In the dark, however, he found that the plants gave out less gas, but that that gas extinguished a flame, meaning that the air was rich with carbon dioxide. Therefore in light plants gave out oxygen, but in the dark they emitted carbon dioxide. He also noticed that the amount of oxygen given out in the day was considerably greater than the amount of carbon dioxide at night. This proved a real barrier, as oxygen itself had only recently been discovered and work on gases was far too recent for this kind of science to be developed to its logical extent. When plants give out oxygen they are absorbing carbon dioxide, and vice-versa, so overall more carbon dioxide goes in than comes out.
Photosynthesis enables the plant to use the carbon in the carbon dioxide to grow.
Ingenhousz proved that the solid matter of plants came from the air, not the soil. Yet he fell short of full knowledge of photosynthesis and remained famous only for his work on inoculations.