THE MICRO-ORGANIC POPULATION OF THE SOIL 255 



Considerable numbers of species have been found, but 

 estimates of total numbers are rendered uncertain by the 

 breaking up of the filaments during the laboratory opera- 

 tions. 



There has been some speculation as to the possible function 

 of algae in the soil. Assuming that they continue to assimilate 

 CO 2 they are, of course, accumulators of energy and of carbo- 

 hydrate material, and while they may thus function at the 

 surface in the light it is difficult to see how they can be other 

 than consumers in the dark recesses of the soil. The possible 

 effects of this accumulation of organic matter in newly formed 

 soils is discussed by Treub l in his account of the recolonisation 

 of Krakatoa after the eruption of 1886, and by Fritsch. 2 



There is also the possibility that algae may take part in 

 nitrogen fixation in the soil. It was at first thought by Frank 3 

 and by Schloesing and Laurent 4 that algae could themselves 

 fix nitrogen, and this view has recently been revived by Moore 

 and Webster. 5 Kossowitsch, 6 however, maintained that they can- 

 not, bacteria alone having this power. He observed, however, 

 that the presence of algae facilitated the process, and concluded 

 that symbiosis occurs bet ween algae and nitrogen-fixing bacteria, 

 the algae supplying the necessary carbohydrate energy material 

 and the bacteria furnishing the nitrogen required for growth. 

 Nakano 7 shows that the relationship with azotobacter holds 

 not only for blue-green but also for certain green algae. 



1 Treub, Notice sur la Nouvelle Flore de Krakatau (Ann. yard. hot. Buiten- 

 zorg, Vol. 7, 1888, p. 213). 



3 F. E. Fritsch, The Role of Algal Growth in the Colonisation of New 

 Ground and in the Determination of Scenery (Georg. Journ., November, 1907). 



3 B. Frank, Ueber den experimentallen Nachweis der Assimilation freien 

 Stickstoffs durch erdbodenbewohnende Algen (Ber. der D. Bot. Ges., vii., 1889, 

 pp. 34-42). 



4 Schloesing, fils, and E. Laurent, Recherches sur la fixation de Vazote libre 

 par les plantes (Ann. de VInstitut Pasteur, vi., 1892, p. 65-115). 



5 Proc. Roy. Soc., 1920, B. 91, 201. 



6 P. Kossowitsch, Untersuchungen iiber die Frage, ob die Algen freien 

 Stickstoff fixtren (Bot. Zeit., 1894, Heft 5, pp. 98-116). 



7 H. Nakano, Untersuchungen iiber die Entwicklungs- und Ernahrungs- 

 physiologie einiger Chlorophyceen (Jour, of Coll. of Science, Imperial Univ., 



Tokyo, vol. xl., 1917, Art. 2, p. 66, etc.). 



