OX ACTINOCOCCUS AND PHYLLOPHORA. 179 



Actinococcus Ktz. 



Literature : (1) Darbish., Beitrag, p. 7, &c. ; (2) Darbish., Phyllophora- 

 Arten, p. 36 ; (3) Gomont, p. 2, &c. ; (4) Kolderup Rosenvinge, p. 33 ; (5) 

 Schmitz, Actinococcus, p. 392. 



Thallus parasitic on other Florideae, the vegetative portion consist- 

 ing of filaments branching iu the interior of the host-plant (intra- 

 matrical portion), and fertile filaments forming a cushion of parasitic 

 tissue on the external surface of the host (extramatrical portion of the 

 thallus). Antheridia and procarpia unknown. Tetraspores formed by 

 cruciate division in radially disposed rows of tetrasporangia. 



Actinococcus Subcutaneus (Lyngb.) K. Rosenv. 



Literature : (1 — i) The same as of the genus ; (5) Schmitz, pp. 369-379. 

 Synonymy ; Actinococcus roseus Ktz. 



Thallus (asexual plant at least) parasitic on the young spermo- 

 phores of Phyll. Brodiaei (Turn.) J. Ag\, which it enters through the 

 ostiole of the small antheridial cavities. The intramatrical portion 

 consists of longish cells in uniserial filaments, which branch in the 

 medullary tissue of the host, forcing their way along the middle 

 lamellae of the cells. The extramatrical portion is formed by filaments 

 arising from the intramatrical tissue which break through the cortex 

 and give rise on the external surface of Phyllophora, to a parasitic 

 cushion of radially disposed rows of cells, which eventually develop 

 into tetrasporangia. The outer and innermost cells of these fertile 

 filaments remain sterile. The tetraspores are formed by cruciate 

 division. Antheridia and procarpia are unknown. It is also not yet 

 known what becomes of the tetraspores, and whether the spores which 

 give rise to the parasitic nemathecia on Phyll. Brodiaei (Turn.) J. Ag. 

 are tetraspores or carpospores. 



In conclusion I have to express my thanks to the c Kgi. Ministerial- 

 Kommission z. Untersuchung d. deutsch. Meere in Kiel ' for permission 

 to make use of the cliches for the illustrations in the text of this paper. 



