How plants grow toward light
When a seed is planted below the surface of the ground, how does it "know"
to grow toward the light?
Plants don't know where the light is, they do respond to gravity. Since
light is usually up, a plant seed grows up and finds light enough to keep things going.
One way that plants below ground can tell which way is up is with the use
of STATOLITHS. Statoliths are dense pieces of material that settle to the bottom of
a STATOCYST. In plants, pieces of starch or another material denser than water will
settle to the bottom of the cell. Somehow the plant cell determines on what side the
statolith has fallen, and then somehow relays a message (probably a chemical) that
tells the bottom cells to grow faster than the top cells, therefore causing upward
growth. There is still quite a lot of mystery in there to be discovered. I got this
explanation from BIOLOGY by Neil Campbell. This is similar to the way in which plants
use chemical signals to help them grow towards light.
Jim Murray "booga"
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Update: June 2012