[UCANSEE2]

Chemotropism and be growing towards sources of nutrients. I would have to look it up.

Towards nutrients, including water. They are actually darn good at finding water. They will break through metal pipes just to get to water.

I would say you don't need to look it up, as it is fairly obvious. You understand it completely.

The problem I had with your response earlier is that you don't see turning towards the Sun the same as growing towards the Sun.

What causes a seed to actually sprout?

(Hint: again, it's not gravity)

[allmendream]

Well of course gravity cannot give the signal for a seed to sprout, gravity is constant. Gravity determines the direction the plant will send its cotyledons by the mechanism I discussed, but it doesn't give the signal to sprout.

I imagine temperature and water might do the trick via chemical signals that activate transcription factors that transcribe genes to produce the proper protein signaling molecules to start the ball rolling; but I just say that as a former farmer and current molecular biologist who took botany a LOOOOONG time ago. ;)