1896 } TOXIC EFFECT OF ACIDS AND SALTS UPON PLANTS 141 
in the above table were used, but it was found that in all except 
the last no growth resulted, and in the 5,4, molecule solution 
only a very small increase in length was noted in the CuSO, and 
CuCl, and none in the Cu(C,H,0,),. The roots at the end of 
the experiment were soft and flexible and showed a greenish 
color similar to the roots of Pisum sativum in the copper solu- 
tions. Two higher dilutions were then used; sida gram-molecule, 
and +y3';yy gram-molecule. In the first of these very slight growth 
occurred during the first twenty-four hours but no further growth 
afterwards, while in the jv2'gpy SOlution the growth was consider- 
able during the entire period of the experiment. The > 9s\;99 
gram-molecule solution is to be considered as the one which will 
first allow the seedlings to grow. That the seedlings of Zea 
Mais should be less sensitive to acids and more sensitive to 
copper salts seems a little strange, but the experiments plainly 
show that this fact is true. 
When CuSO, exists in dilute solution, it will dissociate to 
form *Cu* ions and -SOz ions, and at the degree of con- 
centration of the solutions used the dissociation would be 
practically complete. Hence only copper-ions and ~SOjJ ions 
need be taken into consideration. Now it has already been 
shown in the case of H,SO, that the SOj ion is non-poisonous, 
at least in dilute solutions, so the Cu-ion is left to bring about 
the toxic action. CuCl,, the second salt used, will dissociate 
to form *Cu* ions and two Cl- ions, and here also the disso- 
Ciation will be practically complete in the solutions used, so that 
at this case we have to deal simply with *Cu* ions and cr 
tons. In the experiments with HCl it has been shown that the 
Cl ions are without effect, so that here also the toxic action 
tienes be due to the Cu ions. The next salt, Cu(C,H,O,), will 
dissociate to form +*Cu+ ions and two C,H,O; ions, and here 
also the dissociation will be practically complete in the solutions 
used. Here then we have to deal simply with * Cu* ions and 
C,H,0, ions. That the toxic action of this salt is due entirely © 
to the Cu-ions can be clearly shown from the results obtained - 
for the other copper salts. In the CuSO, and in the CuCl, the 
