In a strict sense, plants do not grow faster in the dark; they grow slower. However, plants seem to grow faster in insufficient light due to rapid cell elongation. In other words, they don't grow faster, they simply stretch. It is important to know that green plants really only grow as a result of photosynthetic processes. Without light photosynthesis ceases and plant tissue develop the characteristic, low-light induced sickly green or white coloration.
Rapid elongation of plant cells in low-light conditions is an emergency response on the part of the plant to return its plant tissues to the light where they can again photosynthesize and live. This would be analagous to standing on the bottom of a swimming pool and stretching to get your nose above water for a breath of life-giving oxygen.
In conditions of total darkness, plant cells will generally expand upward, a process called geotropism. In conditions where a small amount of light is reaching the plant, it will grow toward the brightest source of light in a process called heliotropism. Prolonged exposure to darkness will inevitably lead to the death of a plant.
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