"A last fart: are these the leaves of my dream, vainly falling?

In the original, the image of a dream is combined with the cruder image of passing wind.."

Is the wind representing the fart here?

"Passing wind" is an English euphemism, the original does not use "kaze" (wind) but goes straight for "he" (fart).

The original word order also puts the dream at the start and drops fart right at the end, which I think is funnier than putting it on the first line.

Passing wind is another term (among many others) for farting.