6 STEINBERG: GROWTH OF ASPERGILLUS NIGER 
On comparing the results obtained in this experiment with 
those of the preceding, we become aware of a curious phenom- 
enon—the action of suboptimal zinc concentrations on the growth 
has become less effective. Whereas in Exp. II the addition of 



















































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9 ag 
gf acanane FETE 
a is be =—=n mn 
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u See 
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2 18 20 ae 24 26 









































6 8 lO 12 14 16 
MILLIGRAMS ZINC PER LITER 
Fic. 2. For explanation see text. 
0.01 mg. Zn/L to the cultures resulted in yields of 0.565 gram and 
0.781 gram for the W and Y strains respectively, in Exps. VIII 
and IX the corresponding yields were only 0.287 gram and 0.283 
gram. Even with apparently zinc-free cultures the same change 
had taken place. In the earlier experiment just mentioned the 
yields in the apparent absence of zinc were 0.317 gram and 0.480 
gram for the W and Y strains respectively; while now they are 
0.136 gram and 0.205 gram. It would seem that for suboptimal 
zinc concentrations (or more precisely, concentrations below 0.1 
mg. Zn/L), the initial differences between the W and Y strains 
with respect to the extent of growth have largely disappeared. 
The validity of this assumption will, however, again be discussed. 
Finally, after culturing for thirty-one weeks on the peptone- 
sucrose agar, the tenth generation transfers of the two strains re- 
sulted in the following yields when inoculated into the flasks con- 
taining as usual each 50 c.c. of Pfeffer solution (Exp. XVIII). 
WwW ¥ 
OO ME MN. cu... ee enreg ay 0.177 gram ° 0.222 gram 
Tee tebe aie ie Gedy apa OO Coat aba eg O87. 5 0.440 “ 
0.02 Beg leley Cee enan gre ig 0:38). > O.501r .-** 
0.03 Me cue eee dee Cay s 7 0.563: °° 
0.04 ee eS a eo oa om ee 0.343" " 0.642 >=" 
O06 oe ee oe 9.534." 0.707“ 
