Seeds

[Debbie]

How do seeds in the ground know which way is down in order to grow roots in the right direction?

Debbie

[Coldfire]

Welcome aboard, Debbie!

I’m not much of a biologist myself, but my WAG would be that they grow towards the sunlight/warmth.

[bibliophage]

Not light, but gravity. See http://www.newton.dep.anl.gov/askasci/bio99/bio99441.htm

Answer 1: 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.
Psych
Answer 2: 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.

Welcome to the SDMB, Debbie.

[Phobos]

I think it may be gravity too. Hasn’t there been experiments on the space shuttle with growing seeds? I don’t know what the results were.

Then again, many seeds aren’t buried. So light may be the answer too.

Perhaps it depends on the plant species.

[Debbie]

Thanks for the welcome and the answers to something that’s been bugging me for a long time (ever since I read a story called “Seeds Grow” to my kids)!

Debbie