gemmule

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A small gemma or similar structure, especially a reproductive structure in some sponges that remains dormant through the winter and later develops into a new individual.
2. n. A hypothetical particle of heredity postulated to be the mediating factor in the production of new cells in the theory of pangenesis.

Century Dictionary and Cyclopedia

1. n. In botany: A small bud or gemma.
2. n. The plumule.
3. n. An ovule.
4. n. In zoology, a little bud; a small gemma. Specifically— A germinal mass of spores of some low animals, as sponges.
5. n. In biology, one of the hypothetical living units conceived by Darwin as the bearers of the hereditary attributes of animals and plants.

Wiktionary

1. n. biology A small gemma or bud of dormant embryonic cells produced by some freshwater sponges
2. n. obsolete A hypothetical particle once thought to be the basis of heredity

GNU Webster's 1913

1. n. A little leaf bud, as the plumule between the cotyledons.
2. n. One of the buds of mosses.
3. n. One of the reproductive spores of algæ.
4. n. An ovule.
5. n. A bud produced in generation by gemmation.
6. n. One of the imaginary granules or atoms which, according to Darwin's hypothesis of pangenesis, are continually being thrown off from every cell or unit, and circulate freely throughout the system, and when supplied with proper nutriment multiply by self-division and ultimately develop into cells like those from which they were derived. They are supposed to be transmitted from the parent to the offspring, but are often transmitted in a dormant state during many generations and are then developed. See Pangenesis.

WordNet 3.0

1. n. the physically discrete element that Darwin proposed as responsible for heredity