Jacob's staff vs cow's lungwort

Jacob's staff

noun
  • Verbascum thapsus, the common mullein. 

  • A single straight rod or staff, pointed and iron-shod at the bottom, for penetrating the ground, and having a socket joint at the top, used, instead of a tripod, for supporting a compass. 

  • The ocotillo (Fouquieria splendens), one of certain desert shrubs of southwestern United States and Mexico having slender naked spiny branches that after the rainy season put forth foliage and clusters of red flowers. 

cow's lungwort

noun
  • mullein (Verbascum thapsus) 

How often have the words Jacob's staff and cow's lungwort occurred in a corpus of books? (source: Google Ngram Viewer )