1889.] Tubercles on the Roots of Leguminous Plants. 437 



recorded ; the number of living leaves and of dead ones ; the height of 

 the stem ; number of bads, flowers, and fruits, open and set ; and the 

 number of seeds ripened. 



The tubercles were developed on all but one of the plants, except 

 those in the completely sterilised media. However, I do not propose 

 to go further into these matters at present, simply contenting myself 

 with pointing out that all the evidence at present goes to show that 

 the Leguminous plant gains nitrogen by absorbing the nitrogen >us 

 substance of the bacteroids from the tubercles ; that nitrogenous sub- 

 stances are thus brought by the " bacteroids " ("gemmules") of the 

 infecting organism of the plant ; and that, finally, no satisfactory 

 explanation seems forthcoming as to how the organism obtains this 

 nitrogen in certain cases where no compounds of nitrogen have been 

 added. At any rate, if we regard the pot of sand and its pea as one 

 system, there is in some cases a distinct gain of nitrogen in the crop, 

 and in the sand at its roots. 



Since the publication of my paper in 1887, several observers have 

 attacked the subject from various points of view. The most import- 

 ant papers are those of Vuillemin,* Beyerinck,t and Prazmowski,^ 

 who deal with the histology and biology of the subject ; and those of 

 Hellriegel and Wilfarth, and of Lawes and Gilbert, § who have con- 

 cerned themselves especially with the nitrogen question ; papers on 

 accessory matters by Frank, Yan Tieghem, and a few others have 

 also appeared in the interval. I propose to deal at present only with 

 Prazmowski's papers, since there are several points in them that have 

 special reference to my work on this subject. 



In the 'Botanisches Centralblatt ' for 1888, || appeared a paper by 

 Prazmowski, on the " Root-tubercles of the Leguminosae." After 

 shortly summarising the literature, and the various views promul- 

 gated by different investigators as to the nature of the swellings, the 

 author proceeds to give an account of his own researches. He gives 

 me the credit of having taken a new departure ; speaking critically 

 of the want of experimental proofs for their speculative views on the 

 part of previous observers, he says, " Eine ruhmliche Ausnahme bildei 

 in dieser Beziehung Marshall Ward, welcher zuerst in den Weg des 

 physiologischen Experimentes betreten hat " (p. 217), though he does not 

 regard my methods as complete. 



* "Les Tubercules Radicaux des Legumineuses," ' Annales de la Science Agro- 

 noniique francaise et etrangere,' vol. 1, 1888. 

 f « Botanische Zeitung,' 1888, No. 46, p. 725. 



X ' Botanisches Centralblatt,' 1888, No. 46, pp. 215—285 ; and 1889, No. 33, 

 p. 356. 



§ < Phil. Trans.,' vol. 180, 1889, B, pp. 1—107. 



|| No. 46, pp. 215—285. The paper is an abstract of an address to .the Polish 

 Naturalists' Congress, July, 1888. 



