Well, I don't know if this a criterion, but I've always considered that to be a corm, the part should be roughly radially symmetrical,, e.g,. gladioli. Tubers are not much so, necessarily, e.g., potatoes, dahlias, yams, and more rhizomatous, with some arisaema tubers being roughly radially symmetrical, and tending to be symmetrical around a vertical axis--with tubers not caring. ----- Original Message ----- From: "J.E. Shields" <jshields@indy.net> To: "Pacific Bulb Society" <pbs@lists.ibiblio.org> Sent: Monday, December 14, 2009 10:13 AM Subject: Re: [pbs] corm; was RE: Late fall in Maryland I looked both terms up in the glossary of John Bryan's "Bulbs" revised edition. I don't always blindly trust John, but he did have help putting that volume together. Corm -- underground storage organ, a swollen part of an underground stem Tuber -- underground root modified as a storage organ. The modifier "underground" seems to eliminate pseudobulbs and other above-ground structures. I myself have a hard time distinguishing some tubers from corms. I tend to think of corms as annual or at most biennial structures and tubers and bulbs as perennial structures. Is that reasonable? Our