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



side of the lowermost part of the branches; they are in the 

 specimens found always uniseriated and sessile. 



The sporangia are oblong clavate reaching a length of about 

 20—22/^ and a breadth of 9—11/^. The sporangia found were 

 apparently not quite ripe. 



To judge from the description of Acrochætium Hoytii Collins i) 

 this plant seemingly comes near to my plant. Acrochætium 

 Hoytii seems to have a very similar base, but it has 1—3 erect 

 filaments which only reach a diameter of about 6 n ; further it 

 appears to be more branched and the sporangia are pedicellate 

 and much smaller than those in my species. I wished very 

 much to compare my plant with that distributed in Phycotheca 

 Bor. -Am., No. 1540 and have also examined the material distri- 

 buted but did not succeed in finding the plant in the material 

 to which I had success. 



Acrochætium unipes has only been found once in a depth of 

 about 6 fathoms. 



St. Croix: Frederikssted. 



11. Acrochætium opetigenum nov. spec. 



Thallus 1 — 2 mm altus. Spora germinans globosa, processum 

 decumbentem cuneiformem in cortice hospitis {Dasyæ elegantis) 

 endophyticum et filum erectum sporangiferum procreat. 



Fila erecta, a basi ramosa, cellulis cylindricis ad 80// longis, 

 ad basin ca. 8 — 11^ latis, in media parte 13 — 14// latis ad apicem 

 versus paulo attenuatis ca. 6— 7/i latis. Ghromatophorum parie- 

 tale pyrenoide laterali instructum. 



Ramificatio uberrima, rami sparsi. Monosporangia sessilia 

 aut pedicellata ad basin ramorum 2 — 3 præsentia, oblonga vel 

 subcylindrica, c. 11 // lata c. 27// longa. 



This species is the largest Acrochætium found on the shores 

 of the islands ; well grown specimens reach a height of up to 

 1 — 2 mm or more and form a dense much branched tuft. 



The base (Fig. 36) consists of the original spore from which 

 an elongated cuneate prolongation grows downwards and pene- 

 trates into the tissue of the host plant {Dasya elegans). ' This 

 endophytic part reaches a length of about 20//. 



In some plants, especially the older and more vigorous (Fig. 

 36 h) is furthermore developed one or a few short horizontal 



1) Collins, F. S., Two new species of Acrochætium (Rhodora, vol. 10, 

 1908, p. 134). 



