ناصر عسکری

Plants are characterized by a negative hydrostatic pressure, brought about by transpiration and by capillary activity of xylem vessels (Taiz and Zeiger, 2010). Because of this, a stem that is being cut sucks up what is nearby. Often this is air but it may also be liquid. The diameter of the xylem vessels is 50-100 μm, so when the liquid contains bacteria (that are typically