[40] Fischer, Hugo, “Über Symbiose von Azotobacter mit Oscillarien,” Centr. f. Bakt., 1904, xii. [41] Frank, B., “Uber den experimentellen Nachweis der Assimilation freien Stickstoffs durch Erdbewohnende Algen,” Ber. der D. Bot. Gesellsch., 1889, vol. vii., pp. 34-42. [42] Frank, B., “Ueber den gegenwärtigen Stand unserer Kenntnisse der Assimilation elementaren Stickstoffs durch die Pflanze,” Ber. der. D. Bot. Ges., 1889, vii., 234-47. [43] Frank, B., and Otto, R., “Untersuchungen über Stickstoff Assimilation in der Pflanze,” Ber. der D. Bot. Ges., 1890, viii., 331-342. [44] Gautier and Drouin, “Recherches sur la fixation de l’azote par le sol et les végétaux,” Compt. Rend., 1888, cvi., pp. 1174-76; General Conclusions, p. 1232. [45] Kossowitsch, P., “Untersuchungen über die Frage, ob die Algen freien Stickstoff fixiren,” Bot. Zeit., 1894, Heft 5, S. 98-116. [46] Krüger, W., und Schneidewind, “Sind niedere chlorophyllgrüne Algen imstande, den freien Stickstoff der Atmosphäre zu assimilieren und Boden an Stickstoff zu bereichern?” Landwirtschaftliche Jahrb., 1900, Bd. 29, S. 771-804. [47] Moore, Benjamin, and T. Arthur Webster, “Studies of the photosynthesis in f.w.a.” (I.) “The fixation of both C and N from atmosphere to form organic tissue by green plant cell”; (II.) “Nutrition and growth produced by high gaseous dilutions of simple organic compounds, such as formaldehyde and methylic alcohol”; (III.) “Nutrition and growth by means of high dilution of CO₂ and oxides of N without access to atmosphere,” Proc. Roy. Soc., London, 1920, B. xci., pp. 201-15. [47_a_] Moore, B., Whiteley, Webster, T. A., Proc. Roy. Soc., London, B., 1921; xcii., pp. 51-60. [48] Reinke, J., “Symbiose von Volvox und Azotobacter,” Ber. der d. Bot. Ges., 1903, Bd. xxi., S. 481. [49] Russell, E. J., and Richards, E. H., “The washing out of Nitrates by Drainage Water from Uncropped and Unmanured Land,” Journ. Agric. Sci., 1920, vol. x., Part I. [50] Schloesing, fils, and Laurent, E., “Recherches sur la fixation de l’azote libre par les plantes,” Ann. de l’Institut Pasteur, 1892, vi., pp. 65-115. [51] Schramm, J. R., “The Relation of Certain Grass Green Algæ to Elementary Nitrogen,” Ann. Mo. Bot. Gard., 1914, i., No. 2. [52] Wann, F. B., “The Fixation of Nitrogen by Green Plants,” Amer. Journ. Bot., 1921, viii., pp. 1-29. CHAPTER VII. THE OCCURRENCE OF FUNGI IN THE SOIL. NOTE.--I am indebted to my late colleague Miss Sibyl S. Jewson, M.Sc., for permission to include unpublished data from our investigations on the soil fungi.