Influence of Carbon Dioxide Gas on Plant Growth
Green plants exposed to sunlight must break down carbon dioxide in order to grow. Germination and the stages of growth immediately following it, however, are inhibited by this gas. Extra carbon dioxide added to a green plant’s environment stimulates plant growth, up to a point. Plants grown in sunlight, with their roots immersed in water that was lightly impregnated with carbon dioxide, thrived and gained weight. Plants grown with their roots in distilled water and with atmospheres containing added carbon dioxide gas showed various responses. If they were exposed to the sun, in an atmosphere that was 8 % carbon dioxide, they thrived, but at higher levels of added carbon dioxide, their growth declined, and, at levels of 50 % and above, they died. For plants grown in the shade, growth was inhibited even in atmospheres containing only 8 % carbon dioxide. For plants grown in sunlight, if quicklime was present to absorb the carbon dioxide of the air and water, the plants soon died and vitiated their atmosphere.
Plants grown with their shoots in open air, in the light, and their roots in distilled water assimilated carbon, proving that these plants must be obtaining their carbon solely from the atmosphere, miniscule though that source is, because they could not be drawing it through their roots. Plants of the same weight, grown in darkness, lost carbon. The amount of carbon dioxide decomposed by the green parts of plants is approximately equal to the amount of oxygen they liberate, but a small percentage of the oxygen is retained by the plant, as is all of the carbon. Plants release nitrogen gas.