Stroyansky chuckled. Then he barked like a seal. "The success of the expedition is more important than the fate of four men. Theoretically, anyway. But if I were in your shoes, and I'm glad I'm not, I would do the same. So, good luck, Lane."

"Thanks," said Lane. "I'll need more than luck. I'll also need God's help. I suppose He's here, even if the place does look God forsaken."

He looked through the transparent double plastic walls of the dome.

"The wind's blowing about twenty-five miles an hour. The dust is covering the tractor tracks. I have to get going before they're covered up entirely. My supplies are all packed; I've enough food, air, and water to last me six days. It makes a big package, the air tanks and the sleeping tent bulk large. It's over a hundred Earth pounds, but here only about forty. I'm also taking a rope, a knife, a pickax, a flare pistol, half a dozen flares. And a walkie-talkie.

"It should take me two days to walk the thirty miles to the spot where the tracs last reported. Two days to look around. Two days to get back."

"You be back in five days!" shouted Stroyansky. "That's an order! It shouldn't take you more than one day to scout around. Don't take chances. Five days!"

And then, in a softer voice, "Good luck, and, if there is a God, may He help you!"

Lane tried to think of things to say, things that might perhaps go down with the Doctor Livingstone, I presume, category. But all he could say was, "So long."

Twenty minutes later, he closed behind him the door to the dome's pressure lock. He strapped on the towering pack and began to walk. But when he was about fifty yards from the base, he felt compelled to turn around for one long look at what he might never see again. There, on the yellow-red felsite plain, stood the pressurized bubble that was to have been the home of the five men for a year. Nearby squatted the glider that had brought them down, its enormous wings spreading far, its skids covered with the forever-blowing dust.

Straight ahead of him was the rocket, standing on its fins, pointing toward the blue-black sky, glittering in the Martian sun, shining with promise of power, escape from Mars, and return to the orbital ship. It had come down to the surface of Mars on the back of the glider in a hundred-and-twenty-mile an hour landing. After it had dropped the two six-ton caterpillar tractors it carried, it had been pulled off the glider and tilted on end by winches pulled by those very tractors. Now it waited for him and for the other four men.

"I'll be back," he murmured to it. "And if I have to, I'll take you up by myself."

He began to walk, following the broad double tracks left by the tank. The tracks were faint, for they were two days old, and the blowing silicate dust had almost filled them. The tracks made by the first tank, which had left three days ago, were completely hidden.

The trail led northwest. It left the three-mile wide plain between two hills of naked rock and entered the quarter-mile corridor between two rows of vegetation. The rows ran straight and parallel from horizon to horizon, for miles behind him and miles ahead.

Lane, on the ground and close to one row, saw it for what it was. Its foundation was an endless three-foot high tube, most of whose bulk, like an iceberg's, lay buried in the ground. The curving sides were covered with blue-green lichenoids that grew on every rock or projection. From the spine of the tube, separated at regular intervals, grew the trunks of plants. The trunks were smooth shiny blue-green pillars two feet thick and six feet high. Out of their tops spread radially many pencil-thin branches, like bats' fingers. Between the fingers stretched a blue-green membrane, the single tremendous leaf of the umbrella tree.

When Lane had first seen them from the glider as it hurtled over them, he had thought they looked like an army of giant hands uplifted to catch the sun. Giant they were, for each rib-supported leaf measured fifty feet across. And hands they were, hands to beg for and catch the rare gold of the tiny sun. During the day, the ribs on the side nearest the moving sun dipped toward the ground, and the furthest ribs tilted upward. Obviously, the daylong maneuver was designed to expose the complete area of the membrane to the light, to allow not an inch to remain in shadow.

It was to be expected that strange forms of plant life would be found here. But structures built by animal life were not expected. Especially when they were so large and covered an eighth of the planet.

These structures were the tubes from which rose the trunks of the umbrella trees. Lane had tried to drill through the rocklike side of the tube. So hard was it, it had blunted one drill and had done a second no good before he had chipped off a small piece. Contented for the moment with that, he had taken it to the dome, there to examine it under a microscope. After an amazed look, he had whistled. Embedded in the cement-like mass were plant cells. Some were partially destroyed; some, whole.

Further tests had shown him that the substance was composed of cellulose, a lignin-like stuff, various nucleic acids, and unknown materials.

He had reported his discovery and also his conjecture to the orbital ship. Some form of animal life had, at some time, chewed up and partially digested wood and then had regurgitated it as a cement. The tubes had been fashioned from the cement.

The following day he intended to go back to the tube and blast a hole in it. But two of the men had set out in a tractor on a field exploration. Lane, as radio operator for that day, had stayed in the dome. He was to keep in contact with the two, who were to report to him every fifteen minutes.

The tank had been gone about two hours and must have been about thirty miles away, when it had failed to report. Two hours later, the other tank, carrying two men, had followed the prints of the first party. They had gone about thirty miles from base and were maintaining continuous radio contact with Lane.

"There's a slight obstacle ahead," Greenberg had said. "It's a tube coming out at right angles from the one we've been paralleling. It has no plants growing from it. Not much of a rise, not much of a drop on the other side, either. We'll make it easy."

Then he had yelled.

That was all.

Now, the day after, Lane was on foot, following the fading trail. Behind him lay the base camp, close to the junction of the two canali known as Avernus and Tartarus. He was between two of the rows of vegetation which formed Tartarus, and he was traveling northeastward, toward the Sirenum Mare, the so-called Siren Sea. The Mare, he supposed, would be a much broader group of tree-bearing tubes.

He walked steadily while the sun rose higher and the air grew warmer. He had long ago turned off his suit-heater. This was summer and close to the equator. At noon the temperature would be around seventy degrees Fahrenheit.

But at dusk, when the temperature had plunged through the dry air to zero, Lane was in his sleeping tent. It looked like a cocoon, being sausage-shaped and not much larger than his body. It was inflated so he could remove his helmet and breathe while he warmed himself from the battery-operated heater and ate and drank. The tent was also very flexible; it changed its cocoon shape to a triangle while Lane sat on a folding chair from which hung a plastic bag and did that which every man must do.

During the daytime he did not have to enter the sleeping tent for this. His suit was ingeniously contrived so he could unflap the rear section and expose the necessary area without losing air or pressure from the rest of his suit. Naturally, there was no thought of tempting the teeth of the Martian night. Sixty seconds at midnight were enough to get a severe frostbite where one sat down.