mesosporium
/ˌmɛsə(ʊ)ˈspɔːrɪəm/Botany and Mycology
noun
The middle layer of the wall of any of several types of three-layered spores, especially of the ascospore of a fungus.
Origin
Late 19th century; earliest use found in Mordecai Cooke (1825–1914), naturalist and mycologist. From meso- + -sporium.