Here is some information from Aquatic Plant Central about propagation;
"As seeds start to develop, the enlarged area grows and when the seeds are mature, starts to dissolve. It is highly recommendable to cut off the flower stalk when that happens so that it doesn't make a mess of the aquarium. Inside the pod is a white jelly-like substance that encloses numerous thorny and tan-colored seeds. Separate them from the jelly and transfer them to an area that receives unimpeded light and is protected. A sandy area in a tank with sedate fish or a dish in an emersed setup are ideal. Even scattering them about the foreground of an established tank will result in a fair number of specimens appearing over the next few months."