62 BOTANICAL GAZETTE [JANUARY 
determined as lying between 2/2750 and /3250.7. Then a series of 
varying concentrations of this acid on either side of the toxic limit 
was carried out, placing clear sand, quartz flour, filter paper, and 
paraffin shavings in the solutions. In no case was the apparent death 
limit modified by the presence of these substances. The death limit 
was also determined for a solution of sulfuric acid saturated with 
calcium sulfate, and for the same solution with an excess of calcium 
sulfate, but the solid again had no apparent effect. 
With copper sulfate solutions carbon black was found to decrease 
the toxic effect, just as the authors above cited found to be true for 
the solids with which they worked. In order to bring out the effect 
of the carbon black, copper sulfate in the proportions of one and five 
parts per million of copper was added to the nutrient solution above 
described; a portion of the solution thus prepared was shaken with 
carbon black and then filtered, and wheat seedlings were grown in 
the treated and untreated solution. This series constitutes Experi- 
ment VI. Twenty-four plants composed a culture and the experiment 
lasted twelve days. The results are given in Table III. 
‘TABLE: Tf. 
DATA FOR EXPERIMENT VI. 
Culture no. Medium — eff eign 2 aoe 
Be vp te wee Nutrient solution........... 220-2 
PEGs Lees Do.+1 p. an vas Tenaya ee 67. 
Lege seen Decks pms Cu. Si... 41 
per emner sey eater As 2, a pdt Siig TE 140.2 
sl i a ce toate As 3, but carbon-treated. . T7875 
The growth of the plants was proportional to their transpiration. 
It is evident that the carbon removed sufficient copper to render 
carbon-treated solutions much less toxic than the untreated ones. 
This is a direct corroboration of the work of TRUE and OGLEVEE, 
but with another solid, and in this experiment the filtering out of the 
solid removes any possibility of its having any effect directly upon 
the roots. The explanation of these authors seems to be correct, 
as far as copper sulfate is concerned. The failure in the present 
7 This or aeromine had been made previously, but was repeated for the present 
work. See Cameron, F. K., and BRreazEAate, J. F., Toxic action of acids and salts 
on seedlings. wee aie aia: 8:1-13. 1904. 
i 
