LAG IN WATER ABSORPTION BY PLANTS IN WATER CULTURE WITH RESPECT TO CHANGES IN WIND

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Abstract
Willow cuttings rooted in benches of sand and then placed in large tanks of nutrient solution until they had developed roots and tops were then placed in 32-ounce bottles and connected to a potometer so that any water absorbed by the roots could be measured by the travel of an air bubble along a graduated scale. The influence of wind on transpiration (absorption) was then detd. by placing the plant in a tunnel where the velocity of air could be regulated. A similar technique made it possible to measure evaporation from a standardized atmometer. Several minutes always elapsed between the time the rate of air flow past the leaves of a plant was altered and the attainment of a new and more or less constant rate of water absorption as measured by the potometer. The length of this lag period varied with the time of day and the intensity of various environmental factors which commonly influence the transpiration rate of plants, was greatest with low transpiration rates and usually shortest about midday. Its average value was about 10 min. for plants 30 cm. tall. The lag period for plants with 120-cm. stems was about 14% greater than that for the 30-cm. plants. The use of dilute nutrient and other solutions around the roots of the test plants decreased the absorption rate and correspondingly increased the lag period.