	The Forbidden Fountain that Baum introduces to Oz literature in this book recurs in ensuing Oz books, by Baum and by his various successors. The Fountain is an important feature in "The Magic of Oz" (1919), "The Forbidden Fountain of Oz" (1980), "The Wicked Witch of Oz" (1993), and "Paradox in Oz" (1999).