4 BOTANICAL GAZETTE [JANUARY 
laboratory permitted, and we believe that the concentrations were 
usually accurate. 
The method of operation consisted essentially in suspending 
- the seedlings on glass rods in the solutions concerned for twenty- 
four hours each in each experiment, in such a manner as to immerse 
the radicles. In nearly all cases the plants were under observation 
at least forty-eight hours. Never less than four seedlings were 
used in any experiment and frequently more were employed. The 
average is taken as the result. The seedlings were placed with the 
roots in the solutions, care being taken to use plants in like stages of 
development. Growth was measured from an India ink line placed 
15 ™™ from the tips of the roots at the beginning of the experiment. 
During the exposure to the action of the solutions the culture dishes 
stood in diffused light. The influence of variable factors, such as 
_ temperature, was kept track of by check cultures in distilled water. 
The water was distilled in an apparatus lined with block tin and 
was not, therefore, of the highest purity. It was consistently used, how- 
ever, throughout the season and forms a constant factor in all experi- 
ments. Beakers of 300°° capacity and of similar shape were used. 
In studying the effect of the presence of insoluble substances on _ 
the poisonous activity of the compounds: mentioned, a quantity of 
the sand, filter paper, or paraffin was generally used equal to about 
one-third of the volume of the solution of the poisonous agent. 
Thus, in the beakers used for these cultures about two-thirds of the 
depth of the solution was to be seen above the level of the sediment 
in all but the floating paraffin, in which case the order was inverted. 
After marking the roots and introducing them into the solutions 
under study, the plants were set away for twenty-four hours, at the _ 
end of which time they were again measured and the amount of ; 
growth noted. Usually, to avoid further complications arising in 
the case of prolonged experiments, the results due to exposure of 
eed Se ow 
cn eae hours were sought. 
Th it ee ee a | els ee 
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matel the maximum + 
