house when the short days came and the snow blew across the
country like fine white sand. And he never complained about the lights or
the television or the hot water, except to grumble occasionally that they
were a little old and out of date and that the mail-order catalog showed
that better models were available in Vladivostok.

And Wang would remind the old man, very gently, that a paper-forest ranger
made only so much money, and that there would have to be more saving
before such things could be bought. He did not--_ever_--remind the old man
that he, Wang, was stretching a point to keep his grandfather on the
payroll as an assistant.

Wang Kulichenko patted his horse's rump and urged her softly to step up
her pace just a bit. He had a certain amount of territory to cover, and,
although he wanted to be careful in his checking, he also wanted to get
home early.

Around him, the neatly-planted forest of paper-trees spread knotty, alien
branches, trying to catch the rays of the winter-waning sun. Whenever Wang
thought of his grandfather's remarks about his ancestors, he always
wondered, as a corollary, what those same ancestors would have thought
about a forest growing up here, where no forest like this one had ever
grown before.

They were called paper-trees because the bulk of their pulp was used to
make paper (they were of no use whatever as lumber), but they weren't
trees, really, and the organic chemicals that were leached from them
during the pulping process were of far more value than the paper pulp.

They were mutations of a smaller plant that had been found in the
temperate regions of Mars and purposely changed genetically to grow on the
Siberian tundra, where the conditions were similar to, but superior to,
their natural habitat. They looked as though someone had managed to cross
breed the Joshua tree with the cypress and then persuaded the result to
grow grass instead of leaves.

In the distance, Wang heard the whining of the wind and he automatically
pulled his coat a little tighter, even though he noticed no increase in
the wind velocity around him.

Then, as the whine became louder, he realized that it was not the wind.

He turned his head toward the noise and looked up. For a long minute, he
watched the sky as the sound gained volume, but he could see nothing at
first. Then he caught a glimpse of motion. A dot that was hard to
distinguish against the cloud-mottled gray sky.

What was it? An air t