MOVEMENT of the absorbed water through the vascular system from the xylem terminals in the root to those in the leaf, is called ascent of sap. Sometimes it covers a distance of more than 111 meters against gravitational pull as in the case of a CALIFORNIAN Sequoia sempervirens (111.6 m or 366.2 ft.) and an Australian Eucalyptus regansi 114.4 m).

The problem for PLANT physiologists is, the mechanism of this movement. One atmospheric pressure supports a column of water 10.3 m or 34 ft. or a column of mercury 760 mm high. To raise water from the ground level to the top of the tallest tree requires a top to bottom pressure difference of about 22 atm or bars or 2.2 MPa (Mega Pascal). It is evident that water is not pushed to the top of tall trees by atmospheric pressure.

Movement of the absorbed water through the vascular system from the xylem terminals in the root to those in the leaf, is called ascent of sap. Sometimes it covers a distance of more than 111 meters against gravitational pull as in the case of a Californian Sequoia sempervirens (111.6 m or 366.2 ft.) and an Australian Eucalyptus regansi 114.4 m).

The problem for plant physiologists is, the mechanism of this movement. One atmospheric pressure supports a column of water 10.3 m or 34 ft. or a column of mercury 760 mm high. To raise water from the ground level to the top of the tallest tree requires a top to bottom pressure difference of about 22 atm or bars or 2.2 MPa (Mega Pascal). It is evident that water is not pushed to the top of tall trees by atmospheric pressure.