How jump start banana plant?

A year ago I bought four banana plants (Nymphoides aquatica) from the same
store. Each had a few leaves sprouting. Two went on to produce big leaves,
some reaching to the surface. The other two lost their leaves and have
stayed "dormant." They were all in the same 10-gallon tank and subject to
the same conditions.

Can anyone suggest something to start the dormant plants up again? The
"bananas" are still firm and look healthy. Just no leaves.

BTW, someone suggested propagating these plants by leaving a cut leaf in
the tank. I happened to cut one accidentally and it has indeed sprouted
what look to be roots. The roots are small and grew slowly but that may be
because I moved the leaf to a goldfish tank--cold water.

Greg. Tong
San Francisco, CA, USA
gtong at sirius_com

"Every infinity is composed of only two halves."