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



37 



This species was found in a depth of about 10 meters i) 

 growing upon Dictyota linearis. 



The largest specimen found had a length of up to 2 mm. 



The base of the plant consists of the original spore which 

 during germination penetrates into the epidermal cells of the 

 host forming a process (Figs. 32, 33) ; this is thinnest in its 

 upper end where it passes through the wall of the host broad- 

 ening more out downw^ards getting a somewhat obovate-clavate 

 shape, by means of which the plant becomes more strongly fixed 

 to the substratum. The process reaches in all a length of about 

 35// and reaches often the lower wall 

 in the cell of the host plant. 



The spore itself lies freely above 

 the wall of the host plant; it is 

 nearly spherical with proportionally 

 thick wall ; its diameter reaches a length 

 of about 20—22^. 



From this basal body a single 

 erect fdament grows upwards ; once 

 only did I find two filaments arising 

 from it (Fig. 33 b) ; but in this plant 

 the primary filament had been destroyed 

 and then another one was given off 

 at the side of the first one. 



The erect filament is straight and 

 at first not branched, higher up bran- 

 ches are given off to all sides (Fig. 

 31) ; these are also very straight and 

 issued from the principal filament 

 in an acute angle and most often 

 branched in a similar way. Against 

 their summit all the filaments taper somewhat. 



The cells in the principal filament and the lowermost cells 

 in the branches are cylindric, somewhat thick-walled, their dia- 

 meter reaching a length of about 9 — 11// and their length up 

 to 50//- In the summit on the other hand the cells are only 

 about 5// thick while their length is about 50 — 60//. 



The cells contain a parietal chromatophore with a pyrenoid 

 lying at the wall (Fig. 34). 



The monosporangia (Figs. 31 and 34) occur upon the inner 



1) By a misprint is the depth in Part II (Dansk Bot. Arkiv, Bd. 2, Nr. 2, 

 p. 54 [Reprint p. 210]) said to be 40 meters. 



Fig. 34. Acrochætium unipes 

 nov. spec. Part of the thallus 

 with sporangia. (About 425:1). 



