“What are you doing?” Ariel asked, and Mandelbrot, hurrying up behind her, echoed her question.

“Testing a hunch,” he answered, and swung at the tree with all his might.

It felt as if he had hit a boxer’s training bag: stiff enough to let him know he’d hit something, yet yielding just enough to prevent damage to his knuckles. When he pulled his fist away it left a depression in the tree, a depression that slowly began to fill in until it was once more the same scaly gray bark it had been moments before.

The significance of that was not lost on Ariel. “It’s a robot,” she said in quiet disbelief. “This whole forest is artificial. “

Derec leaned close to the tree and inhaled, then repeated the process with a fern. The tree was sterile, but the fern had the wet, musty smell that only a living plant could produce. “Not everything,” he said, plucking off a frond and handing it to Ariel. “This is real enough. Evidently they cloned what they could and simulated the rest. I’ll bet they plan to let real trees grow up to replace the fake ones as soon as they can, but until then they need something to fill the biological niche, so they do it with robots.”

“You are correct,” a soft, featureless voice said behind him.

Derec turned to the tree. “Did you say that?”

“Yes.”

“Oh.” He arched his eyebrows at Ariel, and she shrugged. “How long before it’s completely natural?” he asked.

“Many years,” the tree replied. Derec looked up into the forest canopy. This tree, and dozens more like it, supported a thick net of leaves-leaves that also had to be artificial. Yet they were green. He tugged at a vine and examined it closely in the dim light: brown. “You’ve solved the color problem,” he said.

“That is correct. We discovered a workable method of changing the color of ordinary dianite when we began producing chameleons. “

Ariel crossed her arms in front of her, a stance she often took when interrogating a robot. The blanket hung from her forearm like a banner. “I don’t care what color it is; how can a fake tree fill in for a real one?” she asked. “Don’t trees provide food for the animals? What are the birds supposed to eat, and the bugs? Or are they fake, too?”

“The birds and bugs are not false. The artificial portions, of the ecosystem provide for their dietary requirements through the use of food synthesizers, much like the automats you find in the kitchens provided for your own use.”

“Food synthesizers? In a tree?”

“That is correct. However, each tree is programmed to deliver only those substances which would normally be found upon its real counterpart.”

“Oh. You mean I can’t ask for a quick glass of water, then?”

“Actually, you may. My obligation to serve humans outweighs the ecological constraints. Do you actually desire a glass of water?”

Ariel looked to Derec, astonishment written allover her face. He shrugged, and with a big grin, she turned back to the tree and said, “Yeah, sure.”

Derec had been eyeing the tree as it spoke. He had half expected to see an enormous pair of rubbery cartoon lips flapping in time to the voice, or at least a speaker grille like the older robots carried, but the tree trunk had remained a tree trunk. No doubt the bark vibrated to create the sound, but there was no particular reason to make it look different while it did so. Now, however, a section of the tree at convenient grasping height smoothed out, grew a rectangular crack, recessed inward a few millimeters, and slid aside to reveal a sparkling glass of clear water. Ariel reached in and took it from the niche, sipped tentatively, and smiled.

“Thanks,” she said.

“You are welcome, Ariel,” the tree said, and the satisfaction in its voice was so thick they could almost see it. Robots, even those in the shape of trees, lived to serve humans.

It had been a satisfying chase. Wolruf panted happily as she trotted through the underbrush, sometimes on two legs, sometimes on all four as the situation warranted. She was getting close; she knew she was getting close, though she had yet to catch even the faintest scent of her elusive quarry.

She wasn’t particularly surprised. There was no wind down here in the ferns to spread a scent around; she would have had to stumble directly across the other’s path in order to smell it, and the way she was puffing and blowing she could have already crossed it any number of times and never noticed. She was a little disgusted with herself, but more for being out of shape than because she had an insensitive nose. Her physique was her own doing, but evolution had given her the nose. It had been a long time since the members of Wolruf’s race had made a living the hard way.

It was an amusing game nonetheless. Whatever she was tracking evidently enjoyed such games as well, for it kept leading her deeper and deeper into the forest, sometimes following beaten paths but just as often not, always letting her inch closer but never quite letting her catch up with it. Wolruf stopped and listened. It had been howling fairly regularly; if it continued its pattern she should hear it again soon.

Sure enough, there came its cry, the same one it had been using for nearly an hour now: Come and get me! Wolruf tilted her head back to answer, but a sudden idea stopped her. She had been playing its game long enough; maybe it was time to switch roles.

She looked around for a tree she could climb and found one draped in vines with a convenient horizontal branch a couple dozen meters overhead. It was even in the direction she’d been moving. Good. She trotted toward it, but didn’t stop. She continued beyond it for a good way, then looped around wide and rejoined her own trail maybe a thousand meters behind the spot where she’d stopped. Following her own scent now, she moved quickly along her trail, careful not to deviate from it and leave two tracks to warn her prey of her intentions.

As she passed beneath the limbs of the tree just before the one she had picked to climb, she took one of its dangling vines and gave it an experimental tug. It stretched a little under her weight, but otherwise it seemed solid enough. Hah. It might offer possibilities. She carried it with her to the other tree, used the vines there to help her climb up its trunk until she stood on the first large branch over the trail. She pulled the vine taut, then paid it back out until she held it a meter or so above the place she had been able to reach from the ground. Then she settled back against the trunk to wait.

There were more insects living higher up in the forest, she discovered. She resisted the urge to slap at them. Ignoring insects and itches was part of the waiting game.

All the same, she hoped her quarry was a better tracker than she was. She didn’t want to stay up in this tree any longer than she had to.

Just when she had almost decided to give away her position with a good long howl, she caught a hint of motion on the path. Here it came! She waited, breath held, while a large gray-and-black-furred creature stepped into view. It was bigger than Wolruf, with a longer, shaggier tail, wider ears, longer face, and smaller eyes set farther apart. A sort of intelligence glimmered there, but as Wolruf took note of the stiff paws on all four feet and the creature’s comfortable quadrupedal stance, she knew that it was not the sort of intelligence with which she could discuss multi-dimensional navigation. She felt a moment of disappointment, but it passed with the realization that, sapient or no, the animal was more than her match in hunting skills. This must be a wolf, she decided. Derec had described them to her once when she’d asked him if her name meant anything in his language.

Derec had also told her a few scare stories about wolves. Wolruf wondered if jumping out and shouting “Boo!” at one was such a wise idea, but upon sober consideration she realized she didn’t have many other options. She didn’t think the wolf would pass beneath her tree without noticing that she had climbed up it, and even though she didn’t think it could climb up after her, she didn’t like the idea of being treed, either. Nor did she think she could outrun it all the way back to the Compass Tower, if it came to a chase. Her only option lay in impressing it enough that it considered her an equal, or maybe even scaring it away.