Sessile, where the pileus is attached directly to the matrix without any stem.
"Studies of American Fungi. Mushrooms, Edible, Poisonous, etc."
George Francis Atkinson
A chill autumn wind, blowing over a sterile plain, bore within its arms a little seed, torn with ruthless force from its matrix on a lofty tree, and dropped the seed upon the sand to perish.
"The Jericho Road"
W. Bion Adkins
He offered, if the Terran Medical would help Darkover lick the trailmen's fever, to coach selected Terran men in matrix mechanics.
"The Planet Savers"
Marion Zimmer Bradley