DWC Bubbler Bucket help!

I am new to the hydro growing methods, but would like to get my feet wet. :) I have read alot and did alot of research on hydrophonic growing. There is just one thing I don't understand and that is on the seedling or clone. How does the roots grow down to the resoivor when their just starting. Do they automatically know where the water is or does gravity just make them go downward to the resoivor. Or are you suppose to keep watering them slightly until the roots grow in between your rock mediums.
For example this peat pellet is at the top of the rock medium and I'm sure the roots aren't very long to reach the resoivor. So how does it survive until the roots go down to the nutrient resoivor. http://www.overgrow.com/image.php?to...=soilvshydro05
Just copy and paste.

When there are no roots, the level of nutes in the bucket must be higher enough to splash the net pot with the bubbles. Then by capilarity, this water goes up to the clone or seedling. But my way to do is the following. I always wait for the roots to be outside the rockwool cube before putting it into the bubbler. Seedling : 1 week ; clones : 3 weeks
Fhydro