So now I'm over halfway through and I seem to be stuck... I have built every building in the tree but I seem to be missing a "seed" resource to be able to build the portals, etc and as far as I can tell, I have no way to produce them.!
Essence is converted into Seeds at the Temple Wing.
Before it will work, the Temple Wing will need to be connected to the Temple via the Wall Sections you can build from the Master Craftsman.
Hope this helps!