I must apologise Ina, Thank you for your correction Dylan. It is I who is in error on this this time, I am not so familiar with the rootstock of Tigridia. Looking them up, I see Brian Mathew puts them down as bulbs along with Trimezia described by him as bulbous/rhizomatous, and Herbertia described as bulbous. I shall look more closely at the rootstock of Tigridia when they are available in the spring here ! However the rule of thumb given is not so good unless Irids excludes the genus Iris as there are many old world Iris which are true bulbs, Iris xiphium is a true bulb! Iris reticulata is too, and Iris serotina, lusitanica, latifolia, Iris magnifica, aucheri, planifolia, palaestina, histroides ....... I grow many bulbous Iris from the old world, as well as many rhizomatous ones. Romuleas, Gladiolus, Crocus, Moreas (Gynandriris) do have corms and occur in the old world too. Peter (UK) On Mon, Jul 23, 2012 at 5:24 AM, Hannon <othonna@gmail.com> wrote: > Tigridia species have true bulbs rather than corms. I believe this is true > for all New World irids with "bulb-like" rootstocks. Corms are the rule in > Old World genera. >