Farr frowned. Reluctantly he released the branch and pushed himself away. “You were? But I feel as if — as if I’m about to be pulled out of this tree…”

“It’s called being frightened of falling.”

“But that’s ridiculous. Isn’t it?” To Farr, “falling” meant losing your grip on the Magfield when Waving. It was always over in a few mansheights at the most — the tiny resistance of the Air and the currents induced in your skin soon slowed you down. Nothing to fear. And then you could just Wave your way around the Magfield to where you wanted to get to.

Dura grinned. “It’s a feeling as if…” She hesitated. “…as if you could let go of this tree, right now, and not be able to stop yourself sliding down, across the Magfield and across the vortex lines, faster and faster, all the way to the Sea. And your belly clenches up at the prospect.”

“That’s exactly it,” he said, wondering at how precise her description was. “What does it mean? Why should we feel like that?”

She shrugged, plucking at a leaf. The heavy plate of flesh came free of its attaching branch with a sucking sound. “I don’t know. Logue used to say it’s something deep inside us. An instinct we carried with us, when humans were brought to this Star.”

Farr thought about that. “Something to do with the Xeelee.”

“Perhaps. Or something even older. In any event, it’s not something you need to worry about. Here.” She held out the leaf toward him.

He took it from her cautiously. It was a bronze-gold plate, streaked radially with purple and blue, about as wide as a man’s hand. It was thick and pulpy — springy between his fingers — and, like the wood, was warm to the touch, although, away from its parent branch, it seemed to be cooling rapidly. He turned it over, prodding it with a fingertip; its underside was dry, almost black. He looked up at Dura. “Thanks,” he said. “What shall I do with it?”

She laughed. “Try eating it.”

After a cautious inspection of her face to make sure this wasn’t some kind of joke — Dura didn’t usually play tricks on him; she was a little too serious for that… but you never knew — Farr lifted the leaf to his lips and bit into it. The flesh of the leaf was thin, surprisingly insubstantial, and it seemed to melt against his tongue; but the taste it delivered was astonishingly sweet, like the meat of the youngest Air-piglet, and Farr found himself cramming his mouth.

Within seconds he was swallowing the last of the leaf, savoring the lingering flavor on his tongue. It had been delicious but really quite light, and had done little but whet his hunger further. He looked around avidly. Here on the upper side of the treetop ceiling he could see the leaves turned downward toward the Quantum Sea, like a layer of broad, flattened child-faces. Farr reached down to pluck another leaf.

Dura, laughing, restrained him. “Take it easy. Don’t strip the whole damn tree.”

Around a full mouth Farr said, “It’s delicious.”

She nodded. “I know. But it won’t fill your belly. Not unless you really do strip the tree… That’s why we have to hunt the Air-pigs, who eat the leaves — and the grass — for us.” She pursed her lips. Then, in a tone suddenly and, to Farr, shockingly similar to their lost father’s, she said, “Let’s have a little lesson. Why do you think the leaves are so tasty?”

Farr thought about that. “Because they’re full of protons.”

Dura nodded seriously. “Near enough. Actually they are laced with proton-rich isotopes — of krypton, strontium, zirconium, molybdenum… even a little heavy iron. Each nucleus of krypton, for instance, has a hundred and eighteen protons, while the tin nuclei of our bodies have just fifty each. And our bodies need protons for their fuel.” The heavy nuclei fissioned in human stomachs. Protons combined with neutrons from the Air to make more tin nuclei — tin was the most stable nucleus in the Air — and gave off energy in the process. “Now. Where does the proton-rich material come from?”

“From the Crust.” He smiled. “Everyone knows that.”

The Crust, no more substantial than Air, was a gossamer solid. Its outermost layer was composed of iron nuclei. Further in, steepening pressures drove neutrons into the nuclei of the solid, forming increasingly heavy isotopes… until the nuclei became so soft that their proton distributions began to overlap, and the neutrons dripped out to form the Air, a superfluid of neutrons.

“All right,” said Dura. “So how do the isotopes get all the way from the Crust to these leaves?”

“That’s easy,” Farr said, reaching to pluck another succulent leaf. “The tree pulls them down, inside its trunk.”

“Using veins filled with Air. Right.”

Farr frowned, feeling his cheeks bulge around the leaf. “But why? What’s in it for the tree?”

Dura’s mouth opened and closed, and then she smiled, her eyes half-closed. “That’s a good question,” she said. “One I wouldn’t have thought of at your age… The isotopes make the leaves more opaque to the neutrinos shining out of the Quantum Sea.”

Farr nodded, chewing.

A flood of neutrinos, intangible and invisible, shone continually from the Sea — or perhaps from the mysterious Core deep beneath the Sea itself — and sleeted through the vortex lines, through the bodies of Farr and the other humans as if they were ghosts, and through the Crust to space. The trees turned slightly neutrino-opaque leaves to that unseen light, absorbing its energy and turning it into more leaves, branches, trunk. Farr pictured trees all over the interior of the Crust, straining toward the Sealight with their leaves of krypton, strontium and molybdenum.

Dura watched him eat for a moment; then, hesitantly, she reached out to ruffle his hair-tubes. “I’ll tell you a secret,” she said.

“What?”

“I’m glad you’re here.”

Briefly he considered pushing her hand away, of saying something funny, or cruel, to break up the embarrassing moment. But something made him hold back. He studied her face. It was a strong face, he supposed, square and symmetrical, with small, piercing eyes and shining yellow nostrils. Not beautiful, but with something of the strength of their father; and now with the first lines of age it was acquiring a bit more depth.

But there was uncertainty in that face. Loneliness. Indecision, a need for comfort.

Farr thought about it. He felt safe with Dura. Not as safe as when Logue was alive… But, he thought ruefully, as safe as he would ever feel again. Dura wasn’t really all that strong, but she did her best.

And this moment, as the others moved away from them, being together and talking quietly and tasting the leaves, seemed to be important to her. So he said, gruffly: “Yes. Me too.”

She smiled at him, then bent to pluck a leaf for herself.

Adda slid silently through the treetops, following the circumference of a rough circle twenty mansheights wide. Then he moved a little further up into the suspended forest, working parallel to the lines of the trunks. The trees grew along the Magfield flux lines, and he kept his spear pointing along the Magfield as he worked his way along the smooth bark.

Save for the low, tinkling rustle of the leaves, the subdued talk of his companions, he found only silence.

He pulled himself back along the length of the tree trunk to the inverted canopy of leaves. None of the Human Beings — except, maybe, Logue’s boy Farr, who was looking a little lost — had even noticed he’d been absent. Adda relaxed a little, munching on the thin, deceptively tasty meat of a leaf. But he kept his good eye wide open.

The Human Beings were bunched together around one trunk, nibbling leaves desultorily and clinging, one-handed, to branchlets. They were huddled together for warmth. Here, where the Air was attenuated by height, it was cold and hard to breathe: so hard, in fact, that Adda felt his reflexes — his very thinking — slowing down, turning sluggish. And it wasn’t as if he had a lot of margin in that area, he reflected. It was as if the very Air which drove his bones was turning to a thin, sour soup.