bitter orange vs sweet lemon

bitter orange

noun
  • A citrus tree of the species Citrus limetta. 

  • The fruit of these species. 

  • A citrus tree of the species Citrus ×aurantium, also called Citrus aurantium. 

sweet lemon

noun
  • A plant of the species Citrus medica (syn. Citrus limetta) or its fruit. 

  • Any of several plants that produce fruit resembling lemon or lime, but less acidic than lemon. 

How often have the words bitter orange and sweet lemon occurred in a corpus of books? (source: Google Ngram Viewer )