Brownie vs dryad

Brownie

noun

  • A junior Girl Scout. 

  • A junior Girl Guide. 

name

  • A nickname of the surname Brown. 

dryad

noun

  • A female tree spirit. 

  • mountain avens, dryas 

How often have the words Brownie and dryad occurred in a corpus of books? (source: Google Ngram Viewer )