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Geo Tropism

From the beginning of germination display roots a tendency to grow downwards, while shoots grow upwards (anisotropic growth). A germinating seed can be turned upside down several times and the root will still start to bend downwards. This behaviour is another example for a tropism, a movement triggered by a stimulus. The question is: what is the controlling stimulus?






"It is not the soil’s humidity that causes the direction of the root, since the root will grow downwards and the shoot will grow upwards even if the plant is placed in an earth-filled tube where the upper part is moist and the lower is dry. If the plant is put into a water-filled tube the lower part of which is exposed to light while the upper is darkened, the direction of growth will still not change: a proof that it is independent of light." (A. de CANDOLLE, 1834/38)



In 1806 show...

Posted by: Janet Valerio

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