Transpiration as a Factor in Crop Production. 
47 
This watering device necessitates frequent weighing in order 
to determine the necessary quantity of water to replace that lost 
by transpiration and thus maintain a fairly constant degree of 
saturation. 
All water was weighed accurately in grams before being added. 
On the floor of the pit were three double tracks upon which 
the potometers, standing on small iron trucks, could be rolled 
back and forth. (Fig. 4. At any one time the potometers stood 
on the middle and one of the outside tracks. At one end of the 
three tracks, a fourth track at a right angle to the others was 
Fig. 5. — Detailed view showing arrangement for weighing potometers to 
determine the daily use of water by corn plants. The shelter contains 
self-recording instruments for temperature, relative humidity, and wind 
velocity in the cornfield, where these transpiration experiments are con- 
ducted. Above the shelter were a wind gauge and rain gauge. 
