1. Measurement of tension is xylem sap indicates adequate amount of pressure of lift the water up even in tallest trees.
2. It is a physical process and does not involve metabolic energy.
3. The tensile strength of xylem sap is in the region of 25-300 atm which is sufficient to withstand any force that attempts to break it.
4. Kramer and Kozlowski (1960) made dendrographic measurements of tree trunks and showed a diurnal variation of the girth. There is decrease during day time as a result of shrinkage of cells. This shrinkage is due to water loss and the resultant tension in the xylem elements.