344 FIXATION OF FREE NITROGEN BY BACTERIA. 



The formation of nodules in these two families was subsequently 

 investigated by D. MORCK (I.), with the result that the faculty 

 was discovered in each one of sixty-five species (from thirty-eight 

 genera) examined. These discoveries were supplemented by H. 

 LECOMTE (I.), who, in 1894, proved that nodules are formed in 

 Arachis hypogcea, the earth-nut, a fact already noted by Poiteau 

 in 1852, but afterwards denied by Ericksson. The nodule bacteria 

 of the Soja bean (Sqja liispida) have been described by 0. KIRCH- 

 NER (II.). On the other hand, neither Morck nor FR. NOBBE (I.) 

 was able to discover the presence of root-nodules on Gleditschia ; 

 and it is found impossible to inoculate this plant by the nodule 

 bacteria of other Leguminosce. Apart from Leguminosce, the organs 

 in question are found (so far as is at present known) only on Alnus, 

 Elceagnus angustifolius, Hippophae, and Podocarpus, all of which 

 are able to thrive in soils destitute of nitrogen. The faculty of 

 nodule formation has also been ascribed to other plants. A. B. 

 FRANK (IV.) goes the farthest in this respect, and, indeed, assumes 

 that all plants are in a position to take up free nitrogen, an 

 opinion also recently expressed by J. STOKLASA (II.). LIEBSCHER 

 (I.) confines his opinion within narrower limits, but ascribes the 

 power of fixing free nitrogen to oats and mustard as well. The 

 statements of Frank and Liebscher have, however, been disproved 

 by the searching criticisms of, e.g. WILFARTH (I.), U. Kreusler, 

 P. Wagner, F. Nobbe, and L. HILTNER (I.) ; and J. H. AEBY (I.) 

 has shown that mustard does not possess the faculty with which 

 it is credited by Liebscher. The same results were obtained by 

 CH. E. COATES and W. R. DODSON (I.) in 1896, in their experi- 

 ments on the cultivation of the cotton plant (Gossypium}. 



194. The Nodule Bacteria. 



The discoveries reported in the foregoing paragraph, and for 

 which we have chiefly to thank Hellriegel and Wilfarth, lead up 

 to the question whether this proved absorption of free nitrogen is 

 effected in the root-nodule itself, or whether, by the influence of 

 this formation, the entire plant particularly the foliage becomes 

 capable of taking up this gas from the atmosphere and fixing it in 

 combination ? 



This latter opinion, which was chiefly supported by A. B. 

 Frank, has been investigated by P. KOSSOWITSCH (I.), who was, 

 however, unable to discern any absorption of atmospheric nitrogen 

 by the parts of the plants above ground. Attention must, there- 

 fore, be concentrated on the root-nodules themselves ; but before 

 going into the question whether and in what manner the nitrogen 

 is fixed by them, it will be necessary to become more closely 

 acquainted with the living organisms they contain, viz., the 

 nodule bacteria. 



The discovery of these bacteria by AVoronin in 1866 was not 



