258 SCIENCE PROGRESS. 



in the soil is revealing to us possible sources of nitrogen- 

 fixation undreamt of hitherto, another and really quite 

 different set of researches has culminated in the recognition 

 of the fixation of that element standing on a still firmer ex- 

 perimental basis. No doubt many of the ancient observers 

 knew of the nodules, or fleshy lumps, on the roots of legu- 

 minous plants. In any case Malpighi knew of them more 

 than 200 years ago, and Linneus described them on 

 Lathyrus. Perhaps the first serious investigation of them 

 was by Lachmann in 1856 (19), and all kinds of opinions 

 were expressed as to their significance, but without under- 

 standing them. In 1866 Woronin (20) discovered that 

 their tissues were filled with bacterium-like organisms, and 

 between that date and 1887, the prevailing opinion was that 

 some living organism of the nature of a myxomycete, a 

 fungus, or a bacterium, makes the tissues of the roots its 

 home. 



In 1887 I (21) showed that a perfectly definite living 

 organism invades the tissues from the soil, and proved con- 

 clusively that this is so because I showed it passing down 

 the root-hairs of beans growing in water-cultures, 1 and 

 explained the relations of the minute bacterium-like 

 organisms which fill the cells of the tissues to the filamen- 

 tous infecting tube which penetrates the root-hair. 



This organism lives symbiotically in the tissues of the 

 root-tubercles, and the truth gradually became clear that 

 not only are these nodules, with their living invaders, not 

 injurious to the leguminous plant, but the latter thrives far 

 better if they are abundant and well developed, than if they 

 are few or absent. 



It would require a long article to do justice to the large 

 amount of detailed work by various observers between 

 1870 and 1890, on the structural details of these tubercles, 

 but the principal names concerned in addition to those 

 given are Frank, Brunchorst, Tschirch, Beyerinck, Praz- 

 mowski, Viullemin and Prillieux (22), and controversy 



1 I mention this especially because there has been a tendency of late 

 to attribute this discovery of the infecting tube passing down the root-hair 

 to later observers. 



