1)at each "node" there are undiferantiated cells (cells that have not received a chemical signle as to what they will become or do) these cells when conditions are right will form roots & will then support the cutting/plant.
2)IBA (a rooting hormone) and others provide the chemical signle for these cells to become roots. the application of IBA only reduces the time need for the roots to form.
3) high humidity is required so the leaves will not loose all the water from the leaf & stem which will not be given a chance to root. remember water is taken into a plant by the roots & if there are none then......
4) leave only 1 leaf at tip. this reduces water loss,
5) 1 to 5 nodes or to 4" long is the best length for a rootless plant to survive & have a chance to form roots.
6) soil temperature (not air temp) should be in the 65-70F temperature range... air temperature should be in the 50-60F range for BEST results
7) Soil should be "light" "loose" "well draines" & not water loged for root development
8) light should be filtered not bright direct sunlight. to reduce water loss in leaf. yet need light to produce the sugars for root formation
I hope this helps

I've read somewhere that Knox gelatine can be used as a rooting medium. Can't find anything on the web so I'm hoping that somebody on this forum has information about this method.

Sand or other coarse media is usually needed to
get a struggling cutting going. It provides
oxygen. If roots are failing due to rot get more
oxygen to the roots.

Adding one more thing to Yiorges list. Take cuttings
when the stems are actively growing, then there is
a balance of harmones ready to make your future
plant a reality.

justplanephil,
There was an article in Canadian Garden Magazine about seed starting in gelatin, but I've never come across any real research about rooting in it (though have read a few things) - I imagine it would be pretty much the same.

My experience with gelatin was that I had problems with fungus -- except in the university laboratory where conditions were perfect and everything could be sterilized.

I did not find that all cuttings did best when actively growing but rather some woody plants did better for me at mid-winter.

What about when you transplant the rooted cutting into a larger pot.Say the cutting takes off and starts to grow vertically,do you just cut it back so it will branch out to become more "shrub like"?

Ron