The objections to vital force theory of Ascent of sap:
1. Strasburger (1889) and Overton (1911) experimentally proved that living cells are not mandatory for the ascent of sap. For this, he selected an old oak tree trunk which when immersed in picric acid and subjected to excessive heat killed all the living cells of the trunk. The trunk when dipped in water, the ascent of sap took place.
2. Pumping action of living cells should be in between two xylem elements (vertically) and not on lateral sides.
