Putz's eyes brightened at the word. "Vater-vorks?" he echoed. "For vot?"
"For the canal, naturally. They have to build up a head of water to drive it through; that's obvious." He looked at the captain. "You told me yourself that to drive water from the polar caps of Mars to the equator was equivalent to forcing it up a twenty-mile hill, because Mars is flattened at the poles and bulges at the equator just like the earth."
"That's true," agreed Harrison.
"Well," resumed Jarvis, "this city was one of the relay stations to boost the flow. Their power plant was the only one of the giant buildings that seemed to serve any useful purpose, and that was worth seeing. I wish you'd seen it, Karl; you'll have to make what you can from our pictures. It's a sun-power plant!"
Harrison and Putz stared. "Sun-power!" grunted the captain. "That's primitive!" And the engineer added an emphatic "Ja!" of agreement.
"Not as primitive as all that," corrected Jarvis. "The sunlight focused on a queer cylinder in the center of a big concave mirror, and they drew an electric current from it. The juice worked the pumps."
"A t'ermocouple!" ejaculated Putz.
"That sounds reasonable; you can judge by the pictures. But the power-plant had some queer things about it. The queerest was that the machinery was tended, not by Tweel's people, but by some of the barrel-shaped creatures like the ones in Xanthus!" He gazed around at the faces of his auditors; there was no comment.
"Get it?" he resumed. At their silence, he proceeded, "I see you don't. Leroy figured it out, but whether rightly or wrongly, I don't know. He thinks that the barrels and Tweel's race have a reciprocal arrangement like—well, like bees and flowers on earth. The flowers give honey for the bees; the bees carry the pollen for the flowers. See? The barrels tend the works and Tweel's people build the canal system. The Xanthus city must have been a boosting station; that explains the mysterious machines I saw. And Leroy believes further that it isn't an intelligent arrangement—not on the part of the barrels, at least—but that it's been done for so many thousands of generations that it's become instinctive—a tropism—just like the actions of ants and bees. The creatures have been bred to it!"
"Nuts!" observed Harrison. "Let's hear you explain the reason for that big empty city, then."