Answer:
The description during the horse race improves the scene by making me feel as though I am in the action and experiencing events at the same time Paul is. I can see Paul taking note of what is around him as he and the grey pass one horse at a time. The description of the horse sizzling like lightning makes Paul's win seem really exciting.
Explanation:
I don't think it is any or much less a sentence.
The rough, rugged and haunted Dallas fascinates Pony. Even before Pony becomes an ace storyteller, Dallas acts as his muse, or inspiration. Pony says,
I used to like to draw his picture when he was in a dangerous mood, for then, I could get his personality down in a few lines. (1.46)
Notice the "used to." This is some subtle foreshadowing. Pony no longer sketches Dally because Dally's already dead when Pony's writing. His death is one of his reasons Pony's writing this piece in the first place
I would have to say it's part of the theme.
Morality and politics is the ethos of the story, aka origin aka theme.
With-out a theme there would be no plot...and no setting.
So...
C. Theme
2.part A when all at once I saw a crowd,/host, of golden Daffodils;'