatum 

 Howe. From the first mentioned species it differs essentially in 

 its smaller size in every respect, and by the proportionally larger 

 basal cell. And Acrochætium catenulatum differs from our plant 

 among other things by its larger size, want of hairs and ap- 

 parently different chromatophore. 



This species has been found upon different host plants, namely, 

 Hypnea, Centroceras, Bryopsis, Chætomorpha, Cladophora etc. It 

 seems to be a common species especially in more sheltered places. 



Var. typica has been found at St. Thomas: in the Harbour and in 

 Magens Bay, at St. Jan: in Cruz Bay and at St. Croix: near Christianssted. 



Var. longiseta. St. Thomas: in the Harbour and at Water Island; 

 St. Croix: at Christianssted. 



