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thai the filaments of the Greenland specimens also vary rather con- 

 siderably with regard to thickness, never, however, exceeding 16 (*, 

 but as mentioned above, the Færoese specimens are oflen much 

 thicker, and in ih is they come very near to the extremely interesting 

 aérial species of the Florideæ Rhodochorton islandicum Rosenv. 1 which 

 Helgi Jonsson gathered on his native island. The Færoese 

 material, which especially resembled Ibis species and which perhaps 

 even makes il doubtful whether Rhodochorton islandicum ought to 

 retain ils valne as a distinct species, was also gathered by Jonsson 

 during his visit to the Færoes in 1897. As the material in question 

 appears to me to be of special interest, I will describe il more fnlly. 

 The material was gathered in Skaalefjord, lale in October. With 

 reference to its habitat J (His son writes in his diary as follows: — 

 »Forms a continuons covering on the rocks, and occnrs most 

 often above the water, but is, however, now and then washed by 

 the waves«. To this I mav remark that there is no doubt whatever 

 thai the alga growing here in the fjord where no tide is felt or 

 where it is almost imperceptible, would not, during summer in 

 calm weather or when a land-breeze was biowing, be wetted by 

 sea-water for a long period, even if it did not grow very far above 

 sea-level, just a few inches higher making a great difference here in 

 Ihe fjord. The Færoese material — a very small quantity — is sterile; 

 it corresponded, as a whole, closely to Rosenvinge's exhaustive 

 description and ligures, but I have not come across such thin de- 

 current threads as, according to Rosenvinge's description, are to 

 be found on Rh. islandicum; it is true that a few thin threads oc- 

 curred intermixed, but from a biologicai point of view they did not 

 seem to be different from the thicker ones. The thickness of the 

 erect branches varied from 16 to 29 //, i. e. between two somewhat 

 greater extremes than tbose mentioned by Rose uvinge. The cells 

 of the lower part are about as long as broad and those of the upper 

 part twice or thrice as long as broad. The cell-walls are often 

 very thick, as much as 5 /*. A few poorly developed filaments of 

 Callithamnion scopulorum occurred intermixed in the material. This 

 Rhodochorton iinpressed me as being a stunted Rhodochorton Rothii 

 which had altered in appearance on account of its habitat, and in 

 the Færoese material I came across the most evenly transitional 

 stages between this peculiar form and typical Rhodochorton Rothii. 



1 Rosenvinge. L. Kolderup: Note sur une Floridée aérienne (Rhodochorton 

 islandicum nov. sp. Botanisk Tidsskrift. 23. Hind, p. (il. København. 1900. 



