Yes, I would start them off in pots. They are like Begonias, the rounded part of the corm sits on the soil. They root and grow from the hollow top of the thing. If in doubt plant them on their sides. They should potted in damp soil, but then not watered until they begin to grow (bit like Rhodohypoxiis). Once they show through the compost they can be watered as normal and planted out when they are growing strongly.
I thought I should report progress, Eric: -
Arisaema Ellatum has produce three stalks about 6 inches high with a cluster of leaves on top. (I think there were three small corms).
Arisaema Fargessii has produced a very promising looking spike about 1 1/4 inches high.
A. Flavum, A. Erubesns and A. Torutosum (??) have still to show.
I followed your instructions and am encouraged that two at least are showing. Is there any hope still for the others? I don't know what the time scale would normally be.
Thanks
Eric H