cucumber vs watermelon

cucumber

noun
  • The edible fruit of this plant, having a green rind and crisp white flesh. 

  • A vine in the gourd family, Cucumis sativus. 

  • A person who is calm and self-possessed. 

watermelon

noun
  • A plant of the species Citrullus lanatus, bearing a melon-like fruit. 

  • A pinkish-red colour, like that of watermelon flesh (also called watermelon pink). 

  • A project that is presented as on schedule when it actually has parts that are falling behind. 

  • The fruit of the watermelon plant, having a green rind and watery flesh that is typically bright red when ripe and contains black pips. 

  • An environmentalist with socialist leanings. 

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