feedstock vs rootstock

feedstock

noun
  • Any bulk raw material constituting the principal input for an industrial process. 

rootstock

noun
  • The necessary basis for something to develop. 

  • A healthy and vigorous-rooted plant that is used in grafting, most commonly as a sound base to support a scion that bears desirable fruit in orchard culture. 

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