16 BOTANICAL GAZETTE [JANUARY 
case the solution without the solid permits a growth rate above that 
seen in the control, this increase is sometimes still further augmented 
by the presence of sand. The results with copper sulfate show a 
number of instances illustrating these different phases of action. — 
It is a well established fact of general physiology that many 
compounds which at certain concentrations act as harmful agents and 
depress activity become in more dilute solutions accelerators of 
activity. If dilution be carried on there arrives a point at which all 
effect ceases, and only the effect of the solvent appears. This has 
been pointed out by Couprn (8) for certain salts. We may represent 
ey ace ae 
7 = 
es Be 
Check growth rate eee —— ee e 
bse ec ioe aa ip ys. Si AGM le sam ce at a > —_— 
2 oa ' 
= = I | 
é ae 
z * " i 
e wee i! 1 
oh TEES ae [1 \ 
fatal depressant neutral accelerant neutral 
Dilution = 
Fic. tr. 
the different physiological phases resulting from the progressive 
dilution of a fatal concentration by a series of terms something like 
the following. Almost instant death (a) is followed by a lengthening 
period of survival (6) with depressed activity when compared with — 
the control in water. This depressant phase is followed by a short 
phase in which the growth rate approximates the control (c). This 
passes over into the more extended acceleration phase (¢d) marked 
age 
pee ete ens : 
by activity beyond that seen in the control. This acceleration rises 2 
to a maximum and with further dilution falls off, until the solution 
becomes practically distilled water in its action on the organism 
(e). This may be represented diagrammatically as above (jig- 1); * 
growth for the twenty-four hours in this case being indicated on the 
_ axis of ordinates, progressive dilution (that is, the degree of dilution) _ 
on the axis of abscissas progressing to the right, the growth of controls . 
in distilled water being regarded as unaffected by other extern 
conditions, and the roots used assumed to be i in the same phase 
