580 A. HESSELBO 



Bryum ventricosum, Fissidens osmnndoides and Philonotis fontana. 



The Sulphur Springs near Krisuvik are, according to 

 Ostenfeld, rather bare of vegetation, and he mentions only Haplozia 

 crenulata as growing near a few of these. The collections contain 

 also Gymnocolea inflata and Polytrichnm commune which were 

 gathered here by Steenstrup, so probably the same species occur 

 on this spot as are, for instance, to be found near Kolvidarhol. 



In the remaining part of Iceland the vegetation of the warm 

 ground has hardly been investigated at all. During my stay at 

 Myvatn in 1909 continual rain and fog prevented me from making 

 a closer investigation of the numerous sulphur springs which occur 

 there. The warm clayey flats were mostly quite bare, only around 

 a single steaming hole, where the temperature of the surface was 

 about 40, grew Riccia bifurca, Haplozia crenulata and Fossombronia 

 Dumortieri. 



A moss-cushion from one of the Solfataras near Kverkfjall, 

 (Eyafjallajokul) collected by Andr. Lundager, consisted of Philo- 

 notis fontana and Riccia bifurca. 



By comparing what is known regarding the moss vegetation of 

 warm ground, it is seen that the composition of the vegetation is 

 dependent on the chemical nature of both the water and the es- 

 caping vapours, and also on conditions pertaining to soil. 



Where the water is free from sulphuretted hydrogen, or where it, 

 at most, contains a trace of it, the Sphagnum vegetation is very 

 luxuriant, especially when the surroundings of the spring are boggy, 

 as is the case in Biskupstungur and near most of the springs in 

 Reykholtdalur. The condition for the formation of a continuous 

 Sphagnetum, in addition to a warm, damp substratum, is an abun- 

 dant development of vapour, which envelops the moss-cushions in 

 a damp, warm atmosphere. The most frequent species is S. papil- 

 losum, which often constitutes the bulk of the Sphagnum carpet, in 

 association with S. cymbi folium, S. angustifolium and S. teres, fre- 

 quently replaced by. or intermixed in patches with, some other 

 species. Scattered in the Sphagnum carpet grew, as a rule, a very 

 vigorous, fruiting form of Polytrichum commune, and usually also 

 Hypnum stramineum, Hylocomium s(]iiarrosum or Acrocladium cuspi- 

 datum. 



Outside the Sphagnum-belt there occurs, on warm, boggy ground, 

 a moss carpet interspersed with Carex spp. and other flowering plants, 

 and chiefly composed of Hypnacea 3 , occasionally also of Philonotis 



