But even this could not convince the canny Martians--for they knew that thousands of years of barbarism were covered only by a thin veneer. At any time, man's innate desire to conquer, pillage, and exterminate another race might break through. The Martians well knew the age-old tactics of infiltration used by colonists of Earth. Consequently, only a few scheduled rocket trips per year were permitted. The personnel of each expedition was restricted to a few scientists, who were carefully investigated. They were allowed to study the language, customs, and art of Mars. But scientific achievements and secrets were taboo. No Earthman was permitted to roam at will on Mars--the knowledge they acquired there was given them by an interviewing committee of high ranking Martians, whose ability to sidestep a direct question was uncanny. Of course, there were a few political hotheads on Earth who advocated building a huge fleet of rocket ships, powered with disintegrators, and sending an expedition to subdue the red planet. Naturally, this merely served to corroborate the bad opinion of Earth held by the superscientists of Mars. A few men, such as Doctor Theller and Art, knew what awful disasters such a move would bring. Not only did the Martians have weapons which made the terribly effective, but uncontrollable, atomic disintegrator look like a clumsy toy, but they could also throw up a force field around their entire planet, at an unknown height, against which any invading ship would smash into blazing fragments. True, there was Venus. Venus, the Jungle Planet. There were two environments of Venus--water and jungle. Both were filled with a teeming growth of nightmarish monsters, among which had been found no intelligent beings. The creatures of Venus were born, fought and ate one another, bred and died. That was all. The whole thing was one vast aquarium. Most of the species had been classified during the ten years following the first landing. There had been many expeditions at first. But gradually they tapered off. Attempts at colonization were given up as hopeless. The climate was sultry and oppressive, but worst of all was the fact that practically all of the vegetation of Venus was poisonous to humans. Any food crops introduced from Earth were strangled by the lush native vegetation, which grew at an incredible rate. Venus had no economic value. Minerals there were, but the expense of freighting them back to Earth by rocket ship made mining impractical. As Elene mulled over these gloomy thoughts, she and Art had covered the short distance from the office to the tube that led to Food Center. As they entered, she saw that he also was preoccupied. In good time, he would tell her what had aroused his sudden enthusiasm. An empty car came by. A photoelectric cell registered their presence in the tube. It stopped, Art dropped a token in a slot in its side, and the door slid silently open. As they entered, Art grinned and said: