Dec. iS, 1916 
Influence of Bordeaux Mixture on Transpiration 537 
longer than the other. The short arm extends through the rubber stopper 
into the cup. The bend of the U turns over the edge of the container and 
the end of the longer arm dips into a reservoir of water below. The 
second glass tube passes through the rubber stopper and ends just at its 
lower surface. To the upper end of this glass tube a short piece of rubber 
tubing is attached. This is closed by means of a pinchcock or screw 
clamp when the instrument is installed. In order to install the instru¬ 
ment, the rubber stopper with its glass tubes is pressed firmly into the 
mouth of the cup. The cup is then buried in the soil of the container 
among the roots of the plant. The end of the long arm of the U-tube is 
dipped into a suitable reservoir of water below. Suction is now applied 
to the short rubber tube. This causes water to rise through the U-tube 
into the cup, filling the latter. When the water has risen and filled the cup 
and the short rubber tube, a pinchcock is applied, thus closing the tube. 
In installing the instrument, care must be taken that all connections are 
tight and that all air is removed from the system. As water is removed 
from the soil by the plant roots, more water passes through the porous 
walls of the clay cup, replacing that absorbed by the roots. In this way 
an approximately constant soil-moisture content may be maintained. 
Any desired moisture content of the soil may be obtained and maintained 
approximately by simply increasing or decreasing the distance between 
the surface of the water in the reservoir and the surface of the water in 
the porous clay cup. 
In experiments such as are here reported, a constant moisture content 
of the soil in which the plants are rooted is of considerable importance, 
and the old method of supplying water to the roots at stated intervals has 
proved unsatisfactory. 
After installing the autoirrigators and sealing the pots the plants 
were allowed to stand a week in order to become adjusted to the new 
conditions before the experiments were begun. 
In each experiment 12 plants were employed. These were chosen 
from a much larger number and were selected with special reference to 
uniformity of size and vigor. The 12 plants were divided into two 
groups, each group constituting a series of 6 plants. In order to expose 
the plants included in a single experiment to the constantly changing 
aerial conditions in such a way that all might be affected in a somewhat 
similar manner, they were arranged in two rows, 6 plants to a row, on 
opposite sides of a greenhouse bench, the rows being placed near the 
edge of the bench. The bench was centrally located and was not in the 
direct path of air currents from open doors or ventilators. As a further 
precaution, the plants were shifted in their positions in the rows each 
day according to a definite plan previously decided upon. 
The plants were weighed each day and the water loss from each plant 
for the time period immediately preceding was determined. The weigh¬ 
ings were made in the order in which the plants were numbered, from 1 
