This flower contains the pollen that will fertilize the ovum (eggs) in the female flower. The catkins then fall from the tree, and make a mess all over your yard. The female flowers stay in the tree, and the fertilized egg develops into the seed, better know as the acorn.
Here is a wheel barrow full of catkins, maple seeds, and a few fallen leaves that my husband swept up from our driveway. You can imagine what the rest of our yard looks like. Now try to imagine all the pollen that was released by these catkins prior to falling from the trees. Achoo!!! God bless you. Now where are the Kleenex and the allergy pills?