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The tree named Yggdrasil plunged toward the heart of the galaxy at very nearly the speed of light, safe within a cone of shadow from a sleet of radiation that otherwise would have charred it to ash in microseconds.

It still clutched the remains of a comet in its roots, so water was not yet a problem. But light and gravity were strangely wrong, interfering with its tropisms.

Yggdrasil was a very confused tree.

Ahead, always, was a funnel of dancing sparks. Behind was a terribly bright light. Yggdrasil's senses told it that it was in the terrifying grip of a one-g gravitational field that was tugging it toward that unnatural sun. It had been trying for twenty years to escape. But when it tried to turn the reflective surfaces of its leaves toward the perpendicular, something always frustrated it.

Yet, wonder of wonders, Yggdrasil never fell. An equal and opposite force applied to a small region of its central trunk prevented that. Yggdrasil knew in its vegetable fashion that a girdle of foreign substance encircled its waist, but its senses were not adequate to tell it about the tether and the gargantuan turnbuckle that anchored the girdle.

A strange thing had happened to the stars as well. They swarmed around the tree in rainbow hoops of color -- violet, then blues, greens, and yellows ahead; orange and progressively darker reds behind. Both ahead and behind, blind disks had blossomed as the stars marched in both directions through the spectrum and disappeared. The rearward blind spot was larger. Over the years it had kept. expanding, compressing the rainbow hoops and pushing them forward until now they circled the coruscating funnelof sparks like concentric halos.

Scores of times Yggdrasil had tried to pick a yellow target star, only to have it change colors and vanish from the universe.

Only the odd pursuing sun had not dopplered through the spectrum. It remained fixed in color and distance, seeming to grow ever brighter against the expanding dark region behind it.

Fretting, Yggdrasil tried to concentrate on growing one of its branches. Its crown -- since it had been prevented from spinning-- was no longer perfectly symmetrical, and this was a branch that needed to catch up. Fortunately, the direction of the tug of gravity was always a guide. Growth, Yggdrasil knew in its simple wisdom, was supposed to be perpendicular.

There was commensal life within the cavities of the errant branch, but it was too insignificant to be noticed. Yggdrasil ignored it. The only verities were light, gravitation, and water.

"I think Yggdrasil needs a tranquilizer again," the tree systems officer said. "It's starting to show signs of trauma."

Bram set down the carton of housewares he had been packing and turned to face her. "Are you sure?" he said.

"I'm afraid so, Captain," she said. "The monitors indicate enzymatic reactions in the heartwood, and gallic acid's showing in the contents of the parenchymal cells."

Mim, coming through into the observation veranda with another armload of empty cartons, heard the exchange, "Oh, no!" she exclaimed. "Right in the middle of moving week!"

Bram shot her an affectionate glance. Mim was well past middle age now-- the mirror showed fewer gray hairs every day -- but her handsome face still preserved some of the lines it had acquired during their four decades together. To Bram's way of thinking, the lines gave her a strength of character and a beauty that he had come to love; it was hard to imagine Mim without them, but youthing was inevitable, and he supposed he would have to get used to it.

"Have you tried readjusting the auxin balance?" Bram said.

The tree systems officer looked worried. "We're close to the limit on that, Captain," she said. "Any more might be dangerous. Yggdrasil knows it's edge-on to something that looks like a sun to it and that half of its crown's in shadow. We can only deceive it so far, then the separate deceptions start to contradict each other. Too many auxins on the lit side, and we could have a very sick tree."

She waited diffidently for his response. The tree systems officer was a grandchild of Jao and Ang, and like many of her contemporaries she tended to treat Bram like a monument. She had not even been born yet when he had begun the immortality project. But Bram knew that she was a first-rate botanist, and he trusted her judgment.

Bram sighed. "All right. I suppose we'd better keep Yggdrasil tranquilized at least through moving week. We can't afford a delay. The branch we're living in is getting a bit bosky. And we're already ten degrees out of plumb." His eyes crinkled humorously. "Besides, we'd have a mutiny on our hands if we held up Bobbing Day."

"Very good, Captain," she said without cracking a smile. She turned smartly on her heel and left.

Bram watched her go. She had made him feel old and hoary. There was no reason for it, he told himself. His apparent age was down to somewhere in the midforties by now. But his body still carried the memory of being much older, and it showed sometimes in the way he moved and in the habit of protective postures. That, too, would pass with time, Bram supposed.

