Dear All John Lonsdale asked "When does the stolon become a corm?". Several species of geophytes, including certain species of lilies, will produce a stolon and at the end of the stolon form a corm, or in the case of Lilium, form a true bulb. Lilium wardii is an example, another is L. lankongense which sometime will travel as much as 12 inches by means of a stolon and then form a bulb. Consequently a bed of this species will soon double in size. Cheers, John E. Bryan