CHEMICAL STIMULATION OF GROWTH OF ASPERGILLUS NIGER 343 
10 : 5 : 102.5 
10 : 5 : 108.75 
10 : 5 : 115.0 
10 : 5 : 121.25 
10:5 : 127.5 
0.787 g. 
0.794 g- 
0.863 g- 
0.829 g. 
0.887 g. 
0.685 ' 
0.819 
0.767 
0.854 
0.824 
0.736 
0.807 
0.815 
0.842 
0.856 
Fructification initiated in all cultures (except the accidental zinc) at about the same 
time — second day. Spores in all cultures brown, except that the membranes of all but 
the' two magnesium sulphate concentrations (77.5 and 83.75) of the W strain had a ring 
of jet black spores on the margins. 
16. The effect of increasing the concentration of the magnesium sulphate in the Pfeffer 
solution. 
Strai 
ti W, 3 
Strain Y, 3 
to :5 :2.5 
10 : 5 : 130 
10 : 5 : 2.5 
10 : 5 : 130 
* 0.908 g. 
0.899 g- 
0.327 g. 
0.756 g. 
0.127 
0.959 
0.362 
0.851 
0.078 
0.859 
0.341 
0.924 
0.081 
0.895 
0.206 
0.784 
0.133 
0.827 
0.268 
0.725 
0.105 
0.888 
0.301 
0.808 
Complete sporulation took place in the W strain in 2 J days; in the Y strain in 2 days. 
* Accidental zinc culture! 
Here again (experiments 7 to 16) we note only a decrease in growth 
resultant upon decreasing the concentration of one or more of any of the 
three components of the Pfeffer nutrient solution. As a result of their 
increase we obtain, however, an increased growth. In the case of NH4NO3 
and KH2PO3 the acceleration of growth is but a moderate one in spite of 
the fact that these compounds were added in so high amounts that the 
action of the impurities they doubtless contained might have been mani- 
fested. Only magnesium sulphate, it will be noted, gave results at all 
comparable to those with zinc, and then only in very high concentration. 
The high concentrations used renders it very probable that the action of the 
magnesium sulphate is to be attributed to the presence of zinc, etc., in 
traces. Since we have seen in previous experiments that the zinc optimum 
is approximately o.i mg, Zn/L, we can calculate that in a ten percent 
solution of magnesium sulphate zinc need only be present in 0.0001 percent 
impurity to be thus added in sufficient amount to cause maximum accelera- 
tion of growth. The results obtained with magnesium sulphate are dis- 
cussed more in detail later. The evidence is quite conclusive, however, 
that neither the ammonium nitrate, the potassium phosphate, nor the 
magnesium sulphate is present in greater than optimum or in toxic concen- 
tration. 
On inspection of the data (see table below) as to the ions whose presence 
results in an acceleration of the growth of A. niger, it is obvious that the 
