Most plant behaviour is influenced by the production of hormones. Of the several types of hormones, the auxins, have been studied extensively. Auxins are a group of substances that affect growth. They produce cellular elongation as well.
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One of the most important environmental factors to which auxins are sensitive, is light. If a potted plant is set on a window sill in such a way as to receive light chiefly from one direction, it grows toward the source of light. This response is called tropism. The factor initiating this is light. Hence it is called phototropism.
Where a stem receives light principally from one direction, there is a migration of auxins from the lighted side to the shaded side. The cells of the stem on shaded side exhibit, as a result, a greater degree of elongation. The result will be a bending towards the light.
We do not think of plants as moving at all. But if we could see certain plants on a fast motion film, we can see this clearly. Some plants move quickly. A pumpkin or cucumber vine may form a complete coil around a string support in ten minutes!
Where a stem receives light principally from one direction, there is a migration of auxins from the lighted side to the shaded side. The cells of the stem on shaded side exhibit, as a result, a greater degree of elongation. The result will be a bending towards the light.
We do not think of plants as moving at all. But if we could see certain plants on a fast motion film, we can see this clearly. Some plants move quickly. A pumpkin or cucumber vine may form a complete coil around a string support in ten minutes!
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