— 365 - 



NW. I cel. common. 



SW. Icel. Reykjavik (CO.) probably common. 

 S. Icel. Eyrarbakki, Vestmannaeyjar. 



Rhizoclonium riparium (Roth) Harv., Rosenv. Grl. Ha valg. p. 913, 

 Deux. Mém. p. 103. 



f. polyrhiza Rosenv. Grl. Havalg. p. 913. 



The Icelandic specimens are 29 — 36(— 43)// thick; the cells are as 

 long as broad or twice as long as broad and the membrane is 1,5—3 

 (—4)// thick. In other respects my plants fully agree with the description 

 given by Rosenvinge (Grl. Havalg. 1. c). It grows gregariously in rock- 

 clefts at or above high-water mark. 



f. valida Fosl., Rosenv. Grl. Havalg. p. 915. 



My plants are 29 — 48// thick; the cells are 

 as long as broad or twice as long as broad and 

 the membrane is (2— )3 — 4( — 5)// thick. It occurs 

 gregariously in rock-clefts at or above high-water 

 mark. Lateral branches, as in f. polyrhiza, do not 

 rarely occur. Judging from my material of these 

 two forms, there is no distinct limit to be drawn 

 between them. The specimens growing in the 

 rock-clefts have numerous rhizoids, as f. polyrhiza, 

 while plants I met with in tide pools at high-water 

 mark had only very few rhizoids. 



f. implexa (Dillw.) Rosenv. Grl. Havalg. p. 915. 



The Icelandic plants are 17—29// thick; the 

 cells are as long as broad or much longer, up to 

 10 times longer than broad, and the membrane 

 is 1,5 — 3// thick. In other respects my plants 

 agree fully with Rosenvinge's description. As 

 mentioned above the cells sometimes attain a con- 

 siderable length, but as both short and long cells 

 occur in the same filament, I think it unnecessary 

 to give a more detailed description of such speci- 

 mens or to give them a name. Fructiferous specimens have been gathered 

 in July— August. The greatest part of the sporangia was emptied and 

 only some few of them contained 9 zoospores. The spores escape through 

 an opening in the middle or nearer one of the ends of the sporangium 

 (cfr. fig. 12). I have also in f. valida occasionally met with emptied spo- 

 rangia of the same appearance. The sporangia are either occurring singly 

 or in rows and fully resemble the sporangia of Rhizoclonium Kerneri Stockm., 



Botanisk Tidsskrift. 25. Bind. 24 



a b 



Fig. 12. Rhizoclonium 

 riparium (Roth) Harv. 

 a two sporangia of R. 

 riparium (Roth) Harv. 

 f. implexa (Dillw.) Ro- 

 senv. (126: 1). 

 b a fragment of a fila- 

 ment of R. riparium 

 (Roth) Harv. f. valida 

 Fosl. showing a spor- 

 angium (215 : 1). 



