ascent of sap experiment

A simple experiment can be conducted to demonstrate that xylem is the tissue involved in ascent of sap. 

Requirements: Herbaceous plant with a soft, semitransparent stem, such as the Balsam plant or Coriander plant.

Procedure: A small Balsam or Coriander plant is taken. Its root system is cut off. The twig is then introduced in a dilute solution of eosin or saffranine stain, in water, taken in a test tube. The test tube is fitted to a stand. The experimental set up is allowed to stand undisturbed for about 2-3 hours. Later the twig is removed and observed. Many parallelly running streaks of colored water can be seen through the semitransparent stem.

Thin blade sections of the stem, petiole and leaf are taken and observed under the microscope. The colored solution of water is seen to be present only in the xylem vessels, clearly indicating that xylem is involved in ascent of sap.

Mechanism of ascent of sap

The mechanism of ascent of sap is one of the most intriguing problem for biologists particularly considering the fact that water and mineral substances are being conducted to a height several meters, against the force of gravity. There have been several speculations and explanations offered from time to time. These explanations are in the form of theories. Among the various theories put forth from time to time. Two theories have stood the test of time. These are root pressure theory and the transpiration pull theory.

image credit: adobe firefly