CULT: Rhizomes vs. tubers

Here are definitions from BIOLOGY OF PLANTS, by Raven, Evert and Curtis:

tuber: an enlarged, short, fleshy underground stem, such as that of the potato.

rhizome: a more or less horizontal underground stem.

Not very informative, eh?  Here's what the botanist down the hall says:

A rhizome is a recumbent, horizontal stem that is at least partially buried
and which elongates horizontally.  It usually has active roots and leaves
attached.  A rhizome may or may not be enlarged for food storage (iris
rhizomes are moderately enlarged; bermuda grass rhizomes are not).

A tuber is an underground stem that is modified more or less strictly for
the function of food storage.  It is usually completely buried and may be
attached to the parent plant only by a thin rhizome.  It usually does not
have active leaves and roots attached, but has dormant buds which can
produce new above-ground stems.  Again the potato is everyone's favorite
example.

So I had to get picky and ask about corms.  A corm is also an underground
stem modified for food storage, but does not elongate, I was informed.  A
corm also grows vertically, not horizontally,and is very compact.  Examples
are crocus and gladiolus corms.

Seems that the bottom line is that whatever modifications plants have had
to evolve to survive, they have evolved them!  This includes modifying
every part of the plant from leaves to roots for food storage.

A lot of botanists trained since the 80's have not had to take a course in
Plant Morphology, which addressed questions like this.  Like most areas of
biology, much of botany has become molecular and cellular in its
orientation, and the old kind of botanical information is being preserved
by gardeners.  I also note a fairly disturbing trend among botanists--a lot
of them don't particularly like plants and have little or no idea how to
grow a whole plant or what its requirements might be.  Here at school we
have two people trained in plant biology, but it's the
entomologist/paleontologist (me) who takes care of the department's
greenhouse!

Bill Shear
Department of Biology
Hampden-Sydney College
Hampden-Sydney VA 23943
(804)223-6172
FAX (804)223-6374
email<bills@tiger.hsc.edu>
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