1896 | TOXIC EFFECT OF ACIDS AND SALTS UPON PLANTS 149 
In all of the solutions by which growth was inhibited the roots 
were quite rigid at the end of the experiment. In the last two 
dilutions growth was noted for the entire period, so the killing 
point is shown to be the 45> gram-molecule solution. The 
seedlings of Zea Mais were started in the xs'5y gram-molecule 
solution which completely inhibited the growth, while the two 
next dilutions allowed growth to continue, so that here the kill- 
ing point is shown to be the z,!55 gram-molecule solution show- 
ing the Zea Mais to be somewhat more resistant than the P. 
sativum, = 
POTASSIUM CYANIDE. 
i 1 | 1 1 
KCN T600 B200 6400 T2800 25600 
mol, mol. mol. mol. mol. 
Mie eee Cae 
2 . mm , mm mm 
Psetiviien Ist 24 hours eee sine 1:25 3 . 2.5 i 
2d 24 hours sa Hoan es 2 3 
“e 
Z. Mais Ist 24 hours ae 25°° a . 
2d 24 hours whee as 6 
The KCN will dissociate to form K* ions and CN7 ions, and 
the dissociation is nearly complete. Since we are dealing here 
with a potassium salt of HCN and quite dilute solutions, the 
amount of undissociated KCN will not be very great. At the 
dilutions used the K+ ion would not produce any toxic action, 
- the poisonous quality of the KCN solutions must be due 
Principally to the CN- ion and to a slight extent to the undis- 
sociated KCN, the effect of which will decrease as the dilutions 
become greater. 
9. Porasstum FERRO- AND FERRI-CYANIDES. 
Experiments were performed with the seedlings of P. sativum 
and Zea Mais and potassium ferro- and potassium ferri-cyanide. 
In the z's and ,1, gram-molecule solutions of K,Fe(CN), the 
Toots were killed, no growth whatever resulting. In zjy molecule 
solution growth was observed during the first twenty-four hours, 
but none afterward. Inthe ,1. and ;1 gram-molecule solution 
Stowth conti “de BE ae e 
‘continued for the entire period. In the K,Fe(CN),, th 
Seedlings were set first in the «4, molecule solution in which no 
