Great game! Interesting ways to use the mushrooms and vines to stop the player from carrying the seed. I would suggest making the player kick up a seed if it is below him though :) Just a personal preference though.
Also, I found a bug where you can carry seeds through vines, making some levels really easy to complete. If you are holding a seed, and then walk toward a wall: and right before hitting it, you jump, which allows the seed to be on the other side.
Other than that, it was a super fun game with great art and sound! Good Job mate!