tubing as shown in the figure. The size of
glass tube should be equal to the size of the
stem. Take care while joining tube and stem
being bound tightly, so that water cannot
escape from the tube. Now, pour some water
in the glass tube until water level can be seen
above the rubber tube. Mark the level of
water (M1) in the tube. Keep your
arrangement aside for 2 to 3 hours. Then
observe and mark the water level (M) in the tube
Is there any increase in the water level?
what is the role of xylem in this action?
The mechanism of water movement in plants
We have seen that there is a push from below due to root pressure on
the columns of water in the xylem vessels, but this is seldom high and in
some seasons it is nil. How does the water reach 180 metres high to the
top of a tree like a eucalyptus?
Let us recall the activity that you performed in lower classes. Why
inner sides of cover become moist? Where do these water droplets or vapour come from ?
We know that this type of evaporation of water through
leaves is called transpiration. Water evaporates through
stomata of leaves and lenticels of stem.
When the leaves transpire, there is a pulling effect on
the continuous columns of water in the xylem vessels. The
top ends of these vessels are surrounded by the leaf’s
mesophyll cells which contain cell sap, so the water is
continuous from the xylem vessels to the walls of the
mesophyll cells from which it evaporates into the air spaces
causing the pull. The water column does not break because
of its continuous molecular attraction. This is a property of
water you demonstrate every time you drink through a straw.
Now we have a picture of the water-conducting system
of a tree. Water is absorbed by osmosis from the soil by
