80 



MISCELLAI^EOUS PAPERS. 



Garden peas in a garden soil naturallj^ inoculated showed the follow 

 ing difference where a heav}^ inoculation was made: 



Efect of heavy inoculation of garden peas on a naturally inoculated garden soil. 



Treatment. 



Number 

 of plants 

 grown. 



Number of 



plants with 



nodules. 



Average 



number of 



nodules. 



Untreated 



15 

 18 



15 

 18 



fii 



Heavj^ inoculation 



19 







It is highly probable that the cause of the formation of more numer- 

 ous nodules in some cases is due not to the great numbers of bacteria 

 which are introduced into the soil but to the quantity of culture medium 

 introduced, which renders the soil solution a materially richer food for 

 the active growth of the nodule organisms. Thus, if a few bacteria 

 are brought into a favorable soil they will multiply rapidl^^, and it is 

 of no particular moment in such a case whether a very few or a large 

 number of bacteria are originally introduced. If, however, enough 

 culture is added so that the soil solution is appreciably improved in 

 food material for both plant and bacteria, then growth will be much 

 more active and nodule formation will be greater. On this h3^pothesis 

 the two results are not at all at variance, the effects produced depend- 

 ing on the soil conditions encountered by the bacteria and the crop. 



The suggestion in a former bulletin « that the slight varietal charac- 

 teristics exhibited by legume bacteria can be readil}^ broken down by 

 cultivation on synthetic nitrogen-poor media seems to hold only for 

 bacteria isolated from plants physiologically related to the subsequent 

 hosts. ^ 



At^^pical experiment is given below: 



Number of nodules produced on tivo varieties of mung bean {Phaseolus viridissimus and 

 P. calcaratus) by cultures from various hosts. 



[Ten plants in each of seven series.] 



A^ariety of mung bean. 



Bacteria 

 from cow- 

 pea. 



Bacteria 



from soy 



bean. 



Bacteria 

 from P. 

 viridissi- 

 mus. 



Without 

 bacteria. 



Phaseolus viridissim^us 



*1 

 





 



77 

 88 

















* Fifteen plants in this series. 



It may be added that the soil used was unsterilized garden soil, 

 naturally inoculated for our common bean, Phaseolus vulgaris, so that 

 the uninoculated check may be said to serve as a cross-inoculation with 

 these organisms also. This theory of varietal differences of nodule^ 



« Bui. 71, Bureau of Plant Industry, 1905, pp^ 25-27. 

 & See Schneider, 111. Agr. Exp. Sta. Bui. 29, 1894, p. 301. 



