Hi Vic,
My own experiences with such temperate aqautic Utrics. as U. macrorhiza, U. purpurea, and U. intermedia seem to contradict the accepted idea that they *must* be allowed to form turions. In particular, I have been growing the same batch of U. purpurea in the same jar for 3 years now without ever having induced or otherwise seen turion production. The plants are healthy and fill the jar. They have however not produced flowers, but then neither have any turion raised plants that I have grown either, so I cannot make any definite claims about whether or not it will affect flower production. My feeling says they will still produce flowers under the proper circumstances, but I'll need to investigate this to be sure.
From my little 'experiments', it seems that turion production begins at 18 deg. C. I have also had some indication that turions may be formed during adverse conditions regardless of temperature, such as over abundance of some kinds of algae, or poor general water quality. Turions produced because of poor water quality seem to be of inferior quality than those produced solely because of low temperatures, but they are still viable, and in fact will begin to form full plants within several months, even if not given any cold treatment.
But despite my experiences, I still do prefer to take a small batch of each species I have and put them outside in the fall so that they will form turions, which I store in the fridge. This gives me a backup should anything happen to my main collection.
Take care!
Chris F.