From: klier@iscsvax.uni.edu
Subject: Re: Bulbs, etc.
Date: 4 Aug 92 21:23:17 -0500

>> How to distinguish between bulbs, corms, tubers, and rhizomes?
>> Can someone give me good "definitions"?
> On pages 43 & 44 in the July 1990 issue of _Horticulture_ magazine,
> there are EXCELLENT descriptions of: Bulb, Scaly bulb, Truncated
> bulb, Bulbil, Bulblet, Corm, Erect rhizome, Rhizome, Sobole, Tuber,
> Tuberous rhizome, Tuberous root, and Tuberous stem. Each definition
> is also illustrated.

HA!  Even most taxonomists don't get THAT picky.  

Bulbs, corms, tubers and rhizomes are all storage tissues of perennial
plants.  Bulbs are modified leaves, corms and rhizomes are modified
underground stems, and tubers are thickened you-name-its.

Cut a bulb cross-wise and you'll see rings -- like onion rings.
You're actually looking at thickened, modified leaves cut in
cross-section.  Cut a bulb longitudinally, and you can see those
modified leaves joining on to a flat plate of stem tissue at the base;
from that "basal plate" of stem tissue, roots will be produced.  If
you're lucky to cut through just right, you'll see a small shoot --
often with flower primordia -- totally enclosed by those leaves.
(That's why bulbs bloom so nicely the first year you plant them --
you're buying pre-started flowers!).  Think "onion" for "bulb".

Corms and rhizomes are both stem tissue, and if you look carefully,
you should be able to find nodes and internodes.  Rhizomes are
generally fairly longish critters, and lie horizontally (or
thereabouts) in the soil.  There are usually small "scale leaves" at
the nodes.  Think "Iris" or "johnsongrass" for "rhizome"

Corms are short, fat upright stems, often covered with a "tunica",
that papery covering you see on gladiolus corms...  Cut into a corm or
rhizome, and you won't find any "onion rings" -- just solid tissue.
Think "Gladiolus".

A "tuber" is a thickened plant part, a root or stem for instance.
Think of dahlia roots that you plant -- those are tuberous roots.
Potatoes are tuberous stems.