My 2¢ worth: when I was in High School we learned that all these propagules – bulbs, corms, rhizomes, tubers and stolons – are modified stems. Defining a geophyte is much more difficult. At best we can offer a fuzzy definition: the plant must be a perennial with a dormant period during which most if not all its living substance is kept in an underground storage organ. I agree with Jim’s discussion, except for his use of the term epiphyte, which usually has a more restricted meaning. David Ehrlich