. Proceedings of the American Society of Agronomy . watered, the top of the pot is covered with arubber cloth to prevent evaporation. Hourly or daily water loss canbe determined by weighing, until the plant has used all the availablewater in the pot. The experiment may be continued by renewing thewater supply, b shows the wire basket method of growing seedlings,the wire basket and surface being covered with paraffin to prevent MONTGOMERY: WATER REQUIREMENTS OF CROPS. 265 evaporation from the soil, and water is added as needed, through theopening where the plants are growing, c illustrates a me
. Proceedings of the American Society of Agronomy . watered, the top of the pot is covered with arubber cloth to prevent evaporation. Hourly or daily water loss canbe determined by weighing, until the plant has used all the availablewater in the pot. The experiment may be continued by renewing thewater supply, b shows the wire basket method of growing seedlings,the wire basket and surface being covered with paraffin to prevent MONTGOMERY: WATER REQUIREMENTS OF CROPS. 265 evaporation from the soil, and water is added as needed, through theopening where the plants are growing, c illustrates a method of grow-ing the plant in a culture solution and determining the water loss bymeasuring the change in level on the graduated siphon. By renew-ing the culture solution from time to time, a very normal plant can begrown in this way for several days or even weeks. Automatic Methods of Securing a Record of the Water Loss. No less than eight automatic methods for determining water losshave been devised, some of which are quite elaborate and two of. Fig. 40.—Automatic apparatus for determining loss of water from plants. which are here illustrated. In a, Fig. 40, the plant is balanced by acounterpoise hanging in a jar of water. The counterpoise is ofexactly one square centimeter in cross area, so that the sinking ofthe counterpoise one centimeter into the water displaces exactly onecubic centimeter. The time at which this displacement takes place isrecorded on a smoked drum operated by clock work. In b the wateris drawn into the evaporimeter through a sifmon, the amount lostbetween each reading being indicated on the graduated hygrometer. Fig 41 illustrates three types of large jars which have been used atthe Nebraska Experiment Station, a is a 5-gallon water jar filledwith soil. In the bottom an inverted flowerpot is placed, with twoglass tubes, through one of which the water is poured. The surfaceof the soil around the plant is covered with several layers of paraffinpaper, to
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