Vital Force Theories

Vital force theories share the basic claim that living cells must be actively involved to lift sap upward - water could not rise on its own through purely dead tissue, in this view. Two specific theories were built on this idea. Godlewski's relay-pump theory (1884) proposed that periodic changes in the osmotic pressure of living xylem-parenchyma and medullary-ray cells act like a chain of small pumps, passing water upward stage by stage. J.C. Bose's pulsation theory (1923) went further, using an instrument he invented called the Crescograph - essentially an electric probe connected to a galvanometer - to detect a rhythmic pulsating electrical activity in the inner cortex whenever the probe was inserted; Bose interpreted this as evidence of a heartbeat-like pumping action by cells associated with the xylem, laterally pushing sap into the conducting cells. Both theories were later seriously undermined: Strasburger (1889) and Overton (1911) showed experimentally that an old oak-tree trunk, killed completely by picric-acid treatment and heat so that none of its cells remained alive, could still conduct water upward when placed in water - proving living cells are not, in fac …