How do plant roots know which way is down? You test this with two setups. First you tip a house plant on its side. Watch how the stem and leaves change direction over one week. Then you soak pinto beans overnight and wrap them in damp paper towels sealed in aluminum foil. Let them sit for three days. Next place the foil packets on a record player spinning at 78 RPM for five straight days. When you open the foil the roots point away from the center of the turntable. The spinning force mimics gravity. The roots respond to it just as they would in soil.