The mulefa made many kinds of rope and cord, and Mary Malone spent a morning inspecting and testing the ones Atal's family had in their stores before choosing what she wanted. The principle of twisting and winding hadn't caught on in their world, so all the cords and ropes were braided; but they were strong and flexible, and Mary soon found exactly the sort she wanted.

What are you doing? said Atal.

The mulefa had no term for climb, so Mary had to do a lot of gesturing and roundabout explaining. Atal was horrified.

To go into the high part of the trees?

I must see what is happening, Mary explained. Now you can help me prepare the rope.

Once in California, Mary had met a mathematician who spent every weekend climbing among the trees. Mary had done a little rock climbing, and she'd listened avidly as he had talked about the techniques and equipment. She had decided to try it herself as soon as she had the chance. Of course she'd never expected to be climbing trees in another universe, and climbing solo didn't greatly appeal, either, but there was no choice about that. What she could do was make it as safe as possible beforehand.

She took a coil long enough to reach over one of the branches of a high tree and back down to the ground, and strong enough to bear several times her weight. Then she cut a large number of short pieces of a smaller but very tough cord and made slings with them: short loops tied with a fisherman's knot, which could make hand- and footholds when she tied them to the main line.

Then there was the problem of getting the rope over the branch in the first place. An hour or two's experimenting with some fine tough cord and a length of springy branch produced a bow; the Swiss Army knife cut some arrows, with stiff leaves in place of feathers to stabilize them in flight; and finally, after a day's work, Mary was ready to begin. But the sun was setting, and her hands were tired, and she ate and slept, preoccupied, while the mulefa discussed her endlessly in their quiet, musical whispers.

First thing in the morning, she set off to shoot an arrow over a branch. Some of the mulefa gathered to watch, anxious for her safety. Climbing was so alien to creatures with wheels that the very thought of it horrified them.

Privately Mary knew how they felt. She swallowed her nervousness and tied an end of the thinnest, lightest line to one of her arrows, and sent it flying upward from the bow.

She lost the first arrow: it stuck in the bark partway up and wouldn't come out. She lost the second because, although it did clear the branch, it didn't fall far enough to reach the ground on the other side, and pulling it back, she caught it and snapped it. The long line fell back attached to the broken shaft, and she tried again with the third and last, and this time it worked.

Pulling carefully and steadily so as not to snag the line and break it, she hauled the prepared rope up and over until both ends were on the ground. Then she tied them both securely to a massive buttress of one of the roots, as thick around as her own hips. So it should be fairly solid, she thought. It had better be. What she couldn't tell from the ground, of course, was what kind of branch the whole thing, including her, would be depending on. Unlike climbing on rock, where you could fasten the rope to pitons on the cliff face every few yards so you never had far to fall, this business involved one very long free length of rope, and one very long fall if anything went wrong. To make herself a little more secure, she braided together three small ropes into a harness, and passed it around both hanging ends of the main rope with a loose knot that she could tighten the moment she began to slip.

Mary put her foot in the first sling and began to climb.

She reached the canopy in less time than she'd anticipated. The climbing was straightforward, the rope was kindly on her hands, and although she hadn't wanted to think about the problem of getting on top of the first branch, she found that the deep fissures in the bark helped her to get a solid purchase and feel secure. In fact, only fifteen minutes after she'd left the ground, she was standing on the first branch and planning her route to the next.

She had brought two more coils of rope with her, intending to make a web of fixed lines to serve in place of the pitons and anchors and "friends" and other hardware she relied on when climbing a rock face. Tying them in place took her some minutes more, and once she'd secured herself, she chose what looked like the most promising branch, coiled her spare rope again, and set off.

After ten minutes' careful climbing she found herself right in the thickest part of the canopy. She could reach the long leaves and run them through her hands; she found flower after flower, off-white and absurdly small, each growing the little coin-sized thing that would later become one of those great iron-hard seedpods.

She reached a comfortable spot where three branches forked, tied the rope securely, adjusted her harness, and rested.

Through the gaps in the leaves, she could see the blue sea, clear and sparkling as far as the horizon; and in the other direction over her right shoulder, she could see the succession of low rises in the gold-brown prairie, laced across by the black highways.

There was a light breeze, which lifted a faint scent out of the flowers and rustled the stiff leaves, and Mary imagined a huge, dim benevolence holding her up, like a pair of giant hands. As she lay in the fork of the great branches, she felt a kind of bliss she had only felt once before; and that was not when she made her vows as a nun.

Eventually she was brought back to her normal state of mind by a cramp in her right ankle, which was resting awkwardl............