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Some Effects of Nitrogen-fixing Bacteria on the Growth of Non- 

 Leguminous Plants. 

 By W. B. Bottomley, M.A., Professor of Botany in King's College, London. 



(Communicated by Prof. J. Eeynolds Green, F.R.S. Eeceived April 20, — Read 



May 6, 1909.) 



During the course of an investigation on " The Cross-inoculation of the 

 nodule-forming bacteria from Leguminous and non-Leguminous plants,"* it 

 was noticed that in all the bacterial cultures prepared from the algal zone of 

 the root-tubercles of eycads taken from below the surface of the soil, 

 Pseudomonas radicicola was associated with a species of Azotdbacter. 



In order to determine to what extent, if any, this association gave an 

 increased power of assimilating free nitrogen, the two forms were obtained as 

 pure cultures by successive platings on a medium composed of maltose 

 20 grammes, monobasic potassium phosphate 0*5 gramme, sodium chloride 

 0'5 gramme, calcium carbonate 0'5 gramme, ferrous sulphate 0"1 gramme, 

 agar 15 grammes, and distilled water 1000 c.c. Separate cultures of each 

 and a mixed culture were then grown in fluid media in duplicate 500 c.c. 

 Erlenmeyer flasks containing 250 c.c. of the above medium, omitting the 

 agar but adding 10 grammes of mannite. Control flasks were kept side by 

 side with the inoculated flasks. 



All the flasks were incubated at 24° C. for 15 days, care being taken to 

 renew the air in the flasks at intervals, then a nitrogen determination was 

 made of the contents of each flask. The results of these analyses gave the 

 following averages : — 



Control - 48 milligramme N per 100 c.c. 



Pseudomonas alone - 91 „ „ „ 



Pseudomonas + Azotobacter .. . 1'24 „ „ „ 



Hence Pseudomonas and Azotobacter together make a powerful combination 

 for the fixation of free nitrogen. 



The bacteria in the root-tubercles of cycads appear to live imbedded in the 

 slime they produce outside the cortical cells in the open spaces of the so-called 

 algal zone. The cortical cells which project into this zone presumably absorb 

 the nitrogenous products of the bacterial activity, and thus the cycad is 

 benefited. If, therefore, this combination of bacteria outside the cortical 

 cells is a direct benefit to the cycas plant, the possibility presented itself that 



* Eeport British Association, 1907. 



