SOIL ALGAE 223 



heathland containing only traces of organic matter, marshy bog, forest 

 humus, and moist sand. The various samples were often taken from 

 quite different localities having the same type of soil. Only 3 out of 34 

 samples of the sandy heathland showed the presence of Cyanophyceae 

 on the surface. Thirty-five samples of the marshy bog soil showed no 

 blue green algae, but contained a few diatoms and grass-green algae. 

 Only 5 samples out of 40 of the forest humus soil contained blue 

 green algae and only 5 species were obtained altogether from soils of 

 this type. The moist sandy soils indicated numerous blue-green algae 

 on the surface. Subsurface samples from below the uncultivated soils 

 were destitute of algae except in the moist sandy soils where they were 

 fairly extensive in distribution. A larger number of blue-green algae 

 was found in cultivated soils. A clay soil, for example, contained 23 

 species of blue-green algae in 35 out of 37 samples and 29 out of 45 

 samples of sandy soil contained 12 different kinds of algae. In general, 

 cultivated soils were found to contain a greater number of blue-green 

 algae than uncultivated, possibly because of the difference in moisture 

 and mineral content. Grass land was richer in species than arable 

 land. Subsurface samples were obtained at a depth of 10 to 25 cm. 

 and, in some cases, at 30 to 50 cm., in a manner to prevent surface con- 

 tamination. Only a few of the samples, coming from soils where there 

 were no surface forms, contained no blue-green algae. Eighteen sepa- 

 rate species were isolated, the number of algae decreasing with depth. 

 In all, 45 species were described, of which 34 belonged to the OsciUatori- 

 aceae and Nostococaceae. 



Esmarch ascribed the occurrence of subsurface forms to their being 

 carried down by soil cultivation and by seepage of surface waters, as 

 well as by earthworms and other soil organisms. By growing blue- 

 green algae in the dark, or burying algae in the soil, then examining 

 microscopically at various intervals of time, the filaments were found to 

 become discolored, finally changing to a yellow color; the filaments 

 disintegrated leaving only spores and heterocysts behind. On moisten- 

 ing and exposing these to light, blue-green growth again appeared. The 

 conclusion was reached, therefore, that blue-green algae cannot persist 

 beneath the surface for any length of time, because of the absence of 

 light and the destructive influence of the soil itself. 



Acid soils were reported 31 to contain a different algal flora from that 

 commonly found in alkaline or neutral soils. Twenty-four species 



31 Petersen, J. B. Danske aerofile alger. Danske Vidensk. Selsk. Skrifter. 

 7 Raekke, Naturv og Mathem. Afd. 12: 7. 1915. 



