Positive gravitropism in roots.
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<lI> Root gravitropic bending.
A  horizontal root of maize bends until its tip becomes vertically
oriented.
<lI> Statoliths settling.
This  is  caused  by  statoliths  ( starch grains) settling to the
bottom of root cap cells.
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   The  statoliths lead to redistribution of auxin and differential rates
   of elongation by cells on opposite sides of the root.
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   Video:  <A ClAsS=MID Href="../../../med/Vid/Campbell7e/Gravitropism-V.swf" oNClick="popurlt('../../../../med/Vid/Campbell7e/Gravitropism-V.swf');txtcolor('gravitropism1','gray');return false;" Id=gravitropism1><iMg sRc="/images/shockwave.gif" aLt='' boRDer=0></A>