Metals and Plants. 
455 
the injury done the plant was of a different nature from ordi¬ 
nary poisoning, and he proposed for the new phenomena the 
name of “Oligodynamic effects”. His idea seemed to be, that 
from metallic copper minutest particles pass into solution, and 
that these particles kill the plants by a different action from 
that of toxic copper salts — perhaps by physical rather than 
chemical means. 1 The phenomena of death of Spirogyra by 
oligodynamic action are, as should be expected, different from 
those when death is caused by much more concentrated copper, 
introduced as a salt. 
The facts in .Niigeli’s paper are final. But his theoretical ex¬ 
planation appears to us improbable and unnecessary, and this 
paper is a partial explanation of our disbelief. 
Every metal in contact with water and air is subject to some 
change. It reacts with the oxygen and carbonic acid dissolved 
in the water, or with the water itself, to form oxides, hydrox¬ 
ides, carbonates, basic carbonates, or acids, which in greater 
or less degree pass into solution. When this chemical action is 
sufficient for the effect to become visible, the metal is tarnished 
or corroded; and even gold and platinum lose their lustre. 
From common observation and scientific research it is known 
that many of the salts which form under such conditions are 
poisonous. Now, since the conditions are present under which 
salts form, and since the salts are known to be toxic, and since 
any kind of solutions of metals in the metallic state is unknown 
to the chemist, it is & priori reasonable to suppose that the in¬ 
jury which a plant suffers in water in the presence of a metal, 
is due to the salts of the metal, just as much as if the salts, and 
not the metal, were introduced directty into the water. 
The injury to the plant will depend largely upon two factors: 
1. The tendency of the metal to get into solution as a compo¬ 
nent of chemical compounds — which we shall designate loosely 
as salts. 
1 This seems to us to be a fair statement of the tenor of Nageli’s work, 
and is the conclusion commonly drawn from him. Cf. Frank and Kruger 
(5), though Nageli does express the belief that the metals dissolve as hy¬ 
droxides, or carbonates. The presence at some time of the metal itself is 
repeatedly emphasized as necessary to produce oligodynamic effects. 
