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



41 



Fig. 38 

 nov. 



Acrochætium rohustum 

 spec. Base of a plant. 

 (About 450: 1). 



fluentia, egrediuntur, et sic discum 



basalem formant, ex cellulis brevi- 



bus, diametro fere æquilongis, pariete 



crasso compositum. Fila erecta a basi 



ramosa, apicem versus sensim pau- 



lum attenuata, in parte basali 9 — 10// 



lata, superne ca. 5 n. Cellulæ cylin- 



dricæ 9 — 10// latæ, inferiores 15 — 



20 fjL longæ, superiores ca. 40 [i longæ, 



chromatophorum parietale, pyrenoide 



laterali instructum continentes. 



Rami sparsi, nonnunquam secun- 



dati, ramulis sparsis, uni-, bi- aut tri- 

 cellularibus, monosporangia gerentibus 

 instructi. 



Sporangia ovata, ca. 11 /« lata et 

 12 — 14// longa. 



This species was found together 

 with several other species upon old 

 leaves of Sargassum vulgare. The base 

 (Fig. 38) of the plant consists of a 

 pluricellular disc composed of thick- 

 walled cells. From this an unicellu- 

 lar, thickwalled process grows down- 

 wards fixing the plant strongly to the 

 host plant ; how far these processes 

 also should serve as haustoria like 

 those described by Rosenvinge for 

 Chantransia cytophaga, I have not been 

 able to decide. The processes reach 

 a length of about 20 fi ; the basal 

 disc is about 8 — 10 /< thick. 



Not having succeeded in finding 

 quite young plants I have not been 

 able to follow the development of 

 the basal disc, but most seemingly 

 the germinating spore produces the 

 process during germination (com- 

 pare Fig, 38) and this grows down- 

 Fig. 39. Acrochætium robustum ^^Yds in the tissue of the host 

 nov. spec. Habit of a plant. 



(About 140 : 1). plant ; afterwards from its upper end 



