1. Roots or stems.
Bulbs, corms, rhizomes and tubers; which are which? There are true bulbs, as in onions and tulips; there are corms, as in liatris and gladiolus; there are rhizomes, as in iris and ginger; and there are tubers, as in potatoes and dahlias. Actually, while we call them all roots, some are really part of the stem, gorged with food for the next generation. The real roots grow from this underground storage system.