What is the perpetual harvest propagation method?
A bowl formation is definitely part of it..
The key of course is to have a separate veg and flowering chamber going at the same time.. Each time a plant is harvested it gets replaced with a clone from the veg room - so that the bud chamber's always filled to capacity.. Eventually, as you learn the flowering times and cloning times of your strains, you can close in on the goal of 100% occupancy (with no extra clones laying around and no place to put them).. This does take a little calculating, but once done you can get on a fairly precise schedule to where you're picking your buds like clockwork.. It's the ideal setup for growing multiple strains with different flowering times..
Since the plants will be of varying sizes, you'll want a hydro or soil system that's conducive to moving them around under the lights - to keep them in that bowl formation (or, if you're vegging under fluoros, in a staircase arrangement.. with the lights hanging diagonally).. You want it to be easy to position the plants wherever you want in the chamber, plus be able take them to the next chamber.. Good systems include ebb/flo and drip, and also soil/pots.. Systems with fixed plant spacing (aero and nft tubes) and/or systems where the roots intertwine may prove difficult in an ever-changing perp-harvest setup..