exocarp vs pericarp

exocarp

noun
  • The outermost layer of the pericarp of fruits; the skin or epicarp 

pericarp

noun
  • The outermost layer, or skin, of a ripe fruit or ovary. 

  • The outer layer of anything. 

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