1§ BOTANICAL GAZETTE [JANUARY 
still in the depressant phase. A solution = 
Soo Permits a growth 
rate of ro™™, still less than the control vente a Pte of ro%™". The 
depressant phase of dilution is still represented, but is nevertheless 
but little below the neutral point. 
The addition of an adsorbing body therefore should carry it 
into the accelerant phase. This is the result seen, and the growth 
of 16™™ compared with the check seems to represent a rate probably 
near the maximum. By making a series of experiments under condi- 
tions like those met in this experiment, in which a graded series of 
solutions of mercuric chlorid alone is used, we should be in possession 
of a calibrated standard by.means of which we could estimate more 
or less accurately the amount of the toxic molecules adsorbed. Similar 
methods of interpretation applied to the results with silver nitrate indi- 
cate with varying degrees of clearness a similar situation. 
The results obtained with copper sulfate illustrate many of the 
different phases of action. In some cases the presence of the solid 
served not only to clearly decrease the harmful action of the salt, 
but even to make survival possible in concentrations otherwise 
promptly fatal. 
In this connection a series of experiments was made to ascertain 
approximately in how far the quantity of solid substance present — 
might influence the action of a toxic concentration of a salt. For 
this purpose a series of six cultures was prepared with like quantities 
of copper sulfate. To five of them prepared sand was added in 
different quantities. The growth rates seen in Table III, August 
ro (p. 7), have been plotted in the following diagram (fig. 2)- 
The growth rate in millimeters is indicated as before on the axis 
of ordinates. The progressive addition of solids is shown on the 
axis of abscissas. Although, unfortunately, no control culture was 
made in this case, we may fairly accept 12™™ as average growth 
in distilled water on the date concerned. This value is plotted as 
the control result. The copper sulfate solution furnishing a basis 
for this experiment is concentrated enough to kill the roots eas 
usually permitting little growth. The addition of 40%™ of 
adsorbs a sufficient amount of copper sulfate to permit half the 
peas | 
amount of growth expected of the control culture, and in addition 
to make sgnsarege the survival of the test objects. Nevertheless, 2 
atior oe 