"The new ones are so earnest," Mim said, reading his thoughts.

"I just wish they wouldn't call me 'Captain' all the time."

She laughed. "But you are captain this year. And you've been elected seven times. That's more than anybody."

"It's only ancestor worship," he said. "Exaggerated respect for all the old father figures. And mother figures," he added hastily.

"Then why was Jao elected only once?" she teased him.

"And never again -- I know, it was a disaster! Jao's the first one to tell you that himself."

"Jao never wanted to be captain in the first place. I sometimes suspect he sabotaged his first term on purpose so they'd never ask him again. But pity poor Smeth. He keeps campaigning, and he hasn't been elected once yet."

"Save your pity. Give him time. He has the next five hundred years to round up the votes. I'll bet that by the time we get to the Milky Way, he'll hold the record for being elected the most often. Because by then he'll be the only one who wants the job."

She giggled appreciatively, though she never would have hurt Smeth's feelings by doing it in his presence.

"And when you remember how he kept telling everybody that he had no intention of coming with us -- that he wouldn't trust his life to an overgrown plant and a jerry-built ramscoop drive!"

Smeth had been a surprise to both of them. Bram had been sure that Smeth would stay behind. By the time the probe project had reached fruition, Smeth had accreted a huge department, with more than a hundred humans beneath him. He had attached himself like glue to the Nar organizational superstructure, and the Nar, thinking they were stepping softly on human sensibilities, funneled everything through him, snowballing his authority. He had nothing to gain by deserting the new egalitarian society that human immortality had brought about. With eternity ahead of him, he had nowhere to go but up.

But when the day had come to board Yggdrasil or be left behind, Smeth had showed up at the shuttleport with a small bag of personal belongings and a string of six biosynthetic walkers, led by a Nar porter bearing his library, instruments, and accumulated records.

"I guess he decided that it was better to be a big floater in a small pool," Bram said.

"Or maybe he simply couldn't bear the idea of all of us leaving without him."

Bram nodded. "After he saw the stampede that developed."

Smeth had not been the only surprise. More than five thousand people had elected to go along on the genesis quest -- almost a third of the human race. The project had tapped a deep longing. The Nar had not underestimated the strength of the buried feelings unearthed in their pets. About ten years into the project, they had begun a program to gather all candidates from the farther worlds, and it had taken another twenty years to bring them all in. Those who had waited too long or who had changed their minds at the last minute had been out of luck.

"Well, I'm glad he decided to come along. It wouldn't be the same without him."

"Yes. I have to admit he's improving."

Mim fell silent. Bram knew she was thinking about Olan Byr. Immortality had come too late for Olan. The project had been a long, hard one, even with the blueprints of Original Man to work from and the full cooperation of the Nar. There had been times when Bram had thought that he himself would grow too old to benefit from it.

Mim had had fifty years to get over her grief for Olan. Forty of them had been spent with Bram. By the time they had drifted together, she had been too old for children. But her fertility had returned during the last few years, and lately she had been thinking about having a baby after she grew another ten or fifteen years younger. But only if tree demographics permitted, she was always quick to add whenever the subject came up. Yggdrasil could easily support another twenty thousand humans-- in fact, about five hundred babies had been born already. But everyone was aware that a long trip lay ahead of them.

Bram reached for her hand, and they exchanged smiles. "Go ahead," she said. "I'll finish the packing. You'd better see to Yggdrasil's tranquilizer. If the drinks get sloshed over the rims of all the glasses on All-Level Eve, Marg will have a fit."

"Life would certainly be simpler," he said, "if we didn't have to rotate our environment thirty degrees every year to keep Yggdrasil from getting lopsided."

She squeezed his hand. "But it wouldn't be half as much fun," she said.

It was an hour's ride to the trunk even by slingshot, but Bram always enjoyed the view. There was no real reason to make the trip -- the tree systems staff was fully competent and, in fact, knew more about the operation of the tree than he did -- but the approaching tree-turning maneuver made a good excuse for the excursion.

He reeled in an empty travelpod, eased it through the lips of the gasket, and clambered inside. The absurdly simple arrangement made the expense of air locks for the external travel system unnecessary; otherwise, twelve air locks would have had been installed. The main rack of cables, like an abacus one hundred fifty miles long, was anchored at a new terminus every year, thirty degrees farther along the rim of the tree's crown, leaving a couple of permanent cables behind for standby access to the abandoned branch.

