Dryads are a type of woodland creature found in Xanth.
Dryads are a type of nymph that usually inhabits trees. If the tree dies, they die. As such, they are quite protective of the woods, seeing trees and other plants as defenseless creatures who need their protection. They sometimes will begin to use fowl language, then stop themselves short of actually using the offensive words as dryads are supposed to appear innocent enough to not know that language.
While yelling at Bink to stop trying to cut down trees, a dryad inadvertantly helps save Crombie's life by mentioning a wounded soldier in a ditch. The dryad then helps Bink find the Spring of Life.