There are many stomata on the underside of plant leaves.
Stomata perform the gas exchange necessary for photosynthesis.
fumarole · blowhole (of a whale, etc.)
pore; stoma
solfatara
air hole; air pocket
vent; ventilation hole; air hole
stomatal transpiration
Compound of 気 (ki, 'air, gas') and 孔 (kō, 'hole, opening'), literally 'air hole'. The term was coined in the context of modern biology to describe stomata and similar structures.