138 BOTANICAL GAZETTE [ AvGuST 
Some experiments with acetic acid also were performed. 
In these, only seedlings of Pisum sativum and Zea Mais were 
used, and the results at the different dilutions are shown in the 
preceding table. 
From the above table it will be seen that ;Q,9 sy00 and 
sty Solutions were used for the seedlings of P. sativum. In 
the ,¥,, solution no growth whatever occurred and at the end of 
the first twenty-four hours the root tips were very soft and 
flabby. In the two remaining solutions considerable growth 
resulted, but it will be seen from the amount of growth that the 
g30y Solution produced a marked retardation. 
For the Zea Mais seedlings much greater concentrations were 
used to start with, since it had been found in the experiments 
with other acids that these seedlings were much more resistant 
In the ,}, solution no growth whatever occurred while im “ 
other dilutions the growth was considerable. The figures ie 
also show that growth was to some extent retarded in the 
dilutions which were not sufficient to kill the roots. Z 
The dissociation of acetic acid is into H* ions and C,H,% 
ions, so that here again we have to deal with H* ions. In this 
acid, however, the degree of dissociation is not complete . se 
dilutions which were used in the experiments. The amount 0” 
dissociation in a ,,, solution is only 12.66 per cent. ao 
to Ostwald,” and in a siz Solution 9.14 per cent. Then here 
have to deal with acertain amount of dissociated acetic acid . 
a certain amount which remains unchanged, the effect of We 
cannot be overlooked. Sodium acetate in equally strong ee 
is non-poisonous and since both sodium acetate and aceti¢ es 
contain C,H,O> ions in common it follows that the CyHs a 
ion is non-poisonous, so that the H+ ions and the undissocia'® | 
acid are left to produce the toxic effect. The part wil 3 
played by these two will depend upon the degree of 
tration of the solution. ae 
It will be noted that in the case of both seedlings pe ie - 
cent. necessary to kill the roots is much greater than in - 
® Zeitschrift fiir Physikalische 
Chemie 3: 174. 
