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In the late 18th century, a Dutch scientist, Jan Ingenhousz, conducted a famous experiment which proved plants produced oxygen. He immersed various plants under water and observed them. He noticed that when they were placed in direct sunlight they released tiny bubbles of gas. When enough gas had accumulated in the container it was able to re-light a glowing splint, indicating the presence of oxygen. To show that it was the light energy and not the heat of sunlight which was necessary, Ingenhousz repeated the experiment with leaves placed near a fire.