No. 4.] GERMAN EXPERIMENT STATIONS. 31)3 



inoculated with a soil extract, obtained 1)}^ shaking some of 

 the soil on which leguminous crops had previously grown, 

 with water. The leguminous crops, after they had con- 

 sumed all the seed nitrogen, began to turn yellow, but very 

 soon recovered themselves, turned green, arew most luxuri- 

 antlv, and reached a full maturity. The grains, after havinor 

 exhausted the seed nitrogen, died in every case. It was 

 observed, however, that, when the soil extract was first heated 

 to 70° C , before being apjilied, it had no effect. It was fur- 

 ther noticed that an extract made from soil taken from land 

 on which leofumes had not been grown for a lomj; while 

 was quite often without any eft'ect. The following analysis, 

 as an example, shows one of the results obtained : — 



When the legumes were manured with nitrogen, Hellrlegel 

 found that they were perfectly al)le to appropriate the nitro- 

 gen applied, and while root nodules were noticed, they 

 were by no means so abundantly developed as when nitro- 

 gen was not applied. 



Professor Hellriegel therefore concluded that the leijumi- 

 nous plants were capable of drawing their nitrogen supply 

 from the air, while, on the other hand, the grains and non- 

 leguminous crops generally had not this power. Further, 

 that the leo:unies were enabled to do this because of the 

 development of the so-called root tubercles, and that certain 

 micro-organisms of the soil were in some way the cause of 

 the tul)ercle development. Hellriegel's results were after- 

 wards confirmed by many other investigators, es|)ecially by 

 Prazmowski,* who, in very carefully conducted experi- 

 ments, where every precaution was used, proved beyond a 



* Die Wurzelknollchen der Erbse (Landw. Versuchsstation, Bd. XXXVII, 1890, 

 p. 161, and Bd. XXXVIII, 1890, p. 1). 



