There are a couple different ways. If you have a large sword, you can carefully split it in half and replant the 2 halves. Another way is when the sword sends out shoots. If you allow the shoots to go out of the tank, they will flower at the nodes. If underwater, they will form roots at the nodes. Each node will be a baby plant. Sometimes I let mine flower just to watch it flower, then I put the shoot back into the water and it starts forming roots at the nodes. I usually wait til the roots are about 3 inches, and a few of them, before cutting the runner off down at the base of the sword, and cutting the individual plantlets off the runner and planting.
Here's a couple of pics of some of my sword shoots....
55G Filstar XP3 - 16" Fire Eel
75G Medium Planted - Filstar XP3 Low Light - Established Feb 2006
There is one other way. Swords form a bulb at the base of the plant. This usually coincides with a slowdown in growth. If you break off the bulb, the plant will generally start a new growth spurt. The bulb can be planted and will start a new plant, sometimes several.
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Will the shoots grow faster submerged or emersed, or does it really depend on the plant? I am asking because I have two swords on one the shoots are growing out of the water with few shoots that are quite large and the other is submerged with more shoots that are much smaller.