We are still using the free cards from The Helpful Garden. I took out the set that contained the parts of the seed. I also poured some birdseed into a container for the kids to examine. Also really helpful are the types of seeds cards (follow the same link.)
After introducing the terms we found the parts on some sunflower seeds. They worked really well! Sunflower seeds tend to be a bit larger so it's easier to spot the parts.
Next, we planted a mini "garden." We used a clear glass container, potting soil, a small clay pot (for a pond), water and alfafa seeds. I used the alfafa sprouting seeds because they tend to shoot up fairly quickly and will fill in most of the dirt. You could totally use any seeds though. It makes for great messy play. In retrospect, I would have made on a "sensory" tub for Indie to mess with and another for Barrett to actually plant.