THE HRYOFHYTA OF ICELAM) 



495 



characteristic form of the leaves and tlie looser cell-lissiie is seen Irom 

 the faet that, in situations where the waler-Ievel is altered, forms may 

 be found growing in tufts, in the lower part of which the stems are 

 tomentose and the leaves normal, while all the young shoots which 

 have developed after the habitat has been inundated have the typical 

 depressa appearance. Likewise are found all possible transitions between 

 P. fontana and the depressa form. 



On mountain heights, where the snow lies long, the slopes are often 

 covered with f. nigresccns Locske, with black, prostrale and hardly to- 



Fig. 8. Philonolis fontana (L.) Brid. Slender l'orin from warni s'ound 



(.Thorlakshver; nat. sizi-). 



mentose stems and light yellowish-green annual shoots. This form has 

 be\'ond doubt originated from the pressure of the snow-covering. The 

 leaves are, as a rule, shortly jiointed. Where the water from the melted 

 snow remains and soaks the tufts the leaves become still more shortly 

 pointed and the cell-tissue looser f. horcalis. Hagen, Loeske . By hot 

 springs P. fontana often occurs abundantly both in the lukewarm water 

 and on the warm claye}' flåts. Here it forms very soft, not cohering 

 tufts. The stems are erect and very slender; the leaves are small, often 

 strongly falcato-secund, longly pointed, highly papillose, and sharply 

 toothed along the margin, with narrow 0.05—0.06 mm. broad nerve. 

 Note. P. calcarea from Frodarheidi (leg. H. J.) is P. seriata. 



189. Philonotis Arnellii Hiisnot. 



N. Iceland: Hof near Eyjafjordur O. D.)!. S\V. Iceland: Thingvellir!; 

 between Reykjavik and Hafnarfjordur!. 



