Guttation is the process of elimination of excess water in from of water drops from the injured margin of leaf or through the hydathodes.
Guttation usually takes place early in the morning when the rate of water absorption and he root pressure are higher and rate of transpiration is low.
The water drops may contain many inorganic and organic substance dissolved in it.
Usually guttation takes place in might when stomata are remain closed. Hydathodes consists of a water pore which remains permanently opened. Below the hydathode there is a small cavity followed by a lose tissue called epithem. Epithem is closely associated with the ends of vascular elements of veins. Particularly the xylem.
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Under higher root pressure the water is given to the epithenm by the xylem of veins. From epithem the water is released into the cavity. When this cavity is vompletely filled up then the droplets ooze out through hydathode.
It is usually takes place at low temperature and higher pH. Guttation is usually found in excess during winter nights or mornings.