156 SOILS. 



the misleading misnomer should be banished from agricultural 

 publications and lectures, at the very least. 



Other Nitrogen-Absorbing Bacteria. An increase in the 

 nitrogen-content of some soils, aside from the action of legu- 

 minous root-bacteria, has long been observed. As already 

 stated, this increase was at first ascribed to certain green algae 

 often seen to develop on the soil surface; but it has now been 

 shown that the nitrogen-gathering function belongs to at 

 least two bacteria, one of which (Clostridium pastorianum} 

 was discovered by Winograclski, the other (Azotobacter 

 chroococcum) by Beyerinck, and has since been farther in- 

 vestigated by Koch, Krober, Gerlach and Vogel, and last by 

 Lipman and Hugo Fischer. According to the latter it seems 

 likely that Azotobacter chroococcum lives in symbiosis with 

 the green algae, all of which, like the Azotobacter itself, de- 

 velop with special luxuriance on calcareous soils. 



Lipman (Rep. Agr. Exp't Station, New Jersey, 1903 and 1904) 

 describes as Azotobacter vinelandii a form somewhat different from the 

 A. chroococcus, the nitrogen-assimilating power of which he tested 

 quite elaborately. He exposed to air pure cultures of A. vinelandii in 

 nutritive solution containing the proper mineral ingredients, and glucose 

 20 grams per liter. 100 cub. centimeters of this solution was exposed 

 in flasks of respectively 250, 500 and 1000 cc. content, therefore having 

 greater surface in the larger flasks. After ten days, the amounts of 

 nitrogen fixed were found to be respectively 1.67, 3.19 and 7.90 milli- 

 grams. When mannite solution was employed instead of glucose, a 

 similar fixation was observed ; and it was also shown that the presence 

 of combined nitrogen in the forms of nitrates or ammonium salts dis- 

 couraged the fixation by the bacillus. 



It was thus clearly proved that A. rinclandii at least does not need 

 symbiosis with algae to fix atmospheric nitrogen ; but experiments with 

 mixed cultures of the above bacillus and another (designated as No, 30 

 by Lipman) proved that when these two co-operate the absorption of 

 atmospheric nitrogen is nearly doubled. As it is probable that this is 

 the case also with other soil bacteria, the importance of this source of 

 nitrogen to plants is obvious ; provided of course that the proper nu- 

 tritive ingredients are present in available form. Lipman shows that 

 among the organic nutrients, besides the sugars, glycerine and the salts 

 of propionic and lactic acids, and probably also others of the same 

 groups, can serve as nourishment to the nitrogen-fixing bacteria. 



