Root
pressure is defined as hydrostatic pressure developed in the root due to
accumulation of absorbed water. It the pressure exerted on the liquid contents
of the cortical cells of the roots, under fully turgid condition this root
pressure pushes the water up the xylem vessels to the aerial parts. It shows
that water absorption is an active process.
Experiment on
root pressure: The root pressure
can be demonstrated in a plant by the following experiment.
Apparatus
required:
A
well watered herbaceous plant, a knife, a rubber tube, a narrow glass tube and
colored water.
Procedure:
Water a
potted herbaceous plant. Keep it over night. Next morning, cut off the stem a
few centimeters above the soil level or near to the root. Fix a long and narrow
glass tube to the cut end of the stump with the help of rubber tubing. Pour a
little colored water in the glass tube and mark its level. The glass tube is
connected to a manometer and whole setup is then left for observation.
Observation: After some time the level of the
colored water rises in the tube. And rise in the level of the mercury of the
manometer shows the measurement of root pressure.
Result and
conclusion:
A
rise in the level of water in the glass tube is due to the pressure exerted by
water exuded from the cut part of the stem.
The
exuding of water from the cut end of the stem is called bleeding. The flow of
water from the cut surface or bleeding when measured by mercury manometer is
estimated to 3-5 atmospheres only.
