60 MASSACHUSETTS HORTICULTURAL SOCIETY. 



capable of producing nodules and fixing nitrogen, unless the 

 conditions were exactly right this function might be entirely 

 lost. 



Experiments soon, proved that this loss of power was the result 

 of growing upon a rich nitrogenous medium. It was as though 

 the bacteria soon discovered that it was easier to get nitrogen 

 out of the substance upon which they were growing than it was 

 to fix it from the air, for it requires a tremendous enei'gy to com- 

 bine free nitrogen. Consequently, they simply degenerated and 

 became lazy, just as a number of other organisms do under the 

 same circumstances, and so long as they were allowed to grow 

 under such luxurious conditions they refused to perform the bene- 

 ficial function for which nature intended them. As soon as this 

 fact was thoroughly demonstrated an attempt was made to find 

 some medium which would sustain the life of the bacteria and 

 yet not enable them to degenerate and lose their beneficial power. 

 By transferring the bacteria to a medium made up of chemically 

 pure salts which contained no nitrogen and solidifying with silica 

 jelly, it was possible to obtain colonies which had never had ac- 

 cess to nitrogen in a fixed form. These colonies could then be 

 transferred to nutrient solutions devoid of nitrogen, and in this 

 way the beneficial function of combining nitrogen from the air 

 was so augmented that chemical tests pi'oved these organisms to 

 be from seven to ten times as eflicient as when they were origi- 

 nally isolated from the nodule. 



Of course large numbers of the original bacteria were not able 

 to stand this sudden transition from a comparatively rich nitro- 

 genous medium to one absolutely devoid of this element, but a 

 few million bacteria more or less makes practically no difference. 

 If one organism persisted it was a matter of a very short time 

 when this could l)e multiplied to any desired quantity. Thus by 

 a process of selection it was possible to obtain a culture which so 

 far as the direct fixation of nitrogen was concerned certainly was 

 very much more efiicient than the ordinary wild, nodule-forming 

 organisms. 



There is one other important element, however, which must be 

 maintained or increased if these organisms are to ])roduce the 

 best results, and that is their ability to j)enetrate the root hairs, 



