All Reed organ pipes have a vibrating reed which controls the sound
produced.  The vibrating reed is usually made of soft brass.  The
vibrating reed is necessarily tuned to approximate in pitch the inner
sympathy of the air mass in it's resonator.  The length of the
vibrating portion of the reed is changed to adjust the vibrating
frequency.  Reed ranks are sometimes topped with flue pipes when the
reed characteristics can no longer be discerned by the listener.

Reedless "Reed" pipes which imitate reed sound are called "Imitative
Reeds".  The Estey Organ Company, for example, produced a few flue
pipes that imitate orchestral woodwinds (poorly).

Imitative "Reeds" are less expensive to manufacture and maintain than
true Reeds.  Also, temperature induced pitch changes of Imitative
"Reeds" track String and Flue pitch changes.  Unfortunately, tempera-
ture induced pitch change with Reed pipes is quite different from the
other pipe families.  For Reeds to stay in tune with other pipes, the
organ temperature must be maintained after tuning.

Reeds have one advantage over Imitative Reeds: they sound better.

Reeds and the Imitative Reeds are grouped with one another in the reed
section of the organ stop tablet.  Reed stops are generally lettered
in red.  Imitative "Reeds" will sometimes have an alternate color.

Bill Finch

 [ Accordion reeds, organ reeds, and true reed pipes don't change pitch
 [ much with temperature and humidity change; it's the flue pipes which
 [ go sharp and flat.  The poor little metal reeds are the minority,
 [ though, so they often get the blame!  -- Robbie