Guttation

Guttation is the appearance of drops of water on the leaves of some vascular plants, such as grasses.

On some nights when atmospheric conditions are not conducive to transpiration (humid and windless), and when there is a high soil moisture, guttation occurs to maintain the flow of water and nutrients through the plant. In that event, the water will exude through special leaf tip cells, hydathodes in the leaves, forming drops of water. Root pressure provides the impetus for this flow, rather than transpiration pull.

Guttation may contain minerals, such as calcium, in solution. On drying, this leaves a white crust on the leaf surface.

Guttation is not to be confused with dew, which condenses from the atmosphere onto the plant surface.