There must be sufficient pulling force . Even though ca . The tensile strength of water must be able to withstand the pull . In other words, the columns of water must not snap as they are being pulled. This was demonstrated by an elegant experiment in which water was centrifuged in Z-shaped tubes.
Water has a very high tensile strength, more than sufficient to withstand the pulling forces.
The xylem should be under a tension . As the tree transpires the diameter of the tree is measured. These experiments show that the diameter of the stem is smallest during the day when transpiration is occurring and largest at night, as we would. Imagine putting your finger on the end of a straw and then sucking on the other end. Tracheids and vessels must be able to withstand tensions without imploding.