Initially, the caps are covered by a peridium-an outer covering layer of tissue.
From the en.wikipedia.org
The lower edge of the peridium is further stretched as it is pulled upward and outward.
From the en.wikipedia.org
Scales begin to appear on the surface of the peridium of some specimens at about this time.
From the en.wikipedia.org
In age, the peridium sloughs off and exposes a brownish spore mass.
From the en.wikipedia.org
The peridium may also rip in such a way that it appears as if there is a ring at the top of the stem.
From the en.wikipedia.org
The torn peridium exposes the internal gleba.
From the en.wikipedia.org
As growth progresses, the stem elongates and the peridium becomes more rounded, increasing in size until maturity.
From the en.wikipedia.org
Typically, the veil tissue is weakest near the attachment to the stem, rather than to the attachment at the edge of the peridium, and the veil separates from the stem.
From the en.wikipedia.org
If the veil tissue at the base of the stem is stronger than that attached to the edge of the peridium, the veil can rip so it remains attached to the stem as a ring.
From the en.wikipedia.org
More examples
Outer layer of the spore-bearing organ in many fungi
The peridium is the protective layer that encloses a mass of spores in fungi. This outer covering is a distinctive feature of the Gasteromycetes.
The outer covering of a fruit-body, consisting of one to several layers; used particularly in gasteromycetes and myxomycetes.
A wall or membrane of sterile cells around a fruiting body (e.g., around a sporangium or delimiting an aecium). (Pl. peridia.) (7)
The wall or limiting membrane of a sporangium or other fruit-body; an outer envelope of hyphae on a sporocarp or other fructification.
(pl. peridia; Gr. peridion "" small leather pouch): the outside covering or wall of a fructification.
The outer layer of the fruiting body of a gasteromycete.