GUTTATION

 In some plants, watery drops ooze out from the injured margins of the leaves where the main vein

ends. This is called guttation. It takes place usually early in the morning when the rate of water

absorption and the root pressure is higher while the transpiration is very low. The watery drops consist of

water in which many organic and inorganic substances are dissolved.

The phenomenon of guttation is associated with the presence of special types of stomata at the

margins of the leaves, which are called water stomata or hydathodes. Each hydathode consists of a

water pore. (Fig.8), which remains permanently open. Below this, there is a small cavity followed by a loose

tissue called an epithem. The epithem is in close contact with the ends of vascular elements (tracheids) of

veins.

Fig.8. Hydathodes: A-Entire leaf showing the position

B-V.S. of the leaf through hydathode

Under higher root pressure, water is given to the epithem by the xylem of the veins. From epithem,

the water is released into the cavity. When this cavity is completely filled with the watery solution, the latter

begins to ooze out in the form of watery drops through the water pore.