Quote from : The Phantom Tollbooth Book

Dictionopolis is the place where all the words in the world come from. They're grown right here in our orchards." "I didn't know that words grew on trees," said Milo timidly. "Where did you think they grew?" shouted the earl irritably. A small crowd began to gather to see the little boy who didn't know that letters grew on trees. "I didn't know they grew at all," admitted Milo even more timidly. Several people shook their heads sadly. "Well, money doesn't grow on trees, does it?" demanded the count. "I've heard not," said Milo. "Then something must. Why not words?" exclaimed the undersecretary triumphantly. The crowd cheered his display of logic and continued about its business.