-_impossible_."

Lawton shook his head. "It isn't at all, sir. We've had it drummed into
us that evolution proceeds at a snailish pace, but what proof have we
that it can't mutate with lightning-like rapidity? I've told you there
are gases outside we can't even make in a chemical laboratory, molecular
arrangements that are alien to earth."

"But plants derive nourishment from the soil," interpolated Forrester.

"I know. But if there are alien gases in the air the surface of the
bubble must be reeking with unheard of chemicals. There may be compounds
inside the bubble which have so sped up organic processes that a
hundred million year cycle of mutations has been telescoped into an
hour."

Lawton was pacing the floor again. "It would be simpler to assume that
seeds of existing plants became somehow caught up and imprisoned in the
bubble. But the plants around us never existed on earth. I'm no
botanist, but I know what the Congo has on tap, and the great rain
forests of the Amazon."

"Dave, if the growth continues it will fill the bubble. It will choke
off all our air."

"Don't you suppose I realize that? We've got to destroy that growth
before it destroys us."

* * * * *

It was pitiful to watch the crew's morale sag. The miasmal taint of the
ominously proliferating vegetation was soon pervading the ship,
spreading demoralization everywhere.

It was particularly awful straight down. Above a ropy tangle of livid
vines and creepers a kingly stench weed towered, purplish and bloated
and weighted down with seed pods.

It seemed sentient, somehow. It was growing so fast that the evil odor
which poured from it could be correlated with the increase of tension
inside the ship. From that particular plant, minute by slow minute,
there surged a continuously mounting offensiveness, like nothing Lawton
had ever smelt before.

The bubble had become a blooming horror sailing slowly westward above
the storm-tossed Atlantic. And all the chemical agents which Lawton
sprayed through the ventilation valves failed to impede the growth or
destroy a single seed pod.

It was difficult to kill plant life with chemicals which were not
harmful to man. Lawton took dangerous risks, increasing the
unwholesomeness of their rapidly dwindling air supply by spraying out a
thin diffusion of problematically poisonous acids.

It was no sale. The growths increased by leaps and bounds, as though
determi