1907] JENSEN—TOXIC LIMITS AND STIMULATION 2 
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IRON NITRATE 
It was found impracticable to grow plants in the nutrient solution 
with which the experimentation was begun on account of precipitation 
of one or more of the salts by such reagents as AgNO,, Pb(NQ,),, 
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Fic. 22.—Iron nitrate series in soil. Sept. 15-21. 1905. 
etc. Hence it was decided to grow them in distilled water, with no 
other element present than the poison. In order to test whether 
results obtained by both methods were comparable, two series, one 
Fic. 23.—Iron nitrate series in soil. Sept. 15-27. 1995. 
in water, the other in nutrient media, to each of which the poison 
had been added in the same proportions, were set up side by side. 
The experimentation 
With Fe,(NO,). proved 
that water grows the 
plants as well as does the 
nutrient solution during 
the time of the experi- pratt <a S 
ment. The curve of Fic. 24.—Iron nitrate series in solution. Sept. 
15-21. 1905. 
maximum growth is as 
great and comes at the same concentration with both. The killing 
Concentrations also coincide. 
The greatest growth ia solution cultures is at 2/2500 to 1/7500, 
while in soil cultures it occurs at 7/1000 to 31/1000. Hence there 
