I think you are observing a phenomenon known as guttation, in which specialized leaf glands occasionally release water droplets. Many small plants possess glands that can emit a clear liquid. Guttation fluid is made up of water and a variety of organic and inorganic compounds.

The word guttation is derived from the Latin word gutta, meaning droplet. Excess moisture in the leaf normally transpires through stomata (minute holes in the leaf) and evaporates. Heat, wind, and dry conditions accelerate this evaporation.  Under conditions of cooler temperature, still air, high humidity, this evaporation slows or halts and excess water may be released through the specialized glands and accumulates at the leaf's tip. At night, the leaf's stomata are closed and you are particularly likely to see evidence of guttation on your plant in the morning.

This accumulation happens most often when soil is very moist. The plant roots absorb moisture from the soil, pushing it up through the plant's xylem (water-carrying tissue) until it reaches the leaves. As evaporation is not "pulling" the water out of the plant, the water inside the leaf has no place to go. Water pressure builds to a point where the plant is simply forced to release the liquid, exuding fluid through specialized glands.

Guttation frequently occurs in tropical plants when high humidity inhibits the natural transpiration, which is simply the loss of water vapor inside the plant to the outside air. It is believed that some plants may also have adapted to release fluids in this manner to reduce the build up of mineral salts in their soil.

For an illustrated example of guttation, see Missouri State University's Grape Guttation page.

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- Courtesy of NYBG Plant Information Service