The process I think you're speaking of is transpiration. If you can physically see water droplets on the leaf you could also be witnessing guttation, though, this depends on whether you are viewing this during the day or night.
If it is indeed guttation, not transpiration, you would be able to see what looks like water droplets on the leaf surface.
when water vapor escapes from a leaf, it is called transpiration.
water vapour or water vapor (in the U.S.)
Mini-Leaf ? Leafette? Small leaf?
Simple leaf
Definetly cellulose
The Weeping Willow leaf (scientific name: Salix Alba 'Tristis') is actually a simple leaf. :) But because of its appearance on the branches, it is sometimes mistaken as a compound leaf instead.
Ovate
Transpiration
Transpiration
water vapour
water vapour
Water vapour.
water vapour
Steam
Water vapour
condensation
>Water Vapour >Moisture
If you are looking for a simple answer...it is water vapour.
humidity