Transpiration as a Factor in Crop Production. 49 
quantities of water are added to covered 4-gallon, glazed earthen 
jars, which stand on a level with and are connected at the bottom 
to the potometers. A constant supply of water is kept in the jars 
so that the soil-moisture content is continually kept fairly uniform 
in all potometers. The water runs from the jar thru a rubber 
connecting tube into a 1-inch, gravel water bed in the bottom of 
the potometer and rises into the soil by capillarity. The distribu- 
tion of moisture thruout the soil mass is shown in Table 2. 
Evaporation is prevented and rainfall excluded by the same 
devices as with the previous potometer. 
The total water used is found by taking the total weight of 
water applied minus the amount remaining in the jar at the close 
of the experiment, and either adding or subtracting the difference 
in initial and final weight of the potometer, according to whether 
it has lost or gained in weight. 
Figure 7 illustrates the manner of weighing these potometers. 
Fig. 7. — Method of weighing potometers where only initial and final weights 
are made to determine the total water used. The potometer is lifted by 
means of differential block and tackle and weighed on steelyard of 2,000 
pounds capacity. At this stage, the corn was reduced to one plant iper 
potometer, several kernels having been planted to insure a full stand. 
