How do seed cells know the difference between top and bottom?

[Tom Roger Kise]

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

What I believe is that the root avoids light, and the top seeks light.
Isn't it so?

-- 
Tom Kise (tomk at ifi.uio.no)
Casparisgt. 11 (http://www.ifi.uio.no/~tomk)
0174 OSLO (22 11 23 65)