You buy their seed to grow wheat, you have a license to grow the wheat but you can't keep any of it to plant next year.
You have a license to use their wheat seeds but not use the copies the plant is making.
- http://www.library.yale.edu/~llicense/ListArchives/0311/msg0... - http://www.nytimes.com/2009/12/18/business/18seed.html
You buy their seed to grow wheat, you have a license to grow the wheat but you can't keep any of it to plant next year.
You have a license to use their wheat seeds but not use the copies the plant is making.