58 H. JONSSON 



SkagafjorSur; while Cystoclonium, Polysiphonia nigrescens and Leathesia 

 do not extend further than the most western part of the north 

 coast (the small fjords in Hunafloi). Only Delesseria sanguined now 

 remains; strictly speaking, this appears to belong to the south and 

 south-west coast, but has on one occasion been found in E. Iceland, 

 cast up on the shore. It did not appear to have come from a 

 distance, and it probably grows there, though I did not come across 

 it in the dredgings. 



Thus all these 53 species have on the whole a southern and 

 western distribution in Iceland. 



The above shows that there is a large neutral territory where 

 the species with a south-western and those with a north-eastern 

 distribution meet and intermingle. This boundary area comprises 

 almost the whole of the north coast, the north-west fjords and, to 

 a certain extent, the northern part of the south-west of the country. 

 (For further details see below under the Floristic Boundaries.) 



THE COMPONENTS OF THE ALGAL FLORA. 



At present 200 species of Marine Algae are known from Iceland. 

 In the plant-geographical groups established by Borgesen and my- 

 self (Borgesen and Jonsson, 14) these are distributed in the 

 following manner. The definition of the groups is here reproduced 

 almost literally from the publication mentioned. 



A. The Arctic Group. 



The species of this group belong to the arctic area of the sea. 

 The southern limit of this area extends from the north and east of 

 Norway southward to the south-east point of Iceland, where the 

 boundary is sharply defined. From E. Iceland the boundary line 

 extends to the north of Iceland between Iceland and Greenland, 

 and then turns considerably southward to the North Atlantic coast 

 of America. The flora of the boreal area of the Atlantic passes 

 without any distinct limit into the arctic algal flora on both sides 

 of the Atlantic. In Iceland the limit is distinct only at the south- 

 east point whereas the boundary is very indistinct on the north- 

 east part of the coast. 



Some of the species of this group occur, but only rarely, 

 south of the border-zone. 



