"What better purifying machine is there than a plot of grass?" shouted Channing. "Weeds, grass, flowers, trees, alfalfa, wheat, or anything that grows and uses chlorophyll. We breathe oxygen, exhale CO_{2}. Plants inhale CO_{2} and exude oxygen. An air plant means just that. It is a specialized type of Martian sawgrass that is more efficient than anything else in the system for inhaling dead air and revitalizing it. And you've tossed the weeds out!" Channing snorted in anger. "We've spent years getting that plant so that it will grow just right. It got so good that the CO_{2} detectors weren't even needed. The balance was so adjusted that they haven't even been turned for three or four years. They were just another source of unnecessary expense. Why, save for a monthly inspection, that room isn't even opened, so efficient is the Martian sawgrass. We, Burbank, are losing oxygen!" The Director grew white. "I didn't know," he said. "Well, you know now. Get on your horse and do something. At least, Burbank, stay out of my way while I do something." "You have a free hand," said Burbank. His voice sounded beaten. * * * * * Channing left the office of the Director and headed for the chem lab. "How much potassium chlorate, nitrate, sulphate, and other oxygen-bearing compounds have you?" he asked. "That includes mercuric oxide, spare water, or anything else that will give us oxygen if broken down?" There was a ten-minute wait until the members of the chem lab took a hurried inventory. "Good," said Channing. "Start breaking it down. Collect all the oxygen you can in containers. This is the business! It has priority! Anything, no matter how valuable, must be scrapped if it can facilitate the gathering of oxygen. God knows, there isn't by half enough--not even a tenth. But try, anyway." Channing headed out of the chemistry laboratory and into the electronics lab. "Jimmy," he shouted. "Get a couple of stone jars and get an electrolysis outfit running. Fling the hydrogen out of a convenient outlet into space and collect the oxygen. Water, I mean. Use tap water, right out of the faucet." "Yeah, but--" "Jimmy, if we don't breathe, what chance have we to go on drinking? I'll tell you when to stop." "O.K., Doc," said Jimmy. "And look. As soon as you get that running, set up a CO_{2} indicator and let me know the percentage at the end of each hour! Get me?" "I take it that something has happened to the air plant?" "It isn't functioning," said Channing shortly. He left the puzzled Jimmy and headed for the beam-control room. Jimmy continued to wonder about the air plant. How in the devil could an air plant cease functioning unless it were--_dead_! Jimmy stopped wondering and began to operate on his electrolysis set-up furiously.