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    What will astronauts (宇航员) eat when a space trip takes years?

    "Lots of fresh vegetables," says Dr. Janet Williams, whose team have spent the last 10 years learning how to grow plants in a space station. And it's a good thing that she has already started her work, because space gardening can be really hard.

    As usual, astronaut George White looked into the closed plant room. He had planted Dr. Williams's quick-growing seedlings in it, but none of the stems were showing. He opened the room to check and found the problem. The stems weren't growing upward and the roots weren't growing downward. On Earth, gravity (重力) helps a plant's stems and roots to find "up" and "down". However, in the space station, there was almost no gravity.

    Dr. Williams suggested a solution: give the plants more light, as plants also use sunlight to find their way. And it worked. When the plants had more light, the stems turned up and the roots went down.

    Now Dr. Williams was free to worry about the next problem: Would her baby plants live to flower? Can we grow food on a space journey?

    Many plants died in the space station. Dr. Williams thought she knew why: the space plants were hungry for air. Plants live by taking up CO₂ from the air. Since a plant uses it up in the air around, the plant needs moving air to bring more CO₂ close to its surface! On Earth, the air is always moving. Gravity pulls down cold air, and warm air rises. And with these air movements, plants get enough CO₂.

    Many earlier experiments with plants in space had used closed rooms. Dr. Williams tried a new greenhouse that had a fan to keep the air move. The plants lovedit. They flowered and even produced more seeds. Using Dr. Williams's method, astronaut George completed the first seed-to-seed experiment in space, and moved one plant closer to a garden in space.

    "And this," says Dr. Williams, "is good news for long-term space travel."