Definition of "ascus" []

• A membranous, often club-shaped structure in which typically eight ascospores are formed through sexual reproduction of ascomycetes. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The mildews may be divided into two genera: _Podosphæra_, with a single ascus in the spore fruit; and _Erysiphe_, with two or more."
• "For instance, in the asci of lichens there are formed from a portion of the protoplasm four or more small ascospores, which secrete a cell-wall and lie loose in the ascus."
• "They are set free by the rupture of the ascus, and germinate by putting out through their walls one or more filaments which branch and form the thallus of a new individual."