322 THORODDSEN 



plants are common: Potentilla anserina, Leontodon autumnalis, Tri- 

 folium repens, Brnnella vulgar is, Gnaphalium uliginosum and G. sil- 

 vaticum, Hydrocotyle uulgaris, Ranunculus acer, Sagina procumbens, 

 Spergula arvensis, Plantago major, P. maritima f. pygmwa, Polygonum 

 persicaria, P. aviculare and various Gramineae, and sometimes Vicia 

 cracca. Where it is damper occur Epilobium palustre, E. alsini- 

 folium, Cardamine multicaulis , Montia rivularis, Limosella aqnatica, 

 Jnnciis lamprocarpus, J. bufonius and some Carices. The composition 

 of these groups of species differs however considerably at the dif- 

 ferent kinds of springs. Of vascular plants the following have been 

 observed exclusively near alkaline hot springs: Hydrocotyle vulgare, 

 Gnaphalium uliginosum, Veronica anagallis, Polygonum persicaria; 

 rare outside the range of influence of hot springs are Galeopsis te- 

 trahit, Plantago lanceolata, P. major and Blechnnm spicant. Moreover, 

 C. Ostenfeld enumerates eight species of mosses which have been 

 found only on warm soil, and three species which are especially 

 connected with a warm ground. In North Iceland some species 

 grow only near hot springs, which in South Iceland thrive also 

 outside the area of the warm soil, for instance, Brnnella vulgaris, 

 Plantago lanceolata, Cardamine mnlticanlis and Drosera rotnndi- 

 folia. In the outlets from both the warm and hot springs an abun- 

 dance of algae often occurs often in a great heat which have 

 not as yet been investigated. Near solfataras vegetation is ex- 

 tremely sparse, and in the immediate neighbourhood of the sul- 

 phurous-acid fumaroles no plant-life can thrive, therefore only bare 

 clayey flats occur there. Ophioglossnm vulgatum grows only near 

 solfataras; in 1882 I found at Bjarnarflag near Myvatn scattered, 

 but numerous, specimens of it on clayey ground which had a tem- 

 perature of 27 G. - it occurred together with Sagina procnmbens and 

 Poa pratensis; and in 1883 I found it near Gunnuhver on Reykjanes 

 also on warm clay in the neighbourhood of sulphur springs. In 

 both localities it occurred together with the otherwise rare Riccia 

 bifurca and Chomocarpon commutatus. C. Ostenfeld found it on 

 Reykjanes in the neighbourhood of steaming holes, "first a crust 

 was found held together by a Stigonema species, then a great many 

 Muscineae of which the most characteristic were Riccia bifurca and 

 Chomocarpon commutatus. Amongst them occurred some other mosses: 

 Pohlia nntans v. filicaulis, Fossombroiua Dumortieri, Bryum ventrico- 

 snm, Fissidens osmundioides and Philonotis fontana, moreover, the cha- 

 racteristic Ophioglossnm vulgatum var. polyphylla" (loc. cit. p. 240). 



