Greetings Meredith:
The tree you are speaking of is called sweetgum (Liquidambar styraciflua). Their fruit is referred to as a ball of capsules. Inside these balls are tiny black/brown seeds that often exhibit low germination potential.
If you are really interested in learning more about propagating sweetgum from seed, please feel free to refer to the following publication:
plants.usda.gov/factsheet/doc/fs_list2.doc
Best of luck!