248 Plant Physiology 



as controls. Place the pots in the greenhouse upon fresh cinders, 

 separating the two lots and protecting the pots as well as practi- 

 cable from contamination by dust or soil from other pots or beds. 

 Water with distilled water only. After the plants have grown 

 sufficiently, compare the two lots, as indicated, for nodule for- 

 mation and amount of growth. 



REFERENCES 



ATKINSON, G. F. Contribution to the Biology of the Organism 

 causing Leguminous Tubercles. Bot. Gaz. 18: 157-166; 

 226-237 ; 257-266, 1893, 4 pis. 



ATWATER, W. O. On the Acquisition of Atmospheric Nitrogen 

 by Plants. Amer. Chem. Jr. 6 : 365-388, 1885. 



BEYERINCK, M. W. Die Bakterien der Papilionaceen-Knoll- 

 chen. Bot. Zeit. 46:723-735; 741-750; 757-771; 

 781-790; 797-804, 1 pi, 1888. 



HARRISON, F. C., and BARLOW, B. The Nodule Organism of the 

 Leguminosse. Its Isolation, Cultivation, Identification, and 

 Commercial Application. Cent. f. Bakt. II Abt. 19 : 

 264-272 ; 426-441, 9 pis., 1907. 



HELLRIEGEL, H., and WILFARTH, H. Untersuchungen iiber die 

 Stickstoffnahrung der Gramineen und Leguminosen. Zeit. 

 des Vereins fur Riibenzucker Industrie. Beilageheft, 234 pp., 

 1888. [Abs. in Biedermann's Central. 18 : 179-185, 1889.] 



KING, F. H., and WHITSON, A. R. Development and Distribu- 

 tion of Nitrates in Cultivated Soils. Wisconsin Agl. Exp. 

 Sta. Bui. 93 : 39 pp., 6 figs., 1902. 



LIPMAN, J. G. Report of the Soil Chemist and Bacteriologist. 

 N. J. Agl. Exp. Station Report for (1907) : 139-204 pp., 

 3 pis., 1908. 



Lurz, L. Les Microorganismes, Fixateurs d'azote Disserta- 

 tion. (1904) : 187 pp., 19 figs., 1904. 



PEIRCE, J. G. The Root-tubercles of Bur Clover and of Some 

 Other Leguminous Plants. Proc. of the California Acad. 

 of Sciences. (3d Ser.) 2 : 295-328, 1 pi, 1902. 



PRAZMOWSKI, ADAM. Die Wurzelknollchen der Erbse. Landw. 



