1916] 
DUGGAR AND DAVIS—NITROGEN FIXATION 433 
selected strains of Azotobacter were tested, and all yielded 
positive results of satisfactory magnitude, as shown in table 1. 
It will be observed in table 1 that slight discrepancies seem 
to occur between different series in respect to the amounts 
of nitrogen recovered—where the different series contained 
presumably the same amounts of initial nitrogen. This, how- 
ever, is only an apparent discrepancy, since, as previously 
TABLE II 
RECOVERY OF NITROGEN AS KNO# ADDED TO SUGAR BEET CULTURE MEDIUM 
Controls 13.8 mg. N : 
Trials (no N added) added as KNO; N d oo 
mg. mg. 8. в: 
1 14.532 28.227 13.695 —.105 
2 14.49 28.048 13.350 —.250 
* 13.8 mg. nitrogen as KNO, added to 50 cc. sugar beet decoction + 10 per cent 
cane sugar. 
mentioned, this work extended over a considerable period of 
time, and although the same lot of culture solutions was used 
for the control flasks and for the flasks in which the organisms 
were grown in any one series, it was nevertheless necessary 
to make up new solutions from time to time for the different 
series. The different series are therefore only approximately 
comparable. 
Now since N-fixation occurs in organisms otherwise so 
physiologically different as Azotobacter, Clostridium, and 
Bacillus radicicola, why may it not occur in all fungi and bac- 
teria, it has been asked time and again. Final answer can be 
given only in accordance with the results of properly planned 
and carefully executed experiments. Moreover, it has been 
shown abundantly that fixation is relatively uncommon among 
bacteria, the capacity being possessed largely by those groups 
mentioned above. As has been indicated, among others, Saida, 
Ternetz, and Stahel have reported fixation for Aspergillus 
niger. Inthe cases referred to the results are scarcely greater 
than might occur as experimental errors. This could not 
apply, however, to the results with Phoma radicis and appar- 
ently not to those with Phoma Betae. Confirmatory evidence 
