THE AÉRIAL ALGÆ OF ICELAND 355 



(1. Bridle-Paths. 



The oldest roads in Iceland are the hiidle-paths (Icelandic: gala) 

 which are foiind all over the Island. They are narrow heaten tracks, 

 only just broad enoiigh for the hoofs ol' a horse. A \o\\ growth of 

 mosses is often found liere, and among these algæ, especially Dia- 

 toms, occur. One would expect the algal vegetation liere to he 

 characterised to some extent by nitrophilous species since there 

 will of course sometimes fall dung on the paths, but at the same 

 time it might be expected that the original character of the soil 

 would assert itself. Sample Nr. 28 is derived from a bridle-palh 

 running across myri, and liere it is obvious that the Diatoni species 

 of the myri predominate, especially Nitzschia amphibia, N. commiinis, 

 and N. Palea, further Rhopalodia gibberula and R. ventricosa, as well 

 as Epithemia Argiis and Eiinotia præriipta /'. ciirta. In the other 

 samples (219, 254, 373) Navicula Atomiis is present as the represen- 

 tative of the nitrophilous species; in two of the samples there are 

 also forms of Navicula miitica. For the remaining species the reader 

 is referred to the list of the individual samples. 



e. Roads and Pnrehj Mineral Soil. 



Macadamised roads have recently been made in various parts 

 of the island, and there, too, an algal vegetation is often found, 

 especially along the margins of the roads. It seems less charac- 

 terised by nitrophilous species than in the bridle-paths, whereas 

 the almost purely mineral nature of the soil seems to be decisive. 

 Hence I liere deal with the algal vegetation of roads in conjunction 

 with that on purely mineral soil which, by the way, is found in 

 spots along the roads. These spots correspond in the main to what 

 I cailed »new soil« in 1915 (p. 301). A commencing growth of moss 

 protonema and small mosses are often found here and among these 

 especially Diatoms and Chlorophyceæ thrive well. The samples 

 included by me in this group are: naked soil GI, 137, 125, 138, and 

 roads 264, 269, 336. The Chlorophyceæ here met with were Kerato- 

 coccns bicandahis, Vaucheria terrestris, and Bolrijdiopsis arhiza. The 

 Diatoni flora is rather variable. The commonest forms are Pinmi- 

 laria borealis and Hantzschia amj)hioxiis, next come Nauicula cincfa 

 V. Henfleri, Achnanthes marginnlata, and Pinnularia appendiculaia 

 V. irrorata. 



