Metaphors

I'm a riddle in nine syllables.
An elephant, a ponderous house,
A melon strolling on two tendrils.
O red fruit, ivory, fine timbers!
This loaf's big with its yeasty rising.
Money's new-minted in this fat purse.
I'm a means, a stage, a cow in calf.
I've eaten a bag of green apples,
Boarded the train there's no getting off.

I'm writing an analysis of this poem for an essay, and I want to get your guy's interpretation on what it stands for.

NO GOOGLING, YOU CHEATERS.

An overall theme + line by line analysis (doesn't have to be in depth) gets you rep!