Seeds are fromed in dihiscent capsule from the fertile flowers. When the capsule is ripe it will split opern. the seeds are very small.

You might be better off waiting a bit until the flower head is dried out and saving the whole darn thing. Those seeds are so tiny that they are darn near impossible to separate from chaff, so it's easiest to just crumble the whole seed head into whatever it is you are saving (or planting) the seeds in.

Ok - thanks for the help!
Sandra