When was the last time she had eaten? It was all she could do not to cram the strange food into her own mouth.

She pulled three of the food pads out of the bowl, then covered over the bowl and stowed it away in its cupboard, desperate that the heavily scented photons which seeped from the food shouldn't wake up Farr.

She held a pad to Adda's lips. "Eat," she ordered.

"City man's pap," he grumbled; but, feebly, he bit into the pad and chewed at it.

"There's nothing wrong with it," she whispered as she fed him. "It's just food."

"And it's good for you," Toba Mixxax called in a loud whisper, turning in his seat to watch. "It's better for your health than meat, in fact. And..."

"But what is it?" Dura asked.

"Why, it's bread, of course," he said. "Made from wheat. From my ceiling-farm. What did you think it was?"

"Ignore him," Adda rasped. "And don't give him the satisfaction of asking what wheat is. I can see you want to."

"You can't see any damn thing," she said absently. She paused. "Well, what is wheat, anyway?"

"Cultivated grass," Toba said. "The stuff which grows wild in the forest is good enough for Air-pigs, but it wouldn't keep you or me alive long. But wheat is a special type of grass, a strain which needs to be tended and protected — but which contains enough proton-rich compounds from the Crust to feed people."

"On pap," Adda growled.

"Not pap. Bread," Mixxax said patiently.

Dura frowned. "I don't think I understand. Air-pigs eat grass and we eat pigs. That's the way things work. What's wrong with that?"

Mixxax shrugged. "Nothing, if you don't have the choice. And if you want to spend your life chasing around forests in search of pigs. But the fact is, per cubic micron of Crust root ceiling, you can get more food value out of wheat than grazing pigs. And it's economically more efficient in terms of labor to run wheat ceiling-farms rather than pig farms." He laughed, with infuriating kindness. "Or to hunt wild pigs, as you people do. After all, wheat stays in one place. It doesn't jetfart around the forest, or attack old men." He looked sly. "Anyway, there are some things you won't get except from cultivated crops. Beercake, for instance..."

"Efficient, "Adda hissed. "That was one of the words they used when they drove us away from the Pole."

Dura frowned. "Who drove us away?"

"The authorities in Parz," he said, his sightless eyes leaking disconcertingly. "I'm talking of a time ten generations ago, Dura... We don't talk of these things any more. The princelings, the priests, the Wheelwrights. Drove us away from the thick, warm Air of the Pole and out into the deserts upflux. Drove us out for our faith, because we looked to a higher authority than them. Because we wouldn't work on their ceiling-farms; we wouldn't accept slavery. Because we wouldn't be efficient."