The fundamental substance or stroma is colorless and homogeneous.
Deep to these is the ovarian stroma, composed of fibrous tissue, and embedded in it are numerous nests of epithelial cells, the Graafian follicles, in various stages of development.
Other series of modifications arise in which the tissues corresponding to the stroma invest the sporogenous hyphal ends, and thus enclose the spores, asci, basidia, &c., in a cavity.
Whether a true sexual process precedes these processes or not does not affect the present question, the point being that the resulting spheroidal "fructification" (cleistocarp, perithecium) has a definite wall of its own not directly comparable with a stroma.
The simpler forms bear the perithecia directly on the mycelium, but the more highly developed forms often bear them on a special mycelial development - the stroma, which is often of large size and special shape and colour, and of dense consistence.