THE AERIAL ALGÆ OF ICELAND 351 



in llieir whole character, and as a malter of faet the algal vegeta- 

 tion appearing here is very similar to that of the ground, especially 

 by tlie occurience of Diatoms. 



II. THE ALGAL VEGETATION OF THE GROUND. 



While the »proto-pleurococcoid« association (ep. Brand 1924) 

 on ])rominent objects is sHghtly developed in Iceland, it is ({uite 

 otherwise with the algal vegetation of the ground itself. As previously 

 mentioned, the wind must be supposed to have a very marked efTect 

 on prominent objects, whereas it will not as a rule be able to exert 

 its full force on the soil itself because this is protecled by all sorts 

 of inequalities in the ground and by its covering of piants which, 

 though low, is as a rule continuous. The soil will furthermore be 

 kept in a constant state of moisture owing to the frequent rainfall. 

 Hence a rich flora of algæ, both Cyanophyceæ, Chlorophyceæ, and 

 Diatoms, will be able to develop here. The physical conditions, too, 

 will evidently favour an algal vegetation. The country is mountainous 

 with w-ater trickling from the earth in many piaces; throughout the 

 summer the snow on the highest peaks is continually melting and 

 forming water that keeps the mountain slopes wet in many piaces. 

 These conditions create numerous good growing-places which cannot 

 find their equal in a flat country like Denmark. Furthermore, the 

 neighbourhood of the hot springs presents special life-conditions. 

 Hence a characteristic flora af aérial algæ is found there. 



Investigations by Esmarch (1911 and 1914), Moore and 

 Karrer (1919), and Moore and Carter (1926) have shown that in 

 addition to the algæ on the surface others are found in the deeper 

 layers of the earth. At the present moment the investigations have 

 been carried dowai to a depth of abt. 3 m. At Rothamsted Experi- 

 mental Station it was found that the number of subterranean indi- 

 viduals and species is almost as great at a depth of 4 inches as at 

 the earth's surface, while at increasing depths the number of indi- 

 viduals as well as species diminishes (John Russell 1923, p. 109). 

 The investigations on this »subterranean Algal Flora« are as yet in 

 their first stage, and I cannot in this work give any information 

 about this community in Iceland, my collections being made as 

 early as 1914. Consequently the following pages will refer exclu- 

 sively to the »Surface Community« (Fritsch 1922, p. 225). 



