achene vs drupe

achene

noun
  • A small, dry, indehiscent fruit, containing a single seed, as in the buttercup. 

drupe

noun
  • a kind of fruit, with a fleshy exterior, formed from the exocarp and mesocarp, surrounding a hardened endocarp which protects the seed. 

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