The boy's mouth worked but no sound emerged; he licked cracked lips, and managed to say: "Rees."

"All right. I'm Pallis. I'm the tree-pilot. Do you know what that means?"

"I… Yes."

"By the Bones, you're dry, aren't you? No wonder you stole that water. You did, didn't you? And the food?"

The boy nodded hesitantly. "I'm sorry. I'll pay you back—"

"When? After you return to the Belt?"

The boy shook his head, a glint in his eye. "No. I'm not going back."

Pallis bunched his fists and rested them on his hips. "Listen to me. You'll have to go back. You'll be allowed to stay on the Raft until the next supply tree; but then you'll be shipped back. You'll have to work your passage, I expect. All right?"

Rees shook his head again, his face a mask of determination.

Pallis studied the young miner, an unwelcome sympathy growing inside him. "You're still hungry, aren't you? And thirsty, I'll bet. Come on. I keep my — and Gover's — rations at the trunk."

He led the boy across the tree surface. Surreptitiously he watched as the boy half-walked across the foliated platform, his feet seeking out the points of good purchase and then lodging in the foliage, so allowing him to "stand" on the tree. The contrast with Gover's clumsy stumbling was marked. Pallis found himself wondering what kind of woodsman the lad would make…

After a dozen yards they disturbed a spray of skitters; the little creatures whirled up into Rees's face and he stepped back, startled. Pallis laughed. "Don't worry. Skitters are harmless. They are the seeds from which the tree grows…"

Rees nodded. "I guessed that."

Pallis arched an eyebrow. "You did?"

"Yes. You can see the shape's the same; it's just a difference of scale."

Pallis listened in surprised silence to the serious, parched voice.

They reached the trunk. Rees stood before the tall cylinder and ran his fingers over the gnarled wood. Pallis hid a smile. "Put your ear against the wood. Go on."

Rees did so with a look of puzzlement — which evolved into an almost comic delight.

"That's the bole turning, inside the trunk. You see, the tree is alive, right to its core."

Rees's eyes were wide.

Now Pallis smiled openly. "But I suspect you won't be alive much longer if you don't eat and drink. Here…"

After letting the boy sleep for a quarter-shift Pallis put him to work. Soon Rees was bent over a fire bowl, scraping ash and soot from the iron with shaped blades of wood. Pallis found that his work was fast and complete, supervised or unsupervised. Once again Gover suffered by comparison… and by the looks he shot at Rees, Pallis suspected Gover knew it.

After half a shift Pallis brought Rees a globe of water. "Here; you deserve a break."

Rees squatted back among the foliage, flexing stiff hands. His face was muddy with sweat and soot and he sucked gratefully at the drink. On an impulse Pallis said, "These bowls hold fire. Maybe you guessed that. Do you understand how they're used?"

Rees shook his head, interest illuminating his tired face.

Pallis described the simple sensorium of the tree. The tree was essentially a huge propeller. The great vegetable reacted to two basic forms of stimuli — gravity fields and light — and in their uncultivated state great forests of trees of all sizes and ages would drift through the clouds of the Nebula, their leaves and branchlets trapping starlight, the nourishment of drifting plants and animals, the moisture of fat rain clouds.

Rees listened, nodding seriously. "So by rotating faster — or slower — the tree pushes at the air and can climb away from gravity wells or towards the light."

"That's right. The art of the pilot is to generate a blanket of smoke to hide the light, and so to guide the flight of the tree.»

Rees frowned, his eyes distant. "But what I don't understand is how the tree can change its rotation speed."

Once again Pallis was surprised. "You ask good questions," he said slowly. "I'll try to explain. The trunk is a hollow cylinder; it contains another, solid cylinder called the bole, which is suspended in a vacuum chamber. The trunk and the rest of the tree are made of a light, fine-fibred wood; but the bole is a mass of much denser material, and the vacuum chamber is crisscrossed with struts and ribs to keep it from collapsing. And the bole spins in its chamber; muscle-like fibres keep it whirling faster than a skitter.

"Now — when the tree wants to speed its rotation it slows the bole a little, and the spin of the bole is transferred to the tree. And when the tree wants to slow it is as if it pours some of its spin back into the bole," He struggled for phrases to make it clearer; dim, half-understood fragments from Scientists' lectures drifted through his mind: moments of inertia, conservation of angular momentum…

He gave up with a shrug. "Well, that's about the best I can explain it. Do you understand?"

Rees nodded. "I think so." He looked oddly pleased with Pallis's answer; it was a look that reminded the pilot of the Scientists he had worked with, a look of pleasure at finding out how things work.

Gover, from the rim of the tree, watched them sullenly.

Pallis stepped slowly back to his station at the trunk. How much education did the average miner get, he wondered. He doubted Rees was even literate. As soon as a child was strong enough he was no doubt forced into the foundry or down to the crushing surface of the iron star, to begin a life of muscle-sapping toil…

And he was forced there by the economics of the Nebula, he reminded himself harshly; economics which he — Pallis — helped to keep in place.

He shook his head, troubled. Pallis had never accepted the theory, common on the Raft, that the miners were a species of subhuman, fit only for the toil they endured. What was the life span of the miners? Thirty thousand shifts? Less, maybe? Would Rees live long enough to learn what angular momentum was? What a fine woodsman he would make… or, he admitted ruefully, maybe a better Scientist.

A vague plan began to form in his mind.

Rees came to the trunk and collected his shift-end rations. The young miner peered absently around at the empty sky. As the tree climbed up towards the Raft, away from the Core and towards the edge of the Nebula, the air was perceptibly brightening.

A distant sound carried over the sigh of the wind through the branches: a discordant shout, huge and mysterious.

Rees looked questioningly at Pallis. The tree-pilot smiled. "That's the song of a whale." Rees looked about eagerly, but Pallis warned, "I wouldn't bother. The beast could be miles away…" The pilot watched Rees thoughtfully. "Rees, something you haven't told me yet. You're a stowaway, right? But you can't have any real idea what the Raft is like. So… why did you do it? What were you running from?"

Rees's brow creased as he considered the question. "I wasn't running from anything, pilot. The mine is a tough place, but it was my home. No. I left to find the answer.»

"The answer? To what?"

"To why the Nebula is dying." Pallis studied the serious young miner and felt a chill settle on his spine.

Rees woke from a comfortable sleep in his nest of

foliage. Pallis hung over him, silhouetted by a

bright sky. "Shift change," the pilot said briskly.

"Hard work ahead for all of us: docking and

unloading and—"

"Docking?" Rees shook his head clear of sleep.

"Then we've arrived?"

Pallis grinned. "Well, isn't that obvious?"

He moved aside. Behind him the Raft hung huge

in the sky.