368 ANNUAL REPORT OP THE Off. Doc. 



fusion, which was capable of infecting the roots and causing the 

 formation of tubercles; and that by heat this organism could be de- 

 stroyed. 



The experiment also showed that the renewal of vigor of the plant 

 in a nitrogen free soil was corelated with the infection of the roots 

 and the formation of tubercles; in other words, tubercle formation 

 and nitrogen assimilation by the plant were interdependent. 



From this point the question of tubercle formation passed from 

 one of mere botanical interest to one of great agricultural import- 

 ance. 



Ward^'^ went even further, and besides showing that tubercles could 

 be produced at will by the inoculation of roots with soil infusions, 

 succeeded in tracing the development of the fungus filaments into 

 the root hairs, and thence into the cortex of the root, where he noted 

 the development of the tubercles at these points of infection. 



In 1888,^^ Beyerinck, succeeded in cultivating the root tubercle or- 

 ganism on artificial media, and described a number of races from dif- 

 ferent plants, which he considers varieties of one species of bacteria 

 and which he names Bacilhis radicicola. 



In 1890, Prazmowski,'^^ by cultivating the organism of the root 

 tubercles of beans ,succeeded in inoculating their roots with pure 

 cultures of the latter by watering sterilized soils in which the plants 

 were grown, with liquid cultures of the organism. 



In 1891, Laurent,^^ by growing legumens in water culture, succeed- 

 ed in inoculating their roots and producing tubercles at the points of 

 inoculation by puncturing them with a needle whose point was con- 

 taminated with root tubercle germs. And a little later, Atkinson^^ 

 succeeded, by growing vetch in water culture, in inoculating their 

 roots and producing tubercles from pure cultures of the organism. 



There is thus no doubt but that tubercles on the roots of legumi- 

 nous plants are produced by infection from without, and by an 

 organism entering the root from the soil. 



The organism as it exists in the soil is probably in the form of 

 bacteria-like bodies, and most soils contain them in greater or less 

 abundance. Their method of infecting the root is best described 

 and figured by Atkinson.^^ 



The bacterial body has the power to penetrate a root hair and is 

 first seen therein as a filament, extending its entire length, as shown 

 in Fig. 7 BC, and thence entering the cells of the cortex of the 

 root, causes their proliferation and the production of a swelling upon 

 the side of the root. Fig. 7 A, which by further growth becomes a 

 tubercle. Within the central cells of this tubercle the filaments can 

 be seen branching in all directions as seen in Fig, 8 A. 



At numerous points are seen irregular swellings, F'g. 8A-B, 



