Inducing Echinodorus spp. to produce bloomstalks

Hello all,

I'm looking for some info on getting my swords to 'flower'.  I have been 
able to propagate E. bleheri (or amazonicus, haven't figured out how to 
tell them apart) and what I think is E. macrophyllus, but I consider it 
cheating as the bloomstalks were already present.  Does anyone know what 
conditions induce flowering?  Any good references to point me too?  I 
also have E. cordifolius, E. osirus, E. bertorii (?) and am looking to 
order a ruffeled sword (E. martii?).  I have been able to propagate the 
E. osirus 
from a shhot off the rootstock and have heard it rarely produces bloom 
stalks.  The E. bertorii has just sulked for a year, so actually I'm more 
interested on info just to get it to survive.  

Thanks in advance,
Paul Bucciaglia