220 Journal of Agricultural Research voi. xii. no. 4 



found that nitrates in the following amounts prevented nodule forma- 

 tions: potassium nitrate, i to 10,000, sodium nitrate i to 2,000, ammo- 

 nium nitrate i to 2,000, and calcium nitrate i to 2,000 and i to 10.000. 

 Hiltner's {24) experiments showed that 5 mgm. of nitrogen as potassium 

 nitrate per liter prevented nodule formation on peas. 



In contrast to these experiments Bassler (i) claimed that results 

 obtained from his work indicated that no effect was noticed by adding 

 nitrates to lupines growing in quartz sand. 



The question naturally arises whether this condition is due to the 

 weakening of the organism brought about by growth in a nitrated 

 environment and to a consequent impairment or entire loss of its infect- 

 ing power, or whether it is caused by some interreaction between the 

 salt and the plant root, tending to increase the latter's resistance to 

 the attack of this particular organism. 



INFLUENCE OP NITRATES ON THE INFECTING POWER OP BACILLUS RADICICOLA 



Some investigations have been carried out to determine what effect 

 nitrates have on the legume organisms themselves. Wilson {46) showed 

 that although nitrates inhibit the formation of nodules, the organisms 

 capable of producing nodules did not lose their vitality or nodule-pro- 

 ducing power when grown in the presence of nitrates. The results of 

 Prucha {41) are in accord with those of Wilson. He found that B. radi- 

 cicola does not seem to lose its infecting power when grown on media 

 containing nitrate. During the course of his work he found that potas- 

 sium and sodium nitrates inhibited the formation of nodules. Further 

 evidence that the organisms appear to retain their vitality in the pres- 

 ence of nitrates is produced by the results of Maze (jj, p. ly-i"/), who 

 showed that legume bacteria were able to fix a slight amount of nitrogen 

 when grown in a soil extract solution containing i per cent sodium nitrate. 

 Herke (22) states that potassium nitrate favors the growth of nodule 

 bacteria. 



However, other investigators state that nitrates have a harmful 

 effect on B. radicicola. Laurent (29, p. 134) found that legume organ- 

 isms failed to grow in a pea or lupine decoction containing nitrate in the 

 form of potassium and sodium salts in amounts equivalent to i to 500 

 and I to 1,000. Moore {35) in his experiments demonstrated that nitrates 

 at I to 10,000 were sufficient to prevent nodule formation. He states 

 that B. radicicola loses its power of infection when grown in a medium 

 containing nitrates. 



From the results cited it can be seen that there is some disagreement 

 as to the influence exerted by nitrates on B. radilcicola. In some cases 

 the organism seems to retain its vitality in the presence of nitrates, 

 while in others it appears to have become weakened. It must be ad- 



