How we cite our quotes: (Chapter.Paragraph)
Quote #1
The forest to either side was a black void full of wild and ancient trees, nothing like the generic carbon-dioxide suckers that decorated the city. (7.33)
There's some hint here that the trees in the city might be genetically engineered or at least severely managed: notice how they "decorated the city," as if they were, well, decorations. Note also that the trees in the city have a purpose, like any other tool. No nature for the sake of nature here
Quote #2
Being in the city all the time made everything fake, in a way. Like the buildings and bridges held up by hoverstruts, or jumping off a rooftop with a bungee jacket on, nothing was quite real there. She was glad Shay had taken her out to the ruins. If nothing else, the mess left by the Rusties proved that things could go terribly wrong if you weren't careful. (9.49)
What's funny about this quote (besides the idea that things can go terribly wrong, that's always hilarious) is that Tally has this feeling pretty early in the book—and she still wants to go back to the city and be made pretty. We learn something about her priorities: she would rather live in a pretty, fake world right now.
Quote #3
"But it's a trick, Tally. You've only seen pretty faces your whole life. Your parents, your teachers, everyone over sixteen. But you weren't born expecting that kind of beauty in everyone, all the time. You just got programmed into thinking anything else is ugly."
"It's not programming, it's just a natural reaction." (10.68-9)
This is one constant argument between Tally and, well, the entire Smoke: are the pretties pretty because of biological reasons or for cultural reasons? If you buy Tally's argument, the pretty surgery just brings out what we naturally like; but if you buy Shay's argument, there's nothing natural about what we find pretty. Notice that each argument revolves around the idea of what's natural. (People love to say that their argument is based on nature, like "Mountain Dew was made by nature to be yummy." Be skeptical. We're pretty sure a caveman would think Mountain Dew was poison.)