Allison stared at him as if expecting him to cringe. Calhoun did not. Allison showed every sign of being an important man who expected his importance to be recognized and catered to. When Calhoun stirred impatiently he got into the car and growled a little. Calhoun took his place. The ground-car hummed. It rose on the six columns of air which took the place of wheels and slid across the field of dark-green plants, leaving the parachute deflated across a number of rows, and a trail of crushed-down plants where it had moved. It reached the highway again. Calhoun ran the car up on the highway's shoulder, and then suddenly checked. He'd noticed something. He stopped the car and got out. Where the ploughed field ended, and before the coated surface of the highway began, there was a space where on another world one would expect to see green grass. On this planet grass did not grow; but there would normally be some sort of self-planted vegetation where there was soil and sunshine and moisture. There had been such vegetation here, but now there was only a thin, repellent mass of slimy and decaying foliage. Calhoun bent down to it. It had a sour, faintly astringent smell of decay. These were the ground-cover plants of Maya of which Calhoun had read. They had motile stems, leaves and flowers, and they had cannibalistic tendencies. They were the local weeds which made it impossible to grow grain for human use upon this world. And they were dead. Calhoun straightened up and returned to the car. Plants like this were wilted at the base of the spaceport building, and on another place where there should have been sward. Calhoun had seen a large dead member of the genus in a florist's, that had been growing in a cage before it died. There was a singular coincidence here: humans ran away from something, and something caused the death of a particular genus of cannibal weeds. It did not exactly add up to anything in particular, and certainly wasn't evidence for anything at all. But Calhoun drove on in a vaguely puzzled mood. The germ of a guess was forming in his mind. He couldn't pretend to himself that it was likely, but it was surely no more unlikely than most of a million human beings abandoning their homes at a moment's notice. III They came to the turnoff for a town called Tenochitlan, some forty miles from Maya City. Calhoun swung off the highway to go through it.