Symbolism, Imagery, Allegory
Storytelling is a very important part of And to Think That I saw it on Mulberry Street. Why, if Marco wasn't such a natural storyteller (more on this in the "Characters" section), we wouldn't be privy to any of the delightful things that he saw on Mulberry Street, now would we?
Marco uses storytelling to make the world more interesting. Instead of accepting things just as they are, he tries to change them for the better. For example:
The story would really be better to hear
If the driver I saw were a charioteer.
A gold and blue chariot's something to meet,
Rumbling like thunder down Mulberry Street! (33-36)
Marco's not satisfied with the driver of the plain old wagon, and he knows that changing that driver to a charioteer will change the story and make things more fascinating. Without this constant need to make the story better, Mulberry Street would just exist as a boring old suburban street in Marco's mind. He doesn't let that happen, though. Marco takes charge and makes his own stories happen. Storytelling, then, represents both Marco's creativity and his interest in taking charge of his own experience.