CHAP. XLII BENTHOS OF LOOSE SOIL 175 



ginous or filiform masses, which are often several centimetres thick and 

 sometimes present the appearance of almost structureless jelly. 



In European hot springs we know of Anabaena thermalis (in water 

 at a temperature up to 57 C.), species of Leptothrix (in Karlsbad at 

 557 C-)> Beggiatoa, Oscillatoria (44-5i C.), Hypheothrix (in Iceland), 

 Tolypothrix lanata (in Greenland at Unartok, 40 C.), as well as others. 

 Lyngbya thermalis is known to occur in Iceland, in Italian mud-volcanoes, 

 and in hot springs in Greenland. 



Many Schizomycetes occur, including true thermophilous species 

 (of which some dozen have been described), sulphur-bacteria, iron- 

 bacteria, and others. Moreover, many diatoms and other more highly 

 organized algae occur. 1 



The highest temperatures so far noted in this connexion are 8i-85 C. 

 in Ischia, 90 C. in the Azores, 2 and even 93 C. (200 F.) in California. 3 

 At Las Trincheras in Venezuela there is a warm spring whose temperature 

 at its source is 85-93 C. ; the algae in this grow in water whose tempera- 

 ture exceeds 80 C. 



The water of many hot springs, which mainly occur in volcanic regions, 

 contains sulphur, calcium, or other mineral bodies, without changing 

 the composition of the vegetation. 



A special form of activity is displayed by certain of these algae, 

 which excrete crystalline concretions of calcium carbonate or of siliceous 

 sinter ; in the Arno travertine is deposited by Cyanophyceae ; and in 

 the hot springs at Karlsbad large masses of calcareous sinter are excreted. 

 In North America numerous hot springs and geysers occur in Yellow- 

 stone Park, and Weed 4 describes the remarkable stone-forming activities 

 here exhibited by algae ; these grow in waters at temperatures of 30- 

 85 C. and lend to the water their various rainbow tints, ranging between 

 red, orange, white, and green, according to the temperature. Cohn 5 

 expresses the opinion that these algae have a peculiar faculty of storing 

 up calcium carbonate. 



Is it not possible that these thermophilous communities of the most 

 lowly organized algae living in hot springs present us with a picture of the 

 oldest vegetation on Earth? Perhaps the Cyanophyceae can even 

 assimilate free nitrogen. 



2. Sub-formation of Sand-algae the aestuarium of tidal shores. On 

 the sandy shores of seas of Northern Europe and of lakes (for example, 

 Michigan, Fureso in Denmark 6 ), there lie, within reach of the tide-water, 

 communities of algae, which form a thin film on or under the surface of 

 the sand, and give to the shore a distinctive colour if they be present 

 in large quantities. On the coasts of Denmark there are various 

 associations of such : chlamydomonadeta, composed of species of Chlamy- 

 domonas and Diatomaceae, which lie loose on the sand which is not 

 cemented together : phycochromaceta formed by Blue-green Algae and 

 diatoms, which, by means of their mucilage, glue together the grains of 

 sand so as to form a thin, firm, more or less crustaceous layer, which is 



1 Respecting North America, see Harshberger, 1897 ; Josephine Tilden, 1898 ; 

 respecting Japan see Miyoshi, 1897 ; and respecting Hungary, see Istvanffi, 1905. 

 1 Moseley, 1875. * Brewer, 1864. 



4 See the literature quoted by Weed, 1887-9. 

 6 Cohn, 1892. Cowles, 1899. 



