[Vol. 6 



16 



ANNALS OF THE MISSOURI BOTANICAL GARDEN 



in the deeper layers is unsatisfactory, as would be expected 

 from the work of others. 



The effect of colloidal ferric oxide in Beijerinck 's 1 solution 

 was also studied. The nutrient solution contained 20 gms. 

 mannite and 0.2 gm. KH2PO4 per 1000 cc. of tap water. A 

 portion was titrated with phenolphthalein, and the calculated 

 amount of normal NaOH added to make the medium very 

 faintly alkaline to phenolphthalein. For the sake of determin- 

 ing the effect of tap water, a second medium was prepared in 

 exactly the same manner except that redistilled water was 

 used. One-hundred-cc. portions were pipetted into 700-cc. 



"Nonsol" Erlenmeyers, and then 1.0 mg. of colloidal Fe2(>3 

 in the form of the solution described above was added to each 

 flask. Since the concentration of salts is less in the Beijerinck 

 solution than it is in the Ashby, and since it lacks CaCOa 

 besides, it was reasonable to expect that the colloidal Fe20* 

 would remain in suspension better in it than in the Ashby. 

 While no difference could be detected in the unheated solu- 

 tions, after autoclaving the Beijerinck medium appeared to 

 be more colored than the Ashby, although partial precipitation 

 occurred in both. The data obtained after a two weeks' incuba- 

 tion at 28-32° C. are reported in table 11 below. For the sake of 

 comparison the data on Ashby 's solution containing 1.0 mg. 

 Fe203 per culture of 100 cc. are retabulated. 



TABLE II 



GROWTH IN PRESENCE OF 1.0 MG. OF COLLOIDAL FE,0, IN DIFFERENT 



NUTRIENT SOLUTIONS 



No. 



Medium 



Treatment 



Water 



N 

 found 

 (mgs.) 



N 

 fixed 



(mgs.) 



10 



Ashby 

 Ashby 

 Ashby 



Beijerinck 

 Beijerinck 

 Beijerinck 



Beijerinck 

 Beijerinck 

 Beijerinck 



Sterile 



Inoc. 



Inoc. 



Sterile 



Inoc. 



Inoc. 



Sterile 



Inoc. 



Inoc. 



Redistilled 

 Redistilled 

 Redistilled 



Redistilled 

 Redistilled 

 Redistilled 



Tap 

 Tap 

 Tap 



1.22 

 Lost 

 4.73 



1.05 

 3.35 

 2.88 



1.13 



Lost 

 7.70 





11 





12 

 19 



3.51 



20 

 21 



22 



2.30 

 1.83 



23 





24 



6.57 



1 In the original Beijerinck medium dipotassium phosphate is used, and, of 

 course, no neutralization to phenolphthalein is necessary. 



