38 



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 fj. and a breadth of 9 11^. The sporangia found were 

 apparently not quite ripe. 



To judge from the description of Acrochastium Hoytii Collins 1 ) 

 this plant seemingly comes near to my plant. Acrochastium 

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

 filaments which only reach a diameter of about 6^; 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. 



Acrochastium unipes has only been found once in a depth of 

 about 6 fathoms. 



St. Croix: Frederikssted. 



11. Acrochsetium opetigenum nov. spec. 



Thallus 1 2 mm altus. Spora germinans globosa, processum 

 decumbentem cuneiformem in cortice hospitis (Dosyae 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 1 p. latis. Chromatophorum parie- 

 tale pyrenoide laterali instructum. 



Ramificatio uberrima, rami sparsi. Monosporangia sessilia 

 aut pedicellata ad basin ramorum 2 3 praBsentia, oblonga vel 

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



This species is the largest Acrochaetium 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 b) is furthermore developed one or a few short horizontal 



1 ) COLLINS, F. S., Two new species of Acrochaetium (Rhodora, vol. 10, 

 1908, p. 134). 



