Hi,
I made that exact trip two years ago. I bought some fresh mushrooms in Holland, then boarded the Eurorail. Even though I was obviously an American tourist, they didn't search me. However, this was two years ago, so keep in mind that things change, and some people just have the luck of getting selected for random searches.
IMO though, if you're just taking pot seeds, they are small enough to stash on your body.
-AR