BACTERIA AS FERTILIZERS. * 61 



for at present, at least, it does not seem that these bacteria are 

 able to obtain sufficient energy outside of the plant to fix nitro- 

 gen in any perceptil)le quantity. It is jn'obable that they need 

 large amounts of carbohydrates to enable them to carry on their 

 important function, and these, of course, are readily obtained from 

 the roots of tlie plant. Consequently if they are not able to enter 

 the plant they are of little or no benefit to the soil. The pene- 

 trative function of these bacteria is generally restricted to a very 

 small motile form which is seldom found within the root nodule 

 after it has developed to any size. 



Growing nodule-forming organisms upon nitrogenous jelly or 

 agar tend to fix the large rod-shaped form which cannot pene- 

 trate the root hairs. In fact it is almost impossible after these 

 bacteria have been grown under what would seem to be the most 

 favorable conditions for a considerable length of time, to cause 

 them to break up into the small root-hair penetrating form. On 

 the other hand, bacteria cultivated upon nitrogen-free media, 

 particularly when kept in liquids, readily break u}) into this small 

 form and thus are able to produce large numbers of nodules filled 

 with bacteria which are at what may be considered their highest 

 state of efficiency. 



In order to test the results of these selected methods several 

 acres of different legumes were planted upon the experiment farm 

 near Washington, part of which was inoculated with bacteria 

 grown upon rich nitrogenous media, and jjart with organisms 

 taken from the same silica jelly agar and thereafter kept growing 

 in solutions absolutely devoid of any fixed nitrogen. The results 

 were very striking indeed. In the case of soy beans some thou- 

 sands of plants grown in rows and inoculated with bacteria cul- 

 tivated after the method of ]S"obbe upon decoctions of soy l)eans 

 with peptone added failed to show a single nodule ; whereas 

 other plants in rows within four feet of these and inoculated with 

 bacteria taken from the same nodule, but grown upon niti-ogen- 

 free media, showed an average of from ten to twenty-five nodules 

 per plant. Of course the contrast above ground was equally 

 striking. 



It will be impossible for me to read you the great number of 

 favorable reports we have had from practical farmers throughout 



