According to capillarity theory, ______ alone causes the ascent of...

According to the physical force theories (which include the capillarity theory proposed by Boehm), the ascent of sap in plants is driven entirely by physical forces (such as adhesion, cohesion, and surface tension) acting within the narrow, tubular structures of dead cells (xylem vessels and tracheids). No living cells or active biological processes are required for this mechanism.

Therefore, physical forces and dead cells alone cause the ascent of sap.

Answer: physical forces and dead cells