Japanese plum vs loquat

Japanese plum

noun
  • A fruit tree, Prunus mume. 

  • A fruit tree, Prunus salicina. 

loquat

noun
  • The Eriobotrya japonica tree. 

  • The fruit of this tree. It is as large as a small plum, but grows in clusters, and contains four or five large seeds. 

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