Metals and Plants . 
457 
than the area of glass that was covered. The last nine elements 
in the tables were available only as samples, of various size, and 
were put into smaller beakers, each receiving only one plant. 
The metals we used were all of them of the best C. P. 
varieties of standard makes. Any impurity would not only in¬ 
validate the results directly, but might also create a miniature 
battery, which, even if the current itself did not influence the 
plants, would certainly, by so-called local action, hasten the 
corrosion of the metals. Before using, the metals were scoured 
with emery cloth or sea sand and washed clean, and then intro¬ 
duced into the beakers without being touched with the hands. 
The water used was distilled from tap water, and may have 
contained carbonic acid and a trace of ammonia. The entire 
distilling apparatus was of glass, and the water obtained the 
first few hours was thrown away, as likely to contain the most 
of whatever could be dissolved from the glass. 
The seedlings used were average plants, selected in every 
case from a large number; and, except in the second experiment 
with Lupinus albus , they were very uniform in all respects. 
At the beginning of the experiment a mark was made with 
India ink 10 mm. from the apex of the root. The numbers in 
the columns headed “Growth” in the tables, express the excess 
in length of these apical zones over the original 10 mm. The 
last change observed in the length of the roots was sometimes 
a contraction, which showed that the growing region, previously 
stretched by the turgor, was dead. When the tables do not 
show this contraction, it may be because the measurements 
were not timed right; or possibly because the plants as they 
died grew up to the limit of their stretching. The plants were 
kept in approximate darkness, but not in an excessively damp 
atmosphere. 
