280 MICROBIOLOGY OF SOIL. 



SOIL INOCULATION.* 



By soil inoculation is now understood the adoption of some artificial 

 method for supplying suitable quantities of nitrogen-fixing organisms to 

 soils deficient in these types. The first attempts at soil inoculation were 

 made in 1886 by Hellriegel and Wilfarth during the course of their 

 studies on the cause of nitrogen accumulation by legumes. They 

 found that when leguminous plants were grown in sterile sand, nodules 



FIG. 71. (See Figs. 70 and 72.) 



were formed on the roots only after the addition of a small portion of 

 aqueous extract of fertile soil, or an extract of crushed nodules, or in 

 some cases (lupines and seradella) by soil itself from a field on which 

 these crops had been grown. The first successful artificial production 

 of nodules by the aid of pure cultures was made in 1889 by Prazmowski 

 in the course of studies on the method of entrance of the organism to the 

 root hairs of the host plant. 



^Prepared by S. F. Edwards. 



