exocarp vs integument

exocarp

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

integument

noun
  • The outer layer of an ovule, which develops into the seed coat. 

  • An outer protective covering such as the feathers or skin of an animal, a rind or shell. 

  • A shell or other outer protective layer. 

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