68 NITROGEN-FIXATION IN LEGUMINOS^ 



flourish in the nodular swellings on the roots of certain leguminous 

 plants. 



The great question as to the possibility or otherwise of utilising the 

 free nitrogen of the air has excited much attention and an enormous 

 amount of research has been devoted to its solution. That leguminous 

 crops apparently increased rather than diminished the amount of 

 nitrogen in the upper part of the soil, although they contained large 

 quantities themselves, had been observed, and use had been made of 

 the fact in agriculture. No satisfactory explanation as to how this was 

 effected was forthcoming until, in 1886, Hellriegel published an account 

 of the bacteria which he found in the root nodules possessed by clover 

 and other leguminous plants. In later papers, in conjunction with 

 Wilfarth, 1 he clearly showed that, living in these nodules were bacteria 

 (Bacillus radicocola), which have the power of bringing about the as- 

 similation by the parent plant of the free nitrogen of the air. From 

 other investigations by the same chemists, and also by Nobbe and 

 Hiltner, Schloesing and Laurent, and others, it has been proved that 

 the various leguminosa have different bacteria, and that assimilation 

 of free nitrogen by a plant depends upon the presence in the soil of 

 the particular micro-organism capable of growing in symbiosis' 2 with 

 it. The importance of this discovery attracted considerable attention, 

 and pure cultures of the nodule bacteria were put on the market for 

 application to soils which might be deficient in them. These prepara- 

 tions were known as nitragin and were not so successful in actual 

 practice as had been hoped. They are, I believe, no longer com- 

 mercially obtainable. This culture of Bacillus radicocola fell into 

 disuse, but in 1903, Hiltner and Stormer 3 claimed to have remedied 

 the defects in Nobbe and Hiltner's earlier preparation by supplying 

 nourishment for the bacteria in the form of grape sugar and peptones 

 (also milk) in the liquid to be used for cultivating the bacteria prior to 

 the inoculation of the seed. 



Moore of the U.S.A. Department of Agriculture, in 1904, also pre- 

 pared these micro-organisms for distribution, and a sensational " boom " 

 was given to the new cultures in popular magazines. He claimed 

 that Nobbe's failure arose from the bacteria being cultivated in media 

 too rich in nitrogen. The new preparation was sent out in the form 

 of cotton wool, impregnated with the organisms and dried. Before use 

 they were to be incubated for twenty-four hours in a solution contain- 

 ing cane sugar, magnesium sulphate and potassium phosphate, then 

 for a further twenty-four hours with the addition of ammonium phos- 

 phate. The liquid was then used for moistening the seed and thus 

 inoculating it. Separate cultures for various leguminous crops were 

 prepared and largely distributed. 



But the results of extended trials under the direction of the Board 

 of Agriculture in Great Britain and in Canada under the Canadian 



1 See Abstracts in Jour. Chem. Soc., 1888, 742 ; 1889, 640. 



2 By this term is meant the living together of two organisms for their mutual 

 welfare, as distinguished from parasitism, in which one organism preys upon an- 

 other to its own advantage, but to the injury of the host. 



3 Berichte v. Inter. Kongress for Angewanclte Chemie, Berlin, 1903, 3, 799. 



