What is "perithecium"

Perithecium \Per`i*the"ci*um\, n. [NL., fr. Gr. ? around + ? box.] (Bot.) An organ in certain fungi and lichens, surrounding and enveloping the masses of fructification.
--Henslow.

n. An ascocarp shaped like a skittle or ball, distinguished by a small pore, the ostiole, through which the spores are released one by one when ripe.

1. n. flask-shaped ascocarp

2. [also: perithecia (pl)]