12 



cells are formed by peri- and anticline walls. By this way of 

 growing the most often very regular dichotomously branched, 

 radial series of cells are formed and as the cells often have nearly 

 the same length the concentric arrangement arises at the same 

 time. A transverse section through the disc shows that this 

 consists of a single layer of cells only; the thickness of the vege- 

 tative cells is about 10 — 12 /^. 



Here and there in the larger discs we find the vegetative 

 cells transformed into sporangia (Figs. 3 d, e); these are much 

 higher than the vegetative cells, about 45 p. high, jar-shaped 

 or like a short bottle, and have each a single rather large, round 

 hole at their top. When this is formed the cuticula bursts and 

 the split formed in this way is seen as a rhomboid scar round 

 the opening. A large number of small zoospores seem to be 

 formed in each cell but I may point out that 1 have had only 

 dried material at my disposal, for which reason I have not been 

 able to see them with certainty. 



This has also made the examination of the cell contents 

 difficult but so far I have been able to see, each cell contains 

 a large parietal chromatophore with irregularly lobed edges 

 covering nearly the whole side of the cell; 1 — 4 pyrenoids are 

 present in each chromatophore. 



Being as yet rather imperfectly known it is of course diffi- 

 cult with certainty to indicate the systematic position of this 

 form. But it seems to me that it might be referred to the Chae- 

 tophoracese, coming here rather near Pringsheimia and Ulvella 

 and related forms. 



As mentioned above it was found growing epiphytic upon 

 a large specimen of Udotea flabellata. Most of the specimens 

 formed small roundish discs but some had grown together as 

 rather large coherent covers. The plant was dredged in a depth 

 of about 20 meters. 



St. Jan: In the Sound between this ishind and St. Thomas ofT 

 Cruz Bay. 



Fam. 3. Goniontiacew. 



Gomontia Bornet et Flaiiault. 



1. Gomontia polyrhiza (Lagerh.) Bornet et Flahault 



in Journal de Botanique, vol. II, 1888, p. 1G3 et Bull, de la Soc. hot. do 

 France, T. XXXVI, 1889, p. CLII, pi. VI— VIII. 



Codiolum polyrhizum Lagerh. in Ofversigt af Kungl Veten.sk. -Akadem. 

 Ffirhandl., 1885, p. 21. 



