gemma vs gemmule

gemma

noun
  • An asexual reproductive structure, as found in animals such as hydra (genus Hydra) and plants such as liverworts (division Marchantiophyta), consisting of a cluster of cells from which new individuals can develop; a bud. 

gemmule

noun
  • Synonym of plumule (“the first bud, or growing point, of a plant embryo, situated above the cotyledons”) 

  • In the obsolete theory of pangenesis propounded by the English scientist Charles Darwin (1809–1882): a hypothetical particle once thought to be the basis of heredity. 

  • Synonym of dendritic spine (“a small membranous protrusion from the dendrite of a neuron that typically receives input from a single axon at the synapse”) 

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