gemmule

noun5

1. •
   (historical) 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.
2. •
   Synonym of plumule (“the first bud, or growing point, of a plant embryo, situated above the cotyledons”).

   • The incipient apical meristem (gemmule) is located between the two cotyledons of the mature embryo and consists of a pocket of approximately 200 meristematic cells[…]. — 1992
3. •
   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”).
4. •
   A small gemma or bud of dormant embryonic cells produced by some freshwater sponges (phylum Porifera) that develops into a new sponge.

   • The increase in size of the gemmule takes place by means of cell growth and division, and by the fusion of neighboring small gemmules. — 1891
5. •
   (no longer used) Synonym of gemma (“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 a new individual can develop”)

   • The gemmules of the Marchantia [a genus of liverworts] are little disc-shaped masses of cells composed of two or more layers. — 1867