Answer: What you describe sounds like a Japanese Alder (Alnus japonica). Here's a link to a website with photos of the tree. http://www.ces.ncsu.edu/depts/hort/consumer/factsheets/trees...
If this is the tree in question, you'll find lots of information about it on the site; if it is not the right alder, you can do a search to try and find a match.
Alder seeds can be broadcast in spring. They need light to germinate, so scatter the seeds and press them against the soil surface so they make good contact, but don't cover them with additional soil. Keep the seedbed moist but not soggy wet. The seeds should germinate in a few weeks.
Best wishes with your seed starting project!
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