gemma vs pustule

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. 

pustule

noun
  • Anything like a pustule, on plants or animals; a small blister. 

  • A small accumulation of pus in the epidermis or dermis. 

  • A pimple filled with pus. 

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