'^i)'2 .lOHS. aOM. PKTKUSKN 



Several invcstif^nlors (Ksmarch (191 1 and 1914). Boye Petersen 

 (1915\ Hrislol (1919 and 1920), Moore and Ka rrer (1919), Moore 

 and Carter (192())) have studied tlie lerrestrial alj^æ by means ol" 

 cultiires. In cultures tliere will ns a rnle devdop species (juite dilTe- 

 renl from Ihose found in the samples on simple microscopical 

 observation. Hence, il" the two niethods of investigation are com- 

 l)ined. as eomplete an algal flora as possible will be oblained. 

 However, as a basis for even the ronghest estimate of the frequency 

 of the individual species, the methods of culture hitherto employed 

 are qiiite useless. If, Iherefore, a description of the individual algal 

 associations and the proportion of their components in Nature is 

 aimed at, direct investigation of collected samples is for the present 

 to be j)referred. In the present work I have exclusively employed 

 this melhod. There is however, no doubt Ihat bv means of cul- 

 tures more terrestrial species may be demonstrated than those here 

 mentioned. At my instigation Mr. M ølhol m- H ansen has collected 

 a series of samples of earth from Iceland in sterile glasses, and 

 these I have used as a starling-j)oint for cultures in which numerous 

 species of algæ have appeared. I hope to be able lo publish the 

 results of this investigation later on. 



1. Soil. 



The loose soil of Iceland may consist of a series of different 

 components of widely varying geological origin. The commonest 

 are perhaps glacial formations, but also alluvial formations such as 

 river gravel, sand, and day are common, while drift-sand often 

 occurs, especially in the interior. Mixed with these soils are nearly 

 always found smaller or greater amounts of volcanic dust, and in 

 the neighbourhood of the volcanoes the soil consisls aliuost exclu- 

 sively of volcanic ashes and dust. Covering the mineral soil there 

 is as a rule a layer of humus which is often turfy. (See Thorodd- 

 sen 1914, p. 251). Little is known of the chemical composition of 

 the scjii. As a rule however. it seems to contain little calcium car- 

 bonate, bul much phosphoric acid and iron (Thoroddsen 1914, 

 p. 2o2). According lo Uspenski (1927) the presence of Ihis sub- 

 slance in greater or smaller amounts is of signal importance to the 

 Iower planls. This might perhaps be studied to advanlage in Ice- 

 land. Thoroddsen states (I. c. p. 253) thai the soil is as a rule 

 covered with acid boggy humus. Mr. Mølholm- H ansen has 

 made a series of determinations of the j)h value of soil and s])rings 



