AMERICAN 
JOURNAL OF BOTANY 
Vol. VI 
November, 191 9 
No. 9 
A STUDY OF SOME FACTORS IN THE CHEMICAL STIMULA-Qf C ii 
TION OF THE GROWTH OF ASPERGILLUS NIGER \ , 
The results obtained in these attempts to effect a still further increase 
in the yield by the addition of free acid during growth as compared to its 
addition before inoculation are not conclusive. While experiments 28 and 
29 would lead one to suspect that the optimum hydrogen-ion concentration 
for growth varies during the growth of the organism, experiments 30 and 
31 do not seem to bear out this assumption. On the other hand, it must 
be admitted that the procedure followed in experiments 30 and 31 is not 
wholly comparable to that in experiments 28 and 29 with respect to the 
degree of the variations in acidity, imposed as they are in one instead of 
several days. I believe, therefore, that the results of experiments 28 and 
29 should be given greater weight than those of experiments 30 and 31. 
The contention of Nikitinsky (48) that A. niger ehminates a "stimula- 
tive" substance into the nutrient solution whose action is frequently 
inhibited by excessive increase in acidity of the cultures seems to me un- 
proven. A glance at experiment 2 (of Nikitinsky) shows that the acidified 
cultures produce a greater yield (first harvest). Reference, moreover, to 
experiments 6, 7, 8, 9, and 11 indicates that in the majority of cases (see, 
however, Penicillium griseum grown on NH4NO3, experiments 7 and 11) 
when the acid formed in the first culture has been neutralized, the resulting 
yield in the second culture does not exceed that in the first. On the other 
hand, the yields for the second cultures, without neutralization of the acid 
formed by the first, show as a rule an acceleration of growth. The growth 
accelerations usually obtained through addition of excess CaCOs, while 
without doubt in some cases due to a reduction in excessive acidity (experi- 
ment 23, culture 3) are in the majority of cases due to other causes, since 
previous observers (Wehmer, 68; Butkewitsch, 8) agree that a decrease in 
growth always occurs. 
We may turn now to some results obtained by the use of a method of 
purification of the culture medium. The marked increase in yield following 
the addition of increased amounts of magnesium sulphate suggested the 
question whether the apparent action of the magnesium sulphate is due to 
Robert Aaron Steinberg 
{Concluded from the October Journal) 
[The Journal for October (8: 311-356) was issued Nov. 20, 1919.] 
357 
