It’s time to pay another visit to the Department of Awesome Natural Phenomena where we’ll learn about the delicate beauty of Guttation:
Guttation is the exudation of drops of sap (xylem) on the tips or edges of leaves of some vascular plants, such as grasses. Guttation is not to be confused with dew, which condenses from the atmosphere onto the plant surface.
At night, transpiration usually does not occur because most plants have their stomata (pores found in the epidermis of leaves, stems and other organs that are used to control gas exchange) closed.
When there is a high soil moisture level, water will enter plant roots, because the water potential of the roots is lower than in the soil solution. The water will accumulate in the plant, creating a slight root pressure.
The root pressure forces some water to exude through special leaf tip or edge structures, hydathodes or water glands, forming drops. Root pressure (osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves) provides the impetus for this flow, rather than transpirational pull. [Source: Wikipedia]