302 THORODDSEN 



unusually large quantity of Viscaria alpina grows at Ulfsvatn (400 

 metres above sea-level). An old lava-stream, south of Krakatindur 

 and NE. of Hekla is almost exclusively overgrown with Oxyria 

 digyna, which otherwise occurs rather rarely on lava. The neigh- 

 bourhood of Eyjafjordur is characterized by a great abundance of 

 Gentiana, and the neighbourhood of Lake Myvatn by its rich vege- 

 tation of Nasturtium palustre and Pleurogyne rotata; Erysimum hie- 

 racifolium, which is otherwise rather rare, occurs abundantly and 

 as large specimens on the islands in Myvatn; Succisa pratensis is 

 very numerous in Sida. A few rare plants have been found only 

 in very far distant habitats, at opposite sides of the island, thus, 

 Ophioglossum valgatum at Gunnuhver at the extreme point of Reyk- 

 janes, and at Bjarnarflag near Myvatn. Drosera rotundifolia grows 

 here and there near Breidifjordur and Faxafjordur and otherwise 

 only in the extreme north between Eyjafjordur and Skagafjordur, 

 Cirsium arvense occurs in a few localities which are as far apart 

 as Grindavik and the Vestmannaeyjar towards the south, and Eyja- 

 fjordur towards the north. 



In Iceland as in other arctic or subarctic countries with a 

 coastal or insular climate there is comparatively but a slight dif- 

 ference in the vegetation of the lowlands and of the plateau, of the 

 mountains and of the valleys; it is very difficult to arrange the 

 species according to their altitudinal zone. Almost throughout the 

 island, and everywhere where plant -life can thrive at all, plant- 

 formations and plant-associations, with a few modifications, occur 

 with a gradually increasing or decreasing luxuriance and number 

 of species according to situation only. With the exception of the 

 highest situated tracts, close to the snow-line, the distribution of 

 the plants and the differences in the vegetation appear to be in a 

 higher degree dependent on local climatic conditions, such as snow 

 and other atmospheric precipitations, wind, conditions of soil, in- 

 clination, more or less sunny exposure, streams and springs rather 

 than on the height above sea-level. A luxuriant vegetation with a 

 lowland character often extends very far upwards on the mountains 

 on the sunny side, or where a suitable degree of moisture and a 

 protective snow-covering afford favourable conditions of life for the 

 vegetation, while in the immediate neighbourhood, and often at a 

 far lower level, cold sharp winds or sand-drifts have destroyed al- 

 most all plant-life and laid the land waste. Exceptionally favour- 

 able localities are allbrded for plants in some places near hot springs 



