148 BOTANICAL GAZETTE [august 
The dilutions were made from the ;+, molecule solution 
the same as for the Ag,SO,. In the first three dilutions 
used for the seedlings of Pisum sativum a growth of a few milli- 
meters occurred during the first twenty-four hours, but the 
second measurement showed no further growth. Those roots 
which were killed remained rigid, but were somewhat discolored 
at the end of the experiment. In the last two dilutions growth 
continued throughout the experiment, so that the killing point 
for the seedlings of Pisum sativum is shown to be the zzs07 
gram-molecule solution. For the seedlings of Zea Mais the 
srévo and y5s';59 gram-molecule was first used, but in both 
of these growth resulted, so two more concentrated soli 
tions were used, which showed the killing point to be the 
qzigx grtam-molecule solution. This, then, shows that the 
seedlings of Zea Mais are able to withstand a much greater 
amount of mercury than the Piswm seedlings. 
The HgCl, will dissociate to form *Hg* ion 
ions, and at the degree of concentration used th 
will be practically complete, so we have to deal simply ™" 
*Hg* ions and Cl- ions. The Cl- ions have been shown is 
be non-poisonous, so the toxic effect must be due to the tea 
mercury. The amount of ionic mercury necessary kill the 
plants may be expressed as follows: | oe 
Pisum sativum : seedlings killed by yoz's00 mol.=1 part HE 
to 510,978 H,O. - 
_ Lea Mais: seedlings killed by ;zhj9 mol.=! par ce 
63,872 H,O, : 
Ss and two eg 
e dissociation 
8. Porassium CYANIDE. oe : 
es effect of CN on the roots of Pisum sativum and 20 ined : 
seedlings was tested by solutions of KCN. The results obtain” 
with different solutions are shown in the table on next ee 
: For the P. sativum seedlings no growth whatever occu 
the {eno and 3x0 gram-molecule solutions, while - ee 
gram-molecule solution growth was noted during the first i 
four hours but no further growth for the second measure oe 
