Answer: Even though your plants were indoors, they were exposed to freezing temperatures because they were close to the window. At night, cold temperatures can radiate through glass. If it's cold enough, the moisture within the tissues of the plant can freeze and expand, rupturing the cells and causing the stems and leaves to wilt. If you keep plants on a windowsill, remove them at night, or place a piece of cardboard between the glass and the plants to help protect them from the cold. Your experiment was still successful - you discovered how very cold temperatures can affect tender young plants.
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