18 FORAGE PLANTS AND THEIR CULTURE 



but preferably with a drill or on a cloudy day. Sunlight 

 is destructive to the bacteria, so the inoculating soil 

 should be harrowed in unless sown with a drill. 



The use of the naturally inoculated soil is open to the 

 objection that it may serve to spread weeds, insects and 

 plant diseases, especially if brought from a distance. 



In some cases, the nodule bacteria are undoubtedly 

 carried on. the surface of the seeds, especially where these 

 are trampled out by animals. Thus plots of guar (Ct/a- 

 mopsis tetragonoloba) , an East Indian legume, were well 

 inoculated when grown for the first time at Chillicothe, 

 Texas, although no closely related legume occurs in North 

 America. In this case it seems practically certain that 

 the bacteria were carried on the seeds. 



Inoculation of the soil for a new legume is sometimes 

 secured by sowing a little of the seed in mixtures, as alfalfa 

 with grass. Frequently some of the plants survive, and 

 when this happens generally to scattered plants through- 

 out a field, it is safe to conclude that the soil is sufficiently 

 well inoculated. 



14. Artificial inoculation. The first artificial cultures 

 of Pseudomonas radicicola were made by Beyerinck in 

 1888. In 1896 Nobbe introduced commercial cultures 

 under the name of nitragin. Commercial cultures have 

 been prepared in various forms; namely, in liquids, upon 

 agar jelly, in dry powders and on cotton. Moore in 1904 

 prepared cultures grown on media poor in nitrogen under 

 the idea that this would select the strains most efficient 

 in fixing free nitrogen, and that these cultures would, 

 therefore, prove beneficial even on soils already inoculated 

 for any particular legume by providing a superior strain. 

 Attempts have also been made to prepare cultures adapted 

 to each soil by growing the bacteria in media prepared 



