1919] 



ALLEN — AZOTOBACTER CHROOCOCCUM 



33 



TABLE X 



• * 



AZOTOBACTER DEVELOPMENT IN F LTERED LOHNIS AND SMITH'S MEDIUM 



Shelf 



Shaker 



Treatment 



Check 

 Check 

 Inoc. 

 Inoc. 



Inoc 

 Inoc 



Same conditions except CaCOi added 





61 



Check 



Shelf 



62 

 63 



Check 

 Inoc. 





64 



Inoc. 





65 



Inoc. 



Shaker 









66 



Inoc. 



530. 

 516. 

 339. 



385. 



Lost but made 

 abundant growth 



328. 



.32 

 .30 

 .75 

 .90 



ft i 



.88 





Glucose 

 (mgs.) 



Nitrogen 



(mgs.) 





464. 

 452. 

 486. 

 251. 



.42 

 .34 

 .41 

 .34 





530. 

 524. 



.39 

 .37 



The clear filtered medium is very poor for the growth of 

 Azotobacter; indeed there is no evidence that growth took 

 place. When calcium carbonate is added growth is better. 

 The fact that growth takes place in this filtered medium, 

 whereas it failed in our firsi; experiment, is probably due to 

 all phosphates not being removed by the method of precipita- 

 tion in this experiment, wher sas they were in the first one. 



Glycerophosphate medium. — In order to prepare a medium 

 which would remain clear and from which the phosphates 

 would not be precipitated by heating in presence of CaCO.i, 

 an organic phosphate was used. Calcium glycerophosphate 

 seemed to be the most promising, since it is soluble in water 

 and does not form a precipitate with any of the salts used in 

 Ashby's solution. Twenty-iour hundredths gm. of this salt 

 carries essentially the same amount of phosphorus as does 

 .2 gm. K2HPO4 and a little more calcium than does .1 gm. 

 CaS04. 2H 2 0. Hence this amount of calcium glycerophos- 

 phate added to the medium {supplies as much phosphorus and 

 calcium to the culture medium as is contained in Ashby's solu- 

 tion. Since the molar weights of K2HPO4 and K2SO4 are 

 practically equal, .2 gm. of E^S04 will carry the same amount 



