Just wanted to say that so far, the plant is proving very ammenable to my culture on a moist to wet medium. Caution has been advised though, although the growth is excellent, the plant might not form its characteristic tubers that will carry it through dormancy. Based on this, I get the feeling that there will be a window prior to dormancy where a very gradual drying will be needed to translocate the reserves stored in the plants leaves to form the storage tubers.
This seems to be a similar case as with U. geminiloba, which I grow just moist when there is no visable and active growth. When I notice new growth, I increase the water until it is a few CM deep in the jar I have it in, raised from the bottom on osmunda. At this time, the plant goes crazy, growing through the osmunda and into the water at the base of the jar. So, I believe from what I am seeing that U. jamesoniana is likely a seasonal hydrophyte, enjoying the water. Once growth stops, I plan on reducing the moisture level to moist, with occasional drenches, afterwhich the excess water will be poured out of the container. This has served me well for my culture of U. geminiloba (although I have yet to flower it).
So far so good. The plant is growing very well, and has nearly doubled in size, but there are no new tubers. The question now is, do I continue the wet culture straight on, or try to encourage tuber formation now during the period of active growth? Like I said, I sense there is going to be a window of time where the plant will need time to make those tubers before going dormant. In U. geminiloba, there is very little sacrifice of leaves when growth stops. If this proves to be the case with U. jamesoniana, we have it made! If the leaves are non-persistent during dormancy as a gene controlled or light activated process, and only the tubers remain, then it is critical to find a way to encourage tuber formation before the leaves disappear.
It's never to early to worry about the dormancy issues. Sebastian, if you can would you ask Peter his thoughts on this? He is the only one I know with hands on experience with long term growing of the plant. Ask him if the leaves persist for him, or vanish during dormancy, and if he does anything to change his conditions to encourage tuber formation.
Things can always change in an eyeblink, but for now, I have to say things are looking good!