So far, the only major internal fast-transit system was limited to one branch -- the one the human population would be living in during the half millennium when they were coasting between galaxies, and Yggdrasil could be allowed to have its normal one-g spin again. But that was one hundred and twenty degrees away at the moment, its halls and compartments standing on their heads, its pools drained, and everything important either moved or lashed down.

Bram took a moment to check out the pod's systems. Nothing could go wrong, of course; there was an FM rescue beeper in every pod that would quickly summon help in an emergency. But for someone serving as year-captain, it would be embarrassing to be stranded halfway along the guide rope and have someone come to fetch him.

He made sure the air bladder carried enough reserve for the hour's trip and that the emergency bottle under the seat was full. He squinted through the hyaloid membrane of the docking chamber's blister and sighted upward along the elastic cable. The several hundred feet of it that he could see before it came invisible against the distant trunk were reassuringly opaque, indicating that the molecular structure was in a mostly crystalline state.

He grinned as he prepared to change that. He got the little bottle of boron trifluoride out of the dashboard and applied a few drops with an eyedropper to the elastomer line, just forward of the bowline knot that hitched it to an interior stanchion.

The pod gave a shudder as the line began to contract. Bram could see the triggered section turning transparent as its molecular structure became amorphous. The transparent portion shot outward, erasing the cable from sight. A few minutes later, when enough miles of cable had been triggered to overcome the one-g force stretching the line, the pod picked up speed, burst through the gasket, and flew up the guideline toward Yggdrasil's distant trunk.

Bram held on. He was glad the process wasn't instantaneous. He wouldn't have fancied a snapped neck. There was a lot of energy stored in a hundred and fifty miles of superelastic line. As it was, the pod would accelerate at a comfortable rate, never passing two g's at its zenith, then slow to a bounce as the trailing cable began to tighten.

The organic elastomer, with a stretch ratio of over a thousand to one, was a by-product of the exodus research program and, by departure time, had already found wide industrial application on the Father World. The raw materials came from Yggdrasil itself -- derived from the adaptive mechanism by which a tree with a three-hundred-mile diameter synchronized the turgor movements of its leaves.

Bram gazed unabashedly through the transparent skin of his rubbery container and admired the outside view.

Straight up, of course, was a silhouette of Yggdrasil's trunk seen against the swirling blizzard of sparks created by the ramscoop field some hundreds of miles in front of the tree.

The silhouette was a short, thick bar, lacking detail. The shower of light was pretty -- even jolly -- but Bram knew that its beauty was a lie. It was the emblem of instant death -- the visible by-product of the inferno of radiation pouring into the probe's magnetic funnel. At more than ninety-nine percent of the speed of light, here in the thick of the galaxy where the H-II clouds were dense, some two hundred trillion hydrogen atoms slammed into every square inch of the electromagnetic shield every second. Even allowing for a gamma factor of twenty thousand -- the last figure Jao had given him-- that worked out to twenty billion high-energy collisions per second within the ship's relativistic time frame.

If that shield were to fail for even a fraction of a second at this velocity, five thousand humans would die before their nervous systems were able to register the fact. And Yggdrasil would turn to stardust.

Bram shuddered. As frightening as that umbrella of sparks was, at least it hid the nothingness beyond-- the blind spot where the crowded wavelengths of light pushed past the visible spectrum and wiped the stars from the universe. The blind spot behind, eerily framing the artificial sun of the fusion stage of the drive, was bad enough.

He let his eyes follow the long, mirror-bright shaft downward to where the fusion flames burned. The waste light had enough red in it for Yggdrasil to carry on photosynthesis, enough ultraviolet for human sunbathers to tan themselves by behind the lenticels of the recreation areas.

The long shaft threaded a dangerous course between Yggdrasil's twin domes. At its closest point it passed within forty miles of the trunk, and Yggdrasil itself had provided extra protection there -- growing a shield of adventitious leaves with their silvery reflective sides facing out. The star tree could handle anything up through x-rays.

The material part of the shaft was its least important aspect. In fact, its tremendous length could not have held up under even moderate lateral stress. It was there to provide support for the winding coils that deflected the roaring streams of ionized hydrogen in their constricted path from the collection area forward to the ignition cage aft.

For a moment Bram tried to imagine what the whole crazy travel arrangement would look like to a hypothetical observer outside the craft -- provided that the observer could see by undopplered light. Or, more to the point, provided that the observer was in the same relativistic frame, matching the spacecraft's course in velocity and direction. Otherwise, the collection of shapes on their long skewer would be foreshortened by a factor of twenty thousand, turning them into a stack of paper-thin disks pierced by a thumbtack.

He decided it would look like a post horn straddled by a leafy dumbbell.

Bram had seen a post horn once, at one of Olan Byr's memorial concerts. The ancient instruments, from lyres to sousaphones, had been part of Olan's legacy. He had been tireless in commissioning reproductions from hints in man's digitally transmitted art masterpieces, dictionary sketches, and clues in the musical notation itself. The post horn was based on one played by an angel in an Annunciation. It was a long, straight tube of brass, tall as the man who played it, with a flaring bell at one end and the smaller flare of a mouthpiece at the other.

Bram closed his eyes for a moment and savored the eccentric image.

The post horn that dragged Yggdrasil by the collar was twelve hundred miles long, with its slender tube aligned along g forces to keep it straight. The bell was an insubstantial net of superfilament, several hundred miles in diameter, that kept its shape by virtue of an independent spin at its rim. Around the bell was a multicolored cascade of sparks, like trumpet notes made visible. A miniature sun burned blindingly in a magnetic cage at the mouthpiece, like a divine breath. And from the flared mouthpiece issued a thin pencil of inspired light as the hadronic photons, their work done, decayed and wreaked havoc with whatever interstellar debris was still left behind in the wake of the probe's sweep.

Pleased with the image, he conjured up the other component of the queer hybrid vehicle.

Yggdrasil would make a compressed sort of dumbbell, he decided, with a short, thick handle and rather flattened hemispheres. More like a pair of fat wheels lying athwart the long axis of the probe. One hemisphere was silver with a green rim facing the fusion fire. The other was brown, laced through with the crystal sparkle of cometary ice and showing an arc of green where Yggdrasil's root system had decided to help out with the photosynthesis.

The looming reality of a wall of foliage rushing past him only a few miles away dissipated the image, and Bram turned his eyes to the view he loved best.

Between the rushing walls of Yggdrasil's twin hemispheres, a spectacular slice of sky was visible. A rainbow of stars made a dazzling arch across the void. Optical effects had crowded the bands of color so close together that the effect was like strands of matched jewels, jumbled together in overlapping profusion.

It was so beautiful that it hurt.

Bram studied the ribbon of stars. Was it narrower than the last time he had looked? It was hard to tell. But the yellow band seemed to have moved a degree forward, and the dull, ominous blanket of reds that faded into the blind spot seemed to have been dragged along by the rainbow hem.

A star whizzed by, changing from purple to blue to green, then to yellow, orange, and red before it was swallowed by the blind spot.

The star must have been very close -- only a few light-days away. At the present gamma, Yggdrasil swept across a light-year in about thirty minutes. That was fast enough to make the nearer stars move at a crawl, changing their colors as they lined up against the background rainbow.

A second violet star popped out of nothingness, riffled through the spectrum, and vanished to the rear.

The first star's companion! Yggdrasil was skirting a double star system.

Bram tried not to worry. Even here in the depths of the galaxy the stars were light-months apart. A collision would be most improbable, Jao had assured him. Even if Smeth's instruments were to show Yggdrasil heading straight toward a star emerging from a dust cloud, there would be minutes -- perhaps hours -- to change course. A lateral nudge of less than half a degree, projected over a minute or two of travel, would always give them margin to spare.

He drank in the glittering, spectacle again, wondering how much longer he would be able to enjoy it. As Yggdrasil's speed increased, eventually the stellar rainbow would shrink into a thin gold rim framing the forward blind spot, and the vortex of hydrogen influx would make it invisible from any part of the tree. He had tried to get a time estimate from Jao, but Jao had been vague. They were slicing the remainder of the speed of light so thin at this point, Jao said, that measurements were meaningless.

He looked up through the top of the pod and saw the trunk rushing toward him. A cluster of external housings was directly above: upside-down bubbles with suspended catwalks. Ten or twenty miles to his left, he saw a portion of the tremendous crystalline girdle that circled Yggdrasil's waist and the secondary tether that would keep Yggdrasil from sliding forward along the shaft during deceleration mode. The tether was of woven viral monofilament a half mile thick, and the double bowline knot that fastened it had been tied, with much tricky maneuvering, by a pair of space tugs. Tension would only make it stronger; with the enormous forces involved, nobody wanted to take chances with extraneous fittings.

Bram noticed that at the moment Yggdrasil was floating free within its circlet; its momentum was temporarily matched with that of the probe.

The trunk filled his view, and then the taffy pull of the counterline slowed the travelpod to a bobbing stop about a half mile below the entry blister.

Bram uttered a mild expletive as he found that the fist-size electric trolley that was supposed to wind him in the rest of the way was out of order.

For a moment he was tempted to exercise a year-captain's prerogatives and signal the hub to reel him in. But he was only a couple of hundred feet from his destination, and the pod's weight was negligible added to his own, even under one-g acceleration. A half hour's worth of muscle power would do it.

With a sigh, he bent to the two-handed windlass and began cranking.

"That ought to do it," Bram agreed.

He tore his gaze away from the massive helical housing of the high-capacity pump. There was a final gurgle that shook the floor as the last of a half million gallons of chemical solution was forced deep into Yggdrasil's sapwood.

The tree systems officer and her hovering assistant gave him bland stares. "I thought the best way to calm Yggdrasil down would be to smooth out the peaks and valleys in phytochrome balance," the TSO said with professional briskness. "There was too extreme a swing between the two pigment forms, and it was driving Yggdrasil crazy."

She gauged his expression for signs of comprehension, apparently decided in his favor, and went on. "You see, the problem is the growing Doppler shift. Unfortunately, all the far-red light comes from the same direction as the fusion light, so that side of the tree's overstimulated. The phytochrome keeps changing back and forth between the far-red-absorbing form and the sunlight-absorbing form, then back again."

Her assistant, even younger than she was, nodded agreement. They were both being patient with the old dodderer.

"Yes, yes," Bram said quickly. "I'm sure you took the right approach."

The assistant cleared his throat and glanced at his boss before speaking. "And at the same time, there's the problem of blue light tropisms at the opposite side of the tree. Where the band of up-shifted light is. Yggie's hormones are working overtime to cope. And you can imagine what that does to his biorhythms."

"I can understand why your department was so concerned," Bram told them in his best sober manner.

They both beamed at him.

"So we added a healthy dose of vitamin A to the tranquilizer to damp down beta-carotene activity," the assistant finished triumphantly.

"Fine," Bram said with a judicious nod. He looked around for a way to make his escape. "Well, that seems to take care of it, so I'll--"

"Of course, you'll want to review our total hormone strategy while you're here, Captain," Jao's granddaughter said. "Shall we start with the tree-turning maneuver?"

Bram gave in to the inevitable and let her lead him over to the far end of the hollow, where a battery of young technicians, wearing the leaf tabards that seemed to be the working costume of the new generation, busily tended the array of giant fermentation tanks where hormone synthesis started.

A half hour later, his eyes slightly glazed, Bram found himself blessedly alone in the brilliant corridor that ran through the trunk's heartwood. Alcoves branched off on either side, each with its neatly painted street sign. Here, forty miles beneath Yggdrasil's bark, a lot of specialized work went on -- plastics manufacturing using leaf sugars as feedstock, the Message broadcasting facility whose vital work could not be interrupted by yearly bough migrations, the central observatory.

There was also a recreation complex with guest suites, increasingly popular with the younger set and the advanced retroyouth crowd, with facilities for sports, swimming, and small-craft sailing. After Yggdrasil left the galaxy and acceleration ceased, it would be a center for such weightless pursuits as flying, flat-trajectory handball, three-dimensional ballet, and, Bram didn't doubt, free-fall sex.

Bram paused to look at the bulletin board. Some members of the trunk staff were choosing up sides for a game of teamball in what would eventually be the flydome. Bram was tempted to join them. But he knew that he'd be invited only through courtesy and deference to his position. At his present chronological age, he'd only be a liability to whatever team was willing to suffer him; better stick to playing with his peers on the occasional Tenday.

Feeling pleasurably sorry for himself -- refraining from reminding himself that he was not as old as he had been twenty years ago -- he gave the bulletin board a regretful last glance and set off down the long arcade toward the observatory.

At least that was one treat he could give himself.

Copyright © 1986 by Donald Moffitt