820 PRINCIPLES OF SOIL MICROBIOLOGY 



the part of a field seeded to barley. The nitrogen content of inoculated 

 plants was found to be much higher than that of uninoculated plants, 

 Nobbe and Richter 6 reporting 4.29 per cent of nitrogen for the first as 

 against 1.85 per cent for the second. These results were soon confirmed 

 by a number of workers in Europe and in America, as shown later. 



In 1896 Nobbe 7 suggested the use of pure cultures of B. radicicola 

 for the inoculation of leguminous plants. A product placed on the 

 market consisted at first of B. radicicola grown on gelatin. However, 

 gelatin was found to be an unsuitable medium for the growth of this 

 organism. It was then replaced by a liquid medium, namely a 2 per 

 cent peptone solution or skimmed milk, 8 and later by agar media. In 

 1902 the use of cotton cultures was introduced. 9 Cotton was placed in 

 a liquid culture of bacteria, then dried and placed in packages. This 

 was accompanied by two packages of nutrient substances, the first con- 

 taining sugar, K 2 HP0 4 and MgS0 4 , and the second ammonium phos- 

 phate. Before using, the cotton was placed in boiled water and the 

 contents of the first package were added. After 24 hours at 20°, the 

 contents of the second package were added and the culture allowed to 

 incubate ; this culture was then used for moistening the seed or for in- 

 oculation of a small amount of soil which was then spread over the field. 

 Usually mixtures of the various legume bacteria were employed. The re- 

 sult proved to be unsatisfactory, due to the fact that the bacteria could 

 not withstand the process of drying on cotton. 10 



Various other preparations, consisting of liquid, semiliquid or solid 

 cultures were soon introduced. However, the early beneficial results 



6 Nobbe, F., and Richter, L. tlber den Einfluss des im Kulturboden vorhand- 

 enen assimilierbaren Stickstoffs und die Aktion der Knollchenbakterien. Landw. 

 Vers. Sta., 59: 167-174. 1903. 



7 Nobbe, F. Einige neue Beobachtungen, betreffend die Bodenimpfung mit 

 rein kultivierten Knollchenbakterien fur die Leguminosenkultur. Bot. Centrbl., 

 68: 171-173. 1896. 



8 Hiltner, L., and Stormer, K. Arb. K. Gesundsamt. Biol. Abt. 3. 1903, 

 151. 



9 Moore, G. T. Bacteria and the nitrogen problem. U. S. Dept. Agr. Year- 

 book 1902-1903, 333-342; Soil inoculation for legumes; with reports upon success- 

 ful use of artificial cultures by practical farmers. U. S. Dept. Agr., Bur. PI. 

 Ind. Bui. 71. 1905. 



10 Simon, J. Die Wiederstandsf;'ihigkeit der Wurzelbakterien der Legumino- 

 sen und ihre Bedeutung fur die Bodenimpfung. Jahresb. ver. angew. Bot. 

 1907. 



