366 ANNUAL REPORT OF THE Off. Doc. 



thermore regarded as the infecting parts, which forced their way into 

 the younger roots and, by their irituting presence, set up a multiplica- 

 tion or proliferation of cells which resulted in the building up of an 

 excrescence or tubercle. 



It VA'as upon the structure of the filaments, and upon how the bac- 

 teroid bodies originated from them, that they differed, and upon this 

 point it is surprising that there should havebeen such a wide diver- 

 sity of view. These two views class themselves under two heads, 

 which, for the sake of convenience, we shall term the endogenous and 

 the exogenous theories. The former was held by Prazmowski, Frank 

 and Maria Dawson, and the latter by Laurent, Ward and Atkinson. 



According to Prazmowski,^^ the leader of the endogenous theory, 

 the infecting agent in the production of the root tubercles is present 

 in the soil as a definite bacterium, which, after Beyerinck, he calls 

 Bacterium radicola. 



Certain of these force their way into the smaller roots and for a 

 time multiply therein; but soon the juices of the plant exert an un- 

 favorable influence upon them, and to protect themselves against its 

 injurious action they excrete a gelatinous substance in which they 

 remain embedded, and in which they continue to multiply. With 

 this multiplication the gelatinous envelope is drawn out into long 

 strands or filaments, containing the rod-shaped bodies or bacteria. 

 As long as these remain protected by their gelatinous envelope they 

 continue to multiply and retain the rod-shaped form. 



As the filaments approach the central portion of the tubercle they 

 Bwell out into rounded vessicles. Later on by the enlargement of 

 these latter the enveloping membrane becomes so thin that it bursts 

 and the enclosed bacteria are set free. From this time they cease to 

 multiply, and by degeneration assume a variety of irregular branched 

 forms, first observed by Woronin, and called by him bacteroids. 

 Prazmowski, therefore, recognized (1) that the filaments were elon- 

 gated pouches of gelatinous matter, the secretion of the bacteria, 

 and in which the infecting bacteria w^ere embedded; (2) that these 

 bacteria multiplied as straight rods within the filaments, or en- 

 dogenously; (3) that by the escape of the bacteria they underwent 

 various degenerations by which they assumed the irregular forms of 

 bacteroids. 



One essential point in Prazmowski's position was that the bac- 

 teroids were degenerated forms. 



Frank™ in his later observation, held to the position of Prazmow- 

 ski, but differed in regarding the gelatinous envelopes as a product of 

 the cell rather than of the bacteria. 



Maria Dawson^° in 1899, also held to the view of Prazmowski. By 

 proper staining she found the filaments to consist of strands of 



