4 STEINBERG: GROWTH OF ASPERGILLUS NIGER 
The next experiment (Exp. IT) gave the following results. 
ING ANGE eae Peale Ga Vote es ESS 0.317 gram 0.480 gram 
WOT es A a ee ae 4 O.565. 0.781 
On the assumption that both strains could, even in the presence 
of the optimum concentration of zinc, produce not more than one 
gram of tissue, it is evident that a higher concentration of zinc 
would be necessary in the case of the W than of the Y strain in 
order to obtain the maximum yield. 
The determination of the minimum concentrations of zinc 
required for the maximum production of tissue was made in quite 
a simple manner. An experiment was first performed in which 
zinc in widely different concentrations was used and the values 
desired thus located approximately as being between two of these 
concentrations. The next experiment was with concentrations be- 
tween these limiting values and differing amongst themselves by 
amounts of 0.01 mg. Zn/L. 
The first experiment which served for the approximate loca- 
tion of the zinc optima is here summarized (Exp. III). 
oe 
0.0 mg. oT Gi cick ei crue ere oae ae a 0.217 gram 0.302 — 
O00T 50 ae Ae eee ee ais oT: 0.620 
0.05 a ici eke Arent: ON Ma a eney o7ag. = O47; 4° 
O.1 ee OA eae a ate a Gace kaa Geeta ray dy dees 0.805 “ 
I.0 Re ee PN car ONs a ce i arss COIS. o.798° .** 
These values are shown plotted in TExT FIG. 1. The minimum . 
_ concentration of zinc capable of bringing about maximum growth 
is, we note, approximately 0.1 mg. Zn/L for the W strain and about 
0.05 mg. Zn/L for the Y strain. We observe, in addition, that 
the maximum yield of the former is slightly the greater. 
The more accurate location of the values sought was attempted 
in a series of cultures differing in zinc content by 0.01 mg. Zn/L 
(Exp. IV). 



WwW y: 
0.0 mg. Zn/L | 0.119 gram 0.0 mg. Zn/L | 0.343 gram 
0.07 = | 0.805 °"* ho 08 ze | 0.344" 
0.08 i. 0.900 ‘* bo O03 re 0.803 
0,09 he | 0.940 “ i 0.04 ct | 806 “* 
0.10 - 0.825 “* ' 9.05 be 0.847 * 





