In column http://www.straightdope.com/columns/020419.html Cecil failed to mention the most obvious plant excretion process.
Dew on grass in the morning is the liquid excretion of the grass during the night.
Grass runs a powerful pumping mechanism to bring moisture from its roots to its leaves where it is used in respiration and photosynthesis.
At night the pumping mechanism keeps on going but there are no processes to use the water - as in daytime - or to evaporate it. The grass can’t use it so it excretes it. The result is dew.
There are those who will no doubt bring up condensation as seen on a cold tin roof, but that is a minor effect compared to the excess liquid pumped out by the grass.