At the bottom of the moving stair the crows were flying in and out of snug little rookeries that had been built for them at the ends of the tube cars, so that they wouldn’t foul the seats. Ten minutes on one of those cars took Kath Two to Aldebrandi Gardens. This was a series of six consecutive blocks that had been constructed as botanical preserves. Each consisted of a rectangular slab of ecosystem covered by a lofty arched glass roof under which simulated Earth landforms had been built. The temperature and humidity of each had been tuned to simulate a different part of Old Earth. Plants and other organisms, sequenced from digital records, had been cultivated here, and supplemented later with birds, insects, and small animals. Creatures fostered and studied here had later been disseminated to factories in other parts of the ring where they’d been propagated in vast numbers and used to seed New Earth.