What about the "tubers" of Bletilla? Some genera of terrestrial orchids (eg. Cyrtopodium, Eulophia) have species with those underground structures, yet other species with them partially buried and others with them totally exposed where they are termed "pseudobulbs" yet they are completely made up of stem tissue?? Isn't "tuber" a swollen root structure, as in Dahlia and some species of Impatiens, as opposed to "corm" made up of stem tissue? Bonaventure