The Doctor had been strolling quickly after her, glancing at the trees around him, but he slowed as soon as that glass wall came into view and he tilted his head back to look up, but how high it went was impossible to tell, thanks to all the trees in the way, pressing up against that wall. He was lifting a hand and moving it out to press into the glass, looking over the glass between his fingers, then around his hands.
After a moment, he pulled his hand away and turned around to look at the trees, stepping away from that wall and touching at the bark of one of the trees, then he tugged one leaf off and rubbed it between his fingers before lifting it to his nose and sniffing it. Then he licked it. Hm. The leaf was dropped back to the ground. "This isn't Earth." There wasn't any way some of these trees could grow here on Earth, they needed special soil, special nutrients.