While sporangia and spores are deposited on top of the substrate when floating detached sporophylls sink and decay, the adult corms of I. tuckermanii are buried so that the upper corm surface is about level with the substrate surface. A mechanism of root production and growth which both pushes substrate out from under the corm and pulls the corm downward is discussed. Fossil lycopods with morphology similar to Isoetes possibly had a similar mechanism.