A corm is by definition a condensed, typically narrow stem comprising several nodes and surrounded by a fibrous tunic. It is annual/biennial, developing at the apex of the previous year's corm. Tubers are fleshy annual/biennial structures, which can comprise either stem or root tissue, and which do not have a tunic. Stem tubers often form at the tips of stolons. Tropaeolum storage organs are fleshy, have nodes, and lack tunics, so they are properly termed stem tubers. Tuberous begonias grow from a perennial structure that is in effect a modified hypocotyl. Technically it is neither a corm nor a tuber, although it is usually called the latter. Russell At 11:13 AM 12/14/2009, you wrote: >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. Russell Stafford Odyssey Bulbs PO Box 382 South Lancaster, MA 01561 508-335-8106 http://www.odysseybulbs.com/