17 



2. A multicellular vertical basal layer 20. A. phacelorhizum. 

 D. The whole plant immersed in the host plant . 21. A. Liagorse. 



In addition is described below .4. ernothrix the base of which 

 I have not succeeded in seeing clearly. 



1. Acrochsetium Sargassi nov. spec. 



Thallus usque ad 700 p altus. E cellula basali, discum par- 

 vum formante, filum erectum, a basi ramosum, egreditur. 



Kami sparsi aut secundati aut oppositi, simplices aut ramosi, 

 ad apicem versus attenuati, in pseudopila sa3pe producti, ex cellu- 

 lis in parte inferiori thalli 5,5 p latis, 9 18^ longis, in superiori 

 parte 2 3/j. latis, 30 40^ longis compositi. 



Ghromatophorum parietale, pyrenoide laterali instructum. 



Sporangia sparsa aut pauca secundata, in ramulis sa?pe bina 

 praesentia, sessilia aut pedicellata, obovata, 10 p longa, 7// lata. 

 Antheridia in ramulis opposita aut plus minus irregulariter 

 aggregata, globularia, ca. 2 // lata; carpogonia lageniformia, 

 sessilia. 



This plant reaches a length of up to 600 700 /*. The 

 base (Figs. 7 and 8 a) consists of a flat disc (about 20^ diameter) 

 formed by the original spore and apparently in a similar 

 way to that found in Acrochastium (Chcmtmnsid) microscopicum 

 Nsegl. var. collopoda ROSENVINGE, described and figured by Ro- 

 SENVINGE in "Deuxieme Memoire sur les Algues mar. du Green- 

 land" (Meddelelser om Granland, XX, p. 412). By means of this 

 small disc the plant is fixed firmly to the host plant (old leaves 

 of Sargassum vulgare). 



From this disc is given off a single filament which immedia- 

 tely begins to branch (Fig. 7). The cells in the lowermost part 

 of the filaments are short and have thick walls ; they are about 

 9// long and 5,5^ broad, in vigorous plants up to 8// broad. 

 Higher up the cells grow longer, up to about 18,, tapering at the 

 same time, and the filaments end with long, thin nearly colour- 

 less, hairlike prolongations which soon die away ; in these the 

 cells are only 2 3 p. broad while their length is about 30 40 u 

 or more. ROSENVINGE also found such discoloured prolongations 

 in several species and compared them with the hair-like organs 

 in the Phseophycese. 



2 



