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How does a seed know where is the top and where is the bottom?

Matthew ComDep at lottery.powernet.co.uk
Fri Apr 18 13:55:11 EST 1997

If you plant a germinating seed in soil, how does the seed know where
is the top and where is the bottom?

In other words, the "leaf part" grows upwards, and the "root part"
downwards. What sensory device does the seed appear to have to know
where to grow.

Resistence theory - Some seeds, such as sunflower seeds, comprise
substantially the petals. The root comes out first. The growing action
pushes the growing organism along underneath the soil. There is less
earth above the seed than below the seed or to the sides. Therefore
the easiest part for expanding plant to take is upwards, as there the
path of least resistance lies.

However, seeds such as nuts or particularly, maize corn, grow
differently. There we have two parts coming out of the seed, one grows
immediately downwards, the other grows upwards.

I have such a seedling on my desk right now. The thin "root" part
definitely grew down, the thicker "leaf" part grew upwards.  So I
think resistance cannot be the factor, else both would grow upwards.

Have experiments been done, turning the seed containers half-way
through the growth process. What do they show? Where might I find

Who knows the answer to this? Please answer per email, I shall reply
with thanks.

NewsGrp at lottery.powernet.co.uk

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