FIXATION OF ATMOSPHERIC NITROGEN 353 



free culture media, dried on cotton and distributed to farmers with a 

 small package of salts from which a culture solution was to be made 

 by the farmer and applied to the seed. This method gave poor results, 

 chiefly because the bacteria could not withstand the drying on cotton. 

 Afterward the cultures were sent in a liquid condition with somewhat 

 more satisfactory results. The dry cotton cultures were exploited 

 for a time by a commercial firm under the name of Nitro-culture, and 

 somewhat similar cultures were placed on the market in England under 

 the name of Nitro-bacferine. Cultures of both kinds, however, were 

 shown to be valueless, both by microbiological and by planting tests. 



Cultures on Agar. — Very satisfactory results were secured from the 

 use of pure cultures at the Ontario Agricultural College, Guelph, where 

 Harrison and Barlow, in 1905, originated the method of growing the 

 bacteria on a nitrogen-poor agar medium. By this method, the farmer 

 has simply to apply the bacteria to the seed just before sowing. These 

 cultures, used on all the common legumes, sown in all kinds of soil, 

 gave favorable results in 65 per cent of cases in trials extending over a 

 period of ten years. Similar agar cultures are now prepared by com- 

 mercial firms who have adopted the method of Harrison and Barlow, 

 and also by some of the U. S. Agricultural Experiment Stations. 



Importance of Inoculation. — Inoculation with pure cultures affords 

 ' the farmer a rapid, easy, and cheap method of supplying the bacteria 

 essential for getting a successful stand of any legumes. Failure to secure 

 a benefit from this method of inoculation may usually be attributed to 

 unsuitable soil conditions rather than any inherent failing in the cul- 

 tures used. No method of inoculation will compepsate for poor 

 physical or chemical condition of the soil itself. The principle of using 

 artificial cultures to be applied with the seed is sound, and if the cul- 

 tures contain large numbers of virile bacteria, there is little reason 

 why they should not prove of benefit when used under soil conditions 

 that would seem to need inoculation. 



Azotobacter Cultures. — Some experimental work has been done in 

 the use of cultures of Azotobacter for soil inoculation. The results are 

 contradictory, and more work needs to be done to prove the value 

 of such cultures. 



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