ascus

Etymology

From New Latin ascus, from Ancient Greek ἀσκός (askós, “a sac”). Doublet of askos.

noun

1. (mycology) A sac-shaped cell present in ascomycete fungi; it is a reproductive cell in which meiosis and an additional cell division produce eight spores.
   The one important character which distinguishes the Ascomycetes from all other fungi is the ascus (plural, asci). This is a sac-like structure in which ascospores are formed following karyogamy and meiosis. 1967, Constantine. J. Alexopoulos, Harold C. Bold, Algae and Fungi, page 101