1914] HASSELBRING—EFFECT OF SHADING 271 
large number of seedlings, 12 were selected as uniform as possible. 
The experimental plants were grown in cylindrical galvanized iron 
tanks 38cm. high and 30.5 cm. in diameter. These tanks re- 
sembled in general construction those described by ForTIER.” 
Each tank was provided with an inlet tube 1.3 cm. in diameter, 
which ran down the inside of the tank to the center of the bottom 
where it ended. The upper end of the tube was closed by a screw 
cap. Each tank was further provided at the rim with two lugs into 
which hooks could be inserted to facilitate lifting and carrying the 
tanks. These tanks were fitted into others just large enough to 
receive them, which were permanently sunk in the ground. To 
prevent the soil from falling into the space between the walls of 
the two tanks, the inner tanks were provided near the rim with 
annular flanges which projected over the rims of the outer tanks. 
In order to prevent rain water from reaching the soil in the tanks, 
they were fitted with covers made in two parts, with flanges inter- 
locking in such a way that water could enter only through the 
opening around the stem of the plant. This was closed as effec- 
tually as possible by means of thin sheet rubber. The covers were 
Placed on the tanks every night and during threatening weather. 
The soil used for filling the tanks was taken from a well-tilled 
field which in former years had been used for growing tobacco and 
other crops. A quantity, somewhat more than sufficient for filling 
the tanks, was placed on the concrete floor of a closed shed, where 
It was thoroughly worked over many times, with the addition of 
Successive small quantities of water until the whole mass was 
brought into a moist, friable condition. The soil was left in a pile 
for a day to allow the moisture to become uniformly distributed 
throughout the mass. On the following day it was again worked 
Over several times and run through a screen preparatory to the 
filling of the tanks. 
Before the tanks were filled, a layer of broken stone was placed 
on the bottom of each in order to form a sort of reservoir for water 
and to prevent the closing of the inlet tube by the soil. By means . 
of the stones the tanks were all brought to the same tare. They 
Were then filled with soil which was tamped as uniformly as possible 
® Fortier, S., Evaporation losses in irrigation and water requirements of crops. 
US. D ept. Agric., Office of Exp. Stations, Bull. 177. 1907. 
