Jan. 2S, 1918 



Nitrogen- A ssimilating Bacteria 



223 



Tabl,E XXX. — Influence of nitrates on alfalfa roots and nodule formation 



a Fungus contamination. 



t> Plant died after few days' growth. 



It will be seen that in a few instances where a high concentration of 

 nitrates occurred the development of the seedlings subsequent to ger- 

 mination ceased. This condition may have been due to too high a con- 

 centration of soluble salts or to inferior seed. However, losses were not 

 sufficiently serious materially to affect the outcome of the experiment. 



In all cases the seedlings grown in agar without nitrate produced 

 nodules when inoculated with B. radicicola. A few nodules appeared on 

 seedlings in cultures containing the loAvest concentration of all three 

 nitrates. The number of nodules in these cases was less than in the 

 control cultures. No nodules whatever developed in any concentration 

 above lo mgm. of nitrate in loo c. c. of medium. Under normal condi- 

 tions in test-tube cultures the nodules make their appearance at about 

 18 to 20 days after inoculation. The incubation of all cultures was 

 extended 40 days after inoculation in order to make certain that no 

 further nodule development would take place. 



The nonproduction of nodules was not due to the failure of the inoc- 

 ulum. In all cases an excellent inoculum growth was obtained, espe- 

 cially in the case where nitrate was present in the medium. Indeed, it 

 was so luxuriant that in many cases the organism grew in considerable 

 quantity far down into the root zone. In many cases where nitrates 

 were present the same pink coloration was produced that was discussed 

 under another caption, on page 216. 



As has been already stated, seedlings of varying ages were inoculated 

 for the reason that it was thought that a more or less prolonged contact 

 of the roots with the nitrate in the medium might serve as an index to 

 27807°— 18 6 



