ASSIMILATION OF FREE NITROGEN 399 



found within the living cells of the roots of a leguminous plant. As a matter 

 of fact no power of fixing nitrogen has been detected in pure cultures of the 

 isolated bacteria until quite recently, and that only under special con- 

 ditions 1 . The root-tubercles may be present in great abundance Nobbe 2 

 counted 4,572 upon a pea-plant as also are the bacteria present in them, 

 so that no such marked fixative power as is possessed by C. Pasteurianum 

 is necessary to produce the maximal gain of nitrogen observed in a legu- 

 minous plant. 



The fixation of nitrogen apparently only occurs in the actual root-tubercles 

 where the bacteria are present 3 , and Kossowitsch's 4 researches point to a localized 

 fixation of nitrogen. The formation and behaviour of the root-tubercles, as well 

 as the growth of the plant under normal and abnormal conditions, are in entire 

 agreement with this conclusion 5 . The absorption of the bacteria as they die 

 affords no evidence to support Frank's conclusion that they are cultivated by the 

 plant merely in order to be devoured n . 



No final decision can as yet be made, and it is not impossible that leguminous 

 plants obtain the power of assimilating nitrogen by interaction with the symbiotic 

 bacteria, although no evidence has been brought forward in support of this view. 

 Frank's dictum that the presence of the bacteria operates as an accelerating 

 stimulus is based upon the incorrect assumption that all Phanerogams have a 

 certain power of assimilating free nitrogen. Various other conclusions have been 

 put forward upon insufficient grounds, and it is too often forgotten that the appear- 

 ance or storage of nitrogenous compounds at a given point does not afford any 

 direct indication as to the place of their production 7 . Active proteid-synthesis 

 may proceed in the green leaves of a leguminous plant, while the root-tubercles 

 may send supplies of amides or simpler nitrogenous compounds to them. 



It has yet to be determined how the nitrogen is assimilated and what is the 

 first product of the assimilatory process, and it is possible that in this respect also 

 specific differences may exist between different bacteria. Nobbe and Hiltner 8 

 suppose that this property resides exclusively in the bacteroids of the root-tubercles, 

 but they do not bring forward any satisfactory proof of this statement. The 



1 Beyerinck, Bot. Zeitung, 1888, p. 798; Prazmowski, 1891, I.e., p. 55; Laurent, Ann. d. 

 1'Inst. Pasteur, 1891, T. V, p. 136; Frank, I.e., 1892, p. 44; Berthelot, Ann. d. chim. et d. phys., 

 1893, vi. sen, T. xxx, p. 425 ; Stutzer, Centralbl. f. Bact, 1896, Abth. ii, Bd. ir, p. 669. Maze has 

 recently obtained positive results under special cultural conditions (Ann. d. 1'Inst. Pasteur, 1897, 

 T. xr, p. 44). 



2 Nobbe, Versuchsst, 1891, Bd. xxxix, p. 335. Cf. also Frank, 1. c., 1890, p. 9 ; Kionka, Biol. 

 Centralbl., 1891, Bd. xi, p. 283. 



3 Frank at first supposed (1. c., 1890, pp. 26, 73) that the bacteria were distributed throughout 

 the entire plant. Zinsser (Jahrb. f. wiss. Bot., 1897, Bd. xxx, p. 423) has, however, shown that this 

 is not the case. 



* Bot. Zeitung, 1892, p. 697. 



5 Cf. Prazmowski, 1. c., 1891, p. 51 ; Frank, Ber. d. Bot. Ges., 1892, p. 271, and Lehrb. d. Bot. 



c Frank, Ber. d. Bot. Ges., 1891, p. 248. Cf. Sect. 65. 



7 Cf. Frank und Otto, Ber. d. Bot. Ges., 1889, p. 331 ; Frank, Bot. Zeitung, 1893, p. 154. 



3 Versnchsst., 1893, Bd. XLir, p. 439. 



