Phototropism or Geotropism?

Phototropism or Geotropism?


 

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Phototropism or Geotropism?  

What about those tomato plants on the windowsill, bending toward the sunlight? If shoots are negatively geotropic, why don’t they grow straight up, no matter what the direction of light?

In many cases, a plant’s phototropic and geotropic responses complement each other. If you plant a seed in midsummer in full sunlight, the shoot will grow straight upward. Which phenomenon is responsible for directing this growth? In this case, both geotropism and phototropism would guide the shoot to grow vertically.

In other cases, the two phenomena work against each other. For example, suppose a seed germinates in the shade of an overhanging rock. If the shoot grows vertically, it will collide with the rock. Instead, the shoot will orient itself toward the brightest light source. Once the shoot reaches the edge of the overhang, it will reorient itself to grow vertically. As you can see, phototropism and geotropism are both elements of the plant’s "guidance system."

Phototropism and Geotropism

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Better bouquets
If you are in a windy spot, be sure to stake or otherwise prop up your cosmos, scabiosa, and any other tall, top-heavy flowers. If the plants are blown over by the wind, the stems will curve to grow upward—resulting in wavy or bent stems that are difficult to arrange in a vase!

 

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