[Armin is not far from where she's examining the tree from the railing. There's a sort of stifled feeling about the air on this ship he can't shake. Claustrophobic. It's not as bad in here, probably because of the tree's potential to generate oxygen, but he still dislikes it. To him, no amount of artificial light can replace the sun. The fact they're literally in the sky can't replace the feeling of the sky. It seems like his life is nothing but a series of prisons, and this one is only marginally different.

He reached out to pull a leaf from the tree's branch. Just one, not enough to hurt it, so he can look at the veins.]

They must have some way of fertilizing all the plants. Recycled waste, perhaps? But that seems like it would require a lot of energy to do safely...