A Photo-rific response.
...positive and negative response). These plant responses are called tropisms. Early researchers, including Charles Darwin and his son Francis, observed that plants curve toward the light. The positive phototropism of stems occurs because the cells on the shady side of the stem elongate. It is believed that a pigment related to the vitamin riboflavin acts as a photoreceptor for light when phototropism occurs. Following reception, the plant hormone auxin migrates from the bright side to the shady side of a stem. The cells on that side elongate faster than those on the bright side, causing the stem to curve toward the light. It’s not yet known how reception of the light is coupled to the production of auxin. This can be demonstrated by removing the ...