1916] 
DUGGAR AND DAVIS—NITROGEN FIXATION 419 
tions. He reports a fixation of 5.1-6.5 mg. per liter, .51-.61 
per 100 ec. of culture solution, which, however, he regards as 
satisfactory positive evidence. 
No investigator has obtained figures comparable to those 
of Latham (709). This work was well conceived and ar- 
ranged with a view to determining the effect of zinc sulphate 
on the nitrogen fixation of Sterigmatocystis migra (Asper- 
gillus niger) abundantly supplied with combined nitrogen.! 
The results published exhibit a variation ranging from a 
nitrogen loss of 42.5 mg. to a fixation of 205.1 mg. per culture, 
on 90 ce. of medium. In view of all the earlier and later 
studies made on fixation by this fungus, granting at the same 
time, of course, possible differences in strains, it can only be 
surmised, perhaps, that miscalculations are accountable for 
these unusual results. It would appear that in making the 
analyses she employed aliquot parts of the culture solution, 
and likewise divided the felt. Such a procedure, however, 
only suggests possibilities and cannot explain the results. In 
the case of maximum fixation, 677.3 mg. of nitrogen are re- 
ported fixed in felt and solution per gram of dry felt pro- 
duced. This is an amount incomparably greater than any- 
thing elsewhere obtained. 
Duggar and Knudson (711) reported only by abstract upon 
extensive series of experiments in which Aspergillus niger, 
Trichoderma lignorum (erroneously given as T. lignicola), 
and several species of Basidiomycetes were employed. Var- 
ious nutrient media were used, including synthetic nutrient 
solutions, leaf decoctions, and decayed leaves ground to a 
fine powder. None of the cultures showed a difference in the 
N-content over the controls sufficient to indicate fixation, 
whether with or without combined nitrogen. It may be stated 
that this work was not published in detail by reason of the 
uniformly negative results. It was intended to pursue the 
work further using ground leaf mould and similar materials 
as nutrient media, but difficulties in obtaining uniform samples 
The nutrient salt solution employed was the well-known Richards’ solution 
patton ^ ХН,ХОз 1 gm., КНоРО, 0.5 gm., MgSO, 0.25 gm., FeCls trace, 
and sugar 5 gm., except that the amount of the nitrate in the different series 
varied from 115.4 to 160.3 mg. per culture, or 50 cc. of solution. 
