wires as roots
I've dealt with many rootless plants myself, both home "grown" and ones that I've bought. I've seen and used two methods that have a fair success rate:
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1) Wiring
This is a very interesting idea that I've seen or heard several professional growers attest to. Apparently the wires keep the plant very still so that new root tips are not jostled as they emerge from the plant. Why this works, I'm not really sure...
After all, most plants are just sitting there -- how can there be enough movement to cause damage to new root tips? One answer I heard was that watering the plant can cause it to shift about. I'm still not totally satisfied with that answer, but that's what I've heard...
I've seen one venerable grower wrap the base of a big multifloral with stiff wire (a little more flexible than clothes hanger material) and make faux roots with it. The real roots seem to have no problem emerging later.
2) Sphag-and-bag
I've tried the sphag-and-bag, or in my case, sphag-and-box, and that has sometimes worked. I think it works best when you grow up the sphagnum for awhile, and new sphagnum starts to grow. Yes, I know that the sphagnum is supposed to be dead when you buy it in the rectangular cubes, but you can grow it given humid enough conditions. And no, I'm not talking about algae, either. Once the sphagnum starts growing again, it's quite apparent since you see new green vegetative matter that resembles miniature blades of newly-grown grass.
In any case, I've been able to root out many rootless seedlings in a small transparent box (6 in x 6 in x 6 in or so in size), and actually with no drainage, or air movement, either! A double slap at conventional wisdom...
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I would estimate that my plant recovery rate using these two methods has been about 75%. It also has a lot to do with how healthy the rest of the plant is (i.e., the part without roots) is in the first place. If it's pretty healthy, it will have a better chance of recovering, whereas a plant with limp leaves and no roots has a more uphill battle.
Terry Root once told me that you can flower paphs with no roots, that foliar feeding could be sufficient for growth. But that's a whole other divisive topic...
There are a few more tricks I've heard; one day soon I'll post them on slipperorchidblog.com.