medulla vs rhizome

medulla

noun
  • The internal tissue of a plant. 

  • The medulla oblongata. 

  • The soft inner part of something, especially the pith of a fruit. 

  • The inner substance of various organs and structures, especially the marrow of bones. 

rhizome

noun
  • A horizontal, underground stem of some plants that sends out roots and shoots (scions) from its nodes. 

  • A so-called “image of thought” that apprehends multiplicities. 

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