I'll join the fray on this one. Put me solidly on the team which is very skeptical about adult bulbs pulling themselves down. Anyone who has raised a pot of crocus seedlings has probably seen the one, long, thick, wrinkled root which sometimes forms right under the new corm. In this case, the pulling down is plausible because the root is as thick (wide) as the corm itself: as the root contracts, the corm is drawn into the space left by the shriveling root. With mature bulbs I don't see how this can happen. For one thing, there are multiple roots pulling in different directions. For another, none of the roots is large enough to form a cavity to receive the adult bulb. I doubt that I could push a mature bulb down into the ground without mashing it. The physics of the purported event is against it. Jim McKenney Montgomery County, Maryland, USA, USDA zone 7, where the only pulling down of bulbs which occurs regularly here is that done by voles!