Guttation

Guttation is the appearance of drops of water on the leaves of some vascular plants. On some nights when atmospheric conditions are not conducive to transpiration (humid and windless), root pressure may be so strong that the plant cannot rid itself of water fast enough. In that event, the water will push out the ends of the veins in the leaves, forming drops of water.

Guttation is not to be confused with dew.