dendritic spine vs plumule

dendritic spine

noun
  • A small membranous protrusion from the dendrite of a neuron that typically receives input from a single axon at the synapse. 

plumule

noun
  • The first bud, or growing point, of a plant embryo, situated above the cotyledons. 

  • One of the featherlike scales of certain male butterflies. 

  • The aftershaft of a feather. 

  • A down feather. 

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