cornflower vs wild bachelor's button

cornflower

adj
  • Of a blue colour, as that of the cornflower; cornflower blue. 

noun
  • Cornflower blue. 

  • A plant of the species Cichorium intybus. 

  • A small annual plant in the family Asteraceae, Centaurea cyanus, usually with bushy blue flowers which grows natively in European cornfields (i.e. wheatfields). 

wild bachelor's button

How often have the words cornflower and wild bachelor's button occurred in a corpus of books? (source: Google Ngram Viewer )