THE AERIAL ALGÆ OF ICELAND 



357 



rum , Plectonema roseohim , Scytonema tolypothrichoides, Aphanothece 

 microscopica. 



In one sample Østrup found 15, in the other 40 species of Dia- 

 toms which were almost all decidedly hydrophilous. At the top of 

 a hillock in mvri at Vallanes (29) Stigonema niinutiim, Gloeolhece 

 rnpestris and Xostoc sp. occuned. On another stretch of myii near 



Fig. 1. Streambed in littoral meadow near Borg. The extensive, tufted mats of 



Vaiicberia sphærospora are seen. 



Vallanes, in a place where tuif had been cut some time before (41), 

 I found Vaiicheria sp. and 11 species of Diatoms, among which 

 Pinnularia horealis was the commonest. A sample (380) from myri 

 at Apavatn contained 12 species of Diatoms, all hydrophilous. 



On the \vhole it may be said that the mj'ri is rich in species 

 of Cyanophyceæ and Diatoms, which are almost all hydrophilous; 

 only on the hillocks, where the algal flora is poorer in species, do 

 terrestrial forms occur. 



h. Lilloral Meadows. 



The nature and vegetation of the littoral meadow have been 

 described by Helgi Jonsson (1913). Its chief characteristic is that 

 it is occasionally flooded with salt water, a faet which radically 



The Botany of Iccland. Vol. II. 24 



