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



varying amounts of sodium and calcium nitrates. The numbers of 

 nodules produced on the alfalfa plants by organisms grown on media 

 containing nitrate do not vary widely from those on the plants inocu- 

 lated v»^ith organisms grown on media containing no nitrate. Not only 

 did the organisms fail to lose their nodule-producing power, but from 

 all appearances their infecting power did not seem to be materially 

 weakened. 



It therefore seems apparent that an explanation for the failure of 

 nodules to develop on leguminous plants in the presence of nitrates is 

 not found in the theory that the organisms producing these nodules are 

 weakened when grown in the presence of nitrates. 



INPLUBNCB OP NITRATES ON ALFALFA ROOTS AND NODULE FORMATION 



The next step taken would naturally be in the direction of a study of 

 the influence of the nitrates on the plant roots themselves in order to 

 determine whether or not they thus are made more resistant to the 

 attack of these organisms. 



A review of the literature shows that almost nothing has been done 

 touching this phase of the question. Wilson {46), studying the effect of 

 certain salts on nodule production, states that possibly the salt has some 

 effect on the root, making it resistant to the attack of the organism. 

 Maze (55, p. 15-17), who also concluded that nitrates did not cause B. 

 radicicola to lose its infecting power, says that nodules do not develop 

 on roots of legumes when nitrates are present because the carbohydrate 

 in the roots is changed into protein material by the absorption of the 

 nitrate. 



Alfalfa seedlings (Medicago sativa) growing in soft agar containing 

 potassium, sodium, and calcium nitrates, as indicated in Table XXX, 

 were used in this study. Quadruplicate tubes were prepared for each 

 amount of nitrate. The higher concentrations of the nitrate were not 

 used, since it was found that germination and subsequent growth were 

 considerably impaired in the presence of such large amounts. The tubes 

 with the mannit agar and nitrate were sterilized at 1 5 pounds' pressure 

 for 30 minutes. These were cooled and sterilized alfalfa seeds planted 

 as given under "Methods used in experiments." The tubes were 

 then placed in the greenhouse under cheesecloth covering and the seeds 

 allowed to germinate. Germination took place in all instances, although 

 it was retarded somewhat by the presence of the nitrate. At the end of 

 five days the first tube of each set was inoculated with three drops of a 

 suspension of JB. radicicola in sterile distilled water. Subsequent inocu- 

 lations were made as indicated in Table XXX. These were made at 

 different intervals in order to allow the roots of the seedlings to remain 

 for a longer time in contact with the media. It was hoped that in this 

 way an idea might be obtained as to the time when the root first became 

 resistant. The results are given in Table XXX. 



