50 Nebraska Agricultural Exp. Station, Research Bui. 6. 
They are lifted by means of a differential block and tackle sus- 
pending a steelyard graduated in half pounds. 
LABORATORY POTOMETER. 1 
Figure 8 illustrates the type of potometer used in part of the 
greenhouse experiments. Corn plants grown in potometers of 
this size must be harvested at an early stage before the small 
quantity of soil has become a limiting factor in growth. 
The apparatus consists of a 4-gallon, glazed earthen jar, 
filled with approximately 35 pounds of fertile soil. An inverted, 
porous, clay flower pot is placed in the bottom of the jar and 
connected with the surface by two f-inch glass 
tubes. Water is added in weighed quantities thru 
one of the tubes by means of a funnel having a 
rubber- tube connection. The second tube pro- 
vides for the escape of the replaced air, as water 
is added. The flower pot serves both as a water 
chamber and as an aerating device. By frequent 
weighing and replacement of water, any amount 
of soil moisture may be rather constantly main- 
tained. Surface evaporation is prevented either 
by sealing with plastic modeling clay (plastocene) or by covering 
with paraffined paper weighted down with gravel. The water 
and potometers are weighed in grams on a Troemner balance. 
Fig. 8.— Small 
laboratory 
potometer. 
RELATIVE GROWTH IN FIELD POTOMETERS AND IN FIELD. 
By growing one corn plant in the standard potometers, 16 
by 36 inches, and supplying fertile soil, the vegetative growth and 
ear development is fully equal to that of plants in a normal 
cornfield under favorable conditions, figure 9 shows a mature 
crop of plants ready to be harvested. 
Table 1 shows the comparative development of Hogue's 
Yellow Dent corn grown in the potometers and in the field 
during four years. During the first three years given, the corn 
was grown two plants per hill, while in 1914, three plants per 
hill were grown. The hills were 3.5 feet apart. 
DISTRIBUTION OF MOISTURE IN SOIL. 
Table 2 shows the moisture content in foot sections in repre- 
sentative potometers of the two large field types. The data for 
the potometers with the coil show how a relatively low degree 
of saturation may be maintained uniformly thruout the soil. 
1 This type of potometer was first used and described by Kiesselbach 
(1910). 
