FIXATION OF ATMOSPHERIC NITROGEN 



105 



compounds found 

 in the soil, prefer- 

 ably sugars, higher 

 alcohols and organic 

 acids; (2) the sym- 

 biotic nitrogen-fix- 

 ing bacteria which 

 live upon the roots 

 of certain specific 

 plants, namely, the 

 Leguminosae, in 

 specialized bodies 

 called nodules, and 

 cause the fixation 

 of gaseous nitrogen, 

 which becomes 

 available to the 

 plants during their 

 growth. The nod- 

 ule-forming bac- 

 teria are also ca- 

 pable of leading an 

 independent exist- 

 ence in the soil, 

 their ability to fix 

 nitrogen under 

 these conditions 

 being still a matter 

 of dispute. It 

 seems likely, how- 

 ever, that while 

 developing inde- 

 pendently of the 

 plant these sym- 

 biotic bacteria fix 

 no appreciable 

 quantities of ni- 

 trogen. 



In addition to 

 these two groups of 



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