Jan. 28, 1918 Nitrogen- Assimilating Bacteria 219 



found. Had the influence of nitrates on the growth and reproduction 

 of B. radicicola been determined in liquid culture, as well as in soil 

 cultures, then a comparison could have been made. Furthermore, the 

 divergencies in the time element, eight weeks' incubation in the liquid 

 cultures and three weeks in the soil cultures, are such as to render futile 

 any attempt at correlation. It may be that the large formation of gum 

 was due to the prolonged incubation. A shorter period of three weeks 

 undoubtedly would show a relatively smaller amount of gum produced 

 as a result of the presence of the nitrate. 



However, from the results of the experiment it is certain that potas- 

 sium, sodium, and -calcium nitrate influence the formation of gum by B. 

 radicicola. The three nitrates studied caused a large increase in the 

 amount of gum obtained by precipitation with acetone. Calcium nitrate 

 caused the least stimulation, but the difference was not large. 



INFLUENCE OF NITRATES ON NODULE FORMATION 



The results of numerous investigations have shown that nitrates 

 retard and oftentimes entirely prevent the formation of nodules on 

 leguminous plants when grown in soil or liquid cultures. Vines (45), 

 working with the horse bean, found that the use of large amounts of 

 nitrate in the form of potassium nitrate retarded nodule formation. He 

 concluded that a decrease in the amount of nitrates meant an increase 

 in the number of nodules. Woods (48) found that leguminous plants 

 assimilated more nitrogen when they were grown in the absence of 

 potassium and calcium nitrate than when thus supplied. His results 

 seem to indicate that nodule development was retarded somewhat by 

 these salts. Similar results were obtained by Frank (16). Nobbe and 

 Richter (37) in 1 902 grew soybeans in a rich garden soil and found upon 

 inoculation that a gain of 74.7 per cent of nitrogen occurred. However, 

 upon the addition of nitrates this gain was considerably reduced, the extent 

 of the reduction corresponding to the amount of nitrate added. About 

 this same time, Wohltmann and Bergen6 (47) using many different 

 types of soils, found that nodules were not formed on the roots of peas 

 when ammonium nitrate was added. Creydt (12) found that sodium 

 nitrate retarded nodule formation on yellow lupines when these legumes 

 were grown in soil. Fred and Graul (j^") found that very small amounts 

 of nitrates did not appreciably decrease nodule formation, but that 

 larger amounts proved detrimental and finally prohibited entirely the 

 development of nodules. 



The presence of nitrates in culture solutions has also been found to 

 reduce and oftentimes to inhibit the formation of nodules on leguminous 

 plants. Marchal (31) concluded that alkaline nitrates in concentrations 

 of I to 10,000 in liquid cultures prevented the formation of nodules on 

 peas. Flamand (13) grew vetch and beans in a nutrient solution and 



