Venus' comb vs cobbler's pegs

Venus' comb

noun
  • An umbelliferous plant, Scandix pecten-veneris. 

cobbler's pegs

noun
  • A noxious weed, Bidens pilosa (beggarticks), with fruits that stick to hair, fur and clothes. 

How often have the words Venus' comb and cobbler's pegs occurred in a corpus of books? (source: Google Ngram Viewer )