Dew Not Confuse It With Guttation

Early morning and droplets of dew hang off the leave of plants - except this is not dew but water of gutattion.  What's the difference?  It sure looks like dew.

Let's take a closer look at one of these 'dew' drops.

Notice that the droplet is at the end of a leaf.  Plants take water out of the soil and release it into the atmosphere as a vapor through openings in their leaves called stomata.   This process is termed transpiration.  Sometimes transpiration is inadequate to remove excess water and instead of vapor, droplets of mineral laden water are released through openings similar to the stomata.  This process is termed guttation and it occurs mostly in the morning when the humidity is high.  It also occurs if the plant has been recently watered.

These shots were taken early in the morning, but it's also possible I'm over watering my tomato plants!  For more information on guttation and plant physiology see http://en.wikipedia.org/wiki/Xylem.