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Unformatted text preview: twigs than in the trunk of trees. The negative transpiration pressure is reflected by a narrowing of the diameter of the tree as xylem cells narrow in diameter from the tension generated. In addition, the rate of xylem movement varies. Virtually no movement occurs at night, when there is no transpiration. In the daytime, the rate of xylem movement depends on environmental conditions such as temperature, wind velocity, and light intensity, as well as solutes in the sap. Studies have shown that the rate of xylem movement increases with K + concentration in the sap, and slows when K + diminishes....
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- Fall '09