Jan. 28, i9i8 Nitrogen- Assimilating Bacteria 217 



This culture was plated three times, each plating being made from a well- 

 isolated colony. The final subculture was taken from a similar well- 

 isolated colony. However, pigment formation in the presence of nitrate 

 persisted in the two final experiments, showing clearly that some reaction 

 took place between the nitrate and the organism grown on the medium. 

 It is of interest to note that the pigment formation in the presence of 

 nitrate was observed in later work where the influence of nitrates on 

 nodule formation was investigated. Prucha (41) found that on agar 

 slopes of medium containing 0.5 per cent of potassium or calcium 

 nitrate, the growth of B. radicicola became opaque and that an iridescent 

 tint was produced. 



Although the results of these experiments may vary somewhat among 

 themselves, taken as a whole it appears evident that B. radicicola may 

 fix a small amount of atmospheric nitrogen when grown without the 

 host plant and on a suitable medium. The addition of various amounts 

 of nitrates as indicated increased somewhat the amount of nitrogen 

 assimilated by B. radicicola. 



INFIvUENCE OP NITRATES ON THE PRODUCTION OP GUM BY BACILLUS RADICICOLA 



Since nitrates, especially in smaller amounts, cause an increase in the 

 number of B. radicicola in pure culture, it was thought advisable to 

 determine what influence these salts have on the production of gum. In 

 culture media favorable to the growth of B. radicicola these bacteria will 

 produce a gelatinous substance which is readily precipitated with 95 per 

 cent alcohol or acetone. Upon the addition of either of these precipi- 

 tants a fairly heavy, water-white, frothy gelatinous mass is formed 

 which soon rises to the surface of the liquid. Upon standing, this mass 

 contracts somewhat, and portions of it may fall to the bottom of the 

 liquid from which it has been precipitated. 



Chemical analyses, according to Buchanan (jo), have shown that this 

 gum is a carbohydrate. Upon hydrolysis with 2 per cent sulphuric acid 

 and 15 pounds' pressure for one hour, Fehling's solution is reduced, 

 showing the presence of a sugar. The gum does not give proteid reac- 

 tions with the Millon, biuret, or xanthoproteic tests. Hence, the gum 

 is not protein in character; nor does it contain nitrogen in the combined 

 form. Clearly it is a nonnitrogenous body. 



In the experiment undertaken to determine whether nitrates influence 

 the fonnation of gum only relative dififerences are noted. No attempt 

 was made to obtain quantitative results. 



Erlenmeyer flasks of i -liter capacity containing 200 c. c. of mannit 

 solution were used. The cultures contained various quantities of nitrate 

 as indicated in Table XXVIII. Triplicate flasks for each amount of 

 nitrate were prepared. In this table these three flasks are represented 

 as "a," "b," and "c." After sterilization at 15 pounds' pressure for 25 

 minutes the flasks were cooled and inoculated with 5 c. c. of a suspension 



