traveller's joy vs virgin's bower

traveller's joy

noun
  • A climbing shrub native to Europe, Clematis vitalba. 

virgin's bower

noun
  • Any of various plants of the genus Clematis, including Clematis virginiana and Clematis viticella. 

How often have the words traveller's joy and virgin's bower occurred in a corpus of books? (source: Google Ngram Viewer